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Proceedings of the Royal Society of Edinburgh. [Sess. 
XXIX.— On Novel Illustrations of Gyrostatic Action. By James G. 
Gray, D.Sc., Lecturer on Physics in the University of Glasgow. 
(Read May 6, 1912. MS. received July 7, 1912.) 
In this paper are described some new spinning-tops, gyrostatic apparatus, 
and illustrations of gyrostatic action devised by the author in the course of 
the last nine months. The apparatus has been built in the workshops of 
the Natural Philosophy Institute of the University of Glasgow, and has 
been employed in illustrating the lectures on rotational motion delivered in 
the Natural Philosophy classes in the course of the session just closed. 
Fig. 1 shows a model aeroplane fitted with a small gyrostat in the 
position of the propeller. The gyrostat is therefore fixed on the front of 
the aeroplane with the plane of its flywheel at right angles to the length 
of the machine. The flywheel of the gyrostat, so fitted, represents exactly 
the rotor of the engine and the propeller of an actual aeroplane. The 
model, with its attached gyrostat, is suspended by means of a thin string 
so as to hang in a horizontal position. If the flywheel is spinning in 
either direction and the aeroplane is struck a small blow so that the 
whole model is made to turn quickly in a horizontal plane about the 
string, it will be found that for one direction of this turning the front end 
of the aeroplane rears up and the back end descends ; for the other direction 
in which the aeroplane may be turned the front end of the aeroplane dips 
down and the hack end rears up. 
This experiment is of great practical value as illustrating a danger 
which persons not conversant with gyrostatic action would hardly foresee. 
The rotor of the engine and the propeller of an aeroplane combine to form 
a powerful gyrostat, the effect of which is to introduce a gyrostatic couple if 
the aeroplane is caused to turn in a horizontal plane. If G be the com- 
bined moment of inertia of the rotor and propeller, their angular 
velocity, the magnitude of the gyrostatic couple tending to cause diving or 
rearing up of the aeroplane, at an instant at which the aeroplane is turning 
in azimuth with speed o> 2 , is Go^wg. If the aeroplane is to be maintained 
in a nearly horizontal position use must be made of the tilting planes, and 
this necessitates stresses being set up in the framework of the machine. 
To avoid straining of the machine, should be kept small — that is, the 
aeroplane should not be turned suddenly. These considerations show con- 
clusively that aeroplane flights are accompanied by considerable danger from 
