The thrust to weight ratio must be higer than one in order to get (VTOL) Vertical lift off and landing. This ratio must be greater than one to lift from the ground with the thrust vector pointed downward during take off and pointed back ward during normal flight. In earlier days the main problem with these aircraft was that thier control was too dificult and the maintenence of engine was difficult too. In this way accident rate or ratio was too high. SO , Harrier was the first air craft with successfull VTOL. There were four vectorizing Nozzels which could be turned vectorially from 0 to 98degrees. WIth the reaction control system with the extra set of small thruster there were no air stream in hover flight accross any control system . Harrier was prior to preveous such jets because of its high roll rate, a small turn radius , and its ability of climb to high altitude abruptly. Another plus point of Horrier was that it lands just like an ordinary plane vectoring the thrust to about 45 degree down . Solution The thrust to weight ratio must be higer than one in order to get (VTOL) Vertical lift off and landing. This ratio must be greater than one to lift from the ground with the thrust vector pointed downward during take off and pointed back ward during normal flight. In earlier days the main problem with these aircraft was that thier control was too dificult and the maintenence of engine was difficult too. In this way accident rate or ratio was too high. SO , Harrier was the first air craft with successfull VTOL. There were four vectorizing Nozzels which could be turned vectorially from 0 to 98degrees. WIth the reaction control system with the extra set of small thruster there were no air stream in hover flight accross any control system . Harrier was prior to preveous such jets because of its high roll rate, a small turn radius , and its ability of climb to high altitude abruptly. Another plus point of Horrier was that it lands just like an ordinary plane vectoring the thrust to about 45 degree down ..