Editing DFS 346

{{Short description|German research aircraft, 1948}}
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{{Infobox aircraft
 |name = DFS 346
 |image = Aircraft 346-P Circa pre-1950.jpg
 |caption = Aircraft 346-P
 |type = Research aircraft
 |manufacturer = [[Siebel]]<br>[[OKB-2]]
 |designer = Felix Kracht
 |first_flight = 346-P in [[1948 in aviation|1948]] as glider<br />346-3 in 13.08 [[1951 in aviation|1951]] with engine<ref name="sultanov">Sultanov, I: "German Experimental Design Bureaus in USSR"</ref>
 |introduction =
 |retired = 14 September 1951
 |produced =
 |number_built = 4<ref name = constr>Aircraft construction history in USSR 1951-1965, 2002</ref>
 |status = Project cancelled
 |unit cost =
 |primary_user = [[Soviet Air Force]]
 |more_users =
 |developed_from =
 |variants = [[Bisnovat 5]]
}}

The '''DFS 346''' (''Samolyot 346'') was a [[Nazi Germany|German]] [[rocket]]-powered swept-wing aircraft which began development during [[World War II]] in Germany. It was designed by [[Felix Kracht]] at the ''[[Deutsche 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 the [[Soviet Union]] where it was completed, tested and flown (with indifferent success).<ref>{{cite web|last=Hallion|first=Richard, P.|title=The NACA, NASA, and the Supersonic-Hypersonic Frontier|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100025896_2010028361.pdf|work=NASA|publisher=NASA Technical Reports Server|access-date=7 September 2011}}</ref>

==Design==
The DFS-346 was a midwing design of all-metal construction. The front [[fuselage]] of the 346 was a body of rotation based on the [[NACA airfoil|NACA-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° swept [[NACA airfoil|NACA]] 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 of [[Wing fence|fences]] on the top of the wings.

==Development==

===Concept===
[[File:Dfs346 box.JPG|thumb|250px|right|Concept art]]
[[File:DFS 228 cockpit test.jpg|thumb|250px|right|Test pilot Rolf Mödel tries out the prone position.]]
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 [[Deutsche Forschungsanstalt für Segelflug|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 [[mother ship]] aircraft for [[air launch]], the carrier aircraft being the [[Dornier Do 217]]. After launch, the pilot would fire the 346's [[Walter HWK 109-509|Walter 509B/C]] twin-chamber "cruiser" engine to accelerate to a proposed speed of [[Mach number|Mach]]{{nbsp}}2.6 and altitude of 30,500 meters (100,000&nbsp;ft). This engine had two chambers — the main, upper ''Hauptofen'' combustion chamber as used on the earlier HWK 509A motor; but capable of just over two short tons (4,410&nbsp;lbf) of thrust at full power (more at altitude), and the lower-thrust ''Marschofen'' throttleable chamber below the main unit of either 300&nbsp;kg (B-version) or 400&nbsp;kg (C-version) top thrust levels mounted beneath the main chamber.  After reaching altitude, the speed could be maintained by short bursts of the lower ''Marschofen'' 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 over [[England]] for a [[reconnaissance|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 [[Nazi Germany|Germany]] or northern [[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|Siebel Werke]] located in [[Halle, Saxony-Anhalt|Halle]], where the first [[windtunnel]] models and partially built prototype were captured by the advancing [[Red Army]].

===Post-War===
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'' means "airplane") 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 (flight)|stall]]s at certain [[Angle of attack|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, 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 a [[B-25 Mitchell|B-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.

==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 Superfortress]] captured in [[Vladivostok]] and successfully flown by [[Wolfgang Ziese]] 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===
[[File:346 ES.svg|thumb|150px|Pilot escape sequence]]
Newly built '''346-1''' 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, he [[Descent (aircraft)|descended]] too fast (his speed was later estimated at 310&nbsp;km/h). After first touching the ground he bounced up to a height of 3–4&nbsp;m and flew 700–800&nbsp;m. At the second descent, the landing ski collapsed and the fuselage hit the ground hard.<ref name="dfs">Deutsche Flugzeuge in russischen und sowjetischen Diensten</ref>

The pilot seat structure and [[seatbelt|safety-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, 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 [[gliding|glide]] flights.<ref name="dfs"/>

The damaged 346-1 was later repaired and modified to '''346-2''' version. It was successfully flown by test pilot P.&nbsp;Kazmin in [[1950 in aviation|1950]]-[[1951 in aviation|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 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.<ref name="dfs"/>

===Final flights===
By the mid-1951 '''346-3''' 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 a [[V speeds|V<sub>NE</sub>]] limit of [[speed of sound|Mach]]{{nbsp}}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&nbsp;ft) above Lukovici airfield, the pilot fired the engine and accelerated to a speed of 900&nbsp;km/h (560&nbsp;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.<ref name="dfs"/>

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&nbsp;ft) and landed safely by parachute. With the loss of this aircraft, the 346 program was abandoned.<ref name="dfs"/>

==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 [[TsAGI]] [[wind tunnel]]. Later scrapped, because it was not flyable.
* '''346-P''' - This [[airframe]] was first post-war build of this plane, and was completed in [[1948 in aviation|1948]] 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 [[prototype]] also featured mounted under wing supports, to help stop the plane when landed.
* '''346-1(A)''' - On 5 May 1949, construction of 346-1 was finished. It had a [[rocket engine]] 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 [[transonic]].

== Specifications (346-3) ==
[[File:DFS-346-1.svg|300px|right]]
[[File:346 ST.svg|thumb|300px|346-3 Cross-section]]
{{Aircraft specifications/switch
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|plane or copter?=plane
|jet or prop?=jet

<!-- Now, fill out the specs.  Please include units where appropriate (main comes first, alt in parentheses). If an item doesn't apply, like capacity, leave it blank. For instructions on using |more general=, |more performance=, |power original=, and |thrust original= see [[Template talk:Aircraft specifications]].  To add a new line, end the old one with a right parenthesis ")", and start a new fully formatted line beginning with * -->
|crew= one, pilot
|capacity=
|length main= 13.45 m
|length alt= 44 ft 1 in
|span main= 9 m
|span alt= 29 ft 6 in
|height main= 3.54 m
|height alt= 11 ft 7 in
|area main= 19.9 m<sup>2</sup>
|area alt= 213 ft<sup>2</sup>
|airfoil= [[DFS 346#Design]]
|empty weight main= 2,100 kg
|empty weight alt= 4,806 lb
|loaded weight main= 5,230 kg
|loaded weight alt= 11,506 lb
|useful load main=
|useful load alt=
|max takeoff weight main=
|max takeoff weight alt=
|more general=
|engine (jet)= [[Walter HWK 109-509]]
|type of jet= [[rocket]]
|number of jets= 1
|thrust main= 7,500 lbf
|thrust alt= 33.4 kN
|thrust original=
|afterburning thrust main=
|afterburning thrust alt=
|max speed main= 560 mph
|max speed alt= 900 km/h (verified)
|cruise speed main=
|cruise speed alt=
|never exceed speed main= 1,723 mph
|never exceed speed alt= 2,765 km/h (estimated)
|stall speed main=
|stall speed alt=
|range main=
|range alt=
|ceiling main= 114,800 ft
|ceiling alt= 35,000 m (estimated)
|climb rate main= 19,680 ft/min
|climb rate alt= 6,000 m/min (estimated)
|loading main=
|loading alt=
|thrust/weight=
|power/mass main=
|power/mass alt=
|more performance=
|armament=
|avionics=
}}

==See also==
{{Aircontent|
|related=
* [[Bisnovat 5]]
* [[DFS 228]]
|similar aircraft=
|lists=
* [[List of World War II military aircraft of Germany]]
* [[List of military aircraft of Germany]]
* [[List of rocket planes]]
* [[List of World War II Luftwaffe aircraft prototype projects]]
|see also=
}}

==References==
{{commons}}
{{Reflist}}

{{DFS aircraft}}
{{Siebel aircraft}}
{{RLM aircraft designations}}

[[Category:1940s German experimental aircraft]]
[[Category:1940s Soviet experimental aircraft]]
[[Category:Germany–Soviet Union military relations]]
[[Category:Cancelled aircraft projects]]
[[Category:Rocket-powered aircraft]]
[[Category:DFS aircraft|DFS 346]]
[[Category:Siebel aircraft]]
[[Category:Mid-wing aircraft]]
[[Category:Aircraft first flown in 1948]]
[[Category:Prone pilot aircraft]]