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).
Chassis frame design, comparing stiffness, construction methods, and materials for the Wraith and Bentley III models.
| Identifier | ExFiles\Box 99\2\ scan0065 | |
| Date | 25th October 1937 | |
| -4- 25.10.37. The results obtained at Shardlow do not seem to have been very reliable, so the majority of them have been omitted. A few, however, are given where no comparative figures have been obtained. WRAITH. Originally the Wraith frame was of box section .082" thick, with only the holes necessary for assembly. This proved to be so noisy that large holes had to be drilled in both sides of the box. To maintain the strength the thickness was therefore increased to .128". It will be noticed that the P.III frame stiffness is due chiefly to the front end rigidity. As compared with the Wraith there are three contributory reasons for this, absence of holes in the side members, the front end of the cross is nearer the front wheels, and the attachment of the pan to the side members is more rigid. It is American practice to rivet their frames together, and only use welding for the centre of the cross. This entails the use of 5/16" and 3/8" diameter rivets which cannot be closed by direct pressure but have to be hammered. I should prefer to use ¼" diameter rivets which can be closed by pressure with a little welding where necessary. We have found that bolted frames give very inconsistent results when twisted, and so we consider that bolts should be done away with altogether in frame assembly. B.III. The .104" thick welded frame is now considerably stiffer than the Wraith frame, which is satisfactory. The new lay out will stiffen up the front end slightly at the expense of the rear end. The nett result should be a slight increase. It will then be possibly to drill lightening holes, preferably lipped as on the Vauxhall wherever they may be thought to be necessary to avoid noise being transmitted into the body. We should be able to get the weight down to 225 lbs with a stiffness figure of 1150 lbs ft/degree. We have investigated the sketch (PD.32) of the lowered chassis frame for Bentley III, and consider that the torsional stiffness undrilled will be slightly greater (1200 lbs.ft/degree unwelded) than the original layout FB.3009. | ||