In Part 1, I discussed how teardrop shapes tend to make for the best aerodynamic efficiency, why that is, and then how things go wrong with many bogus almost-a-teardrop designs. In this article, I’m going to discuss one more aspect of aerodynamic design, how to actually optimize a larger trailer for aerodynamic efficiency, and discuss some faux-aero gimmicks to avoid.
One More Thing To Think About
The teardrop shape does have some usability problems compared to a camper that’s shaped like a fiberglass or sheet metal brick. I totally get why someone would want something different, which is what the faux teardrop posers are trying to do. But, to evaluate how well a cargo or RV trailer is optimized for efficiency, you’ve got to understand one more thing: how size and aerodynamics adds up to an overall efficiency picture.
Overall drag is a function of both the frontal area multiplied by the drag coefficient. Drag numbers bigger than 1 mean the aero is so terrible that it’s as if the vehicle got bigger and disturbed more air. Drag numbers smaller than 1 mean you’re effectively shrinking the car’s size to the air.
This tells us two things: that shape is more important than size, but also that size does matter. If you have two perfect teardrop shapes with one being twice as big as the other, the bigger one is going to have twice the drag of the smaller one. But, a large teardrop shape is better than a smaller brick shape.
In other words, it’s about finding a balance of these two factors and your needs.
Making Bad Shapes Better
Now that we understand how to make a good aerodynamic shape (try to stay as close to a teardrop as possible) and that size is also a factor, we can start looking at how to strike good balances between the needs of the trailer’s owner (whether cargo or as an RV) and efficiency.
The good news is that most of the teardrop shape isn’t detrimental to spaciousness inside the trailer. Rounding the front of the camper often means a little more space in the front, and you can even raise the ceiling a bit to give the roof some slope and get closer to the teardrop. Just look at the rooflines of most modern cars and you’ll see what I mean about that. At worst, you’ll lose a little cabinet space in a camper or not be able to stack cargo as high in the front.
The thing that makes a teardrop shape inconvenient for both camping and cargo is the tail, but once again, cars give us a great clue for dealing with that: the Kammback design. Like a trailer, having a long, long tail at the end of the car just isn’t practical for most cars, unless you’re looking for an Aptera or a Dymaxion car. Car designers figured out that cutting the end of the tail off of the teardrop shape didn’t affect it too much, but only if you end it somewhat abruptly. The abrupt ending of the teardrop shape allows an air curtain to form that keeps the air from rushing into the space behind the car and sucking it backwards.
The end result is that the vacuum area doesn’t form with nearly the intensity that it would behind the back of a brick-shaped vehicle. It’s also far superior to a curvy vehicle like an Airstream trailer or a Volkswagen Beetle, which have a teardrop-like shape that ends too soon without the abruptness of a Kammback design. So, the sudden end that at least gets the air going in the right direction is essential.
We can get another clue from the way this concept has been applied to semi-trucks.
As you can see, the addition of a small tail on the back of the truck that abruptly ends gets the air going in the right direction to minimize the vacuum zone behind the trailer. Other improvements include side skirts (to keep the air from going under the truck), and deflectors in the front to keep the air from getting hung up.
Another Thing That Works: Minimizing Frontal Area
Another thing you can do to minimize aerodynamic drag is start out with a smaller shape. As I pointed out earlier, overall drag equals frontal area multiplied by the drag coefficient. Getting a low coefficient is great, but if you can also make the frontal area smaller to begin with, you’re multiplying smaller numbers together.
The bad thing about this approach, and the reason it often just doesn’t happen at all in RV and cargo trailers, is that making the trailer smaller directly costs interior space to enjoy the camper or pack in cargo. But, there are creative ways around this conundrum.
For RVs, the most common workaround is the pop-up camper, or tent camper. Instead of a big box, you have a small box that can expand when parked. Most of these designs have canvas walls, but some have folding hard sides and others have unconventional a-frame shapes to allow for easy and fast folding and unfolding. Having hard sides is great for insulation and privacy, but usually comes at the cost of weight.
But, these campers are usually still shaped like a brick when folded down — just a very short brick. Most popup campers’ designs could be improved upon in much the same way you’d improve a semi-truck. Fortunately, this is something you could probably do yourself at home if you’re handy with tools and spend some time reading at EcoModder.
Gimmicks To Avoid
Now that we know what actually works, let’s take a quick look at a few things that don’t work very well.
Probably the most common gimmick you’ll see is a brick-shaped trailer where all of the corners are just rounded. Airstreams, Casitas, and many other campers are just rounded off all around, like someone has taken sandpaper to the brick shape or something. This does partially work because rounding the front corners helps the air slide by easier and rounding off the top corners reduces frontal area a bit. But, it’s a disaster in the back in most cases because it ends too soon without an abrupt tail to create a Kammback effect. So, they’re not as great as you might think at first glance.
Another aerodynamic gimmick are bogus teardrop-esque designs. These usually come in the form of oval-shaped campers, “squaredrops,” weird Cybertruck-looking teardrop-like designs, and dome-shaped campers. Almost all of these are designed to look aerodynamically efficient, but have no engineering basis for the shape. Most of these designs have bad little vacuum zones behind them when pulled through the air, and thus don’t really save you much fuel unless they’re really small to begin with.
Worse are designs that are shaped like a bullet, have a rounded front and a back with no tail or kammback, and other sucky front-only aero designs. Once again, these are designed to look like they’re efficient, but fail to solve the biggest aerodynamic problem (the vacuum zone in the back). Some of these designs may actually kind of work — but only if you pulled them backwards!
Another gimmicky design you might come across are HUGE popup campers. Compared to a full-height trailer, these are more efficient because they have a smaller frontal area, but when they’re too big, they often end up super heavy, aren’t much shorter than a normal camper, and aren’t otherwise optimized for aerodynamic efficiency at all.
Buyers Need To Be Aware Of The Junk Science To Drive It From The Market
I wrote this article so that you could share it. Why? Because informing customers is the only way these bogus “aero” designs are going to stop dominating the market. Right now, most people don’t know that they’re being sold a bill of goods.
Perhaps worse, these fake-efficient campers are going to hurt the reputations of otherwise efficient and powerful electric tow vehicles in the coming years. With most of the public falling for the shiny snake oil, we’ll keep hearing things like, “The F-150 Lightning Can’t Even Pull An Efficient Airstream Across Utah Going 90 MPH” or “The Cybertruck Can’t Get My Giant Faux-Teardrop To The North Rim.”
If people know these claims are meaningless, they won’t hold water, but if you don’t inform them, they’ll fall for them hook, line, and sinker.
Featured image: a screenshot from a video showing actual aerodynamic simulations of a teardrop trailer.
Appreciate CleanTechnica’s originality and cleantech news coverage? Consider becoming a CleanTechnica Member, Supporter, Technician, or Ambassador — or a patron on Patreon.
Have a tip for CleanTechnica, want to advertise, or want to suggest a guest for our CleanTech Talk podcast? Contact us here.
Source: Clean Technica