RESEARCH FOR AERONAUTICS—FARREN 263 
distrivution in flight. We have now available a method of great po- 
tency in the electrical resistance strain gauge. This is being used with 
great effect on a large scale in laboratory tests, and its application to 
measurements in flight is being rapidly developed. It will undoubtedly 
prove to be one of the greatest contributions of the research worker to 
improvement in the structures of aircraft. 
Possibly the greatest achievement of the research worker in the field 
of aircraft structures is in discovering how to avoid the dangers of what 
we comprise in the term “flutter.” In my view, there is in the whole of | 
aircraft engineering no better example of the power of mathematical 
analysis, of ingenuity in experiment, and of skill in interpretation. 
The successful attainment of very high speeds, with a remarkably small 
number of serious failures, can only be ascribed to the most skilled use 
of all these resources, guided by systematic review of the results of their 
application. Direct experiment in flight—the only satisfactory 
check—is almost impracticable. Laboratory determination of reliable 
numerical values of the essential quantities involved is extremely dif- 
ficult. Much more information on these is essential for progress, and 
here the designer can justifiably demand all that research can provide. 
STABILITY AND CONTROL 
Up to this point I have said nothing of the contribution of research 
to the production of stable and controllable aircraft. I am glad to 
say that the time is now long past when lack of stability is regarded 
by anyone as a virtue in an aircraft. In fact it is unquestionably a 
most serious defect, whatever the duty of the aircraft. But it has 
always been difficult to define the necessary or desirable margins of 
stability and the associated general stability and control character- 
istics. The designer must, however, have the requirements expressed 
in terms that can be reflected in his lay-out, both as a whole and in 
detail. He must be able to judge fairly accurately how the changes in- 
evitable as a design develops will react on the stability and control, 
and he must have at his disposal means of dealing economically with the 
consequences both of the variation of load distribution resulting from 
operational conditions and of the changes involved in the development 
of the aircraft. 
There is a good deal about the stability and control of aircraft in 
which there has been little apparent change over the period covered 
by the examples I have taken. I believe, however, that this is simply 
because the desirable general characteristics were attained by about 
1918. Since then our main problems have been, first, to preserve them 
substantially unchanged in spite of the profound changes in the form 
of aircraft and, second, to enable the same man to control much larger 
and much faster aircraft. 
619830—45——18 
