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 stresses and bearing loads for the Wraith engine's connecting rod and big-end bolts.
| Identifier | ExFiles\Box 114\2\ scan0073 | |
| Date | 1st October 1934 | |
| To E.{Mr Elliott - Chief Engineer} Copy to McStay. E/TSN.1/MN.1/10/34. 1020 WRAITH STRESSES & BEARING LOADS. Connecting Rod. The direct tensile stress in the neck of this rod at 5000 R.P.M. due to inertia is 14,400 lbs./sq.in. The maximum compressive stress assuming a maximum gas pressure of 650 lbs./sq.in. at low R.P.M. is 22,100 lbs./sq.in. In the standard steel Bentley rod the figures at the same R.P.M. and gas pressure are 21,600 and 39,300 lbs./sq.in. respectively. The equivalent figures on the Kestrel VI curved foot connecting rods are 21,900 lbs./sq.in. tensile stress under diving bombing conditions at 3600 R.P.M. and 56,500 lbs/sq.in. compressive stress under take-off boost (800 lbs. maximum pressure). The figures on the "R" engine were 24,000 lbs/sq.in. and in the neighbourhood of 80,000 lbs/sq.in. respectively. Since this rod is a little longer than we are used to, and also narrower in section at the lower end, I propose working out the whipping stress, which will take a little time. Big-End Bolts. The actual working stress in these bolts is the stress initially put into them by the fitter, and the correct basis of design would be for us to provide a bolt which was not overstressed when tightened up to a load sufficient to prevent separation at the joint; we have not enough information for this however, nor do we use slipping spanners. The maximum stress which would be produced by inertia is 25,100 lbs/sq.in., and the figure for the Bentley with 5/16ths." bolts is 38,300 lbs./sq.in. The latter have stretched in service and have recently been increased 1/32nd." in diameter. The stress due to inertia in the "R" engine bolts was only 22,200 lbs./sq.in., so that we are still a little high. The "R" engine bolts also were made in S/ZNCR, reduction gear steel, whereas S/N is standard on the cars. It would appear preferable to have a lower stress in big-end bolts than we would work to in the rods, owing to the change Contd: | ||