Hawker Siddeley Harrier single lever added in the cockpit. For horizontal flight, the nozzles are directed rearwards by shifting the lever to the forward position; for short or vertical takeoffs and landings, the lever is pulled back to point the nozzles downwards. The Harrier has two control elements not found in conventional fixed-wing aircraft: the thrust vector and the reaction control system. The thrust vector refers to the slant of the four engine nozzles and can be set between 0° (horizontal, pointing directly backwards) and 98° (pointing down and slightly forwards). The 90° vector is normally deployed for VTOL manoeuvring. The reaction control
Hawker Siddeley Harrier testing. The two remaining British-based Kestrels were assigned to further trials and experimentation at RAE Bedford with one being modified to use the uprated Pegasus 6 engine. At the time of the development of the P.1127 Hawker and Bristol had also undertaken considerable development work on a supersonic version, the Hawker Siddeley P.1154, to meet a North Atlantic Treaty Organisation (NATO) requirement issued for such an aircraft. The design used a single Bristol Siddeley BS100 engine with four swivelling nozzles, in a fashion similar to the P.1127, and required the use of plenum chamber burning (PCB) to achieve supersonic speeds.