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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).
Analysis of engine vibrations, focusing on torsional periods, flywheel whirl, and potential improvements.

Identifier  WestWitteringFiles\V\October1930-February1931\  Scan350
Date  23th February 1931 guessed
  
(3)

and we should have to endeavour to make the slipper flywheel more efficient. The master period being 3 per rev. and somewhere about 3600. - i.e. 10,800 per min. would shew on our indicator at this periodicity.

It will be easily understood that items (1), (2), (3), (4), and (5), cannot do any good for these torsional periods, and item (1) might do some harm, but slight improvements might be made by -

(a) Lighter pistons, and
(b) Longer rods,

which do definitely improve over-run vibrations. Our greatest hope of improvement is -

(c) More effective slipper wheel.
(d) More effective engine mounting.

----------

Having discussed the low speed vibrations we next come to the 3 high speed ones as follows:

Firstly, the recently discovered flywheel so called whirl due to want of rigidity of the flywheel mounting or the flexibility of the crankshaft or crankchamber. Now excepting the master torsional period of the crankshaft, thought to be somewhere between 10,000 and 12,000 complete periods per min., we probably (almost certainly) have some vibration at 1 complete cycle per rev. at its maximum when the engine is running 2700 revs. This wants proving but if at 1. 2. or 4. per rev. it cannot be torsional, but must be lateral, and which the diamond mounting may not greatly improve, but it ought to be susceptible to items (1) (2) (3) (4) (5).

Item (1) would naturally bring down the master period, and perhaps make the harmonics slightly more manifest, but if the two couples trying to bend the crankchamber are the cause of this vibration, or even if the end cranks are deflecting the last crank and whirling the flywheel, then balance weights opposing the couples to the extent of even 30 to 50% would be worth fitting to reduce the flywheel whirl and save the crankshaft bearings.

Item (2) is naturally the obvious way to improve this 65 to 70 MPH. vibration by putting up the natural period from 2700 complete vibrations per period, which if it could be raised to 3300 would never be in the speed range of the engine under even the best ordinary road conditions, but might be found with a streamline body.

Item (3) might do some good by helping (2) to put up the period.
  
  


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