Stampie said:This makes me wonder about my Suburban vs my old pickup. In theory the Suburban should be better because it punches the hole and the air doesn't get a chance to come down as much. True?
When I had my F-250 I sometimes had a cap (topper in some parts of the country) on it and sometimes a tonneau cover. The 24 ft enclosed trailer was noticeably easier to pull with the cap on the truck. The first time I pulled the trailer without it I thought there was something wrong with the truck.
APEowner said:Stampie said:This makes me wonder about my Suburban vs my old pickup. In theory the Suburban should be better because it punches the hole and the air doesn't get a chance to come down as much. True?
When I had my F-250 I sometimes had a cap (topper in some parts of the country) on it and sometimes a tonneau cover. The 24 ft enclosed trailer was noticeably easier to pull with the cap on the truck. The first time I pulled the trailer without it I thought there was something wrong with the truck.
This is an interesting bit of info.
kb58 said:Also, at the back of the trailer is a big bubble of low pressure air, basically sucking the trailer back as the engine fights to pull it forward. 18-wheelers sometimes have those big hinged shutters that help bring the cross sectional area down as the air separates, reducing drag "some amount."
In short, if mileage is a big deal, consider driving slower, really, because drag is proportional to speed squared, so slowing from 80 to, say, 65, would reduce drag by 34%. That's a lot and costs nothing!
This is what I was referring to as the beaver tail flaps. Name brand is trailer tail. For a rectangular bluff body I bet these make a measurable improvement. Maybe worth more on a higher L/D trailer
There are a few references on the web that Wells Cargo did wind tunnel testing and found negligible benefit for v-nose, but I haven't seen the report itself.
Lof8 - Andy said:APEowner said:Stampie said:This makes me wonder about my Suburban vs my old pickup. In theory the Suburban should be better because it punches the hole and the air doesn't get a chance to come down as much. True?
When I had my F-250 I sometimes had a cap (topper in some parts of the country) on it and sometimes a tonneau cover. The 24 ft enclosed trailer was noticeably easier to pull with the cap on the truck. The first time I pulled the trailer without it I thought there was something wrong with the truck.
This is an interesting bit of info.
I've proposed we pick up a topper at work for the cross-country tows for this reason. Haven't convinced anyone else yet, alas.
Back on topic...
I find a V nose trailer significantly easier to pull. It feels more stable. I won't ever buy a flat nosed trailer again.
I suspect the sloped too would also reduce drag, simply because it has less frontal area. I have no experience, just my opinion.
(I also think they look stupid, so I'll probably never buy one of those either!) haha!
V-nose , sloped or not, has the same frontal area as a flat trailer with the same H and W.
The added fwd volume may lead to higher tongue weight which is more stable.
I think the V nose would help more for Cd if the truck weren't there, or if towed by a lower sedan type shape. I buy the truck topper theory, it effectively increases L/D. A long shape has 20-30% less drag than a short one.
https://www.wikiwand.com/en/Drag_coefficient
Better analog data would be with the LE and TE forms on a long body.
In reply to MattGent :
I hear what you're saying, but it makes no sense. By that argument, a Miata that was squared out to the full dimensions of the car's sectional dimensions (nearly the size of a refrigerator) would not suffer any aero loss.
Yes, it's the same sized hole. But it punches into the air easier. That's why boats aren't shaped like shoe boxes.
Would you be more comfortable if I referred to it as a CoE?
My flat nosed trailer is a huge billboard going down the road, and it absolutely feels like it.
Just to throw another wrench into things here. I recently had to get a new truck and was cross shopping. Asked some friends what kinda mileage they got towing with their trucks. One came back and made the comparison between a standard 4 place snowmobile trailer (v nose, 28'), a 3 place (narrower square nose), and a big fifth wheel camper. Worst mileage was the 4 place sled trailer, Camper was 1-2mpg better, and the 3 place was another 1-2 better.
Makes sense to me because the really isn't any aero thought to the 4 place, its taller and wider than the truck pulling it. The Camper is even taller but has a roof line designed for aero that slopes down to the back which I'm sure plays a huge factor. A rain drop after all is fat bulbous leading edge and tapered tail....camper mimics that shape. Best was the 3 place and which is no surprise as it was the smallest trailer in frontal area, narrower than the truck pulling it and only slightly taller. In this case the truck is covering most of the frontal area, the unit (truck + trailer) narrows in transition from truck to trailer which again is a mimic of the rain drop shape.
I'd expect ideal drag/efficiency setup to be a bulky tow rig with narrow trailer...or even one that tapers in width and height to be as small a possible at the back. Minimal gap between or even a smooth transition if possible (some semi trucks have a design like this)
I did not like the way that truck towed trailers; I blame the soft progressive front springs due to 4wd.
I have towed our current v-nose with several things, but don't have a comparable flat nose to tow with same stuff for a like for like.
NASA's aero work in wind tunnels (from before I was born) indicates the v on front - with nothing else changed - does NOT help. Tapering the rear would.
From non-comparible towing, I suspect NASA was correct.
Looking at your truck and long trailer would it help to make a pick-up bed topper that would go from the trucks roof angle to about the trailer roof height.
or would the 2 -3 ft or so gap between the back of the bed and nose of the truck stop any gains?
SV reX said:Back on topic...
I find a V nose trailer significantly easier to pull. It feels more stable. I won't ever buy a flat nosed trailer again.
I suspect the sloped too would also reduce drag, simply because it has less frontal area. I have no experience, just my opinion.
(I also think they look stupid, so
I'll probably never buy one of those either!) haha!
When I designed my trailers I looked into it even made a scale model and hooked a little 5 pound weight scale to it.
What made the biggest difference was rounded rather than sharp edges. Picture to follow.
I have no practical aero experience, but the NASA stuff showed that rounding the edges makes a big difference (easy enough, ya'd think it'd be done more) without cutting into usable space. Tapering to the rear helps a bunch, but eats into usable space a lot.
In reply to californiamilleghia :
Used to see the aero wings on Hwy. stuff, so I would think it would help a lot. But no personal experience to say.
In reply to 03Panther :
Working with sheet goods it's difficult and expensive to manufacture in the low volume trailer builders work with.
I spent a lot of time on the patterns to make the molds. I'll bet I had close to 30 gallons of bondo before they satisfied me.
frenchyd said:In reply to 03Panther :
Working with sheet goods it's difficult and expensive to manufacture in the low volume trailer builders work with.
As cheap or easy as slapping two corners together, no. But not what I'd call difficult or expensive.
For an individual, years ago, sure. But not what I mentioned.
I'm not convinced how much it matters. My 2005 F-250 AWD crew cab, towing an enclosed 24 trailer, Miata, and misc crap got 9 mpg. Take the trailer off and it got 9 mpg. The best I ever got was 12 mpg, and that was empty, not towing and snoozing at 55 mph on the highway.
An anecdote going back to the slightly off topic portion of the thread:
I was involved in a late model race situation, and we towed with a 7.3 Ford ambulance. It's body profile was so close to exactly the same as the trailer, you would think we did it on purpose. No real data, but it towed beautifully. Less effected by cross or headwinds than I would have expected from a regular pickup truck.
In reply to car39 :
Hearing you only get 9mpg makes me feel a lot better about my towing setup that does about the same on a gallon. 28' extra high trailer behind a '96 RWD 7.3 powerstroke dually with a significantly heavier car, BIG tool boxes, generator, pit bikes, etc.
03Panther said:frenchyd said:In reply to 03Panther :
Working with sheet goods it's difficult and expensive to manufacture in the low volume trailer builders work with.
As cheap or easy as slapping two corners together, no. But not what I'd call difficult or expensive.
For an individual, years ago, sure. But not what I mentioned.
I was responding to the comment about why more corners in a trailer aren't rounded like mine were. .
Perhaps I should have clarified that and said, rounded corners are difficult and expensive to do.
We tow the racecar on a 20' open trailer. Behind the Suburban we take an MPG hit. Behind our old E450 bus we saw no change. 9mpg loaded or unloaded. That big thing created a big enough hole in the air that the trailer didn't cause a problem.
In reply to car39 :
My 16* foot trailers pulled behind my 1/2 T 4x4 350 V8 pickup carrying about 3500# of race car, tools, and spares. Averages 15-16 mpg. When I towed it with my S10 Blazer (2.8 V6) it averaged 16-17
* does not count VNose and trailer hitch.
Now to be fair, for some reason I seem to get better fuel mileage than most
Ranger50 said:It's still a giant turbulent air blocking piece of metal.
It doesn't matter if it's shaped all aero ish or a flat vertical slab, it still has the same sq foot profile and responds as such.
Pretty sure I'm going to have to disagree with you there. Ya know, there's a reason that birds and fish aren't shaped like bricks.
Given that the front is already a v-nose, improving the aero at the rear of the trailer will make a much bigger difference. You know those truncated pyramid shaped doors you see on the backs of tractor trailers? I think that building a DIY set of those for the rear trailer door(s) will be your best bang for the buck improvement.
JBinMD said:Ranger50 said:It's still a giant turbulent air blocking piece of metal.
It doesn't matter if it's shaped all aero ish or a flat vertical slab, it still has the same sq foot profile and responds as such.
Pretty sure I'm going to have to disagree with you there. Ya know, there's a reason that birds and fish aren't shaped like bricks.
Given that the front is already a v-nose, improving the aero at the rear of the trailer will make a much bigger difference. You know those truncated pyramid shaped doors you see on the backs of tractor trailers? I think that building a DIY set of those for the rear trailer door(s) will be your best bang for the buck improvement.
AIUI, the benefits of the trailer tail thing are real but not huge. Fuel is a huge cost to long-haul trucking companies and if they made a big difference then you'd see them on every trailer out there, not just a handful.
There is a rumor "out there" that these guys a pretty good at aero stuff.
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