Originally Posted by
megan
With some helicopters you can start the engine with the rotor held stationary, once at idle release the rotor brake, provided rapid rotor acceleration which was useful to avoid rotor blade flapping in high winds.
Yes. But this procedure was also found as a reason for a crash or two of a certain U.S. Mil helicopter
AFAIK. Sudden torque increase on shaft and near zero centrifugal force on blades could cause that drag brace, supporting M/R Blade in lead-lag direction, might become compressed instead of stretched during such fast acceleration - a condition, that brace might not be designed for. And repeating it may cause it to fail one day. Only a correct combination of torque and RPM increase will prevent this. I suspect some (big) propellers might have the same problem - part of pitch change bearing loaded with compression (as designed) but other side loaded in opposite direction - with loads spread somewhere else. It was often difficult to expain to some (pilots), that pulling a small airplane on the ground by grabbing a prop blade of variable-pitch propeller might not be a good idea, as pulling the airplane forward this way is entirelly different thing than pulling it thru the air with blades rotating-albeit it looks like there is no difference - at first glance.