First some definitions:
Weight Shift Control (WSC): this is the FAA's term for an aircraft with a hang-glider type wing. These aircraft are also commonly called 'trikes', which is short for 'hang glider trike'. Hang gliders are foot launched: your legs are the landing gear. As people added motors to hang gliders, they made three-wheeled carts that the hang glider sits on top of. This enables you to sit and roll rather than stand and run to launch your glider. The name shortened from 'hang glider trike' to 'trike'. The name 'trike' stuck with this type of aircraft even though most aircraft have a three-wheel tricycle undercarriage configuration.
Other terms that also describe WSC are: Rogallo wing, delta-wing, flex wing, and 2-axis control. You may also hear the term 'microlight' and 'ultralight' which I will explain.
Rogallo: Dr. Francis Rogallo, an American aeronautical engineer (27 Jan 1912 to 1 Sept 2009) pioneered the use of folding wings for NASA space capsules and other aircraft using weight shift control. These laid the foundation for modern hang gliders and trike wings.
Delta wing: this term comes from the triangular shape of the wing resembling the Greek uppercase letter delta (Δ).
Flex-wing: As opposed to 'rigid wing' aircraft, trike wings are designed to flex significantly. The flex is an important part of the design that gives it much of its directional and pitch stability, and helps it turn.
2-axis control: In an airplane, you control 3 axes--pitch, roll, and yaw. In a trike, you can only directly control pitch and roll. The design of the wing makes it self-correcting with regard to yaw. This third axis is controlled automatically.
Ultralight is not a particular type of aircraft. The term describes a set of criteria defined by the US Federal Aviation Regulations (254 pounds max weight, one seat, five gallons of fuel, etc.). If a craft meets these definitions, it is considered an ultralight, and is exempt from many pilot and aircraft regulations regarding licensing and registration. There are airplanes, helicopters, gyrocopters, trikes, paragliders, powered parachutes, and hot air balloons that all can be called 'ultralights' because they fit the FAA criteria.
Microlight: outside of the United States, 'microlight' is the more common term roughly analogous to 'ultralight'. Again, 'microlight' is not a particular type of aircraft (there are airplanes, helicopters, gyrocopters, trikes, hot air balloons, etc. that all could fit the microlight criteria). In many countries the criteria is broader than it is in the US, so an aircraft that does not fit the ultralight criteria in the US may fit some other country's 'microlight' criteria.
As an FAA Designated Pilot Examiner (DPE) I conduct check rides and issue pilot certificates (licenses) on behalf of the FAA. Applicants often come to me for a check ride in a Weight Shift Control aircraft without really knowing how one works. Here are some questions to start your study of how it works.
If a conventional airplane needs a tail for stability, what gives a tail-less wing directional stability? Think archery for a moment: What would happen if you took an arrow, without any tail feathers, and shot it from a bow? (It would tumble end over end). What about throwing a tail-less dart? (It would likely tumble before it reached the dart board). A surfboard, water ski or wind surfer needs a fin at the back to keep it going straight too. So how is it possible for a tail-less wing to fly?
This video explains a lot. It is 23 minutes long. This Department of the Air Force film depicting advantages of the Northrop YB-49 flying wing design over conventional aircraft
http://www.youtube.com/watch?v=WPIZMJv09DY
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