SafeHarbor

Your best bet may be to hope that Airstream will come out with a toy hauler, although I don't think that's very likely.

As far as I tell, a progressive rise topper and and an areoshell on the front of the trailer might be about all that you can do for aerodynamics.

Aerotabs, by the way, are well-proven now. I first saw one in a set used on the Piper Aerostar (fast, pressurized) twin-engined gas airplane back in the early eighties. They were being used to improve airflow over the control surfaces at low speeds. Low speeds for an Aerostar, by the way. is plenty fast for us in our CTDs.

Lamar

Superduty

This is a very technical but very interesting paper.

http://repositories.cdlib.org/cgi/vi...ntext=its/path

It deals with highway tractors.

Leon441

Turbo wing from wind jammer. This will help aerodynamics but is a little unsightly with just the truck no trailer.

1sttruck

"If you follow a truck close enough to catch the draft you won't be able to see what is going on down the road. You also might catch anything that is flipped up by the trailer; tire retread, board, rock, you get the idea."

Last week my wife and I were heading into town and were behind a semi for a couple of miles. I always seem to keep a bit more distance from the vehicle up front than others, and I guess it may have saved our butts as all of a sudden a large piece of sheet metal, it looked a flattened hood, flew up from the behind the truck, got to maybe five or six feet and then veered off to the right and dropped down. It looked like it could have come thru the windshield if we had been following closer, or if it had not veered off to the right I couldn't have dodged it. I'll add a bit more distance behind semis.

Superduty

I got this:



For this:


From here.
http://www.turbodieselregister.com/f...d.php?t=136458

I dunno where he got the curve from, but it is interesting. I think it is that truck pulling a trailer thus 26,000 lbs. I don't know where the 24 HP came from (fan, compressor, A/C, PS pump, alternator = 24HP ? I know the fan can be 30 by itself, but 24 all the time ?)

At 75 MPH, 70% of the power is for air. Speed really sucks the fuel.

203 HP x 0.40 BSFC = 80lbs of fuel an hour = 11.4 gallons/hour. 75/11.4 = 6.6 MPG. The engine might do better than 0.4 BSFC, but probably not much better than 0.35.

Now, if he slowed down to 60 MPH, about 110 HP.
110 x 0.40 BSFC = 44 lbs of fuel an hour = 6.28 GPH. 60/6.28 = 9.54 MPG.

HOHN

Not really. For the same reason that the leading edge in general doesn't have as big an impact on overall aerodynamics.

What happens as you increase velocity against a flat surface is that a high pressure pocket forms along the flat surface, and you technically get a "stagnation point" where air basically stops flowing. Instead, it's just captured into this high pressure pocket.

This high pressure pocket acts almost like a rounded nose, and has the effect of "steering" the air around the front in a rather aerodynamic fashion.

The reason that the trailing edge is so much more important is because you don't get this high pressure pocket to help steer the air flow and make it more stable. Instead, you get a LOW pressure pocket, which is VERY undesirable.

Thge low pressure pocket results in a phenomenon known as "separation". Separation is just when the air stops flowing in a nice stream and instead turns into a random chaotic mess. Separation also can cause a kind of oscillation where where to flow switches rhythmically between two slightly less chaotic flow conditions (but they are unstable, and thus, cannot be maintained).

This oscillation can cause trailer sway (if the sway is due to aero, not axle probs or such). It also is visible when you see a flag rippling in the wind, because the wind experiences a separated, oscillating flow over the flag.

The trick with aerodynamics is to keep the flow as orderly and "unseparated" as possible. The leading edge's high pressure pocket separates the air in a manner that's pretty smooth and not that chaotic.

On the other hand, the low pressure area at the rear of the trailer does NOTHING to help the flow come back together smoothly.

I've actually seen this in the wind tunnel when I was at the Air Force Academy and we tested different shapes.

If you could take a standard 18-wheeler box trailer and fit a large bubble to the rear to help the flow come back together smoothly, the benefits in terms of reduced drag would be VERY good. Alas, the economics prevent it from becoming reality.


Oh, and if you're thinking of fitting a progressively-rising topper to your bed, it's only beneficial if your trailer is very close to the truck.

Based on the posted pic, I'd guess that a progressive-rise topper in your case would do more harm than good, as it's not close enough to allow the air to bridge the gap.


jh

HOHN

Oh, I forgot some interesting aero trivia:

You know why the corners of VW vans (the hippie vans) are rounded?

Because VW found that the top speed of the van was too slow with squared corners. Rounding the edges allowed the vehicle to maintain US hwy speeds with no upgrades in engine performance.

Little things can have big drag consequences.

Scotty

That helps explain why that trailer company not only had the rear shaped on their trailers but also had the front four corners rounded lots.
Its about time you posted something of value Justin. LOL
Just kidding, as you know.

Scotty

IsItFast

Great write up HOHN.

The whole reason I started this thread was I was attempting to find out ways to improve aerodynamics with MY set-up. Several have told me that there was problems with my truck or trailer, slow down or other things to improve MPG. But these weren't issues I was asking about. A few have voiced proper opinions on aerodynamics and I certainly appreciate everyones input even if it isn't related to aerodynamics. It appears there really isn't nothing I can do to greatly improve things (except maybe put a topper on with a deflector at the back).

Since I am in the Plains, there is almost always a small wind coming from the West. Therefor whenever I travel East it almost feels like I lost my trailer. That 5-15 mph tailwind makes a HUGE difference. So unless my truck, trailer and gas gauge all seem to work better only when going East, I am pretty sure it is an aerodyamics issue. Since no one has really gave me a "do this to your truck/trailer and things will improve" answer I am guessing there is not an easy fix.

Rednax

First thing I noticed in the picture is that the trailer appears to be sitting nose high. I always adjust mine for level, first, and the slightest nose-down attitude if I can get it.

And I would go for a better hitch if that is not at least a REESE Strait Line "Dual Cam". A Hensley Arrow, ProPride or Pullrite would be on my list. Anything you can do to eliminate (not damp) incipient trailer sway is going to help. And it makes driving less tiring. Fatigued drivers burn more fuel. Start by properly weighing the vehicles separately, then together (and get tongue weight by itself), and set up the rig according to best practice. RV.net has lots of info.

I watch trailers all the time when on the highway. The combination of wind, road surface and traffic tends to make them move around -- a lot -- even though the motions are small. It adds up to a lot of movement at the end of each mile. I'd also be perfectionistic about wheel balance, brake operation, bearings, alignment and shock absorbers. The effect may not be direct, but the indirect effect of less work at the steering wheel pays off.

An enclosed underside is worth considering, as are the AirTabs HOHN mentioned. Yours would be the perfect candidate.

And slow down. You can't even control your truck over 70 mph, much less a truck + trailer, not when it counts. A tail-heavy toy hauler is about the worst RV on the highway, bar none.

IsItFast

Thanks for the reply Rednax. Not sure how you ran across a 4 year old post but at least you took the time to respond.

Update: I never really did get an fix for aerodynamic loss. I have just more/less learn to accept that a 10mph head or cross wind can be devistating to the performance of a trip.

I believe the picture may be an illusion to it not sitting level since the bottom front slopes up while the top rear slopes up. Though this is all moot since the picture was before I put the larger wheel/tire kit on there. Once I did that I had to purchase a larger drop for the anti-sway kit. Which while we are on that subject I really never had any problem with sway. In extreme cross wind situations I tell that the trailer is pushed from one side or the other but I have never had a problem with sway. I'm not sure the brand of the "weight distribution" kit I have but it is top quality (solid bars and the hitch was about a hundred pounds).

I did use a wind deflector on the cab roof about 2 times but never put it back on since I didn't see any noticeable improvements. Maybe I'll try it again this spring just for fun.

I also have upgraded to an '09 3500 with the 6-speed auto tranny that is incredible. Unloaded mileage with the 6.7 sucks but is way better than my 5.9 when towing....which I'm sure the main reason is the transmission since it doesn't work near as hard.

TJAR66

Slow down. Would be my first suggestion

dfranks

I think at those speeds you are an accident waiting to happen.... a top speed rating of 60mph on those trailer tires equals no insurance in case of accident.

FWIW I have a 34' bumper pull I live in the prairies with all the X and Headwind you can handle, towing into the rockies every weekend and my tranny doesn't hunt. But then I run 285's not those 22's, my mileage is between 12-14mpg

skidlyman

Hmmm Well I've learned a couple things to try from this thread. 1st I will put a nosecone on the front of my 29' forrest River Toyhauler, and airtabs on the back and slowdown to 60mph ! i'm already getting 10 or 11 mpg. lets see what I get then

Rednax

Let me start by writing that when I posted "you can't control" I meant to say that "one can't control", that is, any and all persons operating pickup trucks. Crash statistics for them are terrible, and only the foolish think themselves exempt.

Which while we are on that subject I really never had any problem with sway. In extreme cross wind situations I tell that the trailer is pushed from one side or the other but I have never had a problem with sway.

Again, I see this all the time. Just because it can't be felt from the steering wheel doesn't mean it isn't happening. By which I mean everything from small skips and jumps to the trailer leaning over from a side wind (against a very small amount of possible suspension travel) and the driver is unaware of it. I have seen tractor trailers with the rear tandems catching air under the tires on one side or another . . and the driver -- a professional -- can't "feel" it from the wheel. (But he sure heard the hollerin' on the CB).

Incipient sway is nearly always present. Inadequate weight transfer, cheap anti-sway kit, and changing road conditions present problems for tow rigs. Guessing at weights, failure to confirm proper W-D operation, improper trailer loading (Tongue Weight), etc, all add up. Have someone follow you with a video camera and record how well the units exhibit "unbroken linkage" (out of alignment with each other). It isn't just in lane changes. In trailering, the tail wags the dog. And a small trailer can upset even a "big" truck. Seen it often.

One thing any CDL driver can tell you is how limited, how few choices can be made, with an inherentlyunstable rig. As I see it, anything I can do to improve the margin with my TT is to the good. Road performance is everything, and it is a bit foolish to think that the bigger-the-better the TV is the "safer I'll be" (whistling in the dark).

AND it all pays off in directional stability, fewer steering corrections, and the "effect" on fuel economy is that it highlights effects such as the wind by having eliminated "noise" in the system.