Harrier aircraft flight simulation. Supercomputer image of a Harrier aircraft hovering over a runway in a virtual wind tunnel. The lines beneath the aircraft show the air flow from the aircraft's engine. The lines' colours show the air's tempera- ture gradient, from red (highest), through orange, yellow, green, and blue, to purple (lowest). The Harrier is a Vertical Take-Off and Landing (VTOL) fighter aircraft which directs air from its Rolls- Royce Pegasus engine through 4 swivelling nozzles along the side of its fuselage. The nozzles point downwards for take-off, before rotating backwards to accelerate the aircraft into wing-borne flight.