Potential mpg loss % with custom aero trailer.

[aerohead]

https://ecomodder.com/forum/showthre...ero-38795.htmlBetween whatever drag and increased weight-related rolling-resistance penalty the flatbed incurred, it didn't seem to impact the mpg dramatically.
The trailer would have aggravated frontal area on both sides some. The width and porosity may have increased turbulence and prolonged turbulence, as it really wouldn't have any facility for 'calming' the disturbance.
If your version of Hucho's chapter on commercial vehicles still shows a bus in 'convoy' driving, at varying following distance, you'll see how low the Cd is for the trailing bus at close proximity, and how it lowers the Cd of the tow bus in a 'NASCAR' two-'car' draft.
A light-bodied, 'wake-rider' trailer, half the length of the bus, with some modicum of aft cross-section contraction, would seem unlikely not to get you near a null effect, even with the weight penalty.
I'll try to link to the Greyhound Bus and trailer concept:
It's at #4 (permalink )

[Gschuld]

https://en.m.wikipedia.org/wiki/Drafting_(aerodynamics)

https://m.youtube.com/watch?v=8BeGFqBVX2c

Yes, I have image copies of the buses example from Hucho from a post on this forum. It’s not in the most current edition.

More or less the drafting effect. Works for 200mph NASCAR as well as 25mph cycling racing. I’ve done the cycling thing with fast 3-8+ person lines and the effect is enormous. Being in the wake of the rider(s) in front of you at speed takes WAY less energy. When we went for long rides, guys would jockey to be the one following me because I’m a tall guy with big shoulders. And being tall meant that I was sitting higher on the bike to get the correct leg length to pedal ratio. So that made me even higher off the ground. They said even the difference between being behind me and being in front of me made a noticeable difference in their drag even when we were in the middle of a 8 guy line doing 25mph.

I was really pleased with the numbers I got with the open trailer at 2700lbs.

Now I’m curious what I end up with when pulling the 7x14 cargo trailer for some data.

George

[aerohead]

Hopefully, this a link to the thread: 'Which Trailer shape is better'.
At #82 ( permalink) is the data for the 'NASCAR' bus.
https://ecomodder.com/forum/showthre...r-20662-9.html

[freebeard]

You're getting better at it.

If you copy the link from (permalink) you get https://ecomodder.com/forum/showthre...tml#post415740

If you copy the #xx it obtains https://ecomodder.com/forum/415740-post82.html

Try them. I just pasted those without the and vBulletin linkified them for me. Learn something every day.

[aerohead]

when I was at the permalink, I didn't see an 'address' for it, just the main thread.
how did you isolate it like that? It's waaaaaaaaaaaaaaaaay better!

[Gschuld]

So I tried out my friend’s 2003 7x14 dual axle cargo trailer. 2050lbs empty with 300lbs of stuff inside. So 2350lbs. The trailer has a near flat front with about 6” radius edges on both sides and on top. The front of the cargo trailer front wall was 46” from the back bumper of my Jeep. It pulled great, but you could really feel the extra aero drag. It felt like I was pulling something 3000 lbs heavier, not 500lbs lighter. Lots of extra frontal area, nearly 30” taller than the Jeep, and 12” wider.


MPH 7x14 cargo 24’ open.
MPH. 2250lb. 2720lb.
MPH TR 1. TR 2. No TR. %drop 2. %drop 1

55. 18.3 23.2. 31.1. ——-25.4. 41.2
60. 15.7. 21.3. 27.1. ——-21.4. 42.1
65. 14.1. 20.3. 26.4. ——-23.1. 44.7
70. 13.4. 20.5. 24.9. ——-20.5. 46.2
75. 11.3. 19.6 24.1 —-—19.2. 53.2
80. 10.9. 18.2. 22.5. ——-22.5. 51.6

The difference at 75 and 80 mph is striking. 18.2mpg (with 500lbs more weight) compared to 10.9mpg at 80mph. Aero matters…..

So this tells me that if I loaded my 1400lbs of gear into that 2050lb 7x14 cargo trailer, I’d be at 3450lbs. At 75mph I averaged 11.3mpg at 2550. So add another 900lbs to it and I’d probably see around 10.5mpg at 75mph.

That same 1400lbs of gear totaling 2700lbs of custom aero considered trailer would likely beat my 2700lbs of open trailer with cinder blocks at 75mph (19.6mpg) to say 21mpg.

If so, at the target 75mph, an aero 2700lb all up trailer would get 2x the mileage at 21mpg than the 10.5mpg in an existing factory 7x14 cargo trailer at 3450lbs with the same 1400lb live load. And even better than my buddy Matt pulling a 7x14 cargo trailer at 7.5mpg at the same speed with the same 1400lb live load.
So at 21mpg and $3.15 per gallon, I’d be at $1350 in gas money for the season
At 10.5mpg and $3.15 per gallon, I’d be at $2700 in gas money for the season. A mere $1350 in savings. Naturally I’d have at least $1350 in materials to build the trailer, and a not inconsiderable amount of time to build it.

So based on this alone, I’d be far better off (in dollars and cents) borrowing the 7x14 trailer and getting 1/2 the gas mileage if considering only one seasons use.

On a side note, I pulled my open deck 24’ dual axle trailer again this morning to retrieve a large heavy rolling toolbox (28” deep, 48” tall, 7’ long). I strapped it in lengthwise centered in the trailer with lots of 2” HD ratchet straps centered the wheels fore and aft. Total weight 2760, nearly identical to my earlier test with the same trailer with lower profile cinder blocks as ballast. So same weight, same trailer, more aero drag. I was with a friend for the 1 hour trip, so I just set it at 75mph and left it. Average was 15.2mpg at 75mph, where the cinder block run was 19.6 at 75mph. 4.4 mpg worse with a little more drag on the same trailer at the same weight on the same road, because of the extra drag only.

This is all very interesting, and not far off from where I was theorizing. That’s comforting.

George

[freebeard]

So If I get this correctly and neglecting the two different trailers, Minimum frontal area gets 19.6, 8sq ft [added] frontal area gets 15.2, and 7x(6?) gets 10.5?

I know it's been discussed on Ecomodder, but I went right to the source forum.vbulletin.com/forum: [How to] Create your own vBulletin tables

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Maybe someone else can explain it adequately.

[Gschuld]

Yes, pretty much. FWIW, the 7x12 cargo trailer box is 6’6” tall (7’ 4” off the ground) and 7’ wide.

George

[Hersbird]

Originally Posted by Gschuld

Yes, pretty much. FWIW, the 7x12 cargo trailer box is 6’6” tall (7’ 4” off the ground) and 7’ wide.

George

That 7'4" is the height that matters for frontal aera. Some people quickly find out that lifting a pickup adds a bunch to frontal aera. The same area is not just moved up higher and the extra air doesn't just pass cleanly under.

[freebeard]

Someone should mention the front corners of your Hi-Lo (if that's what it calls itself)