| DFS 346 | |
|---|---|
 Aircraft 346-P | |
| General information | |
| Type | Research aircraft |
| Manufacturer | Siebel OKB-2 |
| Designer | Felix Kracht |
| Status | Project cancelled |
| Primary user | Soviet Air Force |
| Number built | 4[1] |
| History | |
| First flight | 346-P in1948 as glider 346-3 in 13.081951 with engine[2] |
| Retired | 14 September 1951 |
| Variant | Bisnovat 5 |
TheDFS 346 (Samolyot 346) was aGermanrocket-powered swept-wing aircraft which began development duringWorld War II in Germany. It was designed byFelix Kracht at theDeutsche Forschungsanstalt für Segelflug (DFS), the "German Institute for Sailplane Flight". A prototype was constructed but did not reach completion before the end of the war. It was taken to theSoviet Union where it was completed, tested and flown (with indifferent success).[3]
The DFS-346 was a midwing design of all-metal construction. The frontfuselage of the 346 was a body of rotation based on theNACA-Profile 0012-0,66-50. The middle part was approximately cylindrical and narrowed to the cut off to accommodate vertically arrayed nozzles in back. Probably for volume and weight reasons the DFS-346 was equipped with landing skids, both in the original German design and in the later Soviet prototypes; this caused trouble several times.
The wings had a 45° sweptNACA 0012-0,55-1,25 profile of 12% thickness. The continuously varying profile shape caused a stall in certain flight conditions, which caused complete loss of control. This was later corrected by use offences on the top of the wings.
The DFS 346 was a parallel project to theDFS 228 high-altitudereconnaissance aircraft, designed under the direction of Felix Kracht and his team atDFS. While the DFS 228 was essentially of conventionalsailplane design, the DFS 346 had highly-swept wings and a highly streamlined fuselage that its designers hoped would enable it to break thesound barrier.
Like its stablemate, it also featured a self-contained escape module for the pilot, a feature originally designed for theDFS 54 prior to the war. The pilot was to fly the machine from a prone position, a feature decided from experience with the firstDFS 228 prototype. This was mainly because of the smaller cross-sectional area and easier sealing of the pressurized cabin, but it was also known to help withg-force handling.
The 346 design was intended to be air-launched from the back of a largemother ship aircraft forair launch, the carrier aircraft being theDornier Do 217. After launch, the pilot would fire the 346'sWalter 509B/C twin-chamber "cruiser" engine to accelerate to a proposed speed ofMach 2.6 and altitude of 30,500 meters (100,000 ft). This engine had two chambers — the main, upperHauptofen combustion chamber as used on the earlier HWK 509A motor; but capable of just over two short tons (4,410 lbf) of thrust at full power (more at altitude), and the lower-thrustMarschofen throttleable chamber below the main unit of either 300 kg (B-version) or 400 kg (C-version) top thrust levels mounted beneath the main chamber. After reaching altitude, the speed could be maintained by short bursts of the lowerMarschofen cruise chamber. The question of what rocket-motor subtype was to be used (the 509B or -C) is not adequately addressed here.
In an operational use the plane would then glide overEngland for aphoto-reconnaissance run, descending as it flew but still at a high speed. After the run was complete the engine would be briefly turned on again, to raise the altitude for a long low-speed glide back to a base inGermany or northernFrance.
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 toSiebel Werke located inHalle, where the firstwindtunnel models and partially built prototype were captured by the advancingRed Army.
On 22 October 1946, the SovietOKB-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"Samolyot 346" (samolyot means "airplane") to distance it from its German origins, was completed and tested in TsAGIwind tunnel T-101. Tests revealed some aerodynamic deficiencies which would result in unrecoverablestalls at certainangles of attack. This phenomenon involved a loss of longitudinal stability of the airframe. After the wind tunnel tests, twowing fences were installed on a more advanced, longer version of the DFS-346, the purpose of fences was to interrupt the spanwise movement of airflow that would otherwise bring the boundary-layer breakdown and transition from attached to stalled airflow with loss of lift and increase of drag.
This solution was used on the majority of Soviet planes with swept wings of the 1950s and 1960s. In the meantime, the escape capsule system was tested from aB-25J and proved promising. Despite results from studies showing that the plane would not have been able to pass even Mach 1, orders were given to proceed with construction and further testing.
In 1947, an entirely new 346 prototype was constructed, incorporating refinements suggested by the tests. This was designated346-P ("P" forplaner - "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 aB-29 Superfortress captured inVladivostok and successfully flown byWolfgang Ziese in a series of tests. This led to the construction of three more prototypes, intended to lead to powered flight of the type.
Newly built346-1 incorporated minor aerodynamic refinements over the 346-P, and was first flown by Ziese on September 30, 1948, with dummy engines installed. The glider was released at an altitude of 9700 m, and the pilot realised that he hardly could maintain control of the aircraft. Consequently, while attempting to land, hedescended too fast (his speed was later estimated at 310 km/h). After first touching the ground he bounced up to a height of 3–4 m and flew 700–800 m. At the second descent, the landing ski collapsed and the fuselage hit the ground hard.[4]
The pilot seat structure andsafety-belt proved to be very unreliable, because at the end of a rough braking course Ziese was thrown forward and struck the canopy with his head, losingconsciousness. Luckily, he wasn't seriously injured, and after treatment in hospital he was able to return to flying. Accident investigation research team came to the conclusion that the crash was a result of pilot error, who failed to fully release the landing skid. This accident showed that the aircraft handling was still very unpredictable, as a result, all rocket-powered flights were postponed until pilots were able to effectively control the aircraft in unpowered descent, requiring furtherglide flights.[4]
The damaged 346-1 was later repaired and modified to346-2 version. It was successfully flown by test pilot P. Kazmin in1950-1951 winter, but nonetheless these flights also ended "on fuselage". Furthermore, after the last flight of these series, theairframe again required major repairs. On 10 May 1951, Ziese returned to the program, flying final unpowered test flights with the 346-2, and from 6 June, unpowered tests of the 346-3 without accidents.[4]
By the mid-1951346-3 was completed, and Ziese flew it under power for the first time on 13 August 1951, using only one of the engines. Continuing concerns about the aircraft's stability at high speeds had led to aVNE limit ofMach 0.9 being placed during test flights. Ziese flew it again on 2 September and 14 September. On this last flight, however, things went drastically wrong. Separating from the carrier plane at 9,300 meters (30,500 ft) above Lukovici airfield, the pilot fired the engine and accelerated to a speed of 900 km/h (560 mph). The rocket engine worked as expected, and 346-3, quickly accelerating, started ascending and soon had flown in very close proximity of its carrier aircraft.[4]
Ziese then reported that the plane was not responding to the controls, and was losing altitude. Ground control commanded him to bail out. He used the escape capsule to leave the stricken aircraft at 6,500 meters (21,000 ft) and landed safely by parachute. With the loss of this aircraft, the 346 program was abandoned.[4]
General characteristics
Performance
Related development
Related lists
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