The very basic Thrust Measuring Rig or 'Flying Bedstead' was the first British VTOL aircraft and gathered useful data for the P.1127 (Harrier) project. The Bedstead's loaded weight was only about 272kg less than the combined thrust of the two engines, and some of that thrust was ducted away for the control ducts. Each control movement reduced the lifting thrust, requiring a bit more throttle and meaning that it could not be controlled at maximum thrust without a height loss. There was little margin for error — and none at all if one engine faltered. The only plus side was that the engine nozzles were arranged to give thrust (lift) on the centreline so that at least it would plunge vertically rather than flip over. Both Bedsteads did crash, one fatally, and the Harrier adopted a quite different lift system.