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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).
The torsional stiffness of Humber, Hillman, and Sunbeam-Talbot car frames.

Identifier  ExFiles\Box 113\5\  scan0075
Date  24th November 1938
  
1010

Ref. from Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions}
C.c. HY{Tom Haldenby - Plant Engineer}, Rm{William Robotham - Chief Engineer}, Rm{William Robotham - Chief Engineer}/AFM{Anthony F. Martindale}, Ex, Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions}

Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions}1/G.24.11.38.

HUMBER, HILLMAN AND SUNBEAM-TALBOT FRAMES.

I mentioned in my report on this year's Motor Show that Rubery Owen's had promised to send on to me some particulars of the frames of the above cars, and these have now arrived. The particulars relate to the Hillman 14 H.P., the Humber 16 H.P., Snipe and Super Snipe, and Sunbeam-Talbot 3 and 4 Litre cars, and the accompanying table gives the torsional stiffnesses of the three frames.

The method of obtaining the figures was to hold the rear end of the frame, at the rear crossmember; and then to apply torque at a point 11 feet in front of this, by means of a cross bar supported in the middle of the frame and loaded at one side. The loads applied are expressed as torque twisting the frame, and the deflections as angles, over the 11 foot length measured.

According to published figures, the Hillman 14 and Humber 16, Snipe and Super Snipe all have 9'6" wheelbases, while the Sunbeam-Talbot 3 and 4 Litre cars have a 9'10" wheelbase. The twist figures are then accordingly reduced from the 11 foot length to the wheelbase of the particular car in question by simple proportion, a method which will probably give a rather low reading for the frame stiffness between the axle planes as the frame extremities are likely to be less stiff than the centre part. No account is taken of frame hysteresis, which apparently will also make the stiffness figures read low.

If the frame with I section cross were extended to the B.111 length (10'4" wheelbase instead of 9'10") the torsional stiffness would be 905 lbs.ft./degree, and the weight approximately 220 lbs. Increase of stiffness to the B.111 figure given in a report of Rm{William Robotham - Chief Engineer}/Clapham of 25.10.37, for a welded frame of 1420 lbs ft./degree, by increase of gauge of material would increase the weight to 345 lbs. as compared with the 266 lbs. of the B.111 frame. The difference here seems to be due to the side members and cross of the Sunbeam-Talbot frames being appreciably shallower than those of the B.111, and also the side members being boxed in over their whole length.

If the gauge of the lengthened Sunbeam-Talbot frame is increased only enough to equal the stiffness of the bolted B.111 frame, 1150 lbs.ft/degree, the weight would be 280 lbs. i.e. in other words a difference in stiffness corresponding to a weight increase of 65 lbs. can be obtained merely by welding.

Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions}
  
  


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