PDA

View Full Version : Explain this aerodynamic



zugfuhrer
07-21-2007, 01:22 PM
I have compared spit IX with me 109 G2 and and FW 190 A6 found out that the spit got less drag than the 109 and that is ok, but when you chop the throttle, the spit "brakes" much faster than the LW a/c.

The tests:

Crimea map weather fine. 100% fuel, 100% ammo, radiator auto, pitch auto QMB.

Started at sealevel and accelerated to 500 km/h. Then I chopped the throttle (turned into idle) and climbed vertically as good as I could.

I checked the time and alt when the a/c got 0 speed.

The spit reached highest, and the FW 190 reached the lowest altitude.

Test 2 started at sealevel and I accelerated to 500 km/h
Again I chopped the throttle to zero tried to hold my altitude and measured the time and speed until you crash in water.

zugfuhrer
07-21-2007, 01:22 PM
I have compared spit IX with me 109 G2 and and FW 190 A6 found out that the spit got less drag than the 109 and that is ok, but when you chop the throttle, the spit "brakes" much faster than the LW a/c.

The tests:

Crimea map weather fine. 100% fuel, 100% ammo, radiator auto, pitch auto QMB.

Started at sealevel and accelerated to 500 km/h. Then I chopped the throttle (turned into idle) and climbed vertically as good as I could.

I checked the time and alt when the a/c got 0 speed.

The spit reached highest, and the FW 190 reached the lowest altitude.

Test 2 started at sealevel and I accelerated to 500 km/h
Again I chopped the throttle to zero tried to hold my altitude and measured the time and speed until you crash in water.

Capt.LoneRanger
07-21-2007, 01:44 PM
Allied have better anti-skidd-systems http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

AKA_TAGERT
07-21-2007, 01:46 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by zugfuhrer:
I have compared spit IX with me 109 G2 and and FW 190 A6 found out that the spit got less drag than the 109 and that is ok, but when you chop the throttle, the spit "brakes" much faster than the LW a/c.

The tests:

Crimea map weather fine. 100% fuel, 100% ammo, radiator auto, pitch auto.

Start at sealevel accelerate to 500 km/h and chop the throttle and climb vertically as good as it gets.

Check the time and alt when the a/c got 0 speed.
The spit reached highest, lowest the FW 190.

Test 2 start at sealevel accelerate to 500 km/h
Set throttle to zero hold your altitude and take time and speed until you crash in water.
The spit accelerates best and brakes best.
The FW 190 brakes and accelerates worst. </div></BLOCKQUOTE>
<span class="ev_code_white">Got Track? ©®™</span>

M_Gunz
07-21-2007, 01:47 PM
Power of the Spit you used compares to power of the 109 you used is?

zugfuhrer
07-22-2007, 12:09 AM
The tracks are wasted but as every real science postulate it can be done again and under same circumstances and give the same outcome.

The spit accelerated best and braked best.
The FW 190 braked and accelerates worst.
The spit is the heaviest and the 109 is the easiest. So due to the 109:s high drag and low weight it should loose its speed much faster than the hevy and low-dragging spit.

Acceleration more complicated, respond of engine, efficiency of prop drag at different speeds because of vortex and streamlining.
But light mass is easier to accelerate than hevier.
During WWII wich the spit was known for its bad acceleration, but that was reality not virtual reality. The spits acceleration was so bad that orders where given to fly at high speed during patrols over france.

And its fun that the spit didnt brake so fast when flying vertically.

Waldo.Pepper
07-22-2007, 12:46 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Test 2 started at sealevel and I accelerated to 500 km/h
Again I chopped the throttle to zero tried to hold my altitude and measured the time and speed until you crash in water. </div></BLOCKQUOTE>

Test 1 seems ok to me. (By that I mean I agree with the results.)

But I haven't a clue what you did in test 2 (especially after you edited your initial port)

In all seriousness tracks would help.

I am developing a theory that may explain what you are describing, but can't for the life of me understand (so far) what your 2nd test was.

Did you remain at sea level? Did you try to climb after you chopped the throttle, or merely maintain zero alt? etc etc etc.

Not to sound facetious, but if you want to be understood quickly and without confusion then - track please.

Skoshi Tiger
07-22-2007, 01:00 AM
Doesn't the 109 have a manual pitch setting?

The Spitfire has a constant speed propeller. When you cut the throttle the propellor will try to maintain revs by setting the prop to a fine pitch.

Have you tried seting the prop in your 109 to fine as well as cutting the throttle, when you were doing the test?

Worth testing?

Waldo.Pepper
07-22-2007, 01:09 AM
My guess is along the same lines....

I expect that it could be that there is a greater inefficiency of the propeller pitch mechanism on the Spitfire.

Specifically the propeller does not turn to a near feathered position merely by cutting the throttle, or that it does not turn to a near feathered position as quickly as it does on the German planes.

Consequently, there is a greater braking effect of the Spitfire prop.

The-Pizza-Man
07-22-2007, 01:21 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by zugfuhrer:
During WWII wich the spit was known for its bad acceleration, but that was reality not virtual reality. The spits acceleration was so bad that orders where given to fly at high speed during patrols over france.
</div></BLOCKQUOTE>

Your taking things out of context there. Coming to the conclusion that the Spitfire had unusually slow acceleration simply because they recommended high speed cruise when operating in areas defended by fighters that have a 30 mph speed advantage on you is a bit of a leap. Taking specifics and turning them into generalities is not the best thing to do.

VW-IceFire
07-22-2007, 07:25 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by zugfuhrer:
During WWII wich the spit was known for its bad acceleration, but that was reality not virtual reality. The spits acceleration was so bad that orders where given to fly at high speed during patrols over france. </div></BLOCKQUOTE>
That was specifically for the Mark V's in 1942/1943 when they were faced with the FW190s. They did this because they could only catch FW190s at the very top end of their speed range which is a very slow acceleration curve for any WWII fighter. So the orders were there so they were closer to that top end of the speed range as soon as possible. VERY hard to determine that the Spitfire was somehow slow in accelerating from this bit alone and given that it applies to just the Mark V it becomes even more difficult to generalize.

DuxCorvan
07-22-2007, 08:56 AM
Weight? That also plays a role. Inertia, you know.

p-11.cAce
07-22-2007, 09:25 AM
The key to this imho is the usage of CEM or not, and even with CEM off the modeling of the speed at which the prop goes from coarse to fine pitch. I trained for my ppl in a Diamond Katana (the original with the rotax 912) which was equipped with a constant speed prop. When you throttled back and kicked the prop to fine pitch it felt like someone slammed on the brakes. If you just reduced pitch without adjusting the prop the effect was not nearly as pronounced.

zugfuhrer
07-22-2007, 09:30 AM
I used automatic propeller control in all tests.
I have never experienced any difference in how fast my a/c loose speed when prop set to manual or automatic pitch. If you have the possibility to tilt the prop, like in bombers it sure reduces the drag.

During test 2 I started at 200 km/h put the throttle to 100% and accelerated to 500 km/h holding course and alt (100-200m ) as good as I could. I checked the time it took to reach 500 km/h.
At this speed I put the throttle to idle holding course and altitude. Of course I decended at the end because I wanted to crash in the sea. I checked the how fast I lost speed and how long time it took to ditch.

The reason for doing this test was that I have on several occations tried to break myself free from the spit on my 6, but without success.

I thought that the a Me-109 would have better ******ation (physics) than the spit, because of it lower inertia and higher drag.

AKA_TAGERT
07-22-2007, 09:38 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by zugfuhrer:
The tracks are wasted but as every real science postulate it can be done again and under same circumstances and give the same outcome. </div></BLOCKQUOTE>
Not in this case..

As with most pilot accounts there is not enough information to recreate the experiment. Reason I ask for tracks is that most of the time there is nothing wrong with the sim and something wrong with the way the test was done.

Thus I feel confidant that if you provided your track file that I could show you where you made your mistake and that the sim is just fine.

The second half of the problem..

And biggest part of the problem..

Is you provided no real world data to compare to..

Thus you test is based more on your perception of how things should be instead of how they actual were.

JG14_Josf
07-22-2007, 11:44 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Is you provided no real world data to compare to.. </div></BLOCKQUOTE>

http://www.pbase.com/chrisdnt/190_tests

The Fw190A-3 (less performance than the Fw190A-4) out accelerated the Spitfire VB 1942 (more performance than the Spitfire VB 1941) according to the extensive REAL WORLD TESTS done in 1942 by the British Military using a captured (from combat) FW190A-3 against their own front line fighters including a Spitfire IX (1942).

As to the engine on zoom tests performed in REAL LIFE the Fw190A-3 was superior at gaining energy according to the REAL WORLD DATA.

The Spitfire was larger than the Fw190.

The Spitfire was not as aerodynamically well made as the Fw190 (produced more parasite drag).

The Spitfire was not as dense as the Fw190.

There is no way to rationalize (without fantasy) a Spitfire gaining more altitude in a power off zoom test.

http://mysite.verizon.net/res0l0yx/IL2Flugbuch/Anatamy%20of%20Drag%20Test.jpg

Assuming the game has the mass for both planes correct - the power off performance (distance/time) during unloaded vertical flight can only happen if the Fw190 is much larger in size (produces much more parasite drag) to account (physically) for the Fw190s greater mass.

If the game doesn't have the mass variable in correct proportion, then, that error can easily explain the odd (defying physics) behavior in power off zoom performance.

The Fw190 produced a significantly greater amount of thrust so power-on performance should also favor the Fw190 (as the Real World Data confirms).

Not so in the game:

http://mysite.verizon.net/res0l0yx/IL2Flugbuch/DiveZoomTest1b.jpg

The easiest way to see how higher mass planes with high wing-loadings, lower power-loadings, and HIGHER thrust capabilities stack up against planes with lower wing-loadings, higher power-loadings, and LOWER thrust is with EM diagrams.

Note the area of greater performance in white:

http://mysite.verizon.net/res0l0yx/IL2Flugbuch/Corner%20time.jpg

Note the area of greater performance for the light weight fighter in red:

http://mysite.verizon.net/res0l0yx/IL2Flugbuch/Wing%20Loading.jpg

Light weight fighters with power off (all else being equal except internal mass) slow down faster through air resistance – that is a physical fact.

RWD:

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The aircraft has a wide sped range which greatly assists in regaining formation, but care must be taken to avoid over-shooting as its clean lines make deceleration slow. </div></BLOCKQUOTE>

That is the ˜official' British document which documented the Fw190A-3's performance evaluation in July 1942

As to the power-on dive and zoom performance (compared to the game test illustration above):

Dive (time 0 to time 21 in the illustration above):

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Comparative dives between the two aircraft have shown that the Fw 190 can leave the Spitfire with ease, particularly during the initial stages. </div></BLOCKQUOTE>

Again; that above is a better (REAL) performing Spitfire VB (1942) compared to the games Spitfire VB (1941).

Again: that above is a worse (REAL) performing Fw190A-3 compared to the game Fw190A-4.

Zoom climb:

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">With both aircraft flying at high cruising speed and then pulling up into a climb, the superior climb of the Fw 190 is even more marked. When both aircraft are pulled into a climb from a dive, the Fw 190 draws away very rapidly and the pilot of the Spitfire has no hope of catching it. </div></BLOCKQUOTE>

Acceleration (again this is the worse performing Fw190A-3 versus the better performing Spitfire VB (1942) compared to the game's Fw190A-4 versus the Spitfire VB (1941))

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The Fw190 has better acceleration under all conditions of flight and this must obviously be useful during combat. </div></BLOCKQUOTE>

Deceleration: (Again – this is the same British Military REAL WORLD DATA flight test results)

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The aircraft has a wide sped range which greatly assists in regaining formation, but care must be taken to avoid over-shooting as its clean lines make deceleration slow. </div></BLOCKQUOTE>

The last RWD does not compare deceleration performance specific to any particular plane; however – the other side by side tests done are specific to specific REAL WORLD aircraft.

Fw190 versus Spitfire IX (July 1942):

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">When both aircraft were flying at a high cruising speed and were pulled up into a climb from level flight, the Fw 190 had a slight advantage in the initial stages of the climb due to its better acceleration. </div></BLOCKQUOTE>

The above ("pulled up into a climb from level flight") is instantaneous turn performance even if you do not want to believe that it is.

That ˜instantaneous turn performance' shows up on an EM chart.

If they had EM charts in WWII, then, the British evaluation report would include an EM chart where the slight advantage in the initial stages of the climb due to better acceleration would show up as a Ps advantage on the chart just like the F-86 has the white part of the envelope on its EM chart as an advantage over the lighter Mig-15.

The next REAL WORLD DATA entry is telling something specific:

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The initial acceleration of the Fw 190 is better than the Spitfire IX under all conditions of flight, except in level flight at such altitudes where the Spitfire has a speed advantage and then, providing the Spitfire is cruising at high speed, there is little to choose between the two aircraft. </div></BLOCKQUOTE>

As to the PROP PITCH THEORY:

A constant speed prop that is left at the high RPM setting during a throttle off deceleration will decelerate faster due to the energy spent turning the engine compared to a constant speed prop that is set to a low RPM setting during a throttle off deceleration because less energy is spent turning the engine faster.

Auto-prop on the Fw190 and Me 109 linked the constant speed governing (rpm setting) to the ONE throttle lever, so, pulling the throttle on either plane also resets the RPM to a low RPM setting thereby minimizing the energy lost in turning the engine with Windmilling.

Therefore – the engine off zoom climb using auto pitch on the German planes and NOT resetting the rpm to a low rpm setting for the Spitfire should further slow down the Spitfire compared to the German planes because the Spitfire will be windmilling the engine to a higher RPM while the German planes windmill the engine to a lower RPM.

The actual difference in total drag caused by the rpm governor adjusting the prop pitch angle of attack may be difficult to notice while piloting the aircraft because much of the flight will probably be performance in either case with the prop pitch angle being driven to the course pitch stop (seeking lower RPM and minimizing drag).

With the throttle plate closed there is only windmilling that can rotate the engine faster than idle as if the engine were an air compressor (minimum fuel being added to the combustion chambers).

At high speed there is plenty of windmilling power to turn the engine as if the engine were an air compressor. The governor will move the prop pitch to as course a setting as is needed to lower the RPM to the RPM setting set by the pilot (using the prop lever in the Spitfire or using the Throttle lever in the German planes).

The flatter the prop pitch angle of attack the greater will be the total drag force produced by the prop disc and the higher will be the force applied to turn the engine as if the engine were an air compressor.

The German planes (switched to manual control of the prop pitch angle and bypassing the prop governor) can manually drive their props to the flattest pitch (fine pitch) if they want to maximize drag during a controlled deceleration (at the risk of over revving the engine with windmilling power).

The Spitfire, as far as I know, does not have the option of bypassing the rpm governor.

PFS_BlackBird
07-22-2007, 11:52 AM
Rads open or closed?

Spit rads open completely at lower speeds. IIRC also if you chop the throttle.

Two big rads opened = loads of added drag.


BB