402 REPORTS ON THE STATE OF SCIENCE, ETC. 
The greatest height to which a helicopter has ascended is stated in 
official records to be 3.28 feet!® Isuspect that this and other heights which 
have been attained so far have been disappointing to the inventors con- 
cerned, Perhaps their luck was not so bad as they imagined,—just as the 
small boy is not always to be pitied who fails to climb a tree: their engines 
did not fail in the tests they made, but they might have done! Let us con- 
sider for a moment what are the prospects for a helicopter-aeronaut 
whose engines have stopped. 
The Importance of Stability. 
10. Well he has to come down, and he would like to come down slowly ; 
that is to say, he wants to expose as great a resistance as possible to motion 
through the air. Surprising as it may seem, his best procedure is to de- 
clutch the lifting screws. An airscrew free to rotate offers more resistance 
than one which is stopped: indeed, we have shown by recent experiments 
at the National Physical Laboratory that it can be made to give a resist- 
ance approximating to that of a flat plate equal in size to the circle which 
its tips sweep through as they spin.* So we may hope to provide him with a 
kind of parachute, and his plight is less dismal than it at first appeared. 
But resistance to motion is not enough. We must be certain that his 
descent will be steady,—in technical language, that his aircraft, with engine 
stopped, is stable. 
(At this point an illustration was given by means of parachute models 
of the wmportance of stability.) 
The Futility of the Prize Competition. 
11. Itis this problem of stability which must be solved before anything 
can be hoped from the helicopter. There is no reason, from what we know 
of the corresponding problem for aeroplanes, to anticipate that it will 
present any overwhelming difficulty ; but it must be attacked by systematic 
research. And such research ought not to be financed by, and therefore 
kept secret for, the private inventor: if the helicopter has military 
importance, the knowledge obtained will be of national interest, and pro- 
vision should be made accordingly. So I come back to the contention with 
which I started: if there is any future for the helicopter (and of this I 
personally am not convinced), it is a problem which should be referred to 
the research committee and to the professional designer. Nothing could be 
more futile, as a plan for developing it, than the prize competition. 
The High-Speed Aeroplane. 
12. Turning now to another familiar topic, the high-speed aeroplane, 
we need not pause to consider its military importance: in the air, as in 
every other form of warfare, victory lies with the side which can manceuvre 
fastest. On the other hand, it is doubtful whether much assistance can 
be rendered here by systematic research, except on the side of the engine ; 
clearly, if we can increase the power developed by an engine of given 
weight, we shall gain an immediate improvement in speed. The other 
5 Cf. Flight, January 29, 1925. 
* Experiments made since this Discourse was delivered have indicated the — 
possibility of considerably higher resistances. 
