Why quad-line kites are not flown like dual-line kites

This page opens the progression path of the Cramayailes indoor 4-line school, restored by QuadKites.org. It explains why quad-line flying needs its own movements. The text is Thierry Bressure’s, in the first person, translated from French. The three diagrams are the club’s sketches, cropped to remove empty margins.

Quad-line piloting is fundamentally different from dual-line piloting, because the flight aerodynamics are different.

As a reminder, unlike an airplane wing, whose profile creates a difference in airflow speed that produces a pressure difference and therefore upward lift, a dual-line or quad-line kite wing is flat: made of planes, it does not produce lift from a difference in airflow speed between its two faces. It is the tilt that gives lift. A lot of confusion and nonsense is said about this when comparing a kite’s flight to an airplane’s. I will take the time to explain.

For an airplane, the wind from the airflow must be horizontal (tangent to the wing’s plane) for the wing profile to work. If the airplane is pitched up too much relative to the airflow velocity vector, it stalls: the wing no longer has enough surface for the wind to push the wing and the airplane’s weight upward.

In the figure below, the pressure forces are in green and the resulting lift in red.

A kite wing, on the other hand, is flat, and it is the wind that pushes the wing upward by arriving from below! The kite is very light: where the airplane falls, the kite flies.

But what happens when the kite wing is tangent to the airflow velocity vector? As the wing has no shape (even deltas!), there is no depression, and the kite falls, because it has a weight, however small.

A kite flies and can be controlled by the incidence of the planes that make it up.

Let’s look at dual-line kites, whose shape is chosen at the start by the designer. Before flying, the kiter can change the bridle to change the overall angle of incidence. But once in flight, everything is set: it is impossible to change the overall incidence. At most, you can play on the compensation incidence by pulling more on one side or the other.

A dual-line kite without compensation falls, because the two outer planes cancel each other out and the two inner planes cancel each other out as well. The overall angle of incidence given by the bridle lets the kite move forward.

A Revolution-type quad-line kite goes to the essentials. It is simply a plane whose incidence can be changed in flight. It is even made of two independent half-wings, which allows the kite to rotate on itself! The overall incidence can be set by a bridle, but only for comfort, because the pilot can change it completely in flight!

As an approximation, the revo is made of two planes. Strictly speaking, pressurization gives the central part a curved shape that adds a driving component.

With all this in mind, we understand that quad-line flying is really different from dual-line flying. Learning one is not subordinate to the other: learning to drive a car does not require knowing how to ride a motorcycle, and vice versa.

It follows that a learning path specific to quad-line flying is preferable, to acquire piloting skills as quickly and coherently as possible.

The levels of this path are described on the school’s main page.