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XyZspineZyX
11-04-2003, 02:21 AM
Just in case its modelled this way, the P-51's radiator air outlet shutter should be automatic. In real life, the temperature of the coolant determined how much the flap opened. Otherwise, there was a switch in the cockpit with "auto", "open", "closed" and "off." "Auto" was the usual setting.

And when the P-51's radiator opens (the flap opens up), the Mustang should not loose speed. In fact, the Mustang's radiator design created thrust.

If the Mustang is loosing speed with an open radiator, it should not.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 02:21 AM
Just in case its modelled this way, the P-51's radiator air outlet shutter should be automatic. In real life, the temperature of the coolant determined how much the flap opened. Otherwise, there was a switch in the cockpit with "auto", "open", "closed" and "off." "Auto" was the usual setting.

And when the P-51's radiator opens (the flap opens up), the Mustang should not loose speed. In fact, the Mustang's radiator design created thrust.

If the Mustang is loosing speed with an open radiator, it should not.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

Thera
11-04-2003, 03:24 AM
The system still created drag, just not as much as more traditional designs. It didn't make the plane faster.

Quote from Lee Atwood (chief engineer of the P51)

"In the case of the Mustang, the air duct pumping system at full speed at 25,000 feet was processing some 500 cubic feet of air per second, and discharge speed of the outlet was between 500 and 600 feet per second relative to the airplane. This air jet counteracted much of the radiator drag and had the effect of offsetting most of the total cooling drag. To offer some approximate numbers, the full power propeller thrust was about 1,000 pounds and the radiator drag (gross) was about 400 pounds, but the momentum recovery was some 350 pounds of compensating thrust--for a net cooling drag of only some 3% of the thrust of the propeller."

-----------------------------------------


Fools rush in where angels fear to tread.

XyZspineZyX
11-04-2003, 03:34 AM
Actually, some thrust was created. It's called the Meredith Effect.

This alos from Lee Atwood:

Atwood explained, "Both the British and German engineers at the time thought you could test a scale model in a wind tunnel. But the wind tunnel models didn't generate the engine-heat factor, which we successfully controlled within the air scoop to create positive thrust. They were all looking at Mustang's laminar flow wing, which was noted for reducing air friction over the surface of aircraft wings."

Pointing to several mathematical equations, Atwood continued, "The laminar flow wing is great for jet airplanes or in a high-speed dive but had little effect on the P-51's overall performance envelope. You have to attribute the speed increase to the radiator energy recovery (positive thrust), not the characteristic of the wing itself. The wing did help in a dive -- not in level flight. I never mentioned this to anyone during the war."


=================


Nevertheless, the plane should not slow down when the radiator air outlet shutter is opened. It does in the beta.

I tested it at 5000 meters. Pushed the throttle all the way forward until the speed stablized. Opened the radiator outlet door fully and the plane lost about 20 km/h.

This should not happen. Because as your excerpt says:

"This air jet counteracted much of the radiator drag and had the effect of offsetting most of the total cooling drag."



Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

Message Edited on 11/04/0305:54AM by SkyChimp

Thera
11-04-2003, 03:51 AM
The plane slowed down with the radiator open. Read that passage again until you understand that. /i/smilies/16x16_smiley-happy.gif

-----------------------------------------


Fools rush in where angels fear to tread.

XyZspineZyX
11-04-2003, 03:57 AM
But it shouldn't slow down as much as other planes using different methods is the point.

I guess the next issue is how much it slows down by. If its small then its probably accurate, if its significant it probably isn't. But I hear she's a real beauty to fly so I can't wait to try her out! http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif

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"Never in the field of human conflict was so much owed by so many to so few." - Winston Churchill

XyZspineZyX
11-04-2003, 03:57 AM
Thera wrote:
- The plane slowed down with the radiator open. Read
- that passage again until you understand that.

Thera, the open radiator air outlet shutter is the device that allowed the air to flow through, allowing for the compensation of cooling system drag. You do not get the "air jet" effect Atwood refers to uless the flap is open.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg



Message Edited on 11/04/0305:59AM by SkyChimp

XyZspineZyX
11-04-2003, 03:59 AM
That's what I seemed to remember, to.

..

Also, another question.

Is the listed speeds in various data figures in nautical miles or statute miles? If I remember correctly, the US didn't use the nautical mile until 1954.

Is the quoted 437mph speed for the P-51D a nautical mile figure? I seriously doubt that the many publications intended for a wide audience, is written and listed in nm - not to mention, that if the mile-kilo conversion in FB was also in accordance with the nautical mile, instead of the statute mile, then there are some serious problems in many planes with their speed.

The km/h data of FB planes, matches the mph data in statute miles - for instance, the Bf109K-4 tops out around 724~730km/h in FB, which is around 450mph in statute miles, which also matches many publication which list their speed data in miles.

I'm asking this because Eagle keeps insisting 760km/h TAS is 447mph, which, I seriously can't see where he got that figure from. It matches neither nautical nor statute mile figures for conversion.

At anyrate, I'll post my test results at 7620m:

settings\speed(110%)
--------------------
closed.....760km/h
2..........738km/h
4..........711km/h
6..........693km/h
8..........676km/h
open.......660km/h

The rest discussion, is up to you guys.





-----------
Due to pressure from the moderators, the sig returns to..

"It's the machine, not the man." - Materialist, and proud of it!

Message Edited on 11/04/0312:07PM by kweassa

XyZspineZyX
11-04-2003, 04:01 AM
kweassa wrote:
-
- That's what I seemed to remember, to.
-
-
- ..
-
-
- Also, another question.
-
-
- Is the listed speeds in various data figures in
- nautical miles or statute miles? If I remember
- correctly, the US didn't use the nautical mile until
- 1954.
-
-
- Is the quoted 437mph speed for the P-51D a nautical
- mile figure? I seriously doubt that the many
- publications intended for a wide audience, is
- written and listed in nm - not to mention, that if
- the mile-kilo conversion in FB was also in
- accordance with the nautical mile, instead of the
- statute mile, then there are some serious problems
- in many planes with their speed.
-
-
- The km/h data of FB planes, matches the mph data in
- statute miles - for instance, the Bf109K-4 tops out
- around 724~730km/h in FB, which is around 450mph in
- statute miles, which also matches many publication
- which list their speed data in miles.
-
-
-
-
------------
- Due to pressure from the moderators, the sig returns
- to..
-
- "It's the machine, not the man." - Materialist, and
- proud of it!


Almost all USAAF docs list speeds in statute miles, not nautical miles. I have a few WWII era docs from the US Navy that list speeds in knots, but even those are few and far between.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg



Message Edited on 11/04/0306:03AM by SkyChimp

XyZspineZyX
11-04-2003, 04:14 AM
Additionally, the radiator exit shutter was generally set to "Automatic." While I have no concrete proof, I would assume speed tests conducted by the USAAF were done with the same setting. Therefore its logical to conclude that the P-51D's top speed of 437mph was done with exit door open, as surely the combat power setting would have created a rather hot running engine.


Note: I haven't been able to get anything like 760 km/h in level flight at any altitude. I've tested from 3,000 m on up. I'll do some more, though. Top speed should be 703 km/h at about 25,000 feet (7,620 meters).


Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg



Message Edited on 11/04/0306:18AM by SkyChimp

XyZspineZyX
11-04-2003, 04:29 AM
MUSTANG

Commentary by Lee Atwood.


What made the P-51 Mustang the fastest fighter of World War II (before the German jet came along)? The answer depends on whom you ask. The editors at Air & Space/Smithsonian asked the late Lee Atwood, vice president at North American Aviation when the fighter was born, and the question started an interesting correspondence. Atwood's explanation of what gave the Mustang the edge over the Spitfire and Curtiss P-40 was the design of its cooling system, especially the radiator duct's variable exit.
In an address to the Yorkshire Air Museum in June 1998, Atwood described the effect of the design on the Mustang's performance. An excerpt from his speech follows, along with drawings he made to illustrate his point to the editors.

In 1940 we had a young, energetic, and first-class engineering department with competence in aerodynamics, structures, materials, and thermal technologies as developed up to that time, and the factory had a nucleus of expert machine shop, tooling, and production personnel. We gave the Mustang design credit to Edgar Schmued who led the design room effort and brought the components together under the direction of Raymond Rice, who succeeded me as a chief engineer, and the technical specialists.

All these and many others contributed significantly to the project, including Colonel, now General (Retired), Mark E. Bradley who directed the installation of the 85-gallon fuselage tank. He then demonstrated that the longitudinal instability created by this weight behind the pilot could be managed by the combat pilots, and the effective endurance could be increased by some two hours.

In considering the speed performance of the Mustang, which is really its primary advantage and distinction, it is necessary to adjust one's thinking and point of reference to a rather early period in the science of aerodynamics. In the 1930s, there was no jet propulsion, and by any measure of comparison, the technical resources, personnel employed, test equipment and financial expenditures were really insignificant when compared to the aerospace establishment of today. Of course, the basics were there--which involved derivations of Newton's laws and Bernoulli's hydraulic principles--and aero sciences had been basically defined by Prandl, von Karman, and many other mathematical and scientific authorities, but applications to actual aircraft were relatively crude and empirical. Wind tunnel models were the primary proving element in design, and there were still many elements of such testing that had to be estimated or extrapolated with opinion and hope.

In these circumstances it is not very surprising that, among these early practitioners of aeronautical engineering, there were discontinuities of information and differences of opinion on various fine points in the application of general aerodynamic science, as then known, to actual airplane design. This was most apparent in one of the critical aspects of airplane design during the period of reciprocating engines and propeller-driven airplanes. The liquid-cooled designs favored in England and Germany--and also used in the United States and other countries--were generally considered of lower drag because of their in-line cylinder configuration. Air-cooled engines were generally of radial design, with all cylinders facing the cooling air stream, and the diameter was considerably larger.

The well-known radiator became the automobile standard early on, and everyone in the pre-war era had various experiences with these installations and their belt-driven fans. The common experience usually involved adequate cooling at cruising speeds, with frequent over-heating on mountain grades or slow traffic, and the fans were not always adequate to control the temperature. Generally, most people had an occasional bad experience with an overheated engine.

Airplane radiators had a lot of the same troubles, and while separate cooling fans were not seriously considered, ground cooling from propeller circulation alone was frequently inadequate. Basically, the radiators were designed to cool the engines at full power in a climb--which was usually something like half the maximum possible level flight speed with the same power--so at high speed, the cooling capacity was much more than needed.

Now it is clear that we were then quite sure that, as in an automobile, there was no reasonable dynamic use for the warm air discharged from a radiator, and a low and medium speeds, up to say 200 miles per hour, that was quite true. The temperature rise was small, and the expansion was correspondingly modest, and heat energy recovery was insignificant.

However, as engine power increased and better aerodynamic shapes were developed in monoplane designs, we were all slow to realize that, with a normally ducted radiator at high speed, we had at our disposal a really remarkable air pump.

This air pump, like all pumps, had three elements--a compressor stage, a metering or valving stage (radiator core), and a discharge function through an air outlet. This began to be a considerable pumping action as speeds approached 300 miles per hour--and at 400 miles per hour, it had a large potential and could be a considerable fraction of the airplane's total power equation, since the pumping pressure increases as the square of the speed. To make this automatic pump effective, only one thing was required, and that was to choke the outlet enough to keep the pressurized airflow through the radiator just adequate for cooling and to discharge this compressed air at the highest speed possible.

This intuitively easy to follow and was also logical from a general streamlined design point of view--which all designers tried to follow as a matter of course. The potential magnitude of this effect was more difficult to appreciate, however, and since little or no data were available, these possibilities were overlooked in most cases.

In the case of the Mustang, the air duct pumping system at full speed at 25,000 feet was processing some 500 cubic feet of air per second, and discharge speed of the outlet was between 500 and 600 feet per second relative to the airplane. This air jet counteracted much of the radiator drag and had the effect of offsetting most of the total cooling drag. To offer some approximate numbers, the full power propeller thrust was about 1,000 pounds and the radiator drag (gross) was about 400 pounds, but the momentum recovery was some 350 pounds of compensating thrust--for a net cooling drag of only some 3% of the thrust of the propeller.

This air discharge had what can actually be called a regenerative effect. Maximum aircraft speed is the point where the line of power available, created in the engine and delivered by the propeller, crosses the line of power required to propel the plane through the air. Since the propelling force of the pressurized air from the radiator discharge increases as the square of the speed, we have the favorable situation where the faster you fly the more help you are getting from this regenerative air pumping system.

Since this high speed phenomenon could not be effectively measured by regular wind tunnel model test, it was viewed as ephemeral or even imaginary by many in the engineering practice. Actually, it is quite real and has a close relationship with jet propulsion.

Regarding the Mustang, I have always referred to the work of F. W. Meredith of the RAE, whose report (RAE No. 1683) of August 1935, greatly influenced me as chief engineer for North American Aviation to offer the British Purchasing Commission the ducted radiator design configuration in 1940. That report showed how the momentum loss in the cooling radiator could be largely restored when excess cooling air was being forced through the radiator at high speed. As noted before, this involved closing the air exit enough to get a substantial back pressure behind the radiator which largely restored the momentum loss--which was quite large as described above. This was possible, in Meredith's words, because the outlet was "adjusted to suit the speed,o and back pressure was available accordingly.

Here again, while Meredith's analysis was coherent and mathematically instructive, he failed to convey the practical aspects through an example or two, although he did offer a chart showing drag reduction for various discharge area ratios and conditions. The point I am making was that his work was generally in unfamiliar mathematical terms and was poorly understood. In fact, in two cases I know about, it was described in terms of mild ridicule. In any case, some if not most of the designs of wartime aircraft, including the Spitfire, failed to get the full advantage of this available air pump.

It should be pointed out here that the controversy and misunderstanding of the Meredith Effect on the performance of the Mustang developed largely because it was essentially impossible to get a reasonable measure of the effect from wind tunnel models at the time. The mass flow and momentum could not be accurately measured on a scale model, and no large tunnels were fast enough--200 to 400 miles per hour--to get meaningful results.

It has been reported that Messerschmitt made extensive efforts to determine the reason for the low drag of the Mustang, but his wind tunnel measurements did not disclose the restoration of momentum to the radiator cooling air, and most probably could not have done so with the wind tunnel equipment available at the time.

At this point I would like to interpolate what is , to me, a most fascinating element in Meredith's 1935 report. As you may have noted, I have made no reference to the thermal element in the momentum recovery of the radiator cooling air and at the temperatures involved, the air expansion was relatively small and could be neglected. Real jet propulsion, however, involves fuel burning, and the velocity of the gases and heated air is greatly augmented by this high temperature.

In his report, undoubtedly independent of Whittle's jet engine work, Meredith suggests piping the engine exhaust heat and gases to discharge behind the radiator to heat the discharged air just as burning fuel would do. This would have increased the volume and velocity of the discharged air at the same back pressure and increased the favorable thrust force.

Of course, the thrust of the short stack exhausts had been recognized by Sir Stanley ****** of Rolls-Royce in his book, NOT MUCH OF AN ENGINEER, and others, but Meredith's suggestion might have produced a much more powerful effect, but it involved complications and practical difficulties. As far as I can determine, it was never tried on any airplane.

This brings me to the Spitfire comparison, although that is probably a poor choice of words. That airplane was in a class by itself and at the top level of defense against the Luftwaffe in 1940, and was undoubtedly the most important defensive weapon in history. It was some 1,000 pounds lighter than the Mustang and was at the peak of interceptor efficiency and was essentially in classic conformity with the objectives of the RAF fighter command. It overmatched its opposition and was there when most needed.

In the cold illumination of hindsight, however, and probably for reasons I have outlined above, it missed the opportunity to restore much of the air flow momentum to the radiator cooling air and, with it, a possible speed increment of more than 20 miles per hour. The late Jeffrey Quill, Supermarine test pilot, describes the incorporation of the Meredith Effect in the Spitfire in his book, SPITFIRE, A TEST PILOT'S STORY, and that the radiators were enclosed in ducts under the wings. Here I would like to quote from an article "The Mustang Margin" I wrote for the AIR POWER HISTORY JOURNAL which involves some background and detail on the subject. It will, of course, be glad to try to answer any questions you may have at the end of my presentation.

"The most notable and probably the first application of the Meredith Effect was incorporated in the Supermarine Spitfire, one of the world's most successful airplanes. Over 20,000 were built in various models, but the Mark IX, with the Merlin -61 engine, was typical of the later wartime production, and a sketch of this model with detail of the radiator installation is shown. Two aspects of this design are significant. First, the radiator outlet has two positions--that is, fully open and partly closed--and cannot be progressively 'adjusted to suit the speed.' Second the inlet upper wall is a continuation of the lower surface of the wing and expands the duct cross section by rapidly curving upward.

"The first, the non-adjustable exit, of course, is a deviation from Meredith's dictum and precludes the progressive build-up of pressure behind the radiator with increasing speed. However, the second can only be judged in hindsight, from an airplane design point of view. The inlet seemed to be configured properly to recover the ram air pressure, and the first Mustang design had a similar entry opening. It was later apparent that the thin boundary layer of air flowing along the lower surface of the wing was progressively thickening ahead of the duct opening, and that the flow would break away at a point on the upward curve of the duct wall. While the resulting turbulent unsteady flow apparently did not create a serious vibration, it certainly reduced the efficiency of the radiator and prevented a more complete closure of the exit opening, which is necessary to develop the jet thrust. Very interestingly, the R.A.E. Subcommittee on Aerodynamics in 1936--in commenting on the Meredith and Capon reports--rather accurately predicted this problem: 'Experiments upon air-cooled engines in the 24-foot tunnel have shown that it is necessary to pay particular attention to the design of the entrance to cowlings and the cooling ducts in order to avoid loss of energy by the formation of eddies.' (Somewhat easier said than done at that time.)

"In the case of the Mustang, the duct volume was larger and flow instability more violent, creating an unacceptable vibration and rumble. Resourceful engineers at North American, working with wind tunnel models, overcame the problem by lowering the intake upper lip below the wing surface boundary layer, thus beginning a new upper duct surface. In this design, the flow expanded gradually as the duct velocity decreased, and the pressure at the radiator face was reasonably uniform. This permitted the appropriate closure of the exit with a temperature-controlled power actuator, and a minimum pressure drop across the radiator consistent with efficient radiator function and cooling demand.

"As a result, the cooling drag was estimated at only 3 percent of the total and used only something like 40 horsepower for cooling purposes. While the comparable power used for cooling by the Spitfire is not available to me, the measurements made by Rolls-Royce show a total power required for the same speed (400 mph) as 200 horsepower more for the Spitfire than for the Mustang.

"Records show the P-51D's speed was 437 mph and the Spitfire Mk IX speed was 405 mph. While the Spitfire had exposed tail wheel and other small differences from the Mustang, most of the speed difference was in the cooling drag. The Mark VIII with retracted tail wheel is rated at 414 mph at a somewhat higher altitude. Advanced models of both airplanes with higher performance were produced late in the war, but were not available in significant numbers before V-E Day, May 8, 1945.

"It seems that most other contemporary airplanes attempting to take advantage of the Meredith Effect failed for one reason or another to combine an efficient duct system with a properly designed and regulated exit-closing mechanism and did not develop the energy recovery inherent in the Meredith method. They generally used 10 percent or more of their power available at high speed to overcome cooling drag. A notable exception was the DeHavilland Mosquito multi-purpose plane with the same Rolls-Royce engines and which used a wing leading edge radiator mounting with a short and direct inlet duct. The controllable exit opening had a minimum area little more than half that of the Spitfire, and while it was a larger two-engine airplane, it had a speed of 425 mph.

"Since jet engines do not require cooling systems of the type described here, the subject has become moot and of little current importance. There was a time, however, when this rather insignificant subject made a critical difference."


Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

Thera
11-04-2003, 04:31 AM
I'll put the quoted material in simpler terms. I've tutored students who've also had a hard time with math.

Propeller thrust... 1,000 pounds
Raditor drag... -400 pounds
Monentum recovery (thrust)... +350 pounds

That gives you a total of 950 pounds of thrust. That's 50 pounds less thrust than with a closed radiator.

(1000 - 400) + 350 = 950

That's a 5% speed decrease with an open radiator. To put that in simpler terms imagine if you're flying at 500kph. 5% of 500kph is 25kph. That means that an open radiator will cause your plane to go 25kph SLOWER or roughly 475kph.

-----------------------------------------


Fools rush in where angels fear to tread.

XyZspineZyX
11-04-2003, 04:54 AM
Thera wrote:
- I'll put the quoted material in simpler terms. I've
- tutored students who've also had a hard time with
- math.
-
- Propeller thrust... 1,000 pounds
- Raditor drag... -400 pounds
- Monentum recovery (thrust)... +350 pounds
-
- That gives you a total of 950 pounds of thrust.
- That's 50 pounds less thrust than with a closed
- radiator.
-
- (1000 - 400) + 350 = 950
-
- That's a 5% speed decrease with an open radiator.
- To put that in simpler terms imagine if you're
- flying at 500kph. 5% of 500kph is 25kph. That
- means that an open radiator will cause your plane to
- go 25kph SLOWER or roughly 475kph.



Thanks for the math lesson and the insult professor.

I think you are confused as to just what constitutes an "open radiator" on the Mustang.

Whether or not the radiator is "open" or not is determined by the position of the radiator air exit shutter - that little flap like doohickey on the rear of the radiator air scoop.

The exit is the "jet exhaust nozzle" (for lack of better words). If the exit is shut, the there is no momentum recovery.

Read Atwood's entire article yourself, you only posted a tiny portion of it.

There MUST be an exit for there to be any "momentum recovery". If there is no opening, then the propellor thrust must overcome the drag of the radiator scoop. Opening the exit allows for a compensation of the cooling drag.

You can see it in the numbers you posted:

- Propeller thrust... 1,000 pounds
- Raditor drag... -400 pounds
- Monentum recovery (thrust)... +350 pounds
-
- That gives you a total of 950 pounds of thrust.
- That's 50 pounds less thrust than with a closed
- radiator.

If there were no opening, there there is no "momentum recovery." 1,000 lbs - 400 lbs = 600 lbs thrust.



The P-51 in the beta is modelled incorectly:

At high speed (or any speed in the game), the plane is faster with the radiator air exit shutter closed than with it open. This flys in the face of the article you posted. The reason for the high speed of the Mustang was due to the Meredith effect. There is NO meredith effect if there is no way to exhaust the air. There is no way to exhaust the air if the radiator air exit shutter is closed.





Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

Thera
11-04-2003, 04:59 AM
LOL. There's no "momentum recovery" because no momentum is lost due to drag.

-----------------------------------------


Fools rush in where angels fear to tread.

XyZspineZyX
11-04-2003, 05:05 AM
Thera wrote:
- LOL. There's no "momentum recovery" because no
- momentum is lost due to drag.
-
------------------------------------------
-
-
- Fools rush in where angels fear to tread.

Hmm, interesting take.

Are you suggesting that the scoop itself is not part of the cooling system, and that it produces no drag at all if the radiator is closed?





Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 05:36 AM
1.7 Km's = 1 Mile, is that not a true equation? That's how we were taught to convert Kilometers to Miles in the service. Perhaps my match is wrong.
~S!
Eagle
CO 361st vFG


<center>----------------------------------------------------------------------------</center> <center> www.361stvfg.com</center> (http://www.361stvfg.com</center>)
<center>
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XyZspineZyX
11-04-2003, 05:49 AM
My concern here is pretty clear.

In FB, --any amount-- of opening of the radiator air exit flap reduces top speed. Any at all. That's wrong, here's why:

"That report showed how the momentum loss in the cooling radiator could be largely restored when excess cooling air was being forced through the radiator at high speed. As noted before, this involved closing the air exit enough to get a substantial back pressure behind the radiator which largely restored the momentum loss--which was quite large as described above"



Note the word "enough." Closing the exit door ENOUGH to to get a substantial back pressure. But the door can not be closed completely otherwise no air passes thru the radiator and there is no cooling effect. That exit door has to be open enough for it to be expelled, but not so much that excess air is being forced thru the radiator. It's clear that when the Mustang hit its top speed, the exit door was open to some degree. But in FB, if its open to ANY degree, speed is lost. Top speed is achieved in FB when its closed completely.

Admittedly, I don't know what is "enough." I don't know. "Enough" may be half way open at 300 mph, or a little less than fully open at 400 mph. One thing is certain though, "enough" doesn't mean closed. And closed is the only way to achieve top level flight speed in FB.


Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 05:50 AM
Eagle_361st wrote:
- 1.7 Km's = 1 Mile, is that not a true equation?
- That's how we were taught to convert Kilometers to
- Miles in the service. Perhaps my match is wrong.
- ~S!
- Eagle
- CO 361st vFG


I just use this website for everything:

http://www.sciencemadesimple.com/conversions.html

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 05:59 AM
Thanks Chimp I was wrong my math was rong, sorry. 730 Kph comes out to 453 Mph. /i/smilies/16x16_smiley-sad.gif That is a bit too fast for the "D". Again sorry for my poor math. /i/smilies/16x16_smiley-sad.gif
~S!
Eagle
CO 361st vFG


<center>----------------------------------------------------------------------------</center> <center> www.361stvfg.com</center> (http://www.361stvfg.com</center>)
<center>
http://home.comcast.net/~smconlon/wsb/media/245357/site1003.jpg

</center>

XyZspineZyX
11-04-2003, 06:03 AM
Eagle_361st wrote:
- Thanks Chimp I was wrong my math was rong, sorry.
- 730 Kph comes out to 453 Mph.


Yes, that is too fast for the D. But that's precisely the official North American Aviation top speed for the P-51B-1 at 28,800 feet according to NAA report NA-5798 "Flight Test Performance for the P-51B-1."

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:10 AM
What's interesting to me is that two obviously intelligent people are apparently on opposite sides of this issue. I'm not bright enough to know which one of you is correct, but I'm feeling a sick pleasure in realizing that one of you is wrong.../i/smilies/16x16_smiley-happy.gif

Seriously though, this is an interesting discussion and let's hope Oleg and Co. get it right.

Aviar

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XyZspineZyX
11-04-2003, 06:10 AM
Chimp,
Do you think weight would play any role in this, I know the tested "B" did not have the fuselage tank installed. Could that be what takes the 16 Mph out of the "D"?
On another note now knowing that in my tests the "D" model comes out 16 Mph too fast I hope it get's fixed, I don't want to give the Luftwhinners some fuel just for those 16 Mph. I think personally and having ridden second seat in a P-51 quite a few times this is the closest to the real thing I have ever experienced. I love it, I just want it as accurate as possible, including if it is too fast.
~S!
Eagle
CO 361st vFG

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XyZspineZyX
11-04-2003, 06:21 AM
Skychimp, Meredith effect was effective only with "Automatic" setting, not with "Open" setting.

"Automatic" setting opened the flap enough to let the engine get the necessary cooling, and the expanded hot air be released with higher speed because the radiator flap was not completely open. "Open" setting provided a better cooling but it didn't produced the Meredith effect. So the speed decrease with "Open" setting is very much realistic.

Also I doubt the numbers in that article. I agree that Meredith effect could diminish the cooling drag, but to pretend that it actually provided thrust by cooling is exagerated. I'm not aware of any piston powered plane made after ww2 to make such a claim. Do you believe that nobody wanted to reduce the cooling drag after ww2? Let's keep it real Skychimp. The famous surface evaporation cooling reduced the cooling drag by 2/3. But it didn't provide any thrust. It was considered the most advanced solution, even though not practical for a fighter.


<center> http://www.stormbirds.com/images/discussion-main.jpg </center>

Message Edited on 11/04/0312:23AM by Huckebein_FW

XyZspineZyX
11-04-2003, 06:26 AM
437 mph according to my sources was achieved at 10,176 lbs.

10,176 lbs according to the weight charts in AHT is close to the weight for a D with full internal fuel, full ammo, and bomb racks.

I haven't noticed, does the P-51D5-NT in the addon have bomb racks? I think they made about an 8-10 mph difference IIRC.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:26 AM
Not that we can necessarily rely on the 3D model, but even with radiator set to "closed," visually the door is still somewhat open.

--AKD

http://www.flyingpug.com/pugline2.jpg

XyZspineZyX
11-04-2003, 06:27 AM
Huckebein_FW wrote:
- Skychimp, Meredith effect was effective only with
- "Automatic" setting, not with "Open" setting.


And things suddenly take a downturn /i/smilies/16x16_smiley-sad.gif

Huck, unless you have something to contribute, other than your usual American plane bashing, go somewhere else.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:34 AM
SkyChimp wrote:
-
- Huckebein_FW wrote:
-- Skychimp, Meredith effect was effective only with
-- "Automatic" setting, not with "Open" setting.
-
-
- And things suddenly take a downturn /i/smilies/16x16_smiley-sad.gif
-
- Huck, unless you have something to contribute, other
- than your usual American plane bashing, go somewhere
- else.
-
- Regards,
-
- SkyChimp

Whoa there! Control yourself Skychimp. He may be right.

--AKD

http://www.flyingpug.com/pugline2.jpg

XyZspineZyX
11-04-2003, 06:38 AM
Anyways, to adress your points:


Huckebein_FW wrote:
- Skychimp, Meredith effect was effective only with
- "Automatic" setting, not with "Open" setting.

I know that, Huck.



- "Automatic" setting opened the flap enough to let
- the engine get the necessary cooling, and the
- expanded hot air be released with higher speed
- because the radiator flap was not completely open.
- "Open" setting provided a better cooling but it
- didn't produced the Meredith effect. So the speed
- decrease with "Open" setting is very much realistic.

But Huck, if you've read my posts you'd know that it is not just the "open" setting that decreases speed. Opening the radiator ANY AT ALL decreases speed. That's wrong.



- Also I doubt the numbers in that article.

Well, Atwood was one of the designers of the Mustang.



- I agree
- that Meredith effect could diminish the cooling
- drag, but to pretend that it actually provided
- thrust by cooling is exagerated. I'm not aware of
- any piston powered plane made after ww2 to make such
- a claim. Do you believe that nobody wanted to reduce
- the cooling drag after ww2? Let's keep it real
- Skychimp. The famous surface evaporation cooling
- reduced the cooling drag by 2/3. But it didn't
- provide any thrust. It was considered the most
- advanced solution, even though not practical for a
- fighter.

That it provided thrust is probably an overstatement. But whether it provided thrust or simply reduced drag is irrelevant. The relevant point --here-- is that the radiator flap was open to some degree in high speed flight. But it can not be opened to any degree in FB without a speed loss.





Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:39 AM
A.K.Davis wrote:

- Whoa there! Control yourself Skychimp. He may be
- right.
-
---AKD


Do you have anything to add?

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:43 AM
SkyChimp wrote:

- That it provided thrust is probably an
- overstatement. But whether it provided thrust or
- simply reduced drag is irrelevant. The relevant
- point --here-- is that the radiator flap was open to
- some degree in high speed flight. But it can not be
- opened to any degree in FB without a speed loss.


I agree with this. Let's keep our heads cool and hope that 1C will model the Mustang correctly.


<center> http://www.stormbirds.com/images/discussion-main.jpg </center>

XyZspineZyX
11-04-2003, 06:46 AM
Huckebein_FW wrote:
- SkyChimp wrote:
-
-- That it provided thrust is probably an
-- overstatement. But whether it provided thrust or
-- simply reduced drag is irrelevant. The relevant
-- point --here-- is that the radiator flap was open to
-- some degree in high speed flight. But it can not be
-- opened to any degree in FB without a speed loss.
-
-
- I agree with this. Let's keep our heads cool and
- hope that 1C will model the Mustang correctly.


You're right. My apologies.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:51 AM
Thera wrote:
- That's a 5% speed decrease with an open radiator.
- To put that in simpler terms imagine if you're
- flying at 500kph. 5% of 500kph is 25kph. That
- means that an open radiator will cause your plane to
- go 25kph SLOWER or roughly 475kph.
-

Its not that simple. The relationship of thrust and speed, or rather (thrust-drag) and speed, is not linear, that means you dont get 5% more speed for 5% more thrust, or vice versa



I/JG54_SerpentBlade
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XyZspineZyX
11-04-2003, 06:52 AM
SkyChimp wrote:
-
- A.K.Davis wrote:
-
-- Whoa there! Control yourself Skychimp. He may be
-- right.
--
----AKD
-
-
- Do you have anything to add?
-
- Regards,
-
- SkyChimp
-

I already told you that the radiator appears to be somewhat open on the closed setting, but apparently you don't read very well.

It's a beta, so you can read as much into the visual state of the radiator door as you can the speed attained on some arbitrary, non-historical radiator setting.

All other aircraft in the game have visual radiator positions that correspond with the current setting. Even if the pivot point is fixed, it appears that the door would still be somewhat open in its most closed setting in game.

Whether it is correct or not, all other aircraft in the game work on the simple logic that "closed" setting=best speed. If the best speed is achievable with the door somewhat open, and there is no in-game benefit to closing the door completely, why not have the P-51 conform to the same logic as the other planes and simply have the "closed" setting be the optimum for speed.

But I guess we'll just have to wait until we see the real thing, cuz we're not goddam beta-testers, are we?

--AKD

http://www.flyingpug.com/pugline2.jpg


--AKD

http://www.flyingpug.com/pugline2.jpg

XyZspineZyX
11-04-2003, 07:07 AM
A.K.Davis wrote:

- I already told you that the radiator appears to be
- somewhat open on the closed setting, but apparently
- you don't read very well.

Actually, AK, I did read it. I simply didn't comment on it. Because whether or not it "appears" to be open in the closed setting, it is closed, according to the comments that appear when adjusting it.



- It's a beta, so you can read as much into the visual
- state of the radiator door as you can the speed
- attained on some arbitrary, non-historical radiator
- setting.
- All other aircraft in the game have visual radiator
- positions that correspond with the current setting.
- Even if the pivot point is fixed, it appears that
- the door would still be somewhat open in its most
- closed setting in game.
- Whether it is correct or not, all other aircraft in
- the game work on the simple logic that "closed"
- setting=best speed. If the best speed is achievable
- with the door somewhat open, and there is no in-game
- benefit to closing the door completely, why not have
- the P-51 conform to the same logic as the other
- planes and simply have the "closed" setting be the
- optimum for speed.
-

You seem to be the only one fixated on the visual state of the radiator. What it looks like is irrelevant. The game says it closed when its closed. It says its opened when its open. And there are various settings in between. This is what is relevant



- But I guess we'll just have to wait until we see the
- real thing, cuz we're not goddam beta-testers, are
- we?
-
---AKD

You certainly are angry, aren't you. If my posts disturb you this much, perhaps staying out of them is the way for you to go.








Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 07:08 AM
In-game radiator door position on "closed" setting:

http://home.mchsi.com/~131st___vfw/Toads_Stang.jpg


RL picture with radiator door much more open:

http://www.p51.mustangsmustangs.com/Pics/Military/8thAF/11.jpg

The visual state is not irrelevant. The arbitrary "settings" are more of an abstraction than the visual state of the cooling systems in FB.

If this "slightly open" setting is what achieves best speed for Mustang, where is the logic in including a "closed" setting that offers nothing in-game? You would just have a parade of idiots in here bawling that closing the radiator doesn't make the Mustang go faster.

--AKD

http://www.flyingpug.com/pugline2.jpg


Message Edited on 11/04/0306:14AM by A.K.Davis

XyZspineZyX
11-04-2003, 07:39 AM
The 190 shouldn't lose any speed with radiator open either but as it is now the radiator acts like an air-brake. I wouldn't get my hopes up correct or not.

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XyZspineZyX
11-04-2003, 08:56 AM
Yeah but the Fw-190 doesn't need to have the radiator open all the time. /i/smilies/16x16_smiley-wink.gif

http://www.mechmodels.com/images/klv_ubisig1a.jpg


Oh yeah, I'm a P-63 whiner too! /i/smilies/16x16_smiley-very-happy.gif

XyZspineZyX
11-04-2003, 10:54 AM
1. Finally we plan to have it Auto. In real life the temperature of the coolant determided by thermostat, Like on many other aircraft (Bf109F-G-K, Yak-3, Yak-9 late, etc).

2. The drag is present anyway for the closed radiator in P-51D. But in this position the construction of radiator cowling with laminar flow around it really has small drag that allow to get greater speed of the plane itself in comparison with usual radiator cowl placed in that aerodynamically 100% _optimal_ area (like say on Yak-3 or on Yak-9U, that has it in the same place, but hasn't laminar airflow in the place beween radiator airintake and fuselage. Germans also tried to place there after great experimantal works, but it was too late...You may see it on experimental FWs and Bfs). But when it begins to open - drag will increases anyway. So you are worng in your opinion. I know where you took that info /i/smilies/16x16_robot-happy.gif But this isn't professional aerodynamical magazine, be sure. There was just private opinion. The only thing there is correct that the design of radiator cowling was really best comapring to other planes.


SkyChimp wrote:
- Just in case its modelled this way, the P-51's
- radiator air outlet shutter should be automatic. In
- real life, the temperature of the coolant determined
- how much the flap opened. Otherwise, there was a
- switch in the cockpit with "auto", "open", "closed"
- and "off." "Auto" was the usual setting.
-
- And when the P-51's radiator opens (the flap opens
- up), the Mustang should not loose speed. In fact,
- the Mustang's radiator design created thrust.
-
- If the Mustang is loosing speed with an open
- radiator, it should not.
-
- Regards,
-
- SkyChimp
-
<img
- src="http://members.cox.net/rowlandparks/sigstang.
- jpg">
-
-



Oleg Maddox
1C:Maddox Games

XyZspineZyX
11-04-2003, 10:58 AM
Currently in game it is wrong. But that is in external 3D model, but not in the aerodynamical model of P-51.
The visuals of working positions of P-51 radiator will be changed in final 1.2 add-on. Visuals in that choosen case don't play any role for aerodynamics performance. Its calculates in separate aerodynamics models. Hope I was clear.


A.K.Davis wrote:
- In-game radiator door position on "closed" setting:
-
- <img
- src="http://home.mchsi.com/~131st___vfw/Toads_Stan
- g.jpg">
-
-
- RL picture with radiator door much more open:
-
- <img
- src="http://www.p51.mustangsmustangs.com/Pics/Mili
- tary/8thAF/11.jpg">
-
- The visual state is not irrelevant. The arbitrary
- "settings" are more of an abstraction than the
- visual state of the cooling systems in FB.
-
-
- If this "slightly open" setting is what achieves
- best speed for Mustang, where is the logic in
- including a "closed" setting that offers nothing
- in-game? You would just have a parade of idiots in
- here bawling that closing the radiator doesn't make
- the Mustang go faster.
-
---AKD
-
- http://www.flyingpug.com/pugline2.jpg
-
-
- Message Edited on 11/04/03‚ 06:14AM by A.K.Davis



Oleg Maddox
1C:Maddox Games

XyZspineZyX
11-04-2003, 11:01 AM
Oleg_Maddox wrote:Hope I was clear.


Very clear. Makes perfect sense to me.

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XyZspineZyX
11-04-2003, 11:33 AM
Agreed. Thanks Oleg.
/i/smilies/16x16_smiley-very-happy.gif I'd love to arugue that point with you so we cold milk a little more speed from the P-51 lol....but you are 100% correct & that is an argument i know i would loose. /i/smilies/16x16_smiley-sad.gif

- Oleg_Maddox wrote:Hope I was clear.

Clear as crystal Sir.

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XyZspineZyX
11-04-2003, 01:08 PM
Thanks for the clarification, Oleg.

Yup, it's a beta issue.



-----------
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XyZspineZyX
11-04-2003, 06:04 PM
Had a feeling we were all wrong. There's a reason we're not beta-testers.../i/smilies/16x16_smiley-happy.gif

--AKD

http://www.flyingpug.com/pugline2.jpg

XyZspineZyX
11-04-2003, 06:31 PM
Thanks alot Oleg. /i/smilies/16x16_smiley-happy.gif You da man. /i/smilies/16x16_smiley-happy.gif I can't wait for the final product and then with the big add-on the B & C. Whoohoo. /i/smilies/16x16_smiley-happy.gif
~S!
Eagle


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XyZspineZyX
11-04-2003, 07:03 PM
i always thought the closed setting was as near to closed that the plane can get, eg 109f can close its rad completely, while hurricane is always partly open
i guess its a bit telling that war aircraft could totaly close rad. for the extra emergancy speed /i/smilies/16x16_smiley-happy.gif

XyZspineZyX
11-04-2003, 11:50 PM
A.K.Davis wrote:
- Had a feeling we were all wrong. There's a reason
- we're not beta-testers.../i/smilies/16x16_smiley-happy.gif
-
---AKD

You had a feeling you were wrong? So, all that arguing, and the insult about my reading ability, was just for the sake of argument?

Strange behavior.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-05-2003, 12:11 AM
SkyChimp wrote:
-
- A.K.Davis wrote:
-- Had a feeling we were all wrong. There's a reason
-- we're not beta-testers...http://www.flyingpug.com/pugline2.jpg

XyZspineZyX
11-05-2003, 12:48 AM
Oleg_Maddox wrote:
- 1. Finally we plan to have it Auto. In real life the
- temperature of the coolant determided by thermostat,
- Like on many other aircraft (Bf109F-G-K, Yak-3,
- Yak-9 late, etc).

Good news. Auto was the way it was. Auto is the way it should be in FB.



- 2. The drag is present anyway for the closed
- radiator in P-51D. But in this position the
- construction of radiator cowling with laminar flow
- around it really has small drag that allow to get
- greater speed of the plane itself in comparison with
- usual radiator cowl placed in that aerodynamically
- 100% _optimal_ area (like say on Yak-3 or on Yak-9U,
- that has it in the same place, but hasn't laminar
- airflow in the place beween radiator airintake and
- fuselage. Germans also tried to place there after
- great experimantal works, but it was too late...You
- may see it on experimental FWs and Bfs). But when it
- begins to open - drag will increases anyway. So you
- are worng in your opinion. I know where you took
- that info. But this isn't professional
- aerodynamical magazine, be sure. There was just
- private opinion. The only thing there is correct
- that the design of radiator cowling was really best
- comapring to other planes.

Oleg. I appreciate your input here, but you seem to be missing the point I am trying to make.

I'd like to adress your dismissal of the article I posted as "private opinion."

That may be. I'm sure Lee Atwood was a private individual. But to suggest his piece is not credible because it is not in an engineering periodical makes no sense. Lee Atwood's piece would be as true had it been published in a cooking magazine.

For the record, Lee Atwood wasn't "just some guy." Lee Atwood has the credentials that make his "opinion" of the Mustang weightier than any other opinion you may read on these boards, including your own.

Here's a little on Lee Atwood:

" John Leland (Lee) Atwood joined North American Aviation, Inc. in 1934, one year before the firm moved from Dundalk, Maryland, to Southern California. He previously worked at Douglas Aircraft in Southern California, builder of such venerable transports as the DC-3, so he would cross the country twice in a short time.

He soon became a vice president, and in 1938 was named assistant general manager of the company. In 1941, he became first vice president; in 1948 he was elected president; in 1960 he became chief executive officer at the retirement of Dutch Kindelberger; and in 1962 he became chairman of the board."

Lee Atwood was also the chief designer of the P-51's radiator system.

A more complete biography can be seen here:
http://www.boeing.com/history/bna/atwood.html



Lee Atwood states clearly that the radiator thrust is what helped the P-51 achieve its high speeds:

"The laminar flow wing is great for jet airplanes or in a high-speed dive but had little effect on the P-51's overall performance envelope. You have to attribute the speed increase to the radiator energy recovery (positive thrust), not the characteristic of the wing itself. The wing did help in a dive -- not in level flight. I never mentioned this to anyone during the war."

That's Atwoods statement, not mine.

He says the speed increase came from the radiator thrust. Well, you can't get radiator thrust if the radiator air exit shutter is not open. That shutter acts as the "jet nozzle." If it is closed, there is no positive thrust.

Yes, I agree with you that the P-51's radiator duct was very advanced and contributred to the overall aerodynamic efficiency of the aircraft. But it was not just the duct, it was its placement in relation to the canopy, in relation to the wings, etc. I believe the Mustang was one of the first fighters to disply the Whitcomb effect, IIRC.

But there is simply no blinking at the fact that the radiator thrust contributed to the speed of the plane. Atwood says so. And you can not have radiator thrust without the radiator exit flap open to the degree necessary to create the back pressure needed to develope the thrust. Again, Atwood says so. And he designed the system.

Again, read what Atwood wrote:
"In this design, the flow expanded gradually as the duct velocity decreased, and the pressure at the radiator face was reasonably uniform. This permitted the appropriate closure of the exit with a temperature-controlled power actuator, and a minimum pressure drop across the radiator consistent with efficient radiator function and cooling demand."

"As a result, the cooling drag was estimated at only 3 percent of the total and used only something like 40 horsepower for cooling purposes"


What is clear from Atwood's articles is that optimum aerodynamic efficiency was not achieved with the radiator flap closed. It was achieved with it open - open enough to create the necessary back-pressure to create thrust, but not so open that the back pressure can not be created and vented as thrust.

"Both the British and German engineers at the time thought you could test a scale model in a wind tunnel. But the wind tunnel models didn't generate the engine-heat factor, which we successfully controlled within the air scoop to create positive thrust. They were all looking at Mustang's laminar flow wing, which was noted for reducing air friction over the surface of aircraft wings."

Again Atwood, not me.



That's the point I've been trying to make. When you remodel the P-51, it should achieve its highest level flight speeds with the radiator open. Not all the way, but certainly not closed. And its not me that says so, it's Lee Atwood.






Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg



Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-05-2003, 01:06 AM
Skychimp do you have a diagram of the airduct? Because running it through my head I am finding it hard understand how this thrust is created. Thermodynamically I dont know how it could work, but I could be wrong cause there could very well be something I am missing.


"Ich bin ein Wuergerwhiner"

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XyZspineZyX
11-05-2003, 01:16 AM
http://www.icon.co.za/~pauljnr/radsta.jpg


Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-05-2003, 02:09 AM
SkyChimp,

I respect your passion concerning this matter, but I believe Oleg has answered your original topic....his key phrase being.."But when it begins to open - drag will increases anyway. So you are wrong in your opinion."

I'm sure you are aware that Oleg has enlisted the aid of an actual P-51 pilot to test the final FM of the FB Mustang. Obviously, they are in communication concerning the modelling of this wonderful airplane.

Realizing this, I doubt Oleg would make such a definitive statement on this forum without being certain of it's accuracy. I would hope that we could now move on without dragging this out like some other unfortunate threads of the past. This has resulted in Oleg visiting us less and less, and I can't say that I blame him.

SkyChimp, please respect Oleg's decision. Of course, if you can find other substantial information concerning this matter, I'm sure we would all be interested in viewing it. Otherwise, repeatedly posting the same information after Oleg has disagreed with it will not get us anywhere.

SkyChimp, please don't take my comments the wrong way. You are a respected member of the community and your views are always welcome.

Aviar

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Thera
11-05-2003, 02:27 AM
Even that illustration you've posted says that it reduced, but DIDN'T ELIMINATE, radiator drag.

You open the radiator you slow down, there is no question to this.

-----------------------------------------


Fools rush in where angels fear to tread.

XyZspineZyX
11-05-2003, 02:30 AM
Aviar wrote:
- SkyChimp,
-
- I respect your passion concerning this matter, but I
- believe Oleg has answered your original topic....his
- key phrase being.."But when it begins to open - drag
- will increases anyway. So you are wrong in your
- opinion."
-
- I'm sure you are aware that Oleg has enlisted the
- aid of an actual P-51 pilot to test the final FM of
- the FB Mustang. Obviously, they are in communication
- concerning the modelling of this wonderful airplane.
-
- Realizing this, I doubt Oleg would make such a
- definitive statement on this forum without being
- certain of it's accuracy. I would hope that we could
- now move on without dragging this out like some
- other unfortunate threads of the past. This has
- resulted in Oleg visiting us less and less, and I
- can't say that I blame him.
-
- SkyChimp, please respect Oleg's decision. Of course,
- if you can find other substantial information
- concerning this matter, I'm sure we would all be
- interested in viewing it. Otherwise, repeatedly
- posting the same information after Oleg has
- disagreed with it will not get us anywhere.
-
- SkyChimp, please don't take my comments the wrong
- way. You are a respected member of the community and
- your views are always welcome.
-
- Aviar


Respectfully, Oleg hasn't answered anything. He himself has stated his opinion. If he wants to model the P-51 in any manner that suits him, I have no choice but to accept his decision. But I don't have to accept his answer as correct.

And again respectfully, Oleg is not the definitve answer with regards to the P-51's radiator. He's only the final answer as to how it will be represented in his game.

Lee Atwood designed it, oversaw its production, tested it, and explained to the world why the likes of Great Britain and Germany couldn't figure out why the Mustang was as fast as it was. And he stated it was the radiator thrust.

Oleg can disregard the writings of Atwood as just some "private opinion." But some people have a little more weight in their opinions than others. And with regards to the P-51s radiator, no one, Oleg included, carries more credibility than Atwood.

Atwood says the system created thrust which accounted for the planes high speed. You don't get thrust unless the radiator is at least partially open. It's really that simple.





Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-05-2003, 02:35 AM
Thera wrote:
- Even that illustration you've posted says that it
- reduced, but DIDN'T ELIMINATE, radiator drag.
-
- You open the radiator you slow down, there is no
- question to this.


Thera, even Oleg said that radiator drag is there even when it is closed. You seem to be under some impression that there is NO radiator drag when the radiator is closed. There is. That scoop, no matter how artfully designed, is a drag liability.

Opening the radiator to the point where thrust is created counteracts a major portion of the radiator drag.

Go back and read Atwood's ENTIRE article, you posted only a tiny portion of it. The plane had LESS drag with the radiator open enough to create said thrust than it did when it was entirely closed.





Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

Thera
11-05-2003, 05:35 AM
But it never created enough thrust to 100% counteract the drag created by diverting air through the radiator. As your article and picture state so clearly.

By your logic every plane with a radiator wouldn't suffer any ill effects by having a 100% open radiator. But they do, as did the P51. The P51 had a well designed system but it still created more drag when it was open, just not as much as other planes of the era.



-----------------------------------------


Fools rush in where angels fear to tread.

XyZspineZyX
11-05-2003, 05:53 AM
SkyChimp wrote:
- "Both the British and German engineers at the time
- thought you could test a scale model in a wind
- tunnel. But the wind tunnel models didn't generate
- the engine-heat factor, which we successfully
- controlled within the air scoop to create positive
- thrust. They were all looking at Mustang's laminar
- flow wing, which was noted for reducing air friction
- over the surface of aircraft wings."
-
- Again Atwood, not me.

I find Atwood's assertion that German engineers were unaware of this effect somewhat doubtful, since a thrust-producing cooling system was considered at the very beginning of the FW190 development cycle:

"The prototype FW190 flew well enough, although there was some trouble with the BMW 139 engine--the rear cylinders of the two-row radial were prone to overheating. To reduce drag from the radial engine, the prototype was fitted with a special ducted spinner. The cooling air was heated as it flowed past the cylinders and ejected from the rear of the spinner under pressure to provide a little extra thrust. During flight tests, however, it was found that the ducted spinner arrangement gave little reduction in drag. In truth the installation was not worth the bother, and early in the test programme the fighter was fitted with a normal cowling."

--Alfred Price, "Focke Wulf FW190 in Combat"

--AKD

http://www.flyingpug.com/pugline2.jpg

XyZspineZyX
11-05-2003, 07:33 AM
Seems to me that Meredith effect was in action with any plane that had a warm engine, regardless if designers knew about it or not /i/smilies/16x16_smiley-wink.gif .

<center>http://easyweb.globalnet.hr/easyweb/users/ntomlino/uploads/sig.jpg

Fw 190 durbatulŻk
Fw 190 gimbatul
Fw 190 thrakatulŻk,
agh burzum-ishi krimpatul

XyZspineZyX
11-05-2003, 07:43 AM
I don't think you read the whole article right there, Chimp. And the way you keep taking lines out as proofs shows me that. When you printed the bigger chunk with the description of the heat pump action there was a better view of the complexity and subtlety of the subject.

Didn't the full article state how the effect didn't come into its own until high speed was reached? You have to have the ram air and engine heat to make it work, the faster you go the more efficient it gets. So maybe at lower speeds like during hard climbs it's better to just keep the system open and get as much air through there as you can? Or maybe the auto system would do that anyway? It doesn't say anywhere how the system works when coolant flow keeps rising past safe temperature in that article, does it?

Just having air flow inside the system and dragging internally on the radiators makes drag beyond what the opening does if the exits are closed. Getting some back by metering the flow and using heat expansion of the air is a neat trick to be sure but there's nothing in that article stating that at all times, sppeds and altitudes, a closed radiator will make more drag than open on auto. Perhaps in an engineering journal or design notes the full story is presented or perhaps the details are well based speculation arising from test results on where the power comes and goes?

That's all well and good but where fully do you want to take it? At what speed and conditions should it be less drag to open the system? All and any? Maybe so but how can you tell? I'm betting that the true answer isn't going to come about from web and library searches. But wth, there's so much based on speculation anyway, right? All the details can't be modelled so just nail the drag to a single % value regardless and get on with the rest of the sim. Right? Of course the value is the one for full speed, the most efficient by far because otherwise top speed won't be reached, right?

Huckebein and Isegrim will have fits but I'm sure you can live with that, right?

LOL! I see flames! ROFL! NOBODY has accurate charts on this one, I bet! Wwwwhhhheeeeeeee! A new whine-antiwhine! It's like pioneer physics of opinions, 101!


Neal

XyZspineZyX
11-05-2003, 08:14 AM
you would get more thrust the hotter the radiator got, but as speed increases turbulence over the radiators would increase the force it takes to push the air through. I could see the effect helping a lot at low speeds with a hot engine, but at higher speeds the drag caused by the radiator should make a much bigger difference because with the radiator open, the coolant will cool more efficiently causeing exit air temp to be lower and thus thrust from the exit air would be lower. There would of course be an optimum speed and engine temp where it would work the best but there are so many variables it would be super tough to model it accurately.

"Ich bin ein Wuergerwhiner"

"The future battle on the ground will be preceded by battle in the air. This will determine which of the contestants has to suffer operational and tactical disadvantages and be forced throughout the battle into adoption compromise solutions." --Erwin Rommel

http://lbhskier37.freeservers.com/Mesig.jpg
--NJG26_Killa--

XyZspineZyX
11-05-2003, 12:08 PM
SkyChimp wrote:
-
-
-
- Lee Atwood states clearly that the radiator thrust
- is what helped the P-51 achieve its high speeds:
-
- "The laminar flow wing is great for jet airplanes or
- in a high-speed dive but had little effect on the
- P-51's overall performance envelope. You have to
- attribute the speed increase to the radiator energy
- recovery (positive thrust), not the characteristic
- of the wing itself. The wing did help in a dive --
- not in level flight. I never mentioned this to
- anyone during the war."
-
- That's Atwoods statement, not mine.
-

I know. But you undertand it wrong. Is correct that the construction of radiator cowling helps to achive greater speed especially the speed that close to the 0,8M, etc...
But it doesn't make the real additional thrust in a terms of additional thust to engine. Speaking by formulas we of course can implement it as additional thurst if in formula was set the constant radiator drag of some other aircraft radiator construction that was taken for comparison.

And.. I have very detailed description of aerodynamical tunnel research of the wing and radiator airflow for the lend lease P-51B /i/smilies/16x16_robot-happy.gif It was researched very well by Russians becasue it was really designed very good. /i/smilies/16x16_robot-happy.gif


- He says the speed increase came from the radiator
- thrust. Well, you can't get radiator thrust if the
- radiator air exit shutter is not open. That shutter
- acts as the "jet nozzle." If it is closed, there is
- no positive thrust.

Ok that is the point wher you don't understand. No time to explain it in right English terms (I simply don't know many of them, comparing to Russian terms), but in general you need to undertand that no one aerodynamically designed detail may do additional trust in a common for that detail and plane itself airflow. Just becasue if in one place the flow is faster then when 2 flows - one faster and one slowly on the open backside cowl of radiator cowl mix with each other we get something like turbulence and damaged airflow in that place. This one damaged airflow in final makes bad for normal and laminar airflow arounf fuselase, etc. And finally we get anyway decreasing, but not increasing speed.

The fast speed of airflow inside the tunnel of radiator cowl in P-51 , comparing to other types allow to use:
- more effiency of cooling (however still not enough on Mustang with WEP and its why it was limited)
- more small external size radiator cowl
- finally to get more greater speed.


- Yes, I agree with you that the P-51's radiator duct
- was very advanced and contributred to the overall
- aerodynamic efficiency of the aircraft. But it was
- not just the duct, it was its placement in relation
- to the canopy, in relation to the wings, etc. I
- believe the Mustang was one of the first fighters to
- disply the Whitcomb effect, IIRC.

I told the same when I told you about 100% correct place from aerodynamcial point of view. Look for Yak-3, Yak-9 and how was moved from nose to the same place the oil radiato of La-7 comparing to La-5.


- But there is simply no blinking at the fact that the
- radiator thrust contributed to the speed of the
- plane. Atwood says so. And you can not have
- radiator thrust without the radiator exit flap open
- to the degree necessary to create the back pressure
- needed to develope the thrust. Again, Atwood says
- so. And he designed the system.

Look above. It where you are wrong


- Again, read what Atwood wrote:
- "In this design, the flow expanded gradually as the
- duct velocity decreased, and the pressure at the
- radiator face was reasonably uniform. This permitted
- the appropriate closure of the exit with a
- temperature-controlled power actuator, and a minimum
- pressure drop across the radiator consistent with
- efficient radiator function and cooling demand."
-
- "As a result, the cooling drag was estimated at only
- 3 percent of the total and used only something like
- 40 horsepower for cooling purposes"
-

That says all. Or you don't see it?



- What is clear from Atwood's articles is that optimum
- aerodynamic efficiency was not achieved with the
- radiator flap closed. It was achieved with it open
- - open enough to create the necessary back-pressure
- to create thrust, but not so open that the back
- pressure can not be created and vented as thrust.

No, for me it isn't clear becasue I know what he means.


- "Both the British and German engineers at the time
- thought you could test a scale model in a wind
- tunnel. But the wind tunnel models didn't generate
- the engine-heat factor, which we successfully
- controlled within the air scoop to create positive
- thrust. They were all looking at Mustang's laminar
- flow wing, which was noted for reducing air friction
- over the surface of aircraft wings."


What about that Russians tested the P-51 plane itself in the tunnel with working engine? Do you know that TsZAGI tunnel was the biggest in the world for that time?
There also tested He-162 full size for example and many others.../i/smilies/16x16_robot-happy.gif What Russian hadn't for that time - ist vertical tunnel for testing of spin haracterisitics of models, like had it Germans.

-
- That's the point I've been trying to make. When you
- remodel the P-51, it should achieve its highest
- level flight speeds with the radiator open. Not all
- the way, but certainly not closed. And its not me
- that says so, it's Lee Atwood.

Sorry. As I told here it is wrong.



Oleg Maddox
1C:Maddox Games

XyZspineZyX
11-05-2003, 12:42 PM
Thera wrote:
-
- "In the case of the Mustang, the air duct pumping
- system at full speed at 25,000 feet was processing
- some 500 cubic feet of air per second, and discharge
- speed of the outlet was between 500 and 600 feet per
- second relative to the airplane.


There seem to be some serious errors in his math. Have to convert to metric system
500-600 ft/sec exhaust speed, let‚¬īs say roughly 180m/s

500 ft^3/sec airflow = 14.3 m^3 air per second. Density is approx. 0.6 kg/m^3 in this alitude, so there‚¬īs a massflow of 8.5kg/sec through the radiator.

Thrust would be 8.5kg/s*180m/s = 1530N
1530/9.81 = ~160kg = 350lb, exactly what he wrotes

BUT His major error his that he uses the full exhaust speed, but actually you would have to take the DIFFERENCE between outlet and inlet (aircraft travelling) speed (Else an empty cylindric tube would produce thrust too...) . The difference is naturally WAY LOWER.

Even assuming a low speed cruise:
For example P-51 travelling at 400ft/sec = 122m/s = 273mph.
Difference dV = 180-122 = 58m/s , that‚¬īs a third of the full exhaust speed. So you can say it produced just 350/3 roughly 110lb thrust, compensating just for 25% of the radiator drag.

niklas

XyZspineZyX
11-05-2003, 03:14 PM
niklas1 wrote:
-
- Thera wrote:
--
-- "In the case of the Mustang, the air duct pumping
-- system at full speed at 25,000 feet was processing
-- some 500 cubic feet of air per second, and discharge
-- speed of the outlet was between 500 and 600 feet per
-- second relative to the airplane.
-

At sea level mach 1 is just about 1100 feet per second, at 25,000 feet I dunno what mach 1 is but the rough formula of 1.5% per 1000 ft would get 625 fps which while not accurate at least serves to show that the exhaust volume was imparted some forward motion by the passage of the plane.

As Oleg pointed out above, when the airstream from outside flow at full speed mixes with the different speed exhaust the result is drag vortexes. So maybe the real "boost" was in minimizing the difference between the exhaust speed air and the laminar flow air? These kinds of things were not science in the 40's but rather more of an art. AFAIK the modelling of airflow is still a developing practice.

I do wonder about airflow disturbance through bullet and shell holes in airplane wings where pressure differences between above and below should cause flow. A squad member who is working on his AE thesis, IIRC, tells me that for small holes it shouldn't be much. I guess that shot up planes still making it back are proof but it'd be neat to know a sim covered that --- maybe having one wing well perforated would cause noticeable yaw or the drop of the wing would compensate?


Neal

XyZspineZyX
11-05-2003, 04:05 PM
SkyChimp, there are two things you'll need to understand.

1st: The radiator on the P-51 is never really closed. It's just open to different degrees. (Just like LaGG-3 or Yak-9.) You can check blueprints, pictures, anything you like. I bet you'll never find a picture with a fully closed radiator. Well, at least I didn't.

2nd: A nozzle produces less thrust as the exit area increases.
This means: The radiator produces the biggest thrust when on a closed setting. It also creates least drag with this setting. Therefore the aircraft slowes down if you open the radiator.

The only thing you can ask is to change the message "radiator: closed" to "radiator setting 0" but this won't change a thing about P-51 behaviour in this regard. I however, find "radiator: closed" better for understanding.

XyZspineZyX
11-06-2003, 12:09 AM
Oleg_Maddox wrote:

-- Again, read what Atwood wrote:
-- "In this design, the flow expanded gradually as the
-- duct velocity decreased, and the pressure at the
-- radiator face was reasonably uniform. This permitted
-- the appropriate closure of the exit with a
-- temperature-controlled power actuator, and a minimum
-- pressure drop across the radiator consistent with
-- efficient radiator function and cooling demand."
--
-- "As a result, the cooling drag was estimated at only
-- 3 percent of the total and used only something like
-- 40 horsepower for cooling purposes"
--
-
- That says all. Or you don't see it?

I agree, it says all. But it appears you are fixated on the word therein - "closure." But "appropriate closure" does not mean totally closed.

Atwood said it another way:
"As noted before, this involved closing the air exit enough to get a substantial back pressure behind the radiator which largely restored the momentum loss--which was quite large as described above"

---Enough----

The duct had to be closed enough to generate the back pressure, while still permitting enough flow to give the required cooling.

You are suggesting that the Mustang, flying at combat power, made the long, slow climb to 437 mph while the radiator was configured in its most restrictive position.

Not likely.


Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-06-2003, 12:19 AM
JtD wrote:
- SkyChimp, there are two things you'll need to
- understand.
-
- 1st: The radiator on the P-51 is never really
- closed. It's just open to different degrees. (Just
- like LaGG-3 or Yak-9.) You can check blueprints,
- pictures, anything you like. I bet you'll never find
- a picture with a fully closed radiator. Well, at
- least I didn't.

I agree, "closure" is sort of misleading since some flow through occurs even int he most restricted position.



- 2nd: A nozzle produces less thrust as the exit area
- increases.
- This means: The radiator produces the biggest thrust
- when on a closed setting. It also creates least drag
- with this setting. Therefore the aircraft slowes
- down if you open the radiator.

You can tighten up the exit duct on the Mustang as tight as it will go. But a balance has to be struck. The duct has to be closed enough to generate the required back pressure, but cooling still has to take place.

The principal function of the Mustang's radiator is still to cool the engine. And while certainly not incidental, the thrust effect was a secondary function.

You can not choke the radiator to its most restricitive position to generate thrust at the expense of burning up the engine. You have to close the duct enough so that it will generate the maximum thrust WHILE STILL providing sufficient cooling for the engine.

The duct very well may be closed as much as it will go at cruise speed, since much less air is needed to provide cooling. But engine heat builds quickly at combat power, and sustained flying at high power (and high heat) will require a greater cooling effect. That means the duct will have to be opened more. Cooling will take place, and thrust will still be generated.





- The only thing you can ask is to change the message
- "radiator: closed" to "radiator setting 0" but this
- won't change a thing about P-51 behaviour in this
- regard. I however, find "radiator: closed" better
- for understanding.

I like your idea of a "0" thru whatever setting. But ideally, an automatic radiator would be best.



Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-06-2003, 01:11 AM
Here is a page from the British flight manual for ther Mustang III (P-51B) - equipped with the Packard Merlin V-1650-3 which says precisely how much the exit shutter will be open at a given temperature:

http://members.cox.net/rowlandparks/shutters1.jpg



Here is the engine chart for the V-1650-3:

http://members.cox.net/rowlandparks/shutters2.jpg



When the engine chart is compared to the manual page, I come away with the impression that from 60 to about 89 degrees celcius the radiator shutter will be closed. From 90 to 109 degress celsius it will be in an ever greater stage of opening. And from 110 to 140 degrees celcius it will be wide open.

Now, the Mustang achieved it's highest speed on combat power. And it would have taken a few minutes to get to 437mph. Is it unreasonable to believe that on combat power for that long the coolant temperature does rise in excess of 90 degrees celsius ? Because if it does rise to a temperature in excess of 90 degrees celsius, then the shutter is not closed when 437 mph is reached.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-06-2003, 01:28 AM
Here is another page from the manual:

http://members.cox.net/rowlandparks/shutters3.jpg



Combat Power (the power setting max speed was attained at) - 121 degrees celsius.

At 110 degrees the shutter was FULLY open.


I'm sorry Oleg, but I really think you are wrong.



Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-06-2003, 01:31 AM
Hmmm, I have read through this whole thread now a few times. Skychimp, with all due respect, most of what you describe sound correct, but I don't understand how it is any different from what Oleg is writing? I also don't see how what Oleg writes differs from Atwood, except maybe that this "net thrust" thing may be a bit too optimistic. I have read what other aerodynamicists wrote on this (Dave Lednicer for instance), and they believe that the net thrust thing may happen but probably only for a small range of throttle settings, speed and shutter setting combinations. That is not really that important though, because the point is that the cooling drag of the Mustang is still very low compared to contemporary aircraft. Anyway, besides the detail of whether there is a net thrust or just very low drag, where exactly is the problem?

Is the speed at which the shutter opens in the sim too slow for you? When wide open, the "thrust" effect will be lost, so I would assume the design of the thermostat would try to keep the opening as small as possible to maximize the "thrust" effect (or minimize the cooling drag, whichever way you want to look at it), while still allowing the necessary cooling.

From your last post, are you suggesting the shutter should be wide open when at maximum speed?

I guess I am just not following what the problem is...

XyZspineZyX
11-06-2003, 01:57 AM
Oryx wrote:
- Hmmm, I have read through this whole thread now a
- few times. Skychimp, with all due respect, most of
- what you describe sound correct, but I don't
- understand how it is any different from what Oleg is
- writing?...

I think what it has boiled down to now is this:

Oleg (and his ardent supporters) is under the impression that the Mustang's top speed was achieved with the radiator air exit shutter closed (radiator closed).

My position is that is not correct, that it was open, at least to some degree. I believe this because not only does the back-pressure need to be expelled in the form of "thrust," but that cooling HAD to take place. I believe there is no realistic way to accelerate in level flight to 437 mph at combat power with the shutter closed without severely overheating.

I contend that in 1.2-Final the Mustang should achieve its top speed with the shutter open, Oleg says that oepning it will actually decrease speed.

The manual pages above supports my position.



Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-06-2003, 02:09 AM
SkyChimp wrote:

-
- The manual pages above supports my position.
-
-
-
-


no, they don't...

<center><img src=http://hoarmurath.free.fr/images/sighoar.jpg></center>

ZG77_Nagual
11-06-2003, 02:10 AM
This is all good. I'll be surprised if Oleg is not allready aware of these things however.

http://pws.chartermi.net/~cmorey/pics/whiner.jpg

XyZspineZyX
11-06-2003, 02:14 AM
Oryx wrote:

- Is the speed at which the shutter opens in the sim
- too slow for you? When wide open, the "thrust"
- effect will be lost, so I would assume the design of
- the thermostat would try to keep the opening as
- small as possible to maximize the "thrust" effect
- (or minimize the cooling drag, whichever way you
- want to look at it), while still allowing the
- necessary cooling.


Actually, I'm not sure that the thrust will be lost when it is wide open, especially when both temperature and speed are very high, as in a combat-power maximum speed flight.

Atwood said, "This began to be a considerable pumping action as speeds approached 300 miles per hour--and at 400 miles per hour, it had a large potential and could be a considerable fraction of the airplane's total power equation, since the pumping pressure increases as the square of the speed."

At a crusing speed of 250 mph I'm sure the shutter was pretty much closed in order to obtain the necessary back pressure to produce "thrust." But as speed increased with engine power - along with heat - the shutter had to be opened wider to allow for the necessary cooling but still producing thrust. And opened even wider at 400 mph.


I agree that the thrust would be lost if the shutter was wide open, but only at lower more modest speeds. At highest level flight speeds, I don't think that would be the case.



Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-06-2003, 02:18 AM
I'm getting the feeling that the max speed is obtained with the radaitor flap open becuase it is automatic, correct me, but is there a manual setting for the radiator? None of these tests show the P51 with the radiator closed, so in my mind it would go faster. I can see how an efficient design could minimize cooling drag, but I dont see how it could totally negate it, which is what saying its fastest speed was with the radiator open is saying. If anything a better way of making this "jet" would be to duct the exhaust in some way as it is much hotter than the cooling airstream and its expansion would create more of an effect.


"Ich bin ein Wuergerwhiner"

"The future battle on the ground will be preceded by battle in the air. This will determine which of the contestants has to suffer operational and tactical disadvantages and be forced throughout the battle into adoption compromise solutions." --Erwin Rommel

http://lbhskier37.freeservers.com/Mesig.jpg
--NJG26_Killa--

XyZspineZyX
11-06-2003, 02:21 AM
Hoarmurath wrote:

- no, they don't...


They do, Hoarmurath. How can you get to 437 mph in level flight at combat power with the shutter closed without overheating?

The manual says that even at maximum continuous power (normal power) the desired temperature is 90-100 degrees celcius. At this temperature the shutter is already opened. Are you suggesting Combat power, not even to mention military power, is going to generate LESS temperature? It's not, its going to get higher if the shutter doesn't open more. And because its getting higher, the shutter will have to open more to keep the temperature at an acceptable level.

It's right there, in black and white. You folks can deny it all you want and go with the "If Oleg said it, it must be true" philosphy, but the fact is that manual supports that the shutter was open when the P-51 achieved its highest level speed - at combat power.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg



Message Edited on 11/06/0304:31AM by SkyChimp

Thera
11-06-2003, 02:27 AM
Nothing you've posted so far supports your opinion. In fact everything you've posted refutes it. All except these last few documents about operational engine temperature ranges with have nothing to do with it at all.

Maybe if I ask some questions... Why did the P51 have radiator shutters if the plane was faster without them? Why would the pilot have been given an option to both ruin his engine and reduce his top speed by closing the radiator?

-----------------------------------------


Fools rush in where angels fear to tread.

XyZspineZyX
11-06-2003, 02:28 AM
lbhskier37 wrote:
- I'm getting the feeling that the max speed is
- obtained with the radaitor flap open becuase it is
- automatic,

YES! And it's open because the temperature is too high for it to be closed.



- correct me, but is there a manual setting
- for the radiator?

Yes, open and closed.



- None of these tests show the P51
- with the radiator closed, so in my mind it would go
- faster. I can see how an efficient design could
- minimize cooling drag, but I dont see how it could
- totally negate it,

It doesn't totally negate it.



- which is what saying its fastest
- speed was with the radiator open is saying. If
- anything a better way of making this "jet" would be
- to duct the exhaust in some way as it is much hotter
- than the cooling airstream and its expansion would
- create more of an effect.

That's what it does. The faster the plane flys, and the hotter the coolant gets, the more open the shutter can be without lost effect. Remember:

"This began to be a considerable pumping action as speeds approached 300 miles per hour--and at 400 miles per hour, it had a large potential and could be a considerable fraction of the airplane's total power equation, since the pumping pressure increases as the square of the speed."


Pumping pressure increases as the SQUARE OF SPEED.



Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-06-2003, 02:44 AM
Thera wrote:
- Nothing you've posted so far supports your opinion.
- In fact everything you've posted refutes it.

Like what? Spell it out, Thera. It's right there before your eyes, now tell me and the rest of us just what is contained therien that says I'm wrong.



- All
- except these last few documents about operational
- engine temperature ranges with have nothing to do
- with it at all.

How so, Thera? The system is automatic, not manually controlled. The manual clearly states at what temperature the shutters will open, and how much.

Again, I ask how can the Mustang reach 437 mph in level flight on combat power without the shutter opening? Do you believe this can be accomplished while mainatining a temperature under 90 degrees celcius? Remember: 90 degrees celcius is the minimum desired temperature at normal power - and the temperature at which the shutter begins to open. Normal power is the setting below military power, which is the setting below combat power.

Answer that question, Thera.



- Maybe if I ask some questions... Why did the P51
- have radiator shutters if the plane was faster
- without them?

Because without the shutters, there is no way to get air across the radiator. And there is no way the plan could have been faster without them, because it would have overheated long before otherwise reaching its top speed.



- Why would the pilot have been given
- an option to both ruin his engine and reduce his top
- speed by closing the radiator?

Thera, logic sems lost here. You have to keep the engine cool. Top speed is achieved within the parameters set in the manual. The plane was flown with the radiator exit flap set to automatic. The pilot had no contol in this mode. The pilot accelerated to top speed at combat power, and the exit shutter was where it was depending on temperature. The manual says that temperature was in excess of 100 degrees celcius so the shutter MUST have ben open.




Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-06-2003, 02:48 AM
Is it possible that at say 430 mph that closing the shutter and running on the heat mass of the radiator fluid would give a couple minutes of a speed burst?

As to what degree the shutter would be open or closed, on auto that's controlled by the thermostat, right? What controls coolant temperature? Engine heat, airflow and air content are the major variables there with content being heat energy, density and water vapor, I'm guessing. Why wouldn't the P-51 run hotter and need the shutters more open in a hard climb than in a high speed, high alt run? The air way up is less dense and very dry but it's also very cold. Bottling up the air inside the radiator ducting would increase the density though. And from the part about the heat pump, I guess that properly managed that at high speeds more air could be passed through the ducts because the exit velocity is increased.

Still there's nothing I've seen that says a fully closed rad system on a P-51 has more drag than one opened, except for der Chimps interpretations. I'd rather believe the wind tunnel guys although the Brit wind tunnel guys not finding the efficiency of the Mustang may point something out, we don't know if their tests had airflow through the radiator ducts do we?


Oleg!

I'm kind of flat out amazed that the Germans had a vertical wind tunnel just for spins! So advanced! Is that common practice in other countries since?


Neal

XyZspineZyX
11-06-2003, 03:06 AM
WWMaxGunz wrote:
- Is it possible that at say 430 mph that closing the
- shutter and running on the heat mass of the radiator
- fluid would give a couple minutes of a speed burst?

Do you REALLY think that's practical or realistic?
If you cut the flow over the radiator at that speed at combat power, the engine will overheat in seconds.



- As to what degree the shutter would be open or
- closed, on auto that's controlled by the thermostat,
- right?

Yes.



- What controls coolant temperature? Engine
- heat, airflow and air content are the major
- variables there with content being heat energy,
- density and water vapor, I'm guessing. Why wouldn't
- the P-51 run hotter and need the shutters more open
- in a hard climb than in a high speed, high alt run?

If that generated the temperatures necessary to open the shutters, they would open. I'd say it was likely the shutter was open in a wide open high speed run at combat power, and in a slower combat power climb. It depends on the temperature generated.




- The air way up is less dense and very dry but it's
- also very cold. Bottling up the air inside the
- radiator ducting would increase the density though.

I understand what you are saying, but that is not how the system works. Heating the cold air doesn't make it denser, it make it less dense, but with more volume. When air is heated, density is traded for volume. Air expands as it it heated.




- And from the part about the heat pump, I guess that
- properly managed that at high speeds more air could
- be passed through the ducts because the exit
- velocity is increased.

Remember, as speed increased, that pumping action increased exponentially. That means you could potentially have significantly more thrust with the shutter open than when it is more closed if the speed was signifcantly higher.



- Still there's nothing I've seen that says a fully
- closed rad system on a P-51 has more drag than one
- opened, except for der Chimps interpretations.

It depends on speed. At 250 mph it was more than likely more aerodymanic with the shutter closed than it was with it open. But at 400 mph I don't think that is the case. And that is due to the exponential increase in pumping action with speed.



- I'd
- rather believe the wind tunnel guys although the
- Brit wind tunnel guys not finding the efficiency of
- the Mustang may point something out, we don't know
- if their tests had airflow through the radiator
- ducts do we?

It's more than just that. The plane would have to be tested in the wind tunnel up to at least 400 mph with the engine running so as to generate the heat to fully appreciate the system's benefits. Simply sticking a non-running plane in a wind tunnel and testing it with various shutter setting won't give an accurate picture.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-06-2003, 03:13 AM
But with a coolant temp range from 90-120 degrees, not much power can be produced from air expanding at that temp, especially since the air already expanded in that chamber that slows its velocity forward of the radiator. I can see it producing enough to lessen the effect of the cooling drag.


-- which is what saying its fastest
-- speed was with the radiator open is saying. If
-- anything a better way of making this "jet" would be
-- to duct the exhaust in some way as it is much hotter
-- than the cooling airstream and its expansion would
-- create more of an effect.
-
- That's what it does. The faster the plane flys, and
- the hotter the coolant gets, the more open the
- shutter can be without lost effect. Remember:
-
- "This began to be a considerable pumping action as
- speeds approached 300 miles per hour--and at 400
- miles per hour, it had a large potential and could
- be a considerable fraction of the airplane's total
- power equation, since the pumping pressure increases
- as the square of the speed."
-
-
-
- Pumping pressure increases as the SQUARE OF SPEED.
-


Remember drag also increases with the square of speed/i/smilies/16x16_smiley-happy.gif All that air has to get through that radiator, the more the flap is open the more volume it has to push through. I think it is a brilliant system and can easily see how it would lessen the effect of cooling drag, but it cant totally eliminate it. I am saying that if they couldve without boiling the coolant, they couldve gotten more speed out of it with rads closed.


"Ich bin ein Wuergerwhiner"

"The future battle on the ground will be preceded by battle in the air. This will determine which of the contestants has to suffer operational and tactical disadvantages and be forced throughout the battle into adoption compromise solutions." --Erwin Rommel

http://lbhskier37.freeservers.com/Mesig.jpg
--NJG26_Killa--

XyZspineZyX
11-06-2003, 03:23 AM
lbhskier37 wrote:

- Remember drag also increases with the square of
- speed http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

But drag coefficient remains pretty stable until about mach .75 (I have drag coefficient charts for both P-51B and D), at which point it starts to rise signficantly. And we are not talking about achieving those kinds of speeds in level flight.



-I think it
- is a brilliant system and can easily see how it
- would lessen the effect of cooling drag, but it cant
- totally eliminate it. I am saying that if they
- couldve without boiling the coolant, they couldve
- gotten more speed out of it with rads closed.

IF it could be done, PERHAPS a higher top speed could have been achieved. But it couldn't be done, the engine would not have lasted without cooling. And the P-51's 437 mph top speed at combat power was not achieved that way. It was achieved with a cooling effect - that is, radiator open.

That's my contention here: the P-51s top speed was not achieved with the radiator closed. It was open, it had to be. Otherwise the engine would have overheated.





Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg


Message Edited on 11/06/0305:49AM by SkyChimp

XyZspineZyX
11-06-2003, 03:24 AM
Thanks for the explanations, SkyChimp, I think I see better now what the argument is about. It seemed to jump around a lot in the beginning.

SkyChimp wrote:
- Actually, I'm not sure that the thrust will be lost
- when it is wide open, especially when both
- temperature and speed are very high, as in a
- combat-power maximum speed flight.

Well, here I am not sure either. I would assume there is an optimal setting, and I highly doubt that it is with the shutter all the way open. The problem is, the more flow you get through the radiator, and the faster that flow, the higher the drag through the ducts and through the radiator core. So, even if there is an efficient recovery using the Meredith effect, it may not be enough to completely recover the pressure drop over the core (and the other losses through the duct). In addition, if the shutter is open too far you don't get the right amount of backpressure to make use of the Meredith effect. I am pretty sure the most efficient setting would be the one that lets just enough air through for cooling (based on data I am familiar with for other radiator set-ups).

- Atwood said, "This began to be a considerable
- pumping action as speeds approached 300 miles per
- hour--and at 400 miles per hour, it had a large
- potential and could be a considerable fraction of
- the airplane's total power equation, since the
- pumping pressure increases as the square of the
- speed."

Yes, but as I mentioned the drag due to the pressure drop over the radiator core and the friction inside the duct also increases. I don't think anything in Atwood's explanation says that the bigger the shutter opening, the more the "net" thrust. In fact, it is quite clear from his explanation that some constriction is needed to maintain the correct backpressure.

- I agree that the thrust would be lost if the shutter
- was wide open, but only at lower more modest
- speeds. At highest level flight speeds, I don't
- think that would be the case.

I don't think anything in what Atwood wrote confirms this (or denies it for that matter).

As for what would happen with the shutter at maximum speed: I agree, if you are in a climb and full throttle, or accelerating with full throttle from a fairly low speed, you are going to need as much air through the radiator as possible, since the air is moving slowly, and it will probably need to be open to prevent overheating. This is obviously not a very good situation from a cooling drag point of view. However, as speed increase, the airflow increases and the temperature of the coolent should decrease, so the thermostat should start closing the shutter. Now, how much it closes by the time you get to maximum speed I really don't know.

XyZspineZyX
11-06-2003, 03:41 AM
Oryx wrote:

- Well, here I am not sure either. I would assume
- there is an optimal setting, and I highly doubt that
- it is with the shutter all the way open. The problem
- is, the more flow you get through the radiator, and
- the faster that flow, the higher the drag through
- the ducts and through the radiator core. So, even if
- there is an efficient recovery using the Meredith
- effect, it may not be enough to completely recover
- the pressure drop over the core (and the other
- losses through the duct). In addition, if the
- shutter is open too far you don't get the right
- amount of backpressure to make use of the Meredith
- effect. I am pretty sure the most efficient setting
- would be the one that lets just enough air through
- for cooling (based on data I am familiar with for
- other radiator set-ups).


I believe its possible to get a back pressure even if the exit is wide open - as long as the speed is high.

I'm also sure the degree of the Meredith effect varied. It had to, because the cooling needs had to be met. Whatever was left over was the effect you got.

I am not completely convinced the exit was "wide open" at top level speed either (although I also think it could have been). But I AM convinced that it was not at it's most restrictive setting (closed) either. I just don't see how it could be when the plane is at full throttle - combat power.




Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-06-2003, 03:50 AM
SkyChimp wrote:
- I believe its possible to get a back pressure even
- if the exit is wide open - as long as the speed is
- high.

What makes you so sure about this? Why does the higher speed increase the backpressure?

- I am not completely convinced the exit was "wide
- open" at top level speed either (although I also
- think it could have been). But I AM convinced that
- it was not at it's most restrictive setting (closed)
- either. I just don't see how it could be when the
- plane is at full throttle - combat power.

I also don't think it would be at it's most restrictive setting, but on the other hand at maximum speed you get so much mass flow through the radiator that it is not entirely impossible. I highly doubt it would be at the maximum open position though.

XyZspineZyX
11-06-2003, 04:08 AM
Oryx wrote:

- What makes you so sure about this? Why does the
- higher speed increase the backpressure?

Because the pumping action increases as the square of speed. Since that is the case, the shutter could be opened more and more as the speed increased with no loss in back preassure, or even with a possible increase in back pressure. If the shutter were left in place and speed increased, there is no question that the back pressure would increase - but at the expense of cooling effect.



- I also don't think it would be at it's most
- restrictive setting, but on the other hand at
- maximum speed you get so much mass flow through the
- radiator that it is not entirely impossible. I
- highly doubt it would be at the maximum open
- position though.

My position here is heavily influenced by the manual pages I posted. The manual states that the shutter was opened
--fully-- with a coolant temperature of 110 degrees celcius. 110 degrees is just 10 degrees higher than the OPTIMAL normal power setting temperature. And it's 11 degrees lower than the maximum combat power temperature. A level acceleration to 437 mph at combat power is going to likely produce a temperature of at least 110 degrees celcius. Without question, it's going to produce a temperature that opens the shutter to some degree.

And remember, this is an automatic system. The pilot wasn't instructed to open the shutter fully at 110 degrees celcius, it did it automatically.



- I also don't think it would be at it's most
- restrictive setting

That's my position. But Oleg's position is that the P-51 achieved its top speed with the shutter closed. I think he's wrong.


I'm off to bed now. Be back tomorrow evening.




Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg



Message Edited on 11/06/0306:15AM by SkyChimp

XyZspineZyX
11-06-2003, 04:55 AM
110 C. How long could the Mustang maintain full speed before overheating anyway? Prior to that point, the temperature must have been rising from some point. Would the Mustang no longer be going at full speed when the shutter was full open? Any docs?

If there's a time limit for top speed then the cooling system could not be maintaining temperature unless something else was the limit.

Chimp, with enough coolant mass and a phase-change in the coolant between high speed and top speed HP there can be a huge resorvoir of thermal mass in the cooling system. More than mere temperature % will ever show. Read up on state phase changes and maybe temperature-pressure effects (closed system, the pressure won't be at atmosphere).

How many planes could close the rads and still run at peak long enough to make a higher top speed?


Neal

XyZspineZyX
11-06-2003, 05:03 AM
WWMaxGunz wrote:
- 110 C. How long could the Mustang maintain full
- speed before overheating anyway? Prior to that
- point, the temperature must have been rising from
- some point. Would the Mustang no longer be going at
- full speed when the shutter was full open? Any
- docs?
-
- If there's a time limit for top speed then the
- cooling system could not be maintaining temperature
- unless something else was the limit.
-
- Chimp, with enough coolant mass and a phase-change
- in the coolant between high speed and top speed HP
- there can be a huge resorvoir of thermal mass in the
- cooling system. More than mere temperature % will
- ever show. Read up on state phase changes and maybe
- temperature-pressure effects (closed system, the
- pressure won't be at atmosphere).
-
- How many planes could close the rads and still run
- at peak long enough to make a higher top speed?
-
-
- Neal


It doesn't matter, Neal. Even at normal power the shutter would have opened. And there is NO time limit at normal power! Normal power's optimal temperature was 90-100 degrees celsius. That's above the point where the shutter begins to open, and only 10 degrees from being fully open.

Oleg says the Mustang achieved top speed with the shutter in its most restrictive position. It didn't, it couldnt. it would have overheated.

It's time to admit the facts. Oleg is wrong on this one. The Mustang achieved 437 mph in level flight with the shutter open, not closed. I've presented too much evidence for that to even be in question anymore.

At anyrate, speed wasn't the limiting factor, power setting was. Combat Power was limited to 5 minutes.



Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg



Message Edited on 11/06/03‚ 07:08AM by SkyChimp

Message Edited on 11/06/0307:09AM by SkyChimp

XyZspineZyX
11-06-2003, 05:23 AM
SkyChimp wrote:
- Oryx wrote:
-
-- What makes you so sure about this? Why does the
-- higher speed increase the backpressure?
-
- Because the pumping action increases as the square
- of speed. Since that is the case, the shutter could
- be opened more and more as the speed increased with
- no loss in back preassure, or even with a possible
- increase in back pressure. If the shutter were left
- in place and speed increased, there is no question
- that the back pressure would increase - but at the
- expense of cooling effect.

This is where I differ, SkyChimp. You only concentrate on the "pumping pressure" and you ignore the drag in the duct system and through the radiator core.

When working with internal duct flow on an airplane, everything is done as a function of the velocity ratio (w/V) where "w" is the velocity inside the duct (taken at the radiator core) and V is the freestream velocity (the speed of the airplane).

The drag coefficient of the duct system increases exponentially with this velocity ratio. If you have a very well designed system, such as that of the Mustang, the heat added to the system causes a bit of a modification to this drag curve that causes it to dip below the zero drag coefficient value for a short while before it increases again exponentionentially with higher velocity ratios. This is the "Meridith" effect that Atwood talks about. If it drops enough below zero, you can even overcome the overall cooling drag of the airplane (in theory). The important thing about this trend is that it only dips below zero for small velocity ratios. (if you have Hoerner's "Fluid Dynamic Drag", you can see a typical example in Chapter 9, Figure 17).

The velocity ratio in turn is controlled by the shutter setting. The bigger the shutter opening, the higher the velocity ratio. For fairly big shutter openings and high freestream velocity, the static pressure at the exit actually drops below ambient, which increases the velocity ratio through the duct and therefore increases cooling. However, with this increased velocity ratio through the duct you now push it far beyond the area where the CD drops below zero and you get significant cooling drag, but you get better cooling, which is what you are really after under these conditions. However, if the duct was designed properly (again as in the case of the Mustang), then this drag coefficient is still significantly below what it would have been for a system that was not designed to make use of the heat from the radiator to recover the momentum loss.

So, in order to get a net thrust out of the system, you need a low velocity ratio (w/V), which means a small exit area. If you go fast, you need an even smaller exit area due to the scavenging effect of the air at the exit.

In a climb, with the airplane flying slow and the shutter wide open, even the Mustang will suffer from fairly large cooling drag. If the shutter is indeed almost fully open at high speed, as you state, then it will have the same problem. However, if the shutter closes enough at high speed in order to get the velocity ratio low enough to get the CD into the negative region, then you may see a little net thrust. At cruise the conditions are probably better, because you have a lower power setting, the shutter is therefore most likely almost closed, and in turn you get the right kind of velocity ratio to get this net thrust that Atwood talks about, and you end up with very high efficiency.

- My position here is heavily influenced by the manual
- pages I posted. The manual states that the shutter
- was opened
---fully-- with a coolant temperature of 110 degrees celcius.

However, what you posted also states that the shutter only starts to open at 90 degrees Celcius. The optimal operating temperature for the engine is 90-100. If we assume during the climb or early acceleration your temperature increases to around 110 degrees (or maybe even 120) with the shutter fully open, it seems quite likely that as the mass flow through the radiator increases with speed, the temperature can drop again that 20-30 degrees down to 90, which would close the shutter again fully. This in turn would make conditions ideal for the "Meridith effect", decreasing drag (or generating a bit of thrust), allowing the airplane to get to an even higher speed.

The second excerpt you posted only show limit temperatures - it doesn't mean the engine is actually operating at that temperature. Full power in a climb or when you are slow may cause the temperature to get close to the limits posted in that excerpt, but at high speed as your cooling improves, it should be significantly below those limit values.

Of course, I cannot say for sure if the shutter would be closed (or almost closed) at maximum speed, since I don't have actual data or a quote that says so for sure. But based on all the "circumstantial evidence" (if you can call it that), it seems very likely that this may be the case.

XyZspineZyX
11-06-2003, 05:42 AM
{post removed - previous one is clear enough}



Message Edited on 11/06/0307:28AM by Oryx

Thera
11-06-2003, 06:20 AM
All planes at full combat power overheat. That's why it's considered combat power, for use only in limited situations when you need the extra power. There's no reason the P51 is any different from all the others.

-----------------------------------------


Fools rush in where angels fear to tread.

XyZspineZyX
11-06-2003, 12:28 PM
Skychimp, I personally believe that the top speed was reached with radiator closed. I understand your argumentation, but I disagree. I don't think they'd call 437 "max" if it wasn't max. So as long as you don't dig out a document saying: top speed was achieved with radiator on auto, I believe it was set closed. So much on my personal opinion.

Doing some math: Exhaust speed was 500-600ft/s, airflow was 500ft^3 this makes the exhaust area for these figures about 0.83 to 1 ft^2 large. Sadly I don't have precise drawings of the radiator. But the radiator flap is about 50 cm wide and the minimum distance between flap and fuselage is roughly around 15 cm, making it 0.85 ft^2. Fairly close to the numbers above. I therefore am convinced, that the thrust of 350lb at "full speed" was measured with radiator closed. Opening the radiator would therefore

1) significantly increase drag
2) significantly reduce thrust
3) considerably reduce speed

I don't think they flew auto, got 437 and no one tried to go a bit faster by temporarily closing the radiator. The closed radiator still provides a lot of cooling. When achieving top speeds, no one cared about overheating.

(I'd apprechiate any more data on this radiator, best in numbers and drawings.)

XyZspineZyX
11-06-2003, 01:29 PM
So closed don't mean sealed shut?


Neal

XyZspineZyX
11-06-2003, 01:37 PM
I really don't know who is right here, but out of curiosity I looked up some reno air race pictures and the radiators look fairly closed.
http://www.stanford.edu/~malfita/nellis/115.JPG

http://www.stanford.edu/~malfita/nellis/112.JPG


Make of it what you will.

Beergator.

PS Sorry Oleg I couldn't resist the mustang and got a copy of the patch to try out. I loved it. I can hardly wait till the patch comes out.

XyZspineZyX
11-06-2003, 03:07 PM
JtD, (rough measurement) the open area with the flap closed is, rounded off to whole numbers, 16"x2" or 48"^2(0.33'^2). You must use a rear view to find the dimensions, not a plan/side view as it seems you did./i/smilies/16x16_smiley-wink.gif

The inlet is, rounded off to whole numbers, 22"x5" or 110"^2(0.76'^2).

Even making allowances for the oil cooler exit(17"x2" or 34"^2 (0.56'^2)), 48+34=82, this is 75.5% of the inlet area. That is still a lot of air that will build up on the front side of the radiator even with the increased exit velocity of the hot air.

For 'in' to equal 'out', the flap has to be opened at least ~2" more. How much does the hot air volume expand over the intake air volume at 110*C?

Full open has an area of ~240"^2(1.67'^2).

Now maybe I am 'all wet', but this is how I see it.



http://www.thundercycle.com/photos/dropdead2.gif



"Only a dead 'chamber pot' is a good 'chamber pot'!"

Message Edited on 11/06/0309:35AM by MiloMorai

XyZspineZyX
11-06-2003, 03:28 PM
I don't know wether the Mustang had more net drag with the radiator closed. or with it open and thrust from the Meredith effect reducing the cooling drag. However:


- My position is that is not correct, that it was
- open, at least to some degree. I believe this
- because not only does the back-pressure need to be
- expelled in the form of "thrust," but that cooling
- HAD to take place. I believe there is no realistic
- way to accelerate in level flight to 437 mph at
- combat power with the shutter closed without
- severely overheating.

Neil Sterling posted parts of a cooling report on a Spit LF IX, Merlin 66, running 150 octane, 25lbs boost.

With closed radiators (like the Mustang, fully closed radiators still allows some air through), the heat buildup was measured. The part of the report I have gives the suitability of the radiators for particular conditions, generated by the formula:

(max permissable temp - approx standard summer temp) / (observed coolant temp - actual air temp)

The max permissible temp was 125 c, and figures are given for 3,000ft, so I'll gues the air temp at 15c.

That gives 125c - 15c / coolant temp - 15c

110c / coolant temp -15c

The result of this equation for the RAF tests was 1.36, which gives a coolant temperate of 96c.

110c / 95c (coolant temp) -15c (air temp)

110 / 81 = 1.36


The method of testing was to fly for 10 mins at maximum cruising power, followed by 5 mins all out (wep), and take the readings at the end of that.

So, after 5 mins all out, the coolant temp on the Spit had risen to approx 95c with closed rads at 3,000ft in European summer conditions.

The areas of the exit ducts on the Spit were 1.66 sq ft with radiators closed, 3.14 sq ft with radiators fully open.

Note these figures were achieved at 25lbs boost, or 81 in HG.

The Mustang would generate less heat at 18lbs boost (67 in HG), but the temperature would also depend on the coolant volume and radiator exit area when closed, although I believe the Mustang radiator would be more efficient with the same outlet area.

(I may have got the maths wrong, it's not exactly my strong point, but I don't think it's far out)

XyZspineZyX
11-06-2003, 04:32 PM
Thanks for that material, Hop.

- The method of testing was to fly for 10 mins at
- maximum cruising power, followed by 5 mins all out
- (wep), and take the readings at the end of that.
-
- So, after 5 mins all out, the coolant temp on the
- Spit had risen to approx 95c with closed rads at
- 3,000ft in European summer conditions.

There is also another test on the MkXIV prototype here:
http://www.fourthfightergroup.com/eagles/spit14pt.html

It basically says the same thing for maximum speed tests:

"...........(iv) Level speeds were measured at heights between ground level and 16,000 ft. in MS supercharger gear and between 12,000 ft. and 39,000 ft. in FS supercharger gear with the radiator flap closed."

hop2002 wrote:
- I don't know wether the Mustang had more net drag
- with the radiator closed. or with it open and thrust
- from the Meredith effect reducing the cooling drag.
- However:

This is the problem. It is indeed possible that the radiator would have had to be all the way open at maximum power in order to maximize cooling. But that would not minimize cooling drag. The Meredith effect needs a fairly low velocity ratio between the flow inside the duct at the core and the external flow, to actually produce a thrust. This doesn't happen with the flap fully open (see my previous post at the bottom of page 3).

Regards,
Oryx

XyZspineZyX
11-06-2003, 04:33 PM
SkyChimp wrote:
- lbhskier37 wrote:
-
-- Remember drag also increases with the square of
-- speed /i/smilies/16x16_smiley-happy.gif
-
- But drag coefficient remains pretty stable until
- about mach .75 (I have drag coefficient charts for
- both P-51B and D), at which point it starts to rise
- signficantly. And we are not talking about
- achieving those kinds of speeds in level flight.
-
-


/i/smilies/16x16_smiley-happy.gif force of drag increases, not drag coefficient.
F=-.5CpAv^2

I kinda see what you are getting at here with this, you aren't trying to say the mustang should be faster, it should just achieve its top speed when on Auto radiator. As long as having it closed wont allow it to attain max speed before engine overheat I think this is a reasonable claim and should be put in. But if you ran it at full open setting I don't think it would attain max speed because this effect would I'm sure not be linear and if it could attain max speed with radiator full open there would be no reason to ever close it accept on warming up the engine.



"Ich bin ein Wuergerwhiner"

"The future battle on the ground will be preceded by battle in the air. This will determine which of the contestants has to suffer operational and tactical disadvantages and be forced throughout the battle into adoption compromise solutions." --Erwin Rommel

http://lbhskier37.freeservers.com/Mesig.jpg
--NJG26_Killa--

XyZspineZyX
11-06-2003, 05:34 PM
That`s pretty silly `Chimp, no plane becomes faster if it opens the radiators. It may have a good radiator design, and the speed loss being less.

I`d like to point out the the so called Meredith effect was nothing sort of special on the Mustang. Other designs were taking advantage of it for a long long time, ie. Spitfire, Messerscmitt 109, 110, 210, 410 Yakovlevs etc.



Vez√©r√ľnk a B√°tors√°g, K√¬*s√©r√¬Ķnk a Szerencse!
(Courage leads, Luck escorts us! - Historical motto of the 101st Puma Fighter Regiment)

Flight tests and other aviation performance data: http://www.pbase.com/isegrim

XyZspineZyX
11-06-2003, 05:40 PM
MiloMorai wrote:
- JtD, (rough measurement) the open area with the flap
- closed is, rounded off to whole numbers, 16"x2" or
- 48"^2(0.33'^2). You must use a rear view to find the
- dimensions, not a plan/side view as it seems you
- did.

Thank you for the numbers, but I think using a rear view is not correct. The lower edge/plane of the fuselage goes up very steeply once inside the two fins that extend the radiator. (The ones holding the flap.) You can not see this when using a rear view. Therefore the height of the nozzle is higher than it seems when looking from behind. (Me thinks.)

XyZspineZyX
11-06-2003, 09:06 PM
Gentlemen, you are making this into argument, where there is not need for it.

Remember, P-51 for the beta is being tested by real P-51 pilot, who definitely knows all about how radiator shatters works in P-51 and all about its engine cooling.

I'm sure many of us can find another real P-51 pilot explain whole thing for all of us.

There is no need for guessing and arguing in this case.


AKA_Bogun

---------------
The difference between fiction and reality? Fiction has to make sense.

- Tom Clancy

XyZspineZyX
11-07-2003, 12:03 AM
hop2002 wrote:
- I don't know wether the Mustang had more net drag
- with the radiator closed. or with it open and thrust
- from the Meredith effect reducing the cooling drag.
- However...

Thank Hop.

But I'm not sure much can be drawn from this comparison. The ideal operating temperature at Normal Power in the Mustang III was 90-110 degrees celsius. At this temperature, the shutter was just opeing at 90 degrees, and significantly open at 100 degrees.

I'm not sure if the shutter thermostat settings were changed between the P-51B and the P-51D, but its interesting to note that while the V-1650-3 had a maximum coolant temperature of 121 degrees celsius, the V-1650-7 had a limit of 135 degrees celsius.




Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-07-2003, 12:04 AM
Beergator wrote:
- I really don't know who is right here, but out of
- curiosity I looked up some reno air race pictures
- and the radiators look fairly closed.


this one looks about 1/2 way open:

http://www.stanford.edu/~malfita/nellis/112.JPG


Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-07-2003, 12:05 AM
Vo101_Isegrim wrote:

- I`d like to point out the the so called Meredith
- effect was nothing sort of special on the Mustang.

Except that it was specifically designed to take advantage of this effect.



- Other designs were taking advantage of it for a long
- long time, ie. Spitfire, Messerscmitt 109, 110, 210,
- 410 Yakovlevs etc.

But for the most part any effect was incidental, not intended.


Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-07-2003, 12:06 AM
Bogun wrote:
- Gentlemen, you are making this into argument, where
- there is not need for it.
-
- Remember, P-51 for the beta is being tested by real
- P-51 pilot, who definitely knows all about how
- radiator shatters works in P-51 and all about its
- engine cooling.
-
- I'm sure many of us can find another real P-51 pilot
- explain whole thing for all of us.
-
- There is no need for guessing and arguing in this
- case.
-
-
-
- AKA_Bogun


Actually, there isn't much argument. Just a lot of people that disagree with me. However, we've remained relatively civil.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-07-2003, 12:33 AM
SkyChimp wrote:
- Actually, there isn't much argument. Just a lot of
- people that disagree with me. However, we've
- remained relatively civil.

I agree, this has been one of the more civil discussions I have seen here for a while. Also, the disagreement is fairly minor and only on a few small points.

S!

XyZspineZyX
11-07-2003, 01:08 AM
what a dogfight!! Chimp vs the world--love it

pretty clean too.

What he's saying is that according to some designers, p51 slows less with rad open (whether auto or manual) over 300mph than any other AC in the war, and so should be modeled this way.

Note also that oleg refers to wind tunnel tests, while atwood said something about effects not appearing in tunnel because you couldn't get the motor hot enough-- in their tunnel anyway.

he may be right

all the best,

uhoh7

XyZspineZyX
11-07-2003, 01:43 AM
S! Chimp

Fight the Good Fight Man !


""Oleg (and his ardent supporters) is under the impression that the Mustang's top speed was achieved with the radiator air exit shutter closed (radiator closed).

My position is that is not correct, that it was open, at least to some degree. I believe this because not only does the back-pressure need to be expelled in the form of "thrust," but that cooling HAD to take place. I believe there is no realistic way to accelerate in level flight to 437 mph at combat power with the shutter closed without severely overheating.

I contend that in 1.2-Final the Mustang should achieve its top speed with the shutter open, Oleg says that oepning it will actually decrease speed.

The manual pages above supports my position.""


I see it, I've read it and I get it. I tend to agree with the regenerative back pressure being squard at speed and the radiator needing to open to accomplish this.

Maybe we can get Oleg's P51 pilot to tell us the straight story about radiator settings and air pumps!


___



Braveheart's William Wallace said it best:
"I see a whole army of my countrymen, here in defiance of tyranny. You have come to fight as free men, and free men you are. What will you do without freedom? Will you fight? Fight and you may die. Run, and you'll live, at least a while. And dying in your beds, many years from now, would you be willing, to trade all the days from this day to that, for one chance, just one chance, to come back here and tell our enemies, that they may take our lives, but they'll never take our FREEDOM!"

XyZspineZyX
11-07-2003, 02:04 AM
Howdy

Hmmm look up the P-51C Mustang called "Beguine" and see, what they did with the dog house in that.

S! Weasel

XyZspineZyX
11-07-2003, 09:19 AM
Oryx, thanks for the elaboration. I think we're all in violent agreement here, but getting distracted by subtleties as to what constitutes "open" and "closed". Here's my spin:

In its minimum drag setting (not related to temperature yet, bear with me), the shutter is open just enough to be the limiting factor for flow through the duct. The drag through the radiator core doesn't limit flow at this setting, and air flowing into the intake does so by splitting at the intake lip (air inside the leading edge of the lip goes in, air outside the leading edge goes around the intake.) In other words, the intake is sized "just right" for the amount of airflow needed to cool the radiator, which in turn regulates the flow in this state through the thermostat and shutter.

With the shutter full open, a low-pressure area is produced in the aft ducting, drawing more air through the radiator core and the intake (as Oryx mentioned.) In this case the low-pressure downstream causes more air to flow into the intake, "spilling in" around the leading edge of the intake as a result (the intake size hasn't changed after all.) This spilling in, along with the turbulence associated with the low-pressure area in the aft ducting subsequently mixing with the freestream (which Oleg mentioned), creates more drag than the minimum drag setting.

Unfortunately, the shutter is controlled by a thermostat, not a drag sensor. As temperature goes up, the shutter opens to increase mass flow and cooling, at the cost of some drag. The radiator is less efficient due to the higher w/V, but the increased mass flow more than makes up for this. I don't know how much heat gets pumped into the flow by the radiator, but I don't think that it's enough to recover the pressure drop or achieve the Meredith effect. This is a radiator we're talking about, not an afterburner. I was surprised by Oryx's statement that for a small range of specific speeds, throttle and shutter settings there may be a net thrust. Suffice it to say that for sustained climb however, we're not in that range of settings.

I suspect that they designed the ducting such that minimum drag occurred in level flight at intermediate power (normal or cruise setting.) Here, the flap would be mostly closed, velocity ratio would be low (w much less than V), and heat transfer from the radiator would be efficient and adequate. In climb, the shutter would open in response to temperature, increasing mass flow and cooling, at the cost of drag and Meredith effect (w closer to V.) A max speed run would probably be somewhere in between, at least initially. Mass flow would be pretty high already due to the high V, but the shutter would have to open more than at cruise, since I'm guessing that waste heat would increase much more than mass flow for a fixed shutter setting when comparing normal and max conditions. Neal's suggestion of closing the flap manually to gain a temporary increase in speed has some merit, though I'll take SkyChimp at his word that the 437 mph figure was achieved in auto. I don't know how long it took in Combat to get to that speed though, nor whether the pilot descended during the first part of the run to reduce his time in Combat. Neal's idea may have been what Oleg was referring to. His comment about the intake position outside of the turbulent boundary layer lowering drag is also valid (I'm sure he'll sleep more soundly knowing a hack aero engineer in Albuquerque agrees with him.) The relatively high velocity flow off the bottom of the wing helps here, too.

I think Oryx was right about the temps in the manual SkyChimp posted, too. Just because they list a max temp allowed, doesn't mean the engine was operating at that temp for a given power setting as a rule. As to why they don't post "desired" ranges for T/O and Combat, I would guess that because these were transient conditions (and thus not used for enough time to allow "desired" ranges to be relevant), only max allowed values were listed. This doesn't mean that Combat necessarily corresponded to a full open shutter, at least not initially. Oleg hinted that the Combat setting would eventually cause an overheat in the Mustang though, driving the shutter full open sooner or later (with the attendant increase in mass flow at the cost of drag.)

What I hope we see is that 437 mph can be achieved, at least briefly, with the radiator in "auto", and that slightly more than this can be achieved (even more briefly) with the shutter manually closed. Sustained running in Combat power will apparently result in speeds lower than 437 as the shutter opens automatically in response to coolant temperature.

Blotto

"Only the spirit of attack, born in a brave heart, will bring success to any fighter craft, no matter how technically advanced." - A. Galland

"Look, do you want the jets, or would you rather I slap the props back on?" - W. Messerschmitt

http://home.mindspring.com/~blottogg/sitebuildercontent/sitebuilderpictures/14fsPatch.gif

XyZspineZyX
11-07-2003, 11:25 AM
If the shutter control thermostat measured the air temperature back by the shutter instead of coolant temperature then even opening the shutter a little would have an immediate effect and a very nice dynamic control result that could possibly be tuned for airflow purposes?

Manual control... a good idea where your thermostat might get shot off or hit by shrapnel I think, if you had well trained pilots.

I can't agree about the best efficiency being at cruise or intermedaite speeds just because of this part of the report:

This air pump, like all pumps, had three elements--a compressor stage, a metering or valving stage (radiator core), and a discharge function through an air outlet. This began to be a considerable pumping action as speeds approached 300 miles per hour--and at 400 miles per hour, it had a large potential and could be a considerable fraction of the airplane's total power equation, since the pumping pressure increases as the square of the speed. To make this automatic pump effective, only one thing was required, and that was to choke the outlet enough to keep the pressurized airflow through the radiator just adequate for cooling and to discharge this compressed air at the highest speed possible.

I don't think that the Mustang intermediate cruise was that fast as 300 mph and the effect was more efficient as speed went up without saying anything about shutter positions. That last sentence says almost as much as it doesn't!


Neal

XyZspineZyX
11-07-2003, 04:32 PM
I may have a chance to stop by Chino, and look up Steve Hinton, who likely will have a correct answer to help out:


http://www.moviepilots.com/members/hinton.html

Steve took time out in 1979 to establish a new World's Speed Record for piston powered aircraft, ( 499.046 mph ). That record set in a highly modified P-51 Mustang,Red Baron " remained unbeaten for ten years!
Steve participated as an Unlimited Race Pilot for 13 years, flying the " Red Baron",John Sandberg's," Tsunami " and the All Coast racing team's, " Super Corsair ", winning two Gold National Championships (1978 Red Baron and 1985 Super Corsair). Since 1990 Steve has continued his long relationship with air racing as the Official, Reno National Air Races Unlimited Pace Pilot, flying a Lockheed T-33 Jet Pace Plane. Currently, Steve is President of, The Air Museum Planes of Fame and Owner of Fighter Rebuilders,
a world renowned aviation company devoted to the restoration of , " Warbirds ".Both these organizations are located at the Chino Airport, Chino, California.

He was also the pilot who flew the P38 Glacier Girl on her first flight.

Assuming I get the time to swing by today (:



" The first time I ever saw a jet, I shot it down ": General Chuck Yeager, USAF, describing his first confrontation with a Me262 - - -
" Aggressiveness was a fundamental to success in air-to-air combat and if you ever caught a fighter pilot in a defensive mood you had him licked before you started shooting ": Captain David McCampbell, USN, leading U.S. Navy ace in W.W.II.

XyZspineZyX
11-08-2003, 04:40 AM
Neal, interesting thought on mounting the thermostat in the exit duct. The problem with that is that radiator exhaust temperature won't correspond to coolant or cylinder head temp. Opening the shutter will increase mass flow and heat transfer (cooling the radiator) but the duct exhaust air will probably be cooler than for a closed, low flow condition. I think it was controlled by a coolant thermostat, but can't confirm this.

While the pump effect is be more efficient at higher speeds, the curves for pump efficiency, heat generation and heat transfer aren't the same. The sentence:

"To make this automatic pump effective, only one thing was required, and that was to choke the outlet enough to keep the pressurized airflow through the radiator just adequate for cooling and to discharge this compressed air at the highest speed possible."

Makes sense, but what I think happens is that for high power settings, opening the shutter just "enough to keep the pressurized airflow through the radiator just adequate for cooling" isn't possible. To do that, the radiator and ducting would have to be large enough to keep the shutter mostly closed without overheating. I don't believe this was possible (as Oleg mentioned.) Another way of doing it might have been to make the intake variable geometry, stuffing more air in to maintain the backpressure with the necessary mass flow, while achieving better cooling. Either they didn't think of this, or thought it too much trouble. With a fixed inlet, opening the shutter increases the mass flow, improving cooling at the cost of pumping efficiency. Meredith effect can only move so much air (and heat) given the fixed geometry of the intake and radiator.

The reason I say normal cruise was the design target point for the cooling system was that it makes engineering sense. This is where the plane spent most of it's time, so designing a cooling system with much more capacity than for these conditions would mean carrying around a lot more hardware than you'd need most of the time. A system designed for full power would also probably have less pumping efficiency at cruise speed too, affecting range. I can't confirm this, but maybe TBS_TWIGTOTO will have some input from Mr. Hinton.

If nothing else, I'll be in Atlanta for Christmas, and will no doubt swing by the CAF Dixie wing, and talk to the guys there about the 51D they just got from Midland.

Blotto

"Only the spirit of attack, born in a brave heart, will bring success to any fighter craft, no matter how technically advanced." - A. Galland

"Look, do you want the jets, or would you rather I slap the props back on?" - W. Messerschmitt

http://home.mindspring.com/~blottogg/sitebuildercontent/sitebuilderpictures/14fsPatch.gif