Complex Problem – Simple Tool



We’re working to assemble the right spar of our Xenos motor glider, and one of the tough things I found on the left spar was to measure the actual depth of the spar at various locations – the distance from the top of the upper cap to the bottom of the lower. This has to be 7 – 39/64″ from root to tip, and because you insert the flanges of the caps into the web layup, it is a measurement that you have control over when you start to drill things in assembly.

Sonex give you tooling plates that help to set this distance out in the tip section, but getting it right in at the root end is a little more difficult. Well, it turns out not to be that bad, but checking to make sure it is right is a head scratcher. You see, the caps are not flat on the top and bottom, but peaked – so the measurement needs a very deep micrometer – and that can be hard to find. When I did the left one, I jury-rigged some plates, clamped and drilled together to make a Go-NoGo gauge, but wasn’t very happy with it.

The answer? In laying my combination square on the spar, I realized that I could get a very accurate right angle that touched one of the peaks – but how to pick up the other side?  All it took was a trip to our local hardware store to pick up two identical new combination squares ($7.99 each- you can guess where I got them). I took off one of the slides, reversed the little brass wedge so it would fit on the correct side of the rule, and voilà – a nice square Go-NoGo gauge.!

Seeing as how the pieces were not very expensive, I did measure the assembly with my more precise tools at several spots to make sure they were parallel. Now I can use this all along the spar as we drill the caps to the web to make sure we maintain a perfectly sized spar.


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Paul Dye
Paul Dye, KITPLANES® Editor at Large, retired as a Lead Flight Director for NASA’s Human Space Flight program, with 40 years of aerospace experience on everything from Cubs to the Space Shuttle. An avid homebuilder, he began flying and working on airplanes as a teen and has experience with a wide range of construction techniques and materials. He flies an RV-8 and SubSonex jet that he built, an RV-3 that he built with his pilot wife, as well as a Dream Tundra and an electric Xenos motorglider they completed. Currently, they are building an F1 Rocket. A commercially licensed pilot, he has logged over 6000 hours in many different types of aircraft and is an A&P, FAA DAR, EAA Tech Counselor and Flight Advisor; he was formerly a member of the Homebuilder’s Council. He consults and collaborates in aerospace operations and flight-testing projects across the country.


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