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Gaston444
02-28-2011, 07:19 PM
Hello.

I would like to know the if the location of the center of gravity, and of the center of lift, of the various late WWII fighter types is available on reliable plans.

I'm sure game designers must have these location points somewhere.

I would look for the Spitfire Mk IX, FW-190A, P-51D and P-47D.

Gaston

TheGrunch
02-28-2011, 07:22 PM
You would be better served asking the Aces High developers if you want them perfectly accurate, I suspect, due to the way their flight-models work. They are more likely to have this sort of information.

Gaston444
02-28-2011, 07:35 PM
Thanks. I will try them.

If anybody else has any info about this, it is still very much welcome...

Gaston

TheGrunch
02-28-2011, 07:42 PM
Oh, bear in mind that often aircraft carried large amounts of ballast to alter the CoG, especially as initial designs were developed into later marks and variants.

M_Gunz
02-28-2011, 08:00 PM
LOL! CoG changes with load, that's why there's TRIM! It usually doesn't change much in fighters, P-51D between full and empty fuselage tank being towards an extreme. For sure the designers of those planes worked out what range was desirable.

You could put a scale under each wheel of a plane and find out for a single load condition.

FAA Weight and Balance Handbook (http://www.faa.gov/library/manuals/aircraft/media/faa-h-8083-1a.pdf)

The Wiki article. (http://en.wikipedia.org/wiki/Center_of_gravity_of_an_aircraft)


The center-of-gravity (CG) is the point at which an aircraft would balance if it were possible to suspend it at that point. It is the mass center of the aircraft, or the theoretical point at which the entire weight of the aircraft is assumed to be concentrated.[1] Its distance from the reference datum is determined by dividing the total moment by the total weight of the aircraft.[2] The center-of-gravity point affects the stability of the aircraft. To ensure the aircraft is safe to fly, the center-of-gravity must fall within specified limits established by the manufacturer.

There are three FAA references given at the bottom of the article.

Please don't misuse Stress Risers in whatever agenda this is related to. (http://en.wikipedia.org/wiki/Stress_risers)

TheGrunch
02-28-2011, 08:04 PM
I thought that CoG changing with fuel and armament loads went without saying, but I suppose you're right, it's best to be safe, eh? http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

M_Gunz
02-28-2011, 08:40 PM
You know who the OP is.

TheGrunch
02-28-2011, 08:41 PM
That is true. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

TungstenKid
03-01-2011, 02:02 AM
From my radio-control model flying days I know that the CoG had to be around 29% of the wing chord (measured from the leading edge) for a typical non-swept wing, and I daresay the same applies to real aircraft.
It can vary by about 3%, but if it's too far forward the plane will descend even with full 'up' elevator, and if it's too far back the plane will be hyper-responsive to elevator and impossible to fly.
That's why real plane designers pay very careful attention to where the pilot/crew/fuel tanks etc will be to ensure that the CoG pretty much stays put.
Hey, remember the film 'Capricorn One' where Stearman pilot Telly Savalas in the rear cockpit flies Elliot Gould around and has to keep telling him to keep his head down so he can see where he's going?
"Why didn't you sit in the front cockpit?" asks bewildered Gould, to which Savalas replies something like "Do you know anything about flying? No, well shut up!"
The answer of course is the the front cockpit is smack over the CoG, therefore the CoG won't shift an inch when carrying a passenger in the front.

TungstenKid
03-01-2011, 02:09 AM
PS- A guy who was a real-life Loadmaster on a C-130 Hercules wrote an interesting article here-

http://www.thefewgoodmen.com/t....php?6642-Loadmaster (http://www.thefewgoodmen.com/thefgmforum/showthread.php?6642-Loadmaster)

Excerpt-
We used a special sliderule (no electronic calculators back in the 60's) to calculate the balance and the object was to get it around 30% MAC. (Mean aerodynamic chord).
But when we were fully loaded and grossed out 155,000 lbs we would try to load it to achieve 29%. A lot of pilots liked it a bit nose heavy since it was easier to
fly vs tail heavy.
As fuel burned off, the balance would move backward slightly. Of course, we had to know the exact weight of each piece of cargo so we could program it to specific locations called stations.
One of the heaviest loads I recall was a load of 750# bombs, without fuses or tail fins, chained to pallets which weighed in at some 34,000#, if I remember correctly.

Art-J
03-01-2011, 01:17 PM
I think 29% of MAC seems to be a bit too aft, for a WWII style taildragger, I'd say AVERAGE 25% (+/- a few, depending on payload) would be more usual.
Just made a quick browse through some of the scans and manuals downloaded ages ago from the net, sorry, as a Far East theater of ops enthusiast, I don't have much info about Mustang, Spits, German crates etc., but here are some example numbers for other planes:

F4F-3: report no. 1469A says 27,23% in "normal loading condition"

F4F-4: report no. 1471C says 28,87% in "normal loading condition"

F6F-3: flight test report from nov '44 says 25,6% (wheels up, normal loading); 23,3% (wheels down, normal loading); 26,1% (wheels up, overloaded); 23,8% (wheels down, overloaded).

P-38: pilot's manual (AAF 51-127-1) describes front and aft limits - 20% and 32% (that's on one of the first pages, maybe there's more detailed info further, but I havent checked it)

Cheers - Art

WTE_Galway
03-01-2011, 03:42 PM
Originally posted by M_Gunz:
LOL! CoG changes with load, that's why there's TRIM! It usually doesn't change much in fighters, P-51D between full and empty fuselage tank being towards an extreme. For sure the designers of those planes worked out what range was desirable.



Your forgetting the p39 http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

CoG changed radically as you chewed through those 37mm cannon rounds http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif Especially in the early versions.

ImpStarDuece
03-01-2011, 05:03 PM
Trying to punch the fog of ignorance:

Spitfire IX weights and loading data

http://www.spitfireperformance.com/ab197.html

Mk XIV

http://www.spitfireperformance.com/rb141weights.html

Mustang I weights and loading data

http://www.wwiiaircraftperform...ng/ag351weights.html (http://www.wwiiaircraftperformance.org/mustang/ag351weights.html)

All found within two minutes

M_Gunz
03-01-2011, 08:03 PM
Originally posted by WTE_Galway:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by M_Gunz:
LOL! CoG changes with load, that's why there's TRIM! It usually doesn't change much in fighters, P-51D between full and empty fuselage tank being towards an extreme. For sure the designers of those planes worked out what range was desirable.



Your forgetting the p39 http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

CoG changed radically as you chewed through those 37mm cannon rounds http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif Especially in the early versions. </div></BLOCKQUOTE>

Radically by some scale of? As compared to a P-51D with full fuselage tank as opposed to empty fuselage tank?

WTE_Galway
03-01-2011, 08:42 PM
Originally posted by M_Gunz:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by WTE_Galway:

Your forgetting the p39 http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

CoG changed radically as you chewed through those 37mm cannon rounds http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif Especially in the early versions.

Radically by some scale of? As compared to a P-51D with full fuselage tank as opposed to empty fuselage tank? </div></BLOCKQUOTE>

Bell actually issued a directive advising bailing out if the early P39 entered a flat spin and recommended carrying weights equivalent to the ammo loadout if the plane was flown unarmed.

An interview with Nikolay Gerasimovitch Golodnikov 2nd GIAP of the Northern Fleet Aviation (VVS SF) from March 1942 till the end of the war) on the Early P39 spin tendency:



http://lend-lease.airforce.ru/...golodnikov/part3.htm (http://lend-lease.airforce.ru/english/articles/golodnikov/part3.htm)

The center of gravity of the Cobra was exceptionally rearward. We even had 10 kilos of lead weight mounted in the forward portion to unload the tail. Sometimes this center of gravity created problems with the wing and in inverted flight. Once again, during non-combat flights, don’t place any load in the empty rear portion of the fuselage. Somebody didn’t do it and couldn’t make it back. The airplane flew as if balanced on a tip of an awl. Later we gained experience and loaded everything in the forward compartment.


This shot of a recovered Soviet P39 (albeit a Q model) gives a good perspective on just why weight distribution was problematic:

http://lend-lease.airforce.ru/english/articles/sheppard/p39/P39-1.jpg

M_Gunz
03-02-2011, 08:38 AM
Yes worse than P-51D!

Gaston444
03-02-2011, 01:38 PM
The P-39 Ns and Qs were the real problem: The early P-39s were quite good and did not have such a severe CG problem. Experienced Soviet P-39 aces started killing themselves on the N and Q models....

The 37 mm gun was junk too compared to the 20 mm of earlier variants, which is why the earlier ones were kept a long time in US service while the more numerous Q and Ns were happily given to allies.

What the Soviets did: They doubled the size of the oil tank on Q and Ns, and always kept the oil tank full: It was forbidden to fly it with less than a full oil tank. A lot of armor plates were taken out as well.

The early P-39s were said by the Soviets to be the only aircraft they had that could take on the German types in both the horizontal and the vertical. Previously they only had an edge on the horizontal.

One US pilot also said, after mock dogfights with all US types: "At low altitudes I would have flown it against anything."

I would think that, in a turn, the Center of Lift of the main wings moves more than the Center of Gravity...

Gaston

AndyJWest
03-02-2011, 03:19 PM
I would think that, in a turn, the Center of Lift of the main wings moves more than the Center of Gravity...

I'm probably going to regret asking, but why do you think the centre of gravity will move in a turn?

ImpStarDuece
03-02-2011, 05:25 PM
Originally posted by Gaston444:
The P-39 Ns and Qs were the real problem: The early P-39s were quite good and did not have such a severe CG problem. Experienced Soviet P-39 aces started killing themselves on the N and Q models....

You can prove this empirically, I suppose?

The Q models - and to a lesser extent the N - were developed WITH the input of the Soviets, who quite liked the aircraft. The N had some CoG adjustments about a third of the way through the production block.

Which Soviet Aces killed themselves in P-39N/Qs, due to handling issues?



The 37 mm gun was junk too compared to the 20 mm of earlier variants, which is why the earlier ones were kept a long time in US service while the more numerous Q and Ns were happily given to allies.

The majority of 20 mm armed P-39s were given to US Allies. Or, more correctly, supplied under Lend Lease to the UK and Soviet Union, and then reacquired by the USAF later.

The P-400 and P-39D-1/2 were the only 20 mm armed production Aircobras, although there were field refits with Hispano and ShVAK cannon.

Most USAAF units used 37 mm armed versions. I believe the last US units to give up their P-39s were in Italy in 1944, flying 37 mm armed P-39Qs.



What the Soviets did: They doubled the size of the oil tank on Q and Ns, and always kept the oil tank full: It was forbidden to fly it with less than a full oil tank. A lot of armor plates were taken out as well.

Got a reference for this?

Lots of P-39s were lightened in Soviet service (taking out the wing guns, wing tanks and pilot armour were among the most common modifications).

I've never heard of the Russians doubling the size of the oil tank though. Given its location right on the aft bulkhead, and the location of the rear armour, the carburetor intake and the coolant tank, that would be a pretty major modification.



One US pilot also said, after mock dogfights with all US types: "At low altitudes I would have flown it against anything."


Out of interest, which pilot?

M_Gunz
03-02-2011, 06:36 PM
A few US pilots did well with and liked the P-39D's and the majority did not. The biggest draw was the speed, below high alt it was a very fast plane when it came out. Sure you can find quotes from US pilots saying good things about them but if instead of cherry-picking you were to take a representative sample the consensus would be the opposite.

If the Soviets had so much trouble with the N's then it would be addressed in any further development. Hmmmm... let's play a little game and compare Soviet pilots lost in D models directly to those lost in N and Q model, but let's make sure that how many Soviet pilots flew each different model is not factored in because that would be using math.

As I posted above:

You know who the OP is.

Same old same. Please G will you go back to A Few Good Men or find another forum to.. "fertilize"? We already have Raaaid.

BillSwagger
03-05-2011, 08:12 PM
In my research on the P-39, many Russians favored it.
Despite the handling characteristics it was the first plane with any speed that allowed them to compete with the German 109.
There is mention of the handling problems but nothing specific to a particular variant, only that the apparent shift in CoG had initially caught some pilots by surprise. There seems to be no distinguishing factor regarding C0G, accidents and the country that flew them.
Only that most accidents were in training.

Another interesting fact about the P-39 was its tricycle landing gear. What it gained in landing and takeoff stability also took away in strength and ability to land on rough surfaces.
Apparently, the tricycle lay out was not as strong as some of the alternatives.
It may have not been a performance factor, but rather a serviceability factor that made them a consideration for lend lease.
There is some literature that suggests the overall use of the P-40 was preferred over the P-39 for that reason despite having a lower top speed of the two.
I've always found that lend lease aircraft have more foreign advocates than what the Americans had to say about them.

Is that because the Americans had to justify why they were handing over perfectly good aircraft, or were American built aircraft that much better than anything their foreign allies could build? (rhetorical)
I suspect that a war of attrition simply called for more aircraft and while America was not able to make use of their older plane sets, its foreign Allies could sure use more aircraft to man and alleviate the demand of their struggling industry.

AndyJWest
03-05-2011, 08:59 PM
I suspect that in the case of the P-39 it may partly be that it was better suited to the combat situation it faced on the Eastern front than it was in the contexts that the USAAF used it. It was neither a bomber interceptor, nor a long-range escort fighter, but against a Luftwaffe tactical strike force, operating at low level, it was probably more in its element.

Gaston444
03-05-2011, 10:14 PM
Originally posted by ImpStarDuece:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Gaston444:
The P-39 Ns and Qs were the real problem: The early P-39s were quite good and did not have such a severe CG problem. Experienced Soviet P-39 aces started killing themselves on the N and Q models....

You can prove this empirically, I suppose?

The Q models - and to a lesser extent the N - were developed WITH the input of the Soviets, who quite liked the aircraft. The N had some CoG adjustments about a third of the way through the production block.

Which Soviet Aces killed themselves in P-39N/Qs, due to handling issues?



The 37 mm gun was junk too compared to the 20 mm of earlier variants, which is why the earlier ones were kept a long time in US service while the more numerous Q and Ns were happily given to allies.

The majority of 20 mm armed P-39s were given to US Allies. Or, more correctly, supplied under Lend Lease to the UK and Soviet Union, and then reacquired by the USAF later.

The P-400 and P-39D-1/2 were the only 20 mm armed production Aircobras, although there were field refits with Hispano and ShVAK cannon.

Most USAAF units used 37 mm armed versions. I believe the last US units to give up their P-39s were in Italy in 1944, flying 37 mm armed P-39Qs.



What the Soviets did: They doubled the size of the oil tank on Q and Ns, and always kept the oil tank full: It was forbidden to fly it with less than a full oil tank. A lot of armor plates were taken out as well.

Got a reference for this?

Lots of P-39s were lightened in Soviet service (taking out the wing guns, wing tanks and pilot armour were among the most common modifications).

I've never heard of the Russians doubling the size of the oil tank though. Given its location right on the aft bulkhead, and the location of the rear armour, the carburetor intake and the coolant tank, that would be a pretty major modification.



One US pilot also said, after mock dogfights with all US types: "At low altitudes I would have flown it against anything."


Out of interest, which pilot? </div></BLOCKQUOTE>

My source was a long in-depth article in "Le Fana de l'Aviation"...

I'll pull several quotes from it here when I find it: It is somewhere...

It would appear your knowledge of the P-39 is quite erroneous...

You always challenge me to provide my sources: Remember when you told me to provide my sources that Japanese tests showed one Ki-100 could take on 3 Ki-84s and win?

It will be the same outcome here...

Remember this in the future: Liars and fraudsters always make claims that are within the realm of the plausible. When somebody says something that is weird and unexpected, it often means they didn't make it up...

Where did YOU get your source that the Soviets thought the N and Qs were better? It is quite a hilarious claim to make when you know the mods the Soviets had to do to make those later models safer,including full engineering studies and special test flights devoted to these issues...

I'll provide my sources, but I would very much like to see yours as well...

Gaston

Daiichidoku
03-05-2011, 11:48 PM
Originally posted by BillSwagger:
I've always found that lend lease aircraft have more foreign advocates than what the Americans had to say about them.

Is that because the Americans had to justify why they were handing over perfectly good aircraft, or were American built aircraft that much better than anything their foreign allies could build? (rhetorical)


a lot of this is the relatively overall higher build quality of US product, more "luxury" items equipped, the components themselves being generally higher quality, general reliability of the airframe/powerplants, and reasonably secure source of ample spares, as compared to many domestic alternatives

M_Gunz
03-06-2011, 01:04 AM
In 41 and 42 the Russians were more desperate to get fighters that could intercept the fast bombers laying waste to their cities. The Taran showed how desperate the pilots got. Medals for Taran showed how desperate the leaders were to stop the bombers.
The first major use of the IL-2, the single-seater, was interception. The P-40 was considered marginal why? Intercept speed. The P-39 however had the speed and a big gun that was not mainly used for tank busting but for bomber busting. The 20mm versions were nice but what did they ask for and get? The gun more useful against bombers, not fighters.

In the sim 'laboratory' we get skewed views based on game play. Perhaps that's why Oleg prefers to see scripted historic missions.

M_Gunz
03-06-2011, 01:10 AM
Originally posted by Daiichidoku:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BillSwagger:
I've always found that lend lease aircraft have more foreign advocates than what the Americans had to say about them.

Is that because the Americans had to justify why they were handing over perfectly good aircraft, or were American built aircraft that much better than anything their foreign allies could build? (rhetorical)


a lot of this is the relatively overall higher build quality of US product, more "luxury" items equipped, the components themselves being generally higher quality, general reliability of the airframe/powerplants, and reasonably secure source of ample spares, as compared to many domestic alternatives </div></BLOCKQUOTE>

I doubt that all applied in the case of Great Britain. http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif For them it was numbers. For Russia especially in the beginning it was also numbers that mattered, they took what they could get even worn and dated British fighters.

ImpStarDuece
03-06-2011, 07:28 PM
Originally posted by Gaston444:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ImpStarDuece:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Gaston444:
The P-39 Ns and Qs were the real problem: The early P-39s were quite good and did not have such a severe CG problem. Experienced Soviet P-39 aces started killing themselves on the N and Q models....

You can prove this empirically, I suppose?

The Q models - and to a lesser extent the N - were developed WITH the input of the Soviets, who quite liked the aircraft. The N had some CoG adjustments about a third of the way through the production block.

Which Soviet Aces killed themselves in P-39N/Qs, due to handling issues?



The 37 mm gun was junk too compared to the 20 mm of earlier variants, which is why the earlier ones were kept a long time in US service while the more numerous Q and Ns were happily given to allies.

The majority of 20 mm armed P-39s were given to US Allies. Or, more correctly, supplied under Lend Lease to the UK and Soviet Union, and then reacquired by the USAF later.

The P-400 and P-39D-1/2 were the only 20 mm armed production Aircobras, although there were field refits with Hispano and ShVAK cannon.

Most USAAF units used 37 mm armed versions. I believe the last US units to give up their P-39s were in Italy in 1944, flying 37 mm armed P-39Qs.



What the Soviets did: They doubled the size of the oil tank on Q and Ns, and always kept the oil tank full: It was forbidden to fly it with less than a full oil tank. A lot of armor plates were taken out as well.

Got a reference for this?

Lots of P-39s were lightened in Soviet service (taking out the wing guns, wing tanks and pilot armour were among the most common modifications).

I've never heard of the Russians doubling the size of the oil tank though. Given its location right on the aft bulkhead, and the location of the rear armour, the carburetor intake and the coolant tank, that would be a pretty major modification.



One US pilot also said, after mock dogfights with all US types: "At low altitudes I would have flown it against anything."


Out of interest, which pilot? </div></BLOCKQUOTE>

My source was a long in-depth article in "Le Fana de l'Aviation"...

I'll pull several quotes from it here when I find it: It is somewhere...

It would appear your knowledge of the P-39 is quite erroneous...

You always challenge me to provide my sources: Remember when you told me to provide my sources that Japanese tests showed one Ki-100 could take on 3 Ki-84s and win?

It will be the same outcome here...

Remember this in the future: Liars and fraudsters always make claims that are within the realm of the plausible. When somebody says something that is weird and unexpected, it often means they didn't make it up...

Where did YOU get your source that the Soviets thought the N and Qs were better? It is quite a hilarious claim to make when you know the mods the Soviets had to do to make those later models safer,including full engineering studies and special test flights devoted to these issues...

I'll provide my sources, but I would very much like to see yours as well...

Gaston </div></BLOCKQUOTE>

References would be Black Cross Red Star Vol 2/3, the USAAF P-39D,K and Q manuals and Red Star Airacobra.

Also the pilot interviews on lend-leaseairforce.ru.

To whit:

"We received the first Cobras from Moscow, in containers. We assembled them and then were trained on them. These were P-39Qs, perhaps types-1 and -2, from the British order. [Apparently that should be Aircobra I – ed.]. They had yellow camouflage paint on them for North Africa. We trained hard. We had instructors and various types of written materials. Transition was conducted quickly, in five or six days.

Later they ferried Cobras to us or we picked them up in Krasnoyarsk. These were types Q-5, -10, -25, -30, and Q-35. These aircraft were made especially for the USSR. We fought the remaining period of the war only in Q models.

A. S. Did you like the Cobra?

N. G. We liked them. Especially the Q-5. This was the best fighter of all three in which I fought. Of the Cobras, this was the lightest. "

And


"A. S. Describe the machine guns, cannon, and sights.

N. G. The first Cobras that we received from Moscow had a 20mm Hispano-Suiza cannon and two heavy Browning machine guns, synchronized and mounted in the nose.

Later the Cobras arrived with the M-6 [should be M-4 – ed.] 37mm cannon and with four machine guns, two synchronized and two wing-mounted. We quickly removed the wing-mounted machine guns, leaving one cannon and two machine guns."



I'd be interested in the backing for the assertions that:

A) The N and Q models had more CoG problems that earlier P-39s (ie P-400/Airacobra 1 and the P-39D1/2 supplied to the Soviets).
B) The N/Q models started killing "Soviet aces"
C) The P-39 oil tank was doubled in size in Soviet service (ie increased from 7.5 gallons to 15 gallons)
D) It was forbidden to fly the P-39 without a full rear oil tank (especially interesting considering that some USAAF manuals recommend flying with only 6.5 gal in the rear oil tank)
E) The USAAF kept the 20mm armed P-39s in service in preference to the later 37 mm armed versions.

BillSwagger
03-06-2011, 09:41 PM
B) The N/Q models started killing "Soviet aces"

There is no specific reference i can point to although in the past i've used lend-leaseairforce.ru when researching Russian claims. You will find on that site more information on the Aircobra by reading other interviews posted under the P-40 because most P-40 pilots also eventually flew Aircobras.

It is probably safe to say that the P-39 claimed the lives of several pilots in training accidents.
I don't gather some were not Russian, but also some well known Italian pilots were killed in accidents when introduced to the N and Q. It is not known for sure, but most literature seems to blame the difference in center of gravity as the cause of the crash, usually leading to a flat spin where normally a front engined plane would recover.

Just my two cents on that issue.

Bill

ImpStarDuece
03-07-2011, 12:52 AM
Gaston's explicit claim was that the P-39N/Q had severe CoG problems that the earlier models didn't and thus: "Experienced Soviet P-39 aces started killing themselves on the N and Q models...."

This runs counter to all the literature that I have read regarding the P-39 in Soviet service, which seems to indicate that as Soviet experience with the P-39 increased, the rate (if not the actual number) of accidents with the type diminished.

Yes, some P-39 aces may have died from spins due to CoG problems in the later marks. I'm not discounting that possibility. What I am challenging is the notion that this was more likely in later P-39s than in earlier aircraft.

My general impression was that the Soviets evaluated the P-39D (actually Airacobra Is sent over from the UK) and found much to like, but also much that could be improved.

A technical delegation was sent to Bell with some requests on how the aircraft could be improved (like the tail fillet, winterisation of the oil system and deleting the outboard .30 cals). There was some to-ing and fro-ing between the USAAF, Bell and the Soviets over the N/Q models, which were predominately supplied to the Soviet Union.

Gaston444
03-07-2011, 07:54 PM
OK. I'll admit your claims were not baseless.

Now here's for mine:

"Le Fana de l'Aviation" no.451. juin 2007.

It turns out I remembered it upside-down: It was not a doubling of the weight of the oil reservoir, it was a halving, as I had assumed that it was still in front like on other fighter types! I'll concede you were right to question me, and that increasing it was indeed intuitively a big engineering change that should have raised a warning flag, ImpStarDuece... It was a reduction by half of the volume of oil since the oil reservoir was behind the CG... It became forbidden to take off with a full oil reservoir on the N-Qs (I do remember that somewhere it was said that the oil tank was actually changed in size to match the smaller volume)...

Here are quotes from "Le Fana": P. 26: "It had superb maneuverability, but on the vertical its engine lacked power and the Me-109 was at its advantage... (Presumably this mans it would equal or beat the Me-109G in horizontal turns).

P.27: "It had a strong tendency to put itself in a spin: A delay of half a second to effectuate the recovery maneuver, and this caused a flat spin that was nearly always fatal... This was particularly accentuated when the main cannon was emptied."

P.27: "On the Q-10,Q-15 and Q-20, the center of gravity was even more backwards! In a report by the VVS test center on the P-39Q-10, a pilot writes: "The spin is started just by pulling too much on the stick. The worst is an aircraft without ammo but with a full oil reservoir: The execution of any figure is extremely difficult: Any pulling on the stick causes a rapid reduction of the speed and then a spin."

P. 28: "The P-39 spin is the cause of many accidents. In 1944 (more Q and Ns then), in two months there were six causing the death of two pilots killed in just the 1st Air division. In certain units, any notion of doing aerobatic figures generated panic in the unit. These accidents were not only the fate of hastily formed front line piots: Experimented test pilots were the victims of them. In the VVS Test Center, on January 4th 1944, Avtomonov was killed in a P-39N, and, on the 27th of April of the same year, Ovchinnkov killed himself also.

The situation worsened so severely that Bell sent to the USSR a special technical team headed by L. Rogers, responsible for the after-sale...

In addition, it was very hard to bail out because the risk to hit the tailplane was great. Two Soviet aces, N.M. Iskrine and B. B. Ginka, were both severely injured for that reason.

THE REAR FUSELAGE DEFORMS ITSELF

In March 1944, the 11th corp of fighters did a check of all its Aircobras: 15 aircrafts had tail deformations...

Tests were made, and limitations were imposed by the chief engineer of the VVS: Maneuvers without ammo or without extra nose weights were forbidden.

To move the center of gravity forward, the armor of the oil reservoir was removed, especially on the Q-5. (P.29)This measure was not enough on the subsequent models, and all the armor of the carburator was removed (3 plates) and a weight was added ahead of the battery. The tail of the aircraft was also reinforced.... TsAGI elaborated a method of reinforcement that Bell applied in production. Bell on their own also started to use thicker skins and reinforced the lips of the service openings.

Unfortunately, long fold lines still appeared on the rear fuselage, and a new method of additional reinforcement was devised and tested by TsAGI, after which these further reinforcements were applied in the field, carried out directly by the units. 326 aircrafts were concerned.

In other units different tail reinforcements were improvised. But all these reinforcements again displaced the center of gravity to the rear, and again some lightening measures were sought... The simplest measure was to limit the filling of the oil reservoir.

Bell was not left behind in all this, and the last versions of the P-39Q had much reinforced tails with weights in the front fuselage. Despite all this, the sensitivity of the aircraft to start into spins did not go away. Even after the war, pilots kept killing themselves on the Cobra.

P. 25 "Weigth of fire of the 20 mm gun was 192 Kg per minute vs 161 Kg for the 37 mm."

I read elsewhere from a US pilot that in 1944 the 37 mm was unreliable in the Pacific to the point of often firing only one or two rounds before jamming. It also had a completely different trajectory to the 12.7 mm guns, which made it useless for hitting anything using the gunsight... Russians were not so harsh, but here is a pilot's opinion on P. 26:

"If I could have chosen, I would have kept the 20 MM: With the 37 mm, if you fire one shot ahead of him to run across the target, pow, the second which should hit as the nose travels down takes so long to go off that it goes under below the target. True, if I hit with it, the target was hard pressed to survive, but it was hard to hit with especially because there was little ammo."

The US pilot considered the 37 mm as outright junk, and the 20 mm P-39s were seen as far more valuable aircrafts, kept on with engine changes and spares for as long as possible...

As far as flying it against anything at low altitudes, this is pretty much what I have heard from all US pilots who were familiar with it.

The early models, up maybe to the early Ns, were superbly maneuverable, and this was re-introduced apparently in the Kingcobra which also had a very good turning circle.

Most Ns and Qs, it seems to me, were turned over to the Soviets, and the preponderance of US decal markings for kits are for the earlier P-39s, but if anyone has the exact figures by each variant I would be interested to know.

I did read somewhere else that on the later P-39s it was forbidden to take off with a full oil reservoir, and even that a smaller oil tank was made, but apparently not here...

Sorry about the oil tank mix-up, but it does illustrate that the later P-39s were not really an improvement in handling over the earlier types.

Gaston