The Yak-9 represented further development of the successful Yakovlev Yak-7 fighter, a production version of the lightened Yak-7DI, taking full advantage of the combat experience with its predecessor. Greater availability of duralumin allowed for lighter construction which in turn permitted a number of modifications to the basic design.

Yak-9 variants carried two different wings, five different engines, six different fuel tank combinations and seven types of armament configurations. In December 1943 it became possible to install the more powerful M-107 engine on a new Yak-9U airframe: the engine mounting was new with individual faired exhaust pipes; fuselage structure and wings were made of metal and the whole aircraft was covered with a Bakelite skin. Fuel capacity was increased to 106 gallons (781 lb). In order to re-balance the model, the wing was repositioned four inches forward and in order to improve pitch control, the horizontal tail surfaces were slightly reduced. The rear part of the canopy was lengthened and the antenna cable was moved inside it. Usual armament was a ShVAK cannon with 120 rounds firing through a hollow propeller shaft and a UBS 12.7mm machine gun with 170 rounds each.

The State trials took place from January to April 1944. They revealed a clear superiority in top speed over all other fighters in service on the Eastern front, up to 19,800 feet. The aircraft was simple to fly and stable. Unfortunately, the problems with the M-107A engine and moreover all the M-105 variants from which it derived, persisted: power plant overheating, oil leaks, loss of pressure in climbs, intense vibrations, burning out sparkplugs and a short engine life. Despite these defects, the Yak.9U/VK-107 was ordered into production in April 1944 with 1,134 machines produced by December 1944.

World War II

The first Yak-9 entered service in October 1942 and first saw combat in late 1942 during the Battle of Stalingrad. The versatile Yak-9 operated with a wide variety of armament for use in anti-tank, light bomber and long-range escort role. At low altitude in which it operated predominately, the Yak-9 was faster and more maneuverable than its main foe, the Bf 109, but was far less well-armed. A series of continual improvements in performance and armament did not hamper the superb handling characteristics that allowed its pilots to excel at dog-fighting. Soviet pilots regarded the Yak-9's performance as on the same level as the Bf 109G and Fw 190A-3/A-4.

After the Battle of Smolensk, in the second half of 1943, the famed Free French Normandie-Niémen unit became a Groupe and was equipped with the Yak-9. The four flights were named for the towns of Rouen, Le Havre, Cherbourg and Caen. In June 1944, at the beginning of the great summer offensive, the French Yak-9s achieved their first air victories, but suffered their first losses as well, in the Borisov region. On 15 July 1944, the Group was moved to Mikountani, in Lithuania, while German armies were pushed back about 400 kilometers. The French pilots took their Soviet chief air crews in the fuselage of the fighters, but during the trip, Lieutenant Maurice de Seynes' Yak suffered a mechanical failure. The French pilot refused to bail out and thus abandon his Soviet mechanic Biezoloub, who had no parachute. De Seynes attempted an emergency landing instead, but both airmen were killed in the crash.

The first unit to use the Yak-9U, between 25 October and 25 December 1944 was 163.IAP. Pilots were ordered not to use the engine at combat speed since this reduced its life to two or three flights only. Nevertheless, in the course of 398 sorties, the unit claimed 27 Focke-Wulf Fw 190As and one Bf 109G-2, for the loss of two Yaks in dogfights, one to flak and four in accidents. The Yak-9U contributed greatly to Soviet air superiority, and the Germans avoided the Yaks “without antenna mast”.

A large formation of the Yak-9DD version was transferred to Bari (Puglia, Italy) to help Yugoslav partisans in the Balkans.

One of the top-scoring Yak-9 pilots was First Lieutenant A.I. Vybornov. Flying a type–T (equipped with a cannon in the nose) he achieved 19 air victories, plus nine shared. He was awarded the Gold Star Medal of the Hero of the Soviet Union in June 1945.  At the end of the war, on 22 March 1945, L.I. Sivko from 812.IAP achieved the first VVS air victory against a Messerschmitt Me 262 jet fighter, but he was killed soon afterward by another Me 262, probably piloted by Franz Schall, a top scoring Me 262 pilot.

Postwar

During 1949, the USSR provided surplus Yak-9P (VK-107) aircraft to some satellite states in the Soviet bloc in order to help them rebuild their air forces in the wake of the West Berlin blockade. A section of the aircraft's operating manual was accidentally omitted from the translation from Russian into some languages: before starting the Yak-9, it was necessary to hand-crank a small cockpit-mounted oil pump 25 times to provide initial lubrication to the Klimov V12 engine, unlike World War II German and Western fighters equipped with forced closed-cycle lubrication systems. Skipping this unusual but vital step resulted in frequent engine seizures during the takeoff roll and initial climb, causing several fatalities during 1950.

Source: Wikipedia