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 wheel shimmy and tramp, including diagrams of wheel movement.
Identifier | ExFiles\Box 170\3\ img033 | |
Date | 14th July 1933 guessed | |
-4- At A when the wheel meets the ground, it is toed in and produces a side thrust F in the direction of the arrow. This has a moment arm h about the roll axis of the axle. The couple F x h is such as to push the right front wheel down. At E as the wheel starts to leave the ground, the condition is reversed. These couples lead the corresponding displacements of the axle by a phase angle of about 90° and so feed energy into the tramp. [DIAGRAM] C SHIMMY STARTING E END OF SHIMMY A B D F G If the sketch represents a right wheel and A is a spot at the centre of the wheel hub, it is observed that during the shimmy this spot moves in a loop as shown, the rotation of the spot round the loop being the same direction as the rotation of the wheel. When the shimmy is at a maximum, the loop is vertical as shown at B. On drums it has been observed as large as 3 inches high and 1-1/2 inches wide. This indicates a tramp of 3" either side of centre and a wobble of 5° either side of centre. When this occurs at a frequency of 600 cycles a minute and a speed of 50 to 60 miles per hour, it is easy to show that the forces involved are very high. | ||