Long panels below trailers reduce windrag?

I run those belly skirts all the time across I-10 in NM.....the crosswind push effect is actually reduced having them.

Might be the same aspect as when in a crosswind with open trailer, the old rule was to slide tandems all the way back..."eliminates" a lifting point (in front of and behind) the tandems.

Can't claim to be an aeronautic physicist.....hmmmm, yesterday couldn't spell it now I are one joke comes to mind!

The problem I have with them...is that the way our company set them up....or Wabash....you can't slide the tandems any farther forward than the 40' point....sometimes you need that extra 12 inches in front of 40' to get weight off the nose of the trailer.

 

I've used them more lately, and my mpg has increased slightly this month, but who knows if it's due to the skirts. If my load everyday was the same exact weight, weather conditions the same, and same terrain maybe I could tell. There are just too many variables in the real world. At 7.8 mpg right now though so they're definitely not hurting.

 

I think that most of this type of thing is nothing more than a gimmick. I have not spoken to anyone who has actually gained any benefit from installing them on their trailers. It might help, but I think that some people in California have likely invested heavily in this type of technology. If there is an increase in fuel mileage, I don't know that it would be worth the cost.

 

With skirts and wide singles, I gain about 1 mpg over a trailer without skirts running duals.

The difference between the trailers with wide singles and with or without skirts is around 0.2 to 0.3 mpg. Not so much...

So... lets say you're getting 6.5 mpg without skirts, but 6.8 mpg with skirts, and fuel is running $4 a gallon on 130,000 miles per year. Sound about right?

The guy without skirts will use 20,000 gallons of fuel in a year, but the guy with skirts uses only 19118 gallons. Not much difference, eh? That's 882 gallons saved at $4 a gallon is $3528 per year. I know this is all kind of arbitrary, but that's not exactly chump change in the long run. For someone with a sizeable fleet... say 100 trucks that's $352,800.00 per year!

I hear the Smart Truck product works better though...

http://smarttruckbrands.com/undertray.php

 

You also need to weigh the costs with adding these skirts and singles. It might take years to get to the break even point. For more carriers to want to spend the money I think the cost will need to come down or they will need to weigh the cost benefit to them. Since I don't pull vans, it is a non issue for me.

 

They make sure to price these things so they will pay for themselves, but barely. I mean seriously, $4000 for an APU???

 

$4,000?


Double that.



And then some.

 

Lots of people make their own, using a gas generator. But then they're too stupid to plumb up a small car or motorcycle muffler or something to make it quiet, and then have the nerve to back in next to me and fire that thing up when I'm trying to sleep. One time I had to move the truck cuz one of those homemade APU's was too loud. If there hadn't been another parking spot available at the time, I was ready to hop out with a pair of wire cutters and cut the ignition wire on that thing.

I made a 12 volt generator once, not for an APU but for my homemade raft, to extend the range of the deep cycle batteries that ran the trolling motor. It didn't have the power to RUN the trolling motor without the batteries hooked up, but I only used it while we were stopped overnight on an island, camping and getting drunk with loud music from my homemade camping stereo. I made a muffler for that little Briggs & Stratton engine out of an empty disposable propane tank like for a torch. (I used a .22 rifle from a safe distance to make the first hole in the propane bottle and flooded out the residual gas with water before welding on it) That muffler made that engine as quiet as one of those expensive Honda generators. There was no exhaust noise at all, just the sound of everything vibrating, the belt slapping around, valve train noise, etc. If these guys who have the mechanical ability to make their own APU's with a gas generator, I don't understand why they can't make them QUIET too. It's not hard at all.

 

It isn't just the homemade ones. The truck I bought has a Rigmaster on it. First thing I did was put a muffler and tailpipe put on it.

 

Someone explained to me something about why they couldn't tee the APU exhaust into the main stack on the truck. It made sense at the time but I don't remember and can't think of any reason that wouldn't work now. It was something about when the APU and truck engine are running at the same time, something having to do with back-pressure.

I think they should be required by law to have them either plumbed into the main stack, or have their own vertical pipe that runs parallel to the stack, so the exhaust comes out at the top, up high. Even when those things are quiet, the exhaust is still down low where it lingers between the trucks, and some guys sleep with their windows open. They don't need to be breathing that stuff.