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).
Bensport crankshaft, analyzing critical frequencies and damper inertia in comparison to Bentley and other engine models.
| Identifier | ExFiles\Box 178\3\ img033 | |
| Date | 16th January 1932 | |
| A.{Mr Adams} FROM E.{Mr Elliott - Chief Engineer} C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} (Strikethrough) C. to HS.{Lord Ernest Hives - Chair} HY.{Tom Haldenby - Plant Engineer} GRY{Shadwell Grylls} RECEIVED 23 JAN 1932 E1/M16.1.32. K4583 BENSPORT CRANKSHAFT From report HS{Lord Ernest Hives - Chair}/GRY{Shadwell Grylls}3/MA12132.f it is seen, as was anticipated, that the mass of the dynamo armature, coupled to the front end of the crankshaft through fabric joints, acts to some extent as a dynamic balancer on the 6 litre Bentley in reducing the intensity of the major critical, and at the same time raising its speed. These couplings we understand have a limited life, and on the 6 1/2 litre Bentley used in the Le Mans race were worn out due to the frequency with which the engine passed through its maximum period. The same applies to the damper which enlarges the initial slack in driving splines of the multiple plates. We are interested in this combination because of the blower drive on the Bensport, where we shall expect to have two metal couplings with a flexible shaft between/driving the blower. The blower will probably have a certain amount of damping in the form of fluid friction. Naturally the major critical must not be within the working range on this engine. GRY.{Shadwell Grylls} has calculated that the B. 2. crankshaft without any inertia on the nose, but with con. rods, pistons, and balance weights, has a critical frequency of 6000 RPM. by Carter's formula. Also that an addition of 19.7 lbs. ins.² for the damper brings this down to 5000 RPM. From what we know now the further addition of the blower drive may push this up 10 or 12%. We shall get some information from the Alfa on this point. With regard to the inertia of the damper, the fixed part of the J.{Mr Johnson W.M.} 3. drum type is computed at 38 lbs. ins.² or about three times that of the 20/25. disc damper. For the Bensport scaling down in the ratio of .8 linear from J.{Mr Johnson W.M.} 3. the drum inertia would be less than half J.{Mr Johnson W.M.} 3., or within the limit of 19.7 lbs. ins. previously mentioned. Our major critical may therefore come out at about 5500 RPM. The 'China' unit last tested in France reached its master period at 4200., and the J.{Mr Johnson W.M.} 1. unit runs up to 4500. E.{Mr Elliott - Chief Engineer} | ||