Leading edge cuffs are a fixed aerodynamic device employed on fixed-wing aircraft to modify the airfoil used. They may be either factory-installed or, more commonly, an after-market modification.
In most cases a leading edge cuff will "droop" the leading edge of the airfoil. This has the effect of causing the airflow to attach better to the upper surface of the wing at higher angles of attack, thus lowering stall speed. This allows lower approach speeds and shorter landing distances. They may also, depending on cuff location, improve aileron control at low speed. A further benefit is that a cuff may produce a more gradual and gentler stall onset, particularly where the original airfoil had a sharp leading edge shape.
Where a factory modifies an existing design by the addition of a leading edge cuff it is often due to an identified problem or deficiency in the original airfoil used. One example of this is the American Aviation AA-1 Yankee, which was modified with the addition of a leading edge cuff to become the AA-1A Trainer. This was a result of flying schools operating the Yankee demanding a lower approach speed and gentler stall characteristics from the manufacturer.
Several after-market suppliers of STOL kits make use of leading edge cuffs, in some cases in conjunction with such other aerodynamic devices as wing fences and drooping ailerons.
Leading edge cuffs can exert an aerodynamic penalty for the lower stall speed obtained. The amount of the penalty depends on the airfoil design they are installed on and the amount of "droop" that they incorporate. The installation of a leading edge cuff often results in some loss of cruise airspeed. In the case of the modification of the AA-1 Yankee to the AA-1A Trainer the loss of cruise speed amounted to 8 knots or 7%. Better design techniques developed in the 1980s largely mitigated this penalty and leading edge cuffs are used on current high performance light aircraft like the Cirrus SR20 and Lancair Columbia.
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