EAA Chapter 81 Meeting Minutes
June 21, 2008

The June meeting was a Project Meeting at the hangar of Eric Witherspoon at Marana Regional Airpark (Avra Valley).
Eric was at the airport entrance with directions to his hangar and the combination to the gate (very handy, as Lori somehow managed to lose the printed directions somewhere between leaving the house and arriving at the airport in a car.
You would think that we were traveling in an open cockpit airplane).
Meeting was called to order by President Duane Boyd.
There was no Treasurer's report and the previous meeting's minutes had already been published in SkyWriter, so we moved right along to the Project Presentation. Eric is nearly finished building a plans-built Sonex, powered by a Jabiru 3300 flat-six 120 HP engine with hydraulic lifters, and a Sensenich composite-wrapped wooden prop.
It employs a fabricated aluminum plenum for cooling, an Aerocarb which, unlike the usual Bing carburetor, allows manual mixture adjustment, and a custom exhaust header system without muffler.
Eric demonstrated real courage in the act of "whacking off" some of the front cylinders' cooling fins as well as some of the sump fins, to make this engine fit under the stock cowling.
This was not Eric's first Sonex, as he had earlier purchased someone else's incomplete project, but he ran out of money and sold it.
He bought the 2nd set of plans in 2005 and started building in August of that year. The Sonex is a John Monett design, deliberately made with a lot of flat structures and a curved top for ease of construction. Eric hand-hammered the aluminum wing ribs on wooden blocks, but used a factory tool (demonstrated for us) for forming the lightening holes. (I always thought that lightening made its own holes in airplanes, but what do I know).
It took him 100 hours to fabricate the built-up aluminum wing spars, the only part of the aircraft that requires driven rivets.
He used a vise, bending the heavy aluminum 90 degree angle, inch by inch, into the correct configuration.
Must be one heck of a spar, as the Sonex is tested to 11 (positive) Gs at aerobatic weight and 9 Gs at gross.
The Sonex has no real builder's guide, just the entirely adequate plan sheets.

Eric is quite accomplished; he holds Private, Instrument, Commercial, and CFI ratings.
He is also quite innovative; he read an article on using a vacuum cleaner for folding sheet metal evenly and applied it to forming his leading edge. It looks perfect, better than many flying Sonexes (Sonices?).
Eric warned us of the Danger of Divots (flush rivet dimples made too deep) on the leading edge.
He fabricated a tool out of fiberboard for bending 0.090" aluminum.
He polished the sheet aluminum before beginning construction because he thought that it would be easier to do it while it was still flat.
He learned that:

1) Polishing is a heck of a lot of work, and takes way more time than anticipated,
2) When you botch a part and have to make a new one, all the polishing that went into that botched part can make one bitter, and,
3) his polishing days are just about over and he has acquired a real esthetic appreciation for the matte aluminum finish on the wings!
He is using Sika Flex for the canopy attachment, instead of drilling holes, as the latter can lead to cracked acrylic.
The windshield is polycarbonate, incredibly tough, but don't get gasoline on it!
Other details include titanium main landing gear attached to the rear engine mount, non-differential, cable-operated drum brakes, a simple electrical system (but with electric starter) and standard "steam" gauges for day VFR flying.
Eric must have missed Dan Plowman's video demonstration of an overeager homebuilder taxi-testing his wingless aircraft, a demonstration which resulted in its self-destruction via harmonic vibrations.
Apparently, having the wings attached to the airplane changes its harmonic frequency and damps the vibrations safely.
In any event, Eric successfully taxi-tested his wingless Sonex and reports that it handles way better (at least, on the ground) than the Cub in which he learned the Tailwheel Tapdance.
The wings are just about ready to go on, at about 1200 hours into the project.
All those present were appreciative of Eric's craftsmanship and enterprise.
Meeting was officially adjourned at 11 AM when Eric's hangar reached 120 degrees Fahrenheit and we made a tactical retreat to the SkyRider Café for lunch.

Respectfully Submitted by
Secretary Bob Miller