Mikoyan-Gurevich I-250

Mikoyan-Gurevich

Industry	Aerospace, Defense
Founded	1939
Headquarters	Moscow , Soviet Union

The Mikoyan-Gurevich I-250 (also known as Samolet N, or MiG-13) was a Soviet fighter developed under an urgent 1944 initiative aimed at producing a high-speed interceptor to challenge German turbojet fighters like the Messerschmitt Me 262. The Mikoyan-Gurevich bureau opted for a propulsion system more advanced than piston engines but less experimental than jet engines, which were still under development in the USSR. Their solution combined a motorjet—the Kholshchevnikov VRDK (Vozdushno-Reaktivny Dvigatel Kompressornyi, meaning air reaction compressor jet)—powered by a Klimov VK-107 V12 piston engine. Although the aircraft demonstrated promising performance, achieving speeds up to 820 km/h (510 mph) during testing, persistent production difficulties with the VRDK engine ultimately doomed the project, leading to its cancellation in 1948 due to obsolescence.

Design and development

By early 1944, Soviet intelligence had confirmed British and American progress in jet technology and anticipated imminent deployment of German jet and rocket fighters. On 18 February, the State Defense Committee (GKO) mandated that the People's Commissariat for Aviation Industry (NKAP) consolidate all jet research efforts and submit proposals within one month to address the emerging threat. Consequently, NKAP tasked four design bureaus—Lavochkin, Sukhoi, Yakovlev, and Mikoyan-Gurevich—with rapidly developing jet aircraft. Having encountered challenges with ramjets previously, both Sukhoi and Mikoyan-Gurevich selected the VRDK motorjet booster engine under development since 1942.

The VRDK functioned as a motorjet, an early jet engine variant where a compressor is driven mechanically by an external power source. Air was channeled into a stainless steel combustion chamber where fuel sprayed from seven nozzles was ignited, producing thrust through an adjustable exhaust nozzle. The I-250 employed a 1,650-horsepower (1,230 kW) Klimov VK-107R V12 piston engine as its main power source. After takeoff, engaging a clutch at the crankshaft's end activated a gearbox with a 13:21 ratio that transmitted power via an extension shaft to drive the VRDK’s compressor. Air intake for the compressor was drawn through a lengthy duct beginning beneath the propeller spinner inlet, continuing underneath the engine and along the fuselage belly. This duct also supplied air to cool the oil cooler adjacent to the engine; meanwhile, the water radiator was positioned behind the compressor to maximize cooling airflow. A secondary duct diverted some air from the main intake to feed the VK-107’s supercharger when the VRDK operated, boosting engine output to 2,500-horsepower (1,900 kW) at 7,000 m (22,966 ft) altitude. This enhanced airflow also improved heat dissipation from the engine radiator into the exhaust stream. However, VRDK operation was limited to ten minutes per sortie, rendering it dead weight during other flight phases.

File:WRDK.svg

Schematic of I-250's propulsion system

Structurally, the I-250 was an all-metal low-wing monocoque design. Apart from its unique propulsion system, it featured conventional layout elements but with an unusually rearward cockpit positioned near the vertical stabilizer base. The wings incorporated two spars with a thickness ratio of approximately 10% to maintain effective aileron control and prevent tip stall. Frise-type ailerons and slotted flaps were installed for improved handling. Fuel capacity included a 412-litre (91 imp gal; 109 US gal) tank within the fuselage plus two wing tanks of 100-litre (22 imp gal; 26 US gal) each. The conventional landing gear retracted inward; main wheels employed levered suspension while the tail wheel folded aft into a small ventral fin. Initially, propulsion came from a 3.1-metre (10 ft) VISh-105SV propeller driven by the VK-107A engine.

In January 1944, NKAP directed Mikoyan to begin conceptual work on a high-altitude interceptor. By February and March 1945, two prototypes featuring all-metal construction and VRDK propulsion were ordered for testing purposes. Performance targets included reaching 5,000 m (16,000 ft) altitude in 4.5 minutes at full power or 5.5 minutes using piston power alone; maximum speeds aimed were 810 km/h (500 mph) at 7,000 m (22,966 ft) with full power and 700 km/h (430 mph) relying solely on piston propulsion. Armament plans consisted of one 23 mm (0.91 in) autocannon supplemented by two 12.7 mm (0.50 in) machine guns. To support development, TsAGI provided aerodynamic and structural analysis plus wind tunnel testing of full-scale mockups within one month. The Baranov Central Institute of Aviation Motors (TsIAM) committed to delivering three VRDK engines rated at 9-kilonewton (2,000 lb_f) thrust at 7,000 m (23,000 ft), featuring specific fuel consumption of approximately 1,200 kilograms per hour (2,600 lb/h).

NKAP formalized preliminary specifications for the I-250 on 19 September 1944: maximum speed of 825 kilometres per hour (513 mph), takeoff weight near 3,500 kilograms (7,700 lb), and climb to 5,000 metres (16,000 ft) in under four minutes (3.9 minutes). A mock-up inspection on 26 October initially rejected cockpit ergonomics but was later overruled due to advanced prototype construction stages that precluded major redesigns without causing delays. The combustion chamber underwent testing at TsIAM that same month but revealed structural weaknesses requiring reinforcement. Full powerplant trials began in December but encountered repeated failures of the drive shaft connecting piston engine and motorjet components.

The first prototype was completed by 26 February 1945; however, its VRDK unit was not yet ready for installation. It flew initially on either 3 March or 4 April (sources vary), equipped with an AV-10P-60 propeller measuring 3.1 metres (10 ft) diameter and armed with three Berezin B-20 20 mm cannons—one mounted on each side of the nose and one firing through the hollow propeller shaft with 160 rounds per gun. Initial VRDK tests occurred on 8 April during a dive reaching speeds near 710 kilometres per hour (440 mph), but oil cooler leaks necessitated returning it for repairs. By mid-April, VRDK reinstallation faced persistent issues; although speeds approached 809 kilometres per hour (503 mph) at approximately 7,000 metres (23,000 ft), service life limits forced suspension of tests by late May pending completion of second prototype assembly.

The second prototype finished on 19 May but delayed first flight until 26 May due to multiple defects including oil leakage from VRDK compressor components. Attempts were made to resolve these problems by consulting VRDK designers; meanwhile, magneto faults grounded the first prototype through much of June while additional air intakes were added for spark plug cooling improvements. On 3 July, speeds reached up to 820 kilometres per hour (510 mph) at around 6,700 metres (22,000 ft), but tragedy struck two days later when structural failure of the port tailplane caused fatal crash during low-altitude maneuvering; pilot Alexandr Deyev perished after his parachute failed to deploy in time. Investigation attributed accident to exceeding airframe G-load limits.

Despite this setback, authorities ordered ten pre-production units on 27 July 1945 based on belief that mixed-power fighters could aid pilot transition from piston-engine aircraft toward jets; concurrently Sukhoi’s Su-5 program was terminated as inferior compared to I-250 performance.

Following tailplane reinforcement on prototype two, test flights resumed on 20 July; however pilots reported excessive right yaw torque leading to vertical stabilizer enlargement by about 0.63 square metres (6.8 sq ft) surface area among numerous unresolved issues preventing State acceptance trials readiness due mainly to unreliable powerplant operation. Flight testing continued until an engine fire forced emergency landing on 12 July 1946 causing irreparable damage.

Initial production plans assigned Factory No. 381 in Moscow delivery schedules calling for two aircraft by September followed by three in October and remainder before year-end—targets later scaled back drastically due to persistent engine unavailability despite completed airframes awaiting installation. Factory management faced severe criticism amid constant design changes impeding progress; this dissatisfaction extended beyond I-250 as other jet projects lagged behind leadership expectations culminating in March 1946 arrest of Ministry of Aviation Industry head Alexei Shakhurin as demonstration of political displeasure. Subsequent investigations led by new Minister resulted in harsh punishments including arrest of Factory No. 381 director and quality control manager accused of industrial sabotage after rejecting commission findings that apportioned blame broadly among involved parties.

In spite of ongoing production challenges and lack of State acceptance trials submission, NKAP placed an order for fifty additional units on 26 February (these aircraft are sometimes referred to as MiG-13, presumably their intended service designation). Delivery deadlines were repeatedly missed due largely to engine shortages; seven airframes existed without engines by mid-1946. The first I-250 finally passed acceptance on 8 August and flew three days later but suffered engine seal failures and ignition cable damage requiring repairs that caused it to miss scheduled appearance at Tushino Air Display.

On 15 September, all ten pre-production aircraft were delivered—though serial number 3810107 served as static test airframe while serial number 3810110 became dedicated static engine testbed—and transferred to NII VVS (Air Force Scientific Test Institute) for formal State acceptance trials.

On 29 November 1946 Joseph Stalin convened a conference setting future Soviet jet fighter policy for both VVS (Air Forces) and PVO (Air Defense Forces). The Mikoyan-Gurevich MiG-9 was chosen as primary frontline fighter while Yakovlev Yak-15 was assigned training roles due to imminent access to British jet engines plus captured German technology making mixed-power concepts obsolete; nevertheless Stalin insisted that I-250 complete trials with tooling and unassembled parts preserved despite program cancellation.

Completion of testing extended into May 1947 awaiting final VRDK evaluations while Mikoyan attempted marketing aircraft for Soviet Naval Aviation as torpedo bomber escorts; modifications included additional fuel tanks added in wings and fuselage increasing total capacity by 218 litres (48 imp gal; 58 US gal) plus enlarged oil tank raised empty weight to 3,028 kilograms (6,676 lb) and takeoff weight near 3,931 kilograms (8,666 lb).

New State trials commenced on 9 October 1947 but suffered delays due to poor weather coupled with ongoing reliability problems limiting flights—only six sorties totaling two hours twenty-five minutes logged by January’s end—and ground runs of VRDK lasting mere ninety seconds before declaring failure on 3 April 1948.

Specifications (initial prototype)

File:Mikoyan-Gurevich MiG-13 3-view line drawing.png

I-250