This is a copy of the main part of an article I wrote for the Aeromodeller Annual 1971-1972. It may be of interest to F2A fliers and others interested in control line today.

FLIGHT MECHANICS OF CONtrOL LINE WIRES

by P. Soule (U.S.A.)

A number of investigations carried out by the author from 1964 onwards have looked at the forces on control line wires and what they do to the airplane. Although many factors have been subjected to analysis, this article only reports on the major ones in an attempt to make a plain statement about the principal effect of tether wires on models and the major factors influencing these effects.

If you are wondering why you should know something about wire aerodynamics, consider that the wires take 30% (sport models) to 80% (speed models) of the engine horsepower. It seems reasonable that the control line modeller ought to be as familiar with the wires as, say, with the propeller.

Imagine for the sake of simplicity you are flying from an FAI speed pylon on a windless day. Your plane has attained a constant speed. The wire at the wingtip is going as fast as the airplane, the wire at the handle is not moving at all and in between the "airspeed" of the wire (or wires) varies in proportion to the distance from the handle. Most of you have heard that drag goes up with the square of the speed. For example, a doubling of speed makes the drag go up by a factor of four. As one man wrote, "this is because twice as many molecules hit the vehicle and they hit it twice as hard." A statement which may make aerodynamicists wince but it nevertheless has a grain of truth in it.

Ugo Rossi with his winning model, the "Devil" at the 1959 Criterium of Europe in Brussels. The Super Tigre G20V turned a 6 x 8 in. prop. at 17,000 r.p.m. In 1960 Ugo used the same design (with 2-line control) to win the World Championships with a hotly disputed flight during which he whipped the model constantly. F.A.I. antiwhipping rules came in from 1961 ! Subsequently the Rossi Brothers have made their own range of engines.