Why Erbman's Elevator Doesn't Go All The
(by Russ Erb)
(I know what you're thinking, and you're probably right, but that's not the issue I'm talking about here. I do think that's the best subject line I've ever been able to use on this forum.)
As I get closer and closer to the end, I have seen in a few sources that theFAA thinks it is important that I confirm that my control surfaces deflectas far as they are supposed to. With the ailerons, that is not as obvious as it could be, since the deflection is really controlled by the control stick geometry. Those turned out fine.
The rudder deflection was set directly by welding on the control stops at the rudder itself. That was fine.
Then there was the elevator. The deflection of the elevator is set by how the control horn is welded on relative to two tubes in the fuselage. It is supposed to be 30 deg up and 20 degrees down. My deflection ended up being about 26 degrees up and 26 degrees down.
Looking back at the Bearhawk CD, based on what I said, I did it correctly."I used a piece of cord to position the elevator at 30 degrees trailing edge up. I measured this by first aligning the elevator with the stabilizer. I used a Smartlevel to measure the angle on a part of the elevator, then moved the elevator until the measurement at that location had changed by 30 degrees."
The more I thought about it, the more I thought that when I wrote that, it was one to two years after I had actually set the deflection on the elevator. It is highly probable that I had forgotten exactly what I did. I wrote what I thought I should have done, which would be the correct procedure.
Based on data now available, here's what I'm guessing I really did: I leveled the fuselage frame longitudinally. I then adjusted the elevator until it was deflected 30 degrees up...(here's the important part)...relative to *LEVEL*. This would also mean that it was deflected 30 degrees up relative to the Fuselage Reference Line. The problem? The stabilizer is already deflected "up" 4 degrees relative to the fuselage reference line. The result is that when measured relative to the stabilizer (as it should be), theoretically my elevator would go up 26 degrees and down 24 degrees (a 4 degree shift).
Changing this would require something akin to cutting off the elevator horns and rewelding them, with no guarantee that the fix would be better than the original. I don't plan to do anything about it because all I have lost is the last 4 degrees of deflection, which very likely would never be used anyway. If it does become a problem, I'll worry about it then.
Bearhawk #164 "Three Sigma", Rosamond CA
Bearhawk Reference CD