The Horten H.III is a flying wing sailplane built by Walter and Reimar Horten in Germany from 1937 to 1944.
Design The H.III series was an incremental development of the Horten H.II with reduced sweepback of 23°, span increased to 20 m (65 ft 7 in) and modified lateral controls. The wing trailing edges had three movable surfaces; the innermost was a landing flap, but the outer pair were geared differential elevons with the outer elevon having a large upward deflection and only slight downward movement, conversely, the inner elevon had large downward movement and slight upward movement. This arrangement reduced unfavorable yawing moments due to aileron by making use of differential aileron movement but avoided the change in longitudinal trim by the opposing differential of the inner flap pair. In high-speed flight, the nose down trim was provided mainly by the inner elevon section moving downwards, the outer flap deflecting only slightly; this had the advantage of relieving the tips of torsional loads at high speed. Drag rudders, similar to airbrakes fitted in modern gliders, were fitted near the wingtips, providing yaw control similar to those used in the H.II. The first two H IIIs, an IIIa, and an IIIc (w/n 10 & 11) were built in workshops at Cologne in 1938. Subsequent H.IIIs were built at various locations including Peschke Flugzeugban in Berlin, Fürth, Giebelstadt, Minden, Bonn and Göttingen. Built specifically for the 1938 Rhön competitions the H.IIIa was found to have unsatisfactory turning performance, so the H.IIIc, to be flown by Werner Blech, was modified with a canard surface mounted above and in front of the cockpit to assist with pitch control at low speeds. Aerodynamic balance for control surfaces was by a geared tab on the IIIa and b, but on IIId, f, and g the outer flap had a 20% Frise nose which also countered adverse yaw: out-of-balance aerodynamic loads on the elevators were trimmed by a rubber bungee trimmer with the trim datum set by the pilot.
Operational history The H.III was designed to compete at the 1938 Rhön Gliding Competitions at the Wasserkuppe and two aircraft were available at the start of the competition, to be flown by Heinz Scheidhauer and Werner Blech. As the competition progressed the two H.IIIs were achieving reasonable results with Blech leading over Scheidhauer. Near the end of the competition the weather deteriorated with cumulonimbus clouds and rain showers. Blech recognised that he could win the competition outright with a high-altitude flight in one of the clouds. Blech warned the other pilots not to follow him into the same cloud and took an aero-tow from Walter Horten in their Focke-Wulf Fw 56 glider tug. After entering the cloud, several other pilots ignored Blechs warning, including Scheidhauer, and followed him into the large thundercloud. Several less adventurous pilots left the cloud almost immediately, but Scheidhauer's H.IIIa was severely damaged by hail and was seen fluttering to the ground closely followed by Scheidhauer hanging unconscious from his parachute, suffering from severe frostbite. Blech was not so fortunate; his glider was later seen fluttering to the ground without its canopy and trailing a parachute bag, but a search of the wreckage found no trace of Blech, whose ice-coated body was soon found on the Wasserkuppe. When the barometer carried by the H.IIIc was checked the needle had left the trace area at 8,000 metres (26,250 ft), the limit of the barometer's range, meaning the aircraft had exceeded this altitude. Examination of Blech's body revealed a broken nose and neck, pointing to a collision with either his own aircraft, or another, after he had abandoned the H.IIIc. Scheidhauer recovered in hospital over the next six months losing two fingers of his right hand to frostbite. Sponsored by the Luftwaffe, Walter and Reimar had four H.III gliders ready to fly in the 1939 Rhön competition, piloted by Heinz Scheidhauer, Geitner and Flakowsky representing the Luftwaffe and Gotthold Peter representing the DVL. For various reasons the H.IIIs had a lacklustre showing, with a best placing of twenty-second by Scheidhauer, (partly due to his retrieve crew having been detained by customs for four days at the Czechoslovak border, on return from a competition flight). Geitner came last due to his persistent partying at the local hostelries and subsequent lack of fitness for competition flying. All four pilots understandably bemoaned the lack of practice in flying the H.III before the competition. At least one H.IIIb was converted as an ammunition carrier, with bays in the wings designed to house pallets loaded with ammunition, for supplying outlying army posts, but it is unclear if this aircraft carried out operational flights. Training for flying wing pilots was also carried out using two-seater H.IIIg's. Other H.IIIs carried out research into control systems. The H.III was allocated the RLM ID number 8-250 and by inference Horten Ho 250 though this was little used in practice.
Surviving aircraft The centre section of the H.IIIh, (werknummer 31) built at Göttingen in 1944, is preserved at the Smithsonian National Air and Space Museum. The glider was captured by the British Combined Intelligence Objectives Subcommittee in 1945 at Rottweil, moved to Freman Field in America, by 1946 and transferred to Northrop Corporation at Hawthorne, California along with a Horten H.IIIf and the Horten VI V2 in 1947.
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