On Wednesday, 20 August 2014 08:06:04 UTC+2, Glen Labah  wrote:   
   > In article , bob  wrote:   
   >    
   > > To get the necessary performance, the RDC needed two engines.  Each was    
   > > a 6 cylinder 10.8 L 275 hp (later models 300 hp).  A modern engine of a    
   > > similar size might be the MTU 6R 183 TD, with 6 cylinder, 11 L, 422 hp    
   > > and meeting modern emissions standards.  Larger engines are available,    
   > > for example the Cummins QSK19, a 19 L 6 cylinder 750 hp engine used in    
   > > a number of under-floor engine DMUs.  I can't find figures for fuel    
   > > consumption, but I'll wager the modern engines are significantly    
   > > better.  Twin engine DMU vehicless are definitely a thing of the past.   
   >    
   > The thing is that with FRA car bodies the 422 hp would probably not be    
   > enough.  The newest LIRR EMU cars are somewhere around 1,200 horsepower    
   > to meet the performance they want.   
      
   It's the nature of the technology that electric traction will always be able   
   to pack far more power into a given size/weight than a diesel prime mover.    
   For European type operations, somewhere in the 500 hp/vehicle range is   
   adequate for 100 mph operation    
   and 750 hp/vehicle is adequate for 125 mph.  That's based on a ~45 Tonne   
   vehicle weight.  This is entirely within the capabilities of current   
   off-the-shelf under-floor engines[1].   
      
   > The Budd RDC also drove the inside axle of each truck, so at least two    
   > axles were driven.   
   >    
   > With a single engine, would you transmit the power to two trucks?  Or    
   > would you transmit it to a single truck and link the axles so that both    
   > axles on that truck are powered?   
      
   Common practice in Britain is for 2 axles per vehicle to be powered (giving   
   50% powered axles).  That's good enough for commuter-train levels of   
   acceleration, and in the kinds of routes where DMUs are common, 25% powered   
   axles would not pose a problem (   
   ie a single powered axle per car).  Considering that a locomotive hauling 6   
   cars only has 14% powered axles, even 25% is a huge improvement.   
      
   [1] with the caveat that new EU emissions regulations have just come in, and   
   the existing designs are not yet conformal.   
      
   Robin   
      
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