# How to use *Tractive* in a sentence

Thus the diagram shows the

**tractive**force at any instant.Moreover, the average

**tractive**power per locomotive and the average capacity per freight car advanced greatly in this period, although specific figures cannot be given.There are certain fundamental relations common to all

**tractive**problems, and these are briefly considered in §§ i and 2, after which the article refers particularly to steam locomotives, although §§ 4, 5, 7, 8, 9, and 10 have a general application to all modes of traction.The fundamental condition governing the design of all

**tractive**machinery is that the wheels belonging to the axles to which torque is applied shall roll along the rails without slipping, and exert a**tractive**force on the train.The fundamental relation between the applied torque and the

**tractive**force F will be understood from fig.AdvertisementIn the first case all the driving is done on one or at most two axles, sufficient

**tractive**force being obtained by coupling these axles when necessary to others carrying heavy loads.Thus if the maximum horse-power which a locomotive can develop is woo, the

**tractive**resistance R, at 60 m.A side wind causes excessive flange friction on the leeward side of the train, and increases the

**tractive**resistances therefore very considerably, even though its velocity be relatively moderate.To obtain the

**tractive**force the weight on the coupled wheels must be about five times this amount - that is..Dividing thr Hugh by V and multiplying through by 550, 2240W 2240Wa R =Were+W vry t G (23) ' 'an expression giving the value of R the total

**tractive**resistance.AdvertisementFirst, it must be able to exert a

**tractive**force sufficient to start the train under the worst conditions possible on the railway over which it is to operate - for instance, when the train is stopped by signal on a rising gradient where the track is curved and fitted with a guard-rail.If p is the mean pressure at any speed the total

**tractive**force which the engine is exerting is given by equation (25) above.Then the

**tractive**force is, from (25), (149 X 19 2 X2.166)/6.25 =18,600lb =8.3 tons.The engine can only exert this large

**tractive**force so long as the mean pressure is maintained at 149 lb per square inch.Thus although at a slow speed the engine can exert a

**tractive**force of 18,600 lb, at 60 m.AdvertisementIt will be seen at once that with a

**tractive**force of 7400 lb a weight of 37,000 lb (=16.5 tons) would be enough to secure sufficient adhesion, and this could be easily carried on one axle.When the road leads the train up an incline, however, the

**tractive**force must be increased, so that the need for coupled wheels soon arises if the road is at all a heavy one.It is used to a limited extent for mountain-grade goods traffic, and has the advantage over the " Consolidation " or eight-coupled type of lighter axle loads for a given

**tractive**capacity.**Tractive**Force of a Magnet.-Closely connected with the results just discussed is the question what is the greatest**tractive**force that can be exerted by a magnet.If H could be increased without limit, so also could the

**tractive**force.AdvertisementWebb to measure the

**tractive**resistance of trains on the London & North-Western railway, a**tractive**pull or push compresses two spiral springs by a definite amount, which is recorded to scale by a pencil on a sheet of paper, drawn continuously from a storage drum at the rate of 3 in.Coupling Rod These couple driving wheels of the same size together to spread the

**tractive**effort over the coupled wheelbase.The torque corresponding to this couple is F 1 X z D = 2µWID, and hence follows the fundamental relation, 2T = 2F 1 D = 2µWID, or if W now represents the weight supported by the axle, F will be the

**tractive**force exerted on the frame by the two axle-boxes to propel the vehicle, and the more convenient relation is established, T=2FD=2µWD (3) If T has a greater value than this relation justifies the wheels will slip. F is called the "**tractive**force " at the rail.The magnitude of F when p and e are put each equal to unity, is usually called the

**tractive**force of the locomotive per pound of mean effective pressure in the cylinders.There are two steel-clad series-wound motors of 36 B.H.P. For a test load of 120 tons the

**tractive**force is 70 lb per ton, which is sufficient for acceleration, and maintaining speed against wind pressure.Advertisement