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).
Calculation of the effect of wheel rotation on braking, comparing translational and rotational kinetic energy.
| Identifier | ExFiles\Box 5\3\ 03-page072 | |
| Date | 28th December 1922 | |
| X4257 28.12.22. EFFECT OF WHEEL ROTATION ON BREAKING. GII (No account taken of brake drums.) Kinetic Energy of translation of car at 60 m.p.h. .= 1/2 m v^2 / g ft. lbs. m = 4000 lbs, v = 88f.p.s. g = 32.fts^2 = (2000 X 88 X 88) / 32 = 484,000 ft.lbs. Kinetic energy of car = 484,000 ft.lbs. Kinetic Energy of Rotation of one wheel at 60 m.p.h. .= 1/2 I ω^2 / g ft.lbs. where I = movement of inertia ω = angular velocity.(rads per sec) Now for a wheel I = M a^2 / 2 Where M = mass of wheel, a = semi axis perp. to motion. and M = 71 lbs., a = approx. 17 ins. ∴ I = (71 X 17 X 17 X 1) / (12 * 12 * 2) = 71 approx. Also ω = v / r = 88 / 1.42 = 60 approx. .= 1/2 I ω^2 / g = (71 X 60 X 60) / (32 X 2) = 4,000 ft.lbs. K.E. of rotation of all 4 wheels = 16,000 ft.lbs. approx. ∴ % of K.E. attributable to wheel rotation = (16 X 100) / 500 = 16/5 = 3.2% Rm{William Robotham - Chief Engineer} | ||