P-39 vs P-40

[gjs238]

Originally Posted by Juha

It would not be surprising if USAAF. while thinking that most of fighter job would be at low and medium level and so no need for turbo to all fighters there might be some need to high altitude capacity, so they decided to keep turbo in one type and because of reliability problems still around put them in twin engined fighter.

The P-40 was not designed for a turbocharger and never had one to remove.
The XP-39 changes by NACA seem to be limited to aerodynamic streamlining, not other issues.

Turbo equipped planes could be optionally produced sans turbo, such as the P-38's that were sold to Great Britain pre-Pearl Harbor.

[Juha]

Hello gjs
Quote:"The P-40 was not designed for a turbocharger and never had one to remove."

I knew that

Juha

[davebender]

Heavy bombers had priority for the U.S. Army Air Corps just as they did for the RAF. Look at the cost to develop the B-29. A fraction of that money would have provided every Allison engine with a decent supercharger or turbocharger.

[gjs238]

Originally Posted by davebender

Heavy bombers had priority for the U.S. Army Air Corps just as they did for the RAF. Look at the cost to develop the B-29. A fraction of that money would have provided every Allison engine with a decent supercharger or turbocharger.

Academically, that statement is true.
But is that the reason the P-40 didn't have a turbo and the turbo was stripped from the P-39?

I suspect it wasn't an issue of funding or availability, but HOW to make it work.
How would one turbocharge the P-40?
The little I've read indicates that NACA stripped the turbo from the P-39 as one of many aerodynamic streamlining recommendations.

[claidemore]

Originally Posted by davebender

Heavy bombers had priority for the U.S. Army Air Corps just as they did for the RAF.

But they did not yet see the necessity for escort fighters. Early in the war they (the US) thought the bombers would be able to protect themselves.

[davebender]

There you have it. The U.S. Army Air Corps thought their fighter aircraft would be operating at mostly low altitude. So why spend the money putting a decent supercharger / turbocharger on the Allison engine?

[gjs238]

Originally Posted by davebender

There you have it. The U.S. Army Air Corps thought their fighter aircraft would be operating at mostly low altitude. So why spend the money putting a decent supercharger / turbocharger on the Allison engine?

Something is wrong with this...

So the Army issued Circular Proposal X-608 for a high-altitude interceptor aircraft having "the tactical mission of interception and attack of hostile aircraft at high altitude."
The result was the P-38 (which required TWO turbochargers.)

The Army also issues Circular Proposal X-609, a similar single-engine proposal.
The result was the P-39.
Both proposals required liquid-cooled Allison V-1710 engines with turbo superchargers.

Then the P-43 was developed, and fielded, with a turbo supercharger.

The P-43 morphed into the P-47, famous for its turbo supercharger.

Yet, the Army decides for reasons speculated in earlier posts to remove the turbo supercharger from the P-39?
I still strongly suspect is was NACA and the reasons were aerodynamic.

[gjs238]

That's right, but they were very keen on interceptors.

[gjs238]

Originally Posted by gjs238

Why did the P-39 perform, or seem to perform, so much more poorly than the P-40 - particularly in the early war years?

Both were V-1710 powered, sans turbocharger with single stage/single speed supercharger.

I know the P-39 had short endurance.
But what else?

Getting back to where this thread started...

[fastmongrel]

Did they ever try to fit a Merlin engine into the P39. The low level rated Merlin 24 engine with 1600 hp could have made it into a pretty rapid fighter.

[claidemore]

Like VG-33 said, read Golodnikovs interview. Not only is it informative about the P40 and P39, but gives some interesting insight into what performance criteria were actually most important for air combat.

Conversations with N.Golodnikov

Heres an excerpt pertaining to the P39:

A. S. Nikilay Gerasimovich, could the Cobra really contend with the Bf-109G and FW-190 in aerial combat?

N. G. Yes. The Cobra, especially the Q-5, took second place to no one, and even surpassed all the German fighters.

I flew more than 100 combat sorties in the Cobra, of these 30 in reconnaissance, and fought 17 air combats. The Cobra was not inferior in speed, in acceleration, nor in vertical or horizontal maneuverability. It was a very balanced fighter.

and one pertaining to the P40.

N. G. I say again, the P-40 significantly outclassed the Hurricane, and it was far and away above the I-16.

Personally speaking, the P-40 could contend on an equal footing with all the types of Messerschmitts, almost to the end of 1943. If you take into consideration all the tactical and technical characteristics of the P-40, then the Tomahawk was equal to the Bf-109F and the Kittyhawk was slightly better.

Its speed and vertical and horizontal maneuver were good. It was fully competitive with enemy aircraft.

As for acceleration, the P-40 was a bit heavy, but when one had adjusted to the engine, it was normal.

When the later types Bf-109G and FW-190 appeared, the P-40 Kittyhawk became somewhat dated, but not by much. An experienced pilot could fight an equal fight with it.

I flew somewhere around 50 combat sorties and participated in 10—12 aerial engagements in the P-40. Then the regiment became the next in line to replace its equipment—for the P-39 Airacobra.

Basically Golodnikov says the P40 was a good fighter, but the P39 was better.

[Colin1]

There seems to be a fair amount of evidence around that the P-39 was a far more respectable fighter than western allied pilots gave it credit for, within a low-level combat environment even its maximum speed was perfectly acceptable, in fact, in some regimes it was faster than the A6M or Bf109 and was more heavily-armed than the P-51.

I think that the key to the P-39's abilities however was its manoeuvrability. An RAF evaluation document from 1941 stated:

the Bf109 could not compete with the Airacobra in a turn and even if the Bf109 were behind at the start, the Airacobra should be able to out-manoeuvre and get onto the tail of the Bf109 within two complete turns.

On 12Dec41, Col Claire Chennault's AVG went into combat against the Japanese from Mingaladon in Burma using Curtiss P-40B/C variants. Days later, they moved up to Kunming in China to defend the Burma road. For the next six months they would perform well against the likes of the Ki-44 but at least one historian wondered if they might have fared even better had they been equipped with the Bell fighter instead. Rick Mitchell, author of Airacobra Advantage, points out that most aviation experts automatically assume the P-40 to be superior to the P-39. He insists that, on the contrary:

The truth is that no model of the P-40 during its entire service was ever as fast as the slowest version of the P-39. No P-40 was ever armed with the tremendous firepower or knockout punch carried by every P-39. Too many... make the mistake of comparing the P-39, America's earlier modern fighter plane, with much later WWII fighter designs such as the P-47 and the P-51.

So, although the AVG was largely a success, Mitchell believes that their record against the Japanese would have been even higher with Airacobras.

Anecdotally, the P-39 received a mention in a speech from none other than Churchill himself; speaking of the war build-up he promised that Britain would be getting more Spitfires and Airacobras - a curious choice given that the most numerous fighter in the RAF and an aircraft still very much in production, was at the time the Hawker Hurricane.

[Colin1]

Originally Posted by gjs238

How so?

Originally Posted by gjs238

Would it really have been?
Is it possible the NACA changes to the XP-39 improved low/medium level performance?
(not making an argument, just a question)

Originally Posted by gjs238

Allison?
Was the Allison supercharger design so out of touch with other contemporary designs?

Later on, yes - but in 1939?

Hi sorry
didn't see these posts
the blame can be placed at the door of both the USAAC and Allison; before 1938, the USAAC was committed to a program of turbocharged powerplants but Allison had committed to a program of integral, mechanical supercharging in order to simplify production. The only way to introduce second-stage supercharging was as a separate, external unit.
Allison joined forces with Curtiss-Wright to persuade the USAAC to accept the V-1710 in this form for the P-40 contract, relegating the Curtiss aircraft to a low-level role even before it had entered service, though this suited the (quickly outmoded) requirements of the time. The integral, mechanical supercharger was not developed any further throughout its service life in the P-40.

Yet when the V-1710 entered service in the P-38 it was equipped with turbochargers.

Your second post, I don't think so, there seems to be enough existing data to support the notion that NACA had indeed found lift and drag issues with the P-39's airframe and any modifications were designed to overcome that.
The decision to remove the turbocharger seems to have been made without any real controversy; I would guess that the current USAAC thinking of the time that there would be no high-altitude combat between opposing fighters was well embedded enough to negate any panic. Secondly, Bell lauded the financial relief from removing an unfamiliar, unreliable (at the time) unit that was likely to be fraught with expensive developmental problems.

Your third post, similar to an earlier observation you made, I think you have that the wrong way around too; the early V-1710s were hamstrung performance-wise by the management decision to use the integral mechanical power section, it really handicapped the unit development-wise vs the Merlin say. Later versions of the V-1710, the -143/145s, were as good as anything and were used in all versions of the P-82 bar the B (which used Merlins).

[Colin1]

Originally Posted by fastmongrel

Did they ever try to fit a Merlin engine into the P39. The low level rated Merlin 24 engine with 1600 hp could have made it into a pretty rapid fighter.

http://www.ww2aircraft.net/forum/avi...9-a-16729.html (Has a Merlin ever been put into a P-39?)

[MikeGazdik]

An over simplified summation of varous posts if you will:
1) USAAC envisioned their Bomber force not needing escort, hence no "escort fighters" by design.

2) USAAC wanted the high speed high altitude pursuit to intercept enemy bombers attacking the U.S. homeland , which brought the P-38 with turbocharging ONLY to get to bomber altitude.

3) USAAC also believed that the regular pursuits (not the bomber interceptor) would operate at low or medium altitudes and would not need the turbo installation. Hence the P-36 / P-40 designs, and the turbo removed from the P-39 design.

4) Though the USAAC played with other pursuits with turbo installations, mainly Republic P-43 and such, I believe those were nothing more than fleets of working test beds. They didn't really push for a true full scale production pursuit with the turbo installation, until the P-47. Which was at the dawn of , the Battle of Brittain. USAAC by then had much more info coming back from the European conflicts showing they were wrong in the pursuits not needing high altitude abilities. Then it obviously would take a few more years to learn they were wrong in believing their heavy bombers did not need high altitude escort fighters.

5) All that being said, the P-39 is still awesome to my eyes. Nothing looks sexier on the ramp than that slick nosed, tricycle geared beauty with the snappy Allison exhaust blowing out the middle of the fuselage! And seriously, Airacobra! Not a better name for a fighter has been created. (except maybe Spitfire!)