Elevator Trim Tab Woes.

[koda2]

You would think that hooking up a manual trim tab cable would be a no brainer but I have been dealing with this for several weeks and I am getting frustrated.

I built the elevator and trim tab from prepunched parts out of the original kit I bought from another builder. It fits well and the elevator is straight. I mounted the trim tab horn using the prepunched holes, thinking this would be a piece of cake.

No way the manual elevator trim cable would fit. I had 0 degrees down travel and over 90 degrees up travel. The clevis and pin were the wrong sizes. I called Van's twice and they said the cable was the same from the beginning of time and it should fit.

I figured out that my kit used a steel clevis and in those days builders had to make a different kind of trim tab horn that was riveted to the side of the trim tab. Then Vans went to a nylon clevis. I tried to buy a nylon clevis from Van's but they referred me to their supplier. I finally got the nylon clevis from Ray Allen and it is much shorter.

Using this clevis however didn't make much difference so I ended up cutting back the trim tab horn about a half inch. I also cut off some more of the bottom skin on the trim tab. I can now get almost 35 degrees of down travel but the trim tab bottoms solidly against the elevator.

In order to get the cable to work however, I am going to have to move the WD415 back a half inch or more on the elevator cover plate. (The cable is already moved to the end of the allowable travel on the WD415 nut). This will also entail cutting a much longer slot in the cover plate.

There must be something different about this older manual cable. Anyone encounter this kind of difficulty on an older 6 or see any problem with modifying the cover plate?

Dave A.
6A build

 

[Bob Axsom]

Here is a photo of mine

The cable is fine but you have to install it to provide the correct operation as you know and as you are planning to do. It creates a lot of anxiety when you try so hard to make it perfect and the GD factory supplied parts are wrong. After a few years you stop letting it get you down and just call the factory as you have done, take their information which they believe is good (I never experienced them white washing a screw-up but I had to call to get the story) and do what it takes to produce the correct assembly and operation. You really have to deal with this kind of thing in the firewall forward area.

Good luck DLTBGYD.

Bob Axsom

 

[koda2]

New cover plate

Bob,
I have been dealing with issues like this throughout the whole process, so it is nothing new.

Here is what I have figured out so far.
Your plane has the style of horn that is mounted on the outside.
Sometime in 1996-7 Van's must have started selling pre-punched elevator kits and in these the cable runs a little differently through the elevator than in later versions, so unfortunately the two styles can't be mixed.

Compare the two drawings of the before and after. I have the early cable and the later trim tab and elevator.

Also the 7A plans

This is probably why the builder in the other post is having interference problems with the servo... he has an early style elevator.

I made a new plate to anchor the cable further back but it the cable is too high now and binds into the horizontal stab.

I will try a third time to make it work; if it won't my options are to find a 7A cable and hope it is different or switch to electric trim.

Thanks for the pix.

Dave A.
6A

 

[Bob Axsom]

You're going to get it right

You're going to get it right because you have the builder experience and understand the need. My kit was picked up by me and my wife at the factory in North Plains, OR in November 1996. It had multiple trim tab control horns and I'm not sure but I think I made my own. When I made the trim tab some advantages of a slightly different construction seemed apparent to me so there are some minor variations (the end closure for example). I almost never require the trim tab to be "up" (elevator down) but after landing it is always down (to trim for elevator up and nose up) for the approach. I leave it there and take off with that setting using armstrong control to get the desired climb out speed and smoothly dial in the fine adjustment to relieve the pitch control pressure. It is an EXCELLENT system that almost feels biological in response - no pulsing, jerking, runaway or power failure woes. Stick with it and you will like it.

Bob Axsom

 

[koda2]

Success!

I think. It seems to be working properly. Only took a new clevis and pin, grinding off a too long trim tab horn, three cover plates and a bunch of shims under the WD-415 nut.
The suggestion to figure out what it is supposed to function like was a good one. I went back and checked the radius, travel, etc and then used a thick rod to help line everything up so as to prevent binding. I have the designed amount of travel now.

Dave A.
6A build