Page:Aerial Flight - Volume 2 - Aerodonetics - Frederick Lanchester - 1908.djvu/385



Equation (14), where cos θ=1, i.e. for the highest and lowest points of a phugoid, is,

in which C is known and it is required to find the value of H;

or

Let $$\frac{H}{3H_n} = x$$; the equation becomes

which can be solved on a slide rule of the "Gravet;" type as follows:—

Using the ordinary nomenclature for the four scales,

(1) Set the cursor to C on scale D.

(2) Set 3 Hnn on scale B to C2, as indicated on scale A.

(3) Move cursor to 1 on scale B (this divides C2 by 3 Hn).