Ki-61 Relativity

Discussion in 'Engineering Retrospective' started by squirl, Sep 25, 2005.

  1. HoHun

    HoHun FH Beta Tester

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    Hi Hammer,

    >Aircraft have only one cannon, its test weigth of variant aircraft without under wings cannon
    >(not Bf.109G-2/R6 )

    Roger! But is the variant the same one as tested for turn time? I believe it's not.

    That the absence of wing cannon is mentioned means that aircraft with wing cannon were known, too. The Tsagi charts also feature speed and climb graphs for Bf 109G-2/R6.

    >variant 1 Cl man=1,23 Clmax=1,447
    >variant 2 Cl man=1,196 Clmax=1,407
    >variant 3 Cl man=1,348 Clmax=1,586

    >IMHO variant 3 not real for radius 290m and time 20 sec

    Hm, Clmax (3 G) = ~ 1.0 * Clman, so 1.348 appears realistic in my opinion.

    Why do you believe it's not real?

    The weight calculation from the Tsagi charts indicates that 3309 kg were used for the Bf 109G-2.

    Do you have the radii for the other Bf 109 variants as well? I'm sure the Bf 109F had no wing cannon, so it's good for comparison.

    Regards,

    Henning (HoHun)
     
  2. HoHun

    HoHun FH Beta Tester

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    Hi Hammer,

    >U right, but turn speed for Bf.109G-2 highest Bf.109E-3
    >imho 109G-2 320kmph vs 250 kmph for 109E-3.
    >Hence Cl max for 109G-2 < Cl max 109E-3 too for Spit IX and Spit I

    Clmax = const if you don't change the wing.

    Mass (Spitfire IX) > mass (Spitfire I) => Vturn (Spitfire IX) > Vturn (Spitfire I)

    but

    Clmax (Spitfire IX) = Clmax (Spitfire I)

    Weight really is decisive :) That's why we need an exact weight for the Ki-61, too.

    Regards,

    Henning (HoHun)
     
  3. PressLuftHammer

    PressLuftHammer FH Beta Tester

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    Yes u right. turn time and radius for 109G-2/R6 different
    time about 22,5 sec but radius not unknow :(
    But i guess radius for 109G-2/R6 was it is more.

    Yes 109G-2/R6 was too but im not have radius turn for it aircraft.

    1. Spit I and Bf.109E-3 have small different Cl max for over G 3g
    Spi I Clmax=1.45 Bf.109E-3 Clmax 1,49

    2. Calculate Cl max for spit IX LF and Bf.109G-2
    too small different
    Spit IX LF Clmax=1,388 Bf.109G-2 Clmax=1,447

    3. Small different between Clmax calculate for Spit IX, Bf.109G-2 and
    SpitI ,Bf.109E-3.

    Spit I ->Spit IX, Clmax= 1,45->Clmax=1,388
    Bf.109E-3->Bf.109G-2 Clmax=1,49 ->Clmax=1,447


    Bf.109G-2\R6 in russian books can named "109G-2 пятиточечный"(five guns).


    Not have radius for other 109 variant :(
     
  4. HoHun

    HoHun FH Beta Tester

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    Hi Hammer,

    >Yes u right. turn time and radius for 109G-2/R6 different
    time about 22,5 sec but radius not unknow :(

    Ah! I hadn't noticed we were talking about two different Bf 109G-2 times - Pic. 26 has only the G-2/R6 value of ca. 23 s.

    I repeat your Russian test data:

    weigth 3023kg time 20 sec radius 290m result need Clman=1,23

    My calculation yields:

    weight 3023 kg, time 18.4 s, radius 242 m, Clmax = 1.48
    weight 3023 kg, time 20.0 s, radius 290 m, Clmax = 1.23

    Which only tells us that my calculation is consistent :-/

    >1. Spit I and Bf.109E-3 have small different Cl max

    The problem is, the Spitfire data of the RAE report is strange. Note it is "assumed" data. The Emil data was measured, as Alfred Price points out in "Spitfire - The complete fighting history", but unfortunately, I don't have that report.

    NACA made tests of the Spitfire and found they got Clmax = ~ 1.21 in turns at about 3 g (NACA Report L-334). Your calculation from the Russian tests shows 1.18, which is a good match.

    NACA report L-353 also measured a climbing (1 g, full power, flaps and gear up) Clmax = 1.64. The RAE report assumes 1.87, and so the rest of the values are too high, too.

    >Not have radius for other 109 variant :(

    Maybe they are given in Badger's scans? We could ask him.

    Regards,

    Henning (HoHun)
     
  5. PressLuftHammer

    PressLuftHammer FH Beta Tester

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    Certainly.

    Cl max linked with speed and trotle. Turn speed highes climb speed and Cl max (in climb)>Cl max (in turn).
     
  6. HoHun

    HoHun FH Beta Tester

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    Hi Hammer,

    >Certainly.

    The problem is, my calculations don't tell us which Clmax is right :-(

    >Cl max linked with speed and trotle. Turn speed highes climb speed and Cl max (in climb)>Cl max (in turn).

    My point was Clmax (NACA) < Clmax (RAE), and the NACA test was with an specially instrumented aircraft and is fully documented, so it's trustworthy.

    The NACA reports can be found here:

    http://www.hitechcreations.com/forums/showthread.php?s=&threadid=109977&highlight=characteristics

    Regards,

    Henning (HoHun)
     
  7. squirl

    squirl Well-Known Member

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    I know that all of these calculations are valuable as far as the accuracy of this game is concerned, but are we missing the underlying concept here?

    We have to ask ourselves, "Is this the first time anybody has ever tried to calculate these numbers?"

    The activity I have seen in this thread suggests that we have had to start from scratch, moving into areas of research not yet explored by this community. If we are currently "in the dark" about the true nature of the Ki-61's flight model, the developers must have been equally in the dark when the Ki-61 was first changed. Is it a good idea to "fix" something when nobody has any idea how it should be fixed? Is it a good idea to "fix" something when nobody has any idea that it needs to be "fixed" at all? In my opinion, it is a bad idea to do so.

    This discussion should have been held before the Ki-61 was changed, not afterwards.

    Not all is lost, however. If we are to act on the principle that we should conduct research prior to changes, we can simply move past changes into the future. In the case of the Ki-61, we can retroactively delay its flight model changes until further notice, in order to ensure that discussion will precede any changes. This can be accomplished by restoring the Ki-61, and any other flight models, to their original settings.

    It is possible that some of the original Warbirds modeling may be inaccurate, but it is impossible to determine this if there is no discussion - something which seems to have been lacking when the Ki-61 was changed. And one needs only to fly the FH Ki-61 to understand how a lack of discussion can have disastrous results.
     
  8. badger

    badger FH Beta Tester

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    What wing area did you use for calculations?
     
    Last edited: Nov 10, 2005
  9. badger

    badger FH Beta Tester

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    Speaking of NII VVS data for FW-190A it seams the wing area they used are closer to 18,6 m^2 than to 18,3^2 ;)


    http://FH-badger.narod.ru/077.htm
    (4th column take-off weight, 5th - wingloading)

    FW-190A-4: 3989 kg / 214 kg/m^2 = 18,64 m^2




    http://FH-badger.narod.ru/087.htm
    (4th column take-off weight, 5th - wingloading)

    FW-190A-5: 4070 kg / 218 kg/m^2 = 18,67 m^2

    FW-190A-8: 3986 kg / 214 kg/m^2 = 18,62 m^2
     
  10. badger

    badger FH Beta Tester

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    Emil data is strange too in this report:

    http://www.fourthfightergroup.com/eagles/spit109turn.gif

    Note they credited DB601A with 1200 b.h.p. at 12 000 ar 2400 rpm, but a glance at DB601A power curve makes it clear it were unable to produsce such power at such high alt at 2400 rpm. Actually, i believe even DB605A wouldn't be able to produce 1200 bhp at 2400 rpm at 12 000 feet.
     
  11. HoHun

    HoHun FH Beta Tester

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    Hi Badger,

    >Emil data is strange too in this report:

    I agree, but that's just the power figure. The British tested the lift coefficients of the Bf 109E wing und apparently used that data for the comparison.

    In the meanwhile, I have acquired a diagram from German wind tunnel testig showing the lift curve for a Me 109F (perhaps with square wing tips, but that just affects the wing area, Clmax won't be much affected). It shows a Clmax of 1.46 at 18.6° angle of attack (for clean condition, complete airframe, no flaps, no propeller, no slipstream).

    Such a Clmax value should be comparable to that experienced by a real aircraft in a high speed turn, and in fact the British report 1.44 at 6 G, which is very close to the German figure.

    The Spitfire data, on the other hand, appears too high since NACA flight tests with an instrumented aircraft indicated about 1.22 at 3 G, while the British data shows 1.45 at 3 G. (The Russian test was close to 1.2, too, but that may be coincedence.)

    Regards,

    Henning (HoHun)
     
  12. PressLuftHammer

    PressLuftHammer FH Beta Tester

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    22,48 m
     
  13. badger

    badger FH Beta Tester

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    Then i do not fully understand how you calculated 1,18 Clman for Spitfire Mk. IX

    Weight - 3292 kg
    Wing area - 22,48

    Alt - 1 km - pH = 0,1134
    Turn radius - 235 meters

    Did you use this data for calculations?
     
  14. PressLuftHammer

    PressLuftHammer FH Beta Tester

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    I'm use next data:

    Weigth 3293 kg
    Wing Area 22,48m
    Alt=1000m (Density q=1,1116)
    turn radius =235m
    turn time =17,5 sec

    calculate

    V=2*Pi*R/t= 2*Pi*235/17.5=84.33m/s(303.6 kmph)

    a=V^2/R=30.26 m/s^2

    over G=(a/g^2+1)^0.5=(30.26/9.81^2+1)^0.5= 3,24g

    Cy=2*m*g*over G/(S*q*V^2)=2*3292*9.81*3.26/(22.48*1.1116*84.33^2)= 1.185
     
  15. badger

    badger FH Beta Tester

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    Thx, it was mistake on my calculations, now i found it :)

    Still, you have a small one too, in your calculations:


     
  16. PressLuftHammer

    PressLuftHammer FH Beta Tester

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    Thx, u right its my mistake.
    Now recalculate

    Cy=2*m*g*over G/(S*q*V^2)=2*3292*9.81*3.24/(22.48*1.1116*84.33^2)= 1.178