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).
The torsional period and performance issues of the J.3 crankshaft and damper during engine testing.
Identifier | ExFiles\Box 179\3\ img013 | |
Date | 1st March 1932 | |
SECRET. ORIGINAL x 520 x 639 To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls} Ha/Gry.{Shadwell Grylls}6/MJ.1.3.32. c. to Sg.{Arthur F. Sidgreaves - MD} c. to Wor.{Arthur Wormald - General Works Manager} c. to E.{Mr Elliott - Chief Engineer} c. to Ds. c. to Hy.{Tom Haldenby - Plant Engineer} J.3 CRANKSHAFT & DAMPER (Loc.2977). The half torsional period of this engine has been most noticeable when running the engine on the test bed. The engine is fitted with the drum type damper in which the drum and fan pulley are rigidly fixed to the crankshaft nose. The speeds of the half period are - With no damper or fan pulley 2325 R.P.M. With fan pulley and fixed part of damper only 2150 R.P.M. With fan pulley and damper complete 1950 R.P.M.-not so violent. The latter figure leads us to suppose that the damper blocks are not slipping sufficiently. We have therefore compared the constants of this damper with the standard 25 HP. We get - J.3. { (Inertia of fan pulley & drum 25 lbs. in2 - measured.) (Slipping inertia of blocks 37 lbs. in2) (Friction torque at 2000 RPM. 129 lbs. at 17¾" calculated.) } China { (slipping inertia 74 lbs. in.2) (Friction torque 15 lbs. at 17¾".) } The J.3 damper has insufficient inertia and too much damping friction. The alteration of any dimension to increase the inertia also increases the damping in the same ratio. E.{Mr Elliott - Chief Engineer} is therefore giving us a fixed stiffer ring with damping pads loaded by springs and centrifugally on to the drum. This overcomes the difficulty caused by the whole inertia adding to the centrifugal load. We have also run the engine at higher speeds. At 3750 RPM. the whole damper begins to flap violently, though we have been up to 4100 RPM. The vibration at this speed is very pronounced as is also the movement of the damper. A similar but smaller movement of the damper is noticeable on the half period. Ha/H.Orylls. | ||