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Apr 10, 2011, 12:45 PM
Registered User
Littleton, CO
Joined Nov 2010
772 Posts
Super Cub Decalage Shim

I've had a couple of requests to explain how I made the decalage shim for the horizontal stabilizer on my HZ Super Cub. See my "Tweaking the Cub" post on this blog for an explanation of why you might want to do this.

Let me start by saying that the idea here is to reduce the decalage (the difference between the chord angle of the wing and the chord angle of the horizontal stabilizer). This can be done by by changing the angle of either, but I decided that it would be neater and cleaner to change the horizontal stabilizer on the Cub.

Basically, we are going to raise the leading edge of the horizontal stabilizer by inserting a tapered shim between the horizontal stabilizer and the fuselage.

1. First remove the tail feathers from the Cub.

2. Start with a cedar door shim, like the ones you can buy in bundles at Home Depot. Choose one that tapers to almost nothing. If it needs to be sanded to achieve the right dimensions, do it now as it will be more difficult later.

3. Cut off a piece from the thin end about 3 3/8" long.

4. Lay this piece where the horizintal stabilizer would sit on the fuselage (thick end towards the front) and trace out the fuselage shape. Also, use something skinny and sharp to mark the screw holes.

5. Now cut it out and sand the edges as necessary. Paint it if you like.

My shim ended up being about .033" thick on the aft end and about .082" on the fore end for a delta of .049". If you do the trig, this works out to 0.89 degrees. I was shooting for 1 degree (delta = .057") , but this was close enough. If you don't have the tools or desire to do all of this measuring and math, think in terms of raising the leading edge a little less than 1/16"

Now just put your plane back together with the shim and go see how it flies. Hopefully you will be as delighted as I was with the results.

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