The Aeroplane Speaks | Page 9

more later on; but if the side-slip is very bad he may not be able to right the Aeroplane by means of the Ailerons, and then the only thing for him to do is to use the Rudder and to turn the nose of the Aeroplane down and head-on to the direction of motion. The Aeroplane will then be meeting the air in the direction it is designed to do so, and the Surfaces and also the controls (the Rudder, Ailerons, and Elevator) will be working efficiently; but its attitude relative to the earth will probably be more or less upside-down, for the action of turning the Aeroplane's nose down results, as you will see by the illustration B, in the right wing, which is on the outside of the circle. travelling through the air with greater speed than the left-hand wing. More Speed means more Lift, so that results in overturning the Aeroplane still more; but now it is, at any rate, meeting the air as it is designed to meet it, and everything is working properly. It is then only necessary to warp the Elevator, as shown in illustration C, in order to bring the Aeroplane into a proper attitude relative to the earth.''
``Ah!'' said the Rudder, looking wise, ``it's in a case like that when I become the Elevator and the Elevator becomes me.''
``That's absurd nonsense,'' said the Blackboard, ``due to looseness of thought and expression.''
``Well,'' replied the Rudder, ``when 'the Aeroplane is in position A and I am used, then I depress or ELEVATE the nose of the machine; and, if the Elevator is used, then it turns the Aeroplane to right or left, which is normally my function. Surely our roles have changed one with the other, and I'm then the Elevator and the Elevator is me!''
Said Lateral Stability to the Rudder, ``That's altogether the wrong way of looking at it, though I admit''--and this rather sarcastically--``that the way you put it sounds rather fine when you are talking of your experiences in the air to those `interested in aviation' but knowing little about it; but it won't go down here! You are a Controlling Surface designed to turn the Aeroplane about its vertical axis, and the Elevator is a Controlling Surface designed to turn the Aeroplane about its lateral axis. Those are your respective jobs, and you can't possibly change them about. Such talk only leads to confusion, and I hope we shall hear no more of it.''
``Thanks,'' said Efficiency to Lateral Stability. ``And now, please, will you explain your duties?''
``My duty is to keep the Aeroplane horizontal from Wing-tip to Wing-tip. First of all, I sometimes arrange with the Rigger to wash-out, that is decrease, the Angle of Incidence on one side of the Aeroplane, and to effect the reverse condition, if it is not too much trouble, on the other side.''
``But,'' objected Efficiency, ``the Lift varies with the Angle of Incidence, and surely such a condition will result in one side of the Aeroplane lifting more than the other side?'
``That's all right,'' said the Propeller, ``it's meant to off-set the tendency of the Aeroplane to turn over sideways in the opposite direction to which I revolve.''
``That's quite clear, though rather unexpected; but how do you counteract the effect of the gusts when they try to overturn the Aeroplane sideways?'' said she, turning to Lateral Stability again.
``Well,'' he replied, rather miserably, ``I'm not nearly so perfect as the Longitudinal and Directional Stabilities. The Dihedral Angle--that is, the upward inclination of the Surfaces towards their wing-tips--does what it can for me, but, in my opinion, it's a more or less futile effort. The Blackboard will show you the argument.'' And he at once showed them two Surfaces, each set at a Dihedral Angle like this:
``Please imagine,'' said the Blackboard, ``that the top V is the front view of a Surface flying towards you. Now if a gust blows it into the position of the lower V you see that the horizontal equivalent of the Surface on one side becomes larger, and on the other side it becomes smaller. That results in more Lift on the lower side and less on the higher side, and if the V is large enough it should produce such a difference in the Lift of one side to the other as to quickly turn the Aeroplane back to its former and normal position.''
``Yes,'' said the Dihedral Angle, ``that's what would happen if they would only make me large enough; but they won't do it because it would too greatly decrease the horizontal equivalent, and therefore the Lift, and incidentally it would, as Aeroplanes are built to-day, produce an excess of Keel Surface above the turning axis, and that in itself would spoil the Lateral Stability. The Keel Surface should