Control by Inherent Stability.
With machines of the inherent stability class the lateral control is effected by additional means, the planes being designed to automatically right the effects of gusts. This element of inherent stability is obtained by suitably grading the camber and incidence of the wings, until at the wing tips the chord of the plane section forms a negative angle to the line of flight. Although this arrangement is undoubtedly of value, especially for the touring machine of moderate power, its chief fault lies in the relatively slow righting movements, which, although of no great consequence at a reasonable altitude, becomes a source of danger when alighting, and certainly entail the use of ailerons, or warp, to counteract it. The type was well exemplified in this country by the Handley-Page monoplane and biplane, while in Germany it achieved great popularity, surviving in some makes until the latter part of 1916. In the matter of control-surface design it is interesting to note the contrast between the preferences of English and German designers. In almost all German machines the ailerons, elevators, and rudder are balanced, i.e. surface is disposed each side of the hinge-axis, this applying to the small Albatross scouts and to the large machines of the Gotha class; while in this country few examples of this practice occur. The reason for the balancing of controls lies in the desire to reduce the manual strain on the pilot to a minimum; and it appears that with large machines balanced surfaces will be imperative. Several automatic controls have been produced, the most notable perhaps being the Sperry gyroscopic, this being a combination of servo-motor and gyroscope. This apparatus has been well tried.
So far as the arrangement of the control surfaces is concerned, little variation occurs, which condition has obtained from the early days of aviation, but the mechanism governing or directing these movements varied at one time considerably, and although in this country one type of control is used, there are still instances of the use of widely different systems. In former days the practice of individual makers fitting different controls resulted in some arrangements being in exact contradistinction to others, which not infrequently meant, to a pilot taking on a new type, the unlearning of a great deal which practice had rendered instinctive.