The electric motor was connected to a banjo-type rear axle by a Layrub propellor shaft. The propellor shaft is now provided with needle-roller bearings. Fort ships had a triple expansion steam engine and a single screw propellor. Compared to an open-air propellor, a ducted-fan generates more thrust per crossectional-area. Modern dahabiyas still lack a motor-driven propellor. This was the first large iron steamship and the first to use a screw propellor. Next, a sub-contract was accepted from the Bendix Aviation corporation for making propellor controls. Choice of engines is also a function of target propellor speed at cruise. Each propellor had a diameter of and a pitch of . Dunkeswell Airfield Heritage Centre, is situated to one side of the large propellor memorial. During World War II, its propellor works was moved to Birkenhead. It used a propellor design and required a large cabinet to move sub-sonic air mass. The propellor slashed Williams' legs and he was rushed to a hospital for his injuries. Ratier chose Figeac for the abundant wood-supplies in the region, necessary for propellor production.