Quote:
Originally Posted by Joe Perkel
A fascinating exercise in complex aerodynamics, I think the lesson here for us is care in control rigging and assembly.
For the purposes of WWI replica building and operation, directly from the AC 90-89A….
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Joe, What you have here applies to control surfaces. Suppose you needed to add equipment into a wing, say a strobe power supply near the wing tip. Suppose it was real convenient to mount the power supply near the rear spar.
That might actually be a bad idea. Just imagine what happens when the wing experiences the effect of g load. The weight of the power supply twists the wing very slightly toward a higher angle of attack. Now imagine the same wing tip vibrating in an up and down manner. The power supply's weight causes the wing tip to twist in a direction that increases the motion. Now suppose further that the new characteristic twisting oscillation frequency aligns with one of the wing's spanwise vibration modes. This is how you get into flutter below the Vne speed.
In general, mass should be added to surfaces at or slightly ahead of the local center of gravity of that section. There are a lot of knowledgeable and capable certified aircraft mechanics that do not understand this concept.
Mass distribution can be critical.
Sid