Vertical/Short Takeoff and Landing (V/STOL) aircraft
Last updated: September 12, 2009.
Airplanes fly fast but need super-long runways for taking off and landing.
Helicopters can take off and land almost anywhere, but their complex and relatively clumsy rotor systems
mean they can travel at only a fraction of a plane's speed. If you want the best of both
worlds—high speed and land-anywhere versatility—you need a V/STOL aircraft:
one that's capable of "vertical/short takeoff and landing," such as the famous Harrier
jump jet or the tilt-rotor Osprey. How do they work? Let's take a closer look!
Photo: The Harrier—the most famous V/STOL aircraft of them all.
This one is an AV-8B II, landing vertically on the deck of a relatively small US Marine Corps amphibious assault ship.
Photo by Angel Roman-Otero courtesy of US Navy.
How can planes take off vertically?
Airplanes have to travel at high speeds to produce enough lift for
takeoff, but because they are immensely heavy and often carry
substantial cargoes, they can accelerate only very slowly. A typical
runway for a large airliner such as a Boeing 747 is around 2 miles (3
km) long, simply because the plane has to travel this far before it has
picked up enough speed to get off the ground.
Long runways may be fine for passenger aircraft, but military
fighters need to take off in much more confined spaces (for example,
from the deck of an aircraft carrier). Vertical/Short Takeoff and Landing
(V/STOL) aircraft solve this problem by having jet engines whose nozzles
can be swiveled in different directions. During takeoff and landing,
the jets point straight downward so the plane can rise or fall on the
spot or hover like a helicopter. (Some V/STOL aircraft can even
point their nozzles forward so they can fly backward!)
Once the plane is airborne, the nozzles swivel so they're pointing backward and the plane shoots forward like a conventional
airplane.
Photo: A Harrier can hover because, unlike a traditional jet engine, it has four extra nozzles
on the side that can swivel around to direct the engine's exhaust gases straight downward.
Picture by Staci Bitzer courtesy of US Navy.
The best known plane of this sort is the Harrier "jump-jet"
extensively used by the UK Royal Navy and the US Marine Corps. The
Joint Strike Fighter (JSF) currently being developed by Boeing and
Lockheed for the US military will also be a VTOL aircraft.
The US Airforce Osprey plane works in a similar way, but has tilting
propellers instead of jet engines. To land vertically, like a helicopter, it tilts
the propellers upward. To fly horizontally, it points them forward.
Tilt-rotor aircraft
Photo: The Osprey tilt rotor helicopter being refueled for a night mission in Iraq.
Picture by Joe Kane courtesy of US Navy.
Tilt-rotor aircraft combine the maneuverability of a helicopter with
the speed, range, and economy of a small airplane. Like an airplane,
they have wings and propellers. But the propellers can be rotated to
point upward, enabling the airplane to take off and land vertically in
a confined space. Once the craft is airborne, the propellers can be
turned back so it can fly along like a conventional airplane. Boeing's
Osprey is an example of a tilt-rotor craft like this.
Osprey in action!
Ospreys can have their rotors angled forward to fly like planes, pointed upward to hover like helicopters,
or folded up for easy storage on aircraft carriers:
Photos (left to right) by Andy M. Kin, Oscar Espinoza, and Zachary L. Borden,
all courtesy of US Navy.
