DFS 346

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DFS 346

Aircraft 346-P
Type	Research aircraft
Manufacturer	Siebel OKB-2
Designed by	Felix Kracht
Maiden flight	1947
Retired	14 September 1951
Status	Experimental
Primary user	Soviet Air Force
Number built	5
Variants	Bisnovat 5

The DFS 346 was a rocket-powered, high-speed research aircraft designed by Felix Kracht at the Deutsche Forschungsanstalt für Segelflug (DFS - German Institute for Sailplane Flight) during World War II. By the end of the war, the prototype was only half-finished, but was taken to the Soviet Union where it was completed and flown. The Soviets maintained for some time that the craft broke the sound barrier in 1946, but later evidence has made this claim look highly unlikely.

The DFS 346 was a parallel project to the DFS 228 high-altitude reconnaissance aircraft. While the DFS 228 was essentially of conventional sailplane design, the DFS 346 had highly swept wings with wing fences and a highly streamlined fuselage that its designers hoped would enable it to break the sound barrier. Like its stablemate, it also featured a self-contained escape module for the pilot, a feature originally designed for the DFS 54 prior to the war. The pilot was to fly the machine from a prone position, a feature decided upon from experience with the first DFS 228 prototype.

The 346 design was intended to be air-launched from the back of a large aircraft, the baseline being the Dornier Do 217. After launch from the bomber the plane's two Walter 509B engines would accelerate the craft to about Mach 2.6 at about 30,500 m, where it would cut out. In an operational use the plane would then glide over England for a photo-reconnaissance run, descending as it flew but still at a high speed. After the run was complete the engine would be briefly fired again to raise the altitude for a long lower-speed glide back to a base in Germany or France.

Since the aircraft was to be of all-metal construction, the DFS lacked the facilities to build it, and construction of the prototype was assigned to Siebel, which is where it was captured by the Red Army. On 22 October 1946, OKB-2 (Design Bureau 2), under the direction of Hans Rössing and Alexandr Bereznyak, was tasked with continuing its development. The captured DFS 346, now simply called "Aircraft 346" to distance it from its German origins, was completed and subjected to wind tunnel tests, which revealed some aerodynamic deficiencies which would result in unrecoverable stalls in certain attitudes. In the meantime, the escape capsule system was tested from a B-25 Mitchell and proved promising.

In 1947, an entirely new 346 prototype was constructed, incorporating refinements suggested by the tests. This was designated 346-P ("P" for planar - "glider"). No provision was made for a powerplant, but ballast was added to simulate the weight of an engine and fuel. This was carried to altitude by a captured B-29 Superfortress and successfully flown by Wolfgang Zeise in a series of tests. This led to the construction of three more prototypes, intended to lead to powered flight of the type.

The 346-1 incorporated minor aerodynamic refinements over the 346-P, and was flown by Zeise in 1948, with dummy engines installed. The 346-2, on the other hand, had real engines but carried no fuel. On 30 September 1949 Zeise bounced this aircraft on landing, damaging it and seriously injuring himself. While pilot and plane were repaired, Russian test pilot P. I. Kasmin continued test flights with the 346-1. On 10 May 1951, Zeise returned to the program, flying final unpowered tests with the 346-2, and from 6 June, unpowered tests of the 346-3.

The 346-3 was a fully-functional aircraft, and Zeise flew it under power for the first time on 13 August 1951, using only one of the plane's engines. Continuing concerns about the aircraft's controllability at high speed had led to a limitation of Mach 0.9 being placed on test flights. Zeise flew it again on 2 September and 14 September. On this final flight, however, things went drastically wrong. Separating from the carrier plane at 9,300 m (30,500 ft), Zeise fired his engines and accelerated to 900 km/h (560 mph). He then reported that the plane was not responding to the controls, and was losing altitude. He used the escape capsule to leave the stricken aircraft at 6,500 m (21,000 ft) and returned safely to the ground.

With the loss of this aircraft, the 346 program was abandoned.