Lam Aileron: Does It Live Up to the Hype?
We received a press release from Lam Aviation concerning a novel type of aileron, which was said to have brought about remarkable performance gains on a Lancair Columbia testbed. Cruising speed increased by 12 to 16 knots, fuel consumption decreased by 20 to 30 percent, and rate of climb increased by 40 to 50 percent. Useful load rose by 200 pounds. I know that the writer of an advertisement is not under oath, but I wondered how such millennial improvements had been achieved by merely modifying an aileron.
The Lam aileron was developed by Larry Lam, an aerospace engineer who died in 2010. He flew around for years in a two-seat homebuilt with a full-span flap and his novel ailerons. His son Michael is carrying on the idea, with the help of Greg Cole, a respected and innovative sailplane designer and builder.
The Lam aileron is, in effect, a normal aileron split horizontally into upper and lower halves, separately hinged. These can be rigged to behave in various ways — even deflecting simultaneously in opposite directions as speedbrakes — but the most likely arrangement is one in which the upper half deflects upward, like a spoiler, for roll, while the lower half is used like a flap and can actually be part of a continuous full-span flap rather than a separate outboard panel.
In maneuvering flight, such an aileron will likely feel different from a conventional one. For one thing, it should be practically free of adverse yaw, because the parasite drag increment due to aileron deflection is all on the inside of the turn. Control forces may also be lighter, since it is the downgoing aileron that offers more resistance to the pilot, and in this case there is no downgoing aileron.
In normal flight the Lam aileron looks just like any other aileron, however, so it should not affect speed or rate of climb. The large gains reported clearly cannot come from the aileron itself. They come, as it turns out, from the fact that the Columbia with the Lam aileron also has an entirely new wing, designed and built by Greg Cole, with 21 square feet less area and 2 feet more span. The aspect ratio of the new wing is 12; that of the old wing was 9. The reduction in wing area, I assume without an attendant increase in landing speed, is made possible by the fact that the flaps now occupy the full length of the trailing edge.
On a conventional wing, the trailing edge might be 60 percent flap and 40 percent aileron. Because stalling angle of attack diminishes when flaps are deflected, the flapped portion of the wing stalls before the outboard portion reaches its maximum lift, and so some of the lifting potential of the outer panel is lost. Full-span flaps are therefore desirable, but some alternative to conventional ailerons must be found for roll control. Spoilers — spanwise fences emerging from the upper surface of the wing — can be used, but it is often difficult to make them feel right. They tend to have a dead band in the middle, because the first bit of their travel is within the wing’s low-energy boundary layer. The Mitsubishi MU-2 is an example of an airplane that successfully combined full-span flaps with roll-control spoilers, but there are not many others.
Some airplanes, for example the Northrop P-61 Black Widow and early models of the B-52, have supplemented spoilers with small “feeler” ailerons to achieve more pleasant and natural stick forces. A variation consisting of a partial-span flap and ailerons that droop for landing has often been tried as well, despite some degradation of roll performance owing to flow separation on the upper surfaces of the drooped ailerons.