ON THE RESISTANCE OF ROAD VEHICLES TO TRACTION. 3G5 



The Resistance of Hood Vehicles to Tfactimi. — Report of the Committee, 



consistinrj of Sir J. I. Thornycroft (Ghairman)^ Professor H. S. 



HELE-SifAW (Secretary), Mr. T. AiTKEN, Mr. T. 0. Aveling 



(Treamrer), Professor T, Hudson Beare, Mr. W. Worby 



Beaumont, Mr. J. Brown, Colonel R. E. B. Crompton, Mr. B. J. 



DiPLocK, Mr, A. Mallock, Professor J. Perry, Sir D. Salomons, 



Mr. A. 11. Sennett, and Mr. E. Shrapnell Smith. (Drawn W2'> 



at the re<p.iest of the Committee, hy the Secretary^ assisted by Mr. 



J. F. Gill, B.Sc.) 



[Plate XI.] 



Contents. 



PARE 



1. Results of Trials viadv with Committer's Bynamometn- 365 



n. fhiggestions hij Mr. B. J. Dijflock 3(59 



III. Papers read at the Second Intenmtional Cunf/reas oti Automohilism, Paris, 



1903 ' 372 



IV. Negotiations with the War Office 377 



I. Results of Trials made tvith Committee's Dynamometer, 



In the last Report the new dynamometer made for the Committee was 

 described and illustrated, together with an account of the calibration of 

 the apparatus. 



It will have been noticed in the drawing of the instrument that a 

 small screw-down valve was fixed in the circuit of tube which transmits 

 the pressure from the plunger to the recording gauge, this valve being 

 for the purpose of throttling the flow of water, and thus damping the 

 oscillations of the pencil. The principal dimensions of the valve are as{ 

 follows : — 



Width of seat -008 inch 



Smallest diameter of seat . . . 4 . 159.') „ 



Largest ,, ...... ■I((9r5 ,) 



Pitch of screw '046 >, 



It was fouiid that to produce suthcient damping action it was necessary 

 to have this valve off its seat by an amount of not more than '01 5.3 inch. 



It was pointed out by Mi-. A. Mallock, F.R.S., of London (a member 

 of this Committee), that the flow under a constant pressure of a Muid 

 through a thin film-like orifice such as this, might be different in one 

 direction to what it would be when flowing in a reverse direction, owing 

 to the stream-line formation not being symmetrical about the constriction. 



If such were the case the true mean pressure would not be recorded, 

 but some pressure, either greater or less than the true mean, according to 

 which side of the valve was next to the plunger. 



Experiments were made to determine the minimum orifice that might 

 be used, and it was found that equal flow from either side did not occur 

 until the valve was opened by at least half a turn, this corresponding to 

 the valve being raised from its seat a distance of "023 inch. So that there 

 should be no doubt about the orifice being too small, the experiments 

 were conducted with the valve open by a considerable amount, the 

 damping action being obtained by squeezing the rubber tube which 

 connected the gauge to the dynamometer by suitable clips placed on the 

 tube some distance from any change in cross -section. By this means the 



