264 | ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
The foundations of stability and control theory were laid, and well 
laid, long ago. Much labor has been spent on expanding it to embrace 
new developments, such as structural distortion, and on the analysis 
of the controlled and uncontrolled motion of aircraft. A vast amount 
of experimental evidence has been accumulated. Much of this, how- 
ever, is related rather to specific problems than to the systematic devel- 
opment of an understanding of the matter. There is room here for a 
wholesale improvement, particularly by an attack on a wider front in 
flight. I am not among those who criticize our record here on the 
grounds that we did not undertake enough basic work at the time when 
the airplane, as we now know it, first crystallized. I regret that cir- 
cumstances made it impossible to give this work high priority. Had 
we been able to do so, we might have avoided many troubles and saved 
much labor. But I do not believe that, on the balance, we would have 
reached our objective—usable aircraft—more quickly. We relied on 
our past experience, on our ability to improvise, and—most significant 
of all—on our conviction that the theory available was soundly 
founded on experimental evidence. We discovered, by the attacks we 
were forced to make on troubles as they arose, much more about sta- 
bility and control than most of us believed there was to learn. Thus, 
and I believe only thus, could we have advanced at the rate we did. 
It is an excellent example of the interworking of research and 
application. 
In the field of control balance we have made tremendous advances 
in the face of difficulties that are sometimes hardly appreciated. The 
1917 bomber operated at speeds—80 to 100 m.p.h.—at which the pilot 
could provide the forces necessary for control with little or no aero- 
dynamic balance. Take the 0/400 ailerons. The maximum hinge 
moment required was probably equivalent to a force on the pilot’s 
hand of the order of 50 pounds, with ailerons on which the aero- 
dynamic balance was probably no better than one-half. In the Lan- 
caster the same movement of surfaces of about the same size is required 
at 300 m.p.h., requiring nine times the forces. The pilot is no stronger, 
so the aerodynamic balance must reduce the hinge moment to say one- 
eighteenth of that of unbalanced ailerons. This is a difficult require- 
ment but it has been met. 
Suppose we put up the weight at the same wing loading to 100,000 
pounds, one and one-half times that of the Lancaster. The linear 
dimensions will rise in the ratio 1.5/7 and the hinge moment at the 
same speed in the ratio 1.5 */?._ The aerodynamic balance must there- 
fore reduce the hinge moment in the ratio 
1/(2) (1.5)%/2(3)2=1/30 
A similar argument leads to a figure of 1/400 if the weight is increased 
to 500,000 pounds. We can certainly achieve 1/30 and possibly 1/400 
