Improve That Design: How Aircraft Could Have Been Made Better

[Zipper730]

I would note that a P-38J running on 44-1 fuel was allowed to run at 70in of MAP and could climb at over 4,000fpm just above sea level.

Yeah, I kind of remember seeing numbers in the 4000 fpm range on the World War II Aircraft Performance site.

Plane was bit of brick and maxed out at 419mph at 19,800ft.

While I remember hearing the intercooler produced more drag than before, I'm not sure exactly how much. I'd almost swear the 420 mph figure was based on an MP setting that wasn't the maximum and they could hit as much as 440 at higher settings, but there happened to be a degree of conservatism because the plane was flying very close to the point where it would start to run into significant compressibility effects if they nosed over.

Plane had the 20mm replaced by 5th .50 cal MG.

I never knew that...

Note: supercharger, not turbocharger. No high temp ducting back to an aft mounted turbo (a la P38 and P47), and not two stages of intercooling, just a single. All in all, a lighter weight boost system, and all concentrated forward of the firewall.

I forgot about the duct-work matter, and the bulk that came with it (interestingly, I'm not sure how much of a weight difference there is between a turbocharger and a twin-stage supercharger), I just figured: "Two stages of supercharging usually requires an intercooler anyway" (the P-63 didn't have one, but that was because Allison couldn't seem to figure out a liquid-to-air intercooler arrangement, and they ended up using ADI instead). That said, I thought the P-38 had a single intercooler stage and the Rolls-Royce Merlin had (effectively) 1-1/2 stages of cooling (the casing and air passageways between the first and second stage had cooling, and the aftercooler).

...and with exhaust thrust available from the stacks.

Yeah, with the question ultimately coming down to how much horsepower you loose from the supercharger versus the amount of horsepower you gain in the form of thrust (and this varies with speed). If you're speed's above 375 mph and critical altitude is high you can potentially break even.

 

[ThomasP]

Somewhere on the internet . . .

There is an early-war memo mentioning ways to improve the climb performance of the P-38 in service. One of the methods for interception & fighter vs fighter missions, involved the carriage of only 200-300 rpg for the 4x .50 cal instead of the possible 500 rpg, and using the 60-round drum for the 20mm instead of the 150-belt feed. Another weight saving measure was to replace the 20mm with a .50 cal and to remove the armour in front of the 20mm ammunition box. Apparently this was all possible without exceeding the CofG limits.

 

[Shortround6]

. I'd almost swear the 420 mph figure was based on an MP setting that wasn't the maximum and they could hit as much as 440 at higher settings, but there happened to be a degree of conservatism because the plane was flying very close to the point where it would start to run into significant compressibility effects if they nosed over.

The figures are from a test and the test plane had the five .50s. Not that the rest of the planes did.
The plane was even slower at 60 in.
402.5mph, were the 440mph comes from is anybody's guess.

as far as conservatism goes, it would be the other way. You can't lie about physical effects like compressibility. It either happens at a certain speed or it doesn't. If the plane will actually do 440mph and you "lie" about it because you are being conservative you are going to get people killed.

The P-38 was a 1938 design. It is little wonder that a newer plane could have less drag, especially at 400mph because you are running into compressibility effects in drag all over the airplane, not just wing lift.

and again, it is important to remember the altitude. The test P-38J could hit 413mph at 24,000ft using 60in. The superchargers would not deleiver 70in at that height but in the thinner air the plane pickup about 10mph of speed over the 19,800ft height.

 

[tomo pauk]

While any aircraft benefits from more HP, P-38 really needed a much improved streamlining. A lot had to do with the wing section between the pod and booms, windscreen angle, and the shape of the aft section of the pod.

 

[GrauGeist]

While any aircraft benefits from more HP, P-38 really needed a much improved streamlining. A lot had to do with the wing section between the pod and booms, windscreen angle, and the shape of the aft section of the pod.

The numerous air inlets as well as the turbo recess on each boom fuselage contributed to drag, too.

 

[blueskies]

But the 'compressibility' issues were because of the double expansion caused by the tapering of the central pod being coincident with the wing. Keeping the fuselage a constant cross section across the wing would have done more to remedy the compressibility issue than anything else. NACA confirmed this in wind tunnel testing on two different occasions, and Lockheed allegedly built a couple flight test P-38s with extended booms.

 

[Reluctant Poster]

The numerous air inlets as well as the turbo recess on each boom fuselage contributed to drag, too.

 

[GrauGeist]

Plus the several intakes at the front of the cowling, including the small magneto cooling intakes, larger air intakes as well as the radiator/intercooler intakes beneath the prop.

 

[BarnOwlLover]

One suggestion I'd make for the main production P-51 Mustangs was adopt a cowling similar to the XP-51F/G/J and the P-51H. It'd have fewer panels and no "cage" to attach them to. It'd make engine access easier and shed a bit of weight (even if that loss is negligible).

Not to mention that I'd have designed some of the LW's and H's lightweight design features from the start (though not the landing gear--it's obviously strong enough but IMO looks pretty spindly).

 

[drgondog]

One suggestion I'd make for the main production P-51 Mustangs was adopt a cowling similar to the XP-51F/G/J and the P-51H. It'd have fewer panels and no "cage" to attach them to. It'd make engine access easier and shed a bit of weight (even if that loss is negligible).

Not to mention that I'd have designed some of the LW's and H's lightweight design features from the start (though not the landing gear--it's obviously strong enough but IMO looks pretty spindly).

The P-51H was designed to Spitfire design load limits, namely 7.5 and 11G for Design/Ultimate AoA laods, and 4G (vs 7) for landing geat - but retained 1G lateral,

It is common mistake that P51H was 'flimsy' relative to P-51D. It in fact was much stronger save the LG, as the limits were placed for full internal combat load of 9600 pounds. The P-51D at 10200 pounds was stressed at ~ 6.3/9.6 as weight grew from 8000 pounds design weight.

EDIT: Although the original Mustang was designed to Wright Field Airplane Stuctural Standards, it began life at 8G Limit, 12G Ultimate for 8,000 pounds, there were several incremental changes over time to the wing/empennage internal structure in the form of doublers, increased bulkhead thickness/fasteners, shear panel thickness changes which made the D safer in late blocks than say the P-51B-1.

 

[BarnOwlLover]

Landing gear is one area (citing your post) is the one area where I'd argue that the P-51H was "weaker" than the earlier models. Obviously, it got the job done, but seeing a P-51H parked it looks spindly compared to how "beefy" the rest of the plane is. Same thing with the lightweights that spawned the H. It always looked weird to me, though I like the H as a flyer because of its performance--basically it was if Ed Schmued could do it over again (WWSD), and many of those design ideas ended up also in the F-82.

Granted, IMO, the P-51H was a "porker" compared to the XP-51F/G, though to be fair, those were proof of concept planes that I don't think were seriously looked at for production. Still, lighter weight, more power for the H made it the premier Mustang. I'd bet that the Germans and Japanese were glad it got ordered and put into production too late to see much use (no combat use as far as is known, only a few issued to squadrons).

That, and the H did deal with the annoying CG/directional stability issues that the rear fuselage tank caused (taller tail--though not on the very first planes--, longer fuselage, smaller tank), though I did see a reference on here that it could've carried a ton more fuel there than the B/D without hurting handling too much.

 

[drgondog]

Landing gear is one area (citing your post) is the one area where I'd argue that the P-51H was "weaker" than the earlier models. Obviously, it got the job done, but seeing a P-51H parked it looks spindly compared to how "beefy" the rest of the plane is. Same thing with the lightweights that spawned the H. It always looked weird to me, though I like the H as a flyer because of its performance--basically it was if Ed Schmued could do it over again (WWSD), and many of those design ideas ended up also in the F-82.

Granted, IMO, the P-51H was a "porker" compared to the XP-51F/G, though to be fair, those were proof of concept planes that I don't think were seriously looked at for production. Still, lighter weight, more power for the H made it the premier Mustang. I'd bet that the Germans and Japanese were glad it got ordered and put into production too late to see much use (no combat use as far as is known, only a few issued to squadrons).

That, and the H did deal with the annoying CG/directional stability issues that the rear fuselage tank caused (taller tail--though not on the very first planes--, longer fuselage, smaller tank), though I did see a reference on here that it could've carried a ton more fuel there than the B/D without hurting handling too much.

I mentioned the lighter design landing gear allowables above. The XP-51F was considered (as combo interceptor/LR escort) but when it first flew, it was clear that AAF was priortizing range, and thus XP-51F/G were abandoned in favor of P-51H. It was impossible to fit either 50gal or 85 gal fuse tank and keep design allowables for stress. That said,the XP-51F/G had 20gal more than all previous Mustangs until intro of 85gal fuse tank. The increased weight of the H was due to maintenance of full AoA stress allowables with extra 2 guns and ammo and increase of 50 gal fuselage fuel.

 

[GregP]

Plus the several intakes at the front of the cowling, including the small magneto cooling intakes, larger air intakes as well as the radiator/intercooler intakes beneath the prop.

Yes, true. But there aren't any production piston inline airplanes of the time that don't have intakes for the same functions. Sometimers they split the air from one scoop to allocate it to various functions. So, the issue is how much drag they could eliminate with a general "clean up," not really to get rid of the air intakes ... which I'm positive you weren't implying to start with.

 

[BarnOwlLover]

I mentioned the lighter design landing gear allowables above. The XP-51F was considered (as combo interceptor/LR escort) but when it first flew, it was clear that AAF was priortizing range, and thus XP-51F/G were abandoned in favor of P-51H. It was impossible to fit either 50gal or 85 gal fuse tank and keep design allowables for stress. That said,the XP-51F/G had 20gal more than all previous Mustangs until intro of 85gal fuse tank. The increased weight of the H was due to maintenance of full AoA stress allowables with extra 2 guns and ammo and increase of 50 gal fuselage fuel.

Could another reason for weight increase be stressing for underwing stores? I know that there's photos of the British XP-51F carrying drop tanks, but I don't believe it was ever really cleared for other underwing stores (if it made it to production it would've been, but I've never found anything reliable on that front). The H, meanwhile, could carry the same drop tanks, bomb/rocket load at the D.

 

[drgondog]

Could another reason for weight increase be stressing for underwing stores? I know that there's photos of the British XP-51F carrying drop tanks, but I don't believe it was ever really cleared for other underwing stores (if it made it to production it would've been, but I've never found anything reliable on that front). The H, meanwhile, could carry the same drop tanks, bomb/rocket load at the D.

All of the XP-51F/G/J were cleared for 1000# per rack. To my knowledge no rocket stubs, or earlier MX -241 mounts, were installed on any of the four t
types.

 

[BarnOwlLover]

Thanks. I've been looking for that info for a while. Other than what you've mentioned and externally visible differences (different canopy, longer and taller tail, raised cockpit), how else did the H differ from the F/G (I ought to buy a book I got wind of rather than asking here LOL)?

 

[Zipper730]

You know, if they re-oriented the XP-49's development from just being a P-38 with more power to a design with various lessons learned from the P-38's compressibility issues would have been a pretty smart idea. Even if the engine didn't change at all, it would have had superior speed and diving performance figures.

Not sure how that would have affected the L-133, but that was expected to be fully supersonic.

 

[drgondog]

Thanks. I've been looking for that info for a while. Other than what you've mentioned and externally visible differences (different canopy, longer and taller tail, raised cockpit), how else did the H differ from the F/G (I ought to buy a book I got wind of rather than asking here LOL)?

All NA-105 (XP-51F/G/J) were scratch sheet of paper designs,because of the intense scrutiny regarding weight. Offhand I need to get a few more documents but very few P-51H parts moved from NA-105 project. The H was not only dimensionally different (bigger) but the Master Lines were different everywhere also. Additionally the H 'grew' structurally to take the extra 1500-2000 pounds gross weight. I wouldn't be surprised if cockpit and control linkages remained same - but I don't know.

 

[MiTasol]

Yes, true. But there aren't any production piston inline airplanes of the time that don't have intakes for the same functions. Sometimers they split the air from one scoop to allocate it to various functions. So, the issue is how much drag they could eliminate with a general "clean up," not really to get rid of the air intakes ... which I'm positive you weren't implying to start with.

Replacing a lot of those small intakes with NACA intakes would have dropped drag but probably increased weight and definitely made maintenance more complex by having to disconnect the various hoses

 

[Reluctant Poster]

Replacing a lot of those small intakes with NACA intakes would have dropped drag but probably increased weight and definitely made maintenance more complex by having to disconnect the various hoses

The P-47 concealed the turbocharger within a shroud. There are no extraneous intakes. All the air for the induction system including the intercooler comes from the chin intake which also serves the oil coolers. A very slick arrangement.