Trailing‐edge Flaps: A General Review of the Purpose of Flaps and How, and How Far, They Achieve It

THE reader who asks for more wood and less trees in technical discussions of wing flaps has my sympathy, since I have myself been responsible for some denseness of undergrowth. In this article 1 intend to avoid detail somewhat ruthlessly, to stand back and get a long view of the subject, to give, in fact, a freehand sketch rather than a blue print. I shall also try to keep the pilot, where he belongs, in the middle of my sketch. A flap is not something which the research worker can evolve and the engineer fix to an aeroplane without asking the pilot what he thinks about it. It is something which a pilot must now have to enable him to land in comfort, and it is, or it should be, as delicately under his control as elevator or ailerons during this, the most difficult, part of a flight. I must therefore apologise in advance for the liberties 1 shall take with the technicalities of the subject, and also perhaps for keeping the pilot closely at my elbow. Nobody will be able to design a flap from what 1 am going to say ; my object is merely to give a general idea of what flaps are needed for, what they can at present do, and how they can be improved, before the job of designing starts.