elevator trim server

[Josef]

hi there,

has anyone expereinced a runaway elevator trim server installed on a RV-8 / 8A or any other RV model ? Is there any way to limit the maximum trim stroke on the server ?

cheers,

Josef

[WingsOnWheels]

Originally Posted by Josef

hi there,

has anyone expereinced a runaway elevator trim server installed on a RV-8 / 8A or any other RV model ? Is there any way to limit the maximum trim stroke on the server ?

cheers,

Josef

You could make the control horn on the trim tab taller, this would reduce the travel of the tab for a given servo travel.

[Josef]

thanks Colin, will consider this solution.

[Doug]

The critical factor is to ensure the servo itself reaches its own limit stop prior to any linkage binding.

If a trim runaway does occur, binding will load the linkage parts and these might fail while sufficient force is being applied to the control stick to overpower the trim. A failure of the linkage under these conditions could easily result in a greater than max g pitch input.

[Pat Hatch]

Originally Posted by Josef

hi there,

has anyone expereinced a runaway elevator trim server installed on a RV-8 / 8A or any other RV model ? Is there any way to limit the maximum trim stroke on the server ?

cheers,

Josef

If you're referring to Ray Allen Co. servos, they sell a "travel reducer" that is a small plastic part that can be inserted inside the servo to limit stroke. I had to use one once for a rudder trim tab that I designed. The instructions that come with it says that it reduces travel by .2 inch. Not very expensive at all as I recall.

[Alan Carroll]

On my RV-8 I find that I need all (or most) of the available servo travel to be able to trim across the full range of airspeeds. The servo reaches its internal limits before there is any binding of the linkage to the trim tab; it therefore doesn't appear necessary to limit travel for that reason. Preventing or limiting runaway trim is a different question though.

[Josef]

Originally Posted by Alan Carroll

On my RV-8 I find that I need all (or most) of the available servo travel to be able to trim across the full range of airspeeds. The servo reaches its internal limits before there is any binding of the linkage to the trim tab; it therefore doesn't appear necessary to limit travel for that reason. Preventing or limiting runaway trim is a different question though.

hi Allan,
which type / model of server are you using for the elevator trim ?

rgds,

Josef

[flyinga]

FYI; during phase 1 I have flown with full nose up and full nose down trim and it is not a big problem.

[Alan Carroll]

Originally Posted by Josef

hi Allan,
which type / model of server are you using for the elevator trim ?

rgds,

Josef

Josef,

It is a MAC servo that I bought in the late 90s. I believe its a MAC 8A, which is equivalent to the Ray Allen T3-12A (I'll need to look at it to be sure).

[gereed75]

Jim, I would be curious to know what airspeeds you flew at while over riding full up and down trim??

Thanks