▁prototype ▁tor ped o ▁bom ber ▁was ▁modified ▁as ▁the ▁prototype ▁of ▁the ▁Tu - 8 . ▁That ▁aircraft ' s ▁A Sh - 8 2 F N ▁engines ▁were ▁retained ▁rather ▁than ▁use ▁the ▁A Sh - 8 3 M ▁engines ▁originally ▁planned . ▁It ▁was ▁first ▁flow n ▁on ▁ 2 4 ▁May ▁ 1 9 4 7 ▁and ▁kept ▁on ▁manufact urer ' s ▁tri als ▁until ▁ 2 0 ▁April ▁ 1 9 4 8 . ▁These ▁tri als ▁were ▁prolong ed ▁by ▁the ▁numerous ▁difficulties ▁experienced , ▁especially ▁with ▁the ▁def ensive ▁arm ament . ▁It ▁began ▁State ▁tri als ▁on ▁ 2 3 ▁August ▁ 1 9 4 8 ▁which ▁last ed ▁until ▁ 3 0 ▁November ▁ 1 9 4 8 . ▁The ▁report ▁of ▁the ▁N II ▁V VS ▁( Russ ian : ▁Нау чно - И с следова тель ский ▁Ин ститу т ▁Во ен но - Во з ду ш ных ▁Си л ▁N auch no - I ss led ov atel ' ski y ▁Institut ▁Vo yen no - V oz d ush ny kh ▁Sil ▁– ▁Air ▁Force ▁Scient ific ▁Test ▁Institute ) ▁was ▁unf avor able : ▁The ▁performance ▁was ▁not ▁comm ens ur ate ▁with ▁the ▁direct ives ▁stated ▁in ▁the ▁Government ▁Direct ive ▁for ▁the ▁development ▁of ▁the ▁aircraft . ▁The ▁machine ▁was ▁un stable ▁at ▁all ▁the ▁normal ▁center ▁of ▁gravity ▁positions , ▁the ▁wings ▁and ▁under car riage ▁were ▁ins u fficient ly ▁strong , ▁the