Cleaning up Melmoth


I have been flying my homebuilt for more than four years now, and have been recording performance points on almost every flight while looking for ways to reduce drag. The homebuilding community is full of stories about huge successes in drag reduction, but I think those guys must be starting with Wilgas. It turns out that if you begin with a fairly clean airplane, it's not that easy to find ways to make it cleaner.

Mine is a somewhat old-fashioned looking airplane, seating four under a bubble canopy - I like the all-around view - like a Navion or a Meyers. If I wanted to be stylish and up to date, I missed the boat. Though it is built of composites, Melmoth 2 does not have the sweeping curves, artfully blended intersections and gracefully cusped afterbody of a Columbia or a Cirrus. It has a 200 hp engine - a Continental TSIO-360 - which seems pathetically weak compared with the 300-plus horsepower of today's high-performance cruisers.

Drag is conveniently expressed by a number called F, the so-called "equivalent flat plate area." If the name 'F' is cryptic, the explanation is more so, because the equivalent flat plate area of a flat plate is actually quite a bit larger than the plate itself. Anyway, the first Melmoth, an all-metal two-seater which I built between 1968 and 1973, and which traveled to Europe and Japan before being demolished on the ground by a landing Cessna in 1982, had an F of about 2.6 square feet. While I was building Melmoth 2 I estimated that it would come out about the same, because although it was a cleaner airplane in many respects, it was also larger.

It did indeed come out the same, but that was with various fairings missing and without nosewheel doors. I added the fairings and observed only a slight improvement in performance; F dropped from 2.6 square feet to 2.55 - barely a measurable change. As far as the nosewheel well was concerned, I had pretty much persuaded myself, with the help of Hoerner's Fluid Dynamic Drag, that since the well was airtight the air would just flow past it, not into it, and so it would generate little drag. Finally, early last year, I got around to closing it, and was unexpectedly rewarded with a reduction of F to around 2.3 square feet (assuming .84 prop efficiency and .44 specific fuel consumption), which gives 175 knots for a fuel flow of 8.7 gph at 12,000 feet. So much for pessimism.

The speed and economy now are not bad for a roomy - 48-inch inside width - four-seat airplane, but I doubt I will be able to do much to improve them still further. I now need to turn my attention to the low-speed end. After all this time I have still not installed the actuation system for the flaps. Flaps are not really needed when you're just hopping from one 4,000-foot paved runway to another, but after going to all the trouble to build them, I can hardly leave them unused.

One thing I will never be able to improve upon is the awful accessibility, or inaccessibility, of the aft-facing rear seats. They're roomy and comfortable enough once you're in them, but a certain athleticism and a willingness to look foolish are required to reach them. Luckily for me, I always sit in front.

What Comes NextWhen I was talking with Aerion Corporation's Chief Technology Officer Richard Tracy about the proposed Aerion supersonic business jet (Flying, March), I asked him whether the company's plans took into account socioeconomic factors, in particular the growing public awareness of, and irritation with, the astronomical pay levels of corporate executives and, more generally, the growing disparities of wealth and opportunity between the rich and poor in America and, to an even greater degree, in the entire world. Companies already avoid conspicuously displaying their logos on their jets because of stockholder suspicions about how they are used and whether their use really always redounds to the benefit of the company. How much more resistance might there be to airplanes twice as large and costly? Is there a tipping point? When does a corporate airplane become an object not of admiration and respect, but of resentment and derision?

Tracy said, in so many words, that they had not speculated about that issue, and that he tended to view it as a matter of degree rather than of kind. Small numbers of people once traveled laboriously by covered wagon; now great numbers travel effortlessly, at immense speed and often for very trivial reasons, by jet. A supersonic jet is just another point on a continuum, not nearly as far removed from the subsonic jet as the subsonic jet is from the wagon. Still, the continuum of modes of travel is not unbounded, nor is it linear. We are already close to one of its boundaries, namely, certain physical limits on the practical speed of atmospheric travel. Even if supersonic flight were no more costly than subsonic - the proposers of supersonic civil aircraft claim that it will not be - there are certain difficult obstacles, like airframe heating, which starts to be a problem around Mach 2, and the persistence of pollutants dispersed extremely high in the atmosphere, that must be weighed against the expected benefits. We are already going pretty fast, and the faster we go, the less time we save by going still faster. No matter how you value time, and no matter how much of a boost its value receives from the egos of the people who feel the strongest imperative to save it, there is certain to be a point at which the technical, environmental and economic impediments to greater speed outweigh the gain of an hour, or 30 minutes or 10 seconds.

It is a peculiarity of the speed increase from subsonic to supersonic that it cannot be made in small increments. Supersonic flight requires a different sort of airplane, one which is less well suited for subsonic operations, including landing. Besides, the drag hump around Mach 1 obliges airplanes to fly either below Mach 1 or at Mach 1.3 or above - there is a sort of no-plane's-land in between.

The significance of distance, the product of speed and time, is scaled by the size of the planet. If the earth were as large as Jupiter (for the sake of argument, let's ignore the gravitational implications), and it took several days to get from one place to another even on a subsonic jet, the value of raising speed from 450 to 900 knots would be greater than on this relatively compact planet. And time itself is not a fixed measure. How much does an hour or two matter? We pay to go to movies, where we sit for two or three hours and go nowhere at all. People spend whole days on beaches doing nothing. Why is it so necessary to reduce the length of an air trip by an hour or two, or even to cut a 12-hour trip in half?

It's true that an economy-class flight across the United States or to Europe or Asia now taxes human endurance, but that is because there are too many people in airliners. A case could be made that it would be cheaper, and certainly technologically simpler, to make current airliners more comfortable, so that you would be happy to spend more time in them, than to make them faster so that you would not have to. But the supersonic business jet argument seems to say the opposite. The cabins of business jets are full of amenities; one could hardly be better cared for; and yet the people who have them want to spend less time in them rather than more.

I once read a surprising statistic about the Vietnam War. Although most of the fighters of the period were capable of supersonic flight, and the ability to fly 1,000 mph - or whatever - was a bragging point that probably had some influence on the Pentagon acquisitions, only a few minutes of supersonic flight had actually taken place during the entire war. The supersonic capability turned out to have very little practical importance. There may be a lesson there - but maybe not.

Thinking about speed, distance and the future brings to mind some longer-range questions that affect all airplanes, not just a few at the extreme limits of performance and cost. There has been discussion for the past decade or two, on and off, of the probability that sooner or later oil companies would cease to refine avgas. The effort that has been expended upon the development of "omnivorous" engines, mogas STCs, aviation diesels and so on, would not have been if 100LL had an unlimited future. (Avgas, by the way, though it contains only half as much as the old 100/130, deposits 1.3 million pounds, or 64 cubic yards, of metallic lead, a brain-damaging toxin, in the atmosphere each year, in case you wondered why you've been feeling dumber lately.)

Mogas (that is, automobile gasoline), diesel and jet fuel represent three possible alternatives to avgas, requiring, in that order, increasingly difficult technological transitions. But all are fossil fuels, which, whatever your view of world oil reserves, will sooner or later run out and, long before they run out, will grow increasingly prohibitive in cost. Pilots who are young today may see in their lifetimes an even more difficult transition, one away from fossil fuels and to some other method of propelling aircraft - assuming that there are any aircraft left to propel.

A few years ago, at a colloquium on the future of air transportation, the advocates of larger airplanes were arguing with the advocates of faster ones and smaller ones when Burt Rutan offered a characteristically antinomian view. In 50 years air transportation would not be needed at all, he said, because advances in virtual reality, pioneered by the online pornography industry, would render travel unnecessary. The face-to-face meeting and the handshakes that are said to be the raisons d'être of business travel will be delivered, with perfect conviction, by HD goggles and animatronic gloves. You won't need to leave your office, or even your armchair. In fact, the boredom and alienation will be so intense that people will pay to spend 32 hours crossing a virtual country in a nonexistent Ford Trimotor.