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Adjusting Ground Effect

lionheart

lionheart

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us-arizona
Hey all,

How does one effect or tune the Ground Effect setting in the AIR file? I have a grid in AAM (Aircraft Airfile Manager) on table 400 for ground effects, and it has a fall off towards the right.

If I raise up the curve 'higher' along the curve, would that increase my lift for the wing above the ground?


This was my starting point...
3059t350r.JPG
 
I used to try and adjust ground effect to replicate the touchy landing behaviour of the U-2S back then (Area51 add-on).
IIRC, the graph gives you a coefficient that multiplies Cl depending on height above ground. So the higher the point on the graph, the more lift you get.
The issue was that the stall speed would be reduced, leading to totally unrealistic landing speeds.
But I am sure some would succeed modelling something nice.
 
Kekeleou has given the general idea.
The stock aircraft have a 400 like you showed. The horizontal axis is the ratio of wingspan divided by height above ground.
That height is the distance from the aircraft origin to the ground, not the distance from the bottom of the wheels.
The extreme right value has a ratio of 1.0 and a scalar of 1.0. This means that when the distance to ground is the same as the wingspan or higher there is no effect. The scalar values increase the CL as the ratio decreases.
When the distance to ground is half the wingspan the scalar is only 1.03 and when the distance is one tenth of the wingspan it is 1.16. So if your span was 30 feet and the distance from the origin to ground was 3 feet the stock effect would increase the lift by only 16%. For the full 1.25 scalar the ratio is 0.054 or about 1.5 feet, so you would almost never see that effect.

In practice it is the height of the wing above ground that affects ground effect, so a low wing airplane would have more than a high wing one and you could simulate that by giving them different values.

You might have an airplane where the lift coefficient is too high especially with flap down and it struggles to slow down enough to actually land. If this was combined with too much idle thrust, jet or prop, you might take a lot more runway to land. If it was an AI airplane and had bad contact point tuning like the Extra, it might have continuous touchdown smoke and never actually stop. In that case you could give 400 all 1's for scalars which might help.

I should emphasize the fact that the scalars operate on the sum of 404 lift coefficient plus flap delta lift so you could have a substantial increase if the flap CL was high.

I hardly pay any attention to 400 because most of my airplanes land at high AOA, have low CL values because of wing sweep, and relatively narrow wing span. You can not hold off or flare much without dinging the rear fuselage so the landings are mainly controlled crashes.

Roy
 
Thanks for the info on all of that, Roy. Much appreciated. I was hoping to adjust it up quite a bit higher then it is because I have these radical landing gear that are like rudders. They should contain lift, creating a lift cell, increased by ground effect. Experimenting (one time) last night on the scalers, it made no difference in handling, so I thought I would ask. This answers that.

Flaps with full angle seem to cause a balance issue at slow speed. I shouldnt have that, I think. But, I fear it might be a real world issue that the sim has found.
 
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