If a following wing is the size of the leader, assume that its efficiency is 66 per cent per unit of surface.
If it is half the size of the leader, assume that its efficiency is 50 per cent per unit of surface.
If it is half as large again as the leader, assume that its efficiency is 80 per cent per unit of surface.
For intermediate sizes of surface, proportionate values per unit of surface may be assumed.
If we consider the area of the front wing to be unity, and that of the rear wing to be n, and if m be the efficiency of the rear wing per unit of surface, [p088] the above is expressed in the following formulæ, which it will be remembered take account only of wings following each other in the same or nearly the same plane, and are not applicable where one wing is either above or below the plane of the other. In the formulæ, CP is the resultant center of pressure upon both wings expressed in the notation described in Chapter II [◊], CPfw is the center of pressure of the front wings, and CPrw the center of pressure of the rear wings.
If the value of n lie between one-half and unity,
m = n + 13;
while if the value of n lie between unity and 112,
m = 6 + 4n15.
In either case