Could you have designed a better P-39?

[tomo pauk]

Sticking bits and pieces on the outside increases the drag. Same problem as as Bell's attempt's at an external turbo add on.

Not quite as Bell's add on turbo; my idea puts far less parts at the plane's exterior.

You may get your 380-400mph at 20-25,000ft in 1941-43 but if you cut the sea level speed from about 310mph to 270-280mph and the speed at 10,000ft from 350mph to 310-320mph you wind up with a very specialized airplane.

Now why the P-39 with 1325 HP will do only 320 mph @ 10K? P-63 was capable of 350 @ 10K with 1300 HP, despite having 10 % more of equivalent flat plate area (P-39 was making 360 there, with 1100 HP). The 'notorius' Bf-109G-2 was loosing 12-13 mph with wing cannons installed; no increase in power there.
So even if we take external plumbing into account, saying that it would've cut 50 mph, while providing 200 HP more, is highly questionable.

It will also climb worse than a standard P-39 up to about 15,000ft or so. Pulling the wing guns may not be enough (especially if you stick in extra fuel).

Seeing that P-39 climbed better than most (all?) SE fighters made in USA (apart from P-63), I'd say that turbo P-39 wouldn't be at any disadvantage. Regular 39 out-climbed the Spit Vs, IIRC.
We could also mention that, at higher altitude, the advantage would've been even greater (not vs. paddle blade P-47s?). Sure enough, if a commander wants his planes to intercept something, those planes wouldn't be carrying the drop tanks, but have only internal 160 gals.

It is only when the 1425 hp engine becomes available that this starts to look attractive and by then the need for it is fading.

If the low-production models are made (1150 HP), followed with mass produced 1325 HP model (early 1942-mid '43), then such a plane plays far more important role than regular P-39 or P-40. It's also more easily available than P-38. RAF/RAAF are also satisfied costumers. A next step (1425 HP in mid 1943; meaning we have 1600 HP @ WER) is as much expected as P-38H was, but here we talk about all theaters, not just PTO.
Of course, by 1944 a slight redesign of front hull is needed (HMGs staggered, so their ammo boxes can be enlarged to hold 300 rds, 37mm replaced by belt fed Hispano - sorry, P-38). 4-bladed prop. Instead of 2 x 75 gals, it's 2 x 108 in drop tanks.

You do need bigger radiators and oil coolers for the higher powered engines and even the intercooler needs to change from the early version to the late version. The diagrams and pictures were to give you an idea of the size of the pipes/ducts you are dealing with. You can shorten them and change them form square to round or vis versa but you can't make them smaller in cross section (especially forhe higher HP engines)

Same things were true for all planes experiencing increase in engine power, so I see no issues here.

 

[post76]

thrust vectoring.....

 

[krieghund]

This P-39 looks to be doing 353mph at 10k ft.

 

[davparlr]

2. F4F-3 supercharger was a two stage with inter-cooler. back to the weight and space problems of the turbo/P-63

The P-39 definitely needed the performance. There seems to be enough space to work with for the F4F-3 type supercharger. Weight is unknown but should be lighter than the more powerful P-63 engine, so I would guess 150 lbs. This is not insignificant, but I think workable, especially with the removal of the guns. Cg change would need to be evaluated and, if necessary, worked. This could be an issue on such a light aircraft.

5. getting weight out of wings may help but his may mean no extra tanks way out in the wings.

I think improving the efffectivity of the ailerons should solve this problem.

Overall, the P-39 was a small aircraft which would limit its ability to grow and adapt to new missions. It didn't seem to fit in the, in my opinion, correct AAF philosophy of building aircraft to fight over enemy territory not American.

 

[Shortround6]

Here is a picture of one of the two intercoolers on the F4F-3.

http://data3.primeportal.net/hangar/sal_provenzano/f4f-3_wildcat/images/f4f-3_wildcat_16_of_17.jpg

here is a picture of the air intakes for the intercoolers.

http://data3.primeportal.net/hangar/sal_provenzano/f4f-3_wildcat/images/f4f-3_wildcat_01_of_17.jpg

Here is a picture of the duct leading from the intake to the inter cooler.

http://data3.primeportal.net/hangar/sal_provenzano/f4f-3_wildcat/images/f4f-3_wildcat_10_of_17.jpg

The more power over 1000hp you want at altitude the bigger the inter-coolers have to be.

Grumman apparently exhausted the inter-coolers into the wheel wells, P-39 is going to need intakes, ducts and outlets. The second stage apparently increased the weight of the engine by 55-65lbs not including the inter-coolers but this supercharger may not have been big enough to supply more than 1000hp or so worth of air at 19,000ft. It all has to go behind the engine.

 

[pinsog]

Everything I had always read about the P39 said it was a terrible airplane that essentially couldn't get out of it's own way.

Now, thanks to this site, I have learned:
1. It was really fast down low
2. Had very good manueverability
3. Had an initial climb rate, I just read, of 4000 fpm

Why was it's combat performance so bad? Did it's enemies simply orbit above it where it's performance trailed off and zoom and boom it?

 

[gjs238]

Impressions made early in the U.S. part of the war, before good U.S. tactics were developed, may have been lasting.
Same goes for the P-40.

Later war planes benefitted in the reverse.
Not only were they more capable, but better tactics had been developed and adopted by then.
RE: F6F, F4U, P-51, etc.

 

[tomo pauk]

Everything I had always read about the P39 said it was a terrible airplane that essentially couldn't get out of it's own way.

Now, thanks to this site, I have learned:
1. It was really fast down low
2. Had very good manueverability
3. Had an initial climb rate, I just read, of 4000 fpm

Why was it's combat performance so bad? Did it's enemies simply orbit above it where it's performance trailed off and zoom and boom it?

It's combat performance was not so bad; the main customer (Soviets) asked for more P-39s (and Spitfires), instead of P-40s (and Hurricanes). The main shortcomings (low performance above 15K, short range) were not issues at Eastern front air battles. They were for USAAC RAF, however: USAAC was contested (mainly over Guadalcanal, but also elsewhere) by high-flying IJA/IJN bombers their escorts, while air war at ETO demanded both good hi-alt performance good combat range. The combat at Pacific also required good/great combat range, and P-39 was unable to provide it.
Soviets were also stripping down its Cobras (LMGs ammo deleted, some armor radio gear too), in order to extract better performance out of their planes.

 

[gjs238]

Gotta wonder how the AVG would have managed with P-39s.
Or for that matter with anything else besides P-40s.

 

[pinsog]

Does anyone have horsepower figures of P39 vs Spitfire vs Me109 at various altitudes?

 

[Shortround6]

Gotta wonder how the AVG would have managed with P-39s.
Or for that matter with anything else besides P-40s.

Bitter defeat for the AVG using P-39s. Good as they were for dragging the USAAC into the 1940s and giving pilots mechanics something to fly and work on on the second half of 1941 the P-39 was not combat ready at that time. Ships with the P-40s for the AVG sailed in July or Aug of 1941 (?). They needed more maintenance and trouble shooting than the P-40 and would have lead to fewer numbers in the air at any given time. 37mm jammed with monotonous regularity at that time so after the first 2-3 shots from the cannon they were no better armed than the P-40.

 

[post76]

Everything I had always read about the P39 said it was a terrible airplane that essentially couldn't get out of it's own way.

Now, thanks to this site, I have learned:
1. It was really fast down low
2. Had very good manueverability
3. Had an initial climb rate, I just read, of 4000 fpm

Why was it's combat performance so bad? Did it's enemies simply orbit above it where it's performance trailed off and zoom and boom it?

A lot of it also depends on the historical context and when the aircraft was written about.
I find that perceptions and impressions of aircraft change from generation to generation and country to country.
I think seeing later designs like the F4U and F-51 still in use after 1950 may have hogged the stage for less popular designs like the P-39, but if you research Soviet history they give much more detail on their use.
Impressions have nothing left to be weighted against until more information becomes available with time.

 

[post76]

Bitter defeat for the AVG using P-39s. Good as they were for dragging the USAAC into the 1940s and giving pilots mechanics something to fly and work on on the second half of 1941 the P-39 was not combat ready at that time. Ships with the P-40s for the AVG sailed in July or Aug of 1941 (?). They needed more maintenance and trouble shooting than the P-40 and would have lead to fewer numbers in the air at any given time. 37mm jammed with monotonous regularity at that time so after the first 2-3 shots from the cannon they were no better armed than the P-40.

The main issue there would be the tricycle gear. It just wasn't strong enough when used under harsher conditions.
A lot of the P-40s all up weight was said to have stemmed from the undercarriage allowing it to take off or land in less than adequate conditions, something that made it more beneficial to use than a P-39.
I've heard the AVG stuck with the P-40 for other reasons, noting that maintenance was always an issue for them anyway seeing as they had limited replacement parts for the planes they did have.

 

[Shortround6]

A lot of it also depends on the historical context and when the aircraft was written about.
I find that perceptions and impressions of aircraft change from generation to generation and country to country.
I think seeing later designs like the F4U and F-51 still in use after 1950 may have hogged the stage for less popular designs like the P-39, but if you research Soviet history they give much more detail on their use.
Impressions have nothing left to be weighted against until more information becomes available with time.

Another thing to remember is that most Merlin P-51s performed about the same. They were also only on the scene for a short period of time compared to some other aircraft. The Merlin P-51s fought for just under 1 1/2 years in Europe.

The P-39s had more variations and fought over a much longer span of time. A early P-39 flown by the book and limited to 1150hp is going to perform at low altitude much different than a one in late 1942/early 43 that is allowed to use 1490hp of WER.

Flown against the experienced Japanese pilots by green pilots in the south pacific and using the pre-WER power levels is a different "historical context" than flown at low altitude only against less maneuverable planes by experienced pilots on the Russian front.

 

[pinsog]

Didn't the Russians, in addition to removing wing guns, armor and other extra weight, also run the Allison engine well beyond it's standard horsepower rating?

Does anyone know how much horsepower the Russians were able to get out of their P39's?

 

[Shortround6]

I don't know but which power rating are you talking about?

The early P-39s were rated at 1150hp for take-off and held that to 12,000ft, they used 42in of manifold pressure, given good gasoline they were later rated for 1490hp at up to 4,300ft at 56in manifold pressure. They really didn't like over revving much and tended to fail in just a few hours after even a minute or two of over revving (under power not over speeding in a dive). using too much boost is a real gamble depending on the fuel and perhaps the weather. you can get away with a bit more at -30^ than you can at +110^ a little detonation is like knocking in a car. bad detonation can hole pistons, bend or break connecting rods, stretch or break cylinder hold down bolts or studs in just seconds. You tend to hear about the pilots who used it and got home, You don't hear much about the pilots who tried it and crash landed/baled out.

The P-39 K and L used Allisons that were good for 1325hp for take off and 11150 at 11,800ft but were rated for 1580hp WER (60 in pressure) at 2,500ft. This would taper off to the 1150hp at 11,800ft.

The bulk of the P-39s (over 7,000 of them) used an engine good for 1200hp at take off and good for 1125hp at 15,500ft. (44.5 in boost) it was rated at 1410hp at 9,500ft (57in pressure). it used 9.60 supercharger gears which gave the extra performance. They also heated the intake air more and the engine was running closer to the detonation limit which is why it ran the lower pressure at WER.

If you know the pressure the Russians were using you can make a guess at the power.

 

[pinsog]

I don't know but which power rating are you talking about?

The early P-39s were rated at 1150hp for take-off and held that to 12,000ft, they used 42in of manifold pressure, given good gasoline they were later rated for 1490hp at up to 4,300ft at 56in manifold pressure. They really didn't like over revving much and tended to fail in just a few hours after even a minute or two of over revving (under power not over speeding in a dive). using too much boost is a real gamble depending on the fuel and perhaps the weather. you can get away with a bit more at -30^ than you can at +110^ a little detonation is like knocking in a car. bad detonation can hole pistons, bend or break connecting rods, stretch or break cylinder hold down bolts or studs in just seconds. You tend to hear about the pilots who used it and got home, You don't hear much about the pilots who tried it and crash landed/baled out.

The P-39 K and L used Allisons that were good for 1325hp for take off and 11150 at 11,800ft but were rated for 1580hp WER (60 in pressure) at 2,500ft. This would taper off to the 1150hp at 11,800ft.

The bulk of the P-39s (over 7,000 of them) used an engine good for 1200hp at take off and good for 1125hp at 15,500ft. (44.5 in boost) it was rated at 1410hp at 9,500ft (57in pressure). it used 9.60 supercharger gears which gave the extra performance. They also heated the intake air more and the engine was running closer to the detonation limit which is why it ran the lower pressure at WER.

If you know the pressure the Russians were using you can make a guess at the power.

I wish I knew the power rating. I'm not even sure where I read that information. I think I got it off a link off of this sight but I couldn't find it to save my life. As I recall, where ever I read this info, they said that the engines had a VERY short life and had to be changed often. I am 99% sure that I got the info from a link off of this sight and it was an interview with a Russian ace. Maybe someone here knows what I'm talking about.

 

[Ratsel]

The RAF was doing the same engine mods in their P-40E's in N.Africa, up to 70" IIRC. Somewhere around 1600-1700 HP by bypassing the boost controller. Wasn't a common practice and the engines did not last long.

 

[Jabberwocky]

The RAF was doing the same engine mods in their P-40E's in N.Africa, up to 70" IIRC. Somewhere around 1600-1700 HP by bypassing the boost controller. Wasn't a common practice and the engines did not last long.

Perils P-40 page has a December 1942 General Motors Allison document that refers to RAAF pilots overboosting V-1710-39 and -73 engines with the 8.8:1 supercharger ratios (basically a low altitude blower) to 66" and 70" Hg at low altitudes for "prolonged periods".

At 66", the overboosting produced 1745 hp at SL and 1770 hp at 2000 ft. The engines were also subject to over-revving.

At 70", the overboosting at 3200 rpm produced 1780 hp at 3000 ft.

Allison was worried that the overboosting with the 8.8 blower ratio would produce a 'bad precedent' once engines with a 9.6:1 supercharger ratio entered service. However, the engines with the low alt ratio were "apparently" standing up well to the overboosting. Allison recommended an emergency rating of 60", producing 1570 hp for the engine, for the 8.8:1 engines and 57" for the 9.6:1 engines.


EDIT: Did some more checking and it looks like just a week after the Allison/GM memo, the -39 was re-rate to a maximum of 56" (1470 hp at SL) and the -73 was re-rated to a maximum of 60" (1550 hp at SL). Looks like the engines with the 9.6:1 supercharger ration were limited to a maximum of 57" (1360 hp at SL, 1480 hp at 10,000 ft) at least until April 1944.

 

[post76]

I wish I knew the power rating. I'm not even sure where I read that information. I think I got it off a link off of this sight but I couldn't find it to save my life. As I recall, where ever I read this info, they said that the engines had a VERY short life and had to be changed often. I am 99% sure that I got the info from a link off of this sight and it was an interview with a Russian ace. Maybe someone here knows what I'm talking about.

Interview with L.Kulakov
If you back up to "articles" you will find other interviews.

The short engine life (50 hours vs 120 hours) before overhaul was largely because of a different oil quality.
The Russians were told to use a cleaner grade to prevent excessive wear, other than that it was not anymore prone to wear than other engines.
There's also something about a throttle/prop linkage that had to be removed to get more out of the aircraft.
You can read more on that site.
They speak highly of the P-40 and more so the P-39, referring to them as "modern" aircraft compared to their I-16s and LaGGs.