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 vehicle steering behavior and handling characteristics under lateral acceleration at different speeds.
| Identifier | ExFiles\Box 170\3\ img125 | |
| Date | 17th November 1937 | |
| Mr. Grylls, Rolls Royce Limited, Derby. 17. 11. 37. We detect a slight effect between curves plotted against lateral acceleration at max 30 m.p.h. and max 60 m.p.h. It looks, from stop-press information, as though it will pay us to put a protractor on the steering column and read steering wheel angles as well as steering angles. By reducing the steering wheel angles in proportion to the steering ratio they can be plotted right on top of the steering angle curve. There are weird results so far unexplained, but certainly due to tendency of precession torque to reverse at higher lateral accelerations. (See rough sketch). (2). An entirely different approach to the problem of handling is concerned with the "Analysis of the Transient State," on which a vast amount of mathematics has been spilt in Detroit. One thing only sticks in my mind, i.e. that when a turn is starting the steering angle and front slip angle are identical. So that if the steering angle required for a steady turn is greater than the front slip the handling is stable, and if the steering angle for a steady turn is less than the front slip the steering is unstable. The argument is shown in attached chart which ignores possible changes in "attitude" due to traction at high speeds and simply draws a "fixed" curve for front slip, attitude, and roll, and then two lines representing Ackermann at 30 m.p.h. and 60 m.p.h. If I am driving at 30 m.p.h. and start to follow a curve which is going to call for .3g, the first thing I do is to set my front wheels over to about 5º. This gives me .5g lateral acceleration of the front end (actually rather more because the k²/ab ratio of the complete car in plan view is less than unity). As the car settles into the turn this angle is a bit inadequate and I have to advance the steering wheel to give 5.3/4 degrees. Suppose under similar conditions but at 60 m.p.h. I try to take a curve calling for .3g. To get this acceleration out of the front end immediately I have to set the wheels over to 5º as before. But almost instantly I have to come back to 3.1/2º otherwise I oversteer. -2- | ||