Shudder/vibration

[playonwater]

I'm new to the Murphy world with a 912 powered Rebel UL with 3 blade 70" warp taper tip on floats.

Basically it is a very smooth engine but frequently when maneuvering I feel what is more shudder than vibration which comes and goes. Is this just a peculularity of this airframe or unusual?

Thanks for any input
Peter

[Linlei]

Hmm,
I have never experienced any air frame shudder in the Rebel except when I deliberately stall it.
Even then it is relatively benign.
In short I would consider any air frame shudders or vibrations as abnormal and take a long hard look
at where they may be coming from.
Hope this helps.
Mike B.

[Rebel541]

I'm new to the Murphy world with a 912 powered Rebel UL with 3 blade 70" warp taper tip on floats.

Basically it is a very smooth engine but frequently when maneuvering I feel what is more shudder than vibration which comes and goes. Is this just a peculularity of this airframe or unusual?

Thanks for any input
Peter

G'day Pete !

"Shuddering" ..... HHhhmmmmm ... we've never really HAD "shuddering" ........

That needs investigating ...... just to find out WHAT it is !

Problem is ..... it's most likely going to be difficult to nail down if it's NOT something really blatant ........... ( like finding something LOOSE / out of alignment etc )

Either way - you really have to find out hwat the hell it is .....
( and then let us ALL know !!! )

Rick

[Garry]

Is it a shudder or a thrumming? A windscreen that pulled forward and left a gap at the top would produce the latter. Been there, done that.

A shudder would suggest control surfaces. I would be skeptical about blaming it on the engine - too easy to do. If you have a pre-bias caused by knowing something is wrong with X, it is the next step to assume that X is the cause of anything that isn't right in flight, and make wrong decisions about what to do. Clean up all X's prior to flying.

[Sheldon]

Hey Peter

I do have a 912 ul as well. Not on floats. I have not experienced this near as I can tell. Now that said, mine is very light and there is a bit of a tin can feel when I power up, and get rolling. I know some of the guys have added light L sections, I believe in a X pattern bonded with 2 sided tape to remove the tin can effect. I have no interior, only a bulkhead between the sleeper and the main cabin. As far as prop, I am running the IVO medium, 3 blade.
I would like to try the prince / Big bore combo in the furture, but performance is so Bloody good as is, its hard to find a reason to dig into the wallet for now. Keep us posted as to what you find.
best
Sheldon
617R

[AJD76]

G'day Peter,
I've got a 912 UL Rebel with a three blade carbon prop and driven through the reduction gearbox. In the early days of operation, we were chasing a shudder - vibration, that would occur on reducing engine revs. When in the circuit, reducing revs from cruise of around 5000 - 5200 rpm, down to 3500 - 4000, the shuddering would occur. It would come about by the light weight of the prop, and the mismatch in airspeed, airflow over the prop, and engine revs, causing a lashing of the gears in the box. We fixed this, by adding / replacing the overload clutch in the gearbox. (My Dad did the work, and I can't remember if our gearbox didn't come with it and we added it or he replaced the clutch)

This is the bit I'm referring to.
https://www.youtube.com/watch?v=bOR38mQog3I


Also have a look at the Sprag Clutch for wear or breakage. Our motor was built in 1999 or thereabouts and needed some upgrading.
https://www.youtube.com/watch?v=bOR38mQog3I


Good luck and let us know how you get on.

Cheers
Aaron
Victoria - Australia

[irishfield]

Are the float flying wires tied at the center cross?? All sorts of neat noises can come from there if you don't make a little wooden block and safety wire or tie wrap it in place.