# Why not a jet driven P-38?



## delcyros (Aug 9, 2007)

I had an interesting discussion on this. For the search for the most reasonable USAAF jet fighter in ww2 I stumbled over the possibility to refit a jet engine to a P-38 Lighting.

Since we also tend to like what ifs, it´s not going to totally sidetrack this board.

Bell Aircraft had designed a single-seat airplane powered by two turbojets built by General Electric (called I-16 or GEJ31) under British license. The first XP-59 was shipped to Muroc Army Air Base in California, where it flew on Oct. 1, 1942. Called the Airacomet, it offered little advantage over conventional fighters, and the few that were produced served mainly as test beds or trainers.

I wonder why the Lockheed company never considered mounting an early jet engine centrally into the P-38 fuselage. The jet-prop mix A/C would have been a reasonable start to deal with the new propulsion, offering a high degree of safety (never test a new engine in a new airframe) and fullfilling some tactical needs (hunt down V-1 bombs, high speed interception and recon).

Assuming a single GE J-31 turbojet engine is used for reference (weight: 386 Kg, thrust: 748 Kg, avaiability late 1943 for serial production):

engine installation:
The J31 unit has to be installed into the central fuselage section. CoG issues require to move the cockpit section about 2 ft. forward, closer to the nose. In order to avoid a major redesign of the wole section it is advised to use side air intakes under the wingroots for the engine (the nose part remains identical to the historic one), which are not expected to interfere with the cartridge propellant gases of the upper nose mounted guns.

airframe:
The airframe does not need a structural reinforcement. Maximum take off gross weight increases to ~23.000 lbs. It does not appear that the limiting capacity of the landing gear is reached with this loading.

fuel system:

The fuel system requires some major modifications, esspeccially in the midwing section for a larger seperated tankage. The jet engine arguably can use low grade fuel as it´s performance is indifferent to octane grades. 
The increased internal fuel buncerage consists of 110 gallons jet fuel and 350 gallons high grade fuel (460 total)
Either two standart 165 gallons or 300 gallons drop tanks can be used for a total buncerage of 790 to 1060 galloons. Mixed low grade - high grade tanks are not in production but can be put into if required, as long as these are not avaiable, the pilot has to choose whether he uses high grade or jet fuel drop tanks depending on mission parameters.

Serial production:

Could be implemented rapidly without shutting down Lockheeds P-38 production lines. 85% of the tooling can be overtaken.

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My estimated charackteristics of the hypothetical P-38 with jet engine:

A. GROUND HANDLING:
No special caution has to be made except for a larger clearence sector behind the tail during the warm up of the jet engine.

B. TAKE OFF:
The avaiable power for take off with jet engine is greatly increased. A fully-loaded P-38(mod) without use of the jet engine could take off in estimated 1200 ft under zero wind conditions and concrete runways, while with jet assistance, the take off distance reduces to estimated to under 1000 ft. at full load, giving this P-38 modification the shortest take off run of any USAAF Fighter in ww2 service. The aircraft would lift off the runway between 120 to 125 mph, and required very little effort to pull it up in the air. 

C. CLIMB: 
In clean condition, with normal weight, an altiutde of 20.000ft. can be established in less than 6 minutes estimated at full power rating, one of the finest time to altitude figures for ww2 fighters.

D. ACCELERATION:
The P-38 arguably had the fastest linear acceleration of all US propeller planes during WW2 (This was true to for all variants for their respective times). For example, starting at sea level at 250 mph with 14.100lbs gross weight and applying COMBAT power the P-38L's linear acceleration was 4.13 ft/s^2 (1.26 m/s2), whereas the P-51D's linear acceleration was 3.85 ft/s2 (1.17 m/s^2) = (recalculated thrust) to weight ratio of 0.3184. The jet modification will help to improve this outstanding rate by close to 20%, giving a linear acceleration of 4.92 ft/s^2 (1.5 m/s^2) at 16.200 lbs gross weight = thrust to weight ratio of 0.3791. It´s unpredecented acceleration is estimated to be second only to the Me-163 (substantially outaccelerating Me-262, Ar-234, He-162, P-80 and Meteor III!).

E. TOP SPEED:
At sea level, the 36.7% power increase would translate into ~9% more speed or about 382 mp/h (615 Km/h) at sea level applying full power (jet engine) and pushing 70" HG using 44-1 fuel (piston engine setting). The best speed is expected to be 452 mp/h /728 Km/h) at around 18.000 - 20.000ft (this figure is already corrected for the increased parasite drag). This figure is surprisingly 39 mp/h better than the contemporary Bell P-59 Airacobra and 37mp/h better than the contemporary Meteor-I using an almost identic jet engine type, even the improved Meteor-III under investigation in the UK is not expected to exceed 455-475 mp/h at best altitudes (short nacelles version). This would make the P-38 modification one of the fastest allied Fighter of ww2. It should be noted that the comparably low limiting Mach number (0.69) is not affected by the modification and caution must be made not to exceed this speed at altitudes. 

F. MANEUVERABILITY:
The increased wing loading results in trade offs with maneuverability. Roll rate nevertheless is excellent at high speeds due to hydraulic boost. All other figures are slightly under the serial P-38J maneuverability.

G. CRUISE AND RANGE:
Endurance and Range are widely dependant on altitude. The specific fuel consumption of the J31 jet engine is worst at sea level and excellent at high altitudes. Full power endurance is estimated to be 45 minutes on internal fuel only at medium altitude. The most economic range is expected to be about 1850 mls. at 25.000ft. and 230 mp/h cruise speed with two 300 gallons drop tanks.
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Altough not as perfect as possible, such a modification would give the USAAF a reliable jet Fighter with excellent performances and outstanding range (for a jet driven plane) for rather minor modifications. The resulting P-38 could be produced and deployed in larger numbers than either the P-80 or Meteor and pilots were already familar with the behavior of the airframe. 

Instead of redrawing the P-38 from europe the USAAF could reequip some squadrons with this plane in late 44 (a realistic timeframe) and use the fighter in capacities like V-1 hunting, long range (high altitude) recon and medium altitude air superiority fighter.


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## FLYBOYJ (Aug 9, 2007)

The wing, nose section and stabilizer tips of the P-38 were used on the P-80. Close enough?


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## ccheese (Aug 9, 2007)

Didn't the P-38 have compressability problems in a steep dive ? How would
a jet driven P-38 manage this ?

Charles


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## Graeme (Aug 9, 2007)

delcyros said:


> > I wonder why the Lockheed company never considered mounting an early jet engine centrally into the P-38 fuselage.



I suspect that men like Hall Hibbard and Kelly Johnson were always thinking ahead, and a composite powered aircraft wouldn't be the 'Lockheed way'.

Pictured is Hall Hibbard with a model of the Lockheed Model 133, the precursor to the P-80 that was designed around Lockheed's L-1000 jet engine.


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## FLYBOYJ (Aug 9, 2007)

The P-80 used the model 133s wings...


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## Graeme (Aug 9, 2007)

This is what Bell was working on before the P-80 was eventually selected. A single engine version of the Bell P-59, the XP-59B. A jet powered Airacobra of sorts, with air intakes in the wing roots and jetpipe emerging under the tail. Looks sad compared to Lockheed's design/s.


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## evangilder (Aug 9, 2007)

The P-59 was woefully underpowered in any of it's configurations, unfortunately. I don't think just slapping jet engines on a P-38 would be a wise decision. As Charles brought up, the compressibility problem would be made worse at higher speeds. It would have required more engineering than building a new airplane, which is what they did.

While the P-59 was a disappointment in speed and general performance, it did pave the way for other jets that would soon start to appear.


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## drgondog (Aug 9, 2007)

evangilder said:


> The P-59 was woefully underpowered in any of it's configurations, unfortunately. I don't think just slapping jet engines on a P-38 would be a wise decision. As Charles brought up, the compressibility problem would be made worse at higher speeds. It would have required more engineering than building a new airplane, which is what they did.
> 
> While the P-59 was a disappointment in speed and general performance, it did pave the way for other jets that would soon start to appear.



I believe you are absolutely correct.. without a drastic redesign of the P-38, the issues of flow separation on the fuselage creating the wake over the horizontal stabilizer, added to provisioning the 38 for jet engines, doesn't suggest dramatic improvement in high altitude performance (except maybe ceiling and climb near service ceiling) but does imply less range

- if true why screw with jet engines to create an aircraft with marginally better (but distinctly better) low to medium altitude performance with much less range when the P-80 (and Me262) were already better?

The P-82 was probably as good as the 38 for long range escort but thankfully we never had to test that thesis as neither one could handle a MiG (or a 262).


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## delcyros (Aug 9, 2007)

> Cheese wrote: Didn't the P-38 have compressability problems in a steep dive ? How would
> a jet driven P-38 manage this ?



A jet driven P-38 would still suffer from the same problem, which also affected all other ww2 planes and USAAF planes up to including early F-84 models. The serial P-38 had dive breaks which adressed parts of the problem, so that the dive speed remained under the critical speed. Neither fast ww2 plane could dive without encountering serious compressibility buffeting. The problem with the P-38 is that it happens sooner than on other designs and convincibly, the Me-262 could outdive the P-38 as it experienced the same issues at a significantly higher speed, altough that was unknown in the US by then. 



> Graeme wrote: I suspect that men like Hall Hibbard and Kelly Johnson were always thinking ahead, and a composite powered aircraft wouldn't be the 'Lockheed way'.



I share this estimation. It is an explenation how it didn´t came off. The proposed P-38 mix, while strictly hypothetic, uses 1942-43 US technology and therefore is contemporary with the L1000 and M133, but while the P-38 is a reasonable (say realistic) suggestion, the sophisticated 133 airframe and the advanced L1000 engine were dead end developments, which never had a chance to materialize, altough the project contributed to the succeeeding P-80 design in several aspects, notably the wings. 



> Evanglider wrote: The P-59 was woefully underpowered in any of it's configurations, unfortunately. I don't think just slapping jet engines on a P-38 would be a wise decision. As Charles brought up, the compressibility problem would be made worse at higher speeds. It would have required more engineering than building a new airplane, which is what they did.
> 
> While the P-59 was a disappointment in speed and general performance, it did pave the way for other jets that would soon start to appear.



I am confident that this never have been shown to be the case. The P-59 was slow, true, but it definetely was not underpowered. There was more power (in thrust) relative to each single ft^2 area or lbs weight than either the Me-262 or the P-80 had. Acceleration and powerload was excellent. The slow speed is a direct result of unfortunate aerodynamics, most notably the very thick wing and drag sensitive large area of fuselage and wings. 

As I showed above, the P-38 mix is based on very early jet engine technology , avaiable to the US. If the P-38 mix would have flown against the P-59, it´s superior performance may have saved the day. While the P-59 was not selected, the P-38mix gives performances mostly equal to or better than the UK Gloster Meteor III, which uses more recent stages of jet technology. 
Applying thinner propellors to the P-38 (say P-38L like) and more potent jet engines (say GE J33) is not impossible, there at least is some window for limited further development (~500 mp/h top speed at lower altitudes are not impossible at all using late ww2 technologies). Unlike complete new designs, such as the Meteor, Vampire, P-80 and the P-59, the required new tooling processes were limited and a substantial number of planes could be build in the timeframe in question. The pilots did not need a major training on new types and the testing program could have been shortened due to the known properties of the P-38.



> drgondog wrote: - if true why screw with jet engines to create an aircraft with marginally better (but distinctly better) low to medium altitude performance with much less range when the P-80 (and Me262) were already better?



Neither the Me-262 nor the P-80 are avaiable in the timeframe in question. Both will eventually turn out to be better all around jet planes, enjoing a higher top speed and critical Mach speed altough both having some points of tactical inferiority against the P-38: service ceiling, acceleration, range, climb rate and possibly reliability and avaiability in numbers, too. A good range particularely was no keysign for first generation jets (P-80A-late: 1440 mls., P-59B: 950 mls., Meteor-III: 1340mls max. with ventral tank, Vampire MK I: 330 mls., Vampire MK-III: 550 mls., XP-83: 1730 mls.) and the P-38 with a best range of 1850 mls. actually fullfills the 1943 US specification requirements for a long range escort fighter, despite using the early jet engine.
I would put forward time as the reason why such a modification should be considered. Not only would this give the US a more reasonable jet fighter than was the P-59 but it would also give the USAAF total technical superiority over the Luftwaffe in 1944.

One of the more serious shortcomings of early jet engines was the design of the air intake and exhoust pipes. The loss of static thrust caused by long air pipes (P-80, P-84) was up to 8% but could be lowered to 5-6% if properly adressed. Hence the move to gondolas (B-47), even if they add parasite drag. I find the layout of the P-38 allows this to be largely bypassed as the jet engine can be installed into the central fuselage section without exhoust pipes and extremely short intake pipes, indeed. I have been unable to find this detail in other prop-jet mix planes so easily.

best regards thanks for Your comments,
delc


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## Graeme (Aug 9, 2007)




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## evangilder (Aug 9, 2007)

Where on earth did you get the idea that the acceleration on the Aircomet was excellent?

You may want to take a read at this:
Bell P-59 Airacomet

And again, you are talking about drastic changes to the P-38's airframe. You will add weight and drag by adding the engine and will likely have an effect on the overall performance. Lockheed did the right thing by developing a new airframe to go with the powerplant.


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## delcyros (Aug 10, 2007)

Compare the thrust to weight ratio of ww2 jets. The XP-59 is superior to the P-80, Meteor I and III, Me-262 and He-162 and almost as good as the Me-163 (depending on load). This is more than enough justification to disproove that the P-59 was underpowered. It´s only when both are nearing the P-59´s top speed when the remaining acceleration of the P-80 is better than the P-59s.
Physics remains validate for everything unless one is the pope and orders Newton to be burned  !
Neither does Your link contradict this. There is nothing to be read regarding a bad acceleration but spool up time (something pretty different). It´s the top speed and take off run was to be critisized, not the acceleration once full power was developed by the engines.

The P-59B had a thrust of 4.000 lbs and a weight of around 11.000lbs. The P-80a had a thrust of 3.850 lbs and a weight of 11.700 lbs.

I don´t think that Lockheed did something wrong with the P-80. I proposed the P-38 mix as a replacement for the 1941-1944 P-59 not the subsequent P-80a 1943-1946 design. A reasonable estimation for prototype stage is late 42 and for serial production start is nov. 1943. From a strategic point of view, the P-38 mix could be deployed in numbers about contemporary to or instead of the P-51B in europe (at around may 44) as a long range escort or interceptor.

A tradeoff exists in the delayed development of the P-80. However, this does not seem bad to me as A) the P-80 still was in testing stage at wars end and B) I could imagine that the P-80 benefits from additional developmental time.

[edit] thanks Graeme for the P-59 successor picture. It´s the first time I see a pic from the single engined P-59 derivate.


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## delcyros (Aug 10, 2007)

I have spent some minutes retoushing a P-38 bmp into how I think the P-38(i) could look like.

While the appearence is quite different, You see that the modifications are limited. The booms with engines and the complete landing gear as well as the nose and cockpit section, the outer wing section and the tail section can remain identic. The midwing section and the rear and mid fuselage needs to be of a new design. Since the cockpit is moved more forwardly, the mid wing buncerage can be improved in the way I suggested, without drawing an entirely new wing.

I suspect that the weapons arrangement get´s a bit cramped in this appearence, so perhaps it´s better to adopt a normal, long nose version instead?

As pointed out above, this is purely hypothetical. -


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## evangilder (Aug 10, 2007)

Read it again. _The RAF test pilots found the aircraft to be *badly underpowered*, with an unacceptably-long takeoff run. Like all other early jet-powered fighters, the Airacomet suffered from *very poor engine acceleration*._

You can true to puff up the P-59, but the fact of the matter was that the aircraft was a turd, plain and simple. 

You need to look at a cutaway drawing of the P-38 before you start moving parts of the airframe around. You do realize that their are very few open spaces in that airplane, right? Moving the cockpit forward moved it right into the cannon ammunition drum. The air intakes for the jet engine happen to sit right where the nose wheel retracts, plus it is dangerously close to the spent ammo chutes. And now that you have moved the cockpit forward, all of the control cables will need to be rerouted and extended.

Again, more engineering than it's worth. Better to spend the energy on a new airframe around the new engine than to re-engineer an existing design around an engine.


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## delcyros (Aug 10, 2007)

Sorry but engine acceleration is spool up time and this has nothing to do with the airframe of the Bell P-59 but all to do with the jet engine (put the same engine in another plane and You get the same result). Underpowered is unjustified as the two jet engines deliver more than enough thrust compared to the weight of the plane. You have not showed that the opposite is the case, I had hoped You would reflect test pilot accounts of the very time with high performance piston planes and new jet planes with more caution.

You may blame the 1942 jet engine for this, but later mods of the same engine had an improved spool up time, negating Your argument.


Engine acceleration is not acceleration of the plane. I have showed this with powerload figures and thrust to weight figures. While the engine acceleration (spool up time) of new jet engines (not only this one) was indeed worser than -what the RAF test pilots experienced- f.e. high performance piston fighters, the acceleration of the plane itselfe, once full power was delivered by the turbojet was simply superior. 
Galland wrote that the Me-262 due to the poor engine spool up time needed more "acceleration ellbows" than piston fighters - exactly what the RAF testpilots describe. One side is better described as rapidly applied power (in piston A/C of this time) while the jets had slowly applied power. This is not to misinterprete as acceleration because max. acceleration is measured when full power is applied, already. How badly underpowered would be the vaunted Me-262 or even worser: the Ar-234B in Your eyes! It´s two Jumo-004 B3 jet engines delivered only 3.923 lbs of thrust (with B4 engines up to 1960 lbs) while the plane itselfe weighted ~18.000 lbs compared to the "featherweighted" ~11.000lbs P-59B (which had 4000 lbs thrust avaiable). If You insist to say the P-59 was underpowered than I have to remind You that all ww2 jet planes were underpowered and all even to a larger degree than the P-59! 

Your repeated equaling engine acceleration with linear acceleration and use of unreflected texts, while neglecting physics here shows that You have a particularely poor understanding of the matter. Test pilots which tested 1st generation jets never were impressed by stand off acceleration performance after having experienced advanced piston A/C´s - no wonder! What they were impressed of is acceleration at high speed (preferably well above the performance envelope of piston A/C), something the P-59 never was able to show as it had only comparable fight envelopes to piston fighters. Under full power, the P-59 had the potential to outaccelerate all contemporary US/UK and german piston or jet A/C, at least at 250 mp/h. It was not until the Meteor-IV that a plane experienced better acceleration.

The latter part of Your post can be confirmed with my estimations. I have already expressed my doubts that the nose config get´s to cramped. However, it is entirely feasable (altough this forces me to redo the bmp). The normal nose cockpit section is moved forward around 2 ft. This leaves the normal space for nose gear, ammo boxes, cockpit and weaponry. The midwing section with the modifed tankage assembly, a new rear fuselage containing the J31 + side air intakes (external, they do not interfere with the landing gear) are the only new parts next to minor changes in the electric systems. Altough the nose section is moved forward, the cg changes are countered with the jet engine itselfe.

It just has been an idea, nothing to upset us. I could imagine that this layout combines the advantages of piston A/C (rapid applied power) with some of the jet advantages (low weight for power). Another aspect comes to mind: While Jets were expected to have a generally higher performance envelope than piston A/C (and equal performance was considered unstatifying = P59 and He-178 ), all nations regarded the rather shortliving mix A/C as beeing intermediary. Used in such a capacity, the P-38mix is very attractive, proposing a plane with the performance envelope beeing better than the F7 Tigercat but avaiable 1 year earlier...


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## evangilder (Aug 10, 2007)

You are assuming that RAF test pilots only flew the P-59 after flying only piston fighters. Since the Brits were quite ahead of the US in jet aircraft development, I am sure that the comparisons were against the Meteor. I understand how acceleration and spool up time work. It doesn't change the fact that the P-59 was a big disappointment, period.


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## SoD Stitch (Aug 10, 2007)

Good idea, but you used the wrong airframe . . . the XP-58 Chain Lightning would've been a better candidate for a jet engine installation. Basically an enlarged P-38 with more powerful engines (Allison V-3420's), more airframe room to work with, and a lot more fuel onboard (2,000 gals.+). Initial tests with the aircraft weren't exactly successful, mainly due to the tempermental engines (another Allison trademark), but the airframe had a lot of room for development, including room for installing a jet engine in the rear of the centrally-mounted fuselage.


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## FLYBOYJ (Aug 10, 2007)

Agree.....


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## johnbr (Aug 10, 2007)

Or how about a pair of 3000shp turbine.


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## SoD Stitch (Aug 10, 2007)

johnbr said:


> Or how about a pair of 3000shp turbine.



Yeah, if they'd had turboprops in '45, which they didn't. 

Jet turbine technology was in it's infancy as that time; as it was, it was difficult enough to get a jet turbine to operate reliably without trying to bolt on an output shaft to the compressor section, and add a bunch of other stuff (accessory drives, etc.) to an otherwise complicated (for 1945) piece of technology. They had enough trouble with just the engine by itself, let alone an output shaft, harmonic balancers, etc.


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## Graeme (Aug 10, 2007)

delcyros said:


> It just has been an idea, nothing to upset us.



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).


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## SoD Stitch (Aug 11, 2007)

Graeme said:


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



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.


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## delcyros (Aug 11, 2007)

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.


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## Graeme (Aug 11, 2007)

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.



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.



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.


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## evangilder (Aug 11, 2007)

Graeme, there was a short-lived program for a float-plane P-38 for ferrying. From my P-38 presentation notes:


> One interesting E model was equipped with floats for ferrying across the Pacific, which would be later removed for combat operations. The challenge for using floats was that the tail needed to be out of the spray. One of these aircraft had the tail booms lengthened and raised 3 feet! An observer/engineer seat was added behind the pilot, replacing some of the radios. Developments in the Pacific proved that the Navy could deliver the aircraft to their locations and further floatplane development stopped.


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## evangilder (Aug 11, 2007)

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?


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## delcyros (Aug 12, 2007)

> 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:



> The P-59 was disappointing, the P-80 was the better plane, hands down, but she never had a realistic chance to get deployed in action for ww2 and was on the edge to be obsolete in action over Korea.
> The Meteor was a somehow inferior airframe up Mk-III and was to late to see extensive use in ww2 outside the V-1 hunting and ground attack role, the Vampire MK I would be to short legged to be of any use. All these jet´s required very long testing to work out teething problems, effectively preventing their effective deployment.



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.


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## drgondog (Aug 12, 2007)

delcyros said:


> "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.



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..


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## delcyros (Aug 12, 2007)

> 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


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## delcyros (Aug 12, 2007)

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.


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## Graeme (Aug 12, 2007)

delcyros said:


> It seems the idea was not unpopular.



But not very successful.




delcyros said:


> BTW- has anyone a detailed drawing of the sections in question (midwing section and more importantly the center fuselage gondola)?



This may help.


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## SoD Stitch (Aug 12, 2007)

Graeme said:


> From *SoD Stitch*I have very little on Lockheed's P-38 floatplane, do you have more on it?



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.


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## delcyros (Aug 14, 2007)

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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## Graeme (Aug 14, 2007)

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?



Can cutaways be drawn to scale? (isometric?).


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## kool kitty89 (Sep 4, 2007)

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."


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## kool kitty89 (Sep 15, 2007)

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.


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## delcyros (Sep 15, 2007)

kool kitty89 said:


> 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.



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



kool kitty89 said:


> 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.


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.



Yes, a highly fascinating topic, my friend!


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## kool kitty89 (Sep 16, 2007)

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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## FLYBOYJ (Sep 18, 2007)

kool kitty89 said:


> 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.


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.


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## kool kitty89 (Sep 19, 2007)

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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## Soundbreaker Welch? (Sep 20, 2007)

A P-38 called the Black Pearl? 

Kilroy Jack Sparrow wasn't around in WWII. <[:{0


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## FLYBOYJ (Sep 20, 2007)

kool kitty89 said:


> 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?


The P-80 used the L133's wing - the P-80 also used the *wingtips* from the P-38 as well as the nose (although it was turned upside down)


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## kool kitty89 (Sep 20, 2007)

Oh, thanks for the clarification.
Still, does anyone have coments on the impoved compressibillity and buffeting characteristics of the later models I mentioned a few posts back?


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## kool kitty89 (Oct 3, 2007)

I know we've reasoned-out all the reasons of why the P-38 was not converted to jet propultion but here's a website full of alternate configurations of the Lightning just for fun: Translated version of http://www.kristofmeunier.fr/


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## Civettone (Oct 4, 2007)

Impressive site, what an imagination and effort this guy put in! Some of his designs are really fantastic. 

Kris


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## kool kitty89 (Oct 4, 2007)

And based on some of them a configuration of jet engines slung under the booms looks feasible, and it might have been useful as such as an intrim measure for the P-80, though fuel load might still be insuficent.

GE J-31 engines could be used as there were a surplus after the Airacomet was canceled, and from the figures I've seen several hundred J-31 engines were produced (around 300 from what I remember) and with less than 60 production Airacomets this would have left a good amount of spare engines.

With the late model J-31 producing 2000 lbf thrust each this would give a decent thrust-to-weight ratio. Assuming you subtract the diference beween the conventional engines an coresponding equipment (radiators turbochargers, etc), which were, with both engines, over 4000 lbs (compared to the J-31 with only 850lbs each) this would bring the empty weight down to about 10,000 lbs, so a respectable loaded weight would be around 15000 lbs. This would give a thrust/weight of 0.27 which is decent, considdering the Me 262's was 0.28 (it compensated with its good aerodynamics). Assuming max weight is arround 17,000 lbs the thrust/weight would still be over 0.20. But drop-tanks would be a must to provide adequit range, but as said before most of the high-speed problems with the P-38 had been remeded and such a plane wouldn't be going much more than 500mph aniway.

If mounting the jet-engines under the booms, it would be necessary to angle the jet exaust pipes slightly outward as to eliminate jet-wash on the tail-section.

The P-38 also had a better ammo capacity than the P-80, especially in early models.


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## Hop (Oct 5, 2007)

> 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.



I wouldn't rely on Wikipedia too much. The P-38 was restricted to 460 TAS at 20,000 ft, 440 TAS at 30,000 ft. The manual notes that these speeds could be exceeded by 20 mph if the dive recovery flaps were deployed.

That's a pretty low limit for a jet fighter. The ME 262 or Meteor III could exceed that in level flight, let alone a dive.


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## kool kitty89 (Oct 5, 2007)

I'll agree with that, though there were many better alernateves to the P-38 airframe and the XP-80 was already in the works in 1943 so redesigning the Lightning was pointless. Also the F-84 Thunderjet was originally designed around the Thunderbolt airframe, though in the end it shared few, though some similarities. 

Also what units are those TAS measurements in?

It's too bad Bell didn't modify the wings of the P-59 as they were the main problem. Even without altering the thickness the wings could have bees shortened by 2ft each (preferably at the roots) bringing the span down to 41ft. This would inprove roll rate, maneuverabillity, and decrease drag (increasing top-speed). Shortened wings would decrease glide capability, but this was only useful for testing unreliable engines. They would also lessen float on landing. The shortened flaps could be redesigned to double as airbrakes, further improving landing and controll characteristics. The thick wings could have also been used to hold fuel, which I dont think was ever done.

Without the wing modifications, the P-59 had a very high flight ceiling (over 46,000 ft) and could have made a good high altitude recon plane, though the poor visibility through the canopy would be a drawback. Mayby it could have performed Photo recon. 

A P-59B converted for high-altitude recon could have prooved to be symilar, if somewhat inferrior, to the Ar-234B (in recon configuration) though I think the P-59 had better low altitude performance (especially in terms of fuel consumption).
The P-59 also had a better offensive armament, though with only 200 rounds in each of its 3x .50 caliber guns gave it only ~10 sec of firing time (same as the P-80A but with half the firepower). It also had a 37mm M4 cannon, but with only 44 rounds and a rof of only 150 rpm it had limited usefulness. The overall armament was sumilar to Bell's P-39 and P-63, though their firepower was suplimented by underwung gun pods (a total of 4 .50 cal guns), their guns had slightly more ammo, while the cannon generally had less.

It also had a decent bomb/rocket load of 2x 1000lb bombs or 8x 60lb rockets, though I'm not sure these could be carried with the drop tanks but I think they could. With drop tanks the P-59B had a respectable range of 950 miles, but without the droptanks the range was less than 500 miles, limiting its usefulness as a fighter-bomber.


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## kool kitty89 (Oct 31, 2007)

Is the TAS in mph or knots?


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## Hop (Oct 31, 2007)

Sorry, missed the question first time. MPH.


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