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).
Analyzing the causes and characteristics of 'criss-cross' axle vibration or wobble.
| Identifier | ExFiles\Box 28\4\ Scan316 | |
| Date | 21th August 1925 | |
| R.R. 493a (50m) (D.B. 175 25-9-24) J.H.D. EXPERIMENTAL REPORT. -4- Expl. No. REF: HS{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}2/LG21. 8. 25 (1) The strength of the road springs. (2) Their distance apart. (3) The moment of inertia of the front axle. (4) The nature of the tyre. (5) The inflation pressure of the tyre. This criss-cross vibration is always ready to build up if some periodic force is present which occurs with the same frequency. An out of balance wheel supplies the necessary force at a given road speed. An out of balance of 1 lb. at 16" radius exerts a force of 160 lbs. radially at 60 m.p.h. This tends to lift the axle on this side with this force once per revolution. If the criss-cross period of the axle is 1/10 secs, a wobble is built up at this speed. When the axle vibrates in a criss cross manner, a gyroscopic couple is created due to turning the rotating wheel through an angle rapidly - this couple tends to turn the rising wheel inwards and the other outwards. Once the vibration has started it does not seem to be essential that it should keep in step with the wheel revs. exactly shewing that apparently the out of balance is not necessary to keep the wobble going. When each wheel in turn hits the ground at an angle, it is wrenched back to a normal position and then over-runs. The very fact that the wheels are wrenched through a large angle causes a gyroscopic couple which tends to keep the criss cross vibration of the axle going. This is the only explanation we can offer for the fact that we can sometimes start a wobble at 60 m.p.h. and it will build up reaching its max. violence at as low a speed as 30 m.p.h. with a frequency of perhaps little over half that at which it started, which cannot be very near the true criss cross period of the axle. contd:- | ||