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).
Outlining calculations and findings on motor car frame stiffness.
| Identifier | ExFiles\Box 94\4\ scan0014 | |
| Date | 26th October 1934 | |
| 4327 To E.W.H & Da.{Bernard Day - Chassis Design} Copy to Hs{Lord Ernest Hives - Chair}/RM.{William Robotham - Chief Engineer} E/TSN.1/MN.26/10/34. Frame Stiffnesses. I asked Lr{Mr Ellor}/Mr.Horrocks, who is experienced in aircraft structural calculations, to look into a few points in connection with motor car frames. The following facts emerge:- 1. In a channel-section frame braced by a cross, the maximum torsional stiffness from front to rear is obtained when the cross is half the length of the frame (between axles). The stiffness is reduced to half if the cross be extended right on to each end of the frame. 2. Taking as a rough example a frame ten feet long between axles, then if it be 2 feet wide between the side-members its torsional stiffness is only 54% of what it is if it be 3 1/2 feet wide. Thus the torsional stiffness goes up practically directly as the distance between side-members. 3. The above figures are based on a frame and cross all made of the same section channel members approximately 3 1/2" deep, having no torsional stiffness in themselves. All stiffness is in bending. Under torsion of the frame as a whole, the maximum stress occurs at the centre of the cross-member. 4. If we make the side-members of tubes, so as to have some torsional stiffness of their own in addition to their bending stiffness, then for the same weight of metal in the frame and assuming a channel-section cross of half the frame length as before, the overall stiffness is 55% greater. This shows the importance of aiming at torsional stiff-ness in the side-members. Contd: | ||