Building and Flying an Aeroplane / A practical handbook covering the design, construction, and operation of aeroplanes and gliders

by Charles B. Hayward

Only by constant practice in calm air can the student familiarize himself with exactly the amount of warping and rudder control to employ to property offset the lowering of the inner wing in rounding a turn. If this be not corrected, the whole machine tends to bank excessively and will be apt to slide downward in a diagonal direction, Fig. 44. This is a perilous position for the aviator and must be guarded against by the manipulation of the warping control so as to increase the lift of the inner wing of a biplane, at the same time, employing the rudder to counteract this tendency. The use of the rudder is of even greater importance on the monoplane, as, in this case, warping the inner wing tends to direct the whole machine downward instead of raising the inner wing itself. Several bad accidents have resulted from monoplanes refusing to respond to the warping of the inner wing when making a turn. In such machines, the rudder must be practically always employed in connection with the warping of the wings in order to keep the machine on an even keel, although the controls may not actually be interconnected, this being one of the grounds on which foreign manufacturers are trying to make use of the Wright principle, without infringing the Wright patents, as while they employ warping in connection with the simultaneous use of the rudder, the controls are not attached to the same lever as in the Wright machine.

Fig. 44. An Aeroplane "Banking" as it Rounds a Pylon

Lateral resistance must also be taken into consideration in turning, otherwise the machine, if kept on an even keel, will tend to skid through the air and turn about its center of gravity as a pivot. In the case of an automobile, the resistance to lateral displacement is great, though on a greasy surface it may be small, as when the machine skids sideways, a suitable banking of the road being necessary to prevent this on turns. Many hold that the banking of the aeroplane on turns is only the direct effect of the turning itself, but the fallacy of this will be apparent upon a consideration of the law of centrifugal force. It is obvious that to make a turn, some force must be imparted to the machine to counteract the effect of the centrifugal force upon the machine as a whole. And as the sidewise projection of the machine is small, a compensating force must be introduced. This can be done only by previously banking up the machine on the outer wing, so that the pressure of the air under the main plane can counteract the tendency to lateral displacement. The force then acting under the planes is in a diagonal direction, and the angle at which it is inclined vertically depends upon the banking of the planes, it being normal to their greater dimension. This force can be resolved into two forces, one perpendicular and one horizontal, the magnitude of each being dependent upon the degree of banking. When the speed of the machine is higher, the amount of banking must be greater in order to increase the value of the horizontal component in proportion to the increase of the value of the centrifugal force at the higher speed, in spite of the fact that the forces acting under the planes are also greater due to the higher speed.

As the curve commences, the rudder being put over, the difference of the pressures on the two wings, owing to their different flying speeds comes into account, as already explained, and care must be taken that the banking does not increase abnormally. When the turn is completed, the rudder is straightened and the machine is again brought to an even keel with the aid of the wing-warping control, or the ailerons. The effect of a reverse warping to prevent excessive banking, lowering the inside wing tip incidentally, puts a slight drag on that wing and assists in the action of turning, as does also the provision of small vertical planes between the elevator planes of the original Wright machine. Since the adoption of the headless type, these surfaces are placed between the forward ends of the skids and the braces leading down to them.

In making a turn, say, to the left, the outside or right-hand wing is first raised by lowering the wing tip on that side and the rudder is then put over to the left. When the correct amount of banking is acquired, the wing tip is restored to its normal position, and probably the left wing tip may have to be lowered slightly to increase the lift on that side owing to its reduced speed. When the turn is completed, the rudder is straightened out and the left wing tip lowered to restore the machine to an even keel. Both Glenn Curtiss in this country and R. E. Pelterie in France have shown that it is possible to maneuver without using the rudder at all, the ailerons or wing tips alone being relied upon for this purpose.

Before flights in other than calm air are attempted, much practice is required. The machine must be inspected over and over again, and the wind variations studied with a watchful eye. Not until this familiarity with machine and atmosphere be acquired should flying in a wind be attempted. To the man on the ground, wind is simply air moving horizontally, but to the man in the air it is quite different. Not only must he consider horizontal movement, but vertical draughts and vortices as well. A rising current of air lifts a machine, a downward current depresses it, and he must learn to take advantage of the former as the birds do. Horizontal currents affect forward speed over the ground; swirls and vortices create inequalities in wind pressure on the planes and disturb lateral balance. Familiarity with all these atmospheric conditions can be acquired only after long practice. Against every tree, house, hill, fence, and hedge beats an invisible surf of air; upward currents on one side and downward on the other. The upward draught is not usually dangerous, for it simply lifts the machine; but the down draught will cause it to drop. A swift downward glide under the full power of the motor must then be made, to increase the forward speed and consequently the lift. This explains why it is dangerous to fly near the ground in a wind; likewise why the beginner should never attempt flying at first in anything but a dead calm.

Turning in a Wind. When turning in a wind, two velocities must be borne in mind, that of the machine relative to the air and that relative to the earth. The former is limited at its lower value to that of the flying speed of the machine, and the latter must be considered on account of the momentum of the machine as a whole. Change of momentum is a matter of horse-power and weight and is the governing factor in flying in a wind on a circular course. Suppose the flying speed of a machine is a minimum of 30 miles an hour relative to the air, and a wind of 20 miles an hour is blowing. The actual speed of the machine relative to the earth in flying against the wind will be 10 miles an hour. If it be desired to turn down the wind, the speed of the machine relative to the earth must be increased from 10 miles to 50 miles an hour during the turn and a corresponding change of momentum must be overcome. There are two ways of accomplishing this, either by speeding up the motor to give the maximum power, or by rising just previous to making the turn and then sweeping down as the turn is made, thus utilizing the acceleration due to gravity to assist the motor. The wind's velocity will assist the machine also and during the turn it will make considerable leeway, a small amount of which is deducted to counteract the centrifugal force of the machine.

Turning in a contrary direction, i.e., up into the wind when running with it, requires considerable skill, as when flying 50 miles an hour, the tendency on rounding a corner into a 20-mile-an-hour wind would be for the machine to rise rapidly in the air. The centrifugal force at such a speed is also considerable, causing the machine to make much leeway with the wind during the turn. Turning under such circumstances should be commenced early, particularly if there are any obstructions in the vicinity, and considerable skill should be acquired before an attempt is made to fly in such a wind.

Starting and Landing. A machine should always be started and landed in the teeth of the wind, and no one but the most experienced aviators can afford to disregard this advice, certainly not the novice. The precaution is necessary because in landing the machine should always travel straight ahead without the possibility of lurching and consequently breaking a wing, as frequently happens. Contact with the ground is necessarily made at a time when the machine is traveling over it at a speed of 30 to 40 miles per hour and skidding sideways at 10 to 15 miles per hour, all circumstances which tend to wreck an aeroplane.