Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/216

§ 142 dimensional and three-dimensional motion, the infinite strip, and the plane of compact outline.

Our knowledge of other forms is at present somewhat limited. It may be fairly assumed that, just as the value of the constant is, within the limits of observation, the same for the circular as for the square form, so for an ellipse or other tolerably regular elongate form it will be the same as for a rectangle of like proportions. We will therefore confine our attention in the present section to rectangular planes of different proportions.

We have to rely chiefly on the observations of Dines for data. Fig. 89 gives the value of $$C$$ plotted as a function of the length of the plane in terms of its breadth, the form of the plane being represented graphically by the shaded area. The small circles denote the observation data on which the curve is based. The curve is not carried beyond the ordinate proper to the square plane, as it obviously repeats itself, the corresponding abscissae being in arithmetical and harmonical progression respectively.

For planes of highly irregular form no definite rules can be laid down. An assumption that such planes are built up of simpler components will sometimes enable the value of $$C$$ to be