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).
Graph showing parking efficiency versus helix angle for different friction coefficients (μ).
| Identifier | ExFiles\Box 67\4\ scan0338 | |
| Date | 14th July 1927 guessed | |
| FIG. VII PARKING. Y-Axis: EFFICIENCY %σ Values: 90, 80, 70, 60, 50, 40, 30, 20, 10 X-Axis: HELIX ANGLE θ. Values: 5°, 10°, 15°, 20° Curves: μ = .050 μ = .100 μ = .150 | ||