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 wheel hop, focusing on the effects of load and wishbone suspension height.
Identifier | ExFiles\Box 170\3\ img016 | |
Date | 25th February 1936 guessed | |
-4- (4) Effect of Load. In testing on cams we run into all sorts of apparent inconsistencies. When running at a certain frequency with the wheels hopping we will frequently make some change in conditions which will apparently cure the trouble completely at that speed, only to find later that we have merely shifted the resonance peak and that the trouble occurs perhaps more violently than ever at a slightly higher frequency. Consequently a "survey" of the whole range from 300 to, say, 800 cycles/min. has to be made for each change in conditions. One of the chief inconsistencies is the effect of an increase in the load. This will sometimes appear to make the wheel fight much worse, and at other times it will seem to stop the wheel fight. Actually we find that increasing load by adding say 300 lbs. to the front bump will increase the natural frequency of wheel hop from 550 to about 580 cycles/min. (5) Standing Height - Wishbone Suspensions. But it also appears to be true that if the wishbone arms are horizontal at normal load, adding load as above will increase the wheel fight tendency. We think this is because under load the wheels reach a position where their rate of change of camber is considerable, and therefore gyroscopic action is increased. To check this we can adjust the standing height on the T.W. job by winding up the torsion rods. When this height is increased above normal so that the arms are sloping downhill, and the wheels are being thrown up by the cams through the horizontal arm position where the rate of change of camber is zero, we seem to get the best condition for wheel fight. This is new - suggesting that arms which slope downhill at normal load may be better than horizontal arms. Also that raising the shock absorbers 1/2" as tried recently on the Buick may improve wheel fight conditions, especially on turns. It checks with experience on bent arm Dubonnet suspensions in which, in spite of the known preference for low frequency fight on these jobs, there is a detectable increase in wheel fight tendency as the bend angle is increased. The conclusion must be that the wheel fight from hopping of the wheels, that is the high frequency variety of fight, is linked in, to some extent, with gyroscopic effects. | ||