Lippisch DM 1 Reconsidered - Part 2

In this four-part series, curators Russ Lee and Evelyn Crellin take an in-depth look at the Lippisch DM 1, an experimental German glider. At the conclusion of Part 1, construction of the glider had begun in August 1944 by students of the Flugtechnische Fachgruppe (FFG).

Construction of the experimental glider was derailed dramatically on September 11 and 12, 1944, when Allied bombers struck Darmstadt, including the building that housed the FFG D 33 project. Everything the students could salvage from the rubble was moved to Prien Airport at Chiemsee in Bavaria, where students of FFG Munich had operated a large workshop since 1924. Prien had been the starting point of many famous gliding events from 1918 to 1939 including attempts to cross the Alps in gliders and set altitude records. Now, Prien Airport and the FFG Munich workshop became the new home of the glider, where both FFG groups—Darmstadt and Munich—combined their efforts to continue building the aircraft. This collaborative effort led to a new designation for the glider using the letters ‘D’ for Darmstadt and ‘M’ for Munich to rename the aircraft the DM 1. Increasingly difficult wartime conditions, however, prevented Lippisch from assisting further with design and construction.

Students glued, bolted, nailed, and screwed together the cantilever fuselage and various components made of wood, plywood, and steel tubes. They covered the entire glider with 1.6 mm (1/16-inch), 3-ply birch plywood. To cover the very thick leading edges of the wings and vertical stabilizer, the students had to first heat the plywood with steam. These very thick sections were unsuitable for high-speed flight and suggested that Lippisch designed the DM 1 for experiments at low flying speeds. They gave the pilot a window on the cockpit floor to see ahead of the glider at the high pitch angles that would be necessary during launch and landing. To evaluate how the glider handled in flight with the center of gravity at various locations, the pilot could hand-pump 35 liters (9 gallons) of water between two tanks inside the nose and tail of the aircraft. Armament was not planned for this experimental glider.

Looking aft through the nose toward the tail, the pilot’s control stick is at center and tilted to the right. The pilot worked the lever with the red knob at right to pump water between tanks at the nose and tail to adjust the center of gravity of the DM 1. Photo: Ben Sullivan

The students fashioned the wheeled, three-strut, tricycle undercarriage from steel. Contrary to a recent published account stating that the gear was fitted with shock absorbers that had 60 cm (2 ft) of travel, direct observation of the DM 1 aircraft in the Mary Baker Engen Restoration Hangar at the Steven F. Udvar-Hazy Center in Chantilly, Virginia, confirms that the struts are solid steel with no capacity to absorb shocks. To reduce the stress of landing at the high angles of attack required for delta wing aircraft, the struts are set so close together that the glider appeared ready to tip over. Lippisch may have imagined the test pilot would land on a wooden skid or even on the smooth belly of the aircraft since touching down on the gear legs without shock absorbers would probably have damaged the delicate internal wooden structure. Museum treatment specialist Matt Nazarro likened the structure to the fragile insides of a wooden guitar. The design called for ground technicians to retract the undercarriage after they had mounted the glider piggyback onto a larger powered aircraft, so the gear may only have provided the techicians with a convenient way to move the aircraft around on the ground.

Authorities had planned to carry the experimental glider into the air piggyback atop a twin-engine and propeller-driven Siebel 204 A aircraft. The DM 1 pilot would have released from the carrier aircraft at altitude and descended with additional thrust from two solid-fuel rockets at an estimated speed of around 800 kph (500 mph). A former coworker of Alexander Lippisch, test pilot Hans Zacher from the DFS (Deutsches Forschunginstitut für Segelflug, German Research Institute for Gliding), was designated to perform the DM 1 test flights. However, Zacher joined the project at a late stage, and the war ended before the students could finish building the glider.

On May 3, 1945, American troops occupied Prien Airport and found the incomplete glider. German historian and author Hans-Peter Dabrowski wrote in his article Flying Triangle (Klassiker der Luftfahrt, July 2014, p.61) that when U. S. Army General George S. Patton and other high-ranking officers visited Prien on May 9, 1945, the advanced design features of the aircraft impressed them and Patton ordered the students to resume construction and complete the aircraft. Dabrowski also wrote that Dr. Theodore von Kármén argued vehemently to finish the DM 1, and that Major A. C. Hazen of the Air Technical Intelligence Section, U. S. Army Air Forces in Europe, became the project manager.

Hazen worked closely with test pilot Hans Zacher who remained very involved with work on the DM 1. On one particular day, Zacher was visited by group of Americans who had come to study the glider. At the time, they were unknown to Zacher. During small talk he mentioned that he had studied the work of Walter Stuart Diehl, the famous American pioneer of aerodynamics and author of the authoritative Engineering Aerodynamics (1928), who actively participated in and strongly influenced continuing advances in aerodynamics and hydrodynamics. To Zacher's surprise, one of his counterparts identified himself as Walter Diehl. From this encounter a lifelong friendship arose between Zacher and Diehl.

The workshop at Prien Airport would also receive a visit from another famous American before construction of the DM 1 was completed. Find out who next week, but feel free to guess in the meantime.

 Sources: Dabrowski, Hans-Peter. “Flying Triangle,” Klassiker der Luftfahrt, July 2014. Lindbergh, Charles A. The Wartime Journals of Charles A. Lindbergh, (New York, 1970).