Automatic or Coupled Control Surfaces for Aircraft

Citation

Kendrick, James Benjamin (1951) Automatic or Coupled Control Surfaces for Aircraft. Engineer's thesis, California Institute of Technology. doi:10.7907/CN1Q-P992. https://resolver.caltech.edu/CaltechETD:etd-03302009-062149

Abstract

An improved method of aircraft stabilization is described, with wind tunnel test results and stability criteria, and suggestions for use in aircraft design. The method utilizes a new type of control surface consisting of a mechanically coupled fin and rudder, which converts the tail surface into an automatic servo control.

Theory and wind tunnel tests show that the lift curve slope of the tail, [...] may be increased by six times or more in this way, using reasonable but not extraordinary care with manufacturing methods and tolerances.

The dynamic stability criteria are given and compared with wind tunnel tests for nine different balance conditions of two models tested on a swinging arm in the wind tunnel. Four out of the nine cases were stable, and the stability criteria give the correct indication in every case.

Stability analysis is used to indicate the effect of coupled surfaces on the lateral and longitudinal notion of a conventional transport airplane. With the regular control surfaces, this airplane has a spiral divergence, "dutch roll," and a poorly damped long-period longitudinal oscillation. With the coupled tail surfaces, having a very moderate increase in static stability over that of the fixed surfaces, all of the above objectionable characteristics are eliminated, and the resulting airplane modes are shown be either aperiodic or damped periodic motion of a very short period.

The application of such control surfaces to real airplanes appears to be feasible with little change in the design procedure. Several examples are given of coupled tail designs for different kinds of aircraft. The principle is also shown to be applicable to supersonic vehicles. The economic advantages of airplanes equipped with such stabilizers, together with the success of the analysis and test work to date, suggest that this device is worthy of further development and application to aircraft.

Thesis Files