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 methods to raise the critical speed of a Bensport crankshaft.
| Identifier | ExFiles\Box 85\5\ scan0052 | |
| Date | 12th September 1933 | |
| FILES ----- X217. 12.9.33. ------- BENSPORT CRANKSHAFT. -------------------- We have looked into the possibility of raising the critical speed of this crankshaft. The present shaft EB.39 has a half speed period at 2500 r.p.m. and the lightened shaft with larger balance weights at 2350 r.p.m. We first considered increasing the crankpin diameter from 2" to 2.2", the bore of the pin being unchanged namely 1.125". According to Carter's formula the stiffness would be increased 6.5% and the effective inertia 3% giving a gain in speed of 2%. If the additional crankpin mass were balanced no gain would result. Secondly increasing the journal size to 2.750" diameter would raise the period 7%. The weight of 6 big ends is 7.7 lbs. and thus approximate inertia 47.5 lbs. in2. If these were made in Dural to the same drawings providing a saving of 31 lbs. in2 we should gain 5% in critical speed. or with Reduction c'wts 6.4% (320 r.p.m) We do not expect to raise the critical speed by much over 7% by removing all the balance weights. Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls} | ||