This arrangement proved to have the effect anticipated and maintained stability easily on a glider much larger than Lillienthal ever managed with his leg-swinging method.
Directional Control.—We have now followed the development by the Wrights of airplane control as regards:
1. Fore and aft or “pitching” motion, accomplished by an elevator operated by lever.
2. Lateral or “rolling” motion accomplished by wing warping operated by a second lever.
These were the only controls used in the earliest gliders. It remains to consider the third element of control, viz:
3. The directional or “yawing” control, which is accomplished by an ordinary vertical rudder operated by a third lever.
The Wrights found the warping had all the effect anticipated but had also certain secondary and undesirable effects. Whenever they applied the warping lever to correct the rolling motion, the glider responded as far as rolling control was concerned, but at the same time would “yaw” or swerve out of its course to right or left. This was a serious complication. For, in the moment of swerving, the high wing which they desired to depress would advance faster than the low wing, and solely by its higher velocity tended to develop a greater lift and thereby neutralize the beneficial effect of the warp. In many of their early glides, because of pronounced swerving, the warp effect was entirely counteracted and failed to bring the glider back to level; with the result that one wing tip would sink, at the same time swinging backward until the machine was brought to the ground. No amount of controlling could prevent this.
After much bewilderment on this point, the Wrights observed that whenever a wing tip was warped to a large angle its resistance became relatively greater and it slowed up while the opposite side went ahead. They at once hit upon the idea of a rudder, previously considered unnecessary, which they believed could be turned in each case of yawing just enough to create a new and apposing yawing force of equal magnitude.
They therefore attached a rudder at the rear, connecting its tiller ropes to lever No. 2, and giving this lever a compound motion so that one hand could operate either warp or rudder control independently (or simultaneously in proper proportion to eliminate the yawing tendency above mentioned). This combination is the basis of the Wright patents and is essential in airplanes of today.
Great success now ensued in their gliding experiments; the machine was always in perfect control; could be manipulated in any desired manner; turned to right or left, or brought down to earth with safety.