Shake test using applied force vs moment

[vorwald]

Has anyone ever used applied moment in a shake test? A friend asked me to comment on the pro/cons of force/moment on a heliocopter shake test.

 

[GregLocock]

Yes, we use a torsional shaker for driveline development. They are available commercially.

To be honest the advantages are not enormous since we don't have torsional accelerometers to go with them.
Cheers

Greg Locock

 

[hessian]

Yes, in looking at optical point-track system stability in an aircraft external pod rocking-mode situation. It was easier to design a fixture with a pivot at one end and a pivot over the shaker head. Then translational shaker motion creates uniaxial rotary random motion, which input into the optical system stresses the stability control algorithms/hardware. To prevent simultaneous correlated translation (if desired) you have to mount the payload at the stationary hinge. Note all this was done in the preliminary design phases on paper/computer sim. What was ACTUALLY done and the experience was the province of the engineers who stayed with the program.