5x10 Rigid Pop-Up with Foam

[kipa]

I was trying to figure out my lower fairings for this thing when it occurred to me that I was thinking inside the box I had created for myself with the fenders. I had original thought they were worth keeping for standing on and accessing cargo over the cover, but the cargo notion went out with the solar panel installation. Removing them completely makes a lot more sense and cleans up airflow a lot on it's own.

I still think there is more efficiency to be gained mostly around the wheels with fairings, but doing the same loop as before for all road tests, I got a solid 2.6mi/kWh with this setup. 65mph, 92F, moderate traffic, dry, and no AC - windows cracked as before. Head/tail winds were an intermittent 5-10mph.

Summary of changes since the last run:
- Relocated stabilizers
- Fenders removed
- Highly textured Herculiner

I think the bed liner actually helps by creating a boundary layer skin effect, kind of like a shark or golf ball, but I doubt that is easily measured over a short range loop.

One thing I am thinking about is the potential for adding a spoiler to the car. I wouldn't want anything that creates any kind of down force so much as to help raise the wake area higher against the tongue. Not sure that would do anything though, as that is monkeying with the finely tuned engineering of a low drag car vs. making a brick function less like a brick.

 

[kipa]

Realizing I never did an official car-only baseline on my test loop, I just ran it.

75F, 0 wind, almost no traffic, again at 65mph with windows cracked, no AC: 3.3 mi/kWh.

So 0.7kWh loss with the trailer is a 21% hit on efficiency, which exceeds my design goal by nearly 1/3 over an estimated 30% drag penalty. That's a solid win in my book without doing anything else to improve it.

I should have wheel well skirts and wheel covers (both inside and out) installed by next week. The lower fairings I was thinking about are looking like they won't help much given how skinny the 12" wheels and tires are, so I think I have picked most of the low hanging fruit.

I could cleanup some sloppy joints on the underbody panels, but I doubt the entirety of it will get me much if any over 2.7mi/kWh for a 18% drag penalty. I'll drop some spats down from the wheel wells for good measure as they can't hurt.

 

[Pmullen503]

If you really want to get serious, tape pieces of yarn around areas you want to work on. Drive it with someone else filming the yarn blowing around. Turbulence equals drag.

I did this on my first trailer and found A LOT of turbulence between the trailer and TV. There was less turbulence at 70 MPH than 55 MPH! I ended up shortening the tongue and building a tongue box. My typical mileage penalty went from 21% to 17%.

 

[kipa]

I kind of used the rachet strap from my original tub road test that held the tongue cover on as a 'tuft'. It was interesting to watch where the loose end was stable in the wake vs. flailing madly - and what helped me to decide that smoothly profiling the nose of it would be a waste of effort for real improvement.

I'm mostly just looking to see if I can get 200 miles of range from my car while towing. At 55, that may already be the case - and those are going to be the roads where it matters most, such as out in the Steens Mountain wilderness here in Oregon. The deepest parts of it don't leave me much buffer to explore.

Anyway, the wrong wheel covers showed up, and they were also just a garbage fit, so that will have to wait until the middle of next week as different ones are on order.

This is what I came up with for skirts. I'm not certain of what kind of plastic it is. It's not ABS, but I had it on hand and it's a much cleaner look than coroplast would be. Not sure how or with what I can dress up the edges, but I think I can just leave it like this. VHB seems to stick well to both the skirts and the Herculiner, so that part was easy. But you know how that stuff can work, so I am sure it will only fall off when some ridiculously expensive car or a cop is behind me . .

 

[kipa]

While I based the initial design on the Lightship AE.1, I hadn't seen this article about the design process. It breaks down some of what they based their choices on and I tried to emulate a lot of it. So far, that seems to have worked

Using CFD To Design The Most Aerodynamic Travel Trailer - ENGYS

Over the last decade, automotive manufacturers have been continuously innovating new technologies, designs and approaches to maximise the fuel efficiency of combustion vehicles. This has led to an impressive 32% increase in fuel economy of new roadcars [1]. However, no matter how efficient a...

engys.com

Moving along . .

I have not been satisfied with how much of the inner tube material has been working. It's too floppy and not very finished looking. I hadn't seen this rubber sheet until yesterday, but it is looking like a much better material for how I am using the tubes on the wall lowers. Not too thick at 3mm, but a little stiff, and it's really easy to cut clean lines on it, so I will be replacing at least those seals, and using it elsewhere as well such as to trim up the gap between the closed cover and the tub.

https://www.homedepot.com/p/Rubber-Cal-ReUz-Black-48-in-x-600-in-Rubber-Gym-Flooring-Roll-1-Piece-03-275R-50/330734763

Relatively inexpensive too!

I also weighed the fenders and hardware at 20 lbs. now removed.

 

[kipa]

The plan with the wheel covers is to install these both outboard AND inboard on the wheels. I'll have to hog out a large hole to fit around the axle hub inboard, but these are nice and flat and should clean up airflow at the wheels quite a bit.

 

[kipa]

Quick update on skirt efficiency testing: Inconclusive.

Doing the same loop, my economy actually dropped to 2.5mi/kWh, but again with a head/tail wind. It's also possible that consumption data just isn't this accurate with a shorter 26 mile loop. Though I think it can be indicative, clearly, it's not definitive as I am not convinced that adding skirts hurt it. Only way to know would be remove them, but I am not willing to fight the VHB and possible finish damage to prove that point.

 

[Pmullen503]

Short trips are difficult. I make the same trip (14 miles) several times a week with my RC plane hauler and my Chevy Equinox EV. Mileage ranges from 2.5-3.5 mi/kwh. That's a 6% to 30% mileage penalty based on a 1 year average mileage with no trailer.

Even on longer trips mileage varies due to temperature, wind and who knows what else.

 

[kipa]

Replaced and added the upgraded rubber skirting. Looks and should work better overall in my opinion.

 

[kipa]

https://www.homedepot.com/p/Rubber-Cal-ReUz-Black-48-in-x-600-in-Rubber-Gym-Flooring-Roll-1-Piece-03-275R-50/330734763

Relatively inexpensive too!

I just realized this isn't the product I bought. This is. It's a bit thinner.

https://www.homedepot.com/p/TrafficMaster-Smooth-Black-2-ft-2-in-x-Your-Choice-Length-Roll-Stair-Runner-MT4000129/304613565

 

[kipa]

A couple of post-water pen testing photos. No serious or unexpected leaks were seen. The gutters I installed at the rear interior corners worked exactly as intended to route what got inside through a tube to the ground. I just need to go back and do some additional sealing along the upper u-channel/tub joint.

Aside from my wheel covers and some additional exterior trim, this is the completed exterior.

I did have some concern about water pooling in the flat areas on top, but they really don't hold much water without spilling past the corner trim to drain to the outside, so I am not worried about that now.

I do need to add a drain to the forward corners of the rear deck though. Parked level, it is slightly sloped away from the door, but it would definitely pool and leak inside if that incline is reversed.

The new vents on the rear top panel are fixed open to promote convective airflow and avoid suffocation - but they also probably work because this build probably isn't tight enough to worry excessively about that too much anyway.

 

[kipa]

And look what arrived today . . much more pleased with the quality and style of these vs. the ones I returned. (It's difficult to find good quality 12" wheel covers.)

These are nice and snug on the outside, and actually use the bearing cup on the axle to flatten the face out slightly.

And for the inside of the wheels, I just cut straight through with the band saw before cutting a hole in the center for the axle. It attaches firmly to the wheel on the inside without contacting the axle or hub.

Snapping them in closes the kerf of the cut for a firm fit.

Not sure how much it will help, but this was super easy and relatively cheap at $64 for the 4 of them.

 

[kipa]

Looking at the underside pics, I am thinking that skirting extending straight down from the inner and outer frame rails to cover the gap inside the leaf springs may help. I'll probably just make them static pieces with slots for the axle movement.

Those u-bolts look like they could use a trim as well.

 

[kipa]

Quick update on skirt efficiency testing: Inconclusive.

Doing the same loop, my economy actually dropped to 2.5mi/kWh, but again with a head/tail wind. It's also possible that consumption data just isn't this accurate with a shorter 26 mile loop.

Did a little more aero work today, covering frame rail gaps and relocated the stabilizer jacks to the rear, and got no significant change from it, but it was also warmer at 84F. It touched on 2.6mi/kWh at the turn around, but dropped back to a solid 2.5 for the remainder of the return leg.

Same thing with no AC, and just the sunroof and rear windows cracked. Very light traffic and no winds.

It's possible that the car was actively cooling the pack since it was over 95F here today and the sun had just set. I may retest in the morning, but I am not confident traffic will be agreeable.

 

[kipa]

More thoughts about the aerodynamics:

I think one thing compromising my efficiency efforts is just the frame design itself. The dropped tongue frame creates a weird stepped wedge at the front. So it likely creates some unusual vortices as air spills off the sides of it to ultimately roll underneath the frame.

I wouldn't guess that in itself is hurting efficiency since it's all in a messy wake area anyway, but it's clear that air going under the trailer is anything but clean. I was surprised to see that the front frame rail covers on each side blew out sideways after this last test. And while the front rails don't have covers and there is still a significant gap between the rails and tongue box, there is clearly a significant pressure imbalance created in that region. My thinking is that it's simply a significant low pressure area created by the tongue frame right at the corner.

I could probably fix that somehow with additional fairings and see additional drag improvement, but I need to move on to working on the inside and actually using this puppy. I'm happy with how it has turned out and it has exceeded my design goal by a large margin on towing efficiency. Perfecting it is probably going to waste a lot more time with scant gains, so I'm going to better secure those front sections and move on unless I get a better easy idea.

 

[Pmullen503]

I think that the flat back is likely the limiting factor to ultimate aerodynamic efficiency. Getting a truly smooth bottom would help but would be a lot of work. The tongue A frame and axle hanging in the breeze probably limit potential gains.

It's tough to measure small gains on an EV because of other factors affecting the efficiency of the T.V.

I applaud your efforts all the same.

 

[kipa]

Yeah, it's just too arbitrary to pin down with such a short test circuit. Just just completed a loop with a 70F average temp and a 15 mph crosswind produced the same 2.5 m/kWh result. So perhaps that's just a good working average with minimal load at 65.

Interesting coincidence is that it is exactly a 26.2 mile loop - while passing the Eugene area Marathon Coach facility along the way. I only just realized it, so obviously it is now the 'Marathon Test Loop'.

 

[kipa]

Activity on the interior with the front section of my bed platform mostly built. I still need to reinforce under the center section with longitudinal supports since it is only 1/2" ply, as it flexes too much for my liking with only the 3 lateral ones. The platforms on the sides are supported by the 4 walls of the boxes well enough.

This section is 48"l x 57"w x 12"h (11" internal), so I will need to build out another 32" to the rear if I want full queen mattress support.

I'm probably going to end up with a sliding platform that pulls out for that, leaving me just over 16" at the very rear for taller cabinets/seating. I think it's too tight at the front to slide the platform against the bulkhead and still have room for feet. That's definitely not enough clearance for head forward use without a 10" offset to the rear as shown in the second picture.

I am struggling a bit with placement of things I want more accessible in the rear, such as my power station which is quite large at 21" long and stupid heavy at just under 130lbs, but I may have to be more flexible on where I keep that.

It's a lot more weight than I am comfortable putting in the tongue box, and that would create other logistic issues with the toilet and shower space as well as require water sealing it in a box. I'll probably end up having to rotate it between travel and camp positions where it will likely end up, but I'll make it work somehow. Obviously, everything else depends on what the bed will allow.

 

[kipa]

And no sooner did I write that than I remembered that the power station is 13.1" tall. If I simply elevate what I have already built another inch, I can integrate the top of the power station as part of the setup bed platform. So that solves that problem!

 

[kipa]

The 1" frame I built underneath did the trick almost perfectly. The Pecron generator is about 1/16" high along the front and back of it, but the center flat section is dead even now. That will give me a lot more flexibility for moving things around and balancing tongue weight.

I had originally thought I wanted the main platform to slide forward, but that is more complication than I want to deal with, and fixing it in place gives 10" wide storage cubbies around each side, so I am happy with this layout.

I managed to find some $5 milk crates that fit each cubby relatively well too, and after shimming the center ones up 3/16", my need for added supports under the center panel is eliminated with those in place.