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).
Frame deflection and body mounting issues on the 20 HP Goshawk II chassis, proposing a new design.
| Identifier | ExFiles\Box 41\3\ Scan374 | |
| Date | 29th September 1923 | |
| V3730 To LHS{Lord Herbert Scott}, from DA{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork} c. to CJ. HS.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} DA{Bernard Day - Chassis Design}/EV{Ivan Evernden - coachwork}1/M29.9.23. RE. FRAME DEFLECTION & BODY MOUNTING - X.3730 GOSHAWK II. X.3729.X.4260 Derby have fitted up a 20 HP. chassis with tie-bars similar in design to those on the 40/50 and having loaded the chassis until the springs were on maximum bump, have measured the deflections of the side channels both with and without tiebars. The results seem to shew that the tiebars reduce the deflections by 35%. A large amount of deflection occurs aft of the front end of the rear spring(at the joggle in the frame) and we have asked Derby to make further experiments, carrying the tiebars back to the centre line of the axle if possible. To obtain a tiebar system on G.II. with half elliptic springs as effective as on our 40/50 having cantilever springs we think that this condition is essential. With the present system of body mounting in which the runners are bolted to the chassis at 5 places along their length, the frame as it bends and twists due to the surface variations of the road pulls the body about with it. Coachbuilders are ironing and strengthening their bodies to help them to withstand this racking, but so great and incessant are the forces that they can never hope to make a body strong enough to retain the frame flat against it. We are therefore inclined to think that the theoretical method of dealing with the problem would be to entirely relieve the body of chassis deflections, and so permitting of lighter construction in the body itself. With our DA{Bernard Day - Chassis Design}1/M29.9.23., we sent Derby a design of body runner stiffener enabling the body to be carried on four brackets, two fore, and two aft, the runners being bolted directly to the rear brackets, but resting on rubber pads in the front, and are held down by a spring load. Taking a maximum body weight of 1000 lbs, and quota of passengers and luggage of 1000 lbs.(2000 lbs. in all) distributed uniformly, the deflection is about .06", or about half the present frame deflection on maximum bump. At least .030" of this is permanent due to the dead weight of the body, the deflection due to the fluctuating load of passengers being .030". The normal travelling range of deflection due to road variations would be approximately .060" to .120". It will be understood that these deflections are much less frequent and more slowly applied than those of the writhing main frame whose deflections are .400 (maximum). The weight of the stiffener is approx. 17 lbs. and is about equal to the weight of wood and iron saved on the body runner and body irons, together with the reduced number of chassis brackets, whilst the stiffness of the channel contd:- | ||