Various remedies for the handling shortcomings of the LaGG-1 were applied, and the first LaGG-1 prototype to introduce these changes was referred to as the I-301 (from the numerical designation of the factory - GAZ-301). This also featured redesigned outer wing panels incorporating additional fuel tanks. The I-301 entered flight test on 14 June 1940, the modified aircraft being assigned the designation LaGG-3 and most pre-series examples of the LaGG-1 being completed to the later standard.
The LaGG-3 was essentially the series production version of the LaGG-1 with a revised outer wing incorporating fuel tanks, and an armament of one 20mm and two 7.62mm weapons. Fixed wing slats - later replaced by automatic slats - were introduced and balance weights were added on the elevators and rudder, but were later discarded in favour of statically and dynamically balanced surfaces. Weight was reduced as a result of a structural analysis. LaGG-3 deliveries commenced in the spring of 1941, initially with the M-105P engine, but, from late in the year, with the M-105PF of 1260hp at 800m.
Provision was later made to replace one or both machine guns by weapons of 12.7mm calibre, the 20mm hub-mounted cannon being replaced by one of 23mm calibre in some cases, and a pair of 12.7mm underwing guns was sometimes fitted. Three aircraft were each fitted with a 37mm cannon and referred to as LaGG-3K-37s, and one example was fitted with the 1650hp Klimov M-107A engine. Production of the LaGG-3 was completed in the late summer of 1942 with a total of 6,528 built, superseded by the La-5.
Max take-off weight: 3190 kg / 7033 lb
Empty weight: 2620 kg / 5776 lb
Wingspan: 9.8 m / 32 ft 2 in
Length: 8.9 m / 29 ft 2 in
Wing area: 17.5 sq.m / 188.37 sq ft
Max. speed: 570 km/h / 354 mph
Cruise speed: 450 km/h / 280 mph
Ceiling: 9700 m / 31800 ft
Range: 800 km / 497 miles