Flexing Horizontal Stab?
 

I am finishing up the final assembly on my first kit, a Sig LT-40, and have noticed that when I raise and lower the elevator using the servo, the ends of the horizontal stabilizer flex up and down. The elevator had a slight bend in it before I covered it so I shrunk the covering(ultracoat) opposite the bow to straighten it. Worked like a charm. I was careful to get the hinge slots in the center of the control surfaces also. It’s hard to say just how much flex I’m getting, maybe 1/16"-1/8", it is noticeable but doesn’t seem to be binding or tight and the elevator has more than enough movement. I am going to get out the heating iron one more time to see if it will help it any. At this point I plan on flying it as is.

Any thoughts on this matter will be greatly appreciated.

Thanks

Mike E

Flexing Horizontal Stab?
 

I have flown several models which exhibit the same flexing, never yet caused a problem in the air.

Simon.

Flexing Horizontal Stab?
 

Mike,

Some models will do that to a small degree such as yours.

You have the right idea - go flying. :)

Flexing Horizontal Stab?
 

At trainer speeds, it shouldn't be a problem. I wouldn't worry about it.

If you disconnect the control linkage, does the elevator droop under it's own weight? If you invert the plane, does it then fall the other way under it's own weight? In theory, that is what should happen. But CA hinges usually add a bit of resistance to the surface. And if one of them is off by even a hair, it can cause the flex you are seeing.

Oh, do make sure that the stab isn't cracked or anything like that. It's possible for the covering to basically hold a cracked stab together, and the only think you'd see is a little flex like you are talking about. Until you pull hard-up, that is. Ask me how I know ;)

(actually, I caught my plane (not a trainer) that had that problem on the ground, but only after flying it and thinking that the elevator response "felt wrong" that day. It looked and felt ok on the ground, but I went home anyway, and checked more carefully in the shop. I was lucky, the built-up stab had a cracked main spar and would have let go before too long).

Flexing Horizontal Stab?
 

I'll disconnect the control linkage when I get home and check the droop. I know that it droops down when disconnected but I haven't observed it inverted. It moves back and forth freely by hand and with the servo. I'll also inspect the stab for cracks :eek: . The bright yellow ultracoat is almost transparent so I should be able to see something. I have really yanked the control surfaces so I'm sure they are fixed well. Thanks for the help.

Mike E

Flexing Horizontal Stab?
 

oh, btw, when looking at the flex, if the bend is spread along the surface, then it's not broken. If all the flex appears at one point, espeically the joint with the fuse, then it's broken or loose. I don't know if that's clear, but it should be obvious when you look at it carefully.