Horten flying wing: Germany's tailless gliders led the way

Flight Journal, Jun 2000 by Rosenlof, Kim

GERMANY'S TAILLESS GLIDERS LED THE WAY

High in the rafters of a dusty hangar at the Planes of Fame Museum in Chino, California, a tailless sailplane hangs in silent testimony to the German advances in aerodynamic engineering that were way ahead of their time. The plane is a Hoften IV-one of only six Horten aircraft known to have survived WW II out of the 55 built. In its present, unrestored condition, with ailerons missing and faded paint, this Ho IV scarcely conveys its exciting history: built in Nazi Germany; taken to England after the War; used to win soaring competitions and serve as an aerodynamic test platform at Mississippi State University in the U.S.

This Horten's story actually began in prewar Germany, where soaring had become a national pastime as an aftereffect of the Versailles Treaty of WW I. The Allied powers had forbidden any type of powered flight in Germany and, to some, soaring represented a way to collectively thumb their noses at the Allies. Others took the sport seriously and used the engineless platform to continue aerodynamic research that could later be transferred to powered craft.

In the early 1930s, the Horten family of Bonn was bitten by the flying bug. Although the father was not directly involved in aviation, his three boys-Walter, Reimar and Wolfram-- pursued it with a passion, but were initially limited to gliders. While all three obtained a pilot's license and did eventually fly powered aircraft, their claim to fame is the advanced flying wing that they designed, built and flew before and during WW II. The Hortens-Reimar, especially-made several contributions to aerodynamic theory and practice, including the successful operation of flying-wing aircraft before Jack Northrop built his N1M flying wings in the U.S. In fact, after WW II, the U.S. Army Air Corps lent Jack Northrop several captured Horten flying wings for his own research.

In Germany before the War, the Hortens designed and built more than a dozen flying wings, a few of which went into limited production in WW II. During the War, Wolfram was a torpedo bomber pilot and was killed in action in 1940; Walter became a fighter pilot and maintained his commission in the Luftwaffe after the War, eventually retiring as colonel; he passed away in 1998. Reimar was the engineer behind the flying-wing designs; after the War, he fled to sympathetic Argentina to continue his work on tailless aircraft. After Germany's surrender, most of the aircraft the Hortens had built were lost during the Allied occupation. A few aircraft, however, were taken out of the country by U.S. Army personnel, Soviet intelligence officers and British soaring enthusiasts.

With a doctorate in aeronautical engineering, Reimar continued to design flying-wing aircraft in Argentina, and he experimented with delta-wing jet aircraft, hang gliders and sailplanes of various flying-wing configurations. But Horten designs did not gain prominence until the end of Reimar's life, when, before his death in 1994, he was internationally honored for his contributions to aerodynamic theory.

At least four Ho IV gliders were built in Germany, but only two are known to have survived the War. One was found in the U.S.'s occupation zone at the end of the War and eventually reached a soaring club in England. Currently being restored in Oberschleissheim, Germany, this is most likely the Ho IV used by British occupation forces at Orlinghausen in the late 1940s. A detailed account of this Ho IV's modification for CG winch launching and testing at Orlinghausen by long-time Horten pilot Heinz Scheidhauer was published in 1950 in the German soaring magazine, Thermik. Translated into English in "Tailless Aircraft in Theory and Practice" by Nickel, Wohlfahrt and Brown, Scheidhauer notes, "With this method [CG winch], the best possible results were experienced .... The correctly trimmed plane then climbs hands off! The stability is amazingly high .... It is an adventure of peculiar appeal to fly the Ho IV in CG tow-launch. Because of the prone-pilot layout, one climbs in an upright position standing vertically in the sky with free view over the whole airfield."

The other Ho IV that survived the War is LA-AC z25, whose history can be traced to its construction, by Reimar, at the Luftwaffe's Cargo Glider School Number One in Gottingen, where he was in charge of maintenance and repair. In 1941, the prototype Ho IV, with its long, slender, sweptback wings, prone-pilot-position cockpit and unusual control system had been built in Konigsberg. In 1943, tasked with the development of high-performance gliders, Reimar built three more Ho IVs. With an aspect ratio of 21.8, the Ho IVs calculated glide ratio was 37:1, and its pilot's prone position was designed to minimize additional drag. The Ho IV became the showplane of the Horten glider collection and was flown in a number of unofficial competitions in Germany during the War.

Much of the Hortens' work was captured and subsequently lost because of the Allied forces' wartime practice of confiscating aircraft, drawings, parts and anything else of technological importance. In an effort to retain at least one of the handbuilt aircraft, LA-AC z25 was hidden in Gottingen until Reimar was contacted by Austrian Robert Kronfeld regarding use of the glider. In his book "Nurflugel" (translated into English by Peter Selinger), Reimar writes, "Robert Kronfeld approached us in 1945 and obtained a Lend-Lease on it (LA-AC z25), with the understanding that it would be returned to us when soaring was again allowed in Germany. We were surprised to see him ignore the trailer and load the Ho IV onto a waiting DC-3 to be transported to England instead of his native Austria!" On Kronfeld's death a short time afterward, the Ho IV was sold by his widow and went through several British owners. Although he kept track of LA-AC z25 through soaring journals and colleagues' reports, Reimar never saw his Ho IV again.