Design and development
By 1943, the La-5 had become a mainstay of the
Soviet Air Forces, yet both its head designer,
Semyon Lavochkin, as well as the engineers at the
Central Aerohydrodynamics Institute (
Russian: TsAGI), felt that it could be improved upon.
TsAGI refined earlier studies of aerodynamic improvements to the La-5 airframe in mid-1943 and modified La-5FN c/n
[Note 1] 39210206 to evaluate the changes. These included complete sealing of the engine cowling, rearrangement of the wing center section to accommodate the oil cooler and the relocation of the engine air intake from the top of the cowling to the bottom to improve the pilot's view.
[1]
The aircraft was evaluated between December 1943 and February 1944 and proved to have exceptional performance. Using the same engine as the standard La-5FN c/n 39210206 had a top speed of 684 kilometers per hour (425 mph) at a height of 6,150 meters (20,180 ft), some 64 kilometers per hour (40 mph) faster than the production La-5FN. It took 5.2 minutes to climb to 5,000 meters (16,404 ft). It was faster at low to medium altitudes than the La-5 that used the more powerful prototype
Shvetsov M-71 engine.
[2]
Lavochkin had been monitoring
TsAGI's improvements and began construction in January 1944 of an improved version of the La-5 that incorporated them as well as lighter, but stronger, metal wing
spars to save weight. The La-5, as well as its predecessors, had been built mostly of wood to conserve strategic materials such as aircraft alloys. With Soviet strategists now confident that supplies of these alloys were unlikely to become a problem, Lavochkin was now able to replace some wooden parts with alloy components. In addition Lavochkin made a number of other changes that differed from c/n 39210206. The engine air intake was moved from the bottom of the engine cowling to the
wing roots, the wing/fuselage
fillets were streamlined, each engine cylinder was provided with its own exhaust pipe, the engine cowling covers were reduced in number, a rollbar was added to the cockpit,
[3] longer shock struts were fitted for the main landing gear while that for the tail wheel was shortened, an improved PB-1B(V) gunsight was installed, and a new VISh-105V-4 propeller with a
Mach-resistant
airfoil was fitted.
[4] Three prototype 20 mm (0.79 in)
Berezin B-20 autocannon armed the 1944 standard-setter (
Russian: etalon), as the modified aircraft was designated.
[3]