' 
Long after the Wright brothers' success in 1903, above, human-powered flight remained an aviation frontier. 
model planes and gliders. Skilled as 
a pilot and trained as an aeronautical 
engineer, in 1953 he was the first 
American to become international 
soaring (sailplane) champion. 
In the spring of 1976, Doug La- 
mont, the editor of Soaring magazine, 
had asked MacCready to write an ar- 
ticle on hang gliding. It was a dip- 
lomatic gesture because the directors 
of the Soaring Society of America 
were negative about this new, rene- 
gade sport. Lamont hoped that Mac- 
Cready, as an outstanding member of 
the soaring establishment, could put 
hang gliding in perspective for other 
sailplane pilots. The article appeared 
just as the MacCreadys were starting 
their vacation; one of its most inter- 
esting parts compared the perform- 
ance of hang gliders to that of gliding 
parachutes and soaring birds. 
Soon after the trip began, Mac- 
Cready became fascinated with the 
large soaring birds he could see 
through the van’s windshield and 
would stop to scan the sky with bin- 
oculars. Anyone who has seen the 
curving flight of great hawks and vul- 
tures across the skies of the American 
Southwest can understand Mac- 
Cready’s interest, but his motives were 
not those of the ordinary bird watcher. 
In 1949 he had read Alfred Wood- 
cock’s classic paper on soaring sea 
birds, and that tour de force (in which 
Woodcock confirmed a laboratory dis- 
covery in fluid mechanics simply by 
watching birds) had made a deep and 
lasting impression. On this trip Mac- 
Cready became convinced that he 
could make a similar discovery by ob- 
servation. It might not be like Wood- 
cock’s inductive leap into another field 
of science, but perhaps he could reveal 
something new about the birds them- 
selves. 
Watching circling birds became 
first a diversion, then a compulsion, 
then almost the focus of the trip. By 
the time the family reached Florida, 
MacCready was stopping the van and 
getting out to clock the circles of tur- 
key vultures and frigate birds. He also 
tried to enlist his sons as fellow ob- 
servers. Parker MacCready, who was 
16 that July, remembers his father’s 
obsession vividly: “We thought he was 
nuts. He kept forcing us to watch birds 
and estimate their bank angle, and 
count how long it took for them to 
do a 360 [degree turn].” 
On the west coast of Florida, Mac- 
Cready had more time to observe cir- 
cling birds and to sharpen the equa- 
tions he had been writing in his head. 
He found that just by estimating a 
bird’s angle of bank, he could — with 
his knowledge of flight principles — 
calculate the radius of the bird’s cir- 
cular flight path. By timing the circles, 
he could also calculate both the actual 
flight speed and the somewhat higher 
speed at which the bird would be 
flying if it flew in a straight line using 
the same angle of attack (the angle 
at which the air meets a wing traveling 
through it). 
When equipped with an additional 
piece of information — the bird’s “wing 
loading,” or ratio of weight to wing 
area — MacCready could go on to es- 
timate the “coefficient of lift.” In 
aerodynamics, that is the quantity con- 
venient for judging how efficient an 
object with a given shape is at flying. 
Unexpectedly, the average lift coef- 
ficient MacCready arrived at for soar- 
ing birds was 0.9, a considerably lower 
figure than had been reported earlier. 
When he compared this value to the 
lift coefficients of hang gliders, he 
found them surprisingly close. He de- 
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