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View Full Version : oleg, was the compressibility in p-38's addressed?



VF-29_Sandman
02-10-2006, 03:46 PM
majority of the p-38 pilots was saying in the last patch, the 38 would enter compressibility at too low of speed under 25,000 feet making it impossible to fly to mcguire's rule of: never get below 300 mph in a dogfight.

i understand that at alt's above 25,000 feet, the 38 would enter compression very quickly. but under this alt, compression wasnt a problem. was this issue fixed in this patch? oooh, and also i belive other's had a comment about acceleration.

Grey_Mouser67
02-10-2006, 04:42 PM
I checked it and I assure you it is not....I'm thinking the Lightning buffs need to pool our resources and address the climb rates and elevators in the Lightning and see if we can get Oleg to make a few modifications....Target has shown the plane to be undermodelled in climb and there is tons and tons of info out there on compressibility and elevators....

I truly believe that it is impossible to black the pilot out and ANY speed without the use of the airbrake or one of the games exploits...trim and combat flaps at too high speed. There is no mid to late war single engined aircraft that I know of that could not black its pilot out between corner speed and some higher speed determined by aircraft desing.

For all practical purposes, the Lightning has no corner speed.

The-Pizza-Man
02-10-2006, 06:51 PM
The lightnings VNE at 10,000' was 420 mph, at 20,000' it was 360 mph, at 30,000' it was 290 mph. It entered compressibility very early compared to other planes.

Gibbage1
02-10-2006, 08:20 PM
From pilot accounts, compressibility did not effect the P-38 in "thicker air" under 10,000 feet. Also, those numbers are the start of SIGNS of compressability, not the start of compressability itself. The P-38 gave good warning before it reached it with quite a bit of buffett, and then the tuck under if you dont slow down.

I am in contact with a P-38 ace Stan Wood now and I will ask him to clerify this. He spoke of doing dive bombing in the P-38 and "forgetting" his dive brakes and had no problem pulling out. Also an F-5 pilot dove away from 2 Me-262's and had to wait for "thicker air" before the controles would respond. Also the graph in the pilots manual ENDS at 10,000 feet.

At low altitudes, there should be no compressability for the P-38. Thats one of the main problem.

The-Pizza-Man
02-10-2006, 11:08 PM
I've done a few test dives and although its hard to identify the point where control authority is lost but it was around 440-480 mph below 10,000'. It may have actually been a bit faster than that because in a couple of seconds I was 500 mph, which is well beyond safe controllable speed even at sea level. Once thing I did notice is it doesn't seem to enter compressibility soon enough at high altitude, I was over 400 mph indicated at ~20,000 and I still had full control authority.

BfHeFwMe
02-10-2006, 11:48 PM
The really odd thing about it's compressability is nose above horizon it maintains some elevator authority, but dip it below and it's all gone. Why's there a difference if airspeeds are the same?

It's simply incapable of ever being an energy fighter if it can't cash in the energy for use. So what kind of fighter did they build? Turn?

If elevator heaviness was a problem, why boost the ailerons and do nothing to them?

The-Pizza-Man
02-11-2006, 12:23 AM
Thats probably part of the reason why the 38 wasn't all that crash hot flying escort in Europe. German planes had much higher dive speeds and dive acceleration than anything in the pacific, on the japanese side at least.

Gibbage1
02-11-2006, 01:15 AM
Originally posted by BfHeFwMe:
If elevator heaviness was a problem, why boost the ailerons and do nothing to them?

If you did any research into the problem, you would know the problem was not the elivator. It would not matter if it was boosted or not. It was an aerodynamic problem associated with the sound barrier. ALL aircraft in WWII faced this problem. The P-38's design ment that it entered sooner then other aircraft.

The 109 also had very stiff elivator at high speed.

Kocur_
02-11-2006, 03:39 AM
Originally posted by BfHeFwMe:
It's simply incapable of ever being an energy fighter if it can't cash in the energy for use. So what kind of fighter did they build? Turn?


Remember it was designed quite early, i.e. back in 1937, when they didnt know much about consequences of their decisions concerning airfoil and rest of configurtion on high speed flight. And those desisions were made for initially intended purpose of the plane: high alt, long endurance bombers interceptor with meant pursuing good climb and large internal capacity for fuel. Both determined airfols used - unfortunately early in the plane's developement noone cared nor realised what would be consequences of those choices on behaviour in high speed dives.

GR142-Pipper
02-11-2006, 04:33 AM
Originally posted by Grey_Mouser67:
I checked it and I assure you it is not....I'm thinking the Lightning buffs need to pool our resources and address the climb rates and elevators in the Lightning and see if we can get Oleg to make a few modifications....Target has shown the plane to be undermodelled in climb and there is tons and tons of info out there on compressibility and elevators....

I truly believe that it is impossible to black the pilot out and ANY speed without the use of the airbrake or one of the games exploits...trim and combat flaps at too high speed. There is no mid to late war single engined aircraft that I know of that could not black its pilot out between corner speed and some higher speed determined by aircraft desing.

For all practical purposes, the Lightning has no corner speed. The guys that I fly with have been using the Lightning quite a bit because it's just about the only U.S. aircraft that's worth flying (excepting the P-40 and P-39). Relative to the competition, the P-38 doesn't seem to accelerate as fast as in 4.02 and it's top speed seems lower as well. Are your experiences similar to what we've observed or do they differ?

GR142-Pipper

Brain32
02-11-2006, 04:57 AM
I personally tested P38L late for deck speed. Crimea, 12:00, 25%fuel, rads closed, wind off.
595kph was my result. Don't know about acceleration,climb, etc...

The-Pizza-Man
02-11-2006, 07:47 AM
I think what the problem may be is that the P-38 will continue to accelerate into compressibility below 10,000' in a power off dive at 45 degrees. One would expect from reading pilot accounts and the pilot operating handbook that provided the initial dive isn't too steep a pilot who cuts the throttles immediately should slow down enough at lower altitude to regain sufficient control authority to pull out of the dive.

Grey_Mouser67
02-11-2006, 09:47 AM
Originally posted by GR142-Pipper:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Grey_Mouser67:
I checked it and I assure you it is not....I'm thinking the Lightning buffs need to pool our resources and address the climb rates and elevators in the Lightning and see if we can get Oleg to make a few modifications....Target has shown the plane to be undermodelled in climb and there is tons and tons of info out there on compressibility and elevators....

I truly believe that it is impossible to black the pilot out and ANY speed without the use of the airbrake or one of the games exploits...trim and combat flaps at too high speed. There is no mid to late war single engined aircraft that I know of that could not black its pilot out between corner speed and some higher speed determined by aircraft desing.

For all practical purposes, the Lightning has no corner speed. The guys that I fly with have been using the Lightning quite a bit because it's just about the only U.S. aircraft that's worth flying (excepting the P-40 and P-39). Relative to the competition, the P-38 doesn't seem to accelerate as fast as in 4.02 and it's top speed seems lower as well. Are your experiences similar to what we've observed or do they differ?

GR142-Pipper </div></BLOCKQUOTE>

I hadn't speed tested it yet...the only thing I did was jump into it, start a dive at 1000 meters with no trim, no flaps etc and try to pull out like any other aircraft...and at a disgustingly slow speed...550km/hr, my elevator was mired in concrete and I augered in...I needed to see nothing else....

In 4.02, I got the following sea level speeds in Crimea, 100% fuel, noon etc...rad. closed...

J: 580km/hr
L: 570km/hr
L late: 595km/hr

I doubt the plane was touched actually. The spitfires with the messed up sea level speed...that is CW's slower than full winged versions were not corrected either.

If you want to test..the above figures are what I had from 4.02

Viper2005_
02-11-2006, 11:56 AM
The P-38 suffered Mach number related problems. Thus discussion of speed is pointless.

Instead you need to carry out your tests with reference to Mach number.

It is quite a simple task to convert your TAS and altitude to Mach number and there are several utilities available online which will do it for you:

Use google to convert km/h into m/s

Then plug the numbers into this:

http://aero.stanford.edu/StdAtm.html

And out pops a Mach number. This assumes a standard day; as such you must test on the Crimea map, as this is supposed to most closely represent a standard day.

If memory serves you should expect trouble from about M=0.68 or so.

AustinPowers_
02-11-2006, 12:04 PM
Mach in game does not effect the controls, the compressability on the P-38 is directly related to IAS, hence the lockup at low altitude.

Viper2005_
02-11-2006, 12:11 PM
In which case you'll always either have incorrect performance at low altitude or incorrect performance at high altitude. But the way to go about this is to measure the Mach number at which compressibility effects start to bite at various altitudes and to compare that with the historic test data.

Then you'll have something with which to email 1c.

Professor_06
02-11-2006, 12:31 PM
Oleg has posted about the limitaions of the atmosphere design. for some reason he cant turn off compressability below 10,000 ft. I wonder.

I have a speed brake switch on my joystick so to compensate i just turn on the brake for 2 seconds for pullup and the compressability stops and you get an extra 10% of lift for turn fighting. would love to see proper atmospheric model here.

The p38 was a successfull escort. german fights would dive to evade the P38 escorts and at the same time take themselves out of the battle. P38s had one of the best bomber loss ratios in the ETO. Maitenance, high cost and high learning curve were the biggest factor for their replacement.

Kocur_
02-11-2006, 01:34 PM
Originally posted by Professor_06:
Oleg has posted about the limitaions of the atmosphere design. for some reason he cant turn off compressability below 10,000 ft. I wonder.


I wonder why would he "turn it off" below 10.000ft. The only thing that changes IRL is speed of sound - its the more km/h or mph of m/s the lower you are.

Originally posted by Professor_06:
I have a speed brake switch on my joystick so to compensate i just turn on the brake for 2 seconds for pullup and the compressability stops and you get an extra 10% of lift for turn fighting. would love to see proper atmospheric model here.

Funny, cause P-38 did not have "speed brake". OTOH late P-38s had "dive recovery flaps" http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif.

Grey_Mouser67
02-11-2006, 03:36 PM
Originally posted by Professor_06:
Oleg has posted about the limitaions of the atmosphere design. for some reason he cant turn off compressability below 10,000 ft. I wonder.

I have a speed brake switch on my joystick so to compensate i just turn on the brake for 2 seconds for pullup and the compressability stops and you get an extra 10% of lift for turn fighting. would love to see proper atmospheric model here.

The p38 was a successfull escort. german fights would dive to evade the P38 escorts and at the same time take themselves out of the battle. P38s had one of the best bomber loss ratios in the ETO. Maitenance, high cost and high learning curve were the biggest factor for their replacement.

Yes I've heard that before. The unfortunate thing is that other aircraft..Fw's, Hellcats, P-47's also had compressibility issues. The late P-47's and Bearcats had dive recovery brakes installed on them as well.

The issue is that this compressibility is only modelled on the P38 AND it is modelled incorrectly. I just assume ditch the compressibility thing and just model it like other aircraft with a given break up speed and the onset of stiff controls to occur about mach .68-.72 then we'd be done with the discussion and move onto climb rates.

If Oleg would deal with those two opportunities, I think the Lightning fans would have most of the gameplay affecting issues behind them....still some minor things, but the aircraft could be flown as it should. Probably needs slow speed accelarated stall along with acceleration tweaks to be able to cloverleaf but the climb and elevator are much more game play affecting issues.

We need to organize a P38 consortium dedicated to the elevators, climb rates and slow speed accelarated stall!

Professor_06
02-11-2006, 04:30 PM
Originally posted by Grey_Mouser67:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Professor_06:
Oleg has posted about the limitaions of the atmosphere design. for some reason he cant turn off compressability below 10,000 ft. I wonder.

I have a speed brake switch on my joystick so to compensate i just turn on the brake for 2 seconds for pullup and the compressability stops and you get an extra 10% of lift for turn fighting. would love to see proper atmospheric model here.

The p38 was a successfull escort. german fights would dive to evade the P38 escorts and at the same time take themselves out of the battle. P38s had one of the best bomber loss ratios in the ETO. Maitenance, high cost and high learning curve were the biggest factor for their replacement.

Yes I've heard that before. The unfortunate thing is that other aircraft..Fw's, Hellcats, P-47's also had compressibility issues. The late P-47's and Bearcats had dive recovery brakes installed on them as well.

The issue is that this compressibility is only modelled on the P38 AND it is modelled incorrectly. I just assume ditch the compressibility thing and just model it like other aircraft with a given break up speed and the onset of stiff controls to occur about mach .68-.72 then we'd be done with the discussion and move onto climb rates.

If Oleg would deal with those two opportunities, I think the Lightning fans would have most of the gameplay affecting issues behind them....still some minor things, but the aircraft could be flown as it should. Probably needs slow speed accelarated stall along with acceleration tweaks to be able to cloverleaf but the climb and elevator are much more game play affecting issues.

We need to organize a P38 consortium dedicated to the elevators, climb rates and slow speed accelarated stall! </div></BLOCKQUOTE>

I agree completely..But, I think that the work to change the global atmosphere algorithms are probably to to much to change in this series at this time (my guess)... I am hoping for a better atmosphere model in BOB and beyond.

Most fighting takes place under 10,000 ft in game so the compressability issue would be better done if just eliminated rather than fixed.

Im hoping for a atmosphere model that is accurate and goes to 40,000 ft. ( would like to eliminate the arctic star sky also.)

The dive recovery flaps (accessed through "Speed Brake") are a nice touch to the series. For me, I just use the P38 late and stay fast and high, I dont dive unless necessary as I dont like to give up my spped and height advantage. I wait for the enemy a/c to do their dive recovery, then attack. the 38 late is my favorite toy along with the overboosted 47.

but yes, fixing the problem is better then working around it.

DGC763
02-11-2006, 05:12 PM
Maybe the P-38 is suffering from the same thing as the 109. 50lbs of stick force is only being applied at high speeds and that in itself is not enough to intitiate recovery.

The-Pizza-Man
02-11-2006, 07:14 PM
It wasn't a matter of stick force that prevented recovery. In fact deflecting the elevator too much only made the dive steepen as it effectively increased the thickness to chord ratio of the rear stabilizer and reduced the critical mach number.

The problem is that the P-38 dives too fast at alitude and it's terminal dive speed is too fast down low.

It sounds like it can't be fixed though, because of limitations with the game engine.

Grey_Mouser67
02-11-2006, 07:23 PM
It is unlikely that compressibility can be modelled properly, but elevators can be modelled to be "normal" to certain speeds and then stiffen up.

I'm trying to think of the plane that should most "feel" like a P38...of course I'm only going off what I've read because I never flew one...I've often read stories of high speed dives below 20,000 in B&Z, Dive bombing in Lightings was very common and often the dive started at 15,000-18,000 ft with no problems in pull out...it probably aught to behave like the Jug...it is good, but not like the Mustang, Tempest or Fw.

I don't think that it is asking too much to give it a decent elevator. If it is data, pilot accounts, Compressibility info etc...it can be gathered.

WWMaxGunz
02-11-2006, 10:25 PM
And a dive-bombing Lightning pilot from 18,000ft would handle engine and prop just how?

BSS_CUDA
02-12-2006, 07:31 AM
elevator effectiveness has been changed a little, before onset would be around 380MPH and at 400MPH you have no elevator control, now onset is 380MPH and you still have minor elevator control at 420MPH.

as for handleing engine and prop in a dive from 18,000, I'm not sure what your getting at. IRL they would just go engines to idle and let gravity do its thing.

IRL, the 38 compressability by all pilot accounts when a dive was started below 25,000ft was not an issue. it just didnt happen. higher Mach and thicker air prevented it, at 25000ft critical mach for the 38 is .69 thats almost 500MPH TAS and the lower it got the higher that speed would be. the compressability of the 38 was no different than what every other WW2 fighter experienced, but it was the first, there are many pilot accounts from those that survived, of 109's losing all elevator control above 400MPH. it was a common thing and all planes in game should suffer from it.

Kocur_
02-12-2006, 08:08 AM
the compressability of the 38 was no different than what every other WW2 fighter experienced, but it was the first,

Sorry, it was different. Maybe the first, but that, i.e. when it was designed, made it also the worst. Or name any other WW2 fighter having "dive recovery flaps". A device DIFFERENT in its PURPOSE from airbrake. P-38 just had low critical Mach number. Is it modelled properly in the game? I dont know, but relatively speaking P-38 should be the worse of fast fighters.

BSS_CUDA
02-12-2006, 08:52 AM
Or name any other WW2 fighter having "dive recovery flaps" the late P-47 the N I think and the Bearcat, I'm not sure but I think I also heard somewhere that the Tempest had them, I might be wrong on that account.


but relatively speaking P-38 should be the worse of fast fighters. I'm assuming that you are refering to the FW,51, and the 47, I am not familiar with the tempest so I'll not consider it in my comments.
yes the 38 had a slightly lower critical Mach, but again below 25,000ft it was not a factor.the 38 would only be worse in that it had a "slightly" lower top dive speed, with the introduction is the J25-LO and the L series it was actually the best rolling aircraft of the 3 above 370MPH, even better than the vaunted FW. it also had a significantly better climb rate than these 3 at almost 4100FPM. it had a higher or as high a service ceiling than most at 44,000ft, and its top speed of 425MPH (depending of your sources, some have it as high as 430MPH or as low as 419MPH) at critical alt was as good as any of them during the war. I would tend to disagree with you about being the worse of the fast fighters, was it the best? debatable. but it was FAR from the worse,

Viper2005_
02-12-2006, 09:35 AM
P-38 had a tactically useful mach number around 0.68-70 depending upon how brave the pilot was. This was pretty low by the standards of the time.

Spitfire had a tactically useful Mach number of about 0.83 depending upon how brave the pilot was; 0.89 was attained in testing.

Me 262 had a tactically useful Mach number of 0.82

The Me-163 would enter a "graveyard dive" at a Mach number of 0.84.

AFAIK the P-51 had a tactically useful mach number of around 0.74; the P-47 I think was higher, perhaps as high as 0.80-0.82.

Grey_Mouser67
02-12-2006, 09:51 AM
AFAIK, a couple of things lead to the P-38 and its reputation.

First, its prototypes flew in 1941, it was maybe the first combat aircraft to actually fly at 400mph and it was one of, if not the first to have turbosuperchargers which allowed it to fly over 30,000 ft.

Now, standard protocol for all military planes is to climb to its service ceiling and powerdive. More altitude + More Speed + relatively low Mach number = compressibility.

It was the first to encounter it and nobody knew what it was...that is why it was infamous. Many other planes suffered from compressibility there after, but the Lightning was the first and because it was not understood, people did what they always do with things they don't understand....they villianize, mysticize, and fear the unknown.

BSS_CUDA
02-12-2006, 10:13 AM
granted as I said the 38 terminal dive speed was about the only area where it lacked agaist its contemporaries. I'm going by your numbers on Mach but by as much as 100MPH compared to the Spit. but in every other aspect of high speed fighter performance it matched or excelled against those same Aircraft. as most 38 squadrons proved during thier primary roles of bomber escort, terminal dive didnt matter. if you got your enemy to split S and dive away he was out of the fight and not a factor, you didnt need to follow. below 15,000ft where critical Mach of the 38 is approx 515MPH this is now not a factor because top dive speeds cannot easily be acheived. therefore the one main disadvantage the 38 has as a high speed fighter is now a non-factor.

Viper2005_
02-12-2006, 10:55 AM
The P-38 was most certainly not the first combat aircraft to surpass 400 mph or 30,000 feet. Every production Spitfire was dive tested to at least 470 mph IAS before it was handed over to the RAF (later models were taken to 520 mph IAS) and the dive limits in the pilot's notes equate to Mach numbers >0.8 (this in the late 1930s). And the Spitfire I had a service ceiling around 34,000 feet.

The He-100 was capable of speeds in excess of 400 mph in level flight; thankfully the RLM decided to stick with the Bf-109...

The P-38 simply had a low critical Mach number in relation to most other fighters of the period.

It is interesting to note that the Vampire with a similar configuration also had a poor critical Mach number...

<span class="ev_code_RED"> As Cuda points out this doesn't matter much below about 15,000 feet or so because you'll hit your Q limit (or the ground!) before you hit your Mach limit. However, at high altitude it's a pretty serious problem.

NB; the P-38 also lacked in terms of bang per buck - it's a lot of aeroplane to buy and maintain when compared with for example a Spitfire, Mustang or Bf-109.</span>

Kocur_
02-12-2006, 01:00 PM
Originally posted by Grey_Mouser67:

First, its prototypes flew in 1941,

XP-38 flew first on 27 january 1939.

Grey_Mouser67
02-12-2006, 07:55 PM
I stand corrected...should have checked my sources.

The Spitfire, to my knowledge, did not acheive level flight speed of 400 mph in 1939 nor did it hit compressibility in its dive....anyways, while I mis-stated some things, I do believe that the Lightning was demonized because it was the first aircraft to have these issues...but it was far from the last!

HellToupee
02-12-2006, 08:49 PM
http://www2.sala.or.jp/~taira-m/images/HIGH_SPEED_SPIT_03.jpg

BSS_CUDA
02-12-2006, 09:01 PM
Originally posted by Viper2005_:
The P-38 was most certainly not the first combat aircraft to surpass 400 mph or 30,000 feet. Every production Spitfire was dive tested to at least 470 mph IAS before it was handed over to the RAF ok are we talking level flight or dive speed, because every source I've found states that the XP-38 in 1939 was capable of 414MPH in level flight where the 1939 Spitfire and the 109 were in the 350MPH range in level flight, true the HE-100 did also exceed 400MPH but it was never put into production and it would be a question of who did it first in that year since the 38 first flew in Jan 39 and the HE-100 flew in March it would seem that the 38 was first, but clearly it was not the spitfire that was the first to exceed 400MPH in level flight.