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Rodhern / Ferram-Aerospace-Research

Aerodynamics model for Kerbal Space Program
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Improvement: Stability derivatives in slow flight scenarios. #2

Open Rodhern opened 6 years ago

Rodhern commented 6 years ago

There is an issue where the stability derivatives are not determined for slow flight scenarios. The issue is that Cl (coefficient of lift) is checked at -30 and +30 degrees AoA. In slow flight scenarios, with speeds not too far above stall speed, it is easily conceivable that stable level flight is achievable, just not at either -30 nor +30 degrees AoA.

Obviously a lot of thought went in to the present solution. On the other hand, the calculation is only run when the player clicks to update the stability derivatives in the editor, so it might be acceptable to spend more calculation time performing a more brute force style search.

Rodhern commented 6 years ago

In this release, update 2, I have changed the AoA search method to one I hope will work better for slow flight scenarios.

Rodhern commented 5 years ago

It seems that the new AoA search method works better. However, Cl and Cd calculated for the initial condition for the stability derivatives are not updated with the found alpha (AoA). It should be possible to get better stability derivatives accuracy 'almost for free' by doing one more calculation update at the end of each series of iterations.

Rodhern commented 5 years ago

In this release, update 4, the AoA search method takes into account anticipated deflection of pitch control surfaces for stable flight. The new AoA search method is experimental in nature.