A rogallo wing is two partial conic surfaces, sharing one side, with both cones pointing forward. Slow rogallo wings have wide, shallow cones. Fast subsonic and supersonic rogallo wings have long, thin, narrow cones.
A rogallo wing is not very efficient, but the design is forgiving, flexible and inexpensive. Variations work at most Reynolds numbers (almost all real fluids, including air, water, hydrogen, and carbon dioxide) from very low subsonic speeds (5kph in air) to very high supersonic speeds (as high as Mach 25 in air). Further, if constructed from heat-resistant materials with an appropriate engine, it can form the wing of a supersonic waverider.
One of the special properties of the rogallo wing is that it can be constructed from a flexible membrane (such as plastic film or sail-cloth), and a simple A-frame. Using plastic-film and struts permits very inexpensive rogallo-wings to serve as kites. Large rogallo wings can be made to fold or roll into compact packages (i.e. car-top carriers for hang-gliders!). Man-rated rogallo wings usually add a vertical posts near the center to anchor guy wires. Guy wires are placed to make the A-frame more rigid, so the cross-bar of the A-frame will not buckle while maneuvering.
The simplest way to steer and control a rogallo wing is to change its pitch and roll.
Most man-rated rogallo wings change the pitch and roll by suspending the payload or engine on a pendulum beneath the wing, and then moving the pendulum to change the vehicle's center of gravity. On hang-gliders, this is traditionally done by rigidly mounting a guyed trapeze-like triangular bar under the wing, and suspending the pilot prone in a harness within the triangle. The pilot holds and moves the trapeze with his hands.
Kite-like rogallo wings control the pitch with a bridle that sets the wing's angle of attack. A bridle made of string is usually a loop reaching from the front to the end of the center strut of the A-frame. The user ties knots (usually a lark's head) in the bridle to set the angle of attack. Mass-produced rogallo kites use a bridle that's a triangle of plastic film, with one edge heat-sealed to the central strut.
Steerable rogallo kites usually have a pair of bridles setting a fixed pitch, and use two strings, one on each side of the kite, to change the roll.
See also wing and kite flying