USAAF eval of Me-262

Discussion in 'Technical' started by Nikademus, Oct 1, 2009.

  1. Nikademus

    Nikademus Member

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    #1 Nikademus, Oct 1, 2009
    Last edited: Oct 1, 2009
    Hello,

    I was doing some reading up on the P-80 and found an interesting reference on Wiki (pauses for laughter........) about a USAAF evaluation that pitted the 262 against an early P-80 (probably an P-80A or earlier i assume since the mainline P-80C appears to have debuted in 1948. ) The report was quoted as comparing the Shooting Star unfavorably against the 262 despite the latter's greater weight. Yet the "stats" for the two planes suggests that the P-80 should hold a slight edge.

    Anybody have more info on this USAAF eval?

    Thx in advance.
     
  2. vanir

    vanir Banned

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    I suggest looking up test flight reports and early service reports of the P-80, notably that series of fatal and near fatal turbine failures.

    I suspect like with most comparative specifications they are not relevant to actual flying conditions, where all the smaller points like the feel of the aircraft to the pilots hand becomes all important, and its mid range performance and minor design innovations particularly with captured a/c which may contribute to overall flying characteristics, but not adequately recognised on the ground or on paper.

    Did you know the late production Jumo 004B had up to 7% bypass? This was to cool the turbine blades, but also contributed to additional (non-specified) thrust rating and fuel efficiency (probably the reason for the Me-262 very impressive range). That's about thirty years ahead of its time in axial jet design. This is strongly muted however by the substandard strategic materials available to Germany at the end of the war, and hence the unreliability of German manufactured jet engines. Soviet remanufactured Jumo and BMW engines in the late forties are a distinct contrast to the popular reputation of their unreliability, the Soviets raved about them and kept the Yak-17 fitted with remanufactured Jumo-004B's in service well into the fifties with an almost perfect service record, and then sold them to the Chinese where their service lives continued into the sixties. Not bad for a German WW2 jet engine.

    Then there is the good manners of the airframe itself, designed as a completely new train of thought on aircraft design rather than the initial Allied designs of basically fitting jet engines to piston aircraft designs. The Me-262 is noted for stable handling characteristics to transonic speeds, something which cannot be said of contemporary Allied a/c like the Meteor and P-80 which exhibited gross instability and heavy handling above 750km/h. The P-80 also had balance problems which were affected by things such as expending ammunition magazines, test pilots complained that if the magazines were not kept full ballast was needed to maintain good handling to compensate, and speculated that combat pilots would have problems with this (ie. combat landings after a sortie in which ammunition is expended were expected to be dicey).

    These kind of notations lead me to believe the listed specifications of a/c do not really reflect their comparative performance, hence the extent of comparative flight testing performed at places like Wright-Patterson even though the a/c in question had been pulled apart and examined already. For example in another couple of surprising flight tests, the Japanese Ki-84 actually shocked the pilots at Wright-Patterson, who gave it a higher recommendation than the Japanese themselves. And the late (VK-107 motor) Yak-9 they rated better than a P-51D under all conditions. Again the listed specifications would differ but are obviously non-reflective.

    The P-80 was fast, no doubt about that and particularly good at altitude and in the climb. But perhaps under combat conditions the Me-262 was a little nicer to fly and I'm speculating, but this made a telling difference?
     
  3. fibus

    fibus Member

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    This a very enlightening comment.
    I am not surprised about the Yak 9.
    Where can one find your reference material on line.
     
  4. vanir

    vanir Banned

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    #4 vanir, Oct 2, 2009
    Last edited: Oct 2, 2009
    A detailed analysis compiled by John Foster, managing editor of Aviation Magazine I downloaded on PDF from the web, can't remember the site but can be found by searching back editions of that magazine. This edition was published in November 1945 volume 44 number 11 and includes sections written by design teams and engineers and other sections written by the staff editors of Aviation Magazine. The copyright is held by JL McClellan on the pdf reproduction dated 2004.

    It gives a close examination, including parts photographs and diagrams specifically detailing the 7% bypass (bled from the area of the 4th stage of intake compression) and a powered, variable geometry exhaust cone (another simple innovation literally decades ahead of any other design).
    Remanufactured using heat resistant alloys the Jumo 004B returned more than 150 reliable hrs in actual flight testing and 500hrs without incident on the bench. It really is a tremendous engine hampered only by available materials to build it with, in service made with questionable quality steels it had an engine life of 25-30hrs maximum and required full tear down maintenance after 10hrs but there is no engineer who has personally examined this engine who does not state categorically this was entirely circumstantial and that Germany had a real winner with the 004.

    My notes about the P-80 is from the book Test Pilots by Richard Hallion and offers the comments of those who test few the P-80, there is a very good section about the P-80 in fact, its design features and early problems, and of course all about the P-59 (flown to 47,600ft in 1943 or 14.5km altitude), actually there's a funny story about the XP-59 flights, one of the test pilots Jack Woolams used to fly it wearing a Gorilla mask with a cigar hanging out of his mouth, no kidding, and he'd fly up to and alongside training flights of Thunderbolts who nearly crashed upon seeing a propless airplane piloted by a gorilla smoking a cigar. The idea of course was that the project was so top secret that Woolams figured when Army pilots saw a gorilla flying the new jet nobody would believe them if they tried to tell anyone about it. Or something like that. And of course then he'd go out of his way to buzz Army pilots in it, which if they did tell anybody would get him into big trouble.
    I'm not sure but I don't think anyone not part of the program actually reported seeing any propless aircraft flying around California in 1943 and I'm not surprised, but I can just imagine some conversations around the shower rooms on those Army bases.
    "I'm telling you man it had no propellers, and a gorilla was flying it...smoking a cigar."
    "Sure buddy, listen why don't you spend the next few days resting up at the base hospital."

    Oh yeah those P-80A's. Turbulent boundary air used to enter the inlets according to test pilot Le Vier, which caused compressor vibration and that was a serious problem. And General Electric having little experience making jet engines used substandard manufacturing procedures which led to a spate of near fatal turbine failures, quote "then P-80A's started dropping from the skies all over the United States." This wasn't solved until post war.

    Problems about airfame instability at high speed are detailed in the section on the Meteor in Ralf Leinburgers book "Fighter" but is a common theme of test reports of immediate postwar Allied flight testing of any early jet aircraft except the Me-262 which is noted as quite stable and nice to fly at speeds up to 0.88 Mach iirc. All other types, Meteors, P-80 and even the Heinkell job the Salamander He-163 had gross instability at speeds exceeding 750km/h until designs were improved. In fact the Sabrejet is the first postwar jet which solved this problem notably, although the British did improve the Meteor's qualities by redesigning the engine gondolas, mostly picking up an extra 150km/h in the F.3 this way (though you still wouldn't call it pleasant in high speed flight). As far as actual handling goes it appears to me there was the Me-262 and then the (production series) Sabrejet and MiG-15, whilst everything else was a step back.

    There have been recent reproductions of the Me-262 made in the US using small American turbojets with roughly the same thrust rating as the Jumo motors, as such the manufacturer claims their performance should be roughly identical. Pilots of these rave about its handling qualities particularly at high speed, but also throughout the envelope.
     
  5. Tzaw1

    Tzaw1 Member

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  6. red admiral

    red admiral Member

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    The Jumo 004 is not a bypass turbojet. It taps a small amount of high pressure air at the rear of the compressor to cool the turbine disks and bearings before being reintegrated with the main flow. This cannot be viewed as bypass. Moreover, Whittle's and Metrovick's turbojets also used the same method; this is almost never published but is fairly obvious simply by looking at the engines with the fan mounted on the drive shaft between turbine and compressor.

    For bypass turbojets, the earliest idea was from Whittle in the mid 1930s, and then developed further by Griffith and the RAe resulting in the Metrovick F3, the first bypass turbojet in 1943 (also the first propfan, turboshaft and marine gas turbine). The German's ran their own bypass engine, the DB 007 but it's near impossible to find any information.

    Having better quality materials would enable the 004 lifetime to improve giving itself a small improvement in reliability due to fewer material failures. It would not improve any other feature of the design. On the whole, the design was pretty poor, but able to be built in large quantities - though with questionable build quality. You only need to compare it to the Metrovick F2 axial jet to see the design differences (it's a good comparison as the mass flow rate is pretty much identical).
     
  7. NZTyphoon

    NZTyphoon Member

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  8. Milosh

    Milosh Well-Known Member

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    In the book Messerschmitt Me 262 Arrow to the Future Walter J Boyle, NASM, pg 139 it mentions the test was so favourable to the Me262 the test results were suppressed. The Me had better speed and acceleration and equal in climb; the P-80A was easier to handle and had better visibility.

    One also has to ask why Howard Hughes was not allowed to race his Me262 in the Bendix Jet Race?
     
  9. Nikademus

    Nikademus Member

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    Very helpful replies. Most appreciated. I figured it was a matter of Real Life conditions vs. paper stats. Doesn't help too that most of the websites one can tap tend to quote the later P80C/F80C varient. One of the things i like about this website is that it contains members who are willing to look beyond the stats for a deeper evaluation of the various planes. A refreshing change from the more simple...."Look at the stats...this plane is superior" viewpoints I tend to see elsewhere.
     
  10. vanir

    vanir Banned

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    #10 vanir, Oct 2, 2009
    Last edited: Oct 2, 2009
    Please tell me this isn't a droll British versus German technological ingenuity thing, it's so yesterday. You know I read in one British publication a diagram of how the German propeller was just a variable pitch unit that the British pioneered along with a vast underrating of their hydromechanical and electrical a/c management systems, when the funny thing is the aeromechanical screw for example is recognised today as a pretty nifty piece of "new" technology completely different from your typical variable pitch types, whilst the kommandogerat is recognised as a uniquely German innovation never matched by the Allies in wartime.
    England had its technological excellence too, notably radar development well ahead of Germany's, but credit where credit's due in the appropriate areas, patriotism/nationalism/picking sides is a poor argument outside a sports stadium.

    Do you have some links for this Whittle bypass? And it is engineers in the aforementioned publication I cited who refer to the Jumo as having "at least 7% bypass" and they remark about its uniqueness (again as mentioned bled from the area of the 4th compressor stage, this is an important distinction), and the variable geometry exhaust cone, my commments simply reiterate what they wrote about it. Perhaps you should be arguing your point of view with them? And don't forget it is also the Soviet service history of remanufactured Jumos which rave about its reliability, look up how long the Yak-17 remained in service and the celebration of this type due to its excellent motor among the Soviets, Chinese and North Koreans.
    Note that the Yak-15 wasn't in service as long, but most of those used captured Jumos without remanufacturing, just surpulus captured German stocks, though it was in service as a major Soviet postwar fighter alongside the MiG-9 (which used the BMW jets) for a number of years too.

    It is perfectly clear to me, and clearly outlined in authorative, detailed publication the Jumo was far from inferior and was an excellent design with a poor reputation wholly achieved by a lack of strategic materials and the circumstance of late war German industry. The earmarked 004C production series to be fitted to the Gotha 229 had pretty much double the thrust rating as the 004B with no significant design changes, though I accept this is a 'what-if' I'm stepping into on that, but it has to be recognised in fairness 004 series development was of course cut short and hampered in the first place.

    Of course please excuse me if my tone seems condascending as it is not my intention, at worst I am simply rather confused with what I'm reading. Links and diagrams might help. Just speaking freely, hope I did not overly offend :oops:
     
  11. Milosh

    Milosh Well-Known Member

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    The info I have on the 004C is 2238 lb which is not much more than the 004Bs 1984 lb. Even the 004D only had 2315 lb.

    Perhaps you meant the 004H.
     
  12. red admiral

    red admiral Member

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    Genesis of the Jet by Golley is a reasonable telling of Whittle's story. Its got quite a few pictures of various engines with fans and reheat. One of them is patent GB471368, which has a fairly bizarre fan arrangement. A much more rational design was the LR.1, which was the second high bypass turbofan to be designed that I'm aware of. Power Jets were almost finished building the prototype when they were nationalised and work halted. It was a two spool design with a bypass ratio of 2.5.

    The Development of Jet and Turbine Aero Engines by Gunston has the same drawings and a few others.

    The claim of 7% air bleed for cooling is repeated in quite a few publications with exactly the same sentence used. I've no problem with that, but air bleed doesn't make the 004 a turbofan. There is a similar air bleed for Whittle's designs, but this just isn't mentioned. I had to a have a good dig for a picture in the right orientation to show the cooling fan but eventually found a cutaway of the Nene. The cooling fan is mounted on the main shaft between compressor and turbine. The air was used primarily for turbine disk and bearing cooling.

    http://www.flightglobal.com/airspac...ls-royce-nene-engine-installation-cutaway.jpg

    Here's a really obvious cross section of the Metrovick F2 showing the path of the cooling air thats bled off the end of the compressor.

    http://i25.photobucket.com/albums/c84/AviationImages/MetropolitanVickersF2.jpg

    The variable geometry exhaust (not a new invention) was looked at for the UK engines (and variable geometry inlets) but simplicity was preferred given the small difference in thrust available (From an article in the RAE journal a few years ago). Its only when you have much higher temperatures that the pressure thrust becomes more important than that from the mass flow.

    I'm not so sure about the Russian's being so enamoured with the 004 and 003. What I've read on the subject (which isn't a great deal given the limited information not in Russian) seems to state the opposite. Yefim Gordon in Soviet Secret Projects: Fighters gives a summary of jet development indicating that the Russians weren't very happy with them. They did manufacture some improved versions with reheat which powered quite a few of the early postwar prototypes.

    The best source I've found on the 004 is "The Development of the Junkers Jumo 004B—The World's First Production Turbojet" by CB Meher-Homji in ASME journal. Its quite clear in there that most of the problems were due to design (compressor vibration, turbine vibration). Better materials would only improve life of the hot section by less creep, they wouldn't solve the other problems. Build quality isn't that great either on the example I've looked over and that probably adds a bit.

    Compared to the Metrovick F2, which was a contemporary allied axial design (not the later F2/4)
    Thrust: 1980lb for the 004B (though later uprated a bit to 2200lb, and 2640lb in the reheated 004E). 2150lb for the F2 (later increased to 2600lb, then 3850lb with the F2/4 with an additional compressor stage)
    Weight: 1650lb for the 004B (some sources give 1585lb which seems to be without cowlings) 1500lb for the F2
    sfc: 1.4lb/hp-hr for the 004B (which would be higher for the higher thrust, higher temperature 004E) 1.07lb/hp-hr for the F2
    Compressor: 8 stage axial for the 004, 9 stage axial for the F2
    Pressure Ratio: 3.14 for the 004B, 3.5 for the F2 (indicating the F2 should have lower fuel consumption but lower thrust)
    Mass Flow: 46.6lb/s for the 004B, 45lb/s for the F2
    Compressor efficiency: 75-78% for the 004 (actually lower than Whittle's centrifugal types, just), 84% for the F2
    Combustion Temperature: 775°C for the 004, ~750°C for the F2 (indicating the 004 should have greater thrust but higher fuel consumption)
    Turbine: single stage for both (no fir tree roots on the 004 though)
    Turbine efficiency: 79.5% for the 004, 90% for the F2 (mostly because the F2 had free vortex blading)

    I think that's a pretty comprehensive comparison; the 004 doesn't look that great alongside the F2.

    Source for most of the F2 stuff is The Early History of the Aircraft Gas Turbine in Britain by Sir William Hawthorne.

    The 004 had some nice features, the integrated starter motor with pull cord is great, and the Germans made big contributions in some areas like air cooling for turbine blades (alongside AA Griffith), but you can't get too carried away with what was actually produced. The 004 was a fairly simple design, able to be produced in large numbers, which is what was needed. It's actual performance wasn't that great compared to it's contemporaries - but it was enough.
     
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