200 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Jii.v, 



deep. The axle was plnced across t'lc top of the shaft 9nd carried 

 l>y two l)carinjrs with bras? steps; tlie wheel under experiment was 

 fixed on one end of the axle outside tlie bearing, and the counter 

 connected to tlie other end of the axle. The counter was so ffr:\- 

 diiated and arranged that the most correct observation could be 

 taken of the number of revolutions completed in each case. 



A drum 2 ft. 3j in. diameter was fixed on the centre of the axle, 

 and a rope g-inch diameter was coiled on the drum, with the mov- 

 ng weight attached to tlio end of it hanging over the centre o f 

 tlie shaft; the other end was not attached to the drum, but held 

 only by the grip of the second turn of the rope, so that when the 

 rope was run off the drum by the weight falling to the bottom of 

 tlie shaft, the end of the rope detached itself from the drum with- 

 out any check. As there was not any means of descending the 

 shaft to bring up the rope and weight, a tail rope of the same 

 length and size as the main rope was attached to the weight at 

 one end, and the other end made fast at the top of the shaft, the 

 rope hanging double halfway down the shaft; this served to bring 

 up the weight and main rope after they had fallen to tlie bottom 

 of the shaft in each experiment. These two ropes weighed 7 lb. 

 each, and the weight of the main rope caused a gradual accelera- 

 tion in tlie moving weight, varying from nothing at the beginning 

 of th» descent to 7 lb. at the end; whilst the tail rope acting at 

 ta-st with half its weight, caused an increase varying from 34 lb. to 

 nothing at the end. The result was therefore, a total increase of 

 the moving power varying from 3g lb. at the beginning of the 

 fall to 7 lb. at the end; and as this was the same in each case and 

 the moving weight was also the same (5() lb.), its effect may be 

 neglected in ascertiiining the comparative results for the present 

 pui-pose. 



The wheels tried in the experiments were one of the solid 

 wrought-iron disc wheels, a wrought-iron flat-spoked wheel of 

 Losh's pattern, with spokes 3^ inches broad, and a wrought-iron 

 flat-spoked wheel of Iladdan's pattern, with spokes 3^',^ inches 

 broad. These wheels were selected as near the same weight as 

 was practicable, the Losh's wheel being one-length heavier than 

 the disc wheel, and the Haddan's wheel one-forty-sixtli heavier 

 than the disc wheel. All the wheels were 3 feet diameter. 



Deducting in each case the 14 seconds during which the power 

 was in action, the results are 46 seconds with Lush's wheel and 

 .53 seconds with the disc wheel, for the time of motion after the 

 power was detached; which are in the proportion of 100 to 115, 

 showing that 15 per cent, more resistance was experienced by the 

 spoke wheel than by the disc wheel. 



The average result from both sets of experiments is 16| per cent, 

 difference of resistance in favour of the disc wheel, and this is at- 

 tributable to the additional resistance of the air caused by the Hat 

 spokes of the spoke wheel, as the friction of the axle caused the 

 same resistance in each case, the weight being nearly the same of 

 each wheel; and to prevent any change in the friction of the axle, 

 the wheels were changed without taking the axle out of its bear- 

 ings during the experiments. The axle journals were 2^ inches 

 diameter and 2,3 inches length; and the friction of the journals 

 was overcome by a weight of 15,^ lb. acting on the drum when the 

 •wheel was upon the axle, and by a weight of S| lb. when the wheel 

 was taken off. 



As these experiments were made with wheels revolving on a sta- 

 tionary axle, it is requisite to consider what would be the compa- 

 rative effect if the wheels were rolling on their circumference 

 whilst revolving at the same rate on their axle, as in the practical 

 case of the wheels of railway carriages running on a railway. In 

 the former case the motion of the spokes is at a uniform velocity, 

 and always at right angles to the direction of the spokes; but in 

 the latter case of a rolling wheel the motion of the spokes is at a 

 varying velocity, and always inclined obliquely to the direction of 

 the spokes, except at the moment of each spoke being in the verti- 

 cal position. This is illustrated by the accompanying engraving, 

 where the successive positions of'^ the spokes are shown. The 

 outer ends of the spokes move in a cycloidal curve, having double 

 the velocity of the revolution of the wheel when they arrive at 

 the top of the wheel, but becoming stationary at the moment of 

 touching the rail at the bottom of the wheel. The average velocity 

 of the outer ends of the spokes is about 1:1 times greater than 

 when the wheel revolves on a stationary axle at the same rate of 

 revolution. The average velocity of the inner ends of the spokes 

 is about 3 times greater when rolling than when revolving on a 

 stationary axle. As the resistance of the air increases in propor- 

 tion to tlie square of the velocity, the average resistance to the 

 outer and inner ends of the spokes will be about U and 9 times 

 respectively greater in the former than in the latteV case. ' But' 

 this is reduced by the oblique position of the spokes as regards 



the direction of their motion in the rolling wheel; the motion of 

 the spokes being twice dur^ig each revolution in the direction of 

 the spokes, and consequently the resistance of the air reduced to 

 nothing at those points. By measuring upon the diagram the com- 

 parative velocity of several jioints in a spoke in various positions 

 during a complete revolution of the wheel, and the inclination of 

 the spoke to the direction in each of these positions, the following 

 approximate result has been obtained: — that the total resistance of 

 the air to the spokes when the wheel is rolling is 3 times the total 

 resistance to the same spokes when the wheel is revolving at the 

 same rate of revolution on a stationary axle. 



It follows that the result of the foregoing experiments has to be 

 multiplied by 3, and consequently the excess of the resistance of 

 the air to the spoke wheel over the disc wheel would have been 

 3 times I65, or i9^ per cent., if the wheels had been rolling in this 

 case instead of revolving on a stationary axle. This excess of 

 resistance of the spoke wheel would not be so great in the practi- 

 cal case of the wheels of a railway carriage running on a railway, 

 as the friction of the axle journals is greater in that case than in 

 the experiments, from the weight pressing upon them being 

 greater; and consequently the resistance of the air to the spokes 

 of the wheel would then bear a less proportion to the friction of 

 the axle journals. 



Remarks made at the Meeting after the reading of the foregoing Paper. 



Mr. M'CoNNELL said, he had tried two pairs of these wheel centres at 

 W'olverton, and had found them perfectly solid, and they were an excellent 

 job ; they were for the leading and trailing wheels of an engine 3 ft. 9 in. 

 diameter. 



Mr. Smith said, in answer to questions, that his hammer with which the 

 wheels were forged was rather more than 9 tons weight ; it was a helve tak- 

 ing up under the belly, and was driven by bands. The weight of the finished 

 disc wheel was about 4J cwt. ; it was made with the first tools that he had 

 started with, and he had adhered at present to his original section of wheel, 

 but he did not profess it to be the best form of section that might be 

 adopted. He had made ahout 200 of these wheels ; there were some now 

 at work on the Birmingham and Gloucester line, and he had an order to 

 prepare some for the travelling post-office to register the number of miles 

 run by them. As to the cost of the wheel, he was ready to put himself in 

 competition with other parties. 



The President remarked, that the durability or life of the body of the 

 wheel was so very much greater than that of the tyre of the vfheel, which 

 must be renewed when only about a tenth of the life of the wheel was gone, 

 and would then require a secondary process to put on the new tyre; and 

 consequently it appeared to him preferable not to incur any additional ex- 

 pense and trouble by forging the tyre on to the wheel, hut to manufacture 

 the disc alone, and put on a separate tyre in the first instance. 



Mr. Smith replied, that it was not any more trouble to forge the wheel 

 with the tyre than without it; it was easily done, and the cost of manufac. 

 turing the wheel would be less than putting on a separate tyre. There would 

 be a little more trouble and expense in relyring the wheel for the first time, 

 but he thought that the iron of the tyre would be much more durable than 

 any rolled tyre could be, on account of the process of manufacture. 



Mr. WooDHOusE asked what advantage the wheel would possess over a 

 cast-iron wheel if it were forged without the tyre ; but he thought there was 

 certainly danger of fracture from expansion in a cast-iron disc wheel. 



Mr. Beyer remarked, that he had seen some cast-iron wheels that he 

 thought would last as long as wrought-iron ones, and he never could under- 

 stand why they were not more used ; there were many wheels of cast iron, 

 even large driving-wheels of C feet diameter, that had been running many 

 years, and he thought it was an important question of economy in railways. 



The President observed, that when locomotive engines were began, some 

 25 years ago, they were driven to wrought-iron wheels, and thought it a 

 great advantage; and he thought that for rapid railway travelling, they must 

 admit, as a body of engineers, that wrought-iron was better than cast-iron 

 for such purposes. The present facilities for the manufacture of wrought- 

 iron bad been so >tiikingly shown to them on the present occasion, that he 

 thought it was hardly possible to save anything worth mentioning by the 

 adoption of cast-iron, particularly in the expense of a pair of large driving- 

 wheels. 



Mr. Smith said, he bad been informed that the tyres were found to wear 

 longer on solid wheels than on spoke wheels. 



The President remarked, that the tyre of large wheels would no doubt 

 deflect between the spokes, and this would not be the case with a disc wheel ; 

 there was certainly a bending process going on which might contribute to 

 the wear and ttar. But judging from the effects of rigidity in the wear of 

 rails, he thought the tyre would wear faster on a rigid wheel ; it was certain 

 that rails laid on a block road wear much faster than when laid on an elastic 

 road, and the dift'erence in their wear was very marked. 



Mr. MiDDLETON observed, that Mr. Ephraim Uoulton had a patent for a 

 disc weeel, and many of them had been used on the Great Western Radway, 

 but they were not approved, and were all cast aside. 



The President said he believed those wheels were a double disc, and the 

 tyre was riveted on; he understood that one principal reason for their being 

 discontinued, was the singular drum-like noise they made. 



