The Yak-7 started as a trainer for the Yak-1 in January, 1940, and took to the air for the first time in July 1940. Changes in the Yak-1 and Yak-7 took place simultaneously. Movement of the center of gravity further aft avoided nose-overs on landing. Changes in air intakes addressed engine overheating. The re-designation from Yak-1UTI to Yak-7 occurred officially in February 1941.
With the German invasion of the Soviet Union, the Soviet Air Force decided to turn the Yak-7 into a tactical fighter in August 1941. The rear cockpit was removed and covered over. New armament included a 20 mm cannon firing through the propeller boss, and two 7.62 mm machine guns. Six rocket launch rails were installed under the wings. Production began in September 1941, but factory movement to Siberia in October 1941 limited production numbers. The Yak-7 entered combat in defense of Moscow in December 1941.
The Yak-7A powered by the Klimov M-105PA completed acceptance trials with wheels or retractable skis in early 1942. This variant deployed to the Vokhov and Western Fronts in early summer 1942. Combat pilots complained about poor rearward visibility, inherent in both the Yak-1 and Yak-7 aircraft, due to the “razor-back” configuration. A “bubble” canopy was suggested.
The Yak-7B was equipped with increased armament: one 20 mm cannon and two 12.7 mm machine guns. Rocket rails were provided for six unguided rockets. An alternative underwing load was provision to carry two 25 to 100 kilogram bombs. The rocket rails were deleted in May 1942. One in ten aircraft carried a two-way radio.
The heavier armament added to the aircraft moved its center of gravity forward aggravating its inclination to nose over on landing. In compensation an 80 liter fuel tank was added in the rear cockpit. Combat pilots objected to the fuel tank in the cockpit and fighter units at the front tended to remove the tank.
Designers increased the boost pressure of the M-105PF increasing the horsepower from 1,050 to 1,180 hp. This required a modification of the fine pitch on the propeller to access the power. A Yak-7B weight reduction program included lightening the airframe, deleting the wiring for the rockets, and deleting the 80 liter fuel tank.
The Yak-7B entered combat in the summer of 1942, engaging in intense battles over Stalingrad. In one engagement on 20 August Soviet pilots claimed 29 German aircraft shot down for a loss of nine.
An Air Force study of the performance of the Yak-7B revealed that many pilots flew the aircraft with the canopy either open, or removed. Radiator and oil cooler shutters were open, and wheel doors and maintenance access panels were poorly fitted. Pilots operated the engine at a reduced setting of 2,700 rpm resulting in speed reductions of 40 to 50 km/hr.
Aircraft produced at the Moscow plant, as opposed to the plant at Novosibirsk, were of lower quality resulting in speed losses of 25 to 30 km/hr, higher stick forces, and more sluggish maneuverability. Poor production standards or faulty installation resulted in machine gun failures in the Yak-7B. Flawed design of shell ejection chutes and feed sleeves contributed. Cannon failures were caused by poor design of the case ejector chutes and the belt link collectors. Low grade substitutes of various chemicals in the bonding glue resulted in defective bonding of the wooden skin to the internal structure causing the skin to rip away in flight.
Later improvements to the Yak-7B included cutting down the upper rear fuselage and fitting a bubble canopy. Emergency canopy jettison devices were installed. A combined throttle and pitch control, introduced in 1943, reduced pilot work load in combat situations.
Production of the Yak-7B continued to July 1944 with 5,120 being built. The aircraft remained in service to the end of the war, and proved tough enough to take considerable damage in battle and still return safely.
Source: Yakovlev Fighters of World War Two, Yefim Gordon, Sergey Komissarov and Dmitriy Komissarov, Hikoki Publications, Manchester, England, 2015