Stall speed of planes

Discussion in 'Warbirds International' started by demian, Sep 18, 2010.

  1. mumble

    mumble Well-Known Member

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    If you can find some Bf-110 pilot notes, or some useful information, please post it here.
     
  2. Funtom

    Funtom Well-Known Member

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  3. Red Ant

    Red Ant Well-Known Member

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    I didn't mean it like that. I'm just warning you that exec probably won't give much credence to any conclusions based on that data. Sorry if I came across a bit snotty.
     
  4. gandhi

    gandhi Well-Known Member

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    Induced drag: the drag component created by accelerating air perpendicular to the aircraft's motion (lift)

    Parasitic drag: the drag component due to the acceleration of air in the same direction of the aircraft's motion (kind of drag that permits drafting)

    Total drag: the sum of the two

    At low speeds, such as near the stall, induced drag becomes dominant. And drag coefficients are a unit-less measure of how "effective" a wing or shape is at creating drag: the higher, the draggier. Neither speed, air density nor an aircraft's size have much impact on these coefficients (at least within the limits of WW2 aircraft).

    The formula for the induced drag coefficient is simple, because Newtonian physics can account for induced drag (the inescapable truth is that lift is created by pushing air down): Cdi = Cl^2/(pi*aspect ratio)

    And since I can obtain lift coefficients of FH planes using real-world wing area and masses, and can calculate the total drag coefficient based upon how much a FH plane decelerates and descends in a power-off state, the following plots can be made:

    F6F-5 no flaps:
    [​IMG]

    A6M3 no flaps:
    [​IMG]

    So keep in mind, the FH data is the total drag coefficients, while "Theory" is the induced drag coefficient obtained from the FH lift coefficients. In the Hellcat's case, the total drag is 50-100% higher than the theoretical induced drag alone. For the Zero, the total drag is 100-200% higher than just the induced drag.

    So I see there as being three possibilities:

    1. The parasitic drag is much too high. Theory predicts that induced drag should be in the neighborhood of 80+% of the total drag near the stall. Assuming the induced drag is modeled properly, a grossly inflated parasitic drag coefficient may be to blame.

    2. The induced drag is much too high. This is likely, because total drag climbs with lift coefficient like it should due to induced drag, although the individual values are excessive.

    3. A combination of both. This is probably the case. I can isolate parasitic drag coefficients from the induced drag ones by comparing drag in dives with conditions leading up to a stall, although there are still complications (propellers idle vs off, etc.)

    This is actually an apt comparison because the aspect ratio I found for both aircraft is 5.5, which means their induced drag should be nearly identical given equal lift coefficients. Under real conditions, however, the Hellcat would need a higher lift coefficient to match the Zero's turns, creating a lot of drag and negating the Hellcat's power advantage.

    In any case, it appears that a fundamental part of the modeling is way off, making these 2 aircraft (and likely others) bleed energy more than they should during maneuvers. Comparing only these two, a kind of advantage emerges for the Hellcat, in that it's drag is inflated less than that of the Zero.
     

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  5. mumble

    mumble Well-Known Member

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  6. gandhi

    gandhi Well-Known Member

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    Some tests on the Yak3. 100% fuel, mass of 2692 kg, wing area of 14.85, aspect ratio of 5.6.

    No flaps:
    [​IMG]
    (Cl max of 1.53, earlier test in v1.67 yielded 1.52)

    100% flaps:
    [​IMG]
    (Cl max of 2.08, highest result yet)

    Drag plot:
    [​IMG]

    And yet the Yak3 is a drag queen like the other two planes tested thusfar (see lack of data points with flaps). FH total drag values range from 2-6 times induced drag theory. They shouldn't be much more than 25% higher. The lift coefficients look reasonable compared to literature, but are excessive compared to other FH Warbirds.

    If you've flown the Yak3 on the FH, then you know how fun to fly it is. The superb lift coefficients explain why, and I dare say the drag actually helps the Yak. It recovers energy so quickly you can use large changes in speed to your advantage. YF-16 test pilots, flying a much hotter aircraft than the one that made it to production, did as well. They called it "dumping and pumping," referring to energy and maneuvering, respectively.

    For comparison, check out these plots of a Cessna 172. The fact it produces more lift and less drag than many Warbirds here is certainly an open challenge:

    [​IMG]
    [​IMG]
     

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    Last edited: Sep 22, 2010
  7. demian

    demian Well-Known Member

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    [​IMG]

    old Gandhis work for 1.67r2
     
  8. demian

    demian Well-Known Member

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    Gandhi , what do you think about comparing new ki84 and yak3?
     
  9. gandhi

    gandhi Well-Known Member

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    Yak-1B PVO:

    [​IMG]

    Wing area: 17.2 m^2
    Mass: 2883 kg

    CL Max:
    No flaps: 1.42
    Flaps: 1.95

    Stall speed:
    No flaps: 158 km/h
    Flaps: 135 km/h

    Almost as good as the Yak3.
     

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  10. gandhi

    gandhi Well-Known Member

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    Ki-44 II (2764 kg, 15 m^2):

    [​IMG]

    CL Max:
    No flaps: 1.60
    100% flaps: 1.95

    Stall Speed:
    No flaps: 156 km/h
    100% flaps: 142 km/h

    That's right, FH says the Ki-44's wing is between 24 and 30 percent more efficient at creating lift compared to the Zero (depending on flaps). Consider what Rene Francillon wrote in Japanese Aircraft of the Pacific War, "The Ki-44 was restricted against snap rolls, spins, stalls and inverted flight at high speeds..." One could argue that this was at least partly due to the lack of experienced pilots later in the war, but it speaks also to the Ki-44's wing design. The '44 was a good interceptor, but the FH version is so much more than that. In terms of dogfight capability, I think the FH Ki-44 holds the edge over the FH A6M3, which speaks volumes about how crazy things are with the models.

    Spit Vb (3071 kg, 22.5 m^2):

    [​IMG]

    CL Max:
    No flaps: 1.31
    100% flaps: 1.68

    Stall Speed:
    No flaps: 149 km/h
    100% flaps: 131 km/h

    These lift values are high, but not as high as I suspected. Then again, the Spit Vb isn't the most noteworthy of the Spits in the FH lineup. Do note, however, how high the alpha can go before loss of control, about 30 degrees (I suspect it's also possible with flaps). It takes a good FH fighter 1.5-2 seconds to turn that far. The plane's a great snapshooter, and can defeat the few planes that are more agile than it is on that fact alone.
     

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  11. looseleaf

    looseleaf Well-Known Member

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  12. demian

    demian Well-Known Member

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    So, according to those results , Yak PVO is more similar to Yak 3 than one would expect it.. I am not surprised since 109 g2 was one of 109s that could
    maneuver fight in close combat versus Yak3. And this PVO thing can fight easily g2.Not good since it will be out in early 1943 . Reds got another good weapon, if you ask me too good.

    I must change subject now , have to say something about other side (can u believe it? there is actually one more side beside red one) and is concerning japs.
    Last night in training arena we did some comparing of Ki43 versus A6m series. Long story short, what surprised me is fact that Ki43 was not able to outturn any of a6m models. Ki43 was outturned by all 3 models of zero.
    And that doesnt happen like you may expect it after 10-20 turns, it happens sooner.According to old warbirds, ki43 should outturn and kill zero , all 3 of them without hard work. I guess our I153 is actually original ki43...:confused:


    See what Hoof says about original wb :

    In the Main Arena of Warbirds, the Ki43 is the premier Zeke Killer.The Ki43 beats the Zero at it's own game: turning. And the advantage isn't a minor one, in sustained turns the Ki43 is up to a full second faster than the best turner of the A6M series, and two seconds faster than the A6M5 (for each 360 degree turn), the most commonly used Zero. Instantaneous turns are good on this plane too, it is the only plane, other than the A6M2 to break 10 seconds in a single 360
     
    Last edited: Sep 24, 2010
  13. gandhi

    gandhi Well-Known Member

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    I thought it appropriate to do this test with the recent change in RPS trends.

    SpitIXc (3379 kg, 22.5 m^2):

    [​IMG]

    CL Max:
    No flaps: 1.52
    100% flaps: 1.95

    Stall speed:
    No flaps: 145 km/h
    100% flaps: 128 km/h [highlight](lower than A6M3, best Zero model)[/highlight]

    Min. turn radius (sea level, flat turn at CL Max):
    A6M3 100% flaps: 131m
    Spit IXc 100% flaps: [highlight]128m[/highlight]

    A6M3 no flaps: 153m
    Spit IXc no flaps: 165m

    360 turn time (150% stall speed, flat turn at CL Max):
    A6M3 100% flaps: 15.3s
    Spit IXc 100% flaps: [highlight]15.1s[/highlight]

    A6M3 no flaps: 16.6s
    Spit IXc no flaps: 17.2s

    Who needs the speed of the Yak3 when a tighter-turning, vertical maneuver-dominating, Hispano-packing, fast-accelerating ride is available much earlier?

    Notice also the flat peaks of the Cl charts. A gentle stall is the icing on the cake, making maximum performance turns that much easier. The Spitfire is said to have had a gentle stall in real life (washout), but this also degraded the drag benefit of the elliptical wings and meant that only part of the wing could fly at the maximum lift for any given angle...

    Moral of the story, with flaps down on FH the Spitfire IXc is better than any Zero or Ki-43 (A6M3 is better than Ki-43). As is always said, the pilot makes the difference, but for pilots of equal skill the one in the Spit is in an entirely different league compared to his Zeke counterpart.
     

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  14. Mcloud

    Mcloud Well-Known Member

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    Last edited: Sep 25, 2010
  15. gandhi

    gandhi Well-Known Member

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    And now by popular demand the P-38F (7212 kg, 30.43 m^2):

    [​IMG]

    CL Max:
    No flaps: 1.25 (lowest yet recorded)
    100% flaps: 2.34 (highest yet recorded)

    Stall speed:
    No flaps: 200 km/h (125 mph)
    100% flaps: 146 km/h (91 mph)

    A CL max of 2.34 is not excessive for a Fowler flap design, as the scan below shows. The problem, though, is that some planes are more "reasonable" than others.

    From Airplane Performance Stability and Control, by Perkins and Hage:
    [​IMG]
     

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  16. Higgns

    Higgns Well-Known Member

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    Other than this last update changing a lot of flying characteristics on many planes, most of what I've seen in warbirds is slow creeping improvements in the entire planeset taken as a whole........except in the extreme cases like the original KI44 and J2m having to be dumbed down a bit.
     
  17. gandhi

    gandhi Well-Known Member

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    Finished some interesting tests with boa in the TA a while ago. Turns out that the Spit IXc loses somewhat decisively in a sustained turn fight with the Zero, even under the conditions used for the stall test. Why? I think the answer is drag.

    In a bit of justice, physics appears to limit the Spitfire's sustained turning ability. Higher lift coefficients help you turn, but they make drag. Lots of it. It's a square relation, meaning you quadruple your induced drag if you double the lift coefficient. So for the ratio of 1.95 to 1.5 in favor of the Spit IX, it makes about 70% more drag. The Spitfire IXc has "only" 42% more HP than the A6M3, which would roughly be the margin of thrust when speeds are at parity. When I was using flaps and boa wasn't, theory states the Spit makes 2.29 times the amount of drag.

    Indeed, looking at the decelerations from the unpowered CL tests, the Spitfire IXc produced about 10,000 N of drag near its CL max with flaps, while the A6M3 made about 5,000 N with flaps. Without flaps it was about 6-8,000 N for the Spit and 3-4,000 N for the A6M3.

    What does this change? Only a few things. The Spit remains a deadly opponent, capable of eyewatering instantaneous turns, climbs and snapshots. Most Spitfire engagements seldom slow down to sustained turns, in my opinion. And, as always, the Spitfire can use smooth vertical maneuvers to keep energy high to defeat adversaries, as it so often does.
     
  18. mumble

    mumble Well-Known Member

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    Please, no more dumb this down, or uber that some. Let's just make it the way physics says it should be. :znaika:
     
  19. gil---

    gil--- FH Beta Tester

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    That is what i was talking about in PVO thread :) Also add "not loosing parts since 680-690 IAS".

    The only advantage of yak-1-111 is speed at sea level: 535km/h, its about 7-8 kmh faster than 109g2 and 3-4 kmh faster than Ki-44.
    If we compare power, weight and wing area of yak-1-111 (basic is same as PVO) and Ki-44-II, or 109g2 it comes to interesting result, like Ki-44 should make about 1.5 times more parasitic drag at certain speed than yak to compensate 22% of ki power advantage and yak's +14.3% to wing area. Especially if we keep in mind that yak still turns better (so its thinner wings are thinner only in straight flight, when it turns, they are ok. :).

    But in defence of yak i can say that some results of its IRL trials can look too good in compare with other planes due to its simple handling, there are plenty of materials about it, so it should be relatively easy to measure real high limit of its performance. And its trials results may be just closer to theory.
    Thats only guess i can try as reason of one plane being both faster and better turning than its opponent with much more power/mass.
    :dunno:
     
  20. Higgns

    Higgns Well-Known Member

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    I'm not suggesting dumbing down planes.

    I mentioned the dumbing down that had already been done to planes that were glaringly wrong (uber) when first introduced long ago like the J2m and ki44.

    I meant that the planset as a whole has been slowly creeping toward uber with most changes being in the positive direction instead of very small changes pulling back certain planes that outperform thier real life counterparts.

    IEN had troubles with this and still do.