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).
Crankcase distortion tests conducted on a 25 HP engine.
| Identifier | WestWitteringFiles\V\December1930-February1931\ Scan157 | |
| Date | 20th January 1931 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls} c. to SG.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. to AG. K.{Mr Kilner} c. to Dn. Hy.{Tom Haldenby - Plant Engineer} x5000 25.HP. CRANKCASE DISTORTION. We have carried out tests on a 25.HP. crankcase (bottom half absent) to measure deflections both in a vertical and horizontal plane when loaded vertically and horizontally at the centre main bearing. We do not consider that the bottom half should be relied upon to supply any stiffness owing to it being bolted up to a facing only and not spigotted in any way. The crankcase was supported at the end main bearings and loads up to 500 lbs. were applied at the centre main bearing. We find that the stiffness in a vertical plane is 5 times that in a horizontal plane. In a horizontal plane the crankcase deflects in the middle .001" relative to the ends of the crankcase per 100 lbs. of bearing load. At 3000 r.p.m. when pistons 3 and 4 are 90° after T.D.C. the centre bearing load is 5080 lbs. The crankcase therefore ought to deflect 1/20 of an inch. This obviously does not happen. To make sure that the crankshaft affords no stiffness we loaded one in a similar manner to the crankcase, and the deflection at the centre was .014" per 100 lbs. we can therefore say that the crankshaft adds no appreciable stiffness. The fact that the crankcase does not deflect laterally at the centre a total of 1/10" is due to the disturbing force not having time to accelerate the mass of the crankshaft or crankcase through more than a very small distance, we imagine. At T.D.C. the load on the centre main bearing is 9600 lbs this being made up of:- Inertia force 2260 lbs. Centrifugal force of c'shaft 1140 lbs. } X 2. " big end 1400 lbs. } Even if we balance completely the crankshaft and big end we still have the centre main bearing load varying from 4520 lbs. in one direction to 2520 lbs in the opposite direction due to inertia force. Hs{Lord Ernest Hives - Chair}/H.Grylls. | ||