 The Firebrand required significant effort by Blackburn to produce a useful aircraft and the first discussions on a redesign of the aircraft with a <unk> @-@ flow wing took place in September 1943 . The new wing was estimated to reduce the weight of the wing by 700 lb ( <unk> kg ) and increase the aircraft speed by 13 mph ( 21 km / h ) . The extent of redesign increased and this led to a new fuselage and other improvements . In October 1943 , Blackburn 's design staff , led by G.E. Petty , started work on this development of the Firebrand which led to Specification S.28 / 43 being issued by the Air Ministry on 26 February 1944 covering the new aircraft . The specification was designed around a Bristol Centaurus 77 radial engine with <unk> @-@ rotating propellers that allowed the size of the rudder to be reduced . 
