Aviation of Word War II
MiG-3U/I-230 (D, D-01, D-02)
High-altitude Fighter (prototype)
• take off weight 3100 kg,
• top speed 670 km/h;
• ceiling 12500 m;
• climb to 10,000 m in 13 minutes.
The aircraft was called MiG-3U (uluchshennyi, improved). To reach this performance, a considerable reduction in weight would be needed.
The main differences between the MiG-3U and the standard MiG-3 were:
• the fuselage was lengthened and had no central welded truss, but it was an all-wooden monocoque structure with a plywood skin of 3 layers, 1 mm thick in the wing centre section, and two layers in the tail (not a veneer skin like that of the basic MiG-3). This lightened and simplified the structure;
• the cockpit was moved back and raised, and its canopy was widened and raised to improve visibility;
• the main spar of the wing was no longer interrupted by the radiator tunnel;
• main spars of the wing outer panels were no longer made of wood, but of metal;
• wingtip position lights were moved;
• the fin and rudder were modified;
• the horizontal tail surfaces were raised 200 mm to avoid interference with the new tail wheel mechanism;
• the main landing gear was redesigned with different doors and smaller wheels, 600x180;
• the armament comprised two 20 mm ShVAK guns with 150 rounds each, placed over the nose and synchronized; they could fire separately or together;
• the P-310 radiator was placed inside the fuselage, below the cockpit; its main air intakes were located in the wing roots, while two auxiliary intakes were located in the ventral position, on the sides of the oil cooler tunnel;
• the air intakes for the supercharger were still in the wing roots, with the radiator intakes;
• the oil cooler "533" was put in a ventral tunnel between the wheel bays;
• the radio set comprised a RS1-3 transmitter and a RSI-4 receiver;
• the gun sight was a PBP-1 A;
• a new control column incorporating the brake lever, fire control button and press-to-transmit button was installed;
• the oxygen system was the KPA-3bis with a 4 litre bottle;
• access to radio and oxygen equipment was from a hatch on the right side of the fuselage;
• the engine was an AM-35A with 0.732 reduction gear, built with spare parts from an AM-35A and AM-38 because of engine shortages; it was 40 kg heavier than the standard AM-35A;
• the propeller was a AV-5L-126A, of 3.2 m diameter;
• a 4401 bladder-type fuel tank, contained in a box of flame-resistant treated plywood, was installed between engine and cockpit;
• it was possible to install two further tanks in the wings, for a further 210 litres.
The first prototype, D-01, was first flown by test pilot V.N.Savkin on May 31, 1943. During June and July a further 5 aircraft were built, D-02 to D-06. D-04had a larger wing, with a span of 11.14 m and a 18.22 mq area. D-01 completed 28 flight tests, showing problems of engine overheating, particularly of the oil.
D-01 was transferred to NII-VVS on 23 July for state tests. These ran from 28 July to 6 August, led by chief engineer Captain A.S. Rozanov and test pilot B.I. Khomyakov. The tests showed a top speed of 656 km/h at 7000m, and a ceiling of 11,900 m. The aerobatic performance of the D-01 was good, but landing remained difficult. The cockpit was more comfortable, and similar to other up-to-date fighters. Some vibrations were noted in the tail horizontal surfaces. The most evident defect was oil leakage through the coupling of the reduction shaft, especially at high altitude. After every flight, the aircraft returned with the fuselage sprayed with oil from nose to tail. This defect was considered unacceptable by test pilots, but it was probably due to the hybrid engine.
D-01 returned at OKB-155 for repairs and modifications. Then all the prototypes were sent to 12 GvIAP for operational tests. They were flight tested by Leytenant P. A. Zhuravliov and checked by technicians of 12 Gv.IAP. Only D-01 ,D-03, D-04 and D-06 passed the checks and were accepted by the unit, while D-02 and D-05 remained at OKB-155 to change their engines. AM-35 A engines only arrived on October 10. While waiting for the engines, D-02 received longer span wings. After the installation of the engine, D-02 was transferred to 177 IAP, while D-05 had still oil leakages and was transferred to Zavod n.34 to remedy them.