Technicalities: Clipped Wings

On aging and planforms.

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Ray Henning and his Thorp T-18

I met Ray Henning when I was building my first airplane, around 1969 or 1970. I would frequently go to breakfast at a coffee shop called Mr. C's — long extinct — with the late John Thorp and whichever of his cronies happened to be around when that time of the morning came. Mr. C's was pretty far from my house, but Thorp was a good friend, he let me use his brake and shear to cut and bend sheet metal, he was generous with advice, and I liked Mr. C's bear claws.

Thorp's shop was in a Los Angeles suburb called Sun Valley. He had a single employee, a metal man named Vaughn Parker. Parker was a lean, taciturn fellow; he always struck me as being a Midwestern farmer type, though, never having been on any Midwestern farms, I actually don't know whether there even is such a type. Thorp's T-18 homebuilt had been introduced a few years earlier, and builders would come to the shop to use his tooling for wing ribs and fuselage frames and to take advantage of Parker's skill and experience.

Ray was one of them. He had bought the T-18 plans — set No.149 — in 1964, when he was fresh out of graduate school at the University of Arizona with a master's degree in agronomy. They cost $125. He knew nothing about aircraft sheet-metal work — in those days you bought plans and the rest was pretty much up to you because the era of prefabricated plastic kits fleeing from the incomprehensible 51 percent rule was still in the distant future — and spent several years building the fuselage, wings and empennage with Vaughn Parker's help. The FAA signed off the airframe in 1970. By then, Ray's employer, Chevron Agricultural Chemicals, had moved him to Fresno, California. The T-18 had been crated up and moved at Chevron's expense; and it would move again, and again, and again, as Ray transferred first to Iowa, then to Billings, Montana, then back to Fresno, and then, after he retired, to Bozeman, Montana. Work and a family eclipsed the T-18 project. In Iowa, he helped his son Carl build two soapbox racers. In Billings, he devoted his leisure time to fly-fishing and skiing and for some time operated a Taylorcraft dealership. The T-18 remained a bare airframe — as homebuilders invariably say, 90 percent finished, 90 percent to go.

Ray and I were sporadically in touch during all those years. He would appear in Los Angeles and bring crates of oranges or walnuts — controls from agronomic experiments — by my workshop, or we would fly somewhere in my first plane, which I had finished building in 1973. Then, in 2001, Ray turned up in a hangar one row away from mine. The T-18, now 37 years old if you count from the purchase of the plans, came out of its crates. At last, it was in the homestretch.

I was still working on my second Melmoth then, and I felt pretty certain that Ray would get finished before me. After all, he had a virtually complete airframe and the T-18's systems and wiring are quite simple. But I underestimated both Ray's patience and his perfectionism. Unlike me, who wanted above all to get into the air and figured the airplane could be finished later, Ray wanted everything finished before he flew, and finished beautifully. Like many T-18 owners who were old-schooled by Thorp and Parker, he wanted his airplane to be entirely aluminum — no gimcrack fiberglass cowlings, fairings or wingtips — and he became quite skilled at coaxing compound-curved parts out of the reluctant metal, which, compared with supinely passive composites, resembles a rebellious child. Once in a while he would take a few days off to polish away the dull film that Los Angeles, or the nearby Pacific Ocean, spread over the airplane's pristine skins.

Ray worked, as it turned out, seven more years before finally flying his T-18 early in 2008. Mike Melvill, now retired as chief test pilot and astronaut at Burt Rutan's Scaled Composites, made the first flight and then checked Ray out. They both took part in flying off the 25-hour restriction for amateur-built airplanes. That was a great time; after 44 years, N149RH was in the air, cruising — it has a 180 hp Lycoming and a fixed-pitch wood prop — at better than 170 knots and climbing 2,000 fpm. Blindingly unpainted under the California sun, it weighed 936 pounds — almost precisely the same as the T-18 of Thorp himself, who was notoriously parsimonious with ounces and used to remark that the way to build an airplane was to put in "just enough material to keep the rain out" and then to keep loading it up and reinforcing it where it broke until it didn't break anymore.

Ray, who had turned 73, had been planning to move, maybe back to Bozeman, maybe to Carson City, when the plane was done. He was looking forward to some happy years of flying to the next airport for breakfast. But Fate is impatient with happy endings. Ray's eyes had been troubling him for a while, and now it became apparent that he was suffering from macular degeneration, which brings about a loss of sharply focused central vision. The synchronicity of completing the airplane and becoming unable to use it could not have been more perfect, nor sadder. No sooner did Ray start flying the airplane than he had to give up flying.

I notice, on my days hanging around the airport, that a lot of the people there are fairly old. I guess you have to be past retirement to be hanging around the airport on weekdays — but these days, maybe not. Anyway, I always feel terrible for these guys when there's a mishap, something gets dinged or groundlooped, or it becomes difficult for them to get a medical. For all of us out there, flying has been the object of a lifelong affection, and I wish that we and our airplanes could just stroll peacefully into the sunset without any nasty surprises like losing a medical just as we gain a long-awaited airplane.

Ray moved to Seattle. His beautiful T-18 is still down here in Southern California, in a hangar at Tehachapi where the air does not dull the aluminum. He plans to sell it. But he keeps putting off doing it. I understand why. After it traveled with him through most of his adult life, giving up that airplane is going to be like losing an old friend.

Cranks
Much is made of wing planforms — that is, the shape of the wing as viewed from above — but there seems to be little agreement, even among birds, about what sort of planform is best. Elliptical wings, like those of the Spitfire, are always claimed to yield the minimum of lift-related induced drag, though airliners, which are designed for efficiency and for which almost half of their cruising drag is induced, don't have them.

I suspect that the reason for the lack of unanimity about planforms is that most airplanes cruise at speeds at which induced drag is a fairly minor component — the "parasite" resistance, consisting largely of skin friction, predominates — and so comparatively subtle influences on induced drag just don't count for much. Instead, practical considerations determine the shapes of wings.

One of the main categories of practical consideration is structure. The bending stresses in wings are greatest at their roots, so there is a good argument for increasing the chord near the root. Increased chord means increased thickness, which in turn makes the spars stiffer and lighter for a given strength. For swept wings, however, there is another reason to increase the chord near the fuselage. The root of a swept wing is farther forward, with respect to the center of gravity, than that of a straight wing, but the main landing gear has to be placed behind the center of gravity. The solution is a "cranked" wing, with a big kink in the trailing edge, which runs straight across, without sweep, from a point somewhere out along the span. That chord extension permits a strong spar to be placed quite far aft in the wing, and the landing gear is mounted on that spar.

Cherokees, Mooneys, Comanches and their ilk have an extended leading edge, a sort of wedge added to the front of the wing for the inboard two or three feet. A case can be made for a possible reduction in interference drag due to making the root airfoil section thinner, but the real reasons for these extensions are, again, practical ones. They put the front and rear wing-fuselage attachments farther apart, they align the front one with the doorframe, and — does it get any more mundane than this? — they allow the wingwalk to extend up to the front edge of the door.

And you thought it was all about aerodynamics!