 Work on two prototypes was authorised in November 1943 , but proposals for alternative engines delayed progress . In 1945 , it was decided that as well as adding another Centaurus @-@ engined prototype , there should be three prototypes with the Napier E.122 ( a development of the Sabre ) as Specification S.10 / 45 . The Ministry believed that this would enable Blackburn to develop their knowledge of <unk> and structural design and support the engine development at Napier . However , it was found that the S.10 / 45 aircraft could only be balanced if the E.122 <unk> was placed behind the pilot . The necessary redesign and 1 @,@ 000 @-@ pound ( 454 kg ) weight increase , coupled with the limited funds available to the Royal Navy , meant that it could no longer be justified and the S.10 / 45 was cancelled on 8 October . While in final design , the Centaurus 77 engine with <unk> @-@ rotating propellers was cancelled in January 1946 and a conventional 2 @,@ <unk> @-@ horsepower ( 2 @,@ 107 kW ) Centaurus 57 was substituted . This engine was found to require flexible mounts and was modified into the Centaurus 59 . The vertical <unk> and rudder had to be enlarged from 33 to 41 square feet ( 3 @.@ 1 to 3 @.@ 8 m2 ) to counteract the new engine 's <unk> . In September 1946 a strength analysis conducted by the Ministry of Supply revealed that the aircraft would require strengthening to serve as a strike fighter and that a costly redesign would be required to bring it up to requirements . This would have made it comparable in weight and performance to the Westland <unk> which had already flown so no contract was placed for production aircraft . 
