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At the beginning World War II in the West, the German Luftwaffe used small gliders, each carrying nine troops, very successfully in Belgium and Crete. The gliders’ success spurred the Luftwaffe Technical Bureau to call for the design and construction of larger gliders, notably the Messerschmitt Me 321, which was more than 90 feet long, had a wing span of more than 180 feet and was capable of carrying 130 troops.
There was, however, a major problem. The Luftwaffe lacked an aircraft powerful enough to tow such a large glider. In an almost desperate attempt to find a large enough aircraft, German designers hit on the idea of taking two airframes of its most numerous medium bomber, the Heinkel He 111, and joining them with a new 40-foot center wing section carrying a fifth engine.
This twin-fuselage, five-engine aircraft was dubbed the He 111Z “Zwilling,” or twin. It had a crew of seven with the pilot sitting in the left fuselage with the primary mechanic, gunner and a radio operator/navigator. The starboard fuselage carried the co-pilot, a secondary mechanic and another gunner.
Surprisingly, only the pilot had a full set of instruments, and he also had all the controls for the five engines. The co-pilot had only essential equipment and a limited set of gauges with no real redundancy. The landing gear could be worked by either cockpit.
Two He 111Z prototypes were built and proved to have good handling characteristics, though four 600 liter drop tanks were installed to increase the range. However, later tests showed that, while the Zwilling could tow a medium size glider, it did not have enough power on takeoff to tow a fully-loaded Me 321.
To solve the problem, four external rocket assisted takeoff pods were added, one under each fuselage and one underneath each wing. The pods were released by parachute after takeoff. In flight there proved to be no handling problems towing the Me 321.
The He 111Z/Me 321 combination was to have been used in an invasion of Malta in 1942 and as part of an airborne assault on the Soviet cities Astrakhan and Baku in the Caucasus in the same year, but they were not ready in time.
Later, in 1942, there was consideration given to using the Zwillings to help resupply German forces at Stalingrad but the airfields were too small, though Zwillings helped evacuate German equipment and dozens of injured German soldiers personnel from the Caucasus region. The Luftwaffe also considered using the He 111Z/Me 321 to reinforce Sicily after the Allied invasion, but there were no landing zones large enough for the glider.
About 20 Zwillings were produced, but most were shot down or destroyed on the ground in 1944 by marauding 8th Air Force fighters. By the end of the war, only four He 111 Zwillings were in operational condition.
Two other versions were proposed, the He Z-2 long-range bomber and the Z-3 long-range reconnaissance aircraft, but they never left the drawing boards.
While the idea of bolting two fuselages together to make a new airplane might seem farfetched at first blush, it was actually a very valid concept. Before the end of World War II, North American Aircraft began to work on a similar two fuselage design of their P-51 Mustang for long range escort duties in the Pacific.
The aircraft, the P-82 Twin Mustang, was used by the U.S. Air Force as an escort fighter and night fighter through 1951 and scored the first air-to-air “kill” of the Korean War.
(For questions or comments, e-mail Dr. Michel at marshall.michel@spangdahlem.af.mil.)
