Potential mpg loss % with custom aero trailer.

[Gschuld]

Originally Posted by freebeard

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

Yes, the corners mean a lot, even with the cross section of the trailer within the cross section of the Grand Cherokee. My design described originally in this thread has a full round 32” radius front section (top view) like the Aerovault trailers.

https://www.bre2.net/aerovault.info/

There is no need for such a heavily rounded upper section (in profile) as the Aerovault since the top of the designed trailer is 5” below the top trailing edge of the Grand Cherokee roofline.

The full rounded top view shape was intended to minimize the destabilizing effect of cross winds. It’s debatable whether that is worth it. The front of the rounded shape would be within 20” of the bumper of the Jeep. I have a minor aesthetic interest in that shape as well.

George

[Piotrsko]

I thing there's a vortex bubbles off the jeep roof so if the trailer is lower it's still draggy as all heck because it's interfering with that vortex and not smoothing flow.

[freebeard]

By 'your Hi-Lo' I meant Hersbird's, just to be clear. I don't believe he has it any more. I always thought the half-round could have been made of perf metal with RGB LED lights inside, like a Wurlitzer jukebox (when it's parked).

The idea was to modify an existing trailer, adding on instead of carving away. If you yaw the trailer completely over, you can estimate whether two small half-rounds or a large single one would impact the tow vehicle first.

[Hersbird]

Those corners on the High-low were just 8" round 3' sections of HVAC ducts opened up to be 180 degrees instead of 360. So they were 16" half rounds. That trailer although 8' wide and heavier with 2 axles performed similar to my current teardrop but I don't have the same tow vehicle to know for sure. Both my current and previous were 2009 5.7 Hemis on the same size and tread tire, both have 4.1 gearing, but that was a Chrysler Aspen and now I have a Jeep Commander. Both trailers pulling got 12-13 mpg.

[aerohead]

Originally Posted by Gschuld

Yes, the corners mean a lot, even with the cross section of the trailer within the cross section of the Grand Cherokee. My design described originally in this thread has a full round 32” radius front section (top view) like the Aerovault trailers.

https://www.bre2.net/aerovault.info/

There is no need for such a heavily rounded upper section (in profile) as the Aerovault since the top of the designed trailer is 5” below the top trailing edge of the Grand Cherokee roofline.

The full rounded top view shape was intended to minimize the destabilizing effect of cross winds. It’s debatable whether that is worth it. The front of the rounded shape would be within 20” of the bumper of the Jeep. I have a minor aesthetic interest in that shape as well.

George

If the trailer was going down the road, solo, the large radii would be approaching the optimum nose for subsonic flow.
As a trailer though, in train behind the tow vehicle, the JEEP would be doing the initial flow penetration and only 4.5% of body- width-radius would be required for trailer's exposed leading edges, @ zero-yaw.
If the trailer face had this 4.5%, it would take care of the exposed sides, and actually reduce the volume of gap between the JEEP and trailer, covering the 'aero' requirement, although 'jack-knife' clearance would need to be maintained. With 20'' of tow-bar, you'd need to check that.
On NASA's semi-trailer project, the trailer gap = 19.7% drag increase @ zero-yaw, and 17% drag increase in wind-averaged flow. An inflated gap-filler could easily yield this 17-19% savings. If frontal areas were matched, you'd have a Cd 0.16 trailer. Lower with the boat-tail.

[Gschuld]

I get the idea that ideal trailer leading edge shape should differ from the ideal leading edge of it was directly exposed to the undisturbed airflow. The trailer, being within the cross section of the jeep, is “hiding” somewhat in the Jeep’s wake. So the most effective thing is to try to get the two as close as possible reducing the turbulent gap, and allowing the airflow from the Jeep to the trailer to be as seamless as possible.

If I had a flat front to the trailer, with a 4.5% or trailer width radius (3.25” radius) to fully clear the trailer for cornering (90 degree) I’d need 36” from trailer from face to hitch ball. The ball would be 8” from the bumper. So I’d need to be 44” from trailer face to Jeep bumper, at full 90 degree clearance. At 45 degree clearance, I’d still need around 38”.

An advantage of the rounded front shape is that it allows the gap at the center to be at 20” from front face to bumper and allow over 45 degrees cornering clearance.

With a flat front 44” away, I’d need to install some sort of inflatable bladder of some sort or some stretchable material that is impractical in use to help jump that gap. A rounded section seems a good compromise. And I can still add an easily removable divider in the centerline to nearly close the gap between the two sides. However, I have been under the assumption that in a cross wind, the rounded front performs very well allowing breeze smoothly through the gap and reattaching on the other side. This is more useful on trailer shapes with a height well above the tow vehicle though I’m sure.

With only a 6’ total width, and the tires just barely with that width, I’m inclined to keep stability a primary importance. The trailer will be low, with the center of mass of the live load as low as possible. Still I’d like to keep any cross wind effects to a minimum. I’ve driven in some situations where cross winds really shoved my long wheelbase 8000lb l tow vehicle around. My modest wheelbase 5200 lb SUV will only be more susceptible

[Piotrsko]

Originally Posted by Gschuld

So the most effective thing is to try to get the two as close as possible reducing the turbulent gap, and allowing the airflow from the Jeep to the trailer to be as seamless as possible.

With only a 6’ total width, and the tires just barely with that width, I’m inclined to keep stability a primary importance. The trailer will be low, with the center of mass of the live load as low as possible. Still I’d like to keep any cross wind effects to a minimum. I’ve driven in some situations where cross winds really shoved my long wheelbase 8000lb l tow vehicle around. My modest wheelbase 5200 lb SUV will only be more susceptible

Well, the idea should be to integrate the flows across both vehicles so they act as one with no bobbles or swirls at the join. Probably not something that is obvious to accomplish.

I have had trailers that make my7880# CC F250 try to change lanes in winds that didn't bother my 4000# surfer van in the least.

[aerohead]

https://cdn.gardnerweb.com/resources...deview1077.jpgDuring turning and backing the jack-knife clearance isn't negotiable.
It's during most of the trip that it's of no issue.
Long ago, a UK manufacturer attempted a solution. I've never heard of it since.
https://ecomodder.com/forum/member-a...l-trailers.jpg
Here's a link to a commercially-produced gap-filler trying to make a go of it

[freebeard]

If I didn't know the subject, that would be the most confusing picture I've seen today.

www.amazon.com/Clinical-Photography-publication-Eastman-Company...

I believe it was chapter 5 that was on Psychological Clarity. It's more than just context.

Ontopically, have you considered the difference between a Roman and Gothic arch? A Gothic curve in plan would jackknife really well. And act as a vortex trap.

For the tow vehicle, rudders at the two rear corners could be connected by a 4-bar linkage to the trailer's tongue [else electric microcontroller] to dodge the front corner of the trailer.

[aerohead]

Originally Posted by freebeard

If I didn't know the subject, that would be the most confusing picture I've seen today.

www.amazon.com/Clinical-Photography-publication-Eastman-Company...

I believe it was chapter 5 that was on Psychological Clarity. It's more than just context.

Ontopically, have you considered the difference between a Roman and Gothic arch? A Gothic curve in plan would jackknife really well. And act as a vortex trap.

For the tow vehicle, rudders at the two rear corners could be connected by a 4-bar linkage to the trailer's tongue [else electric microcontroller] to dodge the front corner of the trailer.

*In a way, I see what you're saying, although it makes for an exceptionally long gap down the sides as a trailer nose. A massive pressure spike.
* Four-bar would do. NASA just simple hinges from the local hardware store.
* The four-bar would need to be supported from below with a 'floating' castor, or else pot-holes would eventually destroy the mechanism. I struggled to come up with a solution for the gap-filled full-boat-tailed trailer. Interstate-80, west of Denver, was a torture chamber for mechanisms.