THE FORM OF AN AIRPLANE LOOP 
213 
Results and Conclusions . — It will be noted first that the loop 
is far from circular, contrary to the opinions of many pilots I 
have interviewed on this matter. This is to be expected, since 
the velocity of the airplane decreases toward the top of the 
loop. To create a sufficient centrifugal force here, then, a smaller 
radius of curvature is required. The dimensions of this loop are, 
as noted from figure 44, 75 feet broad by 185 feet high. The 
time consumed in making the loop proper is a trifle over five 
seconds. The greatest stresses involved are at point 1.97 where 
the air pressure is nearly four times the normal, and at point 5.92 
where it is nearly three times the normal. It is thus evident that 
a large factor of safety is required in this manoeuvre. In fact 
in these airplanes, the J.N.4 H., the factor of safety is supposed 
to be in the neighborhood of ten to twelve. It ’ will be noted 
further that the greatest stresses in this present case occur before 
the loop proper is executed. These stresses follow always when 
an airplane, following a steep dive, is too suddenly leveled out, 
or directed again upward. In the present case a velocity of about 
100 miles per hour was attained. The high stress at point 1.97 
came from the high velocity, while at point 5.92 it came from the 
small radius of curvature. 
No two loops are ever alike as, for example in the present case, 
a close inspection of the figure reveals that the angle of attack 
varies rapidly from point to point. This is in the pilot’s control, 
and he can never operate his controls with perfect uniformity. 
Altitude is invariably lost on a loop; in this case about seventy 
feet as shown in figure 44, but more was lost actually as the first 
part of the approach is not recorded. 
This method of survey, while somewhat laborious, is capable 
of yielding very accurate results. In the present case there was 
but one light on the airplane, and so only the path of the plane 
as a whole was determined. If three lights were mounted, one 
would have exact information as to the angle of attack, and other 
matters, all of which information would be of the utmost value. 
A great deal of stress has been, and is being laid on tests of 
airplane performances. This method would in the end yield more 
accurate results with far less labor than would many of the 
methods which have hitherto been pursued. 
Physical Laboratory, 
The State University. 
