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# Airplane flight characteristics

## Question

How do you determine what the stall speed of a plane is? Is there a way to do that other than experimentally?

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The stall speed is a little bit under the takeoff speed. I'm not sure if there's a calculator for it though.

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Moving to Gameplay Questions.

5 hours ago, MAFman said:

How do you determine what the stall speed of a plane is? Is there a way to do that other than experimentally?

Basically you just need to try it and see, as far as I know.

For one thing, "stall speed" depends on a lot of factors, including not just the plane design, but also how the various control surfaces are set, how you're piloting it, etc. (And that's before even considering varying atmospheric density depending on elevation and so forth.)

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Posted (edited)

Experiment is certainly the easiest way with KSP.

KSP wings have a very soft stall, with their max lift at 30° AoA and falling slowly after that.   You might not even notice the stall in KSP.

If you are still building airplanes for Duna, I guess you might want to know that KSP does have the force of lift vary according to  ½ CL S ρ v²,
where CL is the coefficient of lift, S is the conventional symbol for total area of the wings, and for density of air (1.1 kg/m³ at Kerbin's sea level)

So to fly nearly level for landing,  Mass × g =  Lift  = ½ CL S ρ v²,
On Duna g is only 0.3 as strong as on Kerbin. And ρ is 0.1 times as dense, even thinner over the higher mountains.  So you would need 3× the wing area for Duna as you need for Kerbin, or you land √3 times faster, but Duna is rough so you want the wing area.

( KSP makes two exceptions to the usual   Lift  = ½ CL S ρ v².  The game reports "relative wing area," where 'relative wing area' = 1 looks like 4 m².  The coefficient CL would normally be nearly constant for speeds below the speed of sound, but KSP makes the maximum CL quite large, about 8 based experiment, at low speeds, reducing it to 4 at 100 m/s and to the more realistic 1 at the speed of sound -- one more reason to use lots of wing to get landing speed well below 100 m/s. )

Edited by OHara

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