Fitting techniques - Graupner airbrake

[lysander]

I am fitting a pair of the pop-up Graupner spoilers for the first time. The top (visible) edge of the blade is of course bare metal. What is the practice for matching this to the wing surface? Do you recess the spoiler using epoxy to place a 1/16 balsa strip to its top edge and then cover it in the normal fashion? Or will the metal take iron-on film e.g. Profilm/Oracover? What do you do?

Might seem a very simple matter but if I build the wing and get it wrong, it is a real pain making it right.

[Don T.]

The only pair of these I ever saw in actual use had a strip of balsa sheeting attached to the edge of the blades that matched the profile of the wing; this in turn was covered to match the plane and you hardly even noticed that they were there unless actuated.

Don T. NN4S

[lysander]

Originally posted by Don T.
The only pair of these I ever saw in actual use had a strip of balsa sheeting attached to the edge of the blades that matched the profile of the wing; this in turn was covered to match the plane and you hardly even noticed that they were there unless actuated.

Don T. NN4S

Yup, there are a couple of 1/8" holes in the top, metal edge of the blade - which is 1/4" wide. I suppose a strip of balsa could be attached with dowels through those holes and epoxy between the strip and the metal blade. It's just that I wonder whether attaching thin balsa to metal is likely to prove dodgy.

Thanks for observation anyway Don!

[Don T.]

I guess how thick the balsa can be is determined by how thick your airfoil is and the position of the spoilers in it; you might be able to get a thicker piece of wood to pin/glue to the metal more reliably than sheeting (but that's speculation on my part). Either way, I doubt that you'd have much trouble with it. You might even consider finding some small self-tapping screws for those holes if you use the thicker wood; by countersinking the heads & then covering over them you'd have a very secure mount that would be all but invisible!

Good luck with your experimentation!

Don T. NN4S

[schrederman]

If the aluminum is cleaned and the glue is applied immediately, you can get a good bond. We used to build Legionairs with aluminum tube spars and attach the ribs with Elmers white glue. I have an old (1976) wing and the bonds are still excellent. We roughed up the tube and cleaned it with lacquer thinner until the paper towel didn't discolor when it was wiped across the aluminum.

I'd like to see pictures when you're done....please....

Jack Womack

[lysander]

I'll apply that advice Jack. As a look at http://www.madeinhouse.co.uk/Acrft_00.html reveals, I have generally used crow or flaperon but just fancied trying these spoiler units out. I'll post pages on my web site on the construction. You can see here http://www.madeinhouse.co.uk/OhmEager02.html that I already tried it once but made the top of the bare blade flush with the wing surface and it never looked right. I am building a second wing for that model now, hence my keeness to get it right this time.