[Gschuld]

Thanks for the thoughts. I’ve debated the front end shape of the trailer quite a bit and the all important gap regarding the turbulent flow.

One limitation for me is the logistical ability to open the rear hatch of the jeep SUV. With the trailer inline with the Jeep, the arc of the lifting hatch requires the trailer nose be a mere 6-8” behind the ball. I have an extra 12” or so as it’s currently set up(but that distance was set because of the turning clearance limit) I do though have more room to close that gap near the hitch further.

What gives me some pause is cross wind effects. From studies that I’ve seen detailing cross wind flow, a rounded front (in top view) was considered very effective at both reducing sway and drag. Sway control in particular has my attention as my as designed single axle distance to hitch is on the short side and I sure don’t want it to be dancing around back there at 75-78mph. I chose to have modest little round around the roof edge because the top front of the trailer is 5” below the projection of the flow coming off the roof of the Jeep(in a 3 degree downward slope FWIW).
So it should, at 75mph, make the short jump to the roof of the trailer without too much hassle. I may be wrong. I have been considering ONE easily removable add on aero aid to the Jeep for towing. Creating a new much larger trailing edge roof lip. The current SRT specific one is extending 12” deep from the natural side profile shape of the back end. I could make a much larger one (in clear coated carbon fiber maybe) that easily clips onto the current one, would be about 30” long rather than 12”, with sides even with the back window edges with a shape coming up vertical from the back surface of the profile of the Jeep closing off as much gap as possible while retaining the clearance needed for trailer articulation. It would help smooth the airflow onto the trailer further giving the flow even less reason to go turbulent.

I’ve considered a centerline cross flow blocker. It could be made with a foam sweep seal and really bisect the air on both sides (removable for hatch access). I could also as you mention use that full rounded profile but bring it to a point at the center reducing the gap 12” farther in the middle (which would not effect my trailer turning clearance).

Weight, yes, no way around that. That additional 2700-3000lbs will have a cost no doubt. My hope is the extra weight will primarily affect highway mileage more negatively the more hilly the terrain is and the more traffic there is on the road. Hills and traffic require more acceleration events, where the extra weight really shows itself.

On flat, steady, no traffic roads at 75mph, I’m hopeful the penalty will be minimal if overall aero efficiency of the Jeep/trailer combo is near equal to the jeep running alone (plausible IMHO). This is also where I suspect the overpowered 6.2 475hp Hemi comes in handy. It has generally been my experience that(in steady flat road open highway running) overpowered vehicles tend to take less of a mpg hit on the highway when adding around 1/2 the weight of the tow vehicle in extra trailer weight compared to a more modestly powered vehicle. The idea being a big engine has to work only a little harder, and a smaller engine has to work much harder than their respective trailerless effort.

The wildcard, for me, is the “ECO” 4cyl mode on this Hot Rod engine. It honestly doesn’t seem to make much difference going in and out of that mode, based on the rolling mpg figures not changing hardly at all when it’s on or off. But I doubt the engineers would have gone through the trouble if it didn’t have some benefit.

When pulling my open 24ft flatbed trailer recently, with a low but moderately draggy load, the jeep was happy running in ECO 4cyl mode for near the same amount than without the trailer at 75mph. That was encouraging since at perhaps 2400lbs trailer weight, it pulled like nothing was back there.

Perhaps tomorrow I’ll take that trailer, load on enough concrete blocks to make 3000lbs all up, and do some highway 75mph mpg runs, then drop off the trailer and repeat the same runs minus the trailer to compare back to back.

I’m confident I can build a trailer that is more aerodynamically efficient behind the Jeep SRT than that big open dual axle trailer. So therefore (hopefully) I should be able to best, if only slightly, the mpg results for that set of tests.

I should have more data soon.

George