Horten H III f
Reimar Horten continued to refine his line of all-wing sailplanes by building at least 18 examples of the Horten III beginning in 1938. Horten fitted this example, called the Horten III f, with a flat-prone couch for the pilot and he probably assigned Werk Nr. 32 to the sailplane when he finished it in 1944 at Göttingen. This Horten III f, the Horten VI V2, and the Wright brothers 1903 Flyer are the only airplanes in NASM collections configured for prone pilotage. To mount the aircraft, a pilot stretched flat on his stomach, bent slightly at the waist and knees, and rested his feet on rudder pedals hinged above his heels. A padded chin rest supported his head which projected into the leading edge of the wing. Clear plastic panels formed the leading edge for several feet above, below, and to either side of the pilot. Visibility was excellent and drag greatly reduced.
Details about the operational history of this glider remain unknown. One month after the war ended, a team of aviation experts working for the C. I. O. S. (Combined Intelligence Objectives Subcommittee) found both the NASM H III f and the H III h. The gliders were recovered "in perfect condition in trailers, with a [sic] full set of instruments" at Rottweil, Germany, on the Neckar River, approximately 60 miles (100 km) southwest of Stuttgart on June 11, 1945. In January 1994, NASM shipped the Horten glider collection (Horten II L, 'III f, 'III h, and the 'VI V2) to the Museum für Verkehr und Technik Berlin, now called the Deutsches Technikmuseum (DTM), and that organization worked until 2004 to restore and preserve these artifacts.
Transferred from the U.S. Air Force
- Country of Origin
- Horten, Reimar and Walter
- Reimar Horten, Germany pre-1945,
- Steel tubing center section covered with plywood and aluminum, wooden wings covered plywood and cotton fabric.
- Wingspan 20 m (66 ft)
- Center Section Length 5 m (16.4 ft)
- Height 1.6 m (5.4 ft)
- Weight Empty 250 kg (550 lb)
- Weight Flying 360 kg (792 lb)
- Maximum Speed 210 km/h (130 mph)
- Best Glide Speed 63 km/h (39 mph)
From 1933 to 1990, Reimar Horten, assisted by his brother, Walter, designed and built a series of swept-wing aircraft without fuselages or tails and they did not use any other surfaces for control or stability that did not also contribute lift to the wing. The National Air and Space Museum owns a Horten II L, Horten III f, Horten III h, Horten VI V2, and the Horten IX V3 turbojet interceptor.
Reimar Horten continued to refine the all-wing sailplane with his third design, the Horten III. Compared to the H II, the wingspan grew about 4 m (13 ft 3 in) but the root chord decreased by .25 m (9 in). By narrowing the root chord and lengthening the wings, Horten increased aspect ratio and this trend continued with Horten's next two sailplane designs. Like the Horten II, the H III center section consisted of welded steel tubes covered with plywood and sheet metal. Horten built the wings entirely from wood. He refined the flight control system by adding a second set of elevons.
From July 1938 until October 1944, at least eighteen Horten III aircraft were constructed at Köln, Berlin, Fürth, Giebelstadt, Minden, Bonn, and Göttingen. This model was built in greater numbers than any other Horten design and both Horten brothers and other pilots flew Horten III gliders in the German national glider competition in 1938 and 1939. Reimar successfully motorized several Ho III sailplanes using a variety of powerplants including Walter Mikron and Volkswagen engines. Horten also modified an Ho III b to carry ammunition in support of Operation Sealion, the proposed invasion of England.
Horten fitted the NASM Horten III f with a flat-prone couch for the pilot. This wing, the Horten VI-V3, and the Wright brothers 1903 Flyer are the only aircraft in the NASM collection configured for prone pilotage. Other nations built aircraft to test this unique layout but these NASM artifacts are among the few examples known to exist today. Horten had experimented with seating position to reduce drag as early as 1935 when he designed the first Horten II with supine seating and flew it in May. At first the seatback in the Horten II was inclined just 18º to the horizon but a 23º position became standard. Even with the pilot's head more upright at this setting, visibility was dangerously limited particularly in the slow speed/high-angle-of-attack regime sailplane pilots often operated in. As Reimar put it, the "main drawbacks are poor forward visibility (even worse to the rear), the pilot's knees being in the field of vision, and difficulties developing proper [control] feel and coordination" (quoted in Reimar Horten, "Flying Wing Pilot Position and Design Options," "Soaring," August 1980, translated by Jan Scott, 23).
Supine seating proved a dead end until the postwar revival but in 1938, work at the Akademische Fliegergruppe Stuttgart led Horten in a new direction. The institute built the all-wood Fs 17 with a flat-prone cockpit to conduct aero medical research on pilots subjected to high-G maneuvers. Reimar saw in the new layout intriguing possibilities for drag reduction. In 1941 he completed the Horten IV, the first all-wing aircraft equipped for prone pilotage. Reimar and Walter Horten intended to acclimate pilots to the prone position by using gliders such as the NASM Horten III f. They hoped to smoothly transition pilots to high-performance Horten aircraft equipped with prone cockpits. These "hot rod" Hortens included the H IV and H VI sailplanes, and the jet-propelled H X.
In spring 1944 at Göttingen, a young mathematician named Karl Nickel sampled the prone layout when he flew a Horten III f (it is not known if this same airplane is now in the NASM collection). Nickel's skeptical friends sounded the alarm. How could a pilot maintain proper 'feel' for the aircraft, whether it was banking slightly left or right, while lying on his stomach? It would be impossible, they claimed, to fly instinctively! The controls could not be moved unless the pilot carefully considered each movement beforehand. What of the pilot's personal comfort? Cross-country glider flights often lasted for hours. Even a thick-necked flyer could not hold his head, particularly in high-G thermalling turns. Blood would pool and the limbs would fall asleep! After landing the stiff, immobile pilot would be unable to hoist himself from the prone couch!
Dr. Nickel's fascinating report appears in Karl Nickel and Michael Wohlfart, "Tailless Aircraft in Theory and Practice (AIAA, 1994) on pages 351-355. It conveys his thoughts and feelings as he flew an all-wing Horten glider from the prone position. "I climb from behind [the aircraft] on the center-section of the flying wing to step inside and lie down in it." His parachute hung across his chest and the packed canopy pillowed his torso. The "lying-trough," he continued, "is well-upholstered with foam rubber and artificial leather. . . there is the chinrest which is easily adjustable. The designer has thought of everything and wants to accommodate the pilot in comfort." Horten had fitted seat belts but their operation was unorthodox. "They are fastened over the back and are released automatically as soon as the cockpit is opened. How Practical!"
The prone position demanded a novel control system. Reimar designed one and installed it in all his prone aircraft. He used a yoke-type wheel to transmit pitch and roll inputs to the elevons. Nickel continues: "For fore and aft movements [the wheel] slides back and forth on almost frictionless bearings along a horizontal tube. Will it be possible," he wondered, "to get quickly accustomed to this?" Once airborne, Dr. Nickel had the answer.
"All of a sudden I am completely baffled: there is nothing unusual, it's exactly as flying while sitting in a seat! I feel the stick force, the sailplane reacts to the smallest control movements. I completely forget that I am lying horizontally in space, that the control column [wheel] looks so strange, that the H III is no normal aircraft."
"[It is as though] I had been flying in prone position for years. . . The first gusts are felt and are counteracted automatically, without thinking. I see my hands moving to act in the correct way, but there is no conscious command from the brain. The bird feels good . . . [and this] reaction comes so strong and unexpected that I wish to sing at once. . . I am so delighted . . . there is nothing to learn about prone flying and everything is so simple. But don't start celebrating too early! We [glider and towplane] just crossed the airport boundary as some heavy gusts arrived. No problem to counteract them, but the result is astonishing: suddenly the tow-rope approaches me at full speed, collides with the canopy and disappears aft [the towpilot released his end of the tow rope]. Instinctively my arm shoots up to protect my head, even though it's unnecessary. Next reaction, release the rope too. In front of me lies an "inviting" high-tension line. Hence push [the wheel to maintain speed], [execute a] 180° turn and with the aid of a tailwind, [fly] back over the fence [airport boundary]. Is there enough altitude for a second turn into the wind [to set up for landing]? There better be; carefully "scraping" the turf a flat turn [at very low altitude] is achieved, [landing] skid lowered, no brake necessary, hold off, and here we are back at the starting point of the flight. Ugh!!!"
A half-hour later he was back in the air: "I am floating again in the air . . . flying over the houses and streets of Göttingen. Wonderful, this marvelous view down through the acrylic glass pane. Exactly as on a street map I can track the roads and alleys with my finger. Seemingly just in front of my face there is that hive of activity. Magnificent to soar and glide high over the rooftops, horizontal in space like a bird. This sort of flying really is the only natural way, how could anybody doubt it ever? The view is unobstructed on all sides through the large canopy, but the most astonishing aspect is the excellent view downward. Slowly we are losing altitude. It's time for a thermal to appear. Oops, here it is. Rudder and aileron, slowly pull up, it's just the same as with any other sailplane. Only the banking at first seems to be excessively large . . ."
Nickel initially made excessively shallow, flat turns but after two hours of practice, he adjusted. His mind began to accept and trust the new sight-picture of a standard turn presented by the Horten III f prone position. Banking turns of 60° became easy and "remained the only difficulty I encountered and it didn't occur anymore during later flights." As he built time flying prone, Nickel considered the problem of pilot comfort on long flights.
"Well, after two hours no bodily strain could be felt, but this could perhaps come with longer flights? . . . on the 7th of August 1943, a comparision test was made. . . Hermann Strebel made the first motorless flight of more than 10 hours in prone position with the Horten H IV over the Wasserkuppe mountain. At the same time I myself [flew] for 7 ½ hours in the [Olympia Meise glider]. [Strebel and I were] quite happy together up there, even though he could often out-fly me because of the better performance of his sailplane. After landing I went to him limping with aching backside. But he approached me laughing and completely fresh and could only shake his head to my envious questions: "No, no bruises, no limbs which went to sleep, no stiffness of the neck, nothing!"
Nickel found other reasons to like the prone pilot position. " . . . for tailless sailplanes the prone position is appropriate. . . The main reason for this is the better view of the outside world . . . This is important in particular during aero-tow. Especially with tailless sailplanes a good view of the towing aircraft can be decisive against flying too low and, consequently, being dragged down by the downdraft behind the tow aircraft."
The H III also had good handling qualities and this no doubt boosted Nickel's enthusiasm for the prone layout. He often witnessed Heinz Schiedhauer putting the Horten III d motorglider through its paces at Göttingen in 1943-44. During Schiedhauer's routine, "he did a flyby a few meters above the ground and, just in front of the onlookers, pulled back the stick abruptly. This created a 'whip stall' with a nearly vertical attitude. There was no tail-slide or roll-off, but rather the flying wing fell down into the normal flying position without loss of altitude and continued her horizontal flight."
Horten assigned Werk Nr. 32 to a Horten III f built in 1944 at Göttingen. The NASM III f may be the last of three 'f' subtypes built. All three aircraft featured prone cockpits for minimum drag. The pilot stretched flat on his stomach, bent slightly at the waist and knees, feet resting on rudder pedals hinged above his heels. A padded chin rest supported his head, which projected into the leading edge of the wing. Clear plastic panels formed the leading edge for several feet above, below, and to either side of the pilot. Visibility was excellent and drag greatly reduced. The wing had a maximum speed of 210 km/h (130 mph) and a best glide speed of 63 km/h (39 mph).
Details about the operational history of this glider remain unknown. One month after the war ended, a team of aviation experts working for the C. I. O. S. (Combined Intelligence Objectives Subcommittee) found both the NASM H III f and the H III h. The gliders were recovered "in perfect condition in trailers, with a [sic] full set of instruments" at Rottweil, Germany, on the Neckar River, approximately 60 miles (100 km) southwest of Stuttgart on June 11, 1945.
For a time, the United States Army Air Forces' Air Technical Intelligence (ATI) branch was interested in Horten flying wing aircraft. ATI assigned inventory control numbers to track the thousands of pieces of German military aircraft, equipment, and hardware obtained during and after the war. The following numbers identified Horten gliders now part of the NASM collection:
Horten II L - T2-7
Horten III f - T2-5042
Horten III h - T2-5039
Horten VI V2 - T2-5040
Inexplicably, ATI lost interest and declared "the Horten Tailless Gliders are of no value to us," according to the "Weekly Activity Report - Technical Intelligence - Week Ending 26 June 1945." The H III f and 'III h vanish into an historical black hole for the next two years. The story resumes on October 22, 1947, when Stanley A. Hall wrote a report called "Horten Tailless Sailplanes." Hall explained that the U. S. Air Force loaned the Horten III f, III h, and VI V2 to the Northrop Aeronautical Institute, across the road from the Northrop Aircraft Company in Hawthorne, California. This loan answered a "joint petition of Northrop Aircraft Inc., and the Southern California Soaring Association [SCSA]." The two organizations wanted the sailplanes "for purposes of inspection by West Coast engineers who, in interests of the development of all-wing aircraft, sought for evidence of similarity between the design practices of American and German engineers."
Northrop personnel planned to test-fly the two Horten III gliders but they arrived "damaged beyond reasonable repair [and] too badly damaged to make photography worthwhile." Despite their condition, a throng of aeronautical professionals turned out to inspect them. Among the curious crowds were Northrop engineers and students of the Northrop Aeronautical Institute, members of the Society of Automotive Engineers and the Institute of Aeronautical Sciences. Many SCSA members turned out too, including engineers from Douglas, North American, Lockheed, and Consolidated. Much attention fell on the Horten VI V2. The sailplane was intact and in fair condition and Northrop considered flying it but decided not to because of safety issues.
The Air Force reclaimed the gliders in 1948 and stored them at the Chrysler's World War II aircraft assembly plant at Chicago Orchard Airport, Park Ridge, Illinois. This huge building also housed more than 80 other World War II Allied and Axis airplanes.
In 1950 hasty preparations for war in Korea forced the eviction of more than fifty of these priceless artifacts, including the Horten gliders. Air Force personnel shipped the aircraft by rail and any too large to fit a boxcar surrendered to the cutting-torch. The collection went to an open plot of land near Silver Hill, Maryland, across the Anacostia River south of Washington. For more than 10 years, most of the collection remained outdoors. In 1962, the site started to take the form we know today as the Paul E. Garber Restoration, Preservation, and Storage facility.
In January 1994, NASM shipped the Horten glider collection (H II L, III f, III h, and the VI V2) to the Museum für Verkehr und Technik Berlin, later renamed the Deutsches Technikmuseum (DTM), and that museum worked to restore and preserve these artifacts until 2004.
Wingspan 20 m (66 ft)
Center Section Length 5 m (16.4 ft)
Height 1.6 m (5.4 ft)
Weight Empty 250 kg (550 lb)
Weight Flying 360 kg (792 lb)
Reference Sources and Suggested Further Reading:
Horten, Reimar. "Flying Wing Pilot Position and Design Options," "Soaring," August 1980.
Lee, Russell. "The National Air and Space Museum Horten Sailplane Collection: Horten II L, III f, III h, and VI-V2," "Bungee Cord," Vol. XXIII No. 4, Winter 1997.
Myhra, David. "The Horten Brothers and Their All-Wing Aircraft." Atglen, Penn.: Schiffer Publishing Ltd., 1998.
Nickel, Karl, and Wohlfahrt, Michael. "Tailless Aircraft in Theory and Practice." Reston, Va.: American Institute of Aeronautics and Astronautics, 1994.
Selinger, Peter F., and Horten, Reimar. "Nurflugel: Die Geschichte der Horten-Flugzeuge 1933-1960." Graz, Germany: H. Weishaupt Verlag, 1983.
Beckh, Harald J. "The Development and Airborne Testing of the PALE Seat."
Horten, Reimar. "Flying Wing Pilot Position and Design Options," "Soaring," August 1980, 23.
Russ Lee, 9-2-04