Aerodynamic forces and moments
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In the "Aerodynamic Forces and Moments" block, are the x/y/z forces assumed to act at the CG (such that the resulting moment from the forces acting at another point would need to be included in the moment coefficient about each axis)?
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Paul
on 30 Apr 2024
Port_1 — Aerodynamic forces
Aerodynamic forces (in the chosen output axes), returned as three-element vector, at the center of gravity in x-, y-, and z-axes.
Port_2 — Aerodynamic moments
Aerodynamic moments (in the chosen output axes), returned as three-element vector, at the center of gravity in x-, y-, and z-axes.
I'm not sure if that answers the question because I don't fully understand the parenthetical.
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Paul
on 3 May 2024
On input, the three force coeficients define the force acting through the center-of-pressure, which is the fourth input port to the block, which "can also be taken as any general moment reference point as long as the rest of the model reflects the use of the moment reference point."
The calculations inside the block add r1 x F to the moment defined by the three moment coeficients, where r1 is the vector from the cg to the cp, though it's really implemented as F x r2 where r2 is the vector from the cp to the cg. You can look under the block mask to see the implementation and open the HL-20 example on the doc page to see how the block is used.
On output, the aerodynamic force should treated as if it is acting through the center-of-gravity and the aerodynamic moment is the result of all aerodynamic forces acting around the center-of-gravity.
At least that's how it all looks to me based on the doc, the block implementation, and the HL-20 example.
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