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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).
Crankshaft torsional vibrations in 6, 8, and twin-6 engines.

Identifier  ExFiles\Box 23\5\  Scan073
Date  1st February 1923
  
hs{Lord Ernest Hives - Chair}/Tsn1/LGS.2.23.

CRANKSHAFT TORSIONAL VIBRATIONS.

6, 8 & TWIN-6 ENGINES.

It is possible to obtain a rough idea of the
severity of torsional vibrations to be expected in the above
three types of engines.

The engines compared here are the standard 20 HP.
RR., a straight-eight with the same size cyls. as the 20 HP., and
a twin-six consisting of two banks of 20 HP. cyls. at 60°. The
8-cyl. engine will be closely approximated to by the Stutz.

There are two separate disturbing torques producing
torsional vibrations, those due to the firing impulses and those
due to the change of kinetic energy in the working parts, known
as the 'inertia torque'. They are both irregular periodic
torques, i.e. not simple in form. The crankshaft has 'periods'
at speeds at which it 'resonates' with harmonics of either of
these torques.

The inertia torque harmonics for any number or
combination of cylinders may be calculated with accuracy as to
magnitude, phase and frequency. This has been done for the
Phantom and 20 HP. in a previous report on 'Balance'.

It is also possible to express the firing torque
of an engine in the form of a 'Fourrier series' of sines and
cosines with arbitrary constants. This has been done for
one cylinder of a 20 HP. RR., and the constants evaluated by
'harmonic analysis' of a torque diagram obtained from an indic-
ator diagram. The series for one cylinder is of the form :

contd :-
  
  


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