A new and less complex alternative to the Handley Page slat

Abstract

This paper investigates various devices designed to delay leading-edge stall and illustrates the superiority of the rotating leading-edge flap. The popular Handley Page slat allows the accelerated air coming from below to be ejected at the abrupt change in chord line. This delays the stall separation and improves the CLmax, thus permitting a higher angle of attack. The Kruger flap hangs down to split the air selectively; however, the abrupt change in airflow at the knee prevents the device from achieving as high a stall angle and CLmax as desired. A flexible fiberglass Kruger flap incorporates the geometry of an ever-opening spiral. This flap allows a high lift coefficient at high inflow angles, but it is a complicated device. The ever-opening spiral concept has been employed in the design of a four-bar linkage device that meets the desired requirements of compact storage. Its simplicity has led to time and cost reductions in design, fabrication, and maintenance. In its simplest form, it uses no cove slots or high-pressure air for boundary-layer control; yet these options can be incorporated for STOL applications where a CLmax near 6 is desired. The device may be retrofitted to update existing aircraft or even be juryrigged in a temporary way to permit quick evaluations of potential performance and handling qualities.