[ARC5] Locomotives

[D C _Mac_ Macdonald]

I should have been more specific. I was speaking of "drawbar pull." 
And also that it applied ONLY to the weight on driving wheels. 
  
* * * * * * * * * * * 
* 73 - Mac, K2GKK/5 * 
* (Since 30 Nov 53) * 
* k2gkk at hotmail.com * 
* Oklahoma City, OK * 
* USAF & FAA (Ret.) * 
* * * * * * * * * * * 
 
 
> From: 1oldlens1 at ix.netcom.com
> To: k1lky at earthlink.net; arc5 at mailman.qth.net
> Date: Wed, 19 Dec 2012 23:57:37 -0800
> Subject: Re: [ARC5] Locomotives
> 
> 
> ----- Original Message ----- 
> From: "Roy Morgan" <k1lky at earthlink.net>
> To: "ARC-5 List" <arc5 at mailman.qth.net>
> Sent: Wednesday, December 19, 2012 10:11 PM
> Subject: Re: [ARC5] Locomotives
> 
> 
> >
> > On Dec 19, 2012, at 10:46 PM, D C _Mac_ Macdonald wrote:
> >
> >> Added weight on the rails for any locomotive means
> >> that heavier train weights can be moved.
> >
> > Right on.
> >
> >> Friction
> >> coefficient of steel wheels on steel rails.. .25.
> >> This means that the maximum weight
> >> that can be moved .. is 25% of the weight of the loco.
> >
> > Actually, the maximum PULLING force would be a quarter of 
> > the weight of the locomotive. I'd expect the force 
> > needed to get a freight car going would be a small 
> > fraction of the weight of the thing.
> >
> > Rail yard workers used to use a long handled prying device 
> > to get a freight car started in motion. It was stuck 
> > under a wheel and the various lever actions provided 
> > mechanical advantage enough to roll a loaded car a short 
> > distance.
> >
> > Roy
> >
> > Roy Morgan
> > k1lky at earthlink.net
> > K1LKY Since 1958 - Keep 'em Glowing!
> >
> For long trains the locomotive could compress the 
> coupler springs in the draft gear by backing slowly, then 
> move forward slowly stretching the train out. That way the 
> train was started progressively.
> I am not sure of the physics of traction but I think 
> the available tractive force is greater than this suggests. 
> The maximum weight of a train that can be started depends on 
> the maximum tractive effort of the locomotive. This is where 
> electric motors are superior to a steam engine. An electric 
> motor can be made to have maximum torque at standstill, that 
> is the electric locomotive will have maximum tractive effort 
> from a standing start where a reciprocating steam locomotive 
> has relatively low starting tractive force and needs to get 
> some speed up to gain it.
> If you want to calculate the frictional forces at the 
> wheels keep in mind that both wheel and track are deformed 
> by the weight of the weight of the locomotive so that the 
> effective area in contact is larger than one might expect. 
> The adhesion between wheels and track depend on the weight 
> on the drivers. Some large steam locomotives had only about 
> half their weight on the drivers, the rest being carried by 
> non-powered trucks.
> Until pretty late horsepower was not considered 
> important, only tractive effort or force. It was Lima 
> Locomotive that first realized that horsepower was very 
> important and began making high horsepower locomotives. 
> These rapidly proved themselves in service so Baldwin and 
> Alco followed suit. This was about the mid-1920s.
> Even though diesel-electric or electric locomotives can 
> be coupled together to yield almost unlimited tractive 
> effort the amount of force that can be applied is limited by 
> the ability of the couplers to transmit it without breaking. 
> So, even with the greater ability to start a heavy train the 
> use of pusher-helpers continued to lessen the stress on the 
> cars.
> 
> 
> 
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com