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).
Vehicle dynamics, discussing moment of inertia, spring frequency, and the application of Rowell's formula.
| Identifier | ExFiles\Box 43\2\ Scan149 | |
| Date | 4th May 1926 | |
| Oy1-E-5426 -2- May 4th, 1926 I. (b) This car however (to judge by the spring cambers) was much heavier than the standard Packard sedan. II. Mock's paper in the S.A.E.Journal for July last, (page 37) gives some most interesting practical examples along the same lines, pointing out the essential difference between a sedan and coupe', and the way in which concentrating weight in the centre makes the springing bad and erratic. Both Rowell and Mock refer to the consequence that often in-creased wheelbase leads to worse riding because it makes every body-type more or less like a coupe'. III. We have naturally wanted to find the moment of inertia of the Phantom car 12-MC at the works. This has an old type enclosed limousine body, is 150" wheelbase, and weighs without passengers 2775 lbs. on front tires and 2900 lbs. on rear tires. (a) Working from Rowell's paper quoted above we blocked the springs either end and bounced the car on its tires (33x6-3/4) one end at a time. (We ought to have bounced it off the tires on plain rims but since the method seems no good we have not gone further.) We got a frequency of 86 per minute at the rear and 118 in front. Sprung weights were taken as 2300 front and 2200 rear. Spring deflection (with 1" deflection added for the tires) was 4.1 front and 8.00 rear. Applying Rowell's formula:- K² = (b² N² - a² S) / (S - N²) (p.25, paper of March 1925) we get a value of 28 feet² for K². But very slight variations in the frequency will give enormously different values for K² or even make it negative. So we believe the above value is not much more than a guess, and the above method of obtaining K² to be worthless. | ||