P38 at high altitude

Discussion in 'Aviation' started by bob44, Sep 24, 2012.

  1. bob44

    bob44 Member

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    Let's talk P38's for a bit.
    Why did the P38 have so many problems flying bomber escort in Western Europe in late 1943, early 1944? Blown engines and such.
    I have read about the cold temps at 30000ft. causing issues with the early models.
    I have not read that other aircraft where having so many problems at high altitudes.
     
  2. Shortround6

    Shortround6 Well-Known Member

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    There were a number of contributing factors. There is a 6-8 page article in an issue ( vol 1 no 2) of the "Torque Meter Journal" at the AEHS website.

    Basically, it comes down to a change in fuel specification, bad piloting technique, an intake manifold problem, improper turbo control adjustment/rigging and a few other minor factors.

    One P-38 squadron on the Indian border blew up at least a dozen engines, almost all of them on one side of the airplane. Turbo controls were not exactly the same on the left and right engines.

    Pilots were being taught to fly (cruise) at high rpm and low boost which was against both Allison's and Lockheed's recommendations. It was bad for fuel economy (range), engine life, pilot survival, and hleped blow up the engines.
     
  3. GregP

    GregP Well-Known Member

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    I work at a shop that does nothing but Allison V-1710 engines. We have engines in all the P-38's in the world except for the Red Bull unit, which doesn't fly much or often due to engine problems caused by another builder. We have a LOT of Allisons out there in P-38's, P-39's, P-40's, various Yaks and some Spitfire replicas. More than 12 have 850 - 1,250 hours on them with no trouble other than normal maintenance. Properly run, the Allison runs and operates just fine. All ours are built to stock Allison specifications except for teh engines for the Yak-3's. Most Yak-3 pwners added a carb intake right over the top of the carb, and they get a LOT or ram air, so the carbuuretors have to be jetted very ruich in the mid-range or the engine lean out due to ram air. All other installations run normally.

    The Allison early-on had issues with the intakes. The intake piping was such that the airflow would impinge on a certain curve and cause a couple of cylinders to run rich with another couple running lean. It toook Allison about 6 - 8 month to clear that up. The solution was a turbuilator in the intake piping. All the engine we build and selll have the turbulator and the mixture disperses evenly.

    A second problems was the European fuels. 100+ Octane fuel in the U.S.A. had 2% aromatics in it. European fuels had up to 20% aromatics, so the carburetors were jetted wrong right from the factory, but ran just fine on US fuel. Once the fuel issue and intake issue had been corrected, the P-38's ran just fine. By that time the P-51 was arriving and there was simply no need for two top fighters in the ETO with two logistics chains and two sets of mechanics, etc. The P-38's were mostly transferred to the Pacific where they ran just fine ON AMERICAN FUEL. Our two top aces, Bong and McGuire, both flew P-38's.

    A third issue not frequently brought up was the lack of an adequate cockpit heater in the P-38. Pilots were freezing during European escort duties and were quite happy in the PTO to remain lower than 30,000+ feet whenever possible.

    The forth issue was caused by hitting the critical Mach number in a dive from altitude, and the dive flaps fixed that one enough to prevent loss of aircraft and pilot. The REAL solution was a different wing profile and perhaps a slight chang in the vertical position of the horizontal stabilizer ... but they never did do it since the war was essentially won by the end of 1943 / early 1944 and the handwriting was on the wall.

    The P-38 had a couple of early issues and the low critical Mach number stayed with it, but it was a formidable fighter until the end of the war.
     
  4. alejandro_

    alejandro_ Member

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    Greg, the fuel composition detail is interesting. Was there any problem with other types (P-39/47/51)? Airacobra served in the RAF and arrived to Europe with USAAF at the same time frame.

    I have saved some discussions on the P-38 performance in Europe over the years. These reports point out at some of the problems. I would also like to emphasize that Luftwaffe was a stronger enemy in 1943/early 1944 than later on i.e. when P-51B/C/D arrived. Also, some of the P-38 advantages when compared to P-47/51 are not the case when compared to German models (climb rate).

    Hubert "Hub" Zemke, P-38, P-47, and P-51 pilot and fighter group commander

    Edward B. Giller, P-38 pilot, 55th Fighter Group

     
  5. alejandro_

    alejandro_ Member

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    20th Fighter Group Headquarters
    APO 637 U.S. Army
    (E-2)


     
  6. Balljoint

    Balljoint Member

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    It’s my understanding that the mach problem with the P-38 originated with the original “interceptor” design spec that required a very high RoC. To meet this spec the wing was designed to be rather thick. This led to a transonic aero phenomenon as the slipstream accelerated over the thick wing. Specifically, the CoP moved back on the wing causing the aircraft to pitch on its back resulting in breakup. Two or three test pilots were killed before the plane was released to service uncorrected.

    The “dive brakes” fix actually functioned to shift the CoP forward into a stable position. After a tough teething period the P-38 matured into a rather good if expensive plane.
     
  7. drgondog

    drgondog Well-Known Member

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    The Dive Brake primarily kept the P-38 from immediately entering into drag Divergence regime leading to transonix Mcr - (which had the effect of moving CoP aft as the shock wave formed at 25% chord and moved aft.. in other words it didn't move anything, it kept 'anything' from moving aft.
     
  8. Balljoint

    Balljoint Member

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    Put much better than my attempt. The pitch was indeed forward and the CoP was stabilized so it didn't wander.
     
  9. drgondog

    drgondog Well-Known Member

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    #9 drgondog, Sep 25, 2012
    Last edited by a moderator: Sep 25, 2012
    The 'later on' was the P-51B which arrived in ETO combat in Sep 1943, then added 2 more in Feb 1944, then 1 more in March, then more in April and May. The two P-51B Groups (354 and 357FG) destroyed far more German aircraft during Big Week and nearly as many as the 10 operational P-47 FG's during Big Week (Feb 20-25, 1944).

    ETO (8th/9th AF FC Victory Credits during Big Week) - The P-38s (10), P-47s (78 ) P-51 (64.5), From start of Big Week to end of March, 1944
    P-38 (35). P-47 (316), P-51B (318.5) where most of the P-51 credits were against LuftFlotte Reich which had been steadily building up with veteran Gruppe's transferring into Germany November 1943 - February 1944. In other words the Reich composition was not 'rookies' -
     
  10. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Shortround6 and GregP covered most of the questions, I'll attempt to answer the bolded one.
    The issues early models had in high alt (and not only there) were mostly connected with insufficient capacity of the intercoolers, so the engine had problems developing the power it was supposed to do. EG. the P-38H was restricted to 1425 HP per engine (with B-33 turbo), while the P-38J was managing 1600 HP, with same engine. The pre-J models have had the intercoolers tailored for 1100-1200 HP engines, and were hard pressed to do their job with growing engine power, while the intercoolers in the J and later models were able to support 2000 HP per engine (maybe more?). The Mike Williams' site has some fine data about the late P-38's V-1710s tested with more than 1600 HP.
    Sure enough, the cold pilot compartment was the issue also with early models.
     
  11. bob44

    bob44 Member

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    Good reading here. Some of this I have seen before, some is new to me.
    A couple of things come to mind.
    First, the frozen turbo regulators. How is it the B17 engines with turbos did not seem to have these problems? Perhaps a different setup than the P38?
    Second, the P38's flying in the Aleutians did not seem to have these cold temp problems. Must have been just as cold or colder. What were they doing different from the European P38's?
     
  12. Aaron Brooks Wolters

    Aaron Brooks Wolters Well-Known Member

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    I found this video on YouTube. Lt. A.F. Shaw is narorrating. He explains to some degree how the got more mileage out of the P-38, if you listen you will hear him mention Lindberg's name. Charles Lindberg spent time in the Pacific as a civilian observer, I did not know this until about a month ago. Looking for that video at the moment. But CB explained and showed them that they could run longer and farther on the same amount of fuel running different settings. I know not enough about this to explain it so I won't try but if I can find the video I will post it. I just thought you guys might like this.
    Here's the link:

    View: https://www.youtube.com/watch?v=Mjlp5rmGM-Y
     
  13. Hop

    Hop Member

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    By the time the P-38 arrived in Europe almost all the aviation fuel was being supplied by the US.

    Early US "100 octane" fuel did have very low aromatics. As a result it had very low rich mixture response, typically rated 100/102.

    When the UK adopted "100 octane" the specification called for a much higher rich mixture performance, typically 100/125 or 100/130. This was achieved with much higher aromatics.

    In 1941 the US adopted a similar specification to the UK, 100/130. This fuel too had an aromatic content of around 20%. It was this fuel that was supplied to Europe.

    If the Allison truly had a problem with the aromatics, which is unlikely, it was a problem with the new, higher performance fuel the US had standardised on, and was producing in vast quantities. The only thing "European" about the fuel is that it was similar to the "100 octane" the RAF had adopted in order to get more power. The US adopted it for the same reason. 100/102 fuel didn't allow enough power to be produced.

    Far more likely is that the P-38 ran in to problems when the US increased the tetra ethyl lead content of 100/130 fuel in 1943. This was done in order to increase production. A letter from the British Air Ministry, after being informed of the change in the US specification:

     
  14. Shortround6

    Shortround6 Well-Known Member

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    Thank you for this information.

    To date a really comprehensive history of aviation fuel in the 2nd World War has yet to be written. And I have a copy of "Development of Aviation fuels" by S. D. Heron. While it contains much information it doesn't usually give exact dates on when certain changes occurred. It was also written in 1949 and may not represent the Axis side very well. While the Author was well acquainted with the Allied side of things he relied on war time reports and probably a hasty post war analysis of the German developments.

    There was not only a problem with the lead content but certain compounds were allowed to be used to stretch the supply of 100/130 fuel. Not only does adding lead cause plug and other problems but the lead usually works on a declining scale. Adding 1 cc of lead can give a pretty good improvement. going from 1cc to 2cc's shows a good improvement, going from 5cc to 6cc shows an improvement that can be measured but is a much smaller improvement than the 1st or 2nd cc. Some of these compounds brought problems of their own and you cannot lead dope most fuel stocks with enough lead to reach 150PN. You may not be able to lead dope some base stocks to reach 130PN.
    Some of these compounds were "heavy" compounds that had higher weight and lower volatility than the bulk of the compounds used in fuel. They tended to separate out or cause the fuel blend to vaporize less readily than early fuel batches. Not a problem in North Africa but over Europe in the winter at 30,000ft?

    The Aleutian Islands are actually not that cold. There is only about a 10-20 degree variation from summer to winter and the average temperature is a few degrees above freezing.

    Back to the poor piloting technique, Low boost and high rpm vs high boost and low rpm. The friction goes up with the square of the speed so the engine is using a lot of power ( relatively speaking) in friction turning the higher rpm while cruising this way. The low boost means the air wasn't heated much in the turbo by compression and then it still went through the inter-cooler leading to cool or cold air in the intake manifold even after the engine supercharger. It also means the engine is running relatively cool and trying to go to full throttle is that much more difficult. Using fewer rpm but more boost means less friction, warmer air in the intake manifold for better vaporization, the turbo spun up a bit more and not lagging if higher power is called for in a hurry, and the engine intake manifolds are bit warmer and a large quantity of fuel air mixture as the engine is "opened up" is less likely to separate out and have raw fuel puddling on the bottom of the manifold.

    Allison was aware of the fuel problem and was working on a new intake manifold before the first P-38H ever got to Europe. New Manifolds were being fitted to production engines (ALL engines?) in Nov or Dec of 1943 and manifolds were sent out into the field for refit.

    Bombers do not fly like fighters, they may be using a higher percentage of their normal power in cruising flight than the P-38. They change altitude much more slowly allowing time for the "frozen" turbo control to catch up. The radials have shorter intake manifolds/runners than the V-12 giving the fuel less opportunity to "puddle". They have a flight engineer to monitor the engines while the pilot flies the plane.

    Slight changes in component location or linkage runs can also affect performance. Why did that P-38 Squadron in the CBI theater blow up 10-12 engines on one side of the P-38 for every one blown up on the other side?
    They found the problem by flying with parts of the cowl removed and a factory representative crammed in the space behind the pilot observing the operation of the linkage.

    As I said earlier this was a problem with many contributing factors.
     
  15. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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  16. GregP

    GregP Well-Known Member

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    Hi Hop,

    It is not "unlikely" the P-38 had issues with aromatics, it is a fact. One of the best people in the world on carbureted engines of the WWII variety is Pete Law. He is local and a good friend of the shop and the planes of Fame Museum. . According to Pete, if you jet for the low aromatic gasoline and then run with the high aromatic gasoline, you will be considerably mis-jetted. Since the later American gas was aromatic adjusted up, the factory carburation settings were ALSO adjusted and they left the factory with correctly-jetted carbs. The P-38 had pretty good ram air flow. It was much better than the P-39, P-40, P-63 flow and the P-38 tended to lean out and mid-range morethan those aircraft did. Still holds true today and the carbs have to jetted correctly.

    Today, we jet for the fuel available today, and our Allisons run JUST FINE, ask any owner of a Yancey's Allison.

    Rod Lewis is running 5 of our engines (4 for his P-38 Glacier Girl ... two at a time, and one for his P-39, Brooklyn Bum). He is a happy camper. So is Tom Friedken, the Planes of Fame, Graham Frew in New Zealand, Bob DeFord with a Spitfire replica, Steven Gray in the UK, and probably another dozen P-40's and assorted tractors and thunderboats. As I stated, our engines are in all the flying P-38's in the world except for the red Bull aircraft in Switzerland. They run engines from another builder. We have a a very healthy backlog right now, too, and demand is good.
     
  17. alejandro_

    alejandro_ Member

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    By 1943 Luftwaffe losses had risen to alarming levels, see graph below.

    [​IMG]

    By the time the Big Week was launched the Luftwaffe had already been weakened, and Allied tactics were much more effective. This led to massive losses (funeral of the Luftwaffe according to some).
     
  18. Hop

    Hop Member

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    That's the point I was trying to make. It's unlikely the aromatic content was a problem for the P-38 in Europe because by the time they started operations they would have been using 100/130 fuel to the standard US specification. The US adopted 100/130 high aromatic fuel in 1941.

    What did change suddenly in 1943 was the lead content of US supplied fuel, and as we have seen from the British tests, it caused major problems for the Allison engine.
     
  19. drgondog

    drgondog Well-Known Member

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    I'm not sure which conclusions are self evident? First what is the source? Second - where is the breakout between MTO/ETO and East? Third - there is no doubt the ETO became more dangerous for Luftflotte 3 pre-Schweinfurt as well as Mitt through October. Another point that the chart displays is that LW losses went down after October 1943 (when 8th AF quit going deep to recover from Aug/Oct Schweinfurt losses)until Feb 1944 when the really big shift to reinforce Reich defenses took place.

    To illustrate your point you might just extrtact Reich/West from all the other losses and display them separately through May 1944.
     
  20. GregP

    GregP Well-Known Member

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    Sorry Hop,

    The P-38 did have problems with European gasoline. We have far too many former P-38 pilots come to the Planes of Fame Museum and our shop telling us it was so for it to be dismissed so easily. One of Joe Yancey's best freinds was Lefty Gardner who flew the P-38 White Lightning for so many years in airshows and at Reno. His son is still a good friend. Lefty was there in Europe when the issue was happening. Mostly he was flying bombers at the time, but got the occasional P-38 flight in himself. He spoke with very many of the P-38 escort pilots and his story of the P-38 was acquired first-hand.

    If people chose to not believe it, that's their choice, but the facts are out there if one cares to dig for them. Since we build the Allison V-1710, we get a lot of war memories via stories from former operational pilots who come visit from time to time. Of course, they are getting fewer these days. They love hearing the engines and it brings back vivid memories for most.

    We definitely have to rejet from stock carb specs to get the engines to run well on modern fuel, but it can be done ... at least WE do it and our engines run very well. Ask any owner of one.
     
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