ON THE RESISTANCE OF ROAD VEHICLES TO TRACTION. 3lo 



Xlir. Description and Drmvings of the New Dynamometer made for 

 the British Association Committee to carry on the Researches. 



The general arrangement of the new dynamometer made for the Com- 

 mittee to carry out the researches on road resistances is shown in Plate III. 

 The apparatus comprises a castor frame, AA, in which can be mounted 

 the wheel, B, to be experimented on, a system of levers, CC, for transmitting 

 to a small plunger, E, the pull exerted on the wheel, and a recording 

 pressure-gauge for registering the same, together with a recoi'ding tacho- 

 meter. 



Frame. — The castor frame is of wrought iron and is rectangular in 

 shape. Its sides are of channel iron, 4 inches by 2 inches by \ inch, and are 

 fastened together at the end by wrought-iron plates, ^ inch thick and 

 5 inches wide, bolted on at the top and bottom. The total length of the 

 frame is 6 feet, and as the end plates have three sets of holes drilled in 

 them, it can be arranged so that the sides are 10 inches, 14 inches, or 

 18 inches apart, to suit the various widths of wheels to be experimented 

 upon. 



Axle and springs. — The axle of the experimental wheel is mounted on 

 springs, one under each side of the castor frame. The springs are 3 feet 

 2 inches centres, and each consists of six plates 2^ inches by y\j inch. 

 When light wheels and loads are used these springs are reduced to a 

 suitable strength by the removal of some of the plates. If desired the 

 axle can be mounted on the frame without springs. 



Loading. — Tiie method of loading the frame is by bolting a series of 

 28-lb. cast-iron weights to the channel-iron sides. These weights are 

 each 2 inches thick, so that when the scroll irons for the si^rings do not 

 interfere, fifty -two or so can be affixed, thus giving a load of 13 cwt., 

 besides the weight of the frame and wheel. This would correspond to a 

 load of about 3^ tons on a four-wheeled vehicle. This arrangement of 

 loading enables the weight to be varied by steps of 56 lb., the weights 

 always being arranged at equal distances on either side of the centre, so 

 that the frame will never be out of balance. 



Attachment of frame to car. — This frame is fixed to the levers which 

 transmit the force to the water by a swivel joint, D, so that it is quite 

 free to vibrate or bounce vertically as over rough ground ; and it can also 

 follow the car freely round any curve without in any way affecting 

 the records, but it is held so that the experimental wheel is always 

 vertical. 



Levers. — The system of levers is so arranged that the frame can be 

 raised or lowered to suit any diameter of wheel or any angle of draught 

 without in any way altering the leverage of the mechanism. They may 

 be described as follows. 



A pair of similar bell-crank levers is mounted on a fulcrum which is 

 capable of being raised or lowered in a vertical slot formed in a steel 

 casting mounted firmly on the back of the car. The distances from this 

 fulcrum to the ends of levers ai'e respectively 14 inches and 28 inches, 

 the longer arm being normally vertical, while the other is horizontal. To 

 the shorter arm are attached two parallel vertical steel rods whose length 

 is capable of adjustment. These rods serve to transmit the pull on the 

 frame to one end of a small horizontal lever, the hydraulic plunger being 

 at its other extremity. The fulcrum of this lever may be moved to either 



