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 wheel fight and the causes of low-speed wabble, including testing methods.
| Identifier | ExFiles\Box 170\2\ img288 | |
| Date | 28th June 1935 guessed | |
| -2- (4) Not only this, but the stiffness is "critical". That is 10% increase in stiffness may, in certain conditions, just turn the corner, and give complete freedom from wheel fight. (5) We think that the expression "transmission of road shocks" is not a correct description of what actually occurs. In some cases bad wheel fight can be produced on a dead-smooth road. We have just finished a great amount of testing on road and on 48" drums (just like yours) aiming to show exactly what "wheel fight" is. By setting the front wheels of the car 5" forward of the center line of the drums, to give an exaggerated "caster" effect, and by "detonating" the cycle by means of flicking the steering wheel, or by means of a bar projecting forward from one steering knuckle, we can produce perfect low speed wabble on smooth drums, at 20-26 mph depending on the car. Or by means of 4 cams on each drum set alternately we can produce a forced wabble, which is not quite the same thing or at the same frequency. Neither of these effects is quite the same as the wheel fight which we produce on the road, which is a mixture of the two. The closest approximation we have found to road conditions is to set the wheels 5" ahead of center and use one cam 1" high and 18" long on one drum only, as a detonator. This gives an excellent imitation of rough road steering conditions including the importance of road speed, which is of course true on the actual road. (6) Following are our conclusions:- (a) True low-speed wabble is a self-energized oscillation which depends on four factors:- (1) A detonation (road bump or flick of steering wheel). (2) A primary oscillating system (the wheel wabble) (3) A secondary oscillating system, in this case, the rocking of the car itself about an inclined axis passing through the base of the windshield and the center of the rear axle. (4) A source of energy (the forward motion of the car). It is essential for wabble to occur that the natural frequencies of 2 and 3 should be of a similar order. | ||