 The five aircraft modified by the factory were given the Klimov RD @-@ 45 engine , the Soviet unlicensed copy of the Nene engine , and all six aircraft , used by the VVS for aircrew familiarization and training . The aircraft completed were later relegated to test duties . One aircraft was used for drone tests and another , redesignated as the Tu @-@ 12LL , mounted various pulse jet engines on a pylon above the fuselage . 
