Soaring birds, such as the red-tailed hawk, above, are less efficiently shaped for flying than once assumed. 
up to 2 horsepower in a brief burst 
and can sustain about 0.25 horsepower 
over an indefinite period of time.) 
Tyler MacCready remembers the 
ride to Williamsburg as “hot and 
buggy.” His father remembers it as 
“pleasant,” even including the inter- 
minable Beatles tapes and Monty Py- 
thon skits. By the end of the day the 
crucial connections had come to- 
gether: MacCready was sure that a 
human-powered airplane could be 
. built by using hang glider technology. 
He didn’t think the visit to Kitty Hawk 
had influenced him. 
If every inventor in history who 
thought of building a human-powered 
airplane had actually built one, we 
would probably have run out of airport 
space long ago. In Paul MacCready’s 
case, the motive for converting his 
private hypothesis into a major project 
was partly financial gain. The £50,000 
($86,000) Kremer Prize was being of- 
fered for the first human-powered 
flight around a figure-eight course 
that met a number of specifications 
concerning altitude, distance, and 
turning. To MacCready, the Kremer 
Competition was a chance to tackle 
a fascinating problem and possibly pay 
off some of his business debts at the 
same time. The combination was 
irresistible. Soon after he arrived 
home in Pasadena, he built what might 
be called a nestling: an eight-foot-span, 
thread-braced balsa wood and tissue 
model of the airplane that would be- 
come the Gossamer Condor. 
To understand MacCready’s con- 
cept, it is necessary to know how a 
hang glider is built. In 1976, the ma- 
jority of hang gliders being flown were 
versions of the triangular, flexible 
wing glider patented by California en- 
gineer Francis M. Rogallo and his 
wife, Gertrude, in 1948. Because of 
the shape of the fabric sail, the visual 
impression of a Rogallo hang glider 
is that of a broad triangular arrowhead 
flying point forward. Only when the 
covering is removed does the funda- 
mental shape of the frame become 
clear. It is really a three-dimensional 
cross, like a child’s jack. 
In a typical Rogallo hang glider, 
the keel tube runs fore and aft, parallel 
to the direction of flight. The crossbar, 
about sixteen feet long, runs horizon- 
tally, at right angles to the keel, and 
the two members are joined where 
they cross. Standing straight up out 
of this central main joint, perpendicu- 
lar to both of the other frame com- 
ponents, is the king post, and directly 
below the main joint is the yoke, or 
control bar, which can be considered 
a divided downward extension of the 
king post. Bracing wires connect the 
tips of these members, and if the wires 
are rigged tightly, a rigid structure 
results. A model of the frame looks 
like a diamond crystal or like two pyr- 
amids joined base to base. 
The two leading-edge spars that 
form the characteristic A-shape of a 
Rogallo wing are superimposed on this 
basic frame. Spanning about twenty- 
four feet, they are joined at the front 
of the keel and fastened to the ends 
of the crossbar, which serves as a 
transverse brace. Stripped of its skin, 
a Rogallo airframe looks more like 
a structural art project than the skel- 
eton of a flying machine. It is un- 
recognizable as a relative of the ele- 
gant and highly developed sailplane. 
In recent years the shapes of hang 
gliders have changed and diversified 
in a search for lower sink rates and 
better control. MacCready predicted 
this evolution in a paper he presented 
to the Soaring Society of America in 
67 
