Twin-engine Curtiss P-40

[lark]

Some additional info to Stargazers last post.

Twin XP-40- One of the more extreme P-40 modifications proposed
was a twin-engine version. No military designation was assigned and
no Curtiss model number is known but it did get to the full mockup stage
using the fuselage of P-40C (41-13456) and two Packard V-1650-1 engines.
Nothing came of this late 1942 project.

so far : Peter M.Bowers in"Heritage of the Hawk" Airpower ,May 1983.

 

[blackkite]

Nose heavy?

 

[Jemiba]

Nose heavy?

Not sure, it looks much more logical, than the actual mock-up and some weight forward of the CG
could have been saved by combining te landin gear with the nacelles. I'm not sure, if the fuselage
is elongated in the model, but that probably would have been another modification.

 

[maccountrypilot]

Just looking at the original pic .... I believe that the plane, if actually built in that manner, would be nose heavy. Now if it were built much like GTX's fictional drawing, then it just might be possible for the plane would be a decent flyer. At any rate, I am attempting to test that. I am building a 53" span, electric R/C version of GTX's design

 

[hesham]

Hi,


here is a profile drawing to P-40 twin engined aircraft.


Aerei Nella Storia

 

[joncarrfarrelly]

Hi,

here is a profile drawing to P-40 twin engined aircraft.

Aerei Nella Storia

Nope, that shows the early P-40/Hawk 81 type engine cowlings, the mockup used Merlin powered P-40F
components. They look very different.

 

[Stargazer]

Nope, that shows the early P-40/Hawk 81 type engine cowlings, the mockup used Merlin powered P-40F
components. They look very different.

I disagree partly. The profile view DOES show a twin-engine configuration (see the thicker line around the cowling, obviously not a single-engine aircraft), though it is not one we've seen previously. Speculation/fantasy on the part of the artist, probably.

 

[Jemiba]

To prevent aggravations: jfc didn't doubt, that the drawing shows a twin engined type.
He just noticed, that the cowlings look like the nose of the early P-40 variants (up to
the P-40C, I think) and so probably weren't housing Packard Merlin engines.

Don't know the Aerei Nella Storia magazine, as I cannot read Italian, but it would be
interesting to get to know the context of that drawing.

 

[Jemiba]

Treid to transalate the relevant page from that mag (Thank you, hesham) and to my
opinion, it's an independent attempt of a reconstruction of the twin engined mock-up.
But as online translator results are to be taken always with a pinch of salt, maybe it's
time to utilise the "SPF Translator Service" ?
Attached is the text from the mentioned article, maybe one of our Italian members
can have a look at it ?

 

[CiTrus90]

A twin-engined P-40C

Amidst the twin-engined fighter projects intended for the US Army during the 30s and 40s, there are some of the lesser known in the whole History of aviation: notably, we allude to the twin engined version of the P-40 and to the Curtiss XP-71 project.

In regards to the first one, we only know it was designed around 1940 and that in 1942 [line missing] (which could have even been a flying prototype) made up of the fuselage of a P-40C (s/n 41-13456) joined to a modified wing with the engines on top, to keep the propellers sufficiently far away from the ground.

It's possible that this project, of which no documentation is left, was part of a series of concepts for a High-Speed Fighter, a sort of forerunner to the XP-71, about which we'll write later on.

In regards to the mock up we talked about before (static or flying) we only have one picture we know of, and we can presume that it would have used the same engines employed on other Curtiss-Wright projects of the era, like the traditional V-12 Allison V-1710-39 (F3R), the 24-cylinder Pratt & Whitney XH-2600 or the inverted V-12 Continental XIV-1400-3 Hyper, all of them water cooled, although for the production run were chosen two Packard (Rolls-Royce) V-1650-1 Merlin developing 1300 hp (or at least that's what relate the very few informations available). Such a progression in regards to the powerplant choice, can give us a chronological reference for the project, due to the fact that all those American experimental engines were under development during the 30s, while the Merlin became available only towards the end of 1940.

We have no known reference about its possible first flight, and it could even be there never was one.

At the roots of what we ourselves called the Twin P-40 - as no official designation for it is known - was surely the will to make a leap forward in regards to the previous P-36, XP-37, XP-40 and XP-42, but also the attempt to jump into the tender spawned by the Circular Proposal 39-775 for a high altitude interceptor. As we know, its winner was the Lockheed XP-49 while the Grumman XP-50 placed second.

The available documentation doesn't mention what the other two proposed projects were and in which order did they place, but it could be that the P-40 Twin came fourth during the evaluation trials that took place in the second semester of 1939.

It's clear, though, that Curtiss kept on developing it for over a year, seeing that both airframe and engine became available only in 1941.

For sure it was thought that the P-40 Twin could be a useful testbed for other contemporary programs.

Hope it can be of use.

Regards.

 

[Stargazer]

That's very nice of you CiTrus90, thanks a lot.

My impression is that this twin-engine P-40 project may have been Curtiss's entry in the XP-50 competition, but of course it's only guesswork based on the year, configuration and general requirements for that specification.

 

[ACResearcher]

A number of years ago a well-known kit designer/friend and I looked at the Twin P-40 at length, more of an exercise of curiosity than anything else - although I did end up having a 1/48th scale resin conversion done for this aircraft that I never released.

Anyway, here is what we decided at the time:

The fuselage strongly appears to be that of P-40D/E, etc.
The serial number appears to be completely spurious and may have been put on just to purposely confuse things or may have been on a tail sitting around.
The engines appear to be Packard Merlins, NOT Allisons. They lack to top air intake typical of the Allisons.

When built up into a model it is a quite impressive edifice, but totally "wrong" on so many levels. I doubt the landing gear could have withstood that much extra weight, nor could the wing spars withstand the number of "g"s to which they would have been subjected in almost any sort of maneuvering. Visibility from the cockpit certainly looks like it would have dramatically limited in a number of important aspects.

Lacking any sort of documentation (I suspect it may exist somewhere in the huge numbers of Curtiss documents being held prisoner and unidentified at the NASM Hazy center), we finally decided in frustration that a bunch of Curtiss engineers and line workers got really drunk one weekend and built the thing out of spite.

I don't know if this helps or not, but at least it may give a grin or two and something more to consider.

AlanG

 

[joncarrfarrelly]

In Curtiss Fighter Aircraft: A Photographic History, 1917-1948 Dean and Hagedorn were unable to uncover any
info on the 'Twin P-40' beyond the single photo, and state their opinion that it was a hoax, created for unknown reasons,
from a short-tail H87 fuselage, P-40D canopy and P-40F cowlings, one of which features a shark mouth.
They also agree that the serial is spurious. The book has a much larger and clearer reproduction of the photo than the
Putnam, and you clearly see how crudely it is put together.

The when and where it was built are both unknown, so stating it was part of the XP-50 'competition'
is a real stretch.

 

[lark]

Still think that Peter M. Bowers in his "Airpower " May 1983 article
'Heritage of the Hawk' was very close.
(reply 40)

 

[Stargazer]

The when and where it was built are both unknown, so stating it was part of the XP-50 'competition'
is a real stretch.

Sure. I didn't "state" it, I merely said that it was my opinion. I will edit my post to make it even clearer that it's only that.

But come to think of it, why would a company bother to put together some hasty non-flying mock-up job as this if not as a design proposal for some competition?

 

[Steve Pace]

The when and where it was built are both unknown, so stating it was part of the XP-50 'competition'
is a real stretch.

Sure. I didn't "state" it, I merely said that it was my opinion. I will edit my post to make it even clearer that it's only that.

But come to think of it, why would a company bother to put together some hasty non-flying mock-up job as this if not as a design proposal for some competition?

Good question! The only reason I can think of is the USN's need of a twin-engine carrier-based fighter that led to the Grumman F7F Tigercat which was also evaluated as the USAAF XP-65. -SP

 

[iverson]

For what little it is worth, I vaguely recall reading that the P-40 twin was a non-flying, ground-handling trainer for twin-engined aircraft, cobbled together from wrecks by maintenance staff. I can neither recall nor find a source, however. So I may be hallucinating.

Be that as it may, I doubt that the photo could be a serious mockup. Mockups are meant to give a 3-D impression of how a proposed aircraft will look and, more importanlty, how the components will fit together. Mockups thus have to look more plausible than this thing does--note the angular "fairings" on the aft end of the nacelles. Mockups are also cheaply and quickly built from cardboard and wood, so that they can be quickly and cheaply built and and modified. Two real engines on a real airframe would thus seem rather inconvenient and potentially costly. Finally, the thing does not look anything like a flyable airplane. Visibility looks very poor from the cockpit, except dead ahead. The nacelles look like they would blank the tailplane and rudder. Even without that, turbulent flow from the necessarily bluff-ends of the nacelles would cause controllability issues. There is no additional fin and rudder area to compensate for the large side area of the big flat-sided nacelles. The center of gravity would have to be way out of kilter with two engines, unless a significant amount ballast was added in the tail.

Finally, I wonder what the attraction of a Packard-powered P-40 twin could have been a time when the obviously better P-38 and P-50 were in service or available and when Packards were already too much in demand for use in the P-38?

 

[Jemiba]

For what little it is worth, I vaguely recall reading that the P-40 twin was a non-flying, ground-handling trainer for twin-engined aircraft, cobbled together from wrecks by maintenance staff. ...

From what is already said in this thread, it's still the most plausible explanation to me !

 

[royabulgaf]

The hoax/ground handling mockup theories make the most sense. Those nacelles look like the boxes the engines came in. The engine weight right over the standard P-40 landing gear? They would snap the first landing.

 

[joncarrfarrelly]

The when and where it was built are both unknown, so stating it was part of the XP-50 'competition'
is a real stretch.

Sure. I didn't "state" it, I merely said that it was my opinion. I will edit my post to make it even clearer that it's only that.

But come to think of it, why would a company bother to put together some hasty non-flying mock-up job as this if not as a design proposal for some competition?

Well, nobody knows whether or not it was put together 'by a company', all that exists is a single photo without provenance.

 

[CiTrus90]

Serial number 41-13456's fate is listed as "condemned Feb 27, 1943" on Joe Baugher's serial site for US aircrafts.

By the way, found a couple more pictures of the same but with different contrast level that might show some more details.

Regards.

 

[airman]

https://youtu.be/sIpv3PW1pQ4 - the flying Twin-engine Curtiss P-40 ( ok, only on a flight simulator)

(the variant T is purely speculative ) .

Watching video i suppose that Twin-engine Curtiss P-40 could be been an experiment for evaluating the two-engines configurations that could be connected with the development of Xp-71.

 

[joncarrfarrelly]

From Dean & Hagedorn.

 

[sienar]

With a higher resolution pic like that I'm starting to wonder if the aircraft actually has a nose. It looks almost like it could be a straight cut, but not quite right enough to be certain.

 

[joncarrfarrelly]

Yep, nothing in front of the firewall.

Here's a pic of a P-40E undergoing a firewall forward rebuild:

 

[GTX]

For what little it is worth, I vaguely recall reading that the P-40 twin was a non-flying, ground-handling trainer for twin-engined aircraft, cobbled together from wrecks by maintenance staff. ...

From what is already said in this thread, it's still the most plausible explanation to me !

I agree

 

[briantk]

I found this little video went down the rabbit hole to see the origin of the picture:

View: https://youtu.be/f8OIbRL-deg?si=qp0xpGyTCe67HBh1


First section, he looks at online origin of the twin engined P-40
Second section, he looks at the where the twin engined P-40 came about, a cursory mention from J Miranda series called Unknown, volume 4.
Third section, he looks potential inspiration for the plane, US military called for twin engined, long range fighter interceptor project, which Grumman G41, Lockheed XP50, X49, Bellanca and Curtiss XP-71.
Fourth section, he looks Dan Hagedorn, who wrote Curtiss Fighter Aircraft: A Photographic History 1917-1948, to see what Dan said about the twin engined P-40. Dan denounce it is hoax as part of wartime misinformation campaign.
Fifth section, looks at history of P-40 that has the serial number that is related to twin engined P-40 from NASM records.
Sixth section, he then looked at the locations where the P-40 was services to see if he can narrow down the location where the picture is taken. He believes it has been taken at Buffalo Municipal Airport, located near Curtiss factory.
Seventh section, author comes to following conclusion: twin engined P-40 is not undocumented prototype, nor misinformation but rather a side project by Curtiss engineers as mockup for postwar airshow.

 

[Justo Miranda]

One of the more extreme P-40 modifications proposed was a twin-engine version.

In 1976 Ernest R. McDowell published a picture of the mock up in the Squadron Signal monograph ‘Curtiss P-40 in action’.

The aircraft was the ex-P-40 C s/n 41-13456 extensively modified with the installation of a P-40 D canopy and two wing mounted Packard/Merlin V-1650-1 engines coming from two P-40 F airplanes.

The serial number fate is listed as ‘condemned Feb. 27, 1943’ on Joe Baugher site of U.S. aircrafts.

In 1979 the picture was credited to National Air and Space Museum (NASM) by Peter M. Bowers in the Putnam book ‘Curtiss Aircraft 1907-1947’.

The picture was republished by the same author in ‘Airpower’ May 1983 and in 2007 by Francis H. Dean in the Schiffer book ‘Curtiss Fighter Aircraft 1917-194’.

In an article published in 'American Aviation Historical Society Journal', spring 2017, Dan Hagedorn revealed that the picture had been taken in the South-West quadrant of the Buffalo Municipal Airport N.Y. which just happened to be the location of the Curtiss-Wright manufacturing facilities.

Between July 2006 and May 2015 the picture was analyzed by the experts of the forum https://www.secretprojects.co.uk/threads/twin-engine-curtiss-p-40.509/ with the result of several interesting theories and the publication of the same picture with different contrast level that might show some more details, including a shark mouth paint in the starboard engine nacelle.

The 68th F.S., 347 F.G. fighting in Guadalcanal between January and June 1943 was the only P-40F unit using shark mouth paint. These aircraft belonged to the P-40 F-15-CU series (c/n 41-19733 to 41-19932).

Possibly the starboard Merlin of the mockup was a surplus engine from one of the damaged aircraft on Guadalcanal and could not reach Buffalo before June 1943.

Grumman Aircraft Engineering Corporation proposed the concept of a lightweight twin-engine point-defence interceptor, with outstanding climb rate, in 1938 the firm won two development contracts with the U.S. Navy and the USAAC.

The naval prototype, named XF5F-1 Skyrocket, was flown on 1 April 1940 powered by two 1,200 hp Wright R-1820 radial engines.

In 1941 flight tests were conducted against eight types of Allied fighters. Hawker Hurricane Mk. IIB, Supermarine Spitfire Mk.VC, Bell P-39 D, Bell XFL-1, Curtiss P-40 D, Grumman F4F, Brewster F2A and Vought XF4U.

These trials revealed the superiority of the Skyrocket in top speed (383 mph) and climb rate (4,000 ft/minute).

The Army prototype, designated XP-50, first flew on 18 February 1941 powered by two 1,200 hp Wright R-1820-67/69 turbo-supercharged engines.

With 423 mph top speed and 4,575 ft/minute the P-50 was superior even the Skyrocket in the point-defence role, but the U.S. navy pressed Grumman into the mass production of Wildcats, Hellcats and Avengers, the aircraft types most urgently needed in the Pacific Front.

On May 14,1941, the turbo-supercharger failure resulted in the destruction of the XP-50 and the project was cancelled.

Theoretically, one P-40 powered by two Merlin engines could exceed 400 mph top speed, 3,450 ft/minute climb rate and over 10,500 lbs gross weight.

In June 1943 the USAAF cancelled the Lockheed XP-49 high-altitude fighter, with 3,300 ft/minute climb rate, in favour of the P-38 J. But the Lightning was a heavy fighter with 2,857 ft/minute climb rate, inferior to those of the Hawker Hurricane Mk. IIB.

After the cancellation of the Curtiss XP-62A on September 21,1943, and the Curtiss XF14C-2 in December, the United States lacked any type of point-defence interceptor.

In these circumstances the non-flyable mock up could have been used to demonstrate that that a twin-engine P-40 could be built with parts coming from the production line, to circumvent the cancellation of the project in favour of the P-40 K, M and N series.

The mock up could be an experiment for evaluating the twin-engine configuration as part of the XP-50 competition.

In the opinion of the experts the construction of a hypothetic flyable prototype would have required the following modifications: installation of an strengthened landing gear, reinforcement of the wing structure, design of a new streamlined nacelles in order to reduce the turbulence over the tail surfaces, increasing the fuselage length and the tailfin area to compensate the large side area of the nacelles, a significant amount of ballast added in the tail in order to preserve the centre of gravity location.

The poor lateral visibility was acceptable in a point-defence interceptor.

The mock up could be just another attempt of Curtiss to save the basic P-40 design, improving performance with increased power and cancelled because the unavailability of Merlin engines.

Or it was a hoax created for unknown reasons?

 

[iverson]

<snip>

Or it was a hoax created for unknown reasons?

I have a hard time seeing this assemblage as a flyable aircraft. Your drawings reinforce my scepticism: the proportions are all wrong. There's too little wing area and too short a fuselage. I'd expect center of gravity issues unless some serious ballast was added to the rear fuselage.

Besides, can a wing and fuselage structure designed for one engine really absorb the power and weight of two?

 

[Justo Miranda]

I have a hard time seeing this assemblage as a flyable aircraft. Your drawings reinforce my scepticism: the proportions are all wrong. There's too little wing area and too short a fuselage. I'd expect center of gravity issues unless some serious ballast was added to the rear fuselage.

Besides, can a wing and fuselage structure designed for one engine really absorb the power and weight of two?

In my opinion, the landing gear should have been installed behind the engines and used the clearance in the wings to install structural reinforcements.