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).
Page detailing the assumptions and calculations for cable speed and pull graphs, based on engine performance.
| Identifier | ExFiles\Box 175\2\ img132 | |
| Date | 31th May 1940 | |
| -2- EV{Ivan Evernden - coachwork}/DB.{Donald Bastow - Suspensions}5/JH.31.5.4. drum sizes and gear ratios. In order to make the picture as easy to follow as possible the graphs of cable speed and pull are plotted on a base of distance run from the commencement of the launch. It will be noticed that we have catered for approx. 4500 ft. of cable, this being the figure the G.I.S. people said they would like and more than their official minimum of 3500 ft. The initial part of the graph is based on the full engine speed of 4000 r.p.m. being attained in the first layer of cable (less some 9 turns left on permanently for cable attachment and adhesion). If this condition is not fulfilled the commencement of the main part of the curves of pull and speed will occur rather further over to the right. As an example of what this means, with the 10" drum and 2.96 ratio a weight of towed object plus cable of 7220 lbs. can be accelerated to 4000 engine r.p.m. in the first layer of cable, and with the 12" drum and 2.225 ratio the corresponding figure is 2180 lbs. The weight of 4500 ft. of cable is about 950 lbs. The reason for showing the pull and speed curves as narrow bands is that actually they would go up in a series of steps, one step for each layer of cable, and as the step from one layer to the next would be of indeterminate shape a band is shown covering the extremes of the steps. Assumption made in making the calculations are:- Phantom III engine power and torque as for E.A. Hall Unit curve S67 Mechanical efficiency of outfit 94% Fluid coupling slip curve deduced from figures supplied by Hydraulic Coupling & Engineering Co. Ltd. Loss of efficiency due to fluid coupling is not included in the 94% efficiency mentioned above. Engine r.p.m. restricted to 4000. EV{Ivan Evernden - coachwork}/DB.{Donald Bastow - Suspensions} FB | ||