(2) The action of gravitation.
(3) The extra lift given by the wing on the outside of the curve, owing to the fact that it travels faster through the air.
Fig. 17.
The centrifugal force acts strictly in proportion to the mass it acts on, but, at the same time it must be remembered that the greater force acting on the greater mass has the greater mass to move. That is to say, that if the top part of the machine was very light and the bottom part very heavy, the force acting on the light part would be sufficient to send that part swinging out when rounding a curve, and the greater force acting on the greater mass at the bottom would be sufficient to send that out to exactly the same degree. Consequently, if only centrifugal force is considered, the whole machine would swing out without any tilting at all, retaining its upright position. But here we must take another factor into consideration, the resistance of the air. This resistance would be greater on the greater surface of the light top part than on the heavy bottom part, and consequently the bottom part would, automatically, swing out most, giving the banking effect. This would be increased by the extra lift given to the outer wing by reason of its greater speed. If we then take the force of gravitation into the problem we shall see that we have two factors—unequal speed and unequal air resistance—tending to bank up the machine, and one force—gravity—tending to pull it straight again. At a certain angle due to the amount of force exerted by each of these, the two opposing factors would balance, and the machine would be in equilibrium.
It would appear that most of the difficulties connected with the low centre of gravity machine are the result of hazy thinking and slip-shod reasoning, and that they do not exist in fact. And let it be remembered that the low centre of gravity machine with short span has not yet been tried except by the writer, who has succeeded in making a paper model on this plan turn in its own length without in any way losing its stability, swaying, banking too much, turning over, sliding sideways, or doing any of the frightful things which some people declare it must do. What it does do is to recover its balance though started from the most impossible positions and always land on its feet.
CHAPTER IV.
SHORT SPAN AND AREA.
Both on account of speed, and also on account of stability, with a low centre of gravity, we are forced in the direction of the short span machine. How are we to construct a machine with a span short enough to damp out swaying and yet with sufficient lifting surface to raise the machine and its load?