Using Thrust to Overcome Weight
Rockets use thrust to reach orbit, but they aren’t the only type of vehicles that direct thrust down to create vertical flight. However, relying on the brute force of thrust to counteract weight requires far more fuel and energy than using the force of lift. Even so, an aircraft that can take off and land vertically can hover, fly slowly, and land in tight spaces—things conventional aircraft cannot do.
The powerful exhaust streams from the jet engine of the Harrier fighter can be directed downward as well as backward, and their direction can be changed in mid-flight. This allows the Harrier to take off vertically, fly forward, stop in mid-air, back up, and land vertically. It can also take off and land like a normal airplane.
Credit: McDonnell Douglas Corporation
Vertical Take-Off and Landing
Vertical takeoff and landing (VTOL) aircraft include fixed-wing aircraft that can hover, take off and land vertically, as well as helicopters and other aircraft with powered rotors, such as tiltrotors. Some VTOL aircraft can operate in other modes as well, such as CTOL (conventional takeoff and landing), STOL (short takeoff and landing), and/or STOVL (short takeoff and vertical landing). Others, such as some helicopters, can only operate by VTOL, due to the aircraft lacking landing gear that can handle horizontal motion.
To take off or land vertically, the powerful exhaust streams from a jet engine can be directed downward as well as backward, and their direction can be changed in mid-flight. This allows fixed-wing aircraft, such as the Harrier or the F-35B, to take off vertically, fly forward, stop in mid-air, back up, and land vertically. They can also take off and land like a normal airplane. A helicopter’s spinning blades create thrust like a large propeller, but the thrust is directed vertically. This allows the vehicle to take off and land vertically and to hover. To move forward, the helicopter tilts slightly to direct some of its thrust forward.
A tiltrotor is an aircraft that uses a pair tiltrotors mounted on rotating engines at the end of a fixed wing to generate vertical and horizontal thrust. It combines the vertical capability of a helicopter with the speed and range of a fixed-wing aircraft. For vertical flight, the rotors are angled so the plane of rotation is horizontal, like a helicopter. As the aircraft gains speed, the rotors are tilted forward, with the plane of rotation eventually becoming vertical. The wing then provides lift, and the rotor provides thrust like a propeller.
