In 1943, the Design Bureau led by Vladimir P. Gorbunov created a further update of the original LaGG-3, still in production in its lightened form at Zavod 31 in Tbilisi.

I-105

The first prototype of I-105 (I for Istrebitel, fighter) was built in May 1943. Compared to late production LaGG-2 (series 70) the new plane featured:

• the back of the fuselage was lowered behind the canopy, in a way that resembles (but was not identical) to what made by Zavod 21 on La-5F and FN;
• the oil cooler was moved from under the nose, that became more streamlined, divided into two sub-units and located under/aside the cockpit; the air entered from two thin protruding intakes under the fuselage, and came out from two outlets, one on each fuselage side;
• the water cooler fairing was modified, changing a bit the lower profile of the fuselage;
• the wing slats were deleted;
• the position lights were moved on the leading edges as on Yaks;
• the hydraulic system actuating the landing gear and the flaps was replaced by a pnematic one;
• the tailwheel was fully retractable, with flush doors;
• the main landing gear had widened doors; it is likely that the shape of the bay was modified too;
• the slats were suppressed;
• the radio antenna was buried in the fuselage;
• the bomb racks were deleted;
• the slot of the syncronized UBS was modified;
• the trim tab of the rudder was splitted, part above the position light, part below;
• the gross weight was reduced to 2749 kg.

The test flight were satisfying, showing an increase of speed of 25 km/h compared to productio LaGG-3s of May 1943, a good turning time of 16 seconds, a climb time to 5000 m of 4.7 minutes and no troubles in handling.

	Aside: image of the first prototype I-105 taken on January 1944, much after its maiden flight in May 1943. . Note that the windshield, the engine and the 4-tubes exhaust stakes were the same of production LaGG-3s. The black-white painting of the prop blades and of the wheel hubs is noteworthy.
	Profile of I-105. The plane featured a standard grey-grey camouflage of AMT-11 and 12, with AMT-7 blue undersurfaces.
I 105-2 The second prototype I-105-2, had some improvements: the more advanced M-105PF-2 emgine, as on Yak-3; prop blades extended on their root to increase thrust; modified panelling of the nose; new 6-pipes exhaust stacks as on Yak-3; armament of one 23 mm VYa gun firing through the prop's hub (instead of 20 mm ShVAK) and a 12,7 mm UBS (the same as I-105); frameless windshield as on Yak-3; the doors of the main landing gear were a bit reduced and were more similar to that of standard LaGG-3s..
	The image from behind shows
	This image shows clearly the new profile of the fuselage,
	This image shows the small size of the stars under the wings and the distance between the new air intakes for the oil coolers.
	Profile of I-105-2. It featured the standard grey-grey camouflage

The prototype was ready to fly only in February 1944 because of delays, and the state tests were made only in May-June 1944.

The state tests weren't very satisfying: the gross weight was 2875 kg, the max speed was 554 km/h at sea level and 618 km/h at 3400 m; it reached 5000 m of altitude in 4.8 minutes.

The maximum speed could be sustained only for 3 or 4 minutes because of water and oil overheating. These performances were inferior to those of the Yak-1M, the prototype of Yak-3, already tested in October 1943.

The program of modernization of the LaGG-3 was deleted, and Zavod 31 in Tbilisi was converted to the production of Yak-3s.

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