Were leading edge ailerons tested?
They were tested in 1935. Since ailerons are thin (thickness-to-chord ratio), they were placed in a leading edge slot, and it was dubbed slot-lip aileron. The study's conclusion is:

The slot-lip ailerons appear to be usable as a form of lateral control device that shows promise of giving improved lateral control and stability at the high angles of attack through the stall, with negligible lag, light control forces, and relatively simple construction. It is desirable that additional tests be made to find the yawing moments given by these ailerons and the effect of the slot on the drag.




The aforementioned additional tests were carried out in 1937; of note:

The more forward the slot-lip is, the higher the lag (control delay after input). It works best when the slot-lip is in the rearmost 20% of the wing.

My understanding of the lag is that it's due to the delay in relieving the low-pressure behind the aileron as it deploys, especially nearer where the lowest pressures exist on the upper surface.

Much higher drag in the order of +10% at high speed and +35% in climb attitudes.


Weick, Fred E., and Joseph A. Shortal. &quot;Development of the NACA Slot-lip Aileron.&quot; (1935). https://ntrs.nasa.gov/citations/19930081340
Shortal, Joseph A. &quot;Wind-Tunnel and Flight Tests of Slot-Lip Ailerons.&quot; (1937). https://ntrs.nasa.gov/citations/19930091678