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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Report page detailing the power required to drive fans, the effect of belt slippage, and the measurement of air stream velocity.

Identifier  ExFiles\Box 75\3\  scan0005
Date  18th September 1924
  
Contd. -4-5 EFC1/T18.9.24.

In the ideal action of the fan, the power is
proportional to the cube of the speed. Here it is proportional
approximately respectively to the 2.8th and 2.7th powers which
indexes are very similar to those which have previously been
obtained for the power required to drive an aero propeller.
On the power curve, dotted extensions are
shown representing the probable continuations on the basis of
no
the belt slip. It will be noted that bigger powers were
possible on the six-blade fan on account of the lower speed
corresponding to equal power, with the consequent effect that
the belt did not so readily slip. This explains what appears
rather paradoxical at first sight, that the falling off of the
power due to slipping is more in evidence in the case of the
three-blade fan than in the case of the six-blade fan. The
slipping of the belt is rather more dependent upon the speed
of the belt than upon the power tension.

(2) Velocity of Air Stream at various speeds.

For this purpose a small anemometer was
utilised. It was not considered worth while measuring the
velocity of the air stream in more than one position of the
anemometer, and therefore a few preliminary experiments were
made with both the six-blade and three-blade fan, to determine
the most suitable position, which was 7.3" from the axis of
the fan vertically upwards, and 18" from the fan horizontally.
In the selected position, the indications of
the instrument, duly corrected according to a correction

Contd.
  
  


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