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).
Front spring stiffness, negative camber, U-bolts, and load stresses.
| Identifier | ExFiles\Box 43\2\ Scan185 | |
| Date | 11th November 1926 | |
| Oy10-E-111126 -2- November 11, 1926. The variation in stiffening effect comes I think from (a) Relative flatness of the short leaf, (b) Degree of pull up on the U bolts (c) Position of spring when pulled up. We find it necessary to give the spring negative camber (say 1") before tightening, to get the clip really tight, and then to "exercise" the spring on the testing machine to let the plates settle into position. It is worth noting however that with the U bolt prongs 2-3/4" apart, and assuming that 2-3/4" at the center of the spring is made inactive by the clip, the stiffening effect should theoretically be about 14%. The stiffness figure we use is the average of two readings 1" either side of the flat position. With this effect and the inclined front shackle I should suppose that to get R.{Sir Henry Royce}'s figure of 30°, the spring as tested on rollers without the clip should have a stiffness not more than 25% of the load (4" deflection). We actually have made a pair of 43-1/2" front springs (14 plate) with an initial stiffness of 26-1/2%, and found them to be changed to 30% by the action of the axle pad alone, without any allowance for inclined shackle. To get 4" deflection on the front spring implies normal load stresses of about 65,000 lbs./sq.in. and final stresses touching rubber possibly 100,000 lbs./sq.in. If we are to get the normal stress in the spring as low as possible we think the inclined front shackle is undesirable because it stiffens the spring without adding any metal to it, and therefore involves higher stresses in the metal for a given flexibility when attached to the car. These suggestions are offered for what they may be worth - possibly nothing. Yours very truly, Maurice Olley MO/E | ||