Clamping Elevators "In Trail"

[tx_jayhawk]

I am preparing to drill the lower portion of the elevator horns that I may install the pushrod. Instructions have you clamp the elevators "in trail" with the HS, then drill away and use a wood block to do the other side.

What I have seen is that there can be up to 0.5 degree difference in the two elevators based on clamp location along the HS/Elevator counterweight area (based on how the skin is sitting, etc.). It would appear that clamping "in trail" is not a perfect procedure.

Getting perfect flight control alignment is something I am willing to spend some time on. Does anyone have any recommendations on how to achieve perfect "in trail" alignment prior to drilling? I'm a little uncomfortable with the clamp method.

Thanks,
Scott
7A Finishing

[JonJay]

.5 deg is very good. With all of the other variances you will have with tips, inconsistencies with the elevators themselves, etc.... I would move on. While presicion is a good thing, dont make yourself sick. Get it done and move on. I would expect your alignment to be better than most already.

[db1yg]

Scott,

I was concerned about the same situation as are you and also wanted perfect alignment of the elevators with each other--the counter weight alignment was secondary since out of sync elevators would create far more negative aerodynamic effect than one counter wt being up or down slightly relative to the HS . To deal with this I bought a couple of long pieces of angle and insured that they were true and straight. I clamped the angles across the elevator trailing edges (mine is a 9 and has non-tapering trailing edges--your 7 will require a slightly diff location) to get the elevators aligned. I double checked the elevator surfaces by using a smart level to insure that the two were the same . I then clamped the two together at the horns and double checked the alignment. THEN I drilled (or should I say redrilled--more on that later) the elevator horns. BTW, as you probably know, this can only be accomplished without the rudder in the way.

Reference the comment on "redrill"--the first time I drilled the horn I simply locked both counter wts in trail, eyeballed the elevator alignments and drilled the horns---only later to realize that the elevators were not perfectly aligned by using this procedure. Although this presented no safety issue, I could'nt stand it. I had the horn welded up and I redrilled using the above process. Others may think it a lot of work for little return---I get some satisfaction in knowing the rigging on my plane is as near to perfect as I am capable of attaining. Anyway, its your plane -- put the level of effort in that gives you a result with which you are comfortable.

Cheers,

db

[alpinelakespilot2000]

Originally Posted by tx_jayhawk

Getting perfect flight control alignment is something I am willing to spend some time on. Does anyone have any recommendations on how to achieve perfect "in trail" alignment prior to drilling? I'm a little uncomfortable with the clamp method.

You might use a fishline connecting the outboard t.e. corners of both elevators to ensure that the trailing edges line up with each other once you clamp the counterbalance arms where they look like they are in trail. If the trailing edges don't line up well with the fish line you might have to moderately adjust the counterbalance arms. It might end up being a case where you choose to split the difference between having the trailing edges aligned and the counterbalance arms aligned. If you have a lot of twist in either elevator, this method might not work well. Get some BIG clamps and clamp the arms at the same location and you should be OK. It will just take some experimenting to see where the clamps work the best.

I would concur with JonJay that you're probably worrying about nothing. 0.5 degrees sure isn't much (Remember, most people built these planes without digital levels!).

Good luck.