Truckers

[LostCause]

Rolling resistance is usually a bigger issue than aerodynamics for semis. Rolling resistance is at their lowest when tires break in...dropping by significant margins as far as I remember. I wonder if LRR tires are being developed (exist?) for the industry...

I do agree that rail is more efficient than trucking, but isn't (large-scale) shipping even more efficient than rail? How about the marriage of the speed of air shipping, capacity of the trucking industry, low congestion of shipping, and some of the efficiency of rail...the ekranoplan.

Ekranoplan

http://www.youtube.com/watch?v=RwKi5...eature=related

Just a little off topic...

- LostCause

[brucey]

I dont plan on designing a new truck, I'm not working for peterbilt.

I was just thinking some simple stuff that anyone can do at home to to THEIR truck help ease the pain of the costs of diesel.

I was reading the papers today about how truckers actually are protesting. 80 truckers drove a couple hundred miles to protest at the state capitol.... I wonder sometimes what they think burning up extra gas, not doing any actual work, and demanding special treatment about something that isn't under the capitols control is going to do.

But oh well, its America. That **** flies all the time.

[elhigh]

I don't agree that rolling resistance is a bigger issue, though it's pretty obvious that with 18 wheels, there's a heck of a lot more rolling resistance on a truck than a car. Add a full load and it gets worse.

With those big gaps, the enormous open belly with girders and spares and tanks hanging in the breeze, and the bluff nose and tail, the aero of a truck is accurately described as "brick-like," if the brick had a few extra cracks added to it.

My understanding is that rolling resistance increases as a linear progression, but aero is a exponential progression. So the rolling load increases, but not as fast as aero drag does.

Trucks are just about the most inefficient way to get bulk goods from here to there. For distribution inside a city they make great sense, but for anything longer than 200 miles I'd say load it on a train.

[RH77]

At some point, someone posted a great link to an informative article published by one of the Diesel engine manufacturers (Cummins, CAT, Detroit Diesel). My other laptop fried with the file

It's posted here somewheres...

Not only does rolling resistance play a part, put you'll see tire alignment, wear, etc.

I like this Wiki page -- efficiency of each mode of travel and transport.

RH77

[LostCause]

Originally Posted by elhigh

I don't agree that rolling resistance is a bigger issue, though it's pretty obvious that with 18 wheels, there's a heck of a lot more rolling resistance on a truck than a car. Add a full load and it gets worse.

My understanding is that rolling resistance increases as a linear progression, but aero is a exponential progression. So the rolling load increases, but not as fast as aero drag does.

I forgot where I read the rolling resistance information, but it depends heavily on speed. Any trucker doing the legal limit (55mph) and not fighting a headwind/crosswind, will see most of his fuel being spent on rolling resistance...especially when brand new tires are fitted. Above 55mph, drag starts shooting up immensely dur to air drags exponential rise (as you've noted).

Again, I've forgotten the exact penalty truckers pay for speeding slightly (~5mph), but I remember it being fairly immense (~25% FE hit, I believe). At 55mph, air drag is a major source of drag...but I am pretty sure it is not the overwhelming source. Ofcourse, lowering it will still help immensely...but the point is that rolling resistance is a big deal in the trucking industry.

- LostCause

[roflwaffle]

Originally Posted by RH77

At some point, someone posted a great link to an informative article published by one of the Diesel engine manufacturers (Cummins, CAT, Detroit Diesel).

Cultural Learnings of America for Make... Er, I mean, Cummins Reveals Secrets to Great MPG. Page six has a nice graph, and according to it, if trucks dropped from ~75mph to ~60mph, they'd see a good ~30+% increase in efficiency. In other words, if they slow down to ~55-60mph across the board instead of the ~70-75mph I've seen, they would see the equivalent of $3/gallon diesel even with prices at $4/gallon due to the increase in mileage. That being said, given the horrible drag coefficient of most rigs, aeromods could probably do the same as slowing down a normal rig.

[RH77]

Originally Posted by roflwaffle

Cultural Learnings of America for Make... Er, I mean, Cummins Reveals Secrets to Great MPG. Page six has a nice graph, and according to it, if trucks dropped from ~75mph to ~60mph, they'd see a good ~30+% increase in efficiency. In other words, if they slow down to ~55-60mph across the board instead of the ~70-75mph I've seen, they would see the equivalent of $3/gallon diesel even with prices at $4/gallon due to the increase in mileage. That being said, given the horrible drag coefficient of most rigs, aeromods could probably do the same as slowing down a normal rig.

Yes, that's it! This should be essential reading for any hypermiler -- the truck techniques transfer to any vehicle quite easily (in most cases).

(It's now saved on the backup computer)

RH77

[DifferentPointofView]

At these speeds - the trailing edge will show much more significant gains. But, given the longness - I'm fairly certain flow has gone turbulent by the time you reach the end of the trailer....

Maybe if they did a partial kammback or something... oh, and remember there's bars in the back, so no boat-tailing from the bottom. If they did the sides, there's still a visibility issue with vehicles hiding inside of the 3/4 boat-tail. So I think a Kammback would be the best bet for the rear.

[trebuchet03]

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

Tires make biggest difference in MPG below 50 mph; aerodynamics is the most important factor over 50 mph.

It makes it sound like aero shouldn't be considered at all below 50...

According to that chart - aero costs ~140hp @50mph, a tad below 100hp @40mph, ~50hp at 30mph....

Seriously, 50hp is half of my engine's output... 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)...

[Big Dave]

Trains are indeed more fuel efficient than trucks. Look at one from the air...it approximates the shape of a spear. Add to that the rolling resistance is the same as a rubber tire on polished glare ice. Railroads are generally laid out along water grade. There is still a bit of track at over 2% grade but there ain't much. Even the UP's Sherman Hill grade and CSX' Cheviot Hill got bypassed.

A train will generally reach what railroaders call the "ruling grade" (a combination of steepness and length) and when the train tops that grade, the engineer can coast the rest of the way to the next stop. Quite often they will top the ruling grade and have to immediately go into dynamic braking.

Another advantage of railroads is that the amount of mainline track (where most of the energy is used) is down to about 10,000 miles. We are reaching the point where mainlines could be electrified. Electrification is well-proven old tech. Electrification allows railroads to free themselves (for mainline use at least) of oi and they could use electricity which in the US is mostly generated by coal or nuclear power. Speaking of dynamic braking, an electrified line can recycle about 85% of the energy needed to climb a hill. When a trian reaches the top of the hill, a dispatcher holds the train until another train starts up the hill. 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.

Drawbacks of electrification: High capital cost. $10 million a mile on average. Railroads run at nearly right angles to high-voltage transmission lines. Lots of new high-voltage rights of way will be needed. Catenary electrification is butt ugly. The US does not have enough excess electricity to run electric mainline operations.