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In late 1944, acting on their own initiative, the design bureau of P.O.. Sukhoi initiated work on a fighter with two turbojets. In November 1945, the aeroplane's conceptual design, which the design bureau designated "L", was submitted for review to the USSR PCAI, and in December it was approved by Chief Engineer of AFRA. The conclusions of the opinion on the conceptual design said that it was of interest to AFRA both in terms of its flight performance (FP) and design and went on to emphasize that the FP would be somewhat better than that of Me-262 of the same type. At the beginning of 1946, the state mock-up committee reviewed and approved a mock-up of the aeroplane.

The 26th February 1946 Resolution of the USSR CPC enacted the 1946-47 aircraft prototype engineering plan. An item of the plan provided for the chief designer and director of plant No 134 P.O. Sukhoi to design and build two prototypes of a single-seat front-line fighter with twin JUMO-004 engines.

The work on the detailed design resulted in engineering changes being introduced into the fuselage, wing, main landing gear and a number other elements and systems; the plane received the manufacturer's designation "K" or Su-9. It was not until after the effort to build a prototype had got under way that the German-made turbojets were replaced with domestic-made substitutes, the RD-10.

The building of the prototype was completed in mid-September, and in early October it was brought to the MAI FRI's airfield. G.M. Shiyanov was appointed senior test pilot, and M.I. Zuyev senior engineer. The maiden flight took place on 13th November 1946.

The manufacturer's tests got bogged down and were not completed until 13th June 1947. This was due to the extensive scope of R&D work on the aircraft as well as the unreliable performance and limited life of the RD-10 engine.

Between August and December 1947, the Su-9 aeroplane underwent governmental tests at the Scientific Research Institute of Air Forces. A.G. Kochetkov was appointed senior test pilot, and I.G. Rabkin was appointed senior engineer.

At the final stage of governmental testing, at the request of the Air Forces, the Su-9 was outfitted with U-5 launch boosters, designed by the NII-1 Scientific Research Institute of USSR MAI, and a brake parachute from the Arado-234 aeroplane. The use of boosters made it possible to nearly halve the takeoff run, with the landing run, once the braking parachute and brake flaps were activated, cut from 1,080 to 600m.

The governmental test report said:

    " 2. The aircraft has the following advantages over similar domestic-made aircraft in production:

    a) more straightforward flight procedures and easier ground maintenance;

    b) the takeoff boosters and braking parachute make it possible to deploy it on aerodromes alongside aircraft with piston motors;

    c) high-performance armaments, completely operational throughout the entire range of altitudes and speeds;

    d) adequate array of special-purpose equipment, communications and flight navigation systems;

    e) an optional Tory scan radar, which gives it an interceptor capability;

    f) the aeroplane's specifications are on a par with production aircraft.

    3. Along with the strong points, the aircraft has faults, which are to be remedied at all costs, with the designers expected to:

    a) increase the maximum allowed Mach number or provide for an automatic recovery of the aircraft from hazardous flight modes;

    b) decrease the load on the control stick from the ailerons and elevator..."

In order to eliminate the faults identified during the governmental testing, the aircraft was outfitted with power-assisted aileron and elevator controls in the first six months of 1948, following which there were additional flight tests.

At the end of March 1948, Air Forces Commander-in-Chief Air Marshal K.A. Vershinin sent to MAI the governmental test report on the Su-9 and a draft resolution of the USSR CM to put it into service as a fighter/interceptor version and into production at plant No 381.

Minister of Aircraft Industry M.V. Khrunichev agreed to accept the Su-9 for production provided the aircraft's run could be spread over two years seeing that a shorter period was not viable. The customer's requirement for a new fighter/interceptor version, which involved replacement of the engines, installation of radar and higher-calibre cannon, was rejected. The USSR's Minister of Armed Forces Marshall of the Soviet Union N.A. Bulganin accepted the arguments of the industry and it seemed that the future of Su-9 was a foregone conclusion.

But as early as 4the June 1948, a resolution of the USSR CM slashed the R&D funding of MAI, along with that of other defence sector departments. This "pulled the plug" on the Su-9 fighter: on 30th June the aeroplane was scrapped due to lack of financing.

The 2nd flying prototype of the Su-9 front-line fighter (so-called "double") was labelled "LK" (Su-11); its construction was started in September 1946. In terms of the design of its basic assemblies, equipment and armaments, the Su-11 did not differ much from the Su-9, with the exception of brake flaps (they were absent).

The wind tunnel studies of the models carried out using CAHI's facilities validated the assumption that the aircraft's flight performance could be improved subject to the engine nacelle profile being altered from the original configuration, with the engines suspended under the wing, in a symmetrical arrangement, "flush" with the wing. The double was initially specified for up-rated RD-10 engines, but in mid-December it was decided to substitute for them USSR-made TR-1 turbojets designed by A.M. Lyulka.

Official authorisation for developing a version with TR-1 engines was given in the USSR CM resolution of 11th March 1947, which enacted the 1947 aircraft prototype development plan. In April 1947 assembly was completed, and on 11th May the plane was brought to the MAI FRI airfield; a team of test personnel, with pilot G.M. Shiyanov and senior engineer V.P. Baluyev among them, initiated flight testing. On 28th May 1947 the Su-11 aeroplane was taken off the ground for its maiden flight. The manufacturer's tests, which were combined with TR-1 engine tests, were completed on 15th April 1948.

The manufacturer's flight test report said that:

" 1. The basic FP of the Su-11 with two TR-1s obtained in the course of the manufacturer's testing, are within the design parameters.

2. There being no TR-1A engines available and the CAHI recommendations to improve the aeroplane's behaviour at high Mach-number speeds having failed to produce a significant effect, we find it impractical to continue R&D work on the aircraft"

As a result, as early as 29th April 1948, the Su-11 was officially decommissioned.

Subsequent work on the next versions of the Su-9 and Su-11 produced in 1947 a design of aircraft entitled "TK," or Su-13. The aircraft's basic design configuration was left unchanged; the wing area was expanded from 20.2m2 to 24.8m2; moreover, in order to increase the machine's critical Mach number, the airfoil thickness ratio was decreased from 12% to 9%, with a swept horizontal tail unit introduced. The aeroplane was designed in two variants, which differed in the array of equipment and weapons. The frontline fighter featured three 37mm cannons, and the fighter/interceptor variant featured two 37mm cannons and a Tory radar scanner. The aeroplane was expected to feature a pressurised cockpit. To increase the flight range up to 2,300 km, the aircraft was also intended to carry additional fuel tanks in the engine nacelles and external fuel tanks.

Two prototypes of the aircraft were planned to be built at plant No 381, but even with the shop drawings completed in their entirety, the failure of the USSR MAI to make a decision made it impossible to start work, there having been just some assembly tooling and a few wing parts produced.

In the summer of 1946, acting on their own initiative, the Design Bureau developed a conceptual design of a two-seat training aircraft with two RD-10 engines meant for training pilots to fly turbojet aeroplanes. The aeroplane's design was similar to that of the Su-9, with an unarmoured two-seat cockpit and two 20mm cannons being the only differences.

The opinion on the conceptual design said that " In the light of the extreme need of the USSR Air Forces for the aircraft under design, it is imperative that the building of a prototype of aircraft be accelerated to make sure it will be available for governmental testing in January-February 1947" Nevertheless, that project, too, failed to be carried through.



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