 The prototype was completed in July and was first flown on 27 July 1947 . Two aircraft were shown at the <unk> Aviation Day <unk> on 3 August 1947 . It completed its manufacturer 's trials in September and underwent the State acceptance trials from 4 October 1947 to 27 February 1948 where it was redesignated as the Tu @-@ 12 . The <unk> VVS ( <unk> @-@ <unk> <unk> <unk> <unk> @-@ <unk> <unk> – Air Force Scientific Test Institute ) report summarized the differences between the Tu @-@ 2 and Tu @-@ 12 as " a considerable gain in speed , an improved rate of climb , a higher service ceiling , but poorer field performance and a considerably greater fuel load required to achieve the same range as the Tu @-@ 2 . " Both the lack of a pressurized cabin that greatly reduced its effectiveness at high altitude and the lack of <unk> equipment for the wing and tail leading edges and the cockpit glazing were noted as major problems . At high speeds it was virtually impossible to traverse and elevate the manually operated <unk> @-@ 68 and Lu @-@ 68 gun turrets . The vibration of the NS @-@ 23 cannon when firing rendered the equipment in the <unk> 's cabin unusable and damaged the cabin glazing . Turning on the <unk> friend or <unk> ( <unk> ) system adversely affected the <unk> system and the radios . New generators had to be installed as the originals did not produce enough electrical power . 
