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.
During World War II several systems akin to the Lam were studied at NACA Langley. In one of them, a Fowler flap traveled aft until its leading edge was below the trailing edge of the aileron, which now supplied roll control in the same way that the movable “direct lift control” slot lips on many airliners and fighters do. In another, the deployed Fowler flap ended up directly under the aileron. The main difference between these proposals and the Lam one is that in them the retracted flap was stowed ahead of the aileron, whereas in the Lam system it nests beneath it.
The main reason full-span flaps are seldom used in production airplanes is that they are not quite as effective as they look. Lift diminishes toward the wingtip, more so on tapered wings. A moderately tapered wing would be hard pressed to gain as much as 25 percent in lifting capability from a 67 percent increase in flap span — that is, from changing a flap occupying 60 percent of the trailing edge to a full-span one. Lam claims only a 16 percent gain in maximum lift coefficient — which means a reduction of only 4 knots at typical landing speeds.
The Lam website provides some performance points for the stock and the modified Columbia. These were measured at 19,000-foot density altitude, where the benefit of increased wingspan is greatest. The airplane has a 300 hp naturally aspirated engine. With a manifold pressure of 15.3 in. Hg, the stock configuration yielded, for example, an indicated airspeed of 120 knots — 161 ktas — at 2,400 rpm and 11 gph, whereas the modified airplane managed 134 kias (179 ktas) at the same power setting. Making the usual assumptions about induced drag, propeller and span efficiencies, and specific fuel consumption, these numbers imply equivalent drag areas of around 3.6 square feet for the stock airplane and 2.8 square feet for the re-winged one.
Since the original clean, composite laminar-profile wing should contribute no more than about 0.6 square foot of drag area, I am at a loss to see where a reduction in drag area of 0.8 square foot can be coming from.
The reported improvement in rate of climb puzzles me as well. The website has the stock airplane climbing at 640 fpm at 8,000 feet, the modified airplane at 860. Supposing that both were tested at 3,400 pounds, that gain of 220 fpm means that almost 27 horsepower was liberated by reducing the wing area. The induced drag of the longer wing is naturally a bit less, but I still find the improvement unexpectedly large.
To be sure, I would not find either the stock numbers or the modified ones incredible if I saw them alone. Neither 3.6 nor 2.8 square feet is an impossible drag area for a 300 hp four-seater. It’s seeing them side by side that makes me scratch my head.
Setting aside the performance claims, however, if the roll effectiveness of the Lam aileron is as claimed I think it’s a promising concept. I wish I had tried it on my own homebuilt, which is a 200 hp retractable-gear four-seater. I could not reduce my wing area, now 105 square feet, without sacrificing the fuel volume for 3,000-mile range, but a computer simulation suggests that a 23 percent gain in maximum lift coefficient might be had by extending the flap to full span. That would reduce the stalling speed by 10 percent and the landing distance by 19 percent — a worthwhile change, even though cruising speed and rate of climb would not be affected.
It has never been a secret that, all other things being equal, an airplane with a smaller wing will go faster than one with a larger wing, or that an airplane with a longer wingspan will climb better and be more at home at high altitude. A reader of the recent Lam Aviation press release or website could be forgiven for taking away the impression that the performance gains being claimed were due solely to the ailerons themselves. The fact that they were recorded on an airplane with an entirely different wing — and, for all I know, other differences — is not emphasized. Like Cheerios, which, as the box says, can help prevent heart disease and lower cholesterol as part of a low-fat diet, Lam ailerons can help improve performance as part of a redesign of an airplane. They are a valuable part — but still only a part.
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