Elevator Trim - Type III

[cgruby]

I've decided I would like to have an elevator trim and am curious what other 's are using out there.

I figured a simple Bowden cable, operating a simple tab would suffice. What about electric trims? Anybody using a model airplane servo?

[avidflyer]

The simplest elevator trim is a piece of bungee cord tied on both ends to the seat truss and wrapping around the joystick. Pull the cord higher up on the joystick for more up elevator. Jim Chuk

[cgruby]

Thanks Jim, That sounds like a good plan. I'll give it a try.

[FoxDB]

I am using a trim kit from Aeroconversions: http://www.aeroconversions.com/products/trim/index.html

[Peteohms]

I am using a trim kit from Aeroconversions: http://www.aeroconversions.com/products/trim/index.html

Got any pictures of your installation?

[FoxDB]

Sorry did not take pictures and it is under the seat

[cgruby]

I am using a trim kit from Aeroconversions: http://www.aeroconversions.com/products/trim/index.html

I've been looking at that. Are you satisfied with it?

[FoxDB]

Cgruby
Yes I have, It is much more sable than using the flap handle as trim. My only complaint is that it still holds the stick up when shut off making more difficult to get my right foot over when getting in or out.

[cgruby]

Cgruby
Yes I have, It is much more sable than using the flap handle as trim. My only complaint is that it still holds the stick up when shut off making more difficult to get my right foot over when getting in or out.

I appreciate your response. I have just placed an order for mine. I was looking at an electric trim arrangement, but it is much more expensive, and probably a little over kill for this little airplane. Manual trims have always worked fine for me. Thanks again.

[Av8r3400]

I figured a simple Bowden cable, operating a simple tab would suffice. What about electric trims? Anybody using a model airplane servo?

Remember: Bowden cables are designed to pull, only. They do not push. You will either need to use them in a pair, pulling opposite directions or with some other method (spring, etc) of moving the surface in the opposite direction.

[jrevens]

A solid wire cable can be used for both pushing & pulling.

[cgruby]

This arrangement uses opposing springs. You spring load one side with a fixed spring and pull it back to neutral with another spring and tension cable.

[Jfquebec]

In first i try to use the rans push pull cable with trim wheel like aeroconversion...i install all the kit and i try it...it working but...when i force a little bit by hand the trim tab ...they have some play..so i remove all that and i install an electric servo..( aerotrim)mucho better..;)No play..
I can send some pic when i comming back home in one week..

Jf
Model 4 1200

[avidflyer]

At least on Avids, and I imagine most Kitfoxes, nose up trim is mostly needed, and not nose down. The Bowden cable can pull on the trim tab to achive that nose up trim. Mostly I just used the trim to adjust for hands free cruise. YMMV Jim Chuk

[Av8r3400]

A solid wire cable can be used for both pushing & pulling.

Maybe I should qualify my statement. The cables I refer to are the small diameter ones commonly found at auto parts stores. These, in the solid core, will provide a small amount of push, maybe a couple of ounces. They will bend and spring very easily with little more force than that. This will also very greatly depending on the amount of core exposed outside the casing.

The larger "teleflex" cables (like the ones used by Rans in their control systems) will push and pull with near equal force, but these are much too large for trim tab use.

[Olle1975]

I prefered to build an aerodynamic trim, because I don't like any tension at my elevatorbolt.....

Olaf

[avidflyer]

I like the throttle cable end for adjustment and locking in place! Jim Chuk

[Olle1975]

Thanks, I think the throttle is the best way for fast- and fine adjustment :)

[HighWing]

Of course more work, but a simpler method than the factory option on the early speedster elevator is what a friend and I put together for his Avid. Instead of welding in a half inch square tube to allow for the tab hinge to be mounted essentially vertically, they mount the hinge horizontally. Welding is also minimized and the tab itself is much simpler to fabricate. In the two pictures shown it is of an enlarged elevator for flair improvement, but the basic elements are shown.

The first picture shows the parts necessary for the modification. As mentioned this elevator is modified to lengthen the chord. The lower bent tube will be welded into the trailing edge of the other side. The view shows bottom side up.

9779

This view shows the location of the hinge and the MAC servo. Again, this is bottom side up.

9780

For comparison, a couple of pictures of the typical Kitfox installation.

The first shows the elevator before covering.

9781

The second picture shows the servo attachment weldments.

9782

The third picture shows the more complex trim tab.

Incidentally, in the Lancair project I helped with the use of instant glue was very frequent as a means to temporarily position parts for drilling etc. That is what is going on here.

9783

[cgruby]

This is a continuation of this thread highlighting what has been done to date. I purchased a small electric linear actuator on E-bay for $40.oo bucks, whith a 12 " stroke. I sort of guessed at the springs until I got something that worked. The pictures show how I chose to install it. I flew for about three hours yesterday and had a real good opportunity to check it out and find it works really well with only subtle changes. The hardest part is making a couple of fittings and wiring.