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

THE PRUEFLING

  After mastering the elements of gliding in the Zoegling type of primary' solo trainer, a pilot could not expect to move at once to the advanced, costly sailplane which might so easily be broken and in some respects would be more sensitive on the controls. There was a considerable gap to be bridged between ‘primary’ and ‘sailplane’. Alexander Lippisch quickly followed the Zoegling primary trainer design with a simple ‘secondary’ type, the Pruefling (Examinee), which appeared at the 1926 Rhoen meeting.
  The new glider was intended for easy construction and repair and although its performance was better, being capable of extended soaring flight, it handled generally like a ‘primary’. The wing was of slightly greater span but had two spars of built up section, with diagonal bracing between them. The wing was supported by parallel struts. There was a fuselage, a wooden frame with hexagonal cross framing, covered with fabric behind the wing and with plywood in front. The two main frames extended upward to form a cabane for the wing mounting, with the cockpit under the centre section. There was an ash skid under the front of the fuselage, mounted on rubber blocks.
  After satisfactory testing, blueprints were issued. Many clubs and manufacturers in Germany and elsewhere, built Prueflings. Examples appeared in England, the USA, Canada and Australia, some continuing in use until at least twenty years after the prototype flew. One Pruefling was purchased by the US Navy for experiments with the dirigible airship Los Angeles. The intention was to develop means for an airship to carry, as parasites, small fighter aeroplanes so that when coming under attack the fighters could be released, drive off the enemy aircraft, and then return to hook on again to the mother ship. The first steps were to find out if the proposed release system would work. The glider was suspended beneath the Los Angeles with the pilot, Ralph S. Barnaby, in the cockpit. When at a suitable height Barnaby released from the airship and dived away safely to make a normal descent.
  Some dissatisfaction with the Pruefling was reflected by the fact that Lippisch soon replaced it with his Falke, which was designed to do the same job.

  Technical data:
  Pruefling. Span, 10.50 m. Wing area, 15.24 sqm. Aspect ratio, 7.23. Empty weight. 105 kg. Flying weight. 195 kg. Wing loading 12.8 kg/sq m. Best glide ratio. 1:14.