WHAT can be done to increase safety, efficiency and comfort in flight of aircraft now in use? In answer, the author describes several devices designed to bring about this result and supplements this with the results of wind-tunnel research. Detailed descriptions of the particular devices mentioned are not included, the object of this paper being to show the great possibilities of their use and the resulting improvement in performance.Among the possible improvements mentioned are variable-lift units, lift-increasing mechanisms with particular reference to a flap developed by the author, an improved rolling control arrangement, locating the tail surfaces out of the propeller slipstream to increase longitudinal stability, reducing the parasite resistance by special circular cowlings for radial engines and wheel fairings and the elimination of lift struts, better utilization of the available engine horsepower by employing a variable-pitch propeller, means for increasing drag when gliding and braking, protection against fire and better visibility.Information concerning an experimental machine embodying some of the devices that the author has built supplements the discussion of the advantages of the different devices. This brief description is supplemented by performance data.WHAT can be done to increase safety, efficiency and comfort in flight of aircraft now in use? In answer, the author describes several devices designed to bring about this result and supplements this with the results of wind-tunnel research. Detailed descriptions of the particular devices mentioned are not included, the object of this paper being to show the great possibilities of their use and the resulting improvement in performance.Among the possible improvements mentioned are variable-lift units, lift-increasing mechanisms with particular reference to a flap developed by the author, an improved rolling control arrangement, locating the tail surfaces out of the propeller slipstream to increase longitudinal stability, reducing the parasite resistance by special circular cowlings for radial engines and wheel fairings and the elimination of lift struts, better utilization of the available engine horsepower by employing a variable-pitch propeller, means for increasing drag when gliding and braking, protection against fire and better visibility.Information concerning an experimental machine embodying some of the devices that the author has built supplements the discussion of the advantages of the different devices. This brief description is supplemented by performance data.