Mitchell moved the S.6 from Napier to Rolls-Royce power

Mitchell considered Bristol and Napier before deciding that the Napier Lion had reached the end of its useful development path. The S.6 therefore adopted a Rolls-Royce R V-12 capable of roughly 1,900 horsepower at 2,900 rpm for no more than an hour at maximum revs. The possibility of destructive failure, along with contemporary test-to-destruction practice, shows how close racing engines operated to their physical limits. The S.6 used an RAF 27 wing section, measured roughly 8 metres long with a 9-metre span, and paired its power with a fixed-pitch, two-bladed propeller. Its landing speed was around 95 mph.