grosbeak

I'm building an AMR Trainer 26 and am trying to check the incidence on the wing and horizontal stabilizers. I asked this question in my build thread but I figured it would get more exposure as a separate thread.


I picked up a Hangar 9 Angle Pro and the optional 36" extension bar at my LHS yesterday.







There are no plans with this kit and the manual makes no reference to a thrust line. I checked the firewall and it was square to the bottom of the plane, which is flat, so I figure I'd use that. So I put the Angle Pro on the workbench and zeroed it.







I set the plane on the bench and checked the wing saddle - +1.1º degrees (I confirmed this despite the minus sign), which is very close to the expected 1.0º.







The horizontal stabilizer mounting surface was 0.0º - right on the money.





Once I got the horizontal stabilizer centred I checked it: - 0.1º. Looking good.


Things started to go wonky at the wing, though. The first time I checked it was +1.6º on the starboard wing and +3.6º on the port wing. This made no sense to me. I tried again and I was able to get +1.0º starboard and +1.6º port, but only after blocking the rear of the wing up a LOT.





Because of the way the wing is built I'm quite sure that it's flat on the bottom, so I'm not sure what's causing these inconsistencies. Shape of the leading and trailing edge, perhaps? If you have insight I'd like to hear it.

cubcrasher

My Feedback: (6)

Might be a twistuhroonie.

countilaw

Definitely sounds like you have a twist in the wing. The wing is a flat bottom wing. So lay one wing panel flat on the work bench and weight it down. Then take an incidence reading on the other wing panel. If there is no twist, the reading should be "0.0" .

Applying a monokote type covering can induce wing warp in a wing that was built straight.

Frank

grosbeak

I really don't think there's a twist in the wing. The way the laser cut parts with their notches, tabs and slots fit together make it just about impossible to impart a twist while building. And I'm getting inconsistent readings when the wing is mounted due, I think, to possible inconsistencies in the shape of the hand-sanded LE... so measuring incidence as described above gives no guarantee of accuracy.

Thanks for the ideas, fellas. For now I will focus on other causes.

grosbeak

It's been suggested to me that for a CNC-cut trainer build I have been overthinking this and AMR agrees so I will set the incidence meter aside for a more advanced build and will proceed with this one!