A trailing-edge flap protruding slightly outside the wing profile has been developed as a stall detector and flight trials on “Anson” and “Provost” aircraft have proved successful. The device gave an adequate stall warning for all conditions of power and landing flaps and operated satisfactorily prior to stalls from steep turns. It was easily adjusted to give any desired warning speed to an accuracy of 1 m.p.h. and gave a two-stage warning, a preliminary warning preceding the final warning by about 3 m.p.h. Continues …