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 sill bending loads and the effects of moving rear support points.
| Identifier | ExFiles\Box 14\8\ Scan288 | |
| Date | 23th June 1930 guessed | |
| - 2 - I am enclosing for your consideration my memo of June 23rd last year to Mr. Olley and prints: SK-403 - Analysis of Sill Bending loads for uniformly distributed load. SK-404 - Similar analysis for concentrated loads as outlined in the memo above. SK-405 - Analysis of Sill Bending showing the effect of moving the rear support forward from 9" in front of the axle to 19" ahead of the axle. The first two curves are a comparison between the loads produced with a uniformly distributed body load of 20 lbs. per ft. run and the same total load concentrated at individual points chosen to bear some sort of resemblance to the loads of individual parts of the body. The similarity between the results of these two curves shows that it is immaterial which style of loading we consider. In this case we get two points of maximum bending moment, one half way between the main supports and the other at the rear support. The idea is to keep these two bending moments the same, so that the maximum we get is kept down to its lowest figure, and by doing this we always get a point of zero bending moment, 20 to 25" forward of the rear axle, that is at the point where the wheel housing joins the main sill and where it is usually impossible to get the maximum depth of sill. SK-405 shows the effect of moving this point of support forward 10" and how it increases the bending moment at the rear support at the expense of the bending moment between the supports and moves the point of zero bending moment forward to 40" from the axle. The effect of moving the rear support back - as you had on 24-EX - is the opposite, to increase the bending moment between the supports and moving the point of zero bending moment back to or beyond the rear axle. If you can arrange this so that the point of zero bending moment comes always at the weakest portion of the sill - i.e. the front of the wheel housing - then you will undoubtedly be getting the best possible results. Note that the difference between the dotted line in SK-405 and the bending moment line in SK-403 is due to using 120" body base in SK-403 and 117" in SK-405. The little red 20 HP was built on these lines, with only two supports each side, and the effect of that was to sell everybody here on the advantages of the deep sill. Yours truly, R.B.Burton RBB/VB Encl. 4 | ||