Hi,

Is there a simple way to build up the elevator where the control horn will be attached so it does not break off? I have seen people CA them. What about a thin piece of ply or steel plating? I am not concerned about how it will look.

Thanks

I have seen light ply used on models that thread the screw into only one side of the elevator but not on models where the screws go all the way through into a plastic backing plate.
I have never seen one break off but a friend of mine did break a screw not long ago.
What kind of airplane and what kind of horns are you using?

Hi, it's a Phoenix Strega with a YS 1.10.

G

drill through the control surface and use screws through the plastic backing plate that comes with the horn. don't over tighten...tighten until the backing plate and control horn are snug and touching the control surface. then 1/4 to 1/2 more of a turn...I will then,one at a time, loosen the screw and use a drop of gel super glue on the screw threads. for torque lock
Never glue the horn to the control surface.

Simple and easy, and you already have the idea. A very thin piece of REGULAR plywood works great. There really isn't any really thin LitePly. And LitePly has very little ability to stand crushing, even the thick stuff.

I recently had a KYOSHO P40 Warhawk flutter the stab/elevator. The stab failed on the LE on both sides and the elevator horn had no problem wrecking the thin elevator balsa. You couldn't see what grade of balsa was in the elevator or the LE under the covering. And darned if you couldn't feel some really good cross braces, so this flutter was a real surprise. Both places had wood that any experienced builder would have rejected. Unfortunately, the ARF factory workers aren't experienced builders or they would have rejected that stuff. And I paid for it. I got off the throttle immediately after hearing the flutter but the elevator would only respond about 5degrees but only at full up or full down. And I was over a soybean field. And managed to control the "landing". So damage wasn't too bad.

The first picture shows where I've stripped the covering for a 1/16" Airply plate. The plate got some lightening holes in it, but not under or near where the horn went. With punk wood you need to get lots of area covered. But you don't want weight, because that actually contributes to flutter of a surface. The 2nd picture shows where I added some diagonal bracing in the stab. I did all the work from the underside so I wouldn't have to screw around trying to match the covering colors. That'd been hard, since the colors had faded like crazy from the sun.

BTW, the design of the stab is pretty good. If you look at the construction near some of the numbers it's obviously sensible design.

You can see the long brace along the TE of the stab at 2. And the short crosspiece and corner brace coming out at 3. Sensible things to have in a builtup stabilizer.

However, just above 1. you can see where the LE failed immediately outboard of the rib. Truth is, that LE wood should have been hard balsa. A lot of people use holdbacks that bear on the stabs. I do. It's cushioned but soft wood won't stand much.

Truth is, it would have made sense to have built up the elevator halves instead of using sheet balsa. The weight of a moving surface has a lot to do with it's flutter potential. Lots of ARFs have lightening holes lazered into full sheet surfaces like that. You can see above 4. where the horn crushed into the wood. And that was after CA had strenghtened it. The ply will solve that however.

i found something from central hobbies web sight.they are showing how to install mk horns but the idea is the same.they have several good tips/tricks that you can incorporate into your airplane.

http://www.centralhobbies.com/buildi...hornsinst.html

It seems like there was a thread on RCU about building plywood control horns. Very intesting, but may have been for the pull-pull system. Anyone aware of that article with pics.

I build control hons from 3 layers of 1/32 aircraft ply glued with med CA so I have 9 plys. I have tested these very harshly and have not had a failure. I glue them into a full depth slot in balsa the thickness of the surface, after boring 2 or three 1/16 holes for clevises or cables. Rudder horns are one piece that go completely thru the rudder and glued with epoxy. I had a plastic horn on a wire elevator joiner break on the first flight.

I build control hons from 3 layers of 1/32 aircraft ply glued with med CA so I have 9 plys. I have tested these very harshly and have not had a failure. I glue them into a full depth slot in balsa the thickness of the surface, after boring 2 or three 1/16 holes for clevises or cables. Rudder horns are one piece that go completely thru the rudder and glued with epoxy. I had a plastic horn on a wire elevator joiner break on the first flight, luckily on the first landing. Sorry about the double entry, I don't know how to erase it.