SunBird “Electric”

First off I would like to thank Ray Hays from Skybench Aerotech for his commitment to producing very high quality laser cut kits and Dave Thornburg for his great design. I was in search of a plane to build for a Speed 400, 7 cell, last plane down event. The Sun Bird’s classic elliptical style wing and T-Tail design attracted me to this aircraft. I ordered two kits from Ray and was quite surprised to see them at my doorstep the next day. After an evening of carefully going over the plans and re-designing the nose section to fit a conventional Speed 400 motor and gearbox, the plane was assembled and covered in approx. 30 hours.

The power system for the Sunbird was designed to give a near vertical climb. The original setup was a 6 volt Graupner Speed 400, Maxon 4.4:1 planetary gearbox (see picture below), 10-6 Graupner folding prop and a 7 cell 500 ma battery. Using the Astroflight Watt meter, the current draw showed about 9 amps. On the first flight it was very clear that this was going to be the plane to beat, but the plane needed more prop or RPM to increase the rate of climb.

 

I switched over to a 5.2 volt Rocket motor and an 11-6 Graupner folding prop and almost doubled the rate of climb. Finally, I achieved about a 45-degree climb drawing about 11 amps. This should give the plane about 6 thirty-second climbs of about 200 feet.

 

The fuselage was the only area that changed from Ray’s original design. The T-Tail was made removable, the wing mounting was changed to an internal style mount.

 

With a re-designed nose, a section carbon fiber was added to the inside of the fuse at the tail section for extra strength, basswood was added in critical areas of the fuse, including a battery hatch on the bottom of the fuselage to increase strength. A modified fuse former was placed at the wings leading edge to hold the 3/16 dowel that was located in the leading edge of the wing. A hatch was created on bottom of fuse to access the 7-cell battery.  The hatch and wing are held in place with steel threaded pin that screws into a blind nut located in the trailing edge of the wing. It also serves as a landing skeg/pin for those pinpoint landings.

 

The T-Tail was made to be detachable by a 2-56 screw and plywood clamp for easy transportation. A hardwood 3/32x1/4” leading and trailing edge was added for strength.

 

The wing was built to plans only adding 1/16 plywood doublers at the external dihedral joints. The ribs were sprayed with a light coat of Kraylon paint to add some color, then covered with clear mylar film from Model Research Labs.

 

 

 

 

 

 

 


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