Potential mpg loss % with custom aero trailer.

[freebeard]

It would be interesting to compare the drag with 20% oversized, equal, and 20% undersized frontal area on the trailer all else being equal.

I suspect some amount undersized is Okay, being compensated by the increased fineness ratio.

I used to see the term 'wake filling' being used. Don't know if it's an actual thing. Trailing edge features can be angled, curved or stepped. So, maybe.

The real killer is the gap. The gap between the cab and bed of a pickup truck is measurable. The trailer I led with at Permalink #7 should have no tow vehicle wake over the top, it's all channeled to the sides.

[redneck]

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I think that something like this might work well. It has a low profile when collapsed and a roofline that follows the template. (don’t tell Julian)











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[aerohead]

I'm hearing you say that at 65-mph, solo, at 75-feet behind a semi with trailer van, your highest mpg is 32.5 ?
And, pulling the trailer with bikes, your all-up weight is around 7,900-lbs?
Do we have an mpg at 65-mph pulling each type of trailer ( open and enclosed ) ?
I saw a 21.5 mpg figure, but not sure how to connect that to the different architectures.
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It's possible, even with a weight penalty, to experience zero mpg loss when pulling a trailer. I've experienced this.
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It sounds like you've studied NASA's aerodynamic truck experiments at Edwards AFB, California.
From those you'll remember that:
1) lowest drag occurred when the tow/ trailer gap was closed ( articulated gap-fillers ).
2) exit frontal area of tow matched forward frontal area of trailer ( a seamless transition).
3) NASA had a full belly pan, you'll have a full belly pan. All is well there.
4) NASA had inset wheels, you'll have inset wheels.
5) NASA dis not have wheel skirts. You could have wheel skirts ( an improvement over the NASA project )
6) NASA had zero longitudinal body camber ( pressure recovery ). Beyond your trailers maximum cross-section, you could conceivably incorporate plan-taper and roof taper, improving on NASA's design ( a fabrication complication, however, exactly what would deliver lower drag ).
7) Flow reaching your 'Dryden' tail would already be oriented towards the wake, and at lower velocity and higher pressure ( like Railton Mobil Special, MG EX-181, Goldenrod, Challenger-I, VW Flow- body, EV-1, etc. ) providing premium onset flow to the boat tail.
You're the only one who knows your requirements for ease and safety when loading and un-loading the bikes.
8) Whatever meaningful drag reduction you achieve, is going to come from a gradual, streamlined reduction of the trailer's body cross-section and tail ( given that all else has been 'cleaned up.'
9) You're appetite for fuel savings vs construction-difficulty-coefficient ( PITA) will decide your course.

[redpoint5]

I pulled a flat trailer with a 16 foot canoe on it last weekend and it appears to have reduced fuel economy by about 10%

[Gschuld]

It’s funny that I have been researching old trailer designs with expandable sections. Thx, and I’ve seen that one before. Also a modern Hi Lo type design was considered.

Aerohead: excellent points.

“9- You're appetite for fuel savings vs construction-difficulty-coefficient ( PITA) will decide your course”. Ha, I like that.

Yes, I managed 32.5mpg average at 65mph with ACC (adaptive cruise control) on at the closest setting the car would allow(estimated 75ft) to the big box semi in front. This was in modestly changing elevations (100ft swings maybe over gradual grades) on the GSP in NJ for maybe a 10-15 minute stretch.

I haven’t pulled trailers much with the Jeep since I got it last year. I’ve got a v10 Excursion(flack jacket on��) that I use for work for the heavy stuff. But I did pull my 24ft open deck dual axle trailer(2 3500lb electric drum brake torsion axles, 6ft wide frame, 1700lbs empty weight) with a long 300 lb load on it that was somewhat draggy but not higher than the Jeep, that I got 17.xx mpg over a 30 minute period doing 75mph with ACC on in no traffic.

I intend to run a few tests soon with other trailers. Specifically with the dual axle 7x14 enclosed cargo trailer. I’m very curious to see how that goes.

My trip back to NJ from Michigan (not pulling a trailer) once again had the Jeep calculated mpg figures match very well with my hand calculated miles/gas used.

I am really impressed with this Jeep Grand Cherokee SRT. Perhaps I’m just so used to my V10 excursion being such a heavy wallowing gas gulping beast on the highway. But after 12 hours on the road in that SRT, I arrive feeling relaxed and not tired at all.

That brings me to another factor in my custom trailer interest. Vintage motorcycle road racing 12-42 hours drive away(42 hours is NJ to Laguna Seca California at 70mph average for 3000 miles one way) has risks involved. Though everyone wants to stay safe and trackside safety precautions and medical services are commendable, people do crash. Sometimes it is a few scrapes, bruises, sprains. Sometimes it’s more than that. Sometimes it’s enough that the injured rider isn’t realistically able to drive himself home.

I’d be going with at times a friend, at times with my wife, and occasionally alone if it can’t be avoided. FWIW, I do have several people from my area that race too that I could have them drive my stuff home in an emergency if I’m driving alone and I get hurt(rare case)

My wife isn’t a fan of pulling trailers on the highway. Her previous experience with it was in the Excursion with the 24ft Haulmark trailer at 6000lbs or so(Excursion rated for towing 11,000lbs) Some bigger cross winds and some close passes on two lane roads by a semi had the trailer swaying enough that she was not at all comfortable with it(yes, with proper loading/hitch weight/load leveler/sway control system)

I’ve done my share of pulling that setup. And though I’m used to it and find it safe and controllable, I will admit that driving such a rig required far more concentrated effort and was far more mentally taxing than driving without the trailer. 12 hours at 65-70mph and I was spent. Throw in a windy day, or tons of rain and I was miserable. That late 1990s architecture is archaic compared to newer big trucks I’ve pulled with FWIW.

A great benefit of an efficiently sized and shaped trailer matched to the SRT should not only benefit from better mpg, but also be far less taxing on the driver on long stints. I’ve done 15 plus hour drives pulling my empty 24ft open deck trailer and it was night and day easier. I had to keep reminding myself it was even back there.

I’d like to have a setup that can logistically accomplish the mission (deliver the bikes and equipment, etc) and hardly be noticeable behind me. If I can do that, I’d feel far more confident that my wife or friend would have little issue driving it. And planning on 75-78mph average where allowed, it makes a difference I’m sure.

There are a few more logistical factors that are influencing my designs, but I’m not including them in an effort to not muddy the waters.

And yes:

5200lbs for Jeep (with 7200lb towing package and a Radarc progressive brake controller)
2700lbs(projected) for loaded trailer with single axle and electric brakes
350 lbs for my passenger and myself. I’m a big tall Danish guy.
8250lbs all up. Could be a little less, maybe 8500lbs or so at the outside.

George

[aerohead]

It will be interesting to see the new data ( we'll never get enough of it ) on the future trailer tests.
I did some Motocross, and TT Scrambles when younger, although, found trials-type riding the most enjoyable. As much as I have a fear of falling, somehow going straight down a cliff on a bike seemed okay at the time.
A safety trade-off for endorphins!

[freebeard]

It’s funny that I have been researching old trailer designs with expandable sections.

We'd all love to see the plan. [The Beatles]

[Gschuld]

Enduro and scramble riding is cool. Nice

Edit: it seems I need 15 posts to be allowed to post links or photos. I’m on 5. It appears I’m still on double secret probation��. I’ll keep the visual presentation suspense a bit longer…. YouTube Gingerman view 2021 and three videos will come up first. Saturday front view and Saturday rear view are both camera views of the same race.

FWIW, here is some video from Saturday’s Sportsman 750 race last weekend at Gingerman Raceway in South Haven Michigan.

Several classes race at the same time, scored separately. The video is from
my pal Matt’s bike. Newest GoPro Hero9 cameras front and back. I’ve partnered up with Matt in something of a sponsor/teammate role on a different bike of the same vintage and type(my race engine, my GoPros, I did the painting, random other $ support).

#64 is Matt’s uncle and 5 time class champion. Matt has been chasing uncle Jeff for 6 years now, getting faster and closer each year. And has take the win a few times himself. Saturday he beat him for the win(from behind), and you can see that uncle Jeff managed to overcook his front brake near the end of the race trying to get back around him and overshot a turn leading to a leisurely cross country escapade in the grass(but didn’t crash it ��)

There was a class of modern sport bikes that started in the first wave. You can see that Matt and Jeff passed nearly all of them. These are +/- 50 year old bikes but are heavily modified and lightened for racing. They are plenty fast.

George

[freebeard]

Originally Posted by Gschuld

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Whatever that is, pick the closest approximation from the smilies.

I thought it was five posts. You reference pictures that don't exist. Use for still pictures, either from a drop box or from an album in your user space.

For video use . So far as I know, there is no way to embed a video in the site so it needs an external address.

[Gschuld]

I got a message when I tried to include links to the YouTube videos when I tried to post my reply, saying I needed 15 posts to insert images or links and I was at 5.

I’ll get there….

George