Wind-Tunnel Research Comparing Lateral Control Devices Particularly at High Angles of Attack: XIII-Auxiliary Airfoils Used as External Ailerons

This is the thirteenth report on a series of systematic tests comparing lateral control devices with particular reference to their effectiveness at high angles of attack. The present tests, conducted in the N. A. C. A. 7- by 10-foot wind tunnel, were made to determine the most feasible locations for lateral control surfaces mounted externally to a rectangular Clark Y wing.

Two sets of external ailerons were used. One had an N. A. C. A. 0012 symmetrical profile and a chord length that was 15 percent of the main wing chord. The other set if ailerons, which was used at only a few test positions, had an N. A. C. A. 22 cambered profile and a chord length of 14.5 percent of the main wing chord. Both ailerons extended over the full span of the main wing and were hinged about an axis on their chord line 20 percent from their leading edge. The range of positions investigated was from 27 percent of the main wing chord ahead of the lading edge of the main wing to 10 percent behind the trailing edge and from 40 percent abo e the chord to 20 percent below the chord.

In each position tested full advantage was taken of any improvement in the performance characteristics of the main wing that was possible to be obtained by special use of the ailerons, Thus, at positions close to the leading edge, where the air loads were suitable, the ailerons were mounted so as to act as automatic slats. Likewise, at positions near the trailing edge of ailerons were arranged to function as flaps in addition to being lateral control surfaces.

The results of the wind-tunnel tests showed that no location tested for external ailerons was entirely satisfactory with respect to both performance and control. The best locations tested lay in a region between the leading edge and 30 percent of the chord back from the leading edge, and from 3 to 9 percent above the upper surface. Choice of a particular location depends on a compromise between good performance, obtainable near the leading edge, and good control, obtainable near the rear of the favorable region.

If it is desirable to use the ailerons as flaps in addition to their function as lateral control devices, the best position lies 2 1/2 percent of the chord behind and 2 1/2 percent below the trailing edge of the main wing.

Flight tests made with external ailerons in one of the positions over the forward part of the wing showed serious practical difficulties due to heavy hinge moments and irregular control-force variation.