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Subject: Macrodactyl Part 3: Designing a macrodactyl


Author:
Wes Boyd
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Date Posted: 10:19:32 05/20/16 Fri

In thinking about the dream that started this line of thought, I realize now that I was reaching for the idea of a dragon. The traditional dragon flew, of course; we all have a mental image of one. In reality, the larger pterosaurs came about as close to the reality of a dragon as anything in the history of the earth.

Now, when I think about dragons and fiction, Anne McCaffrey's "Pern" books come quickly to mind -- people riding around on dragon-back. That's pretty fanciful, of course, but let's face it, we're dealing with fantasy anyway. But then when I ran across the Quetzalcoatlus northropi and Paul Macready's work on building a working half-size model, I got thinking real hard about the question of whether a human could have actually ridden a northropi, ignoring the 65 million year age problem.

Now, I'm not any kind of aeronautical engineer, but I've been exposed to the concepts a little from when I was a pilot long ago. I certainly do not have the knowledge or the intuition of Paul Macready. So, most of the aeronautics discussed here are taken from his article, "The Great Pterodactyl Project." I am not sure where this article was published, but it's taken from the Caltech online library.

When Macready and his research group analyzed what relatively small amount is actually known about the northropi, they came up with some baseline figures including a span of 36 feet, a weight of around 140 pounds, and an aspect ratio (wingspan versus width) of 8. For the sake of ease of construction the working model they built was about half that size, with an 18-foot wingspan, with the idea that it represented a miniature or immature version of the reptile.

With that great a wing span and aspect ratio, a northropi had to have had some of the characteristics of a sailplane, which is to say it can fly all day if it can find air going up. For our purposes, load carrying capacity involves being able to take off and climb, not just jump off a cliff. The ability to get off the ground and power up to soaring levels is what determines payload. Let's arbitrarily say that the lizard had to have sufficient structural integrity to accomplish that with a large enough prey to make it worth the effort.

How much could a pterosaur really haul besides its own weight? For that we have to turn to birds. An eagle weighing 10 to 14 pounds can pick up a small animal or fish weighing in the range of five to six pounds, so for the sake of discussion, let's say 40 to 50 percent of body weight. Recently there was a photo of a European Green Woodpecker with a Least Weasel riding on its back. It is a pretty awesome photo, and probably not faked for a number of reasons I won't get into here. There's no way of telling without examining the actual animals, but a typical weasel of that species weighs around two to three ounces, while the average weight of the woodpecker is in the six to eight ounce range. That isn't real helpful, but puts the payload capability of the woodpecker in the 25 to 50 percent range of its body weight. However, one of the series of photos seems to indicate the bird flying at a high pitch attitude, so it had to have had the power to climb well with the extra weight.

So, let's assume that the typical pterosaur had a possible payload of a third to a half of its body weight. For a 140-pound northropi, that means it would have had a maximum payload somewhere around 40 to 70 pounds. It might easily have been more, since payload percentage increases with size, but that will work as a baseline figure and stay within the envelope. At the upper end of its range, then, it could carry a very small human being such as a child, a pygmy, or a dwarf. Since it probably would fly at 25 to 40 miles per hour, the pilot is not going to be in bare skin -- so much for the bikini-clad temptresses of some science fiction covers, for they would be too cold and windblown. Hitting an insect could be painful. That means there would also have to be the weight of clothing added -- the pilot would wind up being dressed something like a World War I fighter pilot.

Really, we need something bigger to be useful. The northropi is the largest known pterosaur, but who is to say that the fossils of an even larger one might not be found someday? Being a little arbitrary, let's make it half again bigger. We are now talking about a wingspan of 54 feet, an empty weight of 210 pounds, and a payload of 70 to 105 pounds and perhaps more as payload increases with size, up to a point. In fact, let's fudge several areas and make the maximum payload around 125 pounds, which not abnormally small for an adult human. We'll call the result a macrodactyl. I have flown sailplanes of this size (although heavier) and they fly very nicely -- but they did not have the power to get off the ground or gain altitude under their own power. The northropi probably could do this if Macready was right, and that means the macrodactyl could do it, too.

Guidance and control are an issue. Let's say that the macrodactyl is no more intelligent than a horse but just about as trainable. Unlike the "Pern" stories where the rider controlled the dragon by thought, reins might be needed to guide the macrodactyl. That would be interesting, for a horse only has to understand left and right (well, all right, gee and haw) while the Macrodactyl also has to be guided for up and down, as well. But, it ought to be do-able.

Without getting into the details, a macrodactyl is at least theoretically possible on paper. It sure would be fun to fly on one's back -- but there's that little problem of 65 million years. That's what the next article in this series is all about.

-- Wes

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