Locomotive Aero

[uphogger]

Makes sense, I reckon.  My experience with empty hoppers is that once I shut off the throttle, the train would immediately start slowing down at a much more rapid rate than any other type of train.  Probably one of the easiest trains to run.  OTOH, so is a DPU loaded train.  Had an experience once where we went through an interlocking (KO on the old CNW) with 135 cars for Pleasant Prairie, WI.  Two units on the point and one on the rear, we came across the next signal just around the curve at Upton and the junction with the EJ&E.  Normally, I would've brought her to a controlled stop because the track ahead was clear past the signal; however, there was no telling what was running on the J, so I set them up and then dumped them once she started to squat.  The results were absolutely flawless: she stopped smoothly just as sweet as you please.  Ended up it was a track inspector on the J not paying attention to the signals at the interlocking.  Got our air back and went on our way without incident.  Do I like DPU?  Oh, yeah.  But I only work passenger now.

[cefinkjr]

uphogger

Case in point is an empty coal hopper train.  Those open cars are like having 135 (or however many) drogue 'chutes trailing behind you.

Interesting point, uphogger.  Loaded cars would then have less air resistance but that would, of course, be more than countered by the additional weight.

 

Tests on the NYC in the late '60s (or early '70s?) demonstrated that the Central's FlexiVans had significantly less air resistance than an equal number of conventional piggy back cars.  That space between the underside of the trailer and the flat car deck created something of a vacuum like a "drogue 'chute", similar to the space between two box cars but worse.  Add that to the height and weight reduction in leaving the trailer bogie behind and you understand why railroads prefer containers to trailers.

[uphogger]

jrbernier

  The blunt end of a loco has little effect on the overall train speed.  Think of a train as a long shaft - the overall size of the 'point' is quite small in proportion  to the length.  There is more drag from the space between the cars.

Jim

Case in point is an empty coal hopper train.  Those open cars are like having 135 (or however many) drogue 'chutes trailing behind you.

[jrbernier]

  The blunt end of a loco has little effect on the overall train speed.  Think of a train as a long shaft - the overall size of the 'point' is quite small in proportion  to the length.  There is more drag from the space between the cars.

Jim

[ndbprr]

Whay should the engine be aerodynamic when the rest of the train is not?  Gaps between cars and car shapes create tremendous drag to the point the little gained from aerodynamics on the engine is offset by making it more hazardous for the crew to mount and dismount.  Safety first.  Ask any crew what effect a crosswind has on train speed or cold temperatures on wheel bearings.  They can affect a train to the point it is hard to even get it rolling and are of much more practical problems.

[oltmannd]

Acela026

How big a factor is aerodynamics in locomotive design? ... but what about freight locomotives like the ES44AC?

Thanks! Acela

Almost none.  It's a really tiny factor at the speeds freight trains run.

[Acela026]

How big a factor is aerodynamics in locomotive design? Passenger locomotives like the P32AC-DM Genesis probably have a more thought in their design, but what about freight locomotives like the ES44AC?

Thanks! Acela