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View Full Version : P-51D wing break...yes, I have a track



Ratsack
06-08-2006, 09:04 AM
I've just had my first wing break in the new patch. It was low alt, high speed, low G. I don't understand it.

I have the track of the incident (complete with some very bad shooting on my part) if anybody would care to have a squizz and see if they can see what caused it.

It looks like a bug to me, but I have an open mind. PM me if you would like to help me sort this out.

cheers,
Ratsack

Buzzsaw-
06-08-2006, 09:20 AM
Salute

From a USAAF report on the dive characteristics of the P-51:

>>>>>>

2. A series of thirty-one dives was conducted by the Flight Research Branch between 3 August, 1944 and 16 September, 1944. These dives included high and low altitude tests and limited stability tests at high Mach numbers. A complete report of these tests is in the process of preparation at the present: however, the necessary information is forwarded so that it may be made available immediately for operating instructions.

3. The results indicate that the airplane should be restricted to a Mach number of 0.80 due to compressibility difficulties which become increasingly dangerous beyond that point. It is recommended that the airplane be placarded with the following limit diving speeds:-


Pressure Altitude (Ft.) Pilot€s IAS (m.p.h.)
40,000 275
35,000 310
30,000 345
25,000 385
20,000 425
15,000 470
10,000 505
5,000 505

4. Porpoising.- The P-51D airplane, at high speeds, is subject to the longitudinal instability commonly referred to as porpoising. The results to date indicate that the condition may be induced at a Mach number of 0.70 and above, but may be encountered at somewhat lower Mach numbers at low altitude. It is known that the fabric bulge in the elevator surfaces is more critical at low altitudes and may be related to the airplane€s increased tendency to porpoise at lower Mach numbers in that range.


The porpoising is not a severe condition and can be controlled. In the first place, the condition is usually induced by the pilot, since any ununiform elevator stick force will result in the porpoising at high Mach numbers. Any effort on the part of the pilot to counteract this effect will result in increasing amplitude. It may actually be stopped by holding the stick firmly in one position or, in fact, eliminated by trimming forward gradually to near zero stick forces as the dive is entered, thus reducing the amount of forward stick forces necessary to maintain the dive angle.

5. Rolling.- As a Mach number of 0.75 is approached , a slight amount of rolling may become apparent with a simultaneous reduction in aileron sensitivity. This rolling does not become severe, and may be easily controlled.

6. Vibration.- At a Mach number of 0.76 a true effect of compressibility becomes evident in the form of a complete vibration of the airplane. This vibration is caused by a combination of compressibility effects on the wing and the horizontal stabilizer. The condition becomes increasingly severe as the Mach number increases and could eventually cause a primary structural failure.

7. Maximum Limit of Combat.- The airplane has been dived to a maximum Mach number of 0.85 and on several occasions to 0.84. In each case the pilots reported that the vibration became extremely heavy beyond 0.80. In each dive to 0.84 or above the vibration became so severe that the airplane was damaged. The leading edge skin of the wing flap was buckled between rivets, a coolant radiator cracked and hydraulic line broken due to vibration on various dives to 0.84 and above. In extreme war emergency the airplane can be dived to a Mach number of 0.83 (400 m.p.h. Indicated Airspeed at 25,000 ft.), if a very gradual pull-out is made.

<<<<<<<

Link to original document:

http://www.spitfireperformance.com/mustang/p-51d-dive-27-feb-45.pdf

Information courtesy Mike Williams site:

http://www.fourthfightergroup.com/eagles/spittest.html

In my opinion, the ahistorical combinations of extreme tendencies to go out of trim, lack of stability in a dive, easy loss of wings, subpar performance to historical aircraft due to modelling of late 1943 levels of boost, and the poor effectiveness of the .50 calibres, has made the P-51 far from the aircraft it should be.

vocatx
06-08-2006, 10:51 AM
I recently read "Dumb But Lucky..", a book written by a fellow who flew Mustangs over Italy in WWII. It was amazing how many of his squad mates lost wings, as well as elevators in dives. I thought PF had gone over the top on shedding wings, but after reading his book, I'm not too sure.

He also relates a story about a P-38 pilot getting into a flat spin trying to avoid a Me-262 at altitude and spinning all the way down.

I know this sim has it's faults, but reading stories like these makes me think they got it a lot more right than wrong.

To anyone interested in the book: Dumb But Lucky! Confessions of a P-51 Fighter Pilot in World War II, Richard K. Curtis, ISBN 0-345-47636-0

danjama
06-08-2006, 11:00 AM
Got Track?(tm)

WWMaxGunz
06-08-2006, 11:10 AM
Yes there was a problem short while but it was Fixed.
But in the meantime there were planes that went down.
You know, like LaGG-3 varnished coffin? And some other planes?
Fixed.

What has been the policy of Maddox Games about those things?
Those problems are not put in the models that were fixed.
Except for reduced ATA of 190A-4 and what else? Oh yes, all
P-51D's have rearward Center of Mass regardless of fuel state,
they all have exaggerated instability all the time what was
only in real part of the time and extremely rare in fights,
just like badly made Russian planes only less.

So you can find the special short time exceptions all sides and
I hope we don't have the game like that.

justflyin
06-08-2006, 11:26 AM
By far for me, losing a wing happens most in either a P-51 or Ki-84, and usually when I feel that I'm not applying anywhere near the g-forces that I apply in other planes.

It always takes me by surprise in those planes, as I seem to get no warning. Is this accurate, I don't know. My only reference is the game.

Other planes, I know when I'm reaching that breakpoint in speed and that I better not try to turn or I'm going to lose a wing. The P-51 and Ki-84 don't seem to "inform" me the same as the others.

Viper2005_
06-08-2006, 12:30 PM
Originally posted by WWMaxGunz:
Oh yes, all
P-51D's have rearward Center of Mass regardless of fuel state,
they all have exaggerated instability all the time what was
only in real part of the time and extremely rare in fights,
just like badly made Russian planes only less.


At aft CoG the P-51 fitted with aft fuel tanks would actually tighten up in turns, such that forward stick pressure was required to maintain turn rate.

Our P-51s don't do that. Therefore we do not have an aft CoG condition modelled.

VW-IceFire
06-08-2006, 03:53 PM
I had thought Oleg said that even the latest FM available to us in PF does not model a change of CoG based on fuel state. Weight does change and is calculated differently, however, CoG does not shift.

Von_Rat
06-08-2006, 05:20 PM
in a p51, set some down trim on elevators BEFORE you do any hi speed dives, or hi speed manuvers. if you do this you'll almost never lose a wing.

why you should have to do this in a p51 only and not other planes is a whole other argument.

Jasko76
06-08-2006, 05:23 PM
Just a thought: in Swedish service all P-51s had main wing spar replaced by sturdier units. Probably for a good reason.

horseback
06-08-2006, 05:56 PM
Originally posted by Jasko76:
Just a thought: in Swedish service all P-51s had main wing spar replaced by sturdier units. Probably for a good reason. Not really applicable, I think. I doubt that those new wingspars were not installed right after the Swedish Af received their Mustangs. How about telling us when they were put in?

Quite a few Swedish AF P-51s were former USAAF combat aircraft interned after being forced down during the war. This would imply combat damage, low fuel state, or engine trouble (or 'lack of moral fibre'). In any case, most if not all, Swedish AF Mustangs were bought 'used.'

Since a great deal of US advantage over Axis fighters was in their dive capabilities, it seems likely that a significant percentage were stressed more than new built peacetime fighters might have been. Also, I believe the Swedish P-51s were in continuous military service somewhat longer than their USAF counterparts postwar.

A USAF aircraft was retired after reaching 'X' number of hours or a certain level of wear and tear, while the necessarily more frugal Swedes would have to repair and rebuild to keep the aircraft flying. If those new wingspars were installed within two years of delivery, you might have a valid point, but I suspect that most of them were put in after five or more years of continuous service.

cheers

horseback

Jasko76
06-08-2006, 06:07 PM
Spars were replaced right after the planes were received. And if my memory serves me well, Swedish Stangs were pretty fresh specimens, few of them actually saw any combat and vast majority being delivered after the war.
Anyway, all of this can be read in Leif Hellstr¶m's excellent book "J26 Mustang", ISBN 91-85496-71-5. Get it if you can, I think its both in swedish and english.

Bearcat99
06-08-2006, 06:32 PM
While it still happens occasionally it is nowhere near as bad as it used to be. The bottom line in the P-51 for avoiding wingbreaks is... watch your speed... and do everything gently... especially coming out of a dive... if yoiu cant shallow it out then dont go there...

Ratsack
06-08-2006, 08:31 PM
All,

I€m at work at the moment, so I don€t have the track in front of me. However, the conditions as I remember them were:

1. 430 mph IAS
2. 2,000 ft alt
3. left-hand side-slip
4. gentle left-hand roll
5. gentle nose-up pitch
6. 25% fuel
7. Moscow QMB map

The right wing came off at the root.

I was not pulling high Gs. The speed was pretty high, because I€d just dived from about 5,000 feet, but I€d been in near-level flight for quite a few seconds before the wing failed. It wasn€t because of a violent pull out from the dive. Even though the speed was up around the 430 mph mark, the dive limits for the P-51D below 5,000 feet are more than 450 mph.

As I said in my first post, I didn€t apply high Gs to the airframe, and nor was I applying a whole lot of torque with a hard, high-speed roll. I initially thought the bandit€s wingman had snuck up and chewed my wing off, but when I checked the track I found he was not anywhere near a gun solution. I€m mystified.

This is the first wing failure I€ve had on this plane in this patch, and I€ve been mucking around with the P-51D-20 a fair bit in 4.05. I have deliberately thrown it around as violently as I could in the hope of separating a wing, and it hasn€t obliged€¦until last night.

Cheers,
Ratsack

PS €" Mods, I started this thread in order to have an evidence-based discussion of an issue that may shed some light on a possible bug. It€s about the particular characteristics of a particular aircraft as modelled, and whether there is a bug. It is not an historical discussion or debate. I therefore suggest this thread properly belongs back in ORR where I started it, and not in GD where it was moved last night.

vocatx
06-08-2006, 08:36 PM
That sounds about right. One of the examples Lt. Curtis talks about was one of his squad mates folding a wing up after a high-speed low-level pass on the airfield, even though they had express orders not to do this because of the danger of losing a wing. He also mentions many times of the danger of "flirting with the dreaded red line" on the airspeed indicator.

Ratsack
06-08-2006, 08:44 PM
Originally posted by Von_Rat:
in a p51, set some down trim on elevators BEFORE you do any hi speed dives, or hi speed manuvers.

Done. Always. I have elevator and rudder trim mapped to rotaries, and I trim the plane for hands-off, straight and level flight at max-power and high-speed at 90% RPM. I do this while heading in towards the merge. Always.

cheers,
Ratsack

horseback
06-08-2006, 09:19 PM
Originally posted by Jasko76:
Spars were replaced right after the planes were received. And if my memory serves me well, Swedish Stangs were pretty fresh specimens, few of them actually saw any combat and vast majority being delivered after the war.
Anyway, all of this can be read in Leif Hellstr¶m's excellent book "J26 Mustang", ISBN 91-85496-71-5. Get it if you can, I think its both in swedish and english. Just checked Robert Jackson's Mustang:The Operational Record, which kind of glosses over the RSAF's use of the Mustang, but does note that deliveries were completed by March 1948. Since the P-51D/K production run ended in early 1945 (sufficient time for NAA's plant in Inglewood to produce 555 H models before the contract was cancelled on VJ Day), I suspect that most of Sweden's order were delivered used from the suddenly surplus 8th & 9th AF inventories (shorter delivery route).

Unless there was a problem with the extremes of the Swedish winter, I still doubt that the mainspar was too weak for the Swedish AF to safely use.

cheers

horseback

Stackhouse25th
06-08-2006, 10:43 PM
There is a thing called Maneuvering speed. Do not make abrupt control movements beyond this speed, IE pulling so hard it exceeds the G tolerances for the aircraft at that speed because it cannot stall, instead it snaps the wings off.

Just be gentle with it in a high speed dive, know where never exceed speed is, and then tell urself to never go faster than -40KMH of the vNE speed.

I think around 500KMH you can rip the stick back and it will stall out, however 600KMH it will not do that

WWMaxGunz
06-08-2006, 10:45 PM
Originally posted by Viper2005_:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by WWMaxGunz:
Oh yes, all
P-51D's have rearward Center of Mass regardless of fuel state,
they all have exaggerated instability all the time what was
only in real part of the time and extremely rare in fights,
just like badly made Russian planes only less.


At aft CoG the P-51 fitted with aft fuel tanks would actually tighten up in turns, such that forward stick pressure was required to maintain turn rate.

Our P-51s don't do that. Therefore we do not have an aft CoG condition modelled. </div></BLOCKQUOTE>

It has to be a turn with enough neg lift of elevator to shift the CL up past the CM don't it?

And with the overdone elevators we don't get that or perhaps we can in a really tight turn
but how will you know? It's not like you'll feel the joystick loosen up on you unless you
have FFB. What would happen is you have your stick back in the turn and as control forces
lightened up the virtual stick in the cockpit view would move farther back and you would be
mystified as to why your P-51 suddenly went into stall. And no one has reported that, right?

How far back the CM is does affect stability even if it is not 'too far' back. CM far forward
is I believe more stable than CM far back even within reccomended limits.

GR142-Pipper
06-09-2006, 12:23 AM
Originally posted by VW-IceFire:
I had thought Oleg said that even the latest FM available to us in PF does not model a change of CoG based on fuel state. Weight does change and is calculated differently, however, CoG does not shift. So the question is, does the CG always remain aft regardless of fuel state or is it modeled forward all the time? I think it's modeled aft all the time.

GR142-Pipper

Von_Rat
06-09-2006, 12:41 AM
Originally posted by Ratsack:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Von_Rat:
in a p51, set some down trim on elevators BEFORE you do any hi speed dives, or hi speed manuvers.

Done. Always. I have elevator and rudder trim mapped to rotaries, and I trim the plane for hands-off, straight and level flight at max-power and high-speed at 90% RPM. I do this while heading in towards the merge. Always.

cheers,
Ratsack </div></BLOCKQUOTE>
sorry if im misunderstanding you but,,,,,

i dont think triming for straight and level is good enough. i DOWN trim the elevator enough that i have to pull stick back a little for plane to fly level. since ive started doing this ive found i can throw the p51 around at hi speed just as good as a dora, without losing wings.

Ratsack
06-09-2006, 01:02 AM
Originally posted by Stackhouse25th:
There is a thing called Maneuvering speed. Do not make abrupt control movements beyond this speed, IE pulling so hard it exceeds the G tolerances for the aircraft at that speed because it cannot stall, instead it snaps the wings off.

Just be gentle with it in a high speed dive, know where never exceed speed is, and then tell urself to never go faster than -40KMH of the vNE speed.

I think around 500KMH you can rip the stick back and it will stall out, however 600KMH it will not do that

Read my second post.

cheers,
Ratsack