DFS 346
Encyclopedia
The DFS 346 (Samolyot 346) was a German
rocket
-powered swept-wing vehicle subsequently completed and flown (with indifferent success) in the Soviet Union
after the World War II
. It was designed by Felix Kracht
at the Deutsche Forschungsanstalt für Segelflug
(DFS), the "German Institute for Sailplane Flight". The prototype was still unfinished by the end of the war and was taken to the Soviet Union
where it was rebuilt, tested and flown.
of the 346 was a rotation body
based on the NACA-Profile
0,0121-0,66-50. The middle part was cylindrical and narrowed to the square in the back. Probably for capacity 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° swept NACA
0,012-0,55-1,25 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 of fences
on the top of the wings.
The DFS 346 was a parallel project to the DFS 228
high-altitude reconnaissance
aircraft, designed under the direction of Felix Kracht and his team at DFS
. While the DFS 228 was essentially of conventional sailplane design, the DFS 346 had highly-swept wings 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 from experience with the first DFS 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 with g-force
handling.
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, the pilot would fire the 346's Walter 509B/C
engine to accelerate to a proposed speed of Mach
2.6 and altitude of 30,500 meters (100,000 ft). This engine had two chambers, high and low thrust, and after reaching altitude the speed could be maintained by short bursts of the smaller chamber.
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 turned on again, to raise the altitude for a long low-speed glide back to a base in Germany
or northern France
.
located in Halle
, where the first windtunnel models and partially built prototype were captured by the advancing Red Army
.
On 22 October 1946, the Soviet 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 "Samolyot 346" ("Samolyot" - Aircraft) to distance it from its German origins, was completed and tested in TsAGI wind tunnel
T-101. Tests revealed some aerodynamic deficiencies which would result in unrecoverable stall
s at certain angles of attack
. This phenomenon involved a loss of longitudinal stability of the airframe. After the wind tunnel tests, two wing fence
s were installed on a more advanced, longer version of the DFS-346, to correct the airstream separation.
This solution was used on the majority of the Soviet planes with sweptback wings of the 1950s and 1960s. In the meantime, the escape capsule system was tested from a B-25J
and proved promising. Despite results from studies showing that the plane would not have been able to pass even Mach 1, it was ordered to proceed with construction and further testing.
captured in Vladivostok
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.
Newly built 346-1 incorporated minor aerodynamic refinements over the 346-P, and was first flown by Zeise 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, he descended
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.
The pilot seat structure and safety-belt proved to be very unreliable, because at the end of a rough braking course Zeise was thrown forward and struck the canopy with his head, losing consciousness
. 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 further glide
flights.
The damaged 346-1 was later repaired and modified to 346-2 version. It was successfully flown by test pilot P.Kazmin in 1950
-1951
winter, but nonetheless these flights also ended "on fuselage". Furthermore, after the last flight of these series, the airframe
again required major repairs. On 10 May in 1951, Zeise 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.
By the mid-1951 346-3 was completed, 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 stability at high speeds had led to a VNE
limit of Mach
0.9 being placed during test flights. Zeise 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.
Zeise 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.
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
-powered swept-wing vehicle subsequently completed and flown (with indifferent success) in the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
after the World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. It was designed by Felix Kracht
Felix Kracht
Felix Kracht was a German engineer.After graduating from the Technical University of Aachen, he put his theoretical knowledge into practice at the aeronautical association Flugwissenschaftliche Vereinigung Aachen by building the performance glider FVA-10 “Rheinland"...
at the Deutsche Forschungsanstalt für Segelflug
Deutsche Forschungsanstalt für Segelflug
The Deutsche Forschungsanstalt für Segelflug, or DFS was formed in 1933 to centralise all gliding activity in Germany...
(DFS), the "German Institute for Sailplane Flight". The prototype was still unfinished by the end of the war and was taken to the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
where it was rebuilt, tested and flown.
Design
The DFS-346 was a midwing design of all-metal construction. The front fuselageFuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
of the 346 was a rotation body
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
based on the NACA-Profile
NACA airfoil
The NACA airfoils are airfoil shapes for aircraft wings developed by the National Advisory Committee for Aeronautics . The shape of the NACA airfoils is described using a series of digits following the word "NACA." The parameters in the numerical code can be entered into equations to precisely...
0,0121-0,66-50. The middle part was cylindrical and narrowed to the square in the back. Probably for capacity 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° swept NACA
NACA airfoil
The NACA airfoils are airfoil shapes for aircraft wings developed by the National Advisory Committee for Aeronautics . The shape of the NACA airfoils is described using a series of digits following the word "NACA." The parameters in the numerical code can be entered into equations to precisely...
0,012-0,55-1,25 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 of fences
Wing fence
Wing fences, also known as boundary layer fences and potential fences are fixed aerodynamic devices attached to aircraft wings. Not to be confused with wingtip fences, wing fences are flat plates fixed to the upper surfaces parallel to the airflow. They are often seen on swept-wing aircraft...
on the top of the wings.
Concept
DFS 228
-See also:-Bibliography:* Green, William. Warplanes of the Third Reich. London: Macdonald and Jane's Publishers Ltd., 1970 . ISBN 0-356-02382-6.* Myhra, David. DFS 228. Atglen, PA: Schiffer Publishing, 2000. ISBN 0-76431-203-0....
high-altitude reconnaissance
Reconnaissance
Reconnaissance is the military term for exploring beyond the area occupied by friendly forces to gain information about enemy forces or features of the environment....
aircraft, designed under the direction of Felix Kracht and his team at DFS
Deutsche Forschungsanstalt für Segelflug
The Deutsche Forschungsanstalt für Segelflug, or DFS was formed in 1933 to centralise all gliding activity in Germany...
. While the DFS 228 was essentially of conventional sailplane design, the DFS 346 had highly-swept wings and a highly streamlined fuselage that its designers hoped would enable it to break the sound barrier
Sound barrier
The sound barrier, in aerodynamics, is the point at which an aircraft moves from transonic to supersonic speed. The term, which occasionally has other meanings, came into use during World War II, when a number of aircraft started to encounter the effects of compressibility, a collection of several...
.
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 from experience with the first DFS 228
DFS 228
-See also:-Bibliography:* Green, William. Warplanes of the Third Reich. London: Macdonald and Jane's Publishers Ltd., 1970 . ISBN 0-356-02382-6.* Myhra, David. DFS 228. Atglen, PA: Schiffer Publishing, 2000. ISBN 0-76431-203-0....
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 with g-force
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
handling.
The 346 design was intended to be air-launched from the back of a large aircraft, the baseline being the Dornier Do 217
Dornier Do 217
The Dornier Do 217 was a bomber used by German Luftwaffe during World War II as a more powerful version of the Dornier Do 17, known as the Fliegender Bleistift . Designed in 1937 and 1938 as a heavy bomber, its design was refined during 1939 and production began in late 1940...
. After launch, the pilot would fire the 346's Walter 509B/C
Walter HWK 109-509
-See also:-Bibliography:*Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7-External links:*...
engine to accelerate to a proposed speed of Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
2.6 and altitude of 30,500 meters (100,000 ft). This engine had two chambers, high and low thrust, and after reaching altitude the speed could be maintained by short bursts of the smaller chamber.
In an operational use the plane would then glide over England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
for a photo-reconnaissance
Reconnaissance
Reconnaissance is the military term for exploring beyond the area occupied by friendly forces to gain information about enemy forces or features of the environment....
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 in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
or northern France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
.
Prototype construction
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 WerkeSiebel
Siebel, originally Flugzeugbau Halle, was a German aircraft manufacturer founded in 1937 in Halle an der Saale. It was revived as Siebelwerke in 1948. In 1952, it merged with ATG to form Siebelwerke-ATG Gmbh...
located in Halle
Halle, Saxony-Anhalt
Halle is the largest city in the German state of Saxony-Anhalt. It is also called Halle an der Saale in order to distinguish it from the town of Halle in North Rhine-Westphalia...
, where the first windtunnel models and partially built prototype were captured by the advancing Red Army
Red Army
The Workers' and Peasants' Red Army started out as the Soviet Union's revolutionary communist combat groups during the Russian Civil War of 1918-1922. It grew into the national army of the Soviet Union. By the 1930s the Red Army was among the largest armies in history.The "Red Army" name refers to...
.
Post-War
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
T-101. Tests revealed some aerodynamic deficiencies which would result in unrecoverable stall
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
s at certain angles of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
. This phenomenon involved a loss of longitudinal stability of the airframe. After the wind tunnel tests, two wing fence
Wing fence
Wing fences, also known as boundary layer fences and potential fences are fixed aerodynamic devices attached to aircraft wings. Not to be confused with wingtip fences, wing fences are flat plates fixed to the upper surfaces parallel to the airflow. They are often seen on swept-wing aircraft...
s were installed on a more advanced, longer version of the DFS-346, to correct the airstream separation.
This solution was used on the majority of the Soviet planes with sweptback wings of the 1950s and 1960s. In the meantime, the escape capsule system was tested from a B-25J
B-25 Mitchell
The North American B-25 Mitchell was an American twin-engined medium bomber manufactured by North American Aviation. It was used by many Allied air forces, in every theater of World War II, as well as many other air forces after the war ended, and saw service across four decades.The B-25 was named...
and proved promising. Despite results from studies showing that the plane would not have been able to pass even Mach 1, it was ordered to proceed with construction and further testing.
Operational use
In 1947, an entirely new 346 prototype was constructed, incorporating refinements suggested by the tests. This was designated 346-P ("P" for planer - "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 B-29 SuperfortressB-29 Superfortress
The B-29 Superfortress is a four-engine propeller-driven heavy bomber designed by Boeing that was flown primarily by the United States Air Forces in late-World War II and through the Korean War. The B-29 was one of the largest aircraft to see service during World War II...
captured in Vladivostok
Vladivostok
The city is located in the southern extremity of Muravyov-Amursky Peninsula, which is about 30 km long and approximately 12 km wide.The highest point is Mount Kholodilnik, the height of which is 257 m...
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.
First accidents
Descent (aircraft)
A descent during air travel is any portion where an aircraft decreases altitude, and is the opposite of an ascent or climb. Descents are an essential component of an approach to landing...
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.
The pilot seat structure and safety-belt proved to be very unreliable, because at the end of a rough braking course Zeise was thrown forward and struck the canopy with his head, losing consciousness
Consciousness
Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...
. 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 further glide
Gliding
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.Gliding as a sport began in the 1920s...
flights.
The damaged 346-1 was later repaired and modified to 346-2 version. It was successfully flown by test pilot P.Kazmin in 1950
1950 in aviation
This is a list of aviation-related events from 1950:- Events :* Arrow Air is founded.* The Brazilian Navy begins to reestablish an air arm of its own when an aeronautics directorate is created within the Ministry of the Navy.-January:...
-1951
1951 in aviation
This is a list of aviation-related events from 1951:-Events:* Three aerial refueling points are installed on a modified United States Air Force B-29 Superfortress, making it the worlds first triple-point aerial tanker...
winter, but nonetheless these flights also ended "on fuselage". Furthermore, after the last flight of these series, the airframe
Airframe
The airframe of an aircraft is its mechanical structure. It is typically considered to include fuselage, wings and undercarriage and exclude the propulsion system...
again required major repairs. On 10 May in 1951, Zeise 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.
Final flights
V speeds
In aviation, V-speeds are standard terms used to define airspeeds important or useful to the operation of all aircraft including fixed-wing aircraft, gliders, autogiros, helicopters, and dirigibles...
limit of Mach
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....
0.9 being placed during test flights. Zeise 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.
Zeise 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.
Variants
- DFS-346 - First prototype built by Siebel Werke in the early 1940s. Later taken to USSR where the newly formed OKB-2 tested it in TsAGITsAGITsAGI is a transliteration of the Russian abbreviation for Центра́льный аэрогидродинами́ческий институ́т or "Tsentralniy Aerogidrodinamicheskiy Institut", the Central Aerohydrodynamic Institute....
wind tunnelWind tunnelA wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
.Later scrapped, because it was not flyable. - 346-P - This airframeAirframeThe airframe of an aircraft is its mechanical structure. It is typically considered to include fuselage, wings and undercarriage and exclude the propulsion system...
was first post-war build of this plane, and was completed in 19481948 in aviationThis is a list of aviation-related events from 1948:- Events :* Publication of Nevil Shute's novel No Highway set in the world of research into air safety.-January:...
by German engineers. Visually 346-P was identical to the earlier design, excepting a landing gear cowl which was removed primarily for lightening the airframe. This prototypePrototypeA prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
also featured mounted under wing supports, to help stop the plane when landed. - 346-1(A) - On the 5 May 1949 construction of 346-1 was finished. It had a rocket engineRocket engineA rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
mock up installed, and incorporated some minor changes in the rudder and tail design. - 346-2(D) - The same as 346-1, but the rocket engines fitted.
- 346-3 - Only plane that flew rocket-engine powered, and twice went transonicTransonicTransonic speed is an aeronautics term referring to the condition of flight in which a range of velocities of airflow exist surrounding and flowing past an air vehicle or an airfoil that are concurrently below, at, and above the speed of sound in the range of Mach 0.8 to 1.2, i.e. 600–900 mph...
.
Specifications (346-3)