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

THE MINIMOA

  Early in 1935 Martin Schempp and Wolf Hirth founded a new glider manufacturing company at Goeppingen, a small town about 50 km east of Stuttgart. They planned to make a whole range of gliders and sailplanes. The Goeppingen 3 was a performance sailplane based on Hirth’s successful Moazagotl. It was similar in appearance but had a cantilever wing and was smaller, hence it was nicknamed Mini Moazagotl which soon contracted to Minimoa.
  The Minimoa was at first advertised with three different wingspans, 16, 17 and 18 metres, but the 17 metre version was the only one to be built in quantity. Initially, all had skids for landing, but soon a wheel was fitted except to one solitary 18 metre model which was produced later. The first few Minimoas had the wing mounted high on the fuselage, the pilot’s head being almost enclosed within the leading edge. The windscreen and transparent canopy faired neatly to the fuselage but restricted outward view severely. The prototype had an unusual control column, for Wolf Hirth had an artificial leg and it was always difficult for him to clamber into and out of cockpits with the usual ‘stick’ mounted just ahead of the seat. The first Minimoa had a stick suspended from its torque tube in brackets above the cockpit, hanging down in front of the pilot’s face. This arrangement was not popular and was abandoned in favor of the normal control system on all subsequent Minimoas.
  The aerofoil section at the root was Goettingen 681, a less cambered profile than those used on many earlier sailplanes. Just outboard of the bend in the wing, where the ailerons were at their broadest, the profile changed to Goettingen 693 and thence to a thin symmetrical tip with washout.
  To build the Minimoa wing was difficult. The mainspar was strongly ‘gulled’, and at the same time because of the curious planform, it had to curve backward from the same point as the ‘gull’ bend. This necessitated laminating the spars on rather elaborate forms. Errors in workmanship were easy to make but hard to detect. Some early production Minimoas flew one-wing-low since the spars of the two wings were not quite the same shape and subsequently much ingenuity was employed to prevent this. The bird-like wing was attractive, however, and the aircraft was very' stable. The prototype participated in the 1935 Rhoen meeting, where it demonstrated another new feature, split landing flaps along the underside of the wing running from the root to the ‘gull’ bend. Hirth performed brilliantly, flying on 27th July 420 km into Czechoslovakia, though he was a few days too late to claim the world record, Hofmann having flown 474 km in the Rhoensperber just a few days before.
  Three of the high-winged Minimoas were built, the second being exported to Japan, the third to Romania. The prototype too went to Japan with Hirth, and remained behind when he returned.
  Modifications were soon found to be necessary. The pendulum elevators were too sensitive at high speeds, and a fixed tailplane was introduced. In 1936, the wing was lowered on the fuselage, the cockpit canopy being redesigned so that for the first time the pilot now had a good view. A somewhat larger rudder was fitted. Upper surface wing spoilers replaced the split flaps which had proved rather awkward to use. The provision of water ballast, in a tank behind the cockpit, was advertised and the Minimoa was strong enough, with a load factor of 10 instead of the usual 8, to take the extra weight. It was in this form that the Minimoa entered quantity production and became known worldwide. The gracefully shaped wing caught the imagination of pilots and the general public alike and did a good deal to popularise the type. Examples were exported to most countries where any gliding was done; in the USA Lewin Barringer set the National distance record, in South Africa a Minimoa was used to raise the record in stages to well over 300 km and the height record to more than 3000 m. Eric Nessler in France climbed his Minimoa to over 3500 m, and in England Philip Wills became the third Gold ‘C’ pilot on the international list, and the first in England, with his record distance and altitude flights. His Minimoa was also used during the Battle of Britain to fly over the English Channel, towed by an aeroplane, to glide back to the coast to see if the early radar units could detect a wooden glider.
  At the 19th Rhoen Competitions in 1938 in a field of 60 aircraft. 15 Minimoas were entered. Three of these finished in the top ten and on one day seven achieved distances over 300 km. On 3rd August, a Minimoa pilot struck such severe turbulence in cloud that he was thrown out of his aircraft as it broke up around him. His automatic parachute opened but he was amazed to find himself carried upward by the strong uprush of air within the cloud, then he descended, only to be swept up again. This happened several times until at last he was deposited, battered and chilled, on the ground. On 4th August, contestant Guenther Lemm climbed his Minimoa in cloud, without oxygen or blind flying instruments, to 4980 metres. In another Minimoa, Walther Frick, in similar conditions, reached 5500 metres. The official world altitude record was thus broken twice on one day. On 5th August huge cumulonimbus clouds drifted down upon the Wasserkuppe. Eighteen sailplanes are known to have entered one large cloud. Six broke up in flight or collided at great altitudes, two of them being Minimoas and Guenther Lemm, record breaker of yesterday, was killed. Altogether three men died, one of them Blech in the Horten 3 flying wing. Another who survived lost two fingers from frostbite. A solitary Minimoa, however, emerged triumphant. Walter Drechsel weathered hail and ice storms, maintained control in violent turbulence, and climbed until oxygen deficiency compelled him to turn out of the storm. He reached 6687 metres, landing late in the day far away from the Wasserkuppe. The record stood only three months.
  The factory at Goeppingen continued building Minimoas, the later models being fitted with full airbrakes. Various other detail changes were made. Hirth was able to convert one model to a two-seater, the second pilot being housed in a cabin with the seat between main and secondary main fuselage frames. With this aircraft he visited England, but the type did not enter production. In 1939 the Minimoa '39 appeared, but only one was completed. All told, at least 100 Minimoas were built. Several still survive, some in museums, others in flying condition.
  The performance was measured by the DFS and the weights and figures quoted below come from W. Spilger's report of 1938.

  Technical data:
  Minimoa 1936: Span. 17.00 m. Wing area. 19 sq m. Aspect ratio. 15.21. Empty weight. 228 kg. Flying weight. 353 kg. Wing loading. 17.5 kg/sq m. Aerofoils, root, Goettingen 681, midspan, Goettingen 693, tip, thin symmetrical with 10 degrees washout. Best glide ratio. 1 : 25.7 at 69.9 km/h. Minimum sinking speed. 0.70 m/sec at ,60.9 km/h. Sink at 100 km/h. 1.52 m/sec.