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Old 09-22-2022, 05:30 AM   #1
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Aerodynamic Modifications

After reading the recent thread about a trailer being modified for towing behind a passenger car, I thought it would be interesting to find out what, if any, modifications Airstream owners are making to increase aerodynamics and make towing more fuel/energy efficient.

Anyone have any improvements they've made that they'd like to show off?
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Old 09-22-2022, 05:45 AM   #2
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Old 09-22-2022, 05:55 AM   #3
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Old 09-22-2022, 08:39 AM   #4
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We actually saw improvements while towing when we added a roof top tent to our truck 🤷🏽*♂️

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Old 09-22-2022, 09:26 AM   #5
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Hi

Measuring the effect of this or that mod is actually fairly difficult. You (likely) are changing this or that by a couple of percent. Yes, there are things you could do that are past that level .....

The "big deal" mod would be to go (back) to the pointed front / rear configuration. The tradeoff is that you don't get a lot of use out of the extra (maybe) 12' of length you just added to the trailer. If you turn your 25' into a 31' or 37' that's going to add weight. The aerodynamics are better, the weight is worse. Is that a win? .... hmmm .....

Another approach would be to put one of the flexible cowlings between the TV and the trailer. No length adder in that case. Weight still goes up. Hookup / unhook would be interesting / painful ..... Helps on a semi, but you don't see many of them doing it.

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Old 09-22-2022, 09:47 AM   #6
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For the best aerodynamic improvements one would need to reduce the parasite drag from all the "stuff" mounted to the exterior skin. This would mean removing the Air conditioners solar panels awning etc. I guess one could fabricate fairing around all the protrusions. But I think that the juice would not be worth the squeeze.

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Old 09-22-2022, 09:54 AM   #7
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The easiest improvement to make is to drive slower. Since drag is proportional to the square of speed you largest improvement would be to slow down. Take your time.
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Old 09-22-2022, 12:56 PM   #8
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Thor has been going in the wrong direction regarding switching to all the plastic RV industry standard warts on the exterior. Take the current electrical outlets, for one example.


Now in '70s and earlier trailers, they had a forged AL outlet cover that closed flush with the exterior skins:


I understand (but disagree with) the bean counters decision to switch to the plastic warts, but they don't help the aerodynamics.

Some have also gone to a mini split A/C and removed a huge source of drag from the roof, with the added benefit of a lower CG.

There are also flexible solar panels that conform to the curve of the roof.

Those that switch to a compressor fridge can also eliminate the fridge vent from the roof.

Some have also taken off the TV antenna and either gone with a digital one they can place in the window, although my understanding is the range is more limited -- or gone to DVR/DVD or portable satellite or cellular internet for their viewing.
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Old 09-22-2022, 01:19 PM   #9
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My best results came from setting a 14’ canoe above my topper. For that trip, I achieved 8 to 10% better mileage than I normally do.
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Old 10-03-2022, 08:38 AM   #10
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There are also flexible solar panels that conform to the curve of the roof.
Flexible solar panels is a huge no-no unless you're installing them to a serviceable surface. The plastic that allows them to flex will yellow in just a few year's use, and they are nearly impossible to remove.

I installed 6 hard panels a few months ago and have barely noticed a change in mpg. Possibly 1mpg, but likely less. You'll end up spending any fuel savings on the increased labor cost to remove the panels.

I can appreciate the sentiment of this post--I thought about trying to design some sort of aero shield in front of my solar panels--but the effort wouldn't lead to any meaningful gains.

I also wonder if anyone here's ever towed anything besides an Airstream. The difference is hilarious. Box RV's get pushed all over the road from the wind. We're already so much more aero than alternatives.
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Old 10-03-2022, 08:33 PM   #11
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We haven’t bought ours yet (a few years to go) but have been thinking about it FWIW.
  • AS has a blog post about recent aero measurements. What they found is the low hanging fruit (I assume they mean w/out drastic trailer mods) is if you could address the low pressure zone created between the tow vehicle and trailer. If you take a look at the new Tesla Semi you’ll see they have a small gap between the truck and trailer for this reason.
  • Underbody is an area that could be addressed. AFAIK the aluminum shell is nice and flat but it appears there is a square box with a tank or two? Attaching some smooth graduations would help to avoid vortex sections, which is nice as it’s hidden but would take some metal work and whatnot.
  • It would be nice if AS covered the wheels, as they’re non turning this would be ideal, and it looks like the old AS’s are more covered than modern.
  • Small effect, put reverse scoops on the very back undercarriage, ideally get rid of the bumper. The EV concept did this.
  • Of course do something about the A/C sticking out there

I’d be most tempted by the first point. For example, a truck bed cab with a ‘back sliding’ portion that extends the aero shell towards the trailer. Wouldn’t have to touch the trailer much, and I wouldn’t be surprised if even a modest extension had an appreciable effect. Just need to make sure there’s enough clearance for turns.

An easy test of this concept would be to create a box out of 2x4’s and some thin ply which extends out the back of the truck, just like you’re hauling a long load. Would probably look odd but its an interesting thought experiment.

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The easiest improvement to make is to drive slower. Since drag is proportional to the square of speed you largest improvement would be to slow down. Take your time.
Exactly, just keeping it under 60 is huge, also doing some drafting. We’ve never needed to, but for fun on long trips I granny drive and draft, man it makes a difference. Reducing weight does little unless you are going uphill (and EV’s capture much of that on the other side).
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Old 10-03-2022, 08:47 PM   #12
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Flexible solar panels is a huge no-no unless you're installing them to a serviceable surface. The plastic that allows them to flex will yellow in just a few year's use, and they are nearly impossible to remove.



I installed 6 hard panels a few months ago and have barely noticed a change in mpg. Possibly 1mpg, but likely less. You'll end up spending any fuel savings on the increased labor cost to remove the panels.



I can appreciate the sentiment of this post--I thought about trying to design some sort of aero shield in front of my solar panels--but the effort wouldn't lead to any meaningful gains.



I also wonder if anyone here's ever towed anything besides an Airstream. The difference is hilarious. Box RV's get pushed all over the road from the wind. We're already so much more aero than alternatives.


I recently made some enquiries with the distributor of Merlin Flex panels. Airstream has recently switched to using Merlin panels on the 2023 model trailers, although these are still “hard” panels - I believe their made by sticking the Merlin flex panel to a frame by Airstream as Merlin does not seem to make a heard panel.

Anyway the distributor told me that the preferred method for replacing a broken flex panels is to stick the replacement panel directly on top of the broken panel. Apparently these panels are super thin 5/16” I believe so adding another layer is no big deal.
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Old 10-03-2022, 08:50 PM   #13
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Originally Posted by GetawA-S View Post
My best results came from setting a 14’ canoe above my topper. For that trip, I achieved 8 to 10% better mileage than I normally do.


That’s interesting. We towed with 10’ kayaks on the car roof. I was pleasantly surprised to discover no appreciable difference in drag or fuel economy.
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Old 10-03-2022, 08:57 PM   #14
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Originally Posted by jcazes View Post
Flexible solar panels is a huge no-no unless you're installing them to a serviceable surface. The plastic that allows them to flex will yellow in just a few year's use, and they are nearly impossible to remove.



I installed 6 hard panels a few months ago and have barely noticed a change in mpg. Possibly 1mpg, but likely less. You'll end up spending any fuel savings on the increased labor cost to remove the panels.



I can appreciate the sentiment of this post--I thought about trying to design some sort of aero shield in front of my solar panels--but the effort wouldn't lead to any meaningful gains.



I also wonder if anyone here's ever towed anything besides an Airstream. The difference is hilarious. Box RV's get pushed all over the road from the wind. We're already so much more aero than alternatives.


Yes. We borrowed an enclosed cargo trailer on a few occasions - a small one 5’ wide and 10’ long. It weighed about 1000 lbs empty. It obviously was easier to tow than the old 27’ Airstream at lower speeds, but by 60 mph the Airstream seemed to create less drag. And even my wife found the Airstream, at 6x the weight, more stable and easier to tow.
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Old 10-05-2022, 04:44 PM   #15
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Quote:
Originally Posted by Aerowood View Post
For the best aerodynamic improvements one would need to reduce the parasite drag from all the "stuff" mounted to the exterior skin. This would mean removing the Air conditioners solar panels awning etc. I guess one could fabricate fairing around all the protrusions. But I think that the juice would not be worth the squeeze.

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Yep! My 1949 liner was smooth. No Rooftop AC, stream lined lamps, and these windows that are flush. Sometimes the old ones are better designed.
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