WI: NACA Modified P-38

[EverKing]

Well, I found some of the potential changes in the fuel system. It appears the Outer Wing tanks were only factory installed after the J-10 and there is evidence in the pilot manuals that some of these airplanes were field modified by their addition. You can see that in the change in the Auxiliary Fuel Pump switch box photos (which I can't seem to upload right now). Initially, the P-38 had a four position fuel valve selector: MAIN - RES - DROP TANK - OFF; and two booster pump control switches (L and R) with ON/OFF positions. Cross-suction was handled via a separate crossfeed valve with its own control, apart from the selector valves and aux. control box. Some of these aircraft with the 4-position valves show a replacement of the old two-switch aux. control box to a four-switch box: two booster pump (ON-OFF) switches, and two Wing Tank switches (ON-OFF). This means that the wing tanks weren't integrated into the fuel selector valves from the factory but were controlled using their own booster pumps which fed directly to the engine(s)--which is why cross-feed wasn't available for them.

Later aircraft, those equipped with the Wing Tanks from the factory, integrated both the wing tank selection and crossfeed to a five position fuel selector (DROP TANK and OFF were combined into the same position). Even of these there are two variants: "early" models, with the traditional fuel booster system but including a OW Fuel Level test light on the box; and "modified" models with a fully pressurized fuel system using submerged booster pumps in each tank--these had four switches on the aux. control box but they were Boost Pump Master Switches (ON-OFF) and Boost Pump Emergency switches (ON-OFF). In all, that four different fuel management set-ups / fuel systems all applicable in various production blocks and modifications from the J through the end of production in the L.

Apart from the changes required to install and accommodate the Aileron Boosters and Dive Flaps (likely several modifications required for each), the afore mentioned improved Turbo Regulators, and these fuel system changes other possible modifications that may have been included could be the simplified Bomb/Drop Tank/Rocket control box (with the associated auxiliary control switches added to the yoke) and whatever modification Tony mentioned in the video to help with the detonation issue.

That last I find curious as I can't figure out field modifications they would have put in place for that since, from my understanding, that was solved with a manifold redesign by Allison...but I could be wrong there.

The other consideration--that of having all these modification kits on a single plane--is likewise unsolved. It is possible that 1) portions of the modification kits were sent separately, which could explain the existence of aircraft with the four-position fuel selectors and aux. Wing Tank selectors; 2) most of the parts required for the modifications were quite small and light (or were simply templates/instructions on how to modify parts already installed); and 3) there weren't 500 kits, as Tony said in the video, but instead only 200 kits as I've seen mentioned in various other sources.

 

[Draconis]

and whatever modification Tony mentioned in the video to help with the detonation issue.

That last I find curious as I can't figure out field modifications they would have put in place for that since, from my understanding, that was solved with a manifold redesign by Allison...but I could be wrong there.

The other consideration--that of having all these modification kits on a single plane--is likewise unsolved. It is possible that 1) portions of the modification kits were sent separately, which could explain the existence of aircraft with the four-position fuel selectors and aux. Wing Tank selectors; 2) most of the parts required for the modifications were quite small and light (or were simply templates/instructions on how to modify parts already installed); and 3) there weren't 500 kits, as Tony said in the video, but instead only 200 kits as I've seen mentioned in various other sources.

I think your deduction makes sense. And that would've been a pretty extensive project. I would think it likely adds up to 21 items some way or other. And for sure they were shipping more them one planeload of parts and equipment. Regarding the engine fix Tony LeVier mentioned I'd thought he was referring to better control of the charge air temperature at high altitude. Didn't Allison redesign the V-1710s' intake manifolds earlier for the F and G engines? But he didn't go into detail about what that fix was so it's hard to say for sure.

 

[Owltiger]

So as part of a project I was working on for a story in "ASB" I started a conversation with ChatGPT. Although not all of it is relevant here, it is important to note that it states there were multiple aerodynamic and engineering changes available to the Lockheed design team that could have made the ship more aerodynamic and increased performance and other characteristics. Needless to say I have to double check the source materials. One interesting thing it did state is that it WOULD have been possible to create the military M-61 cannon system during this period with materials then available. Of course that assumes someone had the schematics, which gets you back into ASB territory.

 

[Draconis]

Most readers of EverKing's P-38 "what if" are probably familiar with the story of the P-38 called Glacier Girl. For anybody who isn't here is a link to the Wikipedia article about her. https://en.wikipedia.org/wiki/Glacier_Girl

What's quite impressive is how far down the salvagers had to dig to reach the plane. Fifty years was enough to bury it under about 270 feet of snowpack and ice. Really illustrates how glaciers form. The salvagers had to dig a shaft that was roughly equivalent to the height of a 27 story building. Then dig out a cavern around the buried P-38. Then dismantle the plane into small enough pieces that could fit through the access shaft to be winched up to the surface. What a feat. And lastly rebuild the plane.

I'm going to provide some links to a few Youtube videos that describe this achievement and other activities. Some are brief for those who only what a summary and one is quite lengthy for those who would like a more detailed account. And the first one depicts the salvagers having some fun with the recovered 20mm cannon. It surprised me that 50 year old explosive rounds would still function. But they did to a 55 gallon drum's misfortune.

Bang.

Short.

Two Mediums.

And a Long.

I hope any interested readers find some or all of these videos enjoyable and informative.

 

[Draconis]

Seeing the amount of damage even a 50 year old cannon shell did to the 55 gallon drum reminds one of the old debate about which was the better weapon for WW2 fighters. The .50 caliber heavy machine gun or the 20mm cannon. The .50 would have drilled a half inch wide entry and exit holes through the steel sides of the 55 gallon drum. The 20mm explosive round blew off half the side of the drum. Very convincing.

 

[EverKing]

Seeing the amount of damage even a 50 year old cannon shell did to the 55 gallon drum reminds one of the old debate about which was the better weapon for WW2 fighters. The .50 caliber heavy machine gun or the 20mm cannon. The .50 would have drilled a half inch wide entry and exit holes through the steel sides of the 55 gallon drum. The 20mm explosive round blew off half the side of the drum. Very convincing.

No doubt. If the US Hispanos were built to the reliability of the British ones, they would have been incredible.

 

[Driftless]

No doubt. If the US Hispanos were built to the reliability of the British ones, they would have been incredible.

A reverse lend-lease? Have the British build the Hispanos for US use (Oh, nevermind about that pesky production capacity issue)....

The NIH thought was prevalent, but the US did use a number of British designed and built weapons in WW2 - 57mm AT gun, Mosquito, even some Spits. There's more I'm sure, but that's the ones on the top of my cranial cavity.

I am being a bit facetious with my idea, so consider that too.

 

[EverKing]

A reverse lend-lease? Have the British build the Hispanos for US use (Oh, nevermind about that pesky production capacity issue)....

It's not just the British production capacity that prevents it. It's the US Ordinance Dept. They had already built a stockpile of US Spec ammo, which--if I recall--was the root of the problem due to head spacing difficulties in "proper" spec cannons. They'd have to accept the loss of that large stockpile and retool to produce updated spec ammo.

Mind you, this is just from a foggy recollection of something I read a few years so I could be mistaken.

 

[MrCharles]

It's not just the British production capacity that prevents it. It's the US Ordinance Dept. They had already built a stockpile of US Spec ammo, which--if I recall--was the root of the problem due to head spacing difficulties in "proper" spec cannons. They'd have to accept the loss of that large stockpile and retool to produce updated spec ammo.

Mind you, this is just from a foggy recollection of something I read a few years so I could be mistaken.

It was the other way around, sort of. The US made cannons had a chamber which was too long, causing repeated issues with light primer strikes as the cartridge seated too far forwards.

 

[EverKing]

It was the other way around, sort of. The US made cannons had a chamber which was too long, causing repeated issues with light primer strikes as the cartridge seated too far forwards.

Right, that's my recollection for the most part. The "Deep chamber" is a layman's way of describing headspace. What I recall reading was that to simplify supply and varied manufacturing the US spec tolerances were looser in both chamber design and cartridge design, leading to incorrect headspacing when a cartridge in the lower end of the tolerances was loading into a chamber near the higher end of the tolerances. This is what lead the unreliability: the increase in variances allowed within the spec meant that most would fire fine, but a significant number would push too deep leading to soft strikes and subsequent misfire. So, even if the chamber headspacing were corrected to a shorter distance all of the nearly million rounds already produced (I don't remember the exact number but either 600,000 or 900,000 is sticking in my head) would have to be re-checked and large number disposed of for being either too short or too long (the latter would prevent the bolt block from reaching full battery).

 

[Driftless]

Right, that's my recollection for the most part. The "Deep chamber" is a layman's way of describing headspace. What I recall reading was that to simplify supply and varied manufacturing the US spec tolerances were looser in both chamber design and cartridge design, leading to incorrect headspacing when a cartridge in the lower end of the tolerances was loading into a chamber near the higher end of the tolerances. This is what lead the unreliability: the increase in variances allowed within the spec meant that most would fire fine, but a significant number would push too deep leading to soft strikes and subsequent misfire. So, even if the chamber headspacing were corrected to a shorter distance all of the nearly million rounds already produced (I don't remember the exact number but either 600,000 or 900,000 is sticking in my head) would have to be re-checked and large number disposed of for being either too short or too long (the latter would prevent the bolt block from reaching full battery).

Off the top of my head, wouldn't that tolerance issue be more likely tied to specific manufacturers, or specific batch runs? There shouldn't have been much variance in casing length within a run, or by a vendor (IMO).

Of course, once the complete cartridges are produced and shipped, it probably becomes harder to backwards isolate the problem children.

 

[MrCharles]

Right, that's my recollection for the most part. The "Deep chamber" is a layman's way of describing headspace. What I recall reading was that to simplify supply and varied manufacturing the US spec tolerances were looser in both chamber design and cartridge design, leading to incorrect headspacing when a cartridge in the lower end of the tolerances was loading into a chamber near the higher end of the tolerances. This is what lead the unreliability: the increase in variances allowed within the spec meant that most would fire fine, but a significant number would push too deep leading to soft strikes and subsequent misfire. So, even if the chamber headspacing were corrected to a shorter distance all of the nearly million rounds already produced (I don't remember the exact number but either 600,000 or 900,000 is sticking in my head) would have to be re-checked and large number disposed of for being either too short or too long (the latter would prevent the bolt block from reaching full battery).

I’d always thought it was to do with the ordnance dept screwing up the conversion from metric to imperial on the production drawings.

 

[jlckansas]

It was the fact that the ordnance dept. didn't want to order new tooling but wanted to make it with existing US tooling and measurements that was at the root of the problem. There were plenty of items being made metric, example is industrial equipment for overseas markets, You had plenty of ammunition made by US manufactures for foreign countries that were made in metric also and in large quantities.

 

[EverKing]

Off the top of my head, wouldn't that tolerance issue be more likely tied to specific manufacturers, or specific batch runs? There shouldn't have been much variance in casing length within a run, or by a vendor (IMO).

Of course, once the complete cartridges are produced and shipped, it probably becomes harder to backwards isolate the problem children.

Yeah, would you want to track down all of lots, take a random sampling from each, and determine which were within an updated spec and which were not? Plus, do all of this during wartime demand where every lot you "deny" is one less available for the boys fighting? Though, to be fair, an argument can be made that it would be better to have 500,000 rounds with a < 1% failure rate than 800,000 rounds with a 5% failure rate (or more, I just invented those numbers for illustrative purposes).

I’d always thought it was to do with the ordnance dept screwing up the conversion from metric to imperial on the production drawings.

That certainly could have had something to do with it. As I said, I'm basing this off of memory of something I read 6 years ago or so, but it would make sense to me that they may convert Metric tolerances of hundredths of a millimeter (x.xx mm) to the US standard of thousandths of a inch (x.xxx in). Considering each thou is nearly three hundredths of a mm (1/1000 in is 0.0254 mm), the loosening of tolerances could be a natural effect of the conversion.

 

[Andras]

If you scroll down to Chapter 14, the Hispano entry, there is a really good explanation of the whole US Hispano issues here

HyperWar: The Machine Gun (Vol. I/Part V)

 

[phx1138]

Coming in late (yet again🙄 )...

If foreign-spec ammo is an issue (TBH, it smells more of an excuse🤐 ), can't AUS simply (...) procure _it_, instead? (Is that too obvious to be reasonable?)


BTW: bump.😊

 

[Andras]

old video on the power of the turbocharged Allison

 

[phx1138]

old video on the power of the turbocharged Allison

a

Thx for that.

 

[Draconis]

One of the improvements that greatly benefitted the P-38 in real life and also in EverKing's NACA P-38 timeline was the hydraulically boosted power assist for the ailerons. On page 52 of the USAAF's P-38 pilots' manual there is most of a page devoted to using them. It's actually quite brief.

What I found surprising was the strict warning to pilots about never turning the aileron boost on during flight. I had believed that the pilots used the aileron boost at will. Namely when flying at higher airspeeds where the aileron control forces became excessive. Other then that they wouldn't use it. But evidently the aileron boost was always turned on through out the entire flight. Except for under the emergency conditions stated. I don't think there would've been anything wrong with using aileron boost all the time. For nonpilot readers think of power steering compared to manual steering.

The pilots manual doesn't explain why it was prohibited to turn on the hydraulic boost after take-off. I think it might be about avoiding turning on the aileron boost after the engines have started and their hydraulic pumps have pressurized the hydraulic system. If so then after turning on the aileron booster valve in the split second it takes to reach full hydraulic pressure in each of the two aileron hydraulic actuators if there was even a temporary difference in pressure at each actuator it may overstress the connecting linkages between them causing bending or breakage. Because they are joined together by their common connection to the control wheel any hydraulic pressure imbalance must be avoided. The more gradual increase in hydraulic pressure as the engines are started and warmed up would not cause any sharp hydraulic sudden jolts or imbalances.

This is complete speculation on my part and may well be completely wrong. If anybody else has any info on why this prohibition against switching on the aileron boost in flight existed please post a comment.

So, what does a pilot do if he's hasn't followed his, at least mental take off checklist, and finds himself climbing out with the aileron boost off? Go back and land? But maybe there's no time for that. Going on the assumption that my speculation is correct then here is one possible remedy. Climb to a sufficient altitude, maybe about 20,000 feet. Shut down both engines and feather the propellers so there's no wind-milling of the engines which would also drive the hydraulic pumps. Work the flaps to bleed off any hydraulic pressure. Turn on the aileron booster valve. Then restart both engines and rejoin your formation. Happy hunting.

 

[Draconis]

It would seem that the OTL 8th Air Force didn't get the best possible use out of their P-38s. This is an example of an under valued bit of information regarding fuel management. Here are a couple of short excerpts from the Charles Lindbergh website describing Lindbergh demonstrating to the 475th fighter group how to get more range out of their P-38s. http://www.charleslindbergh.com/wwii/

"Lindbergh talked with MacDonald. The colonel then asked the group's pilots to assemble at the recreation hall that evening. The hall was that in name only, packed dirt floors staring up at a palm thatched roof, one ping pong table and some decks of cards completing the decor. Under the glare of unshaded bulbs, MacDonald got down to business. "Mr. Lindbergh" wanted to explain how to gain more range from the P-38s. In a pleasant manner Lindbergh explained cruise control techniques he had worked out for the Lightnings: reduce the standard 2,200 rpm to 1,600, set fuel mixtures to "auto-lean," and slightly increase manifold pressures. This, Lindbergh predicted, would stretch the Lightning's radius by 400 hundred miles, a nine-hour flight. When he concluded his talk half an hour later, the room was silent."

"The group’s chief concern surfaced quickly, that such procedures would foul sparkplugs and scorch cylinders. Lindbergh methodically gave the answer. The Lightning's technical manual provided all the figures necessary to prove his point; they had been there all along. Nonetheless the 475th remained skeptical. A single factor scotched their reticence."

As one can see from the second excerpt Lindbergh convinced the pilots to use more fuel efficient settings to increase the P-38s' range. But Lindbergh didn't discover those settings. Lockheed's test pilots had worked them out earlier. They were in the P-38s pilots manual for anybody to see. Why weren't they used everywhere?

On page 72 of the P-38 pilots' manual the second chart illustrates the permitted boost, engine RPM and mixture settings. Notice the recommended settings region. The left side of the recommended settings shows a maximum boost of 34 inches, 1600 RPM and auto-lean. Right there in the pilots' manual for anybody to see.

Using these settings would have benefitted 8th Air Force bomber escort operations in 1943. I don't know what airspeed 30"/1600RPM/auto-lean would produce at 25K to 30K feet but being less RPM then the maximum cruise settings it would be a little slower. This might have reduced or even eliminated the fuel wasting weaving the P-38 pilots flew to keep from outpacing the bombers. Reduced fuel consumption and less distance travelled (no weaving) equals increased combat radius. How much? Without drop tanks? About 150 miles or more? Of course these increased range settings could have been used anywhere P-38 operations were conducted.

It's puzzling why the 30"/1600RPM/auto-lean weren't used earlier and more widely. Were they not listed in the pilot's manuals for the earlier model P-38s? Could those settings have pushed the C.A.T. too high with the leading edge intercooler? 30 inches of boost isn't very much. Or perhaps nobody with influence and experience looked more closely at P-38 flight operations and offered up some suggestions.