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If you like Paul MacCready's story, you might also like:
Ray Kurzweil,
Robert Langer,
Story Musgrave,
Sally Ride,
Alan Shepard,
Donna Shirley
and Chuck Yeager

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Paul MacCready
 
Paul MacCready
Profile of Paul MacCready Biography of Paul MacCready Interview with Paul MacCready Paul MacCready Photo Gallery

Paul MacCready Interview (page: 3 / 5)

Engineer of the Century

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  Paul MacCready

What is the Kremer prize? How was it established.

Paul MacCready: In the history of aviation, I think there was always an interest in human-powered flight. Leonardo da Vinci drew a man flying in machine. You think of a bird and you wonder, "Can man do that?" Then, when the Wright brothers began engine-powered flight, people realized that human-powered flight is really pretty impractical. Humans put out about a third of a horsepower, but engines can put out 10 horsepower, 100 horsepower, 1,000 horsepower. Eventually airplanes achieved all sort of great goals with those engines, so human-powered flight just got forgotten. But as an old goal, it still lingered in people's minds. There were some tiny prizes put up for it in the '30s which weren't won. Then a group in England called the Manpowered Aircraft Group began working on it on a very low level, hobby basis. One of the stalwarts in that group ran a company owned by the British industrialist Henry Kremer. They were having a three-martini lunch, and Kremer asked how it was going. It wasn't going very well. How can you get it moving? Maybe a prize would be a good idea. I'll put up a prize.

Paul MacCready Interview Photo
So this was not just another ordinary challenge. I think it had great value. The significant prize produced our Gossamer Condor, without which there would not have been a Gossamer Albatross, without which there would not have been the Solar Challenger, or the Pterodactyl. Without all of these there wouldn't have been the Sunraycer, the solar-powered car that won the race across Australia in '87. Without that, there would not have been the Impact, a battery-powered car that is now going into mass production. As you look back, you realize that was a pretty important lunch that took place many decades ago.

It's fascinating that the challenge that Kremer thought about, and the prize money that went with it, coincided with your financial need. What was the next step?

Paul MacCready: With my particular skills, strengths, and weaknesses, it was almost as though the Kremer prize was designed for me. There wasn't anybody in the world as well-situated to handle it. I had knowledge of aerodynamics, but no knowledge of structure, so I could deal more flexibly with new methods. Living in southern California with all the aerospace industries around, if you need some tubing, you just go buy it. If you need it chemically milled, you take it somewhere and they chemically mill it. You couldn't do this in some other state, or some other country. And here you can get a good airport, and an empty hangar, if you hunt around for it. The weather is gentle. It seemed like the perfect spot to win that prize.

Chances have combined to create your interest, and the perfect spot, to meet this challenge. Once all of those things were in place, what was the next step?

Paul MacCready: Every time I came up with an idea, it turned out it was it was the same way the teams in England had been doing it -- elegant groups that made sophisticated aircraft and didn't come close to winning the prize. That proved that those approaches were not very good. Plus I couldn't aspire to make such complex, elegant aircraft as they had made.

So I gave up on it, and went off and did other things. This is a fairly acknowledged way of coming up with inventions. You get yourself all full of details, still can't figure out how to overcome the problems, and you give up and then, suddenly, an idea pops into your mind, or a dream, or something else you are doing, shows you a way to handle it that you would never have gotten by sitting in your office and grinding along in a good linear fashion. It requires getting away, looking at it more dispassionately, or not even looking at it.

I was on vacation, and I realized you could figure out the flight speed and the turning radius of birds soaring in circles -- like you see a hawk, or a turkey vulture do -- by noting the time it takes to do a turn and estimating the bank angle. Just a fun little scientific hobby. You can do it with essentially no tools. Just your wrist watch, and estimating the bank angle. From those two numbers you can calculate the flight speed and turning radius. You have to write a formula, and maybe use a little calculator for it.

We began to be more interested in how one bird compares with another, and how does this compare with a hang glider. Did it fly at the same turn radius? What about sail planes? How much power does each take? What about the power per pound?


I was doing the scaling laws for all of these different flight devices, natural and artificial, in my mind. The scaling laws are pretty simple. And while working on that, I thought back about human-powered flight and realized, why yes, there was a very simple, straightforward way of doing it. Which was merely, you can take any airplane, conceptually, keep the size the same -- I mean, keep the weight the same -- but let the size just get bigger and bigger and bigger in all dimensions, and the power goes down and, conceptually, you can make it big enough so it can get by on the tiny power that a person puts out.

[ Key to Success ] Vision


If you take a hang glider with a 30-foot span, keep the weight around 70 pounds, and swell it up to a 90-foot span, the power you need goes down to one third of what it was, about .4 horsepower, which a good athlete, can put out for some number of minutes. So you didn't need an elegant sailplane-like aircraft. You could have an ugly, dirty-looking, hang glider-type plane. Quick to build. As long as you made it giant, without the weight going up.

That was the basic idea. There is one other idea which is essential, which was how do you make something that big without the weight going up? There, the gimmick was that you did not need the structural safety margin that you need in a regular hang glider, which is going to fly at high altitudes, so if it breaks somebody is going to get hurt. This was only going to fly at ten feet altitude at ten miles an hour. If it broke, who cared? Nobody would get hurt. But also, you could have it just on the very edge of breaking. No safety margin at all. Instead of cables, you use thin piano wire as a structural element. With that idea, and the basic idea of large and light, the problem was solved. There would be a bunch of grunt work, engineering, to actually win the prize, but the idea that assured the prize could be won was in my possession.

All you needed was just the minimal amount of structure and energy to accomplish the goal that had been set.

Paul MacCready Interview Photo
Paul MacCready: Yes. It had to be larger and lighter than any plane had been made until then. It ended up with a 96-foot span and 55 pounds, occasionally up to 70 pounds, which is pretty light. Unprecedented in the way people have made airplanes.

You talk about the 96-foot wing span of the Gossamer Condor. How does that compare with the commercial aircraft most people are familiar with?

Paul MacCready: I forget. I think the DC-9 and the 727 are around that wing span. The 747 would have a 150-foot span, I think. So its smaller than a jumbo jet, but its actually larger than some of the smaller transports that you see in the sky. But a lot lighter, and a lot slower, and it doesn't carry many people, and the people it carries have to work pretty hard.

And there is no drink service.

Paul MacCready: Well, on the cross-channel flight, there was drink service. There was a supply of water for the struggling human engine.

When you started building the Gossamer Condor, did it turn out to be a bigger task than you anticipated?

Paul MacCready Interview Photo
Paul MacCready: Every task I get involved in is a lot bigger than I expect. People who work with me double the time estimates, or increase them by a factor of ten. The latter are usually more correct. We were entering such a new realm of flight you couldn't predict what was going on. Looking back, we did it just right, as quickly as we could. After some early tests and models and a bunch of calculations, we built a first version without even putting a propeller on it, just to see if it would fly, and about how much power it took to keep it up. Then we added a propeller and did a lot of tests with it. It was pretty crummy, very crude, bad stability and control and so on. But because we could rush it out and do tests with it, we began getting good insights about all its difficulties.

Wasn't there one problem that you were able to solve by going back to something that the Wright brothers had learned.

Paul MacCready: We went back to what birds have been doing for a hundred million years. Because the flight was so slow, turns were fairly large, I thought you'd have a wing that always had the same shape, and you could gently get around the turn. But we were having huge problems with the turn and with other aspects of stability and control. We finally did some calculations and realized the huge increase of angle, and the tack you get on one wing versus the other wing. In order to maintain lift, you have to change the angle of the wing. You just plain have to twist the wing, and it suddenly began working pretty well. I should have figured that out ahead of time, and incorporated it into the first vehicle, but because I have mental blinders like everybody else, I went off on what I thought was a simpler approach. I tried to do everything on this project as simply as possible, assuming that the simple answer would work. You knew it wouldn't always, but that saves you a lot of time, so when you get to a troublesome thing, you can spend some time with it.

Then, we took a couple of slabs of balsa wood and made a little model in about an hour, and pushed it around in a swimming pool. That gave us some final insights about what our computer programs were trying tell us. The computer programs were correct, but they didn't give us any insight. This swimming pool event gave us the insight to complete all the stability and control problems. We came up with a final version and it worked.

Tell me about the day you had your first successful flight with the Gossamer Condor.

Paul MacCready: We were getting longer flights each day, cleaning it up, tightening the mylar, getting things that don't ripple as much, and getting the pilot more accustomed to it. To win the prize, we had to do a figure-eight flight around pylons half a mile apart. He did a flight that almost completed the one-mile figure-eight. You have to go over a ten-foot marker, at the very beginning and at the very end. We had done a flight of almost eight minutes, but couldn't get over that last hurdle. It was pretty obvious that the next time, if the weather was right, it was going to work. We got a forecast of appropriate weather, and we got the official observer out. It's a two and a half hour drive from here to get to the airport, so we went out the previous night. We got everything together, and the flight succeeded -- just barely.

How did you feel at that moment?

Paul MacCready Interview Photo
Paul MacCready: I was certainly elated, but I knew we were going to win some time. The real elation was when the idea occurred to me about a year earlier. But this was a great sense of relief, because a project like this costs money, it costs time, you have to coordinate people, and there are never enough resources, never enough people, the weather isn't right, et cetera. There was a lot of pressure, and suddenly the pressure is off. So it was a relief and a great celebration, of course. A few days later, everybody got to fly the plane. A bunch of us been test pilots during the development, but now everybody on the project got to fly it. And all their friends and relatives, and little kids and old ladies. You don't need to be a pilot or an athlete to fly it for a short time. It was fun.

So it was like giving pony rides on the Gossamer Condor.

Paul MacCready: Yes. It was very special.

How long was it before you started thinking about the next project?

Paul MacCready Interview Photo
Paul MacCready: This prize of Henry Kremer's that had stood for 18 years no longer existed, so about four months later, he put up a new prize for a flight across the English Channel, which is a 22-mile flight across a dangerous body of water. I think he expected it to take another 18 years for somebody to do that, because it was so much longer than the one-mile flight. But we just cleaned up the Condor, gave it a more accurately contoured wing, many more ribs, and so on. We focused on structure and didn't pay any new attention to aerodynamics, because that had all been solved in the previous one. This new plane, which we would call the Gossamer Albatross, could get by on maybe a third less power. A bicyclist can put out a little less power for a much longer period of time, so Brian Allen, our pilot, could fly this new plane for hours.

Paul MacCready Interview Photo
We were using carbon fiber composite tubes instead of aluminum, lightweight foam ribs, a lot of sort of space age materials to make a better vehicle. It flew right from the beginning, doing just what it should. We had the usual accidents and control problems, but it was obvious this was capable of winning the prize. It was also obvious that this was going to be a big project, to build back-up airplanes, to test them, get them to break in controlled circumstances, rather than out over the channel, and get them all to England, and wait around for weather, and do more tests there, and rent boats and so on. So we sought sponsorship. The DuPont Company whose materials we were using a good bit of, agreed to sponsor it. It was very surprising that they said yes at first, on a very peculiar human-powered airplane project. They said no a couple of times before they finally agreed.

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This page last revised on Jul 16, 2010 16:26 EDT