Investigation of Full-Scale Split Trailing-Edge Wing Flaps With Various Chords and Hinge Locations

An investigation was conducted in the N. A. C. A. full-scale wind tunnel on a small parasol monoplane equipped with three different split trailing-edge wing flaps. The object of the investigation was to determine and correlate data on the characteristics of the airplane and flaps as affected by variation in flap chord, flap deflection, and flap location along the wing chord. The chords of the flaps were 10, 20, and 30 percent of the wing chord and each flap was tested at deflections from 0° to 75° when located successively at 68, 80, and 88.8 percent of the wing chord aft of the leading edge. The investigation included force tests, pressure-distribution tests, and downwash surveys. The results give the lift, the drag, and the pitching-moment characteristics of the airplane, the flap forces and moments, the pressure distribution over the flaps and wing at one section, and the downwash characteristics of the flap and wing combinations.

An increase in flap chord or distance of the flap from the leading edge of the wing increased the lift of the airplane but had an adverse effect on the wing pitching moment. The L/D ratio of the airplane decreased with increase in flap deflection or flap chord. Flap normal-force coefficients were primarily a function of flap deflection and were relatively independent of flap chord, hinge-axis location, and airplane attitude. The location of the flap center of pressure in percentage of flap chord aft of he hinge axis remained practically constant irrespective of airplane attitude and of flap deflection, chord, or location. Flap hinge-moment coefficients varied with a power of flap chord greater than the square so that with regard to hinge moments narrow flaps were the most efficient in producing a given increase in lift.

Split trailing-edge flaps materially affected the magnitude and distribution of pressures over the entire wing profile. At low angles of attack the predominant effect of the flaps was to increase positively the lower-surface pressures; at high angles of attack, to increase negatively the upper-surface pressures. Downwash surveys indicated that horizontal tail planes located above the wing chord line would be more effective than those below the chord in counteracting the increased diving moment of the airplane with flaps deflected.