Why not a jet driven P-38?

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delcyros said:
It just has been an idea, nothing to upset us.
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Good.

In that case, had you thought of eliminating the piston engines altogether?



I know the jet powerplant you envisage is 'small', so would two suffice? Arranged in a stacked position?



I guess you would have to redesign the tail to prevent scorching? I understand that Lockheed had experimented with this to reduce flutter (unsuccessfully).

 

Yes, they did; and the envisioned floatplane version of the P-38 would also have used the raised tail, if it had been built.

However, it turned out to be the wing-to-fuselage juncture that was causing the problem, so all subsequent versions of the -38 had a large fillet added to the wing/fuselage juncture at the leading edge of the wing.

BTW, those line drawings look an awful lot like the Saab 21R, except the Saab only had one engine.

 
I too think that turboprops are no option due to technology and production avaiability issues.

I also tend to think that the XP-58 is no option due to similar reasons. While the plane offers enough space and fuel, it was a developmental airplane, not to get airborne before june 44. The P-38 is avaiable in numbers since 41 and production and assembly lines were working fully by mid 42 latest.

The proposed pure jet engine version is an interesting option. I now am a bit scared about the potential of the P-38 airframewise! Unbelievable but the plane could be kept in frontline service up to the early 50´s with these modifications:

P-38H - mass production started in may 43. As historical.
"P-38I" -mass production could start in nov. 43 (modifications as shown on top of page 1, mix plane. jet engine: I-16 mod 3)
"P-38P" -mass production could start in mid 44 (modifications: I 16 mod 5 engine + 2 Allisons with high speed props, higher set stabilizer and new nose section with fully pressurized cockpit and bubble type canopy = higher crit Mach figure, higher top speed, more range) 8)
"XP-88A" - developmental plane to be ready in late 44. Both Allison engines are removed, the boom structure fully redesigned. The plane is driven either by two I-16 mod 5 (as suggested by Graeme) or by a single I-40. The Modifications are significant enough to justify the new number. Since the plane is both, lighter and aerodynamically cleaner, it will receive substantial advantages and become a true 500 mp/h class fighter. Basically a Vampire, just better.
"XP-88C" - the final version to be made in the late 40´s. Using an improved I-40 engine and swept back, thinner wings, which turn the plane into a true 600 mp/h class fighter.

Neither the Fw-190, the Bf-109, the Spitfire, the Thunderbolt nor the Mustang or any other high performance piston fighter had a comparable potential for further development -if only explored- than the P-38, impressive.
 
From SoD Stitch

Yes, they did; and the envisioned floatplane version of the P-38 would also have used the raised tail, if it had been built.
Click to expand...

I have very little on Lockheed's P-38 floatplane, do you have more on it?




BTW, those line drawings look an awful lot like the Saab 21R, except the Saab only had one engine.
Click to expand...

The montage of images was to simply try to portray what I had in mind. Yes, the first is the SAAB 21R. The second is the odd looking Yugoslav Government Factories Type 452-2 experimental aircraft.


 
Graeme, there was a short-lived program for a float-plane P-38 for ferrying. From my P-38 presentation notes:
 
Delcyros, by the time you have finished all of those modifications, you have a completely different ariplane anyway, so why spend all that engineering time re-engineering the Lightning when you can start with a fresh new design that won't take tooling away from production aircraft that are needed in the combat zones?
 

It´s perhaps the tooling problem (a complete new plane not only needs to be engeneered in plane and the tooling devices but also requires more developmental time) which cancelled the P-38K. A new design anyway also needs new tooling processes, but uncomparably more. The effect is not a combat plane production reduction but a general delay until the new plane get accepted, the assembly lines get build up, the tooling avaiable and the production starts. A complete new airframe coupled with the new type of propulsion - as it was done in the P-59 - is not a favourable condition to start with. The piston´s had advantages on their own, which were unsurpassed by jets until the late 40´s / early 50´s. The mix propulsion was perhaps the best way to deal with jet problems in between 1942 and 1947.
The key aspect is that while some fewer P-38H and probably no P-38L would have been build, the P-38I is a truly superior plane when it arrive on the continent, the increase in performance may justify the production delay and the USAAF in europe never experienced a P-38 shortage in replacement planes. You also don´t need to retrain all pilots extensively, as it was necessary with "pure" jets, experiencing poor low speed performances.

I had a controversy with a friend of mine, who insisted that the allies while having better jet engines in production, never could bring a jet airframe into combat during ww2:


Of course I disagreed! Since he was referring mostly to the airframes, I looked for something which could be done realistically and stumbled over the P-38.
 

I haven't seen all the specs on the P-38 but recall that Mcr was lower than the 51 and Spit and Fw190D - so the redesign would have to be significant to improve stability at lesser speeds than 600mph as well as increased interference with elevator due to turbulent flow over the centerbody?

I would be suprised, absent a completely swept wing, that the 'late version' could do 600mph.

Just guessing, but the straight section of the wing inboard of the booms would be your first issue and probably define Mcr for the airframe, even with a redesign of centerbody.. moving the center of lift rearward at that moment combined with any flow separation masking the elevators would probably make this bird pitch nose down at that point..
 

It is. The modification of the centerwing part is necessarely the first redesign next to the rear fuselage. The tankage systems needs to be redesigned to suite the jet engine´s fuel requirements and the wingroots needs to be reshaped as well. Aerodynamic compressibility related issues were not fully understood at this point (say earliest design stage 1941-1942) and while we might be able -with 20/20 hindsight- to make it work, the Lockheed designers might eventually not have come to the same solution. Or it goes the other way -Skunk work people had a reputation for doing the unthinkable- who knows?

BTW- has anyone a detailed drawing of the sections in question (midwing section and more importantly the center fuselage gondola)? I have run up down in the net and have been unable to find something barring a rather simple and unscaled cutaway drawing.

best regards,
delc
 
Here a comparison with other jet-prop-mix planes which have been accepted for production:

1.) Convair XP-81 (february 1945 first flight) heavy fighter
24.650 lbs max., 507 mp/h top speed, 2500 mls. range, 35.500 ft. ceiling

-canceled for beeing to late to be os any use against japan. Proposed in response to USAAF requirement for a mixed power escort fighter in 1943.

2.) Curtiss XF-15 C-1 (jule 1945) navy fighter

18.689 lbs max., 469 mp/h top speed, 635 mls. range, ceiling unknown

3.) Douglas XB-42A "Mixmaster" (may 1946) bomber

32.000 lbs, 490 mp/h, 2480 mls, 41.800 ft. ceiling

XB-42, dating from 1943, intended to replace the Douglas A-26 Invader.

4.) Douglas XBTD-2 "Destroyer" (1945) dive bomber

~22.000lbs max., speed, ceiling and range unknown

5.) Grumman XTB3F-1 "Guardian" (december 1946) torpedo bomber

weight, ceiling and range unknown, top sped is 350 mp/h

6.) Martin P4M-1 "Meractor" (oct. 1946) maritime patrol

88.375 lbs max., 410 mp/h, 2840 mls, 16.900 ft. ceiling

in use well into the 50´s!

7.) Ryan FR-1 "Fireball" (jule 44) Fighter

~9.000lbs max., 426 mp/h, 1.430 mls, 42.000ft. ceiling

On the 2/12/1943 the US Navy ordered 100 FR-1" Fireballs" and later in 1944 ordered an additional 600 aircraft, but after VJ day after only 66 aircraft had been made the order was canceled.

It seems the idea was not unpopular.
 
Graeme said:
From SoD StitchI have very little on Lockheed's P-38 floatplane, do you have more on it?
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The P-38 floatplane was a proposal conceived by Hal Hibbard, Lt. Ben Kelsey, and Kelly Johnson to install floats on a "standard" P-38E airframe; the only major modification would have been the upswept empennage. The floats were designed to just bolt-on to the bottom of the engine nacelles, while leaving the standard tricycle landing gear alone for normal land operations. The main impetus for coming up with the proposal was as a solution for ferrying large numbers of aircraft across the Pacific Ocean without having to put them on ships. The theoretical range of the P-38 floatplane was approximately 5,000 miles, as the floats would double as 1000-gallon drop tanks. The proposal also included the provision for jettisoning the floats in-flight in case of combat or a similar in-flight emergency. Also, this way the plane could take-off from water but land on a normal runway.

With the US's victory at Midway, this became a moot point, as P-38's could fly all the way to Midway from either the Aleutians or Hawa'ii. Several plans and artwork were generated by Lockheed depicting the floatplane version, but no prototypes were ever built or even started.

 
Thanks Graeme. I used that picture to give an expression how the side appearence of the center fuselage section would be in comparison to a normal P-38H. Note that the J-31 mod 3 fit´s well into a new rear fuselage. I suspect that the parasite drage is increased slightly and the very section where the engine fits is needed to have a more circular diameter instead of an oval one. This requires a longer exhoust pipe to reduce drag as shown in the picture below. A later mod might adress this problem more properly.

For more details I would need to have a copy from a scale cutaway drawing or the instruction manual for mechanics. Can anyone point me to sources?

Thanks in advance and kind regards,

delc

-
 

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Eric and SoD Stitch, thanks for the info on the waterborne P-38 project.

delcyros said:
For more details I would need to have a copy from a scale cutaway drawing or the instruction manual for mechanics. Can anyone point me to sources?
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Can cutaways be drawn to scale? (isometric?).

 
I found this on wikipedia: "Buffeting was another early aerodynamic problem, difficult to sort out from compressibility as both were reported by test pilots as 'tail shake'. Buffeting came about from airflow disturbances ahead of the tail; the airplane would shake at high speed. Leading edge wing slots were tried as were combinations of filleting between the wing, cockpit and engine nacelles. Air tunnel test number 15 solved the buffeting completely and its fillet solution was fitted to every subsequent P-38 airframe. The problem was traced to a 40% increase in air speed at the wing-fuselage junction where the chord/thickness ratio was highest. An airspeed of 500 mph at 25,000 feet could push airflow at the wing-fuselage junction close to the speed of sound. Filleting forever solved the buffeting problem for the P-38E and later models."

So since they solved buffeting and compressability problems at speeds of 500+mph (which the P-38 could manage in a dive) maby a jet version would have been workable. Even if you slimmed down the (now engineless) nacelles and booms for less drag there'd still be plenty of room for fuel to increase capasity which could bring range up to acceptable standards. Still, it probably wouldn't reach 600mph, but even the P-80A barely made it past 550mph in level flight.

Also, there were turboprops in 1945, the first relatively reliable one was tested in March of '45.(Though I'm not sure this model would have been realistic for the P-80 since it would have been over 40" wide since it was based on the Dewent turbojet)
From Wikipedia: "The first British turboprop engine was the Rolls-Royce RB.50 Trent, a converted Derwent II fitted with reduction gear and a Rotol 7 ft 11 inch five-bladed propeller. Two Trents were fitted to Gloster Meteor EE227 — the sole "Trent-Meteor" — which became the first relatively reliable turboprop powered aircraft. From their experience with the Trent, Rolls-Royce developed the Dart, which became one of the most reliable turboprop engines ever built. Dart production continued for more than fifty years."
 
Also I think Lockheed wouldn't have chosen to adapt the P-38 because, though do-able, Lockheed already had jet airframe sesigns to work with Like the L133 and Bell's single-engine version of the Airacomet (which was reworked into the XP-80).

In addition, Lockheed wasn't chosen to design the craft to be fitted with the GE engines (I-A, I-16, J31) adapted from the british welland. Bell got that contract, and the main reason was that Bell wasn't producing any crucial aircraft at the time (also other reasons like Bell's close proximity to the GE plant), while Lockheed was heavily depended on for wartime production. The reason Lockheed started working on the XP-80 design was started when they were given Bell's plans for their single-engine version because their hands were full with the main design.

At first I wondered why Lockheed even bothered working on Bell's design and didn't simply change the L133 to use a single engine. Then I realized how rushed they were with only180 days to design a working prototype. The more conventional design would be easier to develop in the limited time window.

Bell was pushed into a symilar position, but they were worse off without being allowed to streamline and optimise the airframe, (the government did this to try to shorten development time and to not infringe on other projects) which was probably a bad idea since they could have still made the deadline. Bell also didn't have much information on the performance of the engines to base their design on. All these factors led contributed to the mediocrity of the P-59, which I think had the performance potential of the early Meteors though it's design probably wasn't as adaptible as the Meteor's. If developed properly I think the P-39A would have been comperable to the Meteor F1 and the P-59B comperable to the F3, (both model's had coperable engines too: with the I-16/J31(early model)=the welland and the J31(late model)=the derwent I). But after this Lockheed's designs would have beaten the airacomet in performance and development potential, as well as the use of a single engine which would mean fewer limits on production numbers.

I know I strayed from the main topic a little but it's still interesting and maby I'll get some more intrest in this topic again.
 

This certainly was the case from Lockheeds point of view. I personally regard the P-59 as technology demonstrator plane and little else.

Actually, the L133 was a no go. It´s fuselage cross section reveals that it was dimensionated around a L1000 axial jet engine (a design which never worked), so redesigning the fuselage to fit the larger radial J-31 or -34 is a major task. Add the unprooven airframe concept and Your own observations and You see how wisely Lockheed kept the balance between prooven work and own studies.

kool kitty89 said:
I know I strayed from the main topic a little but it's still interesting and maby I'll get some more intrest in this topic again.
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Yes, a highly fascinating topic, my friend!
 
Thanks for the complement.

The airacomet was also useful as a conversion trainer.
And I wonder why they didn't use low mounted wings on the P-59 like they did with the single engined version. I looks like the engines could fit over the wings (where the air intakes are in the XP-59B pictured on pg 1 of this topic) without the exaust hitting the tailplane.

Any comments on the improvements on the P-38's compressability and buffeting problems?

Perhaps 2 Westinghouse J30 axial jet engines would have worked in the the L133 they were rated at 1600 lbf each (about the same as the welland and early J31) and first entered production in late '44, though problems delayed it until early '45 (when FH Phantom's prototype took to the air for the first time-- though this plane ened up as the navy's equivalant of the P-59 and only 62 were produced) The J30 was the first american axial turbojet to enter production. But by this time the XP-80 would have already been well uner way so it would probably have been more attractive than the L133.
Also I think you mean J33 not J34 as the J34 was another early Westighouse axial turbojet (which was later available with an afterburner), actualy a later development of the J30 and was used in the sucessful McDonnell F2H Banshee as well as the failed Vought F6U Pirate and Curtiss-Wright XF-87 Blackhawk (which looks coincedentaly alot like Gruman's Tigercat.)

I took another look at the L133 design an now see that it's obvious that it needed 2 engines since the 2 exaust exits are on either side or the tail and there were no working sesigns for divergent-exaust engines available yet. I'm not sure of the size of the J31, but it looks like it's about 4 ft wide and from what I've seen of the L-1000 it wasn't too much less than 4ft wide (maby 3 ft) so maby this might have been used, though until the P-59 was canceled these were probably all diverted tward it. But the J31 was in production before the J30 so maby it would have been an option...
Check it out here: General Electric J31 - Wikipedia, the free encyclopedia Here's a clip from the history channel about GE's early engines: Video Clips (click on the 3rd clip)

Here's a pic of the L-1000 and a draft of the L133 design from here: EnginesUSA and L133
 

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You have to realized that military contractors - back then and even today don't have a say in certain situations and this was probably one of them, especially if they are spending government money.

AAF officials never liked the L133 design, but as stated the wing was used on the XP-80.
 
I'm pretty sure the airforce regected the design because of its radical desicn. (as they perfered a more conservative approach and Lockheed had a hard enough time getting them to accept the P-38 design)

Earlier you posted that the P-80 used the P-38's wing, later you said it used the L133's, so which is it?
 
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