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).
Preliminary results of an investigation into the 'Packard System' of crankshaft balancing.
| Identifier | ExFiles\Box 132\1\ scan0089 | |
| Date | 2nd November 1938 | |
| Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} 11/6 BY/B.8/G.2.11.38. Preliminary Results of Investigation of "Packard System" of Crankshaft Balancing when allowance is made for the M.{Mr Moon / Mr Moore} of I's of the cranks being different in the two directions of bending (.i.e. in radial and tangential planes. The effect of the difference in the M.{Mr Moon / Mr Moore} of I's in the two directions is that the shaft only deflects solely in the plane of the applied couple when this plane contains the crank concerned, i.e. when the applied couple is in a radial plane. This condition is never satisfied for all cranks of a 6 cylinder shaft. Thus, when the shaft is loaded by vertical loads, the deflections of the shaft will be horizontal as well as vertical. This means that the method adopted in the recent tests of Wraith and Merlin crankshafts, of measuring only vertical deflections for loads on each pair of crankpins in turn, and then finding the resultant by a vector diagram, with sides parallel to cranks, is not correct. It is necessary to measure displacements in two perpendicular directions. These two displacements have been taken into account in my latest treatment. From the test results of Wraith crankshaft, represented in elliptical diagram B.L.2207, Sheet V, giving vertical deflection under central load of 300 lbs, and substituting these results for θ = 60° and - 30° to Crank 6 (+θ towards crank 5), in my equations, I have deduced the average M.{Mr Moon / Mr Moore} of I. for one crank unit in radial and tangential planes, and find them to be IR = .1 inch^4 units. IT = .2095 " " respectively. Using these values in my latest analysis of the "Packard" system, it is found that the mass required at the centre to balance the deflection caused here by a radial load of 200 lbs at each crank is 260 lbs. at an angle θ = abt 21°6' from crank 6 towards crank 5. It is interesting to note that these results agree almost exactly with those obtained by me (2.6.38) on the assumption that the shaft could be treated as a uniform bar, (viz. mass = 250 lbs. θ = 22°-20'). It is hoped, in time, to extend the investigation to the calculation of bearing loads :- | ||