#219 from R&D
Innovator Volume 5, Number 6
I Owed $100,000
MacCready is founder and chairman of AeroVironment, Inc. in
Monrovia, California, providing products, services, and
developments in environment, alternative energy, and efficient
vehicles. In 1956,
Dr. MacCready was international sailplane champion.
In 1980 he was awarded the Ingenieur of the Century Gold
Medal by the American Society of Mechanical Engineers.
In 1982, he received the annual Lindbergh Award for
contributions "to achieving a balance between technology and
the environment", and has been honored by many groups for
pioneering developments of vehicles for land and air.
I had guaranteed
a loan for my friend to start a company, but the company didn't
succeed and now I was stuck with a $100,000 obligation.
While daydreaming, mining the subconscious, on a vacation
trip in 1976, I mused about a possible connection between this
debt and the 1959 Kremer Prize for human-powered flight that I
knew had reached £50,000. When
I noted in a newspaper that £1 was now worth exactly $2, the
light bulb of invention turned on!
The prize equals the debt!
the vacation, I had the motivation and the opportunity to think
seriously about the Kremer Prize.
With my Ph.D. in aeronautics from Caltech, I knew something
about airplane design. However,
all my early design concepts were like those of some British teams
that had logically started with the most efficient airplanes,
sailplanes, and made streamlined versions lighter and larger.
These elegant, complex machines got off the ground on the
initial high power of the pilot, but could not stay aloft long,
could not turn effectively, and took forever to repair after a
crash. I dropped the
subject from its high priority in my thinking.
A week later,
lateral thinking or serendipity unexpectedly intervened.
I had recently written an article comparing hang gliders to
birds, and was in the process of writing an article on the speeds
and lift coefficients of soaring birds.
While driving along I was making observations on the flight
of hawks and vultures. Note
the time to circle 360o,
and estimate the bank angle, and you can quickly calculate flight
speed and turning radius; look up statistics on wing loading
typical of that species, and you can estimate lift-coefficient,
power per pound, etc. Considering
the scaling laws interrelating birds, hang gliders, and
sailplanes, the new simple solutions to human-powered flight
"Aha!" moment. Keep
weight constant and increase size, and power needed goes down.
Triple all dimensions of a 30-foot span hang glider, and
the power for level flight is cut to 1/3 -- from 1.2 horsepower to
0.4 horsepower, now within the capability of a strong cyclist.
Success was assured, if a plane so large and light could be
constructed, even if streamlining were virtually ignored.
building indoor model airplanes in the 1930s and hang gliders in
the 1970s, both using exterior wire bracing, led the way to the
Gossamer Condor wing structure:
exterior wire bracing (0.030-inch piano wire) supporting
thin-wall aluminum tubes loaded in compression.
The giant size,
while allowing for low power, also presented some disadvantages.
The mass of air with which this huge airplane interacted
greatly exceeded the mass of plane and pilot, which can cause
control troubles, especially while turning. Also, because of the speed, vehicle efficiency would be
decreased by turbulence, even turbulence so light it would be
undetectable in an ordinary airplane.
Unexpected advantages from low speed also presented
minimal flight training was needed, flight testing was easy, and
the many accidents we experienced were gentle.
the huge wing size, and put a high priority on light weight.
The project evolved from there, with an attitude of paying
no heed to how airplanes were designed in the past.
A strategy was to design for ease of construction, repair,
and alteration since changes and damage would be common.
The team also had the philosophy of assuming problems will
be solved by the simplest route.
Sometimes this didn't apply, but in most cases it did, and
the time saved then permitted proper priority to be given to the
problems that turned out to be tough.
We used standard bicycle pedals, cranks, and sprockets for
extracting power from the "engine."
Toy wheels were adequate for takeoff, although they often
had to be replaced. The
leading edges of the wing were made from corrugated cardboard.
But we weren't
tied to this simple approach, as sophisticated computer techniques
were used when needed such as for designing the airfoil and
propeller and working on stability and control challenges.
If a part broke during testing, we'd make it stronger. If some parts had never broken, we would replace them with
weaker but lighter ones.
development, we made approximately 400 flights that included four
major, and innumerable minor, crashes.
Each crash was informative, and helped us toward material
design changes. (This
is not the way to develop airliners.)
We focused doggedly on winning the prize, not even making
complete drawings of the plane until after the prize was won.
We kept improving and cleaning up the plane, and on August
23, 1977, Bryan Allen piloted it around the Kremer course we had
set up at Shafter Airport near Bakersfield, California.
Condor is hanging next to the Wright brothers' 1903 Flyer and
Lindbergh's Spirit of St. Louis at the National Air and Space
Museum (one of five pioneering vehicles by AeroVironment acquired
by the Smithsonian). The
participants in this adventure certainly felt the kind of
excitement that the early flight pioneers must have experienced.
I was surprised at the interest of so many other people in
this "impractical" airplane.
Subsequently, as project after project evolved leading
toward more obvious societal value, I have become wiser and so
better appreciate the non-quantifiable value of pioneering.
Henry Kremer then
put up a £100,000 prize for human-powered flight over the English
Channel. We realized
how readily the Gossamer Condor could be improved, and that a
small decrease in required power greatly extends the time a human
can provide the power. We
built the Gossamer Albatross, a next-step clone of the Gossamer
Condor, using carbon fiber tubes instead of aluminum, many more
ribs to improve the accuracy of wing shape, and greater structural
integrity to provide safety for a much more demanding task.
In 1979, Bryan
Allen piloted the Gossamer Albatross across the Channel on a
fantastic flight lasting about three hours, fighting head winds
and turbulence, and somehow coping with only a 2-hour supply of
water. If it had been high tide the flight would have had to be 150
feet longer and would probably not have succeeded.
The engineers, but not Bryan, were delighted with the
design that had not wasted resources on being better than
supported our Gossamer Albatross program, and then agreed to
sponsor our project for solar-powered flight.
Thus our Solar Challenger in 1981 was piloted 163 miles
from Paris to an airfield in England at 11,000 feet, powered only
by sunbeams. The pilot had to weigh less than 125 pounds for the plane to
fly at all -- solar power will not obsolete jet engines.
the flight included getting the public to appreciate that
photovoltaic cells can be a significant part of the world's energy
future, and being asked by General Motors in 1987 to develop the
AV/GM Sunraycer solar-powered car and later the Impact
battery-powered car. Another
consequence has been our 100-foot solar-powered Pathfinder that in
1995 climbed over 50,000 feet.
Now we are working on a more advanced solar craft that will
incorporate an energy storage system to remain at 65,000 feet for
many months, a practical "non-orbiting satellite" for
telecommunications and stratospheric monitoring.
On the lecture
circuit after the Gossamer Condor program, the most-asked question
was why we had won the Kremer prize while other teams with far
more resources and experience had for years been doing excellent
pioneering but had not come close to winning.
I gave this question a lot of thought.
Finally, after I learned more about the mental blinders
that characterize all humans, I realized that my secret weapon was
being totally inexperienced in aircraft-wing structural design,
while at the same time having familiarity with those fragile
indoor model airplanes of my youthful hobby and the newly-evolving
hang gliders. The
other teams certainly were knowledgeable about hang gliders and
indoor models, but they followed their expertise, the techniques
and principles involved in modifying "state-of-the-art"
aircraft, and did not range out to look at the task
many factors helping creativity, such as persistence, a positive
attitude, treating barriers just as things you get around somehow,
creative associates, opportunity, and good luck.
I highly recommend a $100,000 debt to stimulate motivation.