Yak-7B fighter with M-105PF engine, A.S.Yakovlev

his fighter was the first one of the Yak-7 family equipped with supercharged engine. Actually, the M-105PF engine differed from M-105PA predecessor by increased (re-adjusted) from 910 to 1050mm.Hg carburetor pressure. To ensure reliable operation of the engine, pistons were reinforced and carburetor was modified. Trials of aircraft with this new engine were so encouraging, that government ordered V.Ya.Klimov to switch urgently all production lines to the modified powerplant.

First aircraft to fly with new engine was series Yak-7B N°22-41. Aircraft was tested at NII VVS, on May 30 to June 9 1942. Test team included pilots P.Ya.Fedrovi (OKB), A.N.Lazarev (Factory N°153), test-engineers A.T.Stepanets, K.V.Pouzanov, A.G.Aronov (NII VVS), S.D.Evdolikov, P.S.Limar (LII) et al.

Trials conclusion was positive:

• Speed increase was observed:



below 2800 m	3000 m	4000 m	above 5000 m
25 to 29 km/h	14 to 18 km/h	20 to 35 km/h	same

• Climb time to 5000m was cut by 10%
• Climb during combat turn increased by 100m
• Turn time cut by 1...2sec
• Takeoff run shortened by 50m
• Oil temperature increased by 12°C and water - by 5°C
• Cockpit equipment improved substantially
• Assembly and finish quality improved, but still fails short of desired level

Experience of the Yak-7B M-105PA front line service resulted in yet another package of introduced modifications:

• Airframe was lightened
• Seat jack was lightened and simplified (no in-flight adjustment)
• Lighter cushioned seat back installed
• Frame and skin of the main wheel wells lightened
• Landing gear lightened
• RS-82 launchers and associated wiring removed
• Automatic propeller re-adjusted to match new engine regimes
• Cannon's pneumatic reloading system deleted
• Fuel tank in the ex-rear cockpit eliminated

Armament of new Yak-7B was identical to one of the Yak-7B M-105PA. Cockpit equipment and ergonomic, at the same time, were substantially improved. Finally, cockpit of the Yakovlev fighter reached the world standards for its class.

As a result of all changes, the center of gravity of the Yak-7B M-105PF moved forward. Aircraft became more stable, but landing became more complicated. It was not possible to use wheel brakes to the full advantage, and typical landing roll became longer. During the ground engine trials, ground crew had to hold down the tail to prevent noseover. To cure those shortcomings, serious airframe redesign was required. But at this time Yakovlev OKB was already working on new Yak-9 fighter, and production-built Yak-7B's were not modified.

Unsolved problems of the engine overheat did not allow to use increased engine power to the full advantage, especially during the climb. Uneven fuel consumption from the port and starboard tanks was solved only in 1943 by providing pilot with 3-way valve. Insufficient range and quality of radio equipment was gradually cured by wire shielding and connecting all metal parts together to form better 'ground'.

In 1943 production batch of 13 aircraft was studied at the Novosibirsk Plant. Weight was found with 16kg margin (depending on the armored glass installation and other minor variations). Speed variation was within +/-10km/h of average, depending mostly on the variations in the engine tuning.

Also in the 1943 Yak-7B N°31-01 of 31st batch was modified to achieve maximum performance. Following changes were done:

• Antenna and mast hidden inside the fuselage
• Leading edges of the wing and tailplane polished to 30% of the wing chord
• Two variants of the jet exhaust were tried, exhaust stacks were covered with fairing similar to one of the Bf-109
• Entire aircraft was carefully sealed to exclude 'whistle' drug
• Tailwheel retraction mechanism improved to guarantee complete closing of the tailwheel well covers

Trials of this experimental plane continued until May 15. Performance improved substantially. Installation of exhaust stacks suggested by NII VVS added extra 8km/h to the aircraft speed compared to ones proposed by Yakovlev OKB. Hiding of the antenna inside the fuselage cut the communication range by unacceptable 50%, and was rejected.

Yak-7B M-105PF was built at two factories:

• Novosibirsk N°153 starting August 1942 until December 1943.
• Moscow N°82 starting May 1942 until July 1943.

Aircraft built at Moscow were 25 to 30kg heavier and 15km/h slower. Total production of this type was 5120 aircraft. First seen in combat in August 1942 near Stalingrad.

In December 1942 at the 45^thIAP (F.I.Shinkarenko, North-West Front) Yak-7B M-105PF were modified same way as the Yak-1 was: upper fuselage cut down behind the cockpit and new tear-shaped canopy fitted. Improved pilot's view resulted in win/loss ratio gain.

Flown by many Soviet aces - among them twice Heroes of Soviet Union A.Vorozeikin (52 victories), I.Stepanenko (41 victories), P.Pokrishev (31 victories) and E.Savitski (24 victories).

Created July 16, 2001

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