S.Ransom, R.Fairclough English Electric Aircraft and their Predecessors (Putnam)
The Phoenix P.1 was not the company's first aircraft project. The first was a twin-rotor helicopter observation platform designed by Pybus and embodied in patent 109,672 applied for on 30 September, 1916. The contra-rotating rotors were directly coupled to squirrel cage induction motors with aluminium windings, mounted at the extremities of a box-girder structure, which carried the observer and his parachute. Power for the motors was supplied from a ground or ship-based generator by an electric aluminium cable that served also as a tether. Pybus sought in the smallness of the device a means of reducing the vulnerability of observation platforms, then carried aloft by large unwieldy balloons and kites.