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).
Article from 'The Autocar' magazine about diagnosing and curing steering wheel flapping.
| Identifier | ExFiles\Box 28\4\ Scan020 | |
| Date | 7th September 1912 | |
| R.R. 285A (150 H). THE AUTOCAR, September 7th, 1912. 417 X 457 Useful Hints and Tips. The Flapping of Steering Wheels and a Cure. A CAR which had steered normally gradually began to show undue sensitiveness to the road. This vice slowly developed till at its worst the hand wheel tugged back and forth at the driver's hand, while "outside" observation showed that the two front wheels wagged, or flapped, rather badly. The case was puzzling, as the car was a very good one and most carefully used and tended. When new it had steered as it should, but very early in its career it had commenced to "flap," and by the time four thousand miles had been covered this tendency had developed into a nuisance. It was not constant, but only occurred at certain critical speeds, and seemed to be started by any slight road inequality. Once started, it was as bad on a smooth road as on a rough one, and the only cure was to go faster or slower than the critical speed. Unfortunately, the critical speed was from twenty-five to thirty m.p.h., and, in consequence, there was little peace for the driver. It will be seen that it was a case of very puzzling periodicity. Every part of the steering was examined most carefully; indeed, the investigation did not end there but extended to spring pins, and the springs themselves, and even the tyres were suspected as well as the road wheels. All this was in vain, as everything appeared to be in perfect order. The owner was helped in every possible way by the makers, but, as the trouble was as new to them as to him, they were no more successful in curing it. To cut a long story short, it was at last found that the front springs had settled very slightly, so that the steering pivots were not quite vertical fore and aft, and a cure was effected by placing a steel wedge between each spring and the spring tables on the front axle. The two wedges were split, so that half thickness of each could be tried at a time. Each half was ¾in. deep at the thick end tapering to almost a knife edge, so that the two gave nearly ¼in. effective rise. One half each side was tried first, and found to effect a real improvement; then two were tried and the steering, if not rendered perfect, was at least greatly improved. To make our meaning clear we append sketches in which the final angle of the steering pivots and the thickness of the wedges are purposely exaggerated. It may be interesting to add that the wedges were also tried in the opposite direction, i.e., with the thick ends pointing backward. All this did was slightly to alter the period of the flapping and to make it rather worse than it ever had been, and it came on at a somewhat higher speed when accelerating and lasted to a lower speed when decelerating, also producing another bad period at and around sixteen m.p.h. We should mention that on this car the steering pivots are not inclined outward, the road wheels themselves being canted to bring their points of ground contact in line with the pivots. Altogether, the trouble was a very peculiar one, and the remedy in some respects as peculiar, as all previous experiments we had made had certainly not been in favour of caster steering, yet it will be seen that this is practically what the car now has, though the degree of forward slope on the pivots is far less than indicated in our sketch and is only a very slight inclination indeed. While a cure has been effected we are by no means satisfied with the procedure which led up to it, as it was of the rule of thumb order, and although the desired result has been achieved, it is more or less at the expense of accepted theory and practice. It appears that some vital factor has been ignored, and, if later investigations bring it to light, we shall return to the subject. In the meantime, we see a good many cars with flapping steering wheels, many of which could, doubtless, be cured partially or wholly if a few experiments with wedges were tried, provided the steering is otherwise correctly designed and made. It is quite likely that on some cars the slight forward angle of the pivots would make things worse. If so, the opposite, or slightly backward, lean should be tried. It all depends on the angle assumed by the steering pivots when the car is running on the road. We have little doubt that in the case cited this angle is not the same as when the car is standing, and our theory is that when in motion the pivots are practically vertical. This cannot be verified by observation, however, and it is mainly because of this that a cure must be sought by the process of trial and error. Fig. 1.—Sketch indicating the position of the two steel wedges and the angle (exaggerated) at which they place the front axle and consequently the steering pivots. The view on the right shows the section of the axle, the wedges and the spring clips enlarged. A, wedges; B, front axle. Fig. 2.—One of the pair of duplex steel wedges placed between the front springs and the spring table on the axle to alter the angle of the steering pivots. Fig. 3.—The angle (exaggerated) assumed by the steering pivots after the steel wedges had been inserted between the springs and the spring tables on the front axle. | ||