Rigging Aileron Throws (deflectionz)

A forum about all aspects of the construction and maintenance of the Billy Dawson inspired modified Hatz Classic biplane. Here is the place to ask your questions and get the answers from the real experts.

Re: Rigging Aileron Throws (deflectionz)

Postby alvinsager » Mon Dec 16, 2013 9:56 am

Hi Ebby,
I covered my wings with the Stewart system. I did use the batting on the leading edges, held in place with spray contact cement per their instructions. The process uses lots of cement!!! I wish I tried the roller, brushing was a bit of a pain.
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Joined: Thu Mar 18, 2010 10:29 am

Re: Rigging Aileron Throws (deflectionz)

Postby mmarien » Tue Sep 05, 2017 10:36 am

I was doing the calculations on the aileron travel and discovered the "secret" formula that Ebby was looking for. The amount of travel depends on where the bell crank is in the arc. See sketch below. The basic formula is the sine of the angle but it gets complicated because there is the bell crank arc and the aileron arc.

I used the aileron linkage lengths from the plans and put the aileron idler at the neutral position. To get 25 degrees of aileron up (1 9/16" of linkage travel) the bell crank swings about 30 degrees. On the opposite wing, 30 degrees of bell crank travel only moves the aileron linkage 1 1/16". That calculates out to about 15 degrees aileron down.

As Ebby discovered, if you want to change the aileron differential, just change the bell crank neutral position in the arc. Moving the bell crank closer to the top of the arc increases the differential. If the bell crank is at 90 degrees to the aileron linkage at the neutral position there would be no differential. The up movement would equal the down movement. The problem is the spar is in the way for this to happen. You want some differential though to counteract the adverse yaw.

To get the 25/20 degree differential shown on the plans, turn the bell crank neutral position about 10 degrees clockwise from where I show it.

Something interesting is that at full up deflection, the opposite aileron on a Tiger Moth is in the neutral position. It does move, but it goes across the top of the arc so it end up back in the neutral position at full deflection.

The question I have is, what should the differential be? 25/15 from the aileron linkage lengths given or 25/20 as shown on the plans?

Aileron Bell Crank Details 2.png
Aileron Bell Crank Details 2.png (59.5 KiB) Viewed 204 times

Aileron Details.png
Aileron Details.png (56.28 KiB) Viewed 204 times
Murray Marien - HC 0180
Saskatoon Canada
Posts: 73
Joined: Thu Jul 23, 2015 9:50 am


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