New Gearbox Failure on 912IS - Causes?

Adam Dickson wrote:

What propellor type/diameter are you using?  CSU?

It's a NEUFORM C3 - 65" on a Flight Design CTLSi. 

I don't think it's the gearbox either. Something else on the plane. I've seen this many times on planes where they swear it's the engine or prop. It can be wheel pants and several other things.

Camera Man wrote:

Sean Griffin wrote:

Sounds more like airframe resonance.

Wouldn't I have been experiencing that before though? This problem just started occurring within the last couple flights. Also, wouldn't I be noticing something outside of just cruise flight?

The problem with bits of your aircraft resonating or flapping during flight, is the pilots inability to get out & check where the noise/vibration may be coming from.

That the problem has only recently manifested, does not in anyway make airframe resonance less likely - things (defined as any part of the aircraft that may have been secure/firm before) get loose, wheels rotate, gaskets perish, trim screws/rivets come lose, etc, etc........

The fact that this phenomena occurs during the same stage/state of flight and can be stopped by changing the angle of attack, lends weight to it being airframe related.

Changing the angle of attack changes the "local" air flow direction & strength so inducing or stopping a resonance problem.

My suggestion: Take the time to go over very square mm of the airframe with a metaphorical magnifying glass, tug on all trim, shake wing tips & look for wing root movement, check security/firm latching of all inspection/access hatches/doors, keep an eye out for missing or loose screws/rivets, light fittings/lenses, engine bay should also be carefully scrutinised for cable/hose movement and any loose ducting/baffles- basically put your hands & eyes on every part/component.

I suspect metal skinned aircraft are more likely than composite, wood or fabric to experience this problem.

"The fact that this phenomena occurs during the same stage/state of flight and can be stopped by changing the angle of attack, lends weight to it being airframe related.'

This is why I don't think it's the gearbox and I've seen too many blame the gearbox when it was the airframe.