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).
Technical analysis of high-speed steering wobbles, discussing wheel precession and spring frequency.
| Identifier | ExFiles\Box 28\4\ Scan332 | |
| Date | 24th August 1925 | |
| Tohs. from DA.{Bernard Day - Chassis Design} X457 DA{Bernard Day - Chassis Design}1/M24.8.25. X.457 X.8430 HIGH SPEED STEERING WOBBLES. If the precession of the wheels is a forced one it looks as though a very great torque would be required to keep it going. If, on the other hand, it is the conical precession without torque which Mr. Healey refers to, the moment of inertia of the wheel about the axis of precession ought to be equal to the moment of inertia about the axis of rotation for the period of the wobble to exactly agree with the road speed. The moment of inertia of the road wheel about the king pin seems to be only a little over half that of the axis of rotation. On the other hand the moment of inertia of the wheel about the centre of the axle is very much more than that about the axis of rotation. For Mr. Healey's conical precession to pan out in practice seems to require a resultant point about which the wheel is precessing somewhere between the king pin and the centre of the car. It does not seem impossible that this is the case and it would explain the precession very effectively. One curious point which arises from your results is that though the oscillation is exactly the same speed of the road wheel, the distance between the marks on the road appears to be more than a revolution. Referring to the side steering tube springs it appears to be a coincidence that the natural frequency of the oscillation of the two wheels about the stiff side steering tube springs, namely, those of 3,500 lbs.per.sq.in. rating, seems to very nearly exactly coincide with a speed of 55 to 60 m.p.h. This would no doubt add its quota to maintaining the oscillations. DA.{Bernard Day - Chassis Design} | ||