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 for the Goshawk 11 chassis, comparing tiebar systems and proposing a new body runner stiffener.
| Identifier | WestWitteringFiles\K\September1923\ Scan127 | |
| Date | 1st September 1923 | |
| TO LHS.{Lord Herbert Scott} FROM DA{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork} c. to GS. HS.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} ORIGINAL DA{Bernard Day - Chassis Design}/EV{Ivan Evernden - coachwork}1/M29. 9. 23. X3730 X3729 X4260 BODY RE. FRAME DEFLECTION & MOUNTING. GOSHAWK 11. Derby have fitted up a 20.HP. chassis with tiebars 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 the 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.11. 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/M29923. 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 approximately 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 beam is 9 times that of the wooden runner as is now used. Should however this beam be not stiff enough we can easily increase its stiffness 100% with only slight increase in weight. By attaching the body rigidly only at the extreme rear we do our best to relieve it of all engine vibrations, which is an advantage over the Daimler suspension. (1) | ||