Ho Va, The World's First Composite Aircraft
As a final test, a pair of wings for the primary glider "Hor's der Teufel" were built entirely from synthetic materials. Conventional construction methods were used. Since fewer brackets and other metal parts were needed, a weight saving of 15% was realized, with no loss in strength. The building material consisted mainly of phenol resins; the filler was ordinary paper. No wood at all was used in the wings. The wing bolts were simply inserted into holes drilled in the spar without brackets or bushings. The D-tube was formed by sheets made the same way; the remainder of the wing was fabric covered.
The glider was test flown in May 1936. After the flight tests, one wing was static loaded until it broke, the other left outside without fabric cover for six months, to test its weather resistance. Thereafter it was load tested with special emphasis on its glue joints.
With our new experience, our attention was directed toward the prospects and problems of molded parts, which promised to greatly reduce production time and cost.
Our Air Ministry was interested in a combat aircraft with an unobstructed rearward gun position. The British already had such a machine. Our proposal was a machine with two pusher propellers, and a gun position between them, pointing aft. The Hirth engine factory could deliver an 60 HP engine with both left and right rotation. We would use these on a two place aircraft mat would be tailless, and if possible, a pure flying wing, without a cockpit bubble.
We wanted slow Right characteristics as good as conventional aircraft. This required flaps, which severely altered the pitch moment. To counteract this, we chose rotating wing tips as elevons. A two step leading edge sweepback would approach the ideal parabola shape, and reduce the "Middle-effect" drag.
There were many problems during production. The material would separate due to temperature changes, glue would dissolve protective varnish, insufficient stiffness of molded parts etc.
The first flight assured us that the problems with the "middle effect" was minimal, and the flight was stable. The tests were unfortunately interrupted when an engine failed during takeoff and a wing tip touched the ground, causing a total loss of the aircraft.
It was decided that another H V should be built as quickly as possible, this time from steel tubes and wood to conserve time, while Dynamit A G proceeded with composite material research on their own.
The contrarotating propellers were made of wood, and coated with "Lignofol". These masterpieces were handmade by Peter Kumpel, who also made the "Habicht" propeller.