Page:Aerial Flight - Volume 2 - Aerodonetics - Frederick Lanchester - 1908.djvu/60

§ 19 § 19. Initial Hypothesis. The first hypothetical condition assumed is that the aerodone is only possessed of the three degrees of freedom involved in its longitudinal stability. Thus it is supposed free to move in any direction in a vertical plane containing the line of fight or to rotate about an axis at right angles thereto.

The above condition we may suppose fulfilled either by

FIG. 31.

imagining the aerodone to be constrained in its motion by two parallel vertical guide planes (as suggested in § 7) or we may suppose that lateral stability and constancy of direction are otherwise accounted for, and maintained.

In the second place it will be assumed that the aerodone loses no energy during its flight, either by considering the air as frictionless and the supporting wave as perfectly conserved, or by supposing a force applied in the direction of motion precisely