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This mathematical operation is simple for all the honours students if the drag coefficient is a constant. The resulting formula for the effective drag of the wires:

D =(Rho/2)tLV^2(Cd/4)

Please note that this is the drag for each wire used. The equation says that the drag on the aircraft is 1/4 the drag the wires would have if the whole length moved as fast as the aircraft.

A great deal can be milked out of the above formula. The author has computed (on a digital computer) what happens when Cd is not a constant, when there is a wind, and so on. Whenever a worthwhile conclusion can be drawn from this advanced work it will be mentioned, but we have all the data required. Most of these effects can be accounted for by using a modified value for Cd but for practical computational purposes, Cd is about 1.0 for round wires As an example, take a set of FAI lines : Nominal dimensions (both wires)

L  = 52.3 feet

t = 0.001 feet (0.012 inches)

Rho  = 0.002378 (for sea level)

V =100 mi/hr = 146.67 feet/sec

D = 0.344 pounds per wire assuming Cd=1

The 25% of the lines closest to the plane accounts for 68%, of this load, which explains why monoline fliers sometimes used thick wire in close to the handle to get more control power, but used the minimum diameter permitted. by the rules out near the airplane.