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Cecil

P-51 gear door fairings ripping off in high speed dives

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I'm wondering what the justification is for having the Mustang's gear door covers rip off in a high speed dive?  None of the other planes lose their gear doors.  Instead they lose control surfaces which don't penalize top speed nearly as much.  

 

Here's an example of a 190D9 vs a 109K4DC vs P-51 (150 octane) top speeds after taking damage from overspeeding a dive.  

  • The 190D9 loses a ton of control surfaces readily in an oversped dive.  A new airframe tops out at 339/349/375 mph in continuous, combat, and WEP at SL.  In a high speed dive at ~560 mph indicated, I was able to get both ailerons and an elevator to rip off.  Which meant that during the subsequent top speed run at SL, I had to use rudder to stabilize roll, which induced sideslip.  But it was still able to go 337/346/375 mph in continuous, combat, and WEP.  An average speed loss of just a couple mph for 3 missing control surfaces.
  • Then I tested the 109K4DC.  I ripped both ailerons off at ~580 mph indicated which didn't slow it down at all as far as I could tell.  It still went 321/346/386 mph in continuous, combat, and WEP at SL, even with a bit of sideslip due to me not having ailerons anymore and having to use rudder to stabilize roll.
  • Now on to the P-51.  It tops out at 349/363/390 mph in continuous, combat, and WEP (150 octane) at SL.  But after a high speed dive up to just ~525 mph indicated, the gear doors rip off and afterwards the airframe becomes so draggy that your speed is limited to 284/299/319 in continuous, combat, and WEP at SL.  That's a speed reduction of 60-70 mph depending on power setting.

 

The P-51's top speed gets severely reduced from damage sustained during high speed dives and the damage occurs just 20 mph over the placard dive limit.  No other plane I've tested gets penalized as badly as the Mustang for exceeding its maximum dive speed.  I did some quick tests on some other Bodenplatte planes and the results were similar to the 109/190.  None of them lost their gear doors in a dive.  All of them lose control surfaces and the drag penalty seems minimal

 

We could have a discussion as to whether or not the drag on the airframe is overblown when the gear doors are gone or if the drag penalty isn't high enough when control surfaces are missing, but I'm more interested in the reason why the P-51 is the only plane in the game, as far as I can tell, that has its gear doors flake off in a dive.  I can't find any real life stories or data to indicate that this was an actual worry for the real life airframe.

Edited by Cecil
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TSCHEP 5R/RLB/MEM/2-6258
Wright Field, Dayton, Ohio
Date:- 9th October, 1944


To:- Chief, Aircraft Laboratory
Engineering Division,
Wright Field


Subject:- Compressibility Dive Tests on the North American P-51D Airplane,
(‘Mustang IV’) AAF No.44-14134

1. Reference is made to Inter-Office Memorandum, P.W. Nosker:ffc: 51 dated 27 June, 1944 and Lt. D. B. Parker:PC:51 dated 10 July, 1944 from Chief, Aircraft Laboratory to Chief, Flight Section requesting that compressibility dive tests be conducted on the P-51D airplane.
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

 

 

http://www.wwiiaircraftperformance.org/mustang/p-51d-dive-27-feb-45.pdf

 

"during various dives above 460mph calibrated airspeed excessive deflections of the ammunition and gun bay doors, wheel well fairing doors..."

Edited by CUJO_1970
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16 hours ago, CUJO_1970 said:

"during various dives above 460mph calibrated airspeed excessive deflections of the ammunition and gun bay doors, wheel well fairing doors..."

 

Do you have any other resources pertaining to gear doors?  I see on page 2 of that dive test pdf where it mentions gear doors flexing at high indicated airspeeds and a gear door failure, but then it goes on to say that it resulted in a service bulletin regarding the "maintenance of up-latches" in Oct 1944, presumably to fix the problem.  And then at the bottom of that page it recommends a dive limit of 505 indicated due to gear doors deflecting at high indicated airspeeds, but there's also a ton of after action reports on that website where pilots said they went way beyond the placard limit, hitting speeds upwards and in excess of 600 mph indicated in a dive or one where a pilot said he was over 525 mph multiple times in a dogfight with no mention of damage to any of their airframes.

 

Also I realized you could deploy the landing gear at high speeds in other planes to rip their gear doors off and test how draggy those airframes got.  Here are the results from some quick tests of maximum possible speeds at SL in WEP with gear doors on vs off:

  • 109K4-DC 386/362 mph (24 mph loss)
  • 190D9 375/365 mph (10 mph loss)
  • Spit9 353/342 mph (11 mph loss)
  • Tempest 386/386 mph (0 mph loss)
  • P-38 352/310 mph (42 mph loss)
  • P-47 351/339 mph (12 mph loss)
  • P-51 391/306 mph (85 mph loss)
  • (This last P-51 test has higher speed losses than the first one because when you drop the gear at high speeds you also rip the tail gear door off.)

The results are that most planes barely get slowed down by it, yet the P-51 loses 85 mph of top speed.  Is that right?

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No P-51D should be doing 391 on the deck, with any type of fuel - that might be a reason for such loss of speed. Seriously, P-51 is doing 391 on deck? That's at least 12 mph/19kph faster than any speed test for P-51D on 150 grade fuel I've seen.

 

That's the placarded dive restriction on P-51D posted above, as well as the explanation from Wright Field as to why those restrictions were implemented. Every aircraft had dive restrictions, so it's nothing out of the ordinary.

 

If your looking for specific anecdotes on P-51 structural issue there are many of those, in Freeman's 8th AF history, or you can read Dean's America's Hundred Thousand.

 

Dick Curtiss' Dumb But Lucky:

https://www.google.com/books/edition/Dumb_But_Lucky/ZclvDwAAQBAJ?hl=en&gbpv=1&printsec=frontcover

 

etc etc - there is abundant information on the subject.

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5 hours ago, CUJO_1970 said:

No P-51D should be doing 391 on the deck, with any type of fuel - that might be a reason for such loss of speed. Seriously, P-51 is doing 391 on deck? That's at least 12 mph/19kph faster than any speed test for P-51D on 150 grade fuel I've seen.

 

That's the placarded dive restriction on P-51D posted above, as well as the explanation from Wright Field as to why those restrictions were implemented. Every aircraft had dive restrictions, so it's nothing out of the ordinary.

 

If your looking for specific anecdotes on P-51 structural issue there are many of those, in Freeman's 8th AF history, or you can read Dean's America's Hundred Thousand.

 

Dick Curtiss' Dumb But Lucky:

https://www.google.com/books/edition/Dumb_But_Lucky/ZclvDwAAQBAJ?hl=en&gbpv=1&printsec=frontcover

 

etc etc - there is abundant information on the subject.

 

Do you have a specific page from that book that states that the gear doors should rip off at 520mph?  I don't really want to read a whole book when the information posted in this thread I've read so far says the gear doors shouldn't be ripping off at the speeds they do because they fixed it in Oct' 44 which is before BoP takes place.  That Mustang Encounter's Report that Cecil mentioned is also full of stories of pilots grossly exceeding the placard limits and there being no structural damage.  For the one story you mentioned which notes a bending (not ripping off) of gear doors, there's 10 more stories on that same website saying nothing happened at even higher dive speeds in excess of 600mph+.  The placard limit =/= the speed at which things actually rip off, there's always a hefty margin. 

 

5 hours ago, CUJO_1970 said:

etc etc - there is abundant information on the subject.

 

There is, and it looks like all of the "abundant information" posted in this thread so far indicates that the doors rip off way earlier than they should.

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If you think the Mustang actually did 600+ mph in a dive I probably can't help you.

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20 minutes ago, Chuck_Yeager said:

2079065426_600MPH.thumb.png.a7a3b62e1c8d0b52a69f24aa46d3b483.png

Isn't the pilot who's claiming he had 600mph at 15kft going supersonic if that's true? 

 

Speed of sound at that altitude is around 720mph TAS at -15, and I plugged the numbers into an online IAS to TAS converter and got at least 780mph TAS for 600mph. Am I doing the conversion wrong or is that anecdote a pack of lies?

Edited by 71st_AH_Barnacles
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Basically, not a pack of lies, just mistakes - but he thinks we've never read all that stuff a million times already and some of these guys are hopeless until they learn a little more - especially concerning the P-51.

Edited by CUJO_1970

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40 minutes ago, CUJO_1970 said:

Basically - but he thinks we've never read all that stuff a million times already and some of these guys are hopeless until they learn a little more - especially concerning the P-51.

 

I don't know what to tell you man.  You told me I'm crazy if I think the P-51 ever did over 600mph and there's 13 accounts on that page of P-51s doing over 600mph indicated and 4 more saying 650+. 

If you think I'm hopeless, help me learn.  The literature in this thread says 600mph+ in a dive with no problems.  If you have literature/data that says otherwise please share it so I can learn.  If it's a whole book, can you tell me a page number at least?  I don't want to spend my entire day reading a book that may not even contain the information I'm looking for.

Edited by Chuck_Yeager

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No prop-driven aircraft of the war had the power, aerodynamics, or structural integrity to even begin approaching those speeds - not in a dive or in any other flight attitude.

 

Every single one of those 13 accounts of P-51s going over 600 mph and 4 more saying 650+ may be dismissed completely. That does not mean the pilots were lying - they were simply mistaken and that happened a lot during the war.

 

I already included P-51 placard and link to Wright Field analysis behind placard restrictions - along with two reference works and a book filled with P-51 anecdotes and you want me to provide you with more and then tell you the page number? Until you actually want to learn the truth all the references in the world won't help you and you will continue to believe someone actually went 650+ mph in a Mustang.

 

Contrary to popular belief, reading a book is not such a bad thing.

 

 

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18 minutes ago, Gavrick said:

image.png.f05ae0df463eb423f291304b57a0e1

 

From this source, the fairing issue was fixed in October of 1944, which is before our BoP expansion takes place.  So doesn't that mean that the P-51s we have should have the latch repair implemented and they shouldn't be getting ripped off at 505?

 

2 hours ago, CUJO_1970 said:

No prop-driven aircraft of the war had the power, aerodynamics, or structural integrity to even begin approaching those speeds - not in a dive or in any other flight attitude.

 

Every single one of those 13 accounts of P-51s going over 600 mph and 4 more saying 650+ may be dismissed completely. That does not mean the pilots were lying - they were simply mistaken and that happened a lot during the war.

 

I already included P-51 placard and link to Wright Field analysis behind placard restrictions - along with two reference works and a book filled with P-51 anecdotes and you want me to provide you with more and then tell you the page number? Until you actually want to learn the truth all the references in the world won't help you and you will continue to believe someone actually went 650+ mph in a Mustang.

 

Contrary to popular belief, reading a book is not such a bad thing.

  

 

 

Also, the book you linked me as a source literally has an anecdote of a P-51 exceeding 550mph in a dive with nothing getting ripped off.  The book you linked me to disprove me has evidence in it proving my point. 

 

Have you read this book...?

 

1002480017_P-51550mphdive.png.d2079a7ed13151dbe0da7229e1ce225e.png

 

It's on Page 162, if you wanna check it out.

 

Edited by Chuck_Yeager

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43 minutes ago, Chuck_Yeager said:

From this source, the fairing issue was fixed in October of 1944, which is before our BoP expansion takes place.  So doesn't that mean that the P-51s we have should have the latch repair implemented and they shouldn't be getting ripped off at 505?

 

It would really depend on you, what you are doing with the aircraft and altitude.

 

What it says is that the Mustang should remain structurally intact up to Mach 0.8. This is 600+ mph. (Note: quoted 650+ mph is above that, depending on altitude and atmosphere already in the transsonic region).

Structurally intact doesn‘t mean you‘re not in a region where „things“can start happening. Hence the requested factory warranty at 505 mph. And no, I wouldn‘t expect fairings coming off at 506 mph if they are made to last through 505 mph. But if they come off at 550 mph, you can‘t sue North American for that.

 

EDIT:

Maybe I should add regarding point 7 and 8 of the document posted by Gavrick. Airflow around a structure creates a suction to that surface and any door on that surface, meaning those doors are pulled out (same as you car door) at higher speeds. Depending on the opening angle, they can open more or less, as airflow on that opened surface might further push it open or press it down again after opening a certain angle.

 

Now, the ammo boxes have the hinge in front, meaning if they open prematurely, airflow will keep them from opening more than just a bit. Wheel fairings open sideways, meaning frontal airflow can‘t push them in again, hence they open more, progressively exposing them to slipstream to get torn off if you keep going like that.

 

This is what they observed occasionally at 460+ mph already, those thingys opened a bit, just to close again when slowing down. Hence the request to NA for reinforcing door lock to at least keep everything closed up to 505 mph as factory standard.

Edited by ZachariasX

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13 minutes ago, Chuck_Yeager said:

 

 ...ripped off at 505?

 

Ripped off a 505 at what altitude?

 

The August 1945 USAAF P-51 training manual actually gives lower max dive speeds than CUJO quotes above:

P-51-max-dive-speeds.png

 

 

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2 minutes ago, AndyJWest said:

 

Ripped off a 505 at what altitude?

 

Pretty low, like under 5,000ft.  I understand that the placard max speed is 505, but that's not the actual speed the doors would rip off in real life as they make those limits lower on purpose for margins/safety.  For example, the listed max dive speed for the 109K4 (in game) is 528MPH (850KM/H) but according to OP's tests from the beginning of this thread, the 109 doesn't start getting stuff ripped off until 580MPH.

So the K-4 can exceed it's placard dive speed by almost 50MPH, but the P-51 in game can only exceed it by like ~10MPH before stuff gets ripped off.

Which is why I agree with OP that there's something a little off about the P-51 getting its doors ripped off at such a slower speed compared to the other aircraft when there are plenty of anecdotes in this thread from real P-51 pilots safely exceeding the placard speed by quite a bit with nothing happening.

In short, why are other air frames in game allowed to exceed their placard max speeds by such large margins when the P-51 isn't?  According to the source linked to by the Dev in this thread, the latch issue that caused them to buffet and fall off should have been fixed by the time BoP takes place.

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11 minutes ago, Chuck_Yeager said:

In short, why are other air frames in game allowed to exceed their placard max speeds by such large margins when the P-51 isn't? 

This is not a problem of the airframe as such. It is a problem of how you secure door locks.

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3 minutes ago, ZachariasX said:

This is not a problem of the airframe as such. It is a problem of how you secure door locks.

 

Yes but doesn't the source posted by Gavrick show that the door lock problem was fixed by the time BoP takes place?

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5 minutes ago, Chuck_Yeager said:

 

Yes but doesn't the source posted by Gavrick show that the door lock problem was fixed by the time BoP takes place?

It is fixed when the doors stay on at 505 mph. (Listed max. dive speeds respectively.)

 

Past that speed, NA couldn't care less and you have to pay for the damage yourself. When they said that the Mustang could be flown to Mach 0.8, this means the wings don't come off at that speed and  they expect you coming home. If you for instance oversped your engine by doing so and have to bring it in, you lost some fairings, they charge you for it. But they expect you to be able to come home and be a client in their repair shop until Mach 0.8. Going faster than that, they will be more impressed you coming home and the bill is gonna be higher to make the aircraft airworthy again.

 

On a side note, it is really, really difficult to get exact numers from a pilot that just returned from a mission. I tried hard to memorize settings, speed etc. when flying a real Spitfire. Not having the occasion to take notes, it was not that easy, what helped is I absolutely knew what to expect. That helped. Now, those teenagers fighting for their lives on hours long missions pumped full of adrenaline, I'd take a lot of the "high" numbers as a bit for figuratively speaking. Also, speedometers are far from exact at very high speeds, especially when entering transsonic region. Needels can start shaking viloently, same as the whole airframe. It is truly a bungee jump in it's own way. So I really cut the kids some slack there. What I do believe though that they went all in as fast as they could.

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Chuck_Yeager, have you read the 1945 P-51 manual? As it makes clear,  when diving beyond placarded speeds, doors coming off may be the least of your problems. Compressibility can bring on wallowing, reversal of control forces and the potential for vibrations of an amplitude that can cause structural failure.  If the USAAF decided that Mach 0.8 was safe, they don't seem to have updated the manual to say so. 

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Guys, I'm not worried about the other effects listed in the RL manual, it's just strange to me that when the P-51 exceeds its placard limits by only ~10MPH, its doors rip off for a speed penalty of over 70 MPH. Yet, the K4 can exceed its posted dive limit by 60MPH (up to 580MPH) and have control surfaces rip off for no penalty in top speed.  Doesn't that seem strange to you guys?

 

Lets consider the reverse, does anyone have any K4 documentation stating that it can go up to 580 MPH with no ill effects?

 

Why is there such a huge disparity in how different air frames handle when they exceed their posted limits?  This is the core issue/question that I'm trying to get to without getting too off topic: why can the K4/D9 exceed the limits from their RL manuals by such huge margins when the P-51 can't?  If it's because of the door lock, the source posted by Gavrick shows that it was fixed before BoP.  So what gives?

 

 

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8 minutes ago, Chuck_Yeager said:

Guys, I'm not worried about the other effects listed in the RL manual, it's just strange to me that when the P-51 exceeds its placard limits by only ~10MPH, its doors rip off for a speed penalty of over 70 MPH. Yet, the K4 can exceed its posted dive limit by 60MPH (up to 580MPH) and have control surfaces rip off for no penalty in top speed.  Doesn't that seem strange to you guys?

 

Lets consider the reverse, does anyone have any K4 documentation stating that it can go up to 580 MPH with no ill effects?

 

Why is there such a huge disparity in how different air frames handle when they exceed their posted limits?  This is the core issue/question that I'm trying to get to without getting too off topic: why can the K4/D9 exceed the limits from their RL manuals by such huge margins when the P-51 can't?  If it's because of the door lock, the source posted by Gavrick shows that it was fixed before BoP.  So what gives?

 

 

 

If you aren't worried about other effects listed in the manual, why not? Don't you want the P-51 to be accurately modelled? And no, the source provided by Gavrick doesn't show anything was 'fixed' beyond the 505 mph figure they asked the manufacturers to demonstrate.

 

As for the K4 and the D9, they may be right. They may be wrong. Either way, what happens to them when they overspeed is no reason to alter the P-51. Not if the object is to model it properly.

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9 hours ago, AndyJWest said:

have you read the 1945 P-51 manual

 

I skimmed it.  The problem is that the real life manuals aren't going to detail all the precise speeds at which things start to fail in a dive.  They just set a blanket limit and tell pilots to not exceed it, with the attitude of, "If you wanted to exceed it in real life, good luck.  You'll probably get yourself killed."  Given that this is the case, the devs arbitrarily set structural failure points in their game and when you hit them, bad things happen.  And given that this is ultimately a game, I'm going to butt right up against those speeds.  This is fine as long as they're consistent in their methods. 

 

My problem is that for some reason the P-51 is special in this game, in that it fails just 20 mph over its placard limit.  While you have planes like the P-38 and the Spitfire that can exceed their dive limits by 75 mph and others like the 109 and 190 which can exceed their limits by ~50 mph.  And then when those airframes start to fail, they lose control surfaces.  If you lose a control surface in combat, you're probably going to want to RTB and when doing so, you will barely be slowed down.  Some of these airframes don't lose any speed with control surfaces ripped off.  So, you'll make it back to base just fine because the penalty for overspeeding that airframe is minimal.  The P-51 is again a special case where for some reason when its airframe starts to fail, it's gear doors are the first thing to fly off and your airframe becomes so draggy that you'll probably get chased down and killed.  And the P-51 is yet again special in that if you compare all these airframes with their gear doors missing, the P-51 loses ~5x the airspeed in comparison to all these other airframes.  No other airframe in the game gets crippled as badly as the Mustang does from exceeding limits.  It's not even close.

 

So you have all the other planes in the game, where if you exceed their dive limits (and you have to exceed them by quite a lot), it's not the end of the world.  You can still run away and survive in combat.  Then you have the P-51 (where it's special in 3 different ways that stack, to cripple its airframe in a manner that no other plane in the game experiences), where if you exceed its dive limit by just 20 mph (which is really easy to do), you effectively shoot yourself in the foot and you're a dead man walking.  It's like trying to RTB in a Stuka.  You are not going to make it home.  You're going to get chased down and killed.

 

Seems inconsistent to me.

 

(Edit: commas man, commas.)

Edited by Cecil

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Maybe there is a case for a rework of overspeed damage, for 'consistency'. But only if what it is being consistent with is actual data on the real aircraft. All of them, not just the P-51. Without knowing how they arrived at 'damage speeds' for other aircraft, we don't know which are right and which are wrong. 'Fixing' it by say making the P-51 lose control surfaces at 50 mph over placard speeds might well 'balance' things by reproducing incorrect modelling elsewhere. And to be frank, I don't think the benign loss of a control surface damage from overspeed is particularly realistic anyway. Control surfaces don't usually neatly fall off, leaving the control mechanism intact. When significant parts of an airframe are detached at high speed, it is because of structurally-damaging stresses or flutter. If the airframe is still capable of flight at all, rather than torn apart further, it is going to be severely compromised. A proper rework of overspeed damage would quite likely result in aircraft (including the P-51) being a lot less forgiving to pilots who can't keep to the limits they are instructed to. Unfortunately the multiplayer environment seems to encourage all sorts of ahistorical behaviour, where aircraft are routinely flown in a manner that no pilot who valued his life would contemplate. I don't think it is in the best interests of the simulation to encourage this.

 

On a more general point, I don't think these 'X is wrong with aircraft Y and it is unfair' arguments are at all beneficial, if the object is to encourage accuracy. If something is wrong (or rather, if something can be shown to be wrong, in relation to historical data) that is sufficient reason on its own to raise the matter with the developers. IL-2 GB isn't an abstract e-sport, where 'fairness' is something to be aimed at. Instead the object is to model aircraft as they were historically. Where things were rarely balanced at all. 

Edited by AndyJWest
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On 11/26/2019 at 1:11 PM, CUJO_1970 said:

No P-51D should be doing 391 on the deck, with any type of fuel - that might be a reason for such loss of speed. Seriously, P-51 is doing 391 on deck? That's at least 12 mph/19kph faster than any speed test for P-51D on 150 grade fuel I've seen.

 

I was curious about this so I went and did a little testing offline.  Going from Rheinland Summer, to Fall, Winter and Spring made a huge difference in speed, obviously due to changing density altitude.

 

With 150 octane, 69% fuel, using full throttle and rpm at about 250ft my quick and dirty results were: 368mph/376mph/390mph/376mph.  I'm sure other can do slightly better etc, but for a rough range of numbers at different temps this actually looks pretty reasonable vs tests I've seen.  Obviously the 390 seems really high, but its just the result of flying on a really cold day.  I jumped in a 190A3 and easily exceeded 360mph on the deck on the same map, so it's affecting all the airplanes equally as best I can tell.

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It'd be great if everything was as realistic as possible, but it's not, so it bugs me when there's inconsistencies that affect combat so drastically.  Also, I'm not sure how you could ever enforce historical behavior in a game, even a sim, given that if you die in the game you don't die in real life.  Virtual pilots are always going to have suicidal tendencies.

 

4 hours ago, AndyJWest said:

On a more general point, I don't think these 'X is wrong with aircraft Y and it is unfair' arguments are at all beneficial, if the object is to encourage accuracy. If something is wrong (or rather, if something can be shown to be wrong, in relation to historical data) that is sufficient reason on its own to raise the matter with the developers. IL-2 GB isn't an abstract e-sport, where 'fairness' is something to be aimed at. Instead the object is to model aircraft as they were historically. Where things were rarely balanced at all. 

 

I actually kind of agree.  The problem is that that attitude doesn't help me in the game.  I take little solace in knowing that my P-51 might be more accurately modeled as a 109 chases me down and murders me with 30mm after I tried to dive away because he knows 100% that I screwed up and my airframe is now 70mph slower than it used to be and he doesn't have any of those same limits to worry about.  And we're stuck here scratching our heads wondering how the devs arrived at their decisions about structural failure in a high speed dive.

 

Also in a dive, the P-51 was supposed to become unstable and porpoise, but it doesn't do that in the game.  And you weren't ever supposed to have to use trim to pull out of a dive IRL and they even warned about pulling back too hard because the stick force per G wasn't that much (I think I read ~10 lbs/G at max speed somewhere) and yet you can easily get yourself into a situation where you need trim to save yourself in the game.

 

9 minutes ago, kracerx said:

 

I was curious about this so I went and did a little testing offline.  Going from Rheinland Summer, to Fall, Winter and Spring made a huge difference in speed, obviously due to changing density altitude.

 

Yeah, I used Stalingrad Autumn quick missions for my quick tests which I figured were close to a standard day.  Also you can eek out a few more MPH by dropping the prop pitch a bit and manually overriding your coolant flap positions.

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16 hours ago, AndyJWest said:

 

If you aren't worried about other effects listed in the manual, why not? Don't you want the P-51 to be accurately modelled? And no, the source provided by Gavrick doesn't show anything was 'fixed' beyond the 505 mph figure they asked the manufacturers to demonstrate.

 

As for the K4 and the D9, they may be right. They may be wrong. Either way, what happens to them when they overspeed is no reason to alter the P-51. Not if the object is to model it properly.

 

I should rephrase, I'm not worried about those effects as far as this discussion goes because I don't want to get sidetracked from my main issue which is that some airframes can grossly exceed their placard limits for limited penalty while others can't.  I'd love to see some of the other effects from the RL manual modeled (some of which Cecil pointed out like the proposing and trim usage in recovery), but I don't want to start a whole other tangential discussion about stuff not related to the disparity between what happens when you exceed placard limits in different planes in game.

This is the big question I'd like answered in a nut-shell by the devs: Why can the other airplanes exceed their limits by such huge margins with little to no penalty when the P-51 can't? Is there a historical basis for this?  Does somebody have documentation somewhere saying that planes like the K4 had a manufacturer limit of 850 km/h but pilots routinely took it up to 930 km/h anyway?  I'd love to see that documentation because there seems to be plenty of people in this thread with more knowledge of/access to old tech data then I have.  I guess I'm just really curious how the devs decided on the speed of ~930 km/h being the speed at which things rip off for the K4, and, more importantly, that there's no penalty in speed when those things do rip off.

 

My argument is that the P-51 in game should be able to exceed its placard limits by the same or similar margins as the other planes because of the sheer volume of RL pilot anecdotes that have already been posted in this thread where they grossly oversped the plane and nothing happened.  Yes, I understand the argument that some pilots maybe mis-remembered or exaggerated from excitement during combat, but there's over 20+ real pilot anecdotes in this thread alone claiming speeds over 550 MPH.  I doubt every single one of them exaggerated.  I would buy that argument if it was only a few stories, but the sheer volume of pilots saying they went that fast with nothing ripping off inclines me to believe that the P-51 in game should be able to exceed its placard limits by similar margins as the other planes in game.

Edited by Chuck_Yeager

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The thing is with pilot anecdotes is that they come from the pilots who got away with things, not the ones who's misadventures into overspeed territory ended in a smoking hole. Which is one reason why the developers prefer hard data. And if you want a response to a question from the developers, it is generally better not to phrase it in a manner which suggests they are somehow trying to rig things for some reason or other. 

 

And no, there is no particular reason to assume that the margin between placarded maximum and actual safe limits should be the same for all aircraft. Differing ideas as to what was acceptable, combined with limited data (often hard to gather from a smoking hole) are likely to result in very divergent numbers.

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I hope I don't sound like I'm accusing the devs of rigging the game in favor of German or anything crazy like that, I fly both the airframes in MP quite a bit.  I'm not sure how to point out that the P-51 can't exceed it's placard limits by the same margins as the other planes without sounding biased, it just is the way the game is currently set up.  The P-51 in game is much more strictly held to its placard limits than the other planes and it doesn't seem consistent and I'd like to know what the logic behind it is.

Everyone in MP exceeds the placard limits of their planes by huge margins while the P-51 can't and it seems like the P-51 is currently held to a standard that the other planes aren't.

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20 hours ago, CUJO_1970 said:

No prop-driven aircraft of the war had the power, aerodynamics, or structural integrity to even begin approaching those speeds - not in a dive or in any other flight attitude.

 

Every single one of those 13 accounts of P-51s going over 600 mph and 4 more saying 650+ may be dismissed completely. That does not mean the pilots were lying - they were simply mistaken and that happened a lot during the war.

 

I already included P-51 placard and link to Wright Field analysis behind placard restrictions - along with two reference works and a book filled with P-51 anecdotes and you want me to provide you with more and then tell you the page number? Until you actually want to learn the truth all the references in the world won't help you and you will continue to believe someone actually went 650+ mph in a Mustang.

 

Contrary to popular belief, reading a book is not such a bad thing.

 

 

Are we talking indicated or true? A few aircraft of WW2 could certainly hit 600mph TAS in a dive, they wouldn't go much faster than that though due to drag and other reasons.

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19 hours ago, Legioneod said:

Are we talking indicated or true? A few aircraft of WW2 could certainly hit 600mph TAS in a dive, they wouldn't go much faster than that though due to drag and other reasons.


Yes and they will loose the prop and some parts in the process.
such speeds are simply instrumental errors, especially in the case of pilot's reports.
the best sources are always the factory trials as those test-planes were mostly equipped with special measuring instruments, much more precise than the standard dash-speedometer.
at those speeds(500mph+) the prop act as an airbrake, no WWII prop-airplane could even dream to reach those speeds of 600 without any kind of damage.

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On 11/28/2019 at 2:59 PM, simfan1998 said:


Yes and they will loose the prop and some parts in the process.
such speeds are simply instrumental errors, especially in the case of pilot's reports.
the best sources are always the factory trials as those test-planes were mostly equipped with special measuring instruments, much more precise than the standard dash-speedometer.
at those speeds(500mph+) the prop act as an airbrake, no WWII prop-airplane could even dream to reach those speeds of 600 without any kind of damage.

Depends on the aircraft. No prop aircraft can go faster than the speed of sound thats true but there are props that went 600 mph TAS in a dive and were structurally fine at the end of it. Some aircraft limitations are due to structure, others due to drag/compressability.

 

I'd have to find the it but I've seen a report of the P-47 achieving around 0.83 mach in a dive which is the fastest speed it could achieve in a dive from what I've read, it was structurally sound but near uncontrollable due to compressability. I'm not saying it's common but it's not impossible either.

Edited by Legioneod

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On the P-51 aerodynamic damage would have a larger effect than on other aircraft, due to the initial low drag. If a lost wheel cover would cause the same drag on say a P-51 and a P-47, you'd certainly notice the added drag a lot more on the P-51. Might be in the region of twice the speed loss. However, with other speed losses as posted above ranging from 0 to 42 with a P-47 at 12, 85 certainly is way too much. There may, however, be other damage that is not as visible.

 

That said, the effects of wheel covers on top speed has been investigated in real life. For instance, the removal of the inner landing gear covers on the Fw190A cost about 5 km/h.

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On 11/27/2019 at 8:16 PM, Chuck_Yeager said:

Yes but doesn't the source posted by Gavrick show that the door lock problem was fixed by the time BoP takes place?

 

Here is a Technical Order No. 01-60J-22, regarding the inspection of the landing gear uplocks and fairing door uplocks, dated 1 June 1944; this noted:

Quote

The publication of this Technical Order has been expedited as the instruction contained herein are of vital importance and should be disseminated to all affected personnel without delay....

 

1. Due to the possibility of improper adjustment of the landing gear uplock and the landing-gear fairing door lock which may cause loss of the fairing door during flight, all P-51B, P-51C and P-51D airplanes will be inspected immediately...

 

Thus, it was considered by the boffins that it was a mechanical problem (ie; improper adjustment of uplocks and locks), rather than some aerodynamic flaw, or inherent weakness in the design, that led to the doors bowing, then being lost in flight during high speed dives.

 

Here is a service bulletin Technical Order No. 01-60JE-9, dated 16 September 1944, regarding the in-field retrofitting/installation of landing gear uplocks to existing P-51Ds; it notes that:

 

Quote

2. The instructions for accomplishing this change as contained in North American Service Bulletin 51-188, dated 29 June 1944... 

 

These uplocks were installed to prevent the possibility of the landing gear extending during high-speed manoeuvres, a serious situation that led to the loss of some P-51Ds early in their operational service life.

 

Both of these T.Os predate TSCHEP 5R/RLB/MEM/2-6258 Wright Field, Dayton, Ohio Date:- 9th October, 1944 posted by CUJO-1970, and they predate the North American Service Bulletin No. P-51-198A described in  paragraph 8 of the document on WW II Aircraft Performance, dated 27 February 1945.

This also also noted the P-51 dive tests were conducted between 3 August and 16 September 1944 (the day T.O No. 01-60JE-9 was issued), and that during one dive, the P-51 involved in the tests lost a fairing door and strut fairing: this, too, was caused by badly maintained up latches...

 

In effect, the problems with the landing gear doors described in the memorandum of 27 February 1945 had probably long since been tackled, first with the rigid inspection and adjustment of the landing gear uplocks and door latches, then with the installation of the landing gear latches on Ds

 

The question is, were P-51Ds losing their landing gear fairings after (say) November-December 1944?  The 27 February '45 memorandum doesn't mention anything about landing gear door failures continuing after remedial measures had been effected, and that is probably a good indication that the problem had been solved.

Edited by NZTyphoon
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On 11/28/2019 at 1:46 AM, Chuck_Yeager said:

snip

Mate, everything has certain margin. 109s and every soviet plane have ~100kph margin above dive speed. When people complained, they were told to shut up. I will not do the same, but I will recommend not taking it as Allies vs Axis, but compare each nation's planes with each other.

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In the report linked above they are basically saying that Mach 0.84 means structural damage to the aircraft. I checked that in game, and dove the P-51 to speeds in excess of Mach 0.84 (about 0.87) and there was no damage. With Mach related damage, I think in most cases if you lose wheel covers in game you'd have lost the entire plane and probably your own life in real life. Note of interest - the limits given in the report down to 10k feet are about Mach 0.8, so come with a ~5% reserve compared to the tested numbers.

 

The only way to exceed the structurally limiting 505 indicated without exceeding the critical Mach number is to do it at very low altitude, in which case I've lost wheel covers (at 515+) but did not sustain structural damage (up to 560). From real life there's evidence in test reports that points to issues with panels and covers at considerably lower speeds, so there might be only little reserve. Structurally there should be no problem exceeding 505 as with most other aircraft and there isn't. So all in all I find in game behaviour quite reasonable, with the exception of the huge speed penalty sustained when having lost the covers (OP point is valid).

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10 hours ago, JtD said:

In the report linked above they are basically saying that Mach 0.84 means structural damage to the aircraft. I checked that in game, and dove the P-51 to speeds in excess of Mach 0.84 (about 0.87) and there was no damage.

 

Yeah, I don't think damage from exceeding Mach numbers is modeled in the game.  At least I couldn't find any evidence of it.  The only time planes take damage is from exceeding their IAS limit which pretty much only happens down low.

 

10 hours ago, JtD said:

From real life there's evidence in test reports that points to issues with panels and covers at considerably lower speeds, so there might be only little reserve.

 

I'm still not convinced that losing gear doors that quickly is realistic.  I was reading through the TOs that NZTyphoon posted and the first TO he linked says, "Due to the possibility of improper adjustment of the landing-gear uplock and the landing-gear fairing door lock which may cause loss of the fairing door during flight, all P-51B, P-51C, and P-51D airplanes will be inspected immediately and every 50-hour inspection period thereafter...".  It describes jacking the plane up, removing the landing gear strut fairing and main wheels (so you can see what's going on), and doing gear swings to ensure that the gear fairing door locks were working correctly, adjusted properly, and latching securely.  

 

And I know from reading other P-51 TOs on that website that there are a bunch of different adjustments that have to be made.  There are adjustable pushrods to operate the bellcranks, the gear door latch plates themselves could be shimmed to fine tune their position relative to the latch block on the gear door, the latch rollers could be adjusted vertically by shimming them with washers, the latch cable tension needed to be adjusted properly to ensure the latches firmly engaged, and even the hydraulic actuating strut itself could be adjusted to ensure that the doors closed tightly and conformed to the skin of the wing properly.  Here's a quote from the P-51D Maintenance Manual talking about the gear doors, "This fairing door is designed so that, on closing, the leading edge contacts the wing first.  The actuating strut forces the trailing edge closed; this imposes a preload on the leading edge, which prevents the possibility of flutter while in flight."  It then goes on to say that, "When installing new doors, it may be necessary to trim and form the edges to fit wing, preferably by a sheet metal specialist."  Even the strut fairings were shimmable to ensure a perfect fit to the skin of the wing when the landing gear was retracted.  And then I even read where it told you to test a latched gear door by tugging on it and if the latch let go, to file the latch hook to achieve a better angle of incidence between it and the roller, until you can apply weight to the latched gear door and have it hold securely.  I also saw that they retrofitted the P-51Bs and P-51Cs with front gear door latches in addition to the rear latches they already had, but that the P-51D already had both front and rear gear door latches.  

 

So it seems to me that the loss of a gear door in that real life dive test was ultimately an adjustment issue, hence the TO to check the adjustment of all P-51 gear doors.  It might be the case that they're a little bit of a nightmare to get adjusted and working properly in real life, but unless I'm misunderstanding something, I'm pretty sure the problem is solved with proper adjustment.  I don't think that properly set up latches would result in losing gear doors so quickly after exceeding the IAS limit in real life.

 

10 hours ago, JtD said:

So all in all I find in game behaviour quite reasonable, with the exception of the huge speed penalty sustained when having lost the covers (OP point is valid).

 

Yeah, the in-game drag penalty on the P-51 for losing its gear doors is almost certainly overdone.  It's way higher than any of the other comparable aircraft in the game.  I mean, I remember reading how in real life the Germans would remove the Bf109K4 gear doors on purpose because they had problems with them getting stuck down, so the frontline units just eliminated them altogether.  I'd be interested in seeing real life data on how much that slowed them down.

 

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Why do all the Anecdote Guys completely forget to Mention that your Regular Pitot Tube Airspeed Indicator has an Error of around 12.5% positive at 0.7 Mach, 17.5% posititive at 0.8 Mach and about 25% at 0.9 Mach.

 

That is the Grain of Salt you have to take all of these Speed claims with.

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I'd be more concerned about losing the gear-fairing in the first place.

Then again, I'd probably be scared sh1tless, diving to Vne and not caring about turbulence, slipstreams, wingtip-vortices, etc.

There's a lot of load on those airframes at Vne and I wouldn't want to be the first guy to figure out the wings will come off when going terminal velocity and hitting a rough patch of air.

 

Some airplanes' high-speed limitations (P-47, P-51, Fw 190, etc.) are totally imaginary anyway.

I haven't ever seen a report stating the 190 would shed control-surfaces, neither about the Mustang or Jug or P-38 for that matter. They're Mach-limited for the most part, as drag-rise will cut their terminal velocity short of reaching destructive dynamic pressures. They're also stick-force limited in a way.

 

After all, it's just a game-limitation/ placeholder for trying to keep people from overspeeding their airframes.

Edited by Bremspropeller

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