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).
'pitching' problem in cars, comparing it to a ship's tipping centre and analysing spring and weight dynamics.
| Identifier | ExFiles\Box 67a\2\ scan0019 | |
| Date | 4th September 1927 | |
| XF410 O.W.B. London. C. to Whr.{Mr Wheeler} London. L.H.S.{Lord Herbert Scott - Chair} " E.P. Derby Hm.{Capt. W. Hallam - Head Repairs} " Hs.{Lord Ernest Hives - Chair} " You might remember, a few days before I left London for Australia, mentioning the problem of passengers, particularly those at the rear, being urged forward by small but irresistible impulses accompanied by what you described as "pitching" when our cars were passing over certain types of road surface. I have given some thought to this since I last saw you and cannot help thinking that there is some connection between this and the pitching of a ship in a sea way, though I must admit the analogy is by no means perfect. It seems to me there must be somewhere in our chassis a point similar to what is known at the "tipping centre" in ship building and trimming and that the further aft we can get this "tipping centre" the greater comfort our passengers will enjoy. The matter is complicated by the fact that a car pitches in two ways, that is the whole car pitches on its wheels whilst the sprung portion of the car pitches also on its springs, and further there is a compressible medium between the whole car and the road in the shape of pneumatic tyres, which medium is absent in the case of a ship. The centre of gravity of the whole car will not coincide with the centre of gravity of the sprung weight only and it seems to me likely that the "tipping centre" of the unsprung weight will have a relationship to the centre of gravity of the unsprung weight similar to what the "tipping centre" of the whole weight will have to the centre of gravity of the whole weight, though I am not sure whether the relationship will be a constant or a variable. At present we have so much weight forward that the front springs have a comparatively small amplitude of movement and slow period, while the rear springs have a comparatively large amplitude and high period. If the spare wheels, for instance, were moved aft, the car would recover, as it were, more quickly by the head and less quickly by the stern, thus reducing the vertical acceleration of passengers on the spring rebound. | ||