1921-22.] Gyroscope and “Vertical” Problem on Aircraft. 289 
In the trials carried out by the R.N.A.S. officers of the Gray stabilisers 
the following manoeuvre was frequently performed. Starting with the 
aeroplane moving in a straight path, it was directed into a circular path and 
the circular motion maintained for a considerable time. On straightening 
out the machine the apparatus was found to be upright. The same 
remarks apply to motion on a banked spiral. In fact, if the apparatus is 
forcibly deflected from the true vertical when the aeroplane is on a banked 
Fig. 18. 
curve, the pivoted system, after the required interval of time has elapsed, 
will be found to be erect. 
It was usual, on the conclusion of trials, when approaching the 
aerodrome, to descend in a continuous spiral just previous to entering the 
aerodrome. Following on the spiral motion and the bumps consequent on 
entering the aerodrome, the apparatus was invariably found to be erect. 
Early Models Used. Sun Shadow Trials. 
Fig. 18 shows a view of a pioneer instrument constructed by Messrs 
Elliott Brothers, the well-known instrument-makers. The construction of 
the instrument is precisely that described above, except that three slots 
and balls were employed. 
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