When Did They Realize The P-38 Had Compressibility Problems
- Thread starter Zipper730
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davebender
1st Lieutenant
I'm under the impression the early P-38 had stability problems in level flight. Stability problems when diving were a foregone conclusion.
fubar57
General
Problems with military aircraft are frequently pointed out by the opposition who don't have any vested interest in their opponents sales. If all fighters were twin engine twin boom construction then maybe it wouldn't have had a problem at all. The Spitfire and Hurricane didn't have a problem with negative G maneuvers until they met the fuel injected 109.
- Thread starter
- #5
So, Lockheed assumed compressibility would happen before the plane even flew, but the USAAF just assumed this wouldn't happen because it never happened before? That said, I would not be surprised if they were surprised by the exact speeds at which compressibility would occur.
pinehilljoe
Staff Sergeant
- 767
- May 1, 2016
Warren Bodie goes into a lot detail of the comprehensibility issue in the his book. If you are P38 fan, its a good book.
Amazon product ASIN 0962935905
Amazon product ASIN 0962935905
- Thread starter
- #7
Sounds like a hell of a book.
pinehilljoe
Staff Sergeant
- 767
- May 1, 2016
Mr Bodie was a contributor to Wing/Airpower Magazine. He wrote a 13 part article on the P-38, the book is like a collection of the articles edited together
IdahoRenegade
Airman 1st Class
Bodie mentioned in the book that Johnson wrote about the concern of compressibility while the plane was being designed. In 1938, very little was understood about compressibility and Kelly knew as much as anyone. IIRC he also had consulted with some of the top aerodynamicists in the country looking for input-but the knowledge just wasn't there at the time. The problem was identified IIRC during fairly early flights with the YP planes in '40. But at that time the big focus was just overcoming production difficulties and getting them built at all. Lockheed was screaming for time in a high-speed wind tunnel as soon as the problem was identified-but (according to Bodie) those in charge of the tunnels didn't want to risk damaging them. It took months of delays and intervention by Arnold to finally make it happen. I need to dig the book back out and read it again.
Compressibility wasn't a unique problem to the '38, the Thunderbolt and Corsair also ran into it, both during development and in service (check Bob Johnson's book about the '47). It wasn't as severe on the 'bolt, at least in part likely due to a thinner wing section. The Corsair wasn't typically operated at the extreme altitudes where it became a major issue.
Compressibility wasn't a unique problem to the '38, the Thunderbolt and Corsair also ran into it, both during development and in service (check Bob Johnson's book about the '47). It wasn't as severe on the 'bolt, at least in part likely due to a thinner wing section. The Corsair wasn't typically operated at the extreme altitudes where it became a major issue.
IdahoRenegade
Airman 1st Class
At the time the '38 was designed, nobody really understood compressibility. Kelly Johnson voiced (wrote) about it as a concern with an early report in the design process, and consulted with the best aerodynamicists in the nation at the time. (With his and Kelsey's MIT masters, they probably knew about as much as anyone in the nation at the time). The real crime is that NACA and other sources refused to do wind tunnel tests in their high speed wind tunnels (supposedly out of fear of breaking them). It eventually took an order by Hap Arnold to get that done-but by then the design was in production-and the War Production Board was unwilling to disrupt production for virtually any reason. The dive recovery flaps that were developed in early '43 probably weren't the proper solution (I'd guess that would take a different wing section), but was a band-aid that could be incorporated without a big production hit. The '38 wasn't the only fighter with compressibility issue, at the least the Corsair and P-47 encountered them (the '47 eventually being equipped with the dive recovery flaps developed from the '38). The '38 was simply the 1st to encounter it-because it was the first 400 mph high altitude fighter, and as such the first to encounter it. And being both heavy and powerful, it accelerated very quickly in a dive.
A few big what-ifs with the P-38:
1) What if another production facility (or more) had been brought on-line early in the war (or better before PH)? The 1 Lockheed plant was always under the gun for production. And the plane was in high demand, especially early in the war. Remember, until December '43 when the 51-B finally saw combat, it was the only long-range high performance fighter available. Doubling production early would have meant that they didn't fight as badly outnumbered in virtually every theater. More important, it would offer the opportunity to incorporate design changes without as significant a production impact.
2) What if the '38s in England in mid-late '42 had stayed in England (assuming (1) had happened and that there was production to support N. Africa and SWPA)? They could have had the same long, leisurely intro to high-altitude, long range combat that '47 pilots had. Time for the pilots and ground crews to train on and learn the planes before being thrown into combat. Easier missions dabbling into occupied France and the coast of occupied Europe-before the Germans "surged" fighter support there. Time for Lockheed and Allison to sort out the issues before being thrown into long-range bomber escort. And time to build up the numbers of aircraft so again, they didn't fight so heavily outnumbered. '47 pilots took time to learn their birds and develop combat experience-which they HAD. They had time to develop tactics that best utilized their plane and didn't play into the strengths of the enemy. To the tune of several months before Republic developed a decent drop tank solution to give the '47 reasonable range. Republic had time to sort out the ignition issues that plagued the '47 early on. By the time Bomber Command admitted that unescorted daylight bombing was a fools game, there was desperation to get a long range escort into service. In mid-late '43 the '38 was STILL the only option (Mustang B being a ways out). A relative handful of '38s were rushed in, with green, untrained pilots, ground crews and leadership, with new model planes not "wrung out" for the high altitude escort mission, and thrown in as the only fighters available to go against the now heavily strengthened and reinforced LW, with their best pilots. Fighting heavily outnumbered, farther from their home bases than any previous fighter in history (at least in any volume-might have been some isolated cases, I don't know). My understanding is that when the '51B went into combat, the pilot ranks were heavily populated with former "Eagle Squadron" pilots that had combat experience, in Spits, with Merlins. And very quickly we had LOTS of '51s available. Unlike the situation with the '38.
3) What if the XP-38 hadn't been lost in a publicity stunt, and been available for testing and evaluation while the YPs were being redesigned and built? What if the compressibility issue had been identified in early '39 and a true solution been figured out and incorporated by '41? Perhaps a different, laminar flow wing? What if the wind tunnel test Lockheed was begging for had been done much earlier?
4) What if the '38 with a different wing section had been equipped with the higher-powered turbocharged Allisons available in early '43? The prototype K models featured "paddle props" as well as more powerful engines that improved it's already excellent climb rate. These particular props were larger in diameter and required a different reduction gearing, as well as different sheet metal and internal structure. WPB wouldn't allow Lockheed to stop production for the estimated 2 weeks to cut in these changes. See 1 again...
5) The original '38 design was based on 1000-1100hp turbocharged engines, and featured a very slick, zero drag intercooler in the leading edge of the wings. This was a brilliant approach from an aerodynamic standpoint-no additional cooling system drag was encountered. It did have a couple issues, the first being somewhat damage prone and hard to seal. The bigger issue came when higher powered engines running more boost were introduced. This required more cooling capacity than the wing leading edge coolers could provide, and drove the incorporation of the air-air intercooler mounted in a "chin" under the engine, resulting in additional drag. So even with considerably more HP, speed was only marginally increased. So-what if a air-liquid system was incorporated and efforts made to minimize drag (ala Mustang)? Liquid HXs offer packaging advantages and flexibility, and eliminate the need for large ducts to transfer pressurized air to the HX and back.
Just a few thoughts.
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