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ENGINEERING: E. B. WILSON 
values 0.2, 1.0, 5.0 were successively assigned to r to correspond to mild, 
moderate, and sharp gusts. 
The Uncontrolled Machine. — The result for a head-gust is that, during 
15 to 18 seconds after striking the gust, the machine soars aloft to a 
height from 4/ to 4J/ above its initial level and subsequently executes a 
damped oscillation about the level 3|/ above the original. The effect is 
not seriously affected by the sharpness of the gust (measured by r) but 
is proportional to its intensity (measured by J) . The shock of the gust 
is small. For a rear-gust the effects are reversed in sign, the machine 
falls. A severe rear-gust coming upon a machine flying low might there- 
fore produce serious consequences. 
The major effect of an up-gust is to carry the aeroplane bodily upward 
with it. The oscillations are small, but in the case of a sharp gust, the 
initial acceleration may be considerable and ^bump' the pilot. The 
effects for down-gusts are reversed in sign. 
Little appears to be known in regard to the extent or intensity or per- 
manence of rotary aerial motions, and in the absence of such meteoro- 
logical information, no satisfactory practical conclusions may be stated 
as to the effect of these gusts upon flight. The analysis, however, indi- 
cates that rotary gusts of relatively small intensity may have relatively 
large effects on the motion. 
The Constrained Machine. — If the machine is so constrained that 
^ = 0, the equations of motion reduce to the first two of (1). Substi- 
tution of the numerical data shows that the motion, when disturbed, is 
no longer oscillatory, but approaches the original condition asymptoti- 
cally. The riding of the machine should therefore be steadier. The use 
of data obtained for lower speeds than U = —115.5 feet per second shows, 
however, that the constrained aeroplane loses its dynamical stabiHty at 
a higher speed than the free machine, and to that extent is more danger- 
ous in landing. 
In a head-gust the constrained machine soars steadily (without oscilla- 
tion) up to some / feet above its initial level. Thus the upward swoop 
of 4/ to 4J/ has been eliminated and the final increase in level is less than 
one-third as much as before. In a down-gust the effects are reversed 
in sign. 
The up-gust is again important only for its general convective effect 
upon the machine. In case the gust is sharp, there may, however, be a 
considerable momentary acceleration or 'bump' at first. 
It is interesting to note that if an aeroplane, equipped with the auto- 
matic device, is riding on a breeze which has a leisurely periodic gusti- 
ness, a habile pilot may 'suck' considerable energy out of the gusts. For 
