M.Simons The World's Vintage Sailplanes 1908-45

THE FVA-10, RHEINLAND

  The Aachen Akaflieg began the design of the FVA-10, named Th. Bienen, in 1935. A great deal of wind tunnel work was done to improve the shape of the junction between the wing and fuselage, with results somewhat similar to those produced in the research which resulted in the Fafnir 2. The FVA-10 had a fuselage shape designed to conform as closely as possible to the airflow over the wing. Felix Kracht did most of the stressing for the aircraft, which was a cantilever, gull-winged form with the aerofoil section at the root Goettingen 432, changing at the 'gull' bend to Goettingen 532 and thence to the tip, NACA M-6. The centre section was built integrally with the fuselage, the outer wings being joined to this by vertical steel tapered pins. There was a single mainspar with a plywood-covered leading edge and a light auxiliary spar. Laminations of compressed wood were let into the spar root for additional strength. The aileron drive was unusual, consisting of a torque tube inside the wing, instead of a cable and pulley system. Connection of the controls was automatic when rigging.
  The cockpit was rather cramped. A steering wheel control instead of a simple stick was provided, with a semi-reclining seat, an unfamiliar feature which was disliked by many pilots. The landing wheel was made semi-retractable to give the sailplane a reasonable ground attitude for take-off and landing. The angle of incidence of the wing on the fuselage, set for minimum drag, was very low, so to raise the wing to a lifting angle of attack on the ground necessitated a stalky undercarriage. The belly line of the cambered fuselage was very nearly straight and without the long undercarriage leg it would have been very prone to damage.
  The sailplane was built in a small workshop provided by a friend of Kracht, Ferdinand Schmetz. It was flown in the summer of 1936. Kracht was delighted with its performance but it suffered from serious handling defects. The pitch stability was too great and the elevator control too feeble, a bad combination. It turned out that even with the wheel down, it was impossible to land gently. To land at stalling speed it was necessary to get the aircraft's nose high. The tailskid invariably touched first and the sailplane dropped heavily onto the main wheel which was not strong enough to withstand such shocks. The alternative, to ‘fly on' at higher speed, had results almost as bad. The chances of heavy bouncing were great whichever technique was employed. Unfortunately the spoilers were not effective enough to control the landing.
  Kracht was encouraged by Schmetz to make improvements and the result was the FVA-10B. The root aerofoil was changed to the theoretically superior Joukowsky 433 type, with an increased angle of incidence. Aerodynamically the outer wing panels remained as before. The elevator control was improved by careful attention to the centre of gravity position and control circuit gearing.
  The FVA-10B was now called Rheinland, and flew in May 1937. In the 1937 Salzburg ISTUS competition Kracht ended in second place. He thereafter flew at the 1937 German Rhoen Competitions (not the internationals) and again placed second. The Rheinland won the award for advanced technical design. Schmetz and Kracht soon founded a small company. A completely new fuselage was worked out having a simpler form. Although slightly less efficient aerodynamically, it had more room for the pilot. Now landings could be made without the tailskid touching down first.
  About 29 examples of this model were built. The Rheinland with the old-style fuselage went to a Polish aircraft museum at Krakow. One of the later type was restored and was still flying in England in 1980.

  Technical data:
   Rheinland FVA-10B Span. 16.00 m. Wing area, 11.7 sq m. Aspect ratio, 21.9. Empty weight, 142 kg. Flying weight, 240 kg. Wing loading, 20.5 kg/sq m. Best glide. 1:28 at 85 km h. Minimum sinking speed. 0.60 m/sec at 60 km h. Aerofoils, Goettingen 432 at root tapering to Goettingen 532 at mid-span, thence to NACA M-6 at the tips.
   Rheinland, production version: As for FVA-10B above, but empty weight. 165 kg. Flying weight, 265 kg. Wing loading, 22.6 kg sq m. Root aerofoil, Joukowsky 433.