Truckers

[RH77]

Originally Posted by trebuchet03

Arg... I really hate statements like this...

Yeah, that sounds to be an oversimplified statement -- probably to appeal to city-only drivers to focus mostly on tires, etc. The graph doesn't seem to equate. I used the x=0 as well (which is confirmed by the legend). Probably what their doing is stating that aero and tires are equal at 50, but is actually double, which negates the x=0 assumption of evenness -- which happens at, what ~18 mph?

Originally Posted by Big Dave

Even the UP's Sherman Hill grade and CSX' Cheviot Hill got bypassed.

The UP/BNSF Cajon Pass (~11%) and Tehachapi Loop series at 2.2% is also a tricky combination. But -- it's the main passage from LA to points East (big Intermodal traffic) so they keep rolling. Risky business.

The train at the top of the hill is released and goes into dynamic braking and feeding the electricity back into the catenary, where the climbing train can use it. Very efficient.

That sounds like a great idea -- aside from the cost, the fuel saved on the ascent would pay for itself quickly.

[trebuchet03]

Originally Posted by RH77

Yeah, that sounds to be an oversimplified statement -- probably to appeal to city-only drivers to focus mostly on tires, etc. The graph doesn't seem to equate. I used the x=0 as well (which is confirmed by the legend). Probably what their doing is stating that aero and tires are equal at 50, but is actually double, which negates the x=0 assumption of evenness -- which happens at, what ~18 mph?

I figured it out... Zero is at the line of the item below the one you're looking at. The zero for tires occurs at the top of "other" and the zero for aero occurs at the line for tires. When you calculate the range based on that - it matches the data written (and a graph a few pages down)...

A poor method to communicate data

[roflwaffle]

Originally Posted by trebuchet03

And that said - according to that chart - aero beats tires around 20mph.. what gives? I may be reading that chart wrong (whenever I use a chart like that - the x axis is zero for everything)...

The one right over the 50mph quote, right? It seems about right according to the graph. At 50mph aero power is about the same (It looks it be slightly less, but not by much) as rolling power, and after that aero becomes a larger component by a wide margin.

Edit-OIC! Yeah, that's a funny way to graph it but it allows people who don't have experience with graphs to see the breakdown and differences.

That being said, since IME, a lot of transport companies, such as LTLs, tend to run their trucks at less than 80,000lbs GCW, the point where aero drag is the same as rolling is probably ~30-40mph.

[roflwaffle]

Oh, and the reason why I'm seeing grocery trucks doing 50-55mph consistently is because their GCW is probably less than half of the 80,000lb GCW Cummins assumed, so at 65mph the ratio of aerodynamic to rolling drag is probably about three or four to one as opposed one and a half to one, meaning that as long as they use their gearing well, dropping 15mph probably increases fuel efficiency by ~30-45%. As diesel prices increase/hold, even hedging will become harder, so I imagine carriers will start driving efficiently in greater numbers.

[Arminius]

Look what I found: http://www.alternative-energy-news.i...hybrid-helper/

[Figjam74]

Maybe they should build them like this.



Yes, it was a 727, now it's a limousine with seating for 50, top speed of 124mph (200kph) and runs on a 6 cylinder turbo-charged diesel.

[Chris D.]

picture no worky

[trikkonceptz]

After all this reading I thought about this ... The gap between truck cab and trailer is quite large and no doubt impacts efficiency. What if at highway speeds the fifth wheel was able to draw the trailer closer to the cab thus eliminating or reducing the gap and improving MPG's. I guess a technology very similar to the porsche tails or the VW turbo wing, just on a larger scale.

[Patrick]

Here's an interesting SAE paper on aeromodding big rigs: http://www.solusinc.com/pdf/2003-01-3377.pdf

And here's their website with links to their products in the lefthand column: http://www.solusinc.com/index.html

[Big Dave]

I think Cajon Pass grade is 1.1%. The theoretical max grade for steel wheels on sanded steel rail is about 6% for the locomotive only.

As a rule one uses a cog railway in excess of 5%.

Back on topic, it would astound you how far trains can coast. Quite often you pass the "ruling grade" and coast 50-70 miles or more to the division point. For instance on the old B&O (now CSX) St. Louis division the ruling grade westbound was at Loogootee Indiana. Once over this grade, the train coasted all the way to Cone Yard in East St. Louis. Yep. The train coasted all the way across Illinois and was on the brakes just outside Cone.

Trains are 4-8 times as fuel efficient as rubber-tired vehicles, but they are terrible for door-to-door service.