USA: P-38, P-39, P-40, P-47 (and P-51)

[gjs238]

Did the US spread its resources too thin on four (five including the P-51) fighters?
Should the US have concentrated resources on one or two, rather than four/five?

The P-51 probably fits into this equation as well.
The P-51 probably could have have accomplished the work of all four/five.

PS: I'm thinking pre Pearl Harbor decision making.
Not re-jiggering things around later.

 

[fubar57]

I know nothing of the numbers (climb, dive rate, hp., etc) but I think it was a case of make do with what you had at the time. The -39 and -40 were all the U.S. had until the -47. The -38 was great in the Pacific because of the vast water expanses and that secure feeling the pilots had with the spare engine, The -47 was and is good fighter until the -51 came along and then it became the U.S. ground pounder as well. This is just my opinion and those who know the numbers will be along shortly.

Geo

 

[tomo pauk]

Timing should explain a lot. The P-40 was initially a P-36 airframe with V-12 engine as a retrofit, similar what Italians did later. It helped to timely solve the US problem of not having decent fighters in production and service, with other powers having a headstart due to the preparations to the war (or a commitment in a war).
The P-39 was the 'next gen' fighter, that was to sport a big firepower, along with great altitude performance. The later part didn't pan out, the installation of the turbo was bugged, the drag was too big, so the Bell company was suggested (told?) to ditch the turbo, do some rearranging so the USAF can have a new timely strea of 'good enough fighters, rather than to wait several years for might-have-been turbo P-39s.
The P-38 was of the same generation with P-39, it's turbo installation was far more streamlined affair (tough with it's own caveats), hence the performance was good. The on-board fuel % was less affected once the s-s tanks were added, the big drop tanks provided another boost of usability that it took years for other US fighters to match.
P-47 was partially an insurance against the V-1710 being a flop (Packard Merlin partially served the same purpose) - all previous 'new' US fighters were based around the Allison.
The P-51 came out of a blue, the story is well known, and initially it did not offered anything to the USAF, at least they though it. The capability to accept the 2-stage Merlin (along with other advantages over existing fighters) quickly moved the P-51 in priority list, with new Merlin to be produced also by Packard.

 

[Shortround6]

Tomo has pretty well covered it.

It takes several years to go from even prototype to widespread squadron service.

The P-47 was ordered off the drawing board in in Sept of 1940. First prototype flew May 6th 1941, first production example is finished Dec 21st 1941. Curtiss is building 250-285 P-40s a month in the fall of 1941, Bell is building 128-198 a month and Lockheed is is getting going with 128 built in Nov-Dec. NA builds 138 Mustangs in in 1941.

Republic takes a while to sort out the P-47 and gets up to 61 a month in Aug of 1942 up form 38 in July. Curtiss is having an off month (change in production models?)only 143 but comes back with 416 in Sept, they had been making over 340 a month in March, April and May. Bell has a good month in Aug and builds 309 P-39s. another change over month in Sept sees none followed by 3 in Oct and then 268 in Nov. Aug was a bad month for P38s with just 80 built after 170 in July and 132 in Sept. Aug sees Mustang production falling off as the switch is made to A-36 production.

1942 production totals are:
P-38.....1479 planes
P-39.....1932 planes
P-40.....3854 planes
P-47......532 planes
P-51......634 planes but does not include A-36s. All but a few experimental aircraft have Allison engines.

Giving up on the P-47 and P-51 and trying to upgrade the P-39 and P-40 would have been flogging already dead horses by the time you get to 1943. NOT building P-39s and P-40s in 1941-42 and some of 1943 leaves with not enough planes to cover the areas of combat you are involved in. Late production P-39s and P-40s were pretty much lend lease aircraft.

 

[GrauGeist]

And like in another thread, removing any of these aircraft would have caused a huge imbalance in the historical timeline.

The aircraft the U.S. had at the onset of it's involvement helped to hold the enemy in check until the new/improved fighters could get into service, like the F4F and P-40, for example. Without them, there was nothing the U.S. had in it's inventory that could at least challenge the Japanese on relatively equal terms.

The P-40 was able to provide a force of resistance against German and Italian fighters in the MTO until more capable fighters could be brought to the theater to challenge the Axis.

The P-39 (and P-400) did add to the fight in the Pacific, in spite of it's short-comings and later went on to serve the Russians well in the Eastern war.

The problem with trying to evaluate and make decisions before the war is impossible, as they didn't have a crystal ball to see how these designs would hold up against the enemy under various combat conditions. It was only after first blood was drawn, were they able to get a clearer picture of how to get a better design to overcome the enemy's aircraft...

 

[drgondog]

In my opinion the choice you are asking is whether one or more should not have been developed.

I would say all needed to be developed as we should not have put all future capability to change mission with an airframe that looked great based on aerial warfare concepts in 1939 but prove to be inadequate in 1943.

Our enemies never developed the heavy bomber strategic capability that both the P-47 and P-38 were designed to intercept. The Mustang was overlooked by the AAF until spring 1942 and was modified into a great escort fighter with escort range deemed impossible in 1941 when we went to war.

The P-40 was an adequate fighter on all theatres and available in numbers to bride the combat introduction of both the P-47 and P-38 but had to be kept in front deployment until the production numbers enable replacement of both the P-40 and P-39 starting in mid 1943.

The timeline for the P-47, P-51 and P-38 was within months of entry date had the AAF killed the P-39 and P-40 before Pearl harbor which would not been a very good idea

 

[gjs238]

OK, there's a lot here, let's pick one for now...

The P-39 was the 'next gen' fighter, that was to sport a big firepower, along with great altitude performance. The later part didn't pan out, the installation of the turbo was bugged, the drag was too big, so the Bell company was suggested (told?) to ditch the turbo, do some rearranging so the USAF can have a new timely strea of 'good enough fighters, rather than to wait several years for might-have-been turbo P-39s.

At this point, what if the Bell company is told - this thing bites...
Make licensed P-40's, P-38's, P-51's, etc.

 

[GrauGeist]

OK, there's a lot here, let's pick one for now...
At this point, what if the Bell company is told - this thing bites...
Make licensed P-40's, P-38's, P-51's, etc.

Without the P-39, U.S. forces may have lost Henderson field to the Japanese, who were determined to take it back. The fierce ground attack by the P-39 gave U.S. ground forces the edge they needed to hold their ground and force the Japanese back.

 

[gjs238]

Without the P-39, U.S. forces may have lost Henderson field to the Japanese, who were determined to take it back. The fierce ground attack by the P-39 gave U.S. ground forces the edge they needed to hold their ground and force the Japanese back.

Perhaps the US would have fared better with more P-40's.

 

[GrauGeist]

Perhaps the US would have fared better with more P-40's.

I honestly don't think that the P-40 could have replaced the P-39. The P-39 was a capable adversary to the Japanese fighters, like the A6M...it wasn't better, but it was well armored and could at least hold it's own in a fight AND the P-39 had the firepower to rip a KI-43 or A6M to shreds. The only shortcoming to the P-39 in early 1942, was that the Japanese had experinced pilots while the American pilots were green, yet the early encounters between the two were standoffs.

Like I mentioned earlier, the P-39 was able to perform ground attack against Japanese ground forces and naval units, like transports with a greater success than the P-40 was capable of.

Removing the P-39 would have left a large void in the timeline. Especially, for example, in the critical year of 1942 where the P-39 was making valuable contributions to a desperate situation. You would have to find well over 1,000 other types to fill that hole and hope they could deliver the same results...

 

[kool kitty89]

Did the US spread its resources too thin on four (five including the P-51) fighters?
Should the US have concentrated resources on one or two, rather than four/five?

The P-51 probably fits into this equation as well.
The P-51 probably could have have accomplished the work of all four/five.

Don't forget all the Navy fighters too: F2A, F4F. F4U, F6F, F8F. And of those, timeline and performance wise, the Corsair is more at home with the USAAF fighters. (or rather, it'd have an easier time fitting in as a front line Army fighter than Navy, as it did land based USMC -with some gains from omitting wing folding, tail hook, and other naval requirements)

Granted, the army's fixation (and inconsistent policies) on turbocharging and focus on their hyper engine project didn't help matters either. (had at least some impact on killing a turbo P-39, seems to have killed even prototypes of a turbo P-40 -follow on to the P-40 and less successful YP-37, and definitely crippled Allison's auxiliary supercharger development) Similar policies may have prevented potential Army interest in the Corsair as well. (I don't believe Vought ever approached the army with such a proposal, but I'm more posing the possibility of it being curtailed or rejected on similar grounds ... that and the P-47 ended up vindicating the utility of a turbocharger for high alt work; still the XF4U flew a full year earlier and had medium/high altitude performance better than any US fighter flying in 1940 other than the YP-38 -and had fewer development problems and greatly superior roll rate)

For Navy fighters, there's really no substitute for the F6F. (barring hypothetical -untested historically- wing modifications to the corsair, like slots to correct the tip-stall and related torque roll and spin issues -fixed slots would add drag, of course and slats are a much bigger engineering undertaking)

The F4U is also limited in engine availability, though Army interest (and funding) in that may have forced P&W to shift priorities and/or expand production capacity earlier on.

The P-39 was the 'next gen' fighter, that was to sport a big firepower, along with great altitude performance. The later part didn't pan out, the installation of the turbo was bugged, the drag was too big, so the Bell company was suggested (told?) to ditch the turbo, do some rearranging so the USAF can have a new timely strea of 'good enough fighters, rather than to wait several years for might-have-been turbo P-39s.

After the XP-39's heavy redesign, there were no further attempts in a tightly integrated turbo installation on the P-39 at all. (there were some dorsal 'saddle' pack modules tested that apparently weren't worth the low altitude performance loss and weight gain, but nothing akin to the turbo embedded in the belly as on the XP-39)

A bunch of aerodynamic problems with the basic airframe got addressed due to the XP-39 tests, and it wasn't the turbocharger but the intercooler installation that was the problematic portion of the system. (too much drag, poor location and not enough cooling capacity) That issue probably wouldn't be effectively solved without developing a water-air intercooler to replace the bulky air-to-air arrangement. (surface cooling as the P-38 did with the wing leading edges- method might have worked too, but probably would have the same vulnerability and inadequacy issues as the P-38, and with the engine placement on the P-39, ducting all the way to wing leading edges might not have been practical so using fusealage and possible wing/wing root )

The Production P-39s also had the entire oil and coolant radiator system embedded in the belly, so turbocharger placement would have to account for that as well.


From what I understand, turbocharger use ended up strictly limited by 1940 and proposals to use them on the P-39 and P-40 were denied by the USAAF while the P-38 and P-47 were the exceptions there. This does make some sense given the P-38 ended up near the top of the USAAF's priority of the pre-war fighters (P-37, P-38, P-39, P-40) with the P-39 and P-40 relegated more to stop gaps. That may have made more sense if not for the delays in volume production and service readiness of the P-38. --Granted, this same logic should have incited more interest in aux supercharger development by Allison, but contradictory bureaucratic issues and misplaced spending allocation among other things might explain that. (that goes for both funds allocated by congress AND allocation/interest on the Army end of things as well -cases like the A-36 is a more obvious example of the Army wanting the plane but having to find workarounds for securing funds from congress)

I may be mistaken here, but it seems the US Army was more interested in big, powerful, potent heavy fighters than most other air forces, with less concern on production cost. (which did have some reason to it as I've argued for the cost to performance benefits for the P-38 vs P-40 and P-39 -including pilot survivability; the P-47 would obviously have major advantages there too; honestly it's similar arguments to those I've posed for the Fw 187's value vs the 109 ... and 110 and I suppose has some merit for B-17 vs B-18 as well)

The P-51 came out of a blue, the story is well known, and initially it did not offered anything to the USAF, at least they though it. The capability to accept the 2-stage Merlin (along with other advantages over existing fighters) quickly moved the P-51 in priority list, with new Merlin to be produced also by Packard.

The P-51 seems to have been solely held back by perception and bureaucratic issues. Compared to the P-39 and P-40 it had obvious value from the start in all around performance and range using the same engines. And the Army may not have shown excessive interest of funded the project when it was on the drawing board, but once the prototypes were flying, interest and production orders were pretty forthcoming. (going so far as to use the A-36 derivative to expand production beyond available 'fighter' allocation)

 

[Shortround6]

The turbo P-39 was trying to put a quart into a pint pot. (1000ml into 500ml bottle for our metric friends). The radiators and oil coolers on the original XP-39 didn't work worth spit and needed larger ducts, the original inter cooler was too small (way too small) and wouldn't come close to doing the job needed. Without over a dozen extra cubic feet of volume in the fuselage there just isn't enough room.

One can judge the likelihood of a turbo P-40 by looking at the XP-37, YP-37 and XP-60 fighter

The weight of the turbo is not a big problem. The Problem is the size of the intercooler and the size of the ducts needed to carry the intake air and the cooling air for the intercooler. It just won't fit without some major surgery.
The extra drag on the P-39 mock ups cost around 40mph below 15,000ft. A P-39 could outrun a Zero at low altitude rather easily. With the turbo the new P-39T or P-40T may be able to out run them at high altitude but they will loose the ability to out run them at low altitude.

I may be mistaken here, but it seems the US Army was more interested in big, powerful, potent heavy fighters than most other air forces, with less concern on production cost.

The US, even before 1939/40, was interested in fighters with longer range than European fighters, in part simply due to the size of the United States. Trying to move fighters with a range of 400-500 miles around the US to meet threats in different areas was a major headache. There is a tale about one P-40 squadron moving from the west coast to the east coast (If I remember right) that took about two weeks to get all its aircraft moved the entire distance. Between refueling stops, malfunctions and weather. The US policy (at least in the very late 30s) was to put the auxiliary or ferry tank inside the fuselage. Want to stick a 55 gallon drum in a Spitfire or 109 and see what it does to the fuselage size?

I an not saying it was a good idea or a bad one but there was more to it than simply saying the US liked big airplanes.

 

[kool kitty89]

Giving up on the P-47 and P-51 and trying to upgrade the P-39 and P-40 would have been flogging already dead horses by the time you get to 1943. NOT building P-39s and P-40s in 1941-42 and some of 1943 leaves with not enough planes to cover the areas of combat you are involved in. Late production P-39s and P-40s were pretty much lend lease aircraft.

Indeed, though the P-39 and P-40 themselves weren't really in a different class of design/engineering/airframe performance than the likes of the Spitfire or Bf 109. The difference being the RAF HAD no P-47 equivalent (or F4U equivalent -but that was more an engine than airframe issue given the R-2800 MADE the Corsair and Thunderbolt and might have made the Typhoon as well -or say Bristol Centaurus being serviceable at 2000 HP in 1941 with altitude performance on par with the F4U-1's engine).

The RAF might have had a P-38 if there'd been serious heavy support/interest in twin merlin engined heavy fighter/interceptors while Germany had the Fw 187 and later Fw 190 yet continued to pour resources into the Bf 109, 110, and Me 210/410.

In fact, compared to the Spitfire, Hurricane, and 109, the P-40 and P-39 both had some rather outstanding features like notably superior range and superior structural strength (at the expense of weight -as with all american fighters save maybe the F2A), lower drag in the P-39's case as well. (with any given engine performance, the P-39 seems to be the best interceptor of the bunch in terms of top speed and decent climb -higher weight being somewhat balanced by low drag) The P-39 also should have been a good candidate for the MK 108 and possibly even MK 103.

The P-39 is several years newer than the Spitfire or 109, and had NACA testing to help refine it, so drag improvements aren't that surprising. It's more of the same vintage as the Fw 190 though the latter is closer in size/weight to the P-36/P-40. The P-36/P-40 itself is a pretty well streamlined design for being the same age as the 109 and Hurricane, and slightly older than the Spitfire. Both the P-40 and P-39 also had better high-speed handling than the other aircraft and better all-around visibility (prior to the hooded spit) and the P-40 in particular had a slightly roomier cockpit and I believe a better heating system than the spitfire. (the P-36 also had a heater before the spitfire)

The fact of the matter is, though, that the USAAF had several superior options by 1942, so focusing on P-51, P-38, and P-47 production makes tons of sense. Without the P-51, a V-1650-3 powered P-40 might have become a staple of the USAAF. (particularly with Curtiss's attempted successors falling flat) The P-47 may have become the staple escort fighter for the ETO, and the reduced drag/weight and improved range/fuel efficiency of the P-47J may have put greater emphasis on getting that into service as well. (the lightened wing and streamlined cowling should have benefited the late P-47D production blocks too, ie even without the R-2800-57, the P-47J airframe should have supplanted P-47D production)

Honestly, even with the P-51 on the scene, the greater survivability, exceptional high-altitude performance, and comfortable cockpit (improved situational awareness) of the P-47D might have made it more worthwhile if it could be produced in enough numbers. (even aside from preserving the lives of american airmen, there's the cold logistical angle of having fewer aircraft downed, more ability to limp back to base on damage, and greater ability to develop highly skilled, experienced pilots before being captured or killed)

Both the P-47 and P-38 likely would have been of greater post-war value as well, particularly if the P-47J had entered production (or the P-47N had adopted the same nose) and displacing some of the need for the P-82 or P-51H to ever enter production. (including as a night fighter -build more P-38Ms and possibly finally introduce the P-38K's prop)

And yes, the P-47J and P-38K would both have been pushing closer to their critical mach limits than the P-51 ever did in level flight, but so long as they were fitted with dive recovery flaps this should have been acceptable. (aside from hypothetical wing modifications that never actually took place, namely wing root extensions akin to the Me 262 HG-I or slightly akin to the P-51's wing root -wing root extensions engineered to also include fuel tankage may have been a better alternative to the P-47N's wing as well, same goes for expanding P-38 fuel capacity) I'm also not suggesting they intentionally adopt swept/delta wing roots, but the standard streamlined inner wing extensions fillets tend to end up 'swept' by design and a straight taper is cheaper/easier to build than a more refined curve. (like on the XP-67) Thinner airfoil profiles increasing critical mach and high speed drag was more universally understood or at least more consistently inferred in the early 1940s.

I'd appreciate it if anyone with greater engineering knowledge could correct me on this, but modifying the leading (and possibly trailing) edges of the wing close to the root seems like one of the simpler modifications to improve critical mach number and reduce compressibility issues including turbulence ahead of the tailplane. (not including that caused by the tailplane's airfoil itself) If nothing else it seems like a more useful experiment than the laminar flow wing tested on the P-47

The timeline for the P-47, P-51 and P-38 was within months of entry date had the AAF killed the P-39 and P-40 before Pearl harbor which would not been a very good idea

Yes, and even in some alternate reality where the XP-38 never crashes and the entire program progresses a full year sooner (Lockheed tooling and production capacity expansion included), you at very least would want the P-40 in production though the C model until volume production of the P-38E/F could meet service demands (possibly along with supplemental un-turbocharged models -probably using F3R/F3L engines in place of similar engines being allocated to P-39D and P-40D/E production)

Changes less aerodynamic testing dependent aspects like a flight stick rather than yolk (potentially extended to aid with mechanical advantage for aileron operation), greater emphasis on cockpit heating/ventilation improvements (cool vent air for hot cockpit conditions would also be significant) and overall cockpit comfort improvements might have been possible to accomplish early on, independent of aerodynamic and structural issues. The same would apply to an increased twin-engine pilot training program. (especially efficient if the bulk of USAAF fighters are twins, let alone a single type)





All that said: with the historical P-38 development timeline, hypothetical P-38's using basically the same un-turbocharged engines couldn't displace the P-39 and P-40 prior to 1942. (or 1942 on the production line, perhaps 1943 in service)

I also forget for sure, but seem to recall that the direction of rotation on the V-1710 was easier to change on the production line (maybe in the field) than most contemporary designs, sort of going along with the modular nature of the design.


Merlins should still be allocated to P-51s as soon as they're available. (that includes the several thousand V-1650-1s that would otherwise go to P-40F/Ls -other V-1650-1s going to Hurricane/Lancaster production would be stuck with those unless British/Commonwealth allocation priorities changed)

 

[kool kitty89]

The weight of the turbo is not a big problem. The Problem is the size of the intercooler and the size of the ducts needed to carry the intake air and the cooling air for the intercooler. It just won't fit without some major surgery.
The extra drag on the P-39 mock ups cost around 40mph below 15,000ft. A P-39 could outrun a Zero at low altitude rather easily. With the turbo the new P-39T or P-40T may be able to out run them at high altitude but they will loose the ability to out run them at low altitude.

The P-39 'saddle' mount turbos seem far from the attractive option compared to more embedded arrangements, especially with a liquid intercooler. (short of that, it's not going to be practical without excess drag) Same goes for the P-40: you could certainly do better than the configuration on the YP-37, but short of a compact water-to-air intercooler the increase in drag is simply going to be too much.

For that matter, an aux supercharger stage on the V-1710 (even a side-mounted one avoiding a length increase) probably isn't going to much out-perform the V-1650-1 until water injection or an intercooler is introduced. Likewise, the 2-stage merlin would have been pretty well useless and a waste of weight/bulk over the Merlin 20 series without its intercooler. (the Merlin 46 probably would have gained a good deal of performance at all altitudes with the improved charge density an intercooler could offer -or water injection but I suppose the same would be true for the charge heating on the 9.6:1 supercharged V-1710)

For that matter, there is one other option for a turbo P-39 or P40: no intercooler at all, and water injection used for combat power with strict limits to manifold pressure/temperature at normal/cruise power. That does require development and testing of a water injection system, but the engineering overhead there might be less than that required of an effective air-water intercooler. (and in any case, appears to be what Allison themselves favored)

Aside from that, might it also have been possible to adopt a smaller turbocharger in combination with the 8.8 supercharger gearing? (especially if the GE turbos heated the charge more than allison superchargers, but minimizing the size/weight of the turbo itself would have some benefit either way)


It's not just the auxiliary supercharger stage that Allison's funding/engineering resources limited, but things like solving the problems with the supercharger gearing to allow the 9.6:1 ratio, addressing the bottlenecked intake manifold, and possibly eliminating the backfire screens sooner. Even with that little 9.5" impeller (and overall supercharger dimension constraints -to avoid redesigning the entire accessories section), overall improvements may have been possible to remain directly competitive with the single-stage, single-speed merlin contemporaries, or possibly even do a bit better if water injection had been added. 2 speeds would be nice, but managing performance on par with the Merlin 45/50 series alone would be pretty good for the time. Allison did experiment with different impeller and diffuser arrangements, but I'm not sure how much changed on any production engines. (supercharger performance from the V-1710-33 of the P-40B to V-1710-73 of the P-40M seemed pretty much identical)

 

[tomo pauk]

OK, there's a lot here, let's pick one for now...

At this point, what if the Bell company is told - this thing bites...
Make licensed P-40's, P-38's, P-51's, etc.

Bell producing the P-40 instead of P-39 does not add much IMO. The P-51 is too late, the 1st non-turbo XP-39B is delivered in Nov 1939; Bell producing P-51s instead the P-63s would've make plenty of sense, though. Bell produced 939 P-39s before 1942, vs. only 208 of P-38s by Lockheed in the same time, so we'd probably see a deficit of some 500+ US-produced fighters prior 1942 with Bell producing the P-38.

...
A bunch of aerodynamic problems with the basic airframe got addressed due to the XP-39 tests, and it wasn't the turbocharger but the intercooler installation that was the problematic portion of the system. (too much drag, poor location and not enough cooling capacity) That issue probably wouldn't be effectively solved without developing a water-air intercooler to replace the bulky air-to-air arrangement.

The turbocharger, along with 4 waste gates was a draggy affair, all sticking out in the slipstream. The intercoolers were without boundary layer separator, and without any means to control the cooling air passage - it means drag and low capacity for intercooling.

...
The P-39 is several years newer than the Spitfire or 109, and had NACA testing to help refine it, so drag improvements aren't that surprising. It's more of the same vintage as the Fw 190 though the latter is closer in size/weight to the P-36/P-40. The P-36/P-40 itself is a pretty well streamlined design for being the same age as the 109 and Hurricane, and slightly older than the Spitfire. Both the P-40 and P-39 also had better high-speed handling than the other aircraft and better all-around visibility (prior to the hooded spit) and the P-40 in particular had a slightly roomier cockpit and I believe a better heating system than the spitfire. (the P-36 also had a heater before the spitfire)

The Spitfire aged the best, when compared with P-40, P-39 and Bf 109. We can be sure that early Spitfire (I to V) would've been even better with earlier adoption of fully covered undercarriage, faired mirror, internal armored glass and early installation of 6 exhaust stacks per side. Not sure whether deletion of snow guard on the ram air intake would've be safe for all-weather operation, deleting it gives 8.5 mph on the Spit V.

 

[drgondog]

Kool Kitty wrote:

And yes, the P-47J and P-38K would both have been pushing closer to their critical mach limits than the P-51 ever did in level flight, but so long as they were fitted with dive recovery flaps this should have been acceptable. (aside from hypothetical wing modifications that never actually took place, namely wing root extensions akin to the Me 262 HG-I or slightly akin to the P-51's wing root -wing root extensions engineered to also include fuel tankage may have been a better alternative to the P-47N's wing as well, same goes for expanding P-38 fuel capacity) I'm also not suggesting they intentionally adopt swept/delta wing roots, but the standard streamlined inner wing extensions fillets tend to end up 'swept' by design and a straight taper is cheaper/easier to build than a more refined curve. (like on the XP-67) Thinner airfoil profiles increasing critical mach and high speed drag was more universally understood or at least more consistently inferred in the early 1940s.

There was not a clear understanding of boundary flow and separation behavior due to negative pressure gradients aft of a forming shock wave until very late in the war and far too late to alter existing designs.

The Only way to eliminate the earlier Mcrit for the P-38 would have been to replace the entire wing with a laminar flow wing similar to the P-51. That would have pushed the Mcr from ~.68 to perhaps .72 given a same T/C (the P-38 23018 was a couple of percent fatter and the a/c was at ~ .25C whereas the 45-100 was 16% and a/c was at ~.45C. The immediate nose down pitch phenomena would have been delayed until the full shock at ~45% Chord with complete separation behind it - which in turn would immerse the horizontal stab/elevator in the associated increase of turbulent wake and greatly diminish elevator authority.

I'd appreciate it if anyone with greater engineering knowledge could correct me on this, but modifying the leading (and possibly trailing) edges of the wing close to the root seems like one of the simpler modifications to improve critical mach number and reduce compressibility issues including turbulence ahead of the tailplane. (not including that caused by the tailplane's airfoil itself) If nothing else it seems like a more useful experiment than the laminar flow wing tested on the P-47

two ways at that time (in historical knowledge context) to delay Mcrit:
1.) decrease the T/C ratio either by deepening the cord of the wing while maintain the original max Thickness, or reducing the Max Thickness while retaining the existing plan form (i.e. replace the existing 23018 to 23016 if that derived same basic internal volume required for fuel and did not require extraordinary beefing up of the wing structure (i.e. Spar weight due to requiring greater bending resistance with shallower beam heighth.
2.) replace existing conventional airfoil with Laminar Flow type with Max T/C pushed back from .25 to . 40%+ Chord.


Something that always gets lost in 'what if' discussions of P-38K and P-47N/J is the extraordinary requirements to modify from P-38J (in cost) by adding a Rolls 1650-7 or the change in the wing; and the GW and cost of the redesign of the P-47N over the D - is that it took ALL the evolutions of both airframes to nearly match or slightly exceed (P47N/J to P-51D) of either the P-51D or P-51H if we keep model introduction in parallel - but ALL P-47s were approximately 1.5X in delivery cost plus 1.4-1.5X in operating cost and ALL P-38s were approximately 2X in delivery and 2X+ on Operating cost.

 

[kool kitty89]

Bell producing the P-40 instead of P-39 does not add much IMO. The P-51 is too late, the 1st non-turbo XP-39B is delivered in Nov 1939; Bell producing P-51s instead the P-63s would've make plenty of sense, though. Bell produced 939 P-39s before 1942, vs. only 208 of P-38s by Lockheed in the same time, so we'd probably see a deficit of some 500+ US-produced fighters prior 1942 with Bell producing the P-38.

With Bell producing P-38s (and no production P-39s/P-400s), IF they could get the tooling patterns in a timely manner, expecting exactly half the production volume of individual fighters would seem realistic. Overall monetary expenditure may have been somewhat less (P-38 was not quite 2x the cost of the P-39 at similar volumes, and omitting the turbo/intercooler systems should help) but overall man-hours, material, and especially engines would be major limiting factors. If they couldn't get the tooling set up quickly, it may have been somewhat worse than that.

Still, with only half the number it may have still been more worthwhile given the myriad of performance advantages for the P-38 over the P-39 (even assuming similar engines). Bell's experimentation with ejector exhaust and ram intake on the redesigned P-39 might have helped accelerate redesign of the P-38's cowling and exhaust stacks as well. (the 12 individual exhaust stacks per side in particular seems interesting, and while not all P-39s used it, the return on the P-63 says something about its usefulness)

The turbocharger, along with 4 waste gates was a draggy affair, all sticking out in the slipstream. The intercoolers were without boundary layer separator, and without any means to control the cooling air passage - it means drag and low capacity for intercooling.

You'd definitely want boundary layer separators, or similar overlapping ducting on the intercooler and any external radiators (like the P-38's tail radiators and the P-40's chin radiator) reducing turbulence and improving airflow over the radiator surfaces. (at least part of it relates to the venturi effect and has a good deal in common with NACA cowling and duct research, including those applied to thrust augmentation for rocket/jet exhaust)

The same could apply to the exposed hot section of the turbocharger, a duct shrouding that portion may have both aided cooling of the turbine/exhaust and reduced drag. (possibly improved jet thrust from the waste gates and turbine exhaust as well)

I'm actually surprised this wasn't tried on the P-38, including the P-38M where it would have hidden the exhaust glow at night. (or maybe it was tried and omitted from production for other reasons)

The Spitfire aged the best, when compared with P-40, P-39 and Bf 109. We can be sure that early Spitfire (I to V) would've been even better with earlier adoption of fully covered undercarriage, faired mirror, internal armored glass and early installation of 6 exhaust stacks per side. Not sure whether deletion of snow guard on the ram air intake would've be safe for all-weather operation, deleting it gives 8.5 mph on the Spit V.

The spitfire and 109 had the best consistently improving engine upgrades too, and the Americans had better options than the P-40 and P-39, so direct comparisons are a bit more difficult. The P-39 was substantially faster than its similarly powered counterparts, in spite of being heavier. (the P-39N and Q performed better than the Spitfire V in a number of areas in spite of their engines still not quite matching the Merlin 45 ... granted, the Spit IX was in production by that point)

The P-39 really could have needed that 9.6:1 supercharger gearing sooner even with the 1941 manifold pressure limits, that and using the hispano cannon as standard, working on improving the 20 mm ammunition capacity, introducing a re-cocking system to clear jams (like the P-38 -something facilitated by nose mounted guns and not practical in wings until the post-war M3 variant), and seriously consider deleting the wing guns, possibly in favor of additional small fuel cells but if nothing else just to save weight on those 4 M1919s and (up to) 4000 rounds of .30 cal ammunition. (if the cutaway diagrams I've seen are accurate, the outer wing gun bays appear to have significant space for added fuel tankage)
http://img525.imageshack.us/img525/2236/bellairacobrai1939airen.jpg

 

[kool kitty89]

The Only way to eliminate the earlier Mcrit for the P-38 would have been to replace the entire wing with a laminar flow wing similar to the P-51. That would have pushed the Mcr from ~.68 to perhaps .72 given a same T/C (the P-38 23018 was a couple of percent fatter and the a/c was at ~ .25C whereas the 45-100 was 16% and a/c was at ~.45C. The immediate nose down pitch phenomena would have been delayed until the full shock at ~45% Chord with complete separation behind it - which in turn would immerse the horizontal stab/elevator in the associated increase of turbulent wake and greatly diminish elevator authority. [/B]

I was under the impression that the reason the P-38 suffered critical mach issues at lower speeds than contemporary aircraft with similar or thicker airfoils of similar types (including the Corsair) related to the pod/boom arrangement leading to accelerated airflow along the root section of the wings (on top of being the thickest section of the wing), so modifying the airfoil profile there alone could have dramatically impacted initial onset of compressibility problems.

The Incomplete Guide to Airfoil Usage also lists the P-38 as using 23016 at the root, so is that another error on their part? (they seem to have a loose definition of 'root' as well, and seemed to start with the inboard wing section rather than the actual root on the F4U -listing 23015 rather than 23018 as it is at the oil cooler intakes)

1.) decrease the T/C ratio either by deepening the cord of the wing while maintain the original max Thickness, or reducing the Max Thickness while retaining the existing plan form (i.e. replace the existing 23018 to 23016 if that derived same basic internal volume required for fuel and did not require extraordinary beefing up of the wing structure (i.e. Spar weight due to requiring greater bending resistance with shallower beam heighth.
2.) replace existing conventional airfoil with Laminar Flow type with Max T/C pushed back from .25 to . 40%+ Chord.

#1 is mostly what I had in mind with the high degree of leading edge taper on the extension intended to avoid decreasing internal volume/strength without totally obliterating the pilot's forward-downward field of view. (the engine nacelles compromised that badly enough as it was) Any delta/sweep effect would have been incidental. (as would any wing fence effect of the nacelles)

That or combining 1 and 2, extending the chord and changing the airfoil shape, but minimize changes to the existing internal wing structure. (ie build out from the existing wing and manipulate the 23018 shape into something thinner and potentially smoother flow or lower lift/lower drag -aside from specific laminar flow designs, simpler symmetrical or near symmetrical NACA airfoils with little/no chamber should help as well -NACA 00xx series airfoils were fairly common pre-war with both the B-17 and P-39 using them -0018 and 0015 I believe)

Something that always gets lost in 'what if' discussions of P-38K and P-47N/J is the extraordinary requirements to modify from P-38J (in cost) by adding a Rolls 1650-7 or the change in the wing; and the GW and cost of the redesign of the P-47N over the D - is that it took ALL the evolutions of both airframes to nearly match or slightly exceed (P47N/J to P-51D) of either the P-51D or P-51H if we keep model introduction in parallel - but ALL P-47s were approximately 1.5X in delivery cost plus 1.4-1.5X in operating cost and ALL P-38s were approximately 2X in delivery and 2X+ on Operating cost.

The P-38K is the P-38J/L with modified nacelles accepting larger, broader chord propellers with slightly larger spinners. Improvements in take-of performance, acceleration, turn, and climb would have been more significant than top speed (akin to the P-47 switching to paddle props) but some gain in speed and increase in ceiling were experienced as well.

And as to the P-47, delays in production for shifting from the D model is valid as well, and I was mostly suggesting it be adopted in place of the P-47M and N (or adopting the J's cowling on the N). Mentioning using the late model D's engines in the J airframe was more a comment on the off change that production capacity for the J model ramped up more rapidly than expected and outstripped R-2800-57 production.


I was also more seriously alluding to their post-war use compared to the P-51H and P-82.


Edit: in terms of sheer all around performance and dogfighting ability, the P-47J (not M or N) would be the one to actually challenge the P-51. It was lighter than the P-47D and made the compromise of carrying 6 rather than 8 guns (though I believe still higher ammo capacity than the P-51) while using the more streamlined cowling and more powerful engine. Any gains in range over the production D models would have been from weight/drag reduction and not fuel capacity increase. (by extension, the introduction of the 200 gallon belly tub tank would have been even more useful and made more serous reason for omitting the performance hampering wing pylons -all improving fuel efficiency as well, though obviously not close to Mustang levels)

It did predate the transition to the bubble canopy, and as far as I know was never modified to such a configuration so performance impact is up to conjecture.

And in any case, yes, the Mustang would remain the best place to invest in using V-1650s and modifications adapting them to the P-38 would be rather wasteful and pointless.

 

[wuzak]

The P-38K is the P-38J/L with modified nacelles accepting larger, broader chord propellers with slightly larger spinners. Improvements in take-of performance, acceleration, turn, and climb would have been more significant than top speed (akin to the P-47 switching to paddle props) but some gain in speed and increase in ceiling were experienced as well.

The P-38K also used a V-1710 with a different reduction gear ratio, which apparently changed the thrust line, requiring the changes to the nacelles.

 

[Shortround6]

The same could apply to the exposed hot section of the turbocharger, a duct shrouding that portion may have both aided cooling of the turbine/exhaust and reduced drag. (possibly improved jet thrust from the waste gates and turbine exhaust as well)

I'm actually surprised this wasn't tried on the P-38, including the P-38M where it would have hidden the exhaust glow at night. (or maybe it was tried and omitted from production for other reasons)

The hot sections were exposed for a reason. Cooling of the turbine blades. It may not have been the most elegant way especially in way of streamlining put failed turbines tended to throw large (compared to bullets) around at high speed. Some American aircraft had steel scatter shields between the turbines and cockpits crew sections.
http://static.rcgroups.net/forums/a...196332-209-P-38 Turbocharger.jpg?d=1312733318

You have the drag of the installation vs the drag of teh ducts needed to bring cooling air to the turbine and back away form it again if the trubo is buried. Since at full boost the waste gate is closed and all the exhaust gas is exiting the turbo through the exposed turbine blades you also need a duct to get rid of the exhaust gases. The P-47 used a buried turbo and that is part of the reason it was so bulky, certainly not the only reason though.