XP-67 Moonbat

[Scott Kenny]

The Army was well aware that the I-1430 wasn't going to be continuing. That program had been cancelled while the XP-67 prototype was still being built. Mr Mac had gone around the various offices with concepts for production engines, and a contemporary memo by the Army's XP-67 project officer, John Aldridge, talks about them: "...in view of the feeling that come what may, there is no chance of further engines of this [I-1430] type being built, an engine change in the second [XP-67 prototype] airplane is the most advisable move to make. McDonnell proposes to make this change to either an Allison two-stage engine or the Rolls-Royce 14SM engine. Along with installation of one of those alternate types of engines, McDonnell proposes to install J-32 Westernhouse (sic) Jet Unit in the space now occupied by the turbo in each engine nacelle... This proposal was presented to General Carroll who directed that the matter be held in abeyance pending clarification of the engine allocation picture. Mr. McDonnell wanted to have the program approved at once as he feels that he has man-power available to start work immediately, and should it be decided to put the airplane in production, large savings in time would be accomplished by taking action now..." There's a handwritten note at the bottom of the preserved copy of this memo: "Carroll proposes - (1) select best available engine for No. 2 airplane; (2) if the second a/c is a success, go into production."

J32s? Those make less thrust than the radiator duct of a P-51D...

But Col Marshall S Roth (Engineering Division, Wright Field) painted a more realistic picture in a telephone conversation with Col R. C. Wilson (Chief of Development Engineering) on July 14, 1944. "McDonnell has been in here several times selling the idea of installing the Rolls-Royce engine with the I-70 in back... [his] conversation will lead you to believe that all there is to it is a couple of new engines and the I-70 in back but it is not that. It is a complete new airplane. The nacelles will have to be changed, and an extra wing panel added, raise the pilot's cockpit, added span, need a new tail, etc. The peculiar shape of that airplane requires everything to be faired in from one thing to another which when put all together means a complete new airplane."

As much as I might wish otherwise, Roth was absolutely right about this. McDonnell's own surviving 3-views of the mixed-propulsion aircraft show very clearly that it would have shared the general shape of the XP-67 but the new nacelles were designed to fit tightly around the I-1430 (whose frontal area was 27% smaller than the V-1710 version contemplated for substitution, according to XP-67's Case History report) would be taller, meaning that the cockpit would have to be raised higher in order to even preserve the already poor vision to the side. That would mean new forward and after fuselage as well, to preserve the shape contouring philosophy that was the basis of the whole concept. So it would be pointless to give MAC either of the alternate engines since neither would fit inside the XP-67's airframe, and there was no time or money (or honestly patience) to have MAC do detail design and wind tunnel testing for what was being shown around in cartoon form as P-67C (fighter) and P-67E (recce).

Bugger.

But now I know how to model it for gaming. Go find a 1/285 scale model when everything else is 1/300.

 

[stever_sl]

J32s? Those make less thrust than the radiator duct of a P-51D...



Bugger.

But now I know how to model it for gaming. Go find a 1/285 scale model when everything else is 1/300.

Jet engine choices were pretty limited in 1944! The early ones were pretty anemic, but actually I'm not sure what Aldridge was talking about. After extensive (and expensive!) archive searches we've only been able to turn up 2 drawings of notional P-67 mixed propulsion layouts, and neither mentions J32. One is labelled "G.E. Type I-20 Unit" which would have been the J39 if it had gone into production. (This is also the engine specified in McDonnell Engineering Report #236, describing the hoped-for Service version, P-67C.) The other is unlabelled but shows an outline of what looks like a centrifugal-flow turbojet rather than a J32's axial flow type. It seems likely that Aldridge had his wires crossed and just said the wrong thing, as did Roth in his conversation with Wilson when he spoke of "I-70" instead of "I-20." At least that's my best guess.

 

[Scott Kenny]

Jet engine choices were pretty limited in 1944! The early ones were pretty anemic, but actually I'm not sure what Aldridge was talking about. After extensive (and expensive!) archive searches we've only been able to turn up 2 drawings of notional P-67 mixed propulsion layouts, and neither mentions J32. One is labelled "G.E. Type I-20 Unit" which would have been the J39 if it had gone into production. (This is also the engine specified in McDonnell Engineering Report #236, describing the hoped-for Service version, P-67C.) The other is unlabelled but shows an outline of what looks like a centrifugal-flow turbojet rather than a J32's axial flow type. It seems likely that Aldridge had his wires crossed and just said the wrong thing, as did Roth in his conversation with Wilson when he spoke of "I-70" instead of "I-20." At least that's my best guess.

Thanks!

Those J39s are a much bigger unit than the J32, and almost certainly larger in diameter than the turbocharger used on the XI-1430 or the V-1710 including ductwork.

Personally, I'd want to stick a J30 in the back of the nacelles. The J30 is 19" in diameter and 100" long, the J31 (which was developed into the J39) is 42" in diameter and 72" long. Both engines are ~800lbs, and both engines make over 1400lbs thrust, with the J31 making 1650. (The J34 is a much bigger and heavier engine, ~1200lbs)

Looks like you'd want either a Merlin or the Allison V-1710-119, to have two-stage supercharging on the engine to open up space for a jet engine.

 

[stever_sl]

Looks like you'd want either a Merlin or the Allison V-1710-119, to have two-stage supercharging on the engine to open up space for a jet engine.

The I-1430 was perfectly capable of being fitted with better superchargers, and in fact it originally had a 2-stage 2-speed supercharger, as a letter from Continental to AAF Materiel Command on 5 October 1943 describes:

“1. In accordance with your [i.e. AAF Materiel Command] request, we have carefully review [sic] our overall experimental and research program and submit herewith a revised proposal for the Model XI-1430-9A Engine, in lieu of our proposal dated 18 June 1943, and request the substitution of the following program for the program set forth in Contract #w535 ac-39568 (Ref. a, b, c, and d).
“2. The Model XI-1430-9A Engine will be essentially the same as the Model I-1430-A1 Engine, except that it will have a single-stage – single speed supercharger in place of the two-stage – two-speed supercharger...”