[Yossarian]

With delivery of my Rivian anything but imminent, I've been thinking about how to get the most range when towing a camper.

I had a chance to view some airflow simulations of generic pickup truck and a generic SUV towing a [email protected] 400 teardrop camper. The airflow was much cleaner with the SUV and the camper than with the pickup. I would guess then, that the range of the R1S would be somewhat greater than the R1T towing that kind of load, assuming both had the same size battery. We don't know what the capacity of the "larger capacity" battery pack for the R1S will be, but we do know that it will be less than the R1T Max Pack's 180 kWh. If the capacity is about 15% less, let's say 150 kWh, it may well be the case that towing range for both R1S Longer Range and the R1T Max, is roughly the same. Be interested to hear thoughts on this speculation from those with more of a technical background than I have.

With drag being the primary determinant of range, it seems to me that it may be worth considering doing something to make the tow load more slippery. While the front face of my [email protected] 320 is rounded, and the rear tapered, the camper is 93.6" high and 81" wide. That means it sticks up about 16" above the 77.3" roof line of the R1S, though it is a bit narrower (the R1S is 81.8 wide). Would adding a wing to the back of the roof to direct the airflow up a bit be worth considering? How about the poor man's solution of putting my Thule cargo box on the R1S, mounted as far rearward as it can go and still not impede the cargo hatch?

Another, much more expensive way to get more aero may be to change campers. Alto in Canada makes a 20', 2,600 lb aluminum camper with a tapered front and rear that the company claims is the most aerodynamic of any camper on the market. You can see the shape in the snip below. The height of this trailer (the A-2124) is 93", so it sticks above the roof like by the same amount as the [email protected]; it has a pointed front and sloped roof however. Alto also makes a teardrop-style camper that collapses for towing, their "R" (for retractable roof) series. This trailer is only 83" high so well below the R1S roof line. And it has the familiar teardrop rear end as well. Thoughts on this one? There are thumbnails of both below.

No rush on answers, my Rivian ain't gonna be in my driveway anytime soon.

This is the Alto A-2124:

And this is the R-1713:

 

[JP Deshaies]

You have a very interesting question and I can add my 2 cents. Being in aerospace industry, I can confirmed that the teardrop shape is one of the worst shape for a RV. Mainly because of the turbulence created at the back of the teardrop RV. The straight side walls combined by the steep drop at the back creates kind on contrails sees on aircraft without winglets because of pressure differential. Those turbulences can be compared to 2 big parachutes that you pull behind the RV. About the difference between R1T and R1S, you’re right that the SUV will be better in the air because of the reduce air gap between the vehicle and the RV compare to the pickup bed. The Alto A2124 is very interesting and we can note that model has his side wall and the roof designed to reduce the pressure differential hence the drag. Among the bests RV to optimize the range, you have the Bowlus at the top but way too expensive. The Airstream is very good too because of the smooth and rounded surface and the Alto A2124 is great too. At the end it’s really a personal choice but I hope that’s helping you.

 

[Yellow Buddy]

You have a very interesting question and I can add my 2 cents. Being in aerospace industry, I can confirmed that the teardrop shape is one of the worst shape for a RV. Mainly because of the turbulence created at the back of the teardrop RV. The straight side walls combined by the steep drop at the back creates kind on contrails sees on aircraft without winglets because of pressure differential. Those turbulences can be compared to 2 big parachutes that you pull behind the RV. About the difference between R1T and R1S, you’re right that the SUV will be better in the air because of the reduce air gap between the vehicle and the RV compare to the pickup bed. The Alto A2124 is very interesting and we can note that model has his side wall and the roof designed to reduce the pressure differential hence the drag. Among the bests RV to optimize the range, you have the Bowlus at the top but way too expensive. The Airstream is very good too because of the smooth and rounded surface and the Alto A2124 is great too. At the end it’s really a personal choice but I hope that’s helping you.

What are you thoughts on the aerovault trailer? it’s not a camper but does it have merit? Or is it taking advantage of my lack of knowledge?

About the Aerovault and spec sheet - Aerovault

Learn more about the design and structure of the Aerovault, along with what is considered standard. Dimensions and size information available on these spec images.

www.bre2.net

 

[JP Deshaies]

The Aerovault brings many great aerodynamics benefits: closed under belly to optimize the air flow, smooth and rounded surface where it is possible and they added a similar concept of winglets at the rear top to break the turbulence coming from each sidewalls. His weakness remains the flat rear end that will create a vortex but at one point, you are stuck with the utility factor, in this case, you need that big square surface to have the trailer usable. Overall, a great design to carry cars or other stuffs when you compared to other trailers on the market.

 

[Yossarian]

I'd like to see trailer manufacturers publish data such as frontal area and drag coefficients, preferably several sets with various tow vehicles. That would be a great help for those of us who plan to use EV's to tow, particularly for those of us with a lot of time to kill before our vehicles will be delivered.

On the Aerovault, I'll defer to folks like @JP Deshaies who are far more knowledgeable in things like fluid dynamics than I am, but I take a lot their claims with a grain of salt. They call sharp angles "tricks" and make the assertion that "sharp angles don’t help [reduce drag] much." That may be true in some cases, but certainly cannot be universal. Super-sonic aircraft like the F-14 and F-15 are largely sharp angles, so . . .

That said, there is a lot truth in the Aerovault hyperbole, but their trailer is not one that can easily be used as a camper.

 

[Yossarian]

The Aerovault brings many great aerodynamics benefits: closed under belly to optimize the air flow, smooth and rounded surface where it is possible and they added a similar concept of winglets at the rear top to break the turbulence coming from each sidewalls. His weakness remains the flat rear end that will create a vortex but at one point, you are stuck with the utility factor, in this case, you need that big square surface to have the trailer usable. Overall, a great design to carry cars or other stuffs when you compared to other trailers on the market.

You beat me to the post JP.

The A2124 also has a closed underside, and a tapered rear which I'd guess will help at least to some extent in mitigating the vortex. Alto claims that the A2124 offers a "50% reduction in drag" and "15% reduction in fuel consumption." While those sound impressive, they are kind of meaningless without additional data. A 50% reduction in drag compared to what - any trailer design of any size? And 15% less fuel use no matter what engine type and displacement?

 

[Yellow Buddy]

His weakness remains the flat rear end that will create a vortex but at one point, you are stuck with the utility factor, in this case, you need that big square surface to have the trailer usable.

I imagine because it's for the ramp function. How would you modify the rear end in an ideal world if you didn't need a ramp?

 

[JP Deshaies]

You beat me to the post JP.

The A2124 also has a closed underside, and a tapered rear which I'd guess will help at least to some extent in mitigating the vortex. Alto claims that the A2124 offers a "50% reduction in drag" and "15% reduction in fuel consumption." While those sound impressive, they are kind of meaningless without additional data. A 50% reduction in drag compared to what - any trailer design of any size? And 15% less fuel use no matter what engine type and displacement?

You are bringing a good point, the data reference is always essential to support that kind of statement. I cannot confirmed but I believe Safari Condo is comparing their A2124 drag coefficient to their worst aerodynamic camper which is the teardrop R series. That could explain the 50% in drag reduction. Only them can confirm that opinion.

 

[JP Deshaies]

I imagine because it's for the ramp function. How would you modify the rear end in an ideal world if you didn't need a ramp?

The best way to optimize the rear end of a trailer is to elongate the rear with the side wall and the roof. You can notice on the road that some semi trucks are using kind of flapper at the back on the side walls and the roof that are oriented about 45 degrees towards the inside to create a pseudo elongation of their trailer and cover part of the rear door. That reduce the drag hence fuel saving.

 

[JP Deshaies]

The best way to optimize the rear end of a trailer is to elongate the rear with the side wall and the roof. You can notice on the road that some semi trucks are using kind of flapper at the back on the side walls and the roof that are oriented about 45 degrees towards the inside to create a pseudo elongation of their trailer and cover part of the rear door. That reduce the drag hence fuel saving.

 

[JP Deshaies]

I imagine because it's for the ramp function. How would you modify the rear end in an ideal world if you didn't need a ramp?

I would say that the best way is to have a conic door that a long streamlined shape to minimize the drag but to access the inside of the trailer, you will need that door to be lift completely to access a ramp and/or the inside of the trailer. If you don’t need to put a car, you can also have a fix conic rear portion and have a sidewalls door to access inside.

 

[Yellow Buddy]

I would say that the best way is to have a conic door that a long streamlined shape to minimize the drag but to access the inside of the trailer, you will need that door to be lift completely to access a ramp and/or the inside of the trailer. If you don’t need to put a car, you can also have a fix conic rear portion and have a sidewalls door to access inside.

Thank you for the details.

 

[JP Deshaies]

Thank you for the details.

 

[Yossarian]

I see a largely unfulfilled need for a camper in the 20 foot range with decent ground clearance, adequate water storage, solar power and sufficient LiFePO4 battery storage for dry camping for up to a week, and most importantly, having an optimized drag profile, optimized for EV towing. A second need may be a slide-in camper with a similar dry-camping capability and aero profile, about 51" wide and not too much longer than 84".

 

[mkg3]

With drag being the primary determinant of range,[email protected] 320 is rounded, and the rear tapered, the camper is 93.6" high and 81" wide. That means it sticks up about 16" above the 77.3" roof line of the R1S, though it is a bit narrower (the R1S is 81.8 wide). Would adding a wing to the back of the roof to direct the airflow up a bit be worth considering? How about the poor man's solution of putting my Thule cargo box on the R1S, mounted as far rearward as it can go and still not impede the cargo hatch?

1) weight has a huge impact on range in addition to drag.

2) R1S is 81.8 w/folded side mirrors. actual body width width <80"

3) Wing, depending on angle and orientation, may help but will definitely add drag to the R1S. Airflow field beheind the rear hatch is fully separated (adverse pressure gradient) and is already one of the biggest source of R1S drag. What might help when towing any closed trailer is to energize the airflow before it separates by adding vortex generators (VG) along the top and the bottom on R1S. this will delay/help keep the flow separating long/far enough so that the trailer aero will see non-separated flow. Note that if the flow is already separated, the trailer is not adding to the base drag, until its aft end where 2nd base drag is introduced.

4) Thule cargo box is a really bad idea. Sorry, you've introduced more drag in every category.

 

[mkg3]

They call sharp angles "tricks" and make the assertion that "sharp angles don’t help [reduce drag] much." That may be true in some cases, but certainly cannot be universal. Super-sonic aircraft like the F-14 and F-15 are largely sharp angles, so . . .

Sharp edges controls where the flow separates and aero designers can use that knowledge to manage the aero characteristics of that object.

As for F-14 and -15, some of the flat surfaces controls the supersonic flow needs, such as oblique shocks for inlets or shock-shock interactions.

 

[Yossarian]

Sharp edges controls where the flow separates and aero designers can use that knowledge to manage the aero characteristics of that object.

As for F-14 and -15, some of the flat surfaces controls the supersonic flow needs, such as oblique shocks for inlets or shock-shock interactions.

1) weight has a huge impact on range in addition to drag. . .

2) R1S is 81.8 w/folded side mirrors. actual body width width <80"

3) Wing, depending on angle and orientation, may help but will definitely add drag to the R1S. Airflow field beheind the rear hatch is fully separated (adverse pressure gradient) and is already one of the biggest source of R1S drag. What might help when towing any closed trailer is to energize the airflow before it separates by adding vortex generators (VG) along the top and the bottom on R1S. this will delay/help keep the flow separating long/far enough so that the trailer aero will see non-separated flow. Note that if the flow is already separated, the trailer is not adding to the base drag, until its aft end where 2nd base drag is introduced.

4) Thule cargo box is a really bad idea. Sorry, you've introduced more drag in every category.

Does the comment regarding sharp/flat angles mean that those surfaces only help at high and supersonic speeds? That would seem to imply that the claim by Alto regarding the reduced drag of their rather pointy and flat angled A2124 camper is bunk, or at least, mostly hype. Is that truly the case?

On weight, everything I read about towing with EV's seems to indicate that weight is very secondary player to drag in reducing range. Could it be that weight is more of a factor in reducing range with ICE vehicles than is drag, with the reverse the case for EV's?

Regarding the Thule, my experience with it is that it actually improves my mileage (very modestly) when I'm towing my teardrop. While I'm sure it introduces some drag, it has a pretty streamlined shape and a dimpled surface said to help with airflow:

This decrease in fuel consumption while towing similar sized teardrops also seems to be true for those with canoes or kayaks are mounted on their TV's (at least that's what's reported on my teardrop forum.) Could it be that the drag introduced by these kinds of roof-mounted items is slight and is more than offset by inducing lower overall drag for the TV/camper combination?