Let af represent the resultant of the vertical components of the pressure on the wings; the horizontal component will lie in the line ae.
FIG. 4. Diagram showing relation under certain conditions of thrust, C. P. and C. G.
Let the center of gravity be in the line bd, and the resultant thrust of the propellers be represented by cd.
Let W = weight of aerodrome.
Let T = thrust of propellers.
Then if we neglect the horizontal hull resistance, which is small in comparison with the weight, equilibrium obtains when W × ab = T × bd.
Second case. The diagram (Fig. 5) represents the same system of forces as Fig. 4, but in this case the point of support is directly over the center of gravity g, when the axis of the aerodrome is horizontal.
Let W = weight of aerodrome.
Let T = thrust of propellers.