1. #11
    M_Gunz's Avatar Banned
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    Originally posted by Kettenhunde:
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">the Ju-88 was about 9 km/h TAS faster in level flight at 10m
    Your speed will increase while in GE. Same power but with less drag equals more power available.

    It is not a "lift increase" but rather induced drag is dramatically reduced. Lift and drag are connected by design. The reduced in drag means the wing can lower its angle of attack to provide the amount of lift required. This increases the amount of available AoA to the aircraft. You can now use the same AoA at a lower velocity.

    Lift production stays the same and will only meet the amount of force required. </div></BLOCKQUOTE>

    This part:
    You can now use the same AoA at a lower velocity.

    And these:
    It is not a "lift increase" but rather induced drag is dramatically reduced.
    Lift production stays the same

    Are they not contradictory?
    I can see that with less drag you can go faster and get more lift for same AOA or same speed with more AOA
    or same speed on less power but how to get same lift with same AOA at lower velocity without "lift increase"?
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  2. #12
    Are they not contradictory?

    No they are not. In fact this is a key concept to the correct understanding of how airplanes work.

    Look at the force of lift over Coefficient of Lift and AoA:

    We can also see in the figure that the lift force curve is perfectly constant, which is reassuring,
    http://www.vanhaesendonck.com/...s.html#fig-force-ias

    GE allows our wing to move to a lower Coefficient of Lift at a lower angle of attack at a slower speed to produce the same amount of lift force.
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  3. #13
    AndyJWest's Avatar Senior Member
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    In a steady state, lift = weight. The point is that in ground effect you can get the same lift with less drag, or in the (simpler to demonstrate) case I give with constant power, same lift with lowered induced drag gives excess power, and hence increases speed. It is easier to measure speed accurately in IL-2 than induced drag, though the results I get make sense in this context.

    It might just be possible to measure the change in AOA (though not the absolute values, as I don't know the angle of incidence relative to the aircraft datum) - this will need averaging a decent sized sample of values at each of the different speeds and altitudes.
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  4. #14
    Good explanation, AndyJWest.
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  5. #15
    WTE_Galway's Avatar Senior Member
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    Most obvious example of ground effect in real life is these things ...

    http://www.youtube.com/watch?v...PzDM&feature=related
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  6. #16
    JtD's Avatar Senior Member
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    Try switching off "wind and turbulence" and the extra km/h at low altitude are gone.
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  7. #17
    JtD's Avatar Senior Member
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    The whole thing got me curious, so I did a little test, where I'd fly the P-38 at 2-5 and 40-50 meters altitude at various low speeds. This would give some AoA's and some cl's. The graph below sums it up, while I wouldn't want to bet at the exact characteristics (I would need to keep altitude exactly constant for that), it is obvious that there is some extra lift at low altitude in game and the ground effect is modeled. Please note that wind and turbulence have been turned off for this test, you leave it on you get other results.

    I'd suppose the ground effect goes up to something like 5m only, which is why the red line is steeper than the other - I started at 5m and kept descending down to 2-3m. So it might be parallel to the green at a higher level. Like I said, not exact, just proof of concept.

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  8. #18
    AndyJWest's Avatar Senior Member
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    Interesting stuff, JtD. The effect of turning off "wind and turbulence" needs further investigation - I'll repeat my tests with this.

    I've also had a brainwave - I may be able to run a test at constant altitude above sea level, running over one of the mountain-top runways on the relevant map, just to confirm that it is proximity to the ground that is causing the effect. More to follow...
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  9. #19
    one of the patches a while back, forget which one, had really prenounced ground effect, and then it got toned down with future patches.
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  10. #20
    JtD's Avatar Senior Member
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    Originally posted by AndyJWest:
    I've also had a brainwave - I may be able to run a test at constant altitude above sea level, running over one of the mountain-top runways on the relevant map, just to confirm that it is proximity to the ground that is causing the effect. More to follow...
    It might be easier to fly on a map like Burma, where you have rivers at altitudes higher than 0. More flat terrain than just a runway.
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