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).
Comparing frame flexibility and 'jellying' on the J.III model versus the standard 25 HP.
| Identifier | ExFiles\Box 104\3\ scan0160 | |
| Date | 8th June 1932 | |
| YS380 To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Les.{Ivan A. Leslie} c. to Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. to E.{Mr Elliott - Chief Engineer} Dn. c. to Hy.{Tom Haldenby - Plant Engineer} Hs{Lord Ernest Hives - Chair}/Les.7/KT. 8.6.32. J.III. FRAME The frame jellying of J.III is worse than a standard 25 HP. It has been therefore questioned as to whether the front of the frame is more flexible on J.III than a 25 HP. Difficulty in closing the bonnet when one wheel is on the curb and bonnets knocking on the scuttle are direct evidence of the frame flexing. To avoid these troubles a greater clearance is necessary between the bonnet and radiator, and the bonnet and scuttle. Large bonnet clearances are unsightly. We have taken measurements of different chassis showing the movement of the bonnet when the diagonal road wheels are raised 3" from the ground. From the figures we find that T.2. with a solid radiator mounting is considerably the worst. On the road the centre radiator mounting overcomes the majority of the movement. The figures are surprising with regard to J.III, for we find that the average bonnet movements are under half that of a 25 HP. Therefore no unsightly bonnet clearance is necessary for J.III. From our road experiences of jellying the only real progress has been made by damping the front of the frame from the inertia of the engine or radiator and engine combined. Such damping also improves the steering. We think that a weak frame requires less to damp it than a rigid frame, unless the frame is made so immensely rigid that no damping is necessary. With flexible engine mountings a very rigid frame is practically impossible. On the road we should be inclined to say that J.III gives the impression of a stiff frame with no damping. That is that J.III requires slightly inferior road surfaces to excite the frame, but when it is excited the amplitude and time before it regains steadiness is greater than a 25 HP. Owing to the extreme flexibility of the front engine bearers of J.III no appreciable change c ont'd | ||