7A elevator spar crack

DanH said:

I suspect calculation would show the most significant load applied to that hinge point is not aerodynamic. Besides, the aero loads are not very cyclical.

Instead, take a look over your shoulder the next time you light off the engine, and later when you pull the mixture for shutdown. You'll see the tip of the elevator containing the heavy lead mass do a hard, wet-dog shake. It probably oscillates 2" or more at 3 to 5 hertz.

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But wouldn't that tend to put more load on the outer bearing rather than the middle one?

DanH said:

Instead, take a look over your shoulder the next time you light off the engine, and later when you pull the mixture for shutdown. You'll see the tip of the elevator containing the heavy lead mass do a hard, wet-dog shake. It probably oscillates 2" or more at 3 to 5 hertz.

Click to expand...

Would you expect to see this "shaking" even when the stick is held (full aft)? (So it is flexing rather than simply pivoting about the hinge line...)

Dean Pichon said:

Would you expect to see this "shaking" even when the stick is held (full aft)? (So it is flexing rather than simply pivoting about the hinge line...)

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Yes.

To be precise, some of the tip displacement is due to flex of the horizontal surfaces, and some is due to rotation of the fuselage around its longitudinal axis. The rotation is an equal and opposite reaction to the oscillating acceleration of the propeller/crankshaft mass. There is nothing abnormal about either the flex or the torque reaction.

If we get really precise, there is a very small hinge moment because the mass balance weight is near the oscillating tip while much of the opposing elevator mass is located more inboard, and thus sees less acceleration. It would be best to simply ignore this detail. It is not important in the context of this discussion, and almost guaranteed to confuse some readers.

Can you document your fix?

DanH said:

Instead, take a look over your shoulder the next time you light off the engine, and later when you pull the mixture for shutdown. You'll see the tip of the elevator containing the heavy lead mass do a hard, wet-dog shake. It probably oscillates 2" or more at 3 to 5 hertz.

Click to expand...

I KNEW I shoulda' bought that Innodyn.

wet dog shake

Mine doesn't seem to do that

Engine shut down pro

Instead, take a look over your shoulder the next time you light off the engine, and later when you pull the mixture for shutdown. You'll see the tip of the elevator containing the heavy lead mass do a hard, wet-dog shake. It probably oscillates 2" or more at 3 to 5 hertz.[/QUOTE]

You might try the shut down procedure outlined in the older Mooney Manual. Idle at 1000 pull the mixture to idle cutoff and as the engine quits pull the throttle closed it will stop some of the shaking. Mike