Why was the La-7 so fast ???

Discussion in 'Aviation' started by timmy, Sep 3, 2014.

  1. timmy

    timmy Member

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    I cannot figure it out

    Under 10 000ft nothing could touch this thing!

    So let's compare it with say a FW-190 A8

    LA-7 14 cyl 41 lt radial 1700hp vs FW-190 A8 14 cyl 41 lt radial 1700hp
    LA-7 weight 3500kg vs FW-190 A8 weight 3500kg

    So unless the La-7 has a huge Aerodynamic Advantage over the FW-190, which I doubt
    I cannot see where this plane gets all its speed from. What am I missing here ???

    [​IMG]

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  2. Denniss

    Denniss Active Member

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    Supercharger setup and supercharger air intake were optimized for lower alts (Fw 190 suffered from internal air intake somewhat). Plus aerodynamic improvements on the La-7.
    One has to be careful with soviet data though, Prototypes tended to be way faster than production machines.
     
  3. tomo pauk

    tomo pauk Creator of Interesting Threads

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    #3 tomo pauk, Sep 3, 2014
    Last edited: Sep 3, 2014
    The aerodynamic advantage for the La-7 would be 4 gun barrels chutes less. The wing area was also smaller by some 5%. The weight figures from the post #1 here are way off, loaded A-8 was 1/3rd heavier than the La-7. For a more realistic comparison, the lighter Fw-190 versions, with less armament-related drag, were making 580-590 km/h at lower altitudes, and 660 km/h at 6-7 km.
    The La-7s produced in 1944, on the other hand, were barely beating 650 km/h mark; it took some time (talk 1945) to produce the serial examples that can do 670 km/h.

    So - the La-7 was fast because it featured a big powerful engine installed on a small airframe, while featuring a modest weapon fuel 'fraction'.

    BTW, the 'TsAGI book' charts tables tend to show many Western aircraft in an unfavorable light, better to use data from Williams' site for those.
     
  4. drgondog

    drgondog Well-Known Member

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    Both the FW 190A-8 and FW 190D-9 airspeeds shown are suspiciously low at SL.. the FW SL speed of 346mph is at 1.42 ata while the A-8 speed with 1.65 ata is 359mph.

    Not enough known about La 7 test and engine ratings to offer lucid comments
     
  5. buffnut453

    buffnut453 Well-Known Member

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    Why is the La-7 so fast? Soviet propaganda perhaps? Naaah...couldn't be! :)
     
  6. Ivan1GFP

    Ivan1GFP Member

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    A better comparision is between the La-5FN and the La-7.
    Both aircraft had the same engine and nearly the same weights, dimensions and planform and yet the La-7 is 20 mph faster. All of it was done with aerodynamic improvements.

    The most obvious changes were
    1. A laminar flow wing.
    2. A reshaped cowl.
    3. A relocated oil cooler.

    The laminar flow wing would presumably offer some improvement. The typical low maximum CL would be partially offset by the leading edge slats that was typical of the Lavochkins.
    The oil cooler was probably relocated on the theory that the further back you put a radiator, the better the aerodynamics because the air is turbulent behind the cooler. Perhaps it even makes some use of the Meredith effect.

    As for the Russian table, The relative speeds are questionable. The typical FW 190A-8 was a LOT faster than this graph shows. I figure a good estimate would be around 415 mph at 1.42 ATA and prbably a bit faster with 1.65 ATA War Emergency Power. This is from the USN test of a captured FW 190G-3 which was done without War Emergency Power.
    The speed claim for the La-7 is typicall 423 mph and 402 mph for the La-5FN. The Lavochkins also carry less armament, ammunition and fuel.

    As for loaded weights, a better number for a normal loaded weight for the FW 190A-8 would be around 4380 kg. Depending on the source, it can be anywhere between 4300 and 4400 kg. I can point you to a thread in which I discussed this topic in another forum.

    - Ivan.
     
  7. tomo pauk

    tomo pauk Creator of Interesting Threads

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    The La-7 was still using the NACA 23000 series wing, as was the LaGG-3, La-5 and Fw-190. Laminar flow wing was introduced with La-9.
     
  8. Juha

    Juha Well-Known Member

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    Late war Soviet fighters had very good aerodynamics.
     
  9. timmy

    timmy Member

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    It's making a bit more sense now

    Got my weight figures from wiki, I should have looked a bit deeper
     
  10. Milosh

    Milosh Well-Known Member

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    Your weight for the Fw190A-8 is empty weight. Normal loaded is 4400kg.
     
  11. DerAdlerIstGelandet

    DerAdlerIstGelandet Der Crew Chief
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    Terri-tzu oh where are you? ;)
     
  12. Ivan1GFP

    Ivan1GFP Member

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    If that is the case that the airfoil is a 23000 series, then why do you think it was so much faster?
    I thot the wing was a lot of the improvement, but if not, then how is La 7 so much faster than the La 5FN?

    - Ivan.
     
  13. Koopernic

    Koopernic Active Member

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    Ome of the problems with this chart is that from late 1943 BMW started introducing various improvements to the BMW801. The result is that By June 1944 both the BMW801D2 on the Fw 190A8 and the BMW801TS of the Fw 190A9 were producing 2000hp, not 1700hp.

    The sea level speed was thus 360mph (nearly 580kmh) which is of course much faster than the charts indicate. The engine produced about 590kmh (365mph) on the Fw 190A5, which was still in use.

    The BMW801TS had I believe slightly different supercharger settings and impellor fluid dynamics which showed up as an improvement at high altitude. The Fw 190A9/BMW801TS was set up with a supplementary fuel tank that could hold fuel, MW-50 or GM-1 depending on mission. If MW-50 was implemented it would have increased power to 2200hp. May have seen use on Bombers.

    La 7 probably was fast due to a smooth wooden skinning. The Fw 190 lacked a laminar flow wing, like the P-51 or Tempest, while the Germans seem to have allowed excessive weight growth to develop in the aircraft. It was rather over gunned in my estimation with 4 x 20mm canon and 2 machine guns. I can't see the value of the MG.

    The next engine for the Fw 190 was the BMW801F with 2400hp or 2600hp with MW-50, it was intended for the Fw 190A10 with an enlarged wing though I suspect it would have just gone into the A9 instead.

    The power growth of the Jumo 213 was running slightly ahead of the BMW 801 or at least mass of great interest to the Luftwaffe because of its ability to work better with MW-50 with lower octane fuels. Speed of the Fw 190D13/R25 with the Jumo 213EB engine was expected to achieve 400mph at sea level and 488mph at altitude. By optimising the single stage two speed Jumo 213A as a 'bodden motor' ie sea level motor sea level speeds of 400mph were also possible and run.

    I'm assuming the Fw 190A9 with BMW801F would achieve about 390-400mph at sea level given the 20% to 30% greater power and exhaust thrust.

    Although the Germans were movoing to the Ta 152C and Ta 152H with their greater wing areas and fuel capacity the Fw 190D9 with the same engines was clearly going to be much faster at low altitude. They would have ended up with an armament of 3 x 20mm MG213 revolver canon which were being tested on Fw 190 at the end of the war. The outer wing gun stations would become fuel tanks.
     
  14. Koopernic

    Koopernic Active Member

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    #14 Koopernic, Sep 3, 2014
    Last edited: Sep 3, 2014
    Ome of the problems with this chart is that from late 1943 BMW started introducing various improvements to the BMW801. The result is that By June 1944 both the BMW801D2 on the Fw 190A8 and the BMW801TS of the Fw 190A9 were producing 2000hp, not 1700hp.

    The sea level speed was thus 360mph (nearly 580kmh) which is of course much faster than the charts indicate. The engine produced about 590kmh (365mph) on the Fw 190A5, which was still in use.

    The BMW801TS had I believe slightly different supercharger settings and impellor fluid dynamics which showed up as an improvement at high altitude. The Fw 190A9/BMW801TS was set up with a supplementary fuel tank that could hold fuel, MW-50 or GM-1 depending on mission. If MW-50 was implemented it would have increased power to 2200hp. May have seen use on Bombers.

    La 7 probably was fast due to a smooth wooden skinning. The Fw 190 lacked a laminar flow wing, like the P-51 or Tempest, while the Germans seem to have allowed excessive weight growth to develop in the aircraft. It was rather over gunned in my estimation with 4 x 20mm canon and 2 machine guns. I can't see the value of the MG.

    The next engine for the Fw 190 was the BMW801F with 2400hp or 2600hp with MW-50, it was intended for the Fw 190A10 with an enlarged wing though I suspect it would have just gone into the A9 instead.

    The power growth of the Jumo 213 was running slightly ahead of the BMW 801 or at least mass of great interest to the Luftwaffe because of its ability to work better with MW-50 with lower octane fuels. Speed of the Fw 190D13/R25 with the Jumo 213EB engine was expected to achieve 400mph at sea level and 488mph at altitude. By optimising the single stage two speed Jumo 213A as a 'bodden motor' ie sea level motor sea level speeds of 400mph were also possible and run.

    I'm assuming the Fw 190A9 with BMW801F would achieve about 390-400mph at sea level given the 20% to 30% greater power and exhaust thrust.

    Although the Germans were movoing to the Ta 152C and Ta 152H with their greater wing areas and fuel capacity the Fw 190D9 with the same engines was clearly going to be much faster at low altitude. They would have ended up with an armament of 3 x 20mm MG213 revolver canon which were being tested on Fw 190 at the end of the war. The outer wing gun stations would become fuel tanks.

    The mike William site ww2 performance testing has charts with some of the boost improvements.
     
  15. timmy

    timmy Member

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    #15 timmy, Sep 3, 2014
    Last edited: Sep 4, 2014
    Yes I agree, even without laminar flow this plane should be fast. But really this fast ???

    Well I'm not really doubting the Germans had planes close to equal performance by 1944

    I really chose the Fw 190 A8 (early model) to make a point
    To me that model had the same big engines producing the same horsepower as the LA-7
    So all things being equal their performance should be similar :D

    But as has been pointed out to me the Russian plane does in fact have a weight advantage
    Possibly an Aerodynamic Advantage as well. Better Supercharger settings would also explain the speed

    Still if those charts are correct the Russians got a lot of plane for just 1700 hp
    Maybe it had some excellent ram effect qualities as well ????

    Edit: I keep quoting the LA-7 as having 1700 HP, when in fact I think its 1850 HP. Damn you Wikipedia :oops:
     
  16. Ivan1GFP

    Ivan1GFP Member

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    Aren't you a bit optimistic here?
    At 1.58 ATA at sea level, the 190A-8 was making about 2050 HP and reaching 359 mph.
    What kind of power output would it take to hit 390 mph at SL?

    - Ivan.
     
  17. Koopernic

    Koopernic Active Member

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    #17 Koopernic, Sep 4, 2014
    Last edited: Sep 4, 2014
    I'm using a calculation.

    Fw 190A8 at 2000hp with BMW 801D2 580kmh/360mph
    Fw 190A9 at 2000hp with BMW 801TS 578kmh/359mph
    The above are at a boost pressure of 1.58 or 1.65 ata or so.

    The following power increase were planned:
    BMW801TS 2200hp at 1.82 ata by using MW50, this is a 10% increase. The cube root of 1.1 is 1.032 so we might expect 596kmh/369mph.

    The speed at sea level is still under 50% of Mach so the rule is still fairly good. Remember also that jet thrust is providing around 10% of the power not taken into account in this calculation and only a square law applies to jet thrust increase.

    The BMW801F was expected to provide 2400hp and 2600hp with MW50. This is a 20% and 30% increase over the 2000hp BMW801TS. Using a cube law we would get 1.062 as cube root of 1.2 suggesting a speed of 614kmh/380mph and
    taking the cube root of 1.3 we get 1.095 and so a speed of 630kmh/391mph.

    359mph with 2000hp
    369mph with 2200hp
    380mph with 2400hp
    391mph with 2600hp

    Maybe even better since the power increases are mainly from boost pressure increases and so jet thrust might be up disproportionatly.


    The FW 190D9 speed is well documented: 376mph at 2100hp, possibly 385 or so with good tolerance of the airframe gap. 400mhh was reached with a version the Fw 190D9 with its 1st stage supercharger optimised for seal level power and 390 with C3 fuel.

    This is the "A Ladder also boden motor". Its probably at 1.8 or 2 ata though. I wouldn't think the Jumo 213 was much more aerodynamic than the BMW801 which is a very small frontal area.

    The 400/488 mph speed for the Fw 190D13/R25 comes from the Volume 3 of the Smith Creek book on the Fw 190.

    Champion of speed really was the P-51 with 150PN fuel, well over 410mph/660km at sea level.

    The Western allies had outstanding fuel. I would say Soviet fuel was fairly mediocre, about the same standard as German, which is why Russians used fuel injection on their engines as well.

    Laminar flow is worth a lot in drag reduction once Mach exceeds 0.5 or so as it has a high Mach limit.

    Germans did have laminar flow wings on Me 309 and BV 155 but neither entered production. One would have though that a simple conversion of Fw 190 to laminar flow wing would have added 20mph/30kmh.


    I am only using educated guess but the cube law works perfectly up to Mach 0.5 when I have checked the estimate against real life flown. There is a chart of power versus speed for a B-17E at 15000ft ranging from 600hp to 1200hp and the cube law works perfectly up to 317mph (about Mach 0.45). The chart is at ww2 performance testing.

    I would not dare to estimate the speed improvement at high altitude due to effects of Mach at high altitude and changes in engine full throttle height due to the higher boost failing.

    We don't know enough about Russian aircraft, please stick around.
     
  18. tomo pauk

    tomo pauk Creator of Interesting Threads

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    #18 tomo pauk, Sep 4, 2014
    Last edited: Sep 4, 2014
    Some of the refinements include installation of the U/C wheel well covers, weight was also supposedly cut down some 150 kg, the oil cooler features the boundary layer splitter (shades of P-51), and A/C nose is without much of the lumps bumps.

    The speed of the La-5 with the ASh-82FN engine is variously listed between 620 and 684 (!) km/h here:

    laas.JPG

    For completeness sake:

    laas2.JPG
     
  19. razor1uk

    razor1uk Well-Known Member

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    As a joke, ...they were fast because other wise Stalin or the Commissars would get them...
     
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  20. tomo pauk

    tomo pauk Creator of Interesting Threads

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    If I may cut in:

    In low gear, the max permissible (over)boost for the BMW 801D was 1.58, in high gear it was 1.65. Power setting known as "Erhöhter Notleistung" (roughly: "Increased emergency power"). Under the 'Start und Notleistung', max boost was 1.42 ata.
    For the 801TS, the max boost for "Erhöhter Notleistung" was 1.82 ata. 2200 PS before cooling fan power is deduced. 'Start und Notleistung' max boost was 1.65 ata; 2000 PS minus 70 PS for the fan.

    Not this old chestnut :)
    1.82 ata was a 'simple' overboosting. This chart (here) shows that Fw-190A-8 carried no MW-50 mixture, ditto for the A-9.

    It was more aerodynamic, as shown on the table posted several times elsewhere on this forum (erstwhile by our member with nickname 'bada')

    Standard Soviet fuel on the onset of the Op Barbarossa was of oct rating = 95. During the 1st war years the fuel quality varied a bit, that convinced Soviets to lower the compression ratios on some engines, like at the AM-38F (from 6.8:1 at AM-38 to 6:1); because of that, ever greater boost was to be used. The AM-42 went down to 5.5:1 with CR!
    The Germans decided to increase the CR when going from the BMW 801C to 801D, that might be called as a self-inflicted wound - greater CR means it is not so easy to overboost the engine when hi-oct fuel becomes available.
    Only major Soviet engine that used fuel injection was the ASh-82FN, with Klimovs and Mikulins staying with multiple carburetors.
     
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