Aerodynamic drag help

[gudmund]

don't know yet if it will help?, but in the next month or so, I hope to find out being I am planning on heading east across the states from here in the PNW (8-9000 mi planned trip) The 'spoiler' came out good - am happy with it Had to install the canopy tracks for mounting the Yakima cross-bar and than bought a 1/4 inch thick piece of Plexi-glass for the panel it-self. This trailer is 4 inches higher than the PU, but now with the 'spoiler', it is now 1 inch above the trailer. But, now as far as 'pay-back' if it does work? It will take 'awhile', being there is 'about' $300 in the whole setup ($120 in the 'New" canopy tracks I installed myself - $25 for the 'used' Yakima cross-bar - $60 for the Yakima track mounts - and last, $80 for the Plexi-glass panel) - '$$$', here to day - gone yesterday.....................

[jimbo69ny]

Hey you guys are talking my language. I am about done with my squardrop foamie range extending trailer. I focused on aero with my build.

You can check it out on my youtube channel. youtube.com/jimbo69ny
Here is one of my latest videos. https://youtu.be/FhIBSeqz7Jo

[Socal Tom]

So the main issue with a flat back is that it creates a "vacuum" behind the trailer that tries to hold you back. As I understand it, the idea with the flaps on the semi trailer is that they give the wind something to "stick to" so that it can be directed into the vacuum, reducing the impact. There are a few other things you might do to help, something like a Kammback design
https://en.wikipedia.org/wiki/Kammback
I think the Kammback is also what leads to the flaps on the semi trailer, some sort of downwards slope, before you have the flat back seems to have a significant improvement.

[gudmund]

after 9685 miles this year with this spoiler on top of the truck towing the tear - it is time to report back with the 'mileage' results. (May not be the best comparison being most of my travels are in the west coast area driving the Cascade Mountains here in Wash/Ore/Calif/Canada) But last year my travels with-out the spoiler, I drove 5195 miles using 327.8 gallons = 15.88 mpg overall. This year so far = 9685 miles using 560.7 gallons = 17.29 mpg with it. 6700 miles was the trip over the Rockies and onto Minn. and back with the rest (1605 mi) being just completed a few days ago from home here, back into the Rockies/Cascades of Mont/Idaho and Wash. (all of the way to Salmon, Id. with the return route over Lolo Pass, Id, the finish route of our 5th Tearjerker Crawl) - this trip was a lot of N/S/E/W hill climbing between camp sites. But overall, there has been a +1.4 mpg increase in overall fuel mileage so far. I do have a few planned slight modification changes to do to the spoiler over the winter and will try to remember to report back in a year or so on the future results - but so far -overall- there seems to have been a 'plus' in mpg in doing this add on so far - but there 'maybe' just take a 'bit' of time in the 'pay$$back' after spending about $300 to build it = oh well, -$Money$ - here today, gone yesterday - it's only $$ and you can't take it with you after you are gone, so I might as well spend it now.............................

[Sparksalot]

What the big rigs are doing is a modern version of what's called a Kamm Tail. 50 years ago, many race cars where designed around this. Kamm did aerodynamic research on the true teardrop shape, then modified it by cropping the tail of the teardrop. He found you can significantly shorten the length of your vehicle, while maintaining the low drag, if you start the teardrop, then crop it.

Probably the most famous example is the Shelby Daytona Coupe.

[Aguyfromohio]

Keep in mind that over-the-road trucks and world class racing teams are happy to chase the last few percent of drag reductions because it is worth so much money to them. Tens of thousands of dollars in fuel savings for a big long haul semi, and all the prize money for a racing team. For me and my teardrop the possible fuel savings are not enough money to justify making any compromises to the size or shape of the trailer.
Of course, your mileage may vary...

[Pmullen503]

On my 1700 mi trip a couple weeks ago I spent $221 on gas. Without the trailer it would have been $200. Some of that is just the effect of extra weight, some (most?) is extra drag. I think it would be tough to cut the drag in half but if I could it would only save $10 on a trip like that.

[gudmund]

Just did the math on the 'payback' of the $300 I spend for this 'spoiler' and I now realize it won't be as long as I had thought. If this +1.4 mpg increase I have realized 'so far' in the last almost 10,000 miles holds true - I am almost $halfway$ there in paying for it already. At the 15.9 mpg that I had averaged last year - it would have taken 1260 gallons of gas to drive 20,000 miles - at the 17.3mpg I have now been averaging this year, it will come to 1160 gallons being used for same 20,000 mile drive = that would be 100 gallons of gas saved and at the '+/-' $3.00 per gallon cost of gas, that equals the $300 I paid to build this spoiler......................

[trevize1138]

Hello!

New member here. I don't yet have a teardrop but I'm looking into either buying or building one and aerodynamic drag is a major factor for me due to one of my potential tow vehicles: A Tesla Model 3. I mention it because most of the conversation is about fuel economy and money saved on that with the conclusion that the financial savings are pretty minor. But with EVs it's a bit different because electricity (even at fast charging stations) is already cheaper.

But wind drag will reduce my battery range more than just about anything. A gas-powered vehicle is already very inefficient so extra drag reducing the efficiency further doesn't make as big of an impact. An EV is about 3x more efficient in its use of energy so every little thing can cause major changes in range. At most an EV has 300 miles of range and if that's reduced to 150 or less that's a lot of extra stopping. Out here in the upper midwest the fast charging stations are spaced out such that if my range while towing dropped to 100 miles or less it might become questionable whether I could make it from one stop to the next.

I guess it's something to keep in mind as more and more EVs come on the road and especially as this next year a lot of the new EVs are going to be in the CUV category. Aerodynamics so far may only mean saving a lot of money if you're dealing in economies of scale because you own a large trucking company. If you have a gas-powered vehicle you're saving pennies but with an EV these days it could mean needing to call a tow truck if you're towing a camper into a headwind.

[gudmund]

in 2016 when at the Lake Shasta, Calif. Teardrop gathering a lady(Doctor) from San Fran. showed up in this '14 Tesla towing a 1 person 'Little Guy' tear. She said Tesla and her were working together on this. She said Tesla had figured she would loss maybe 20/25% of her driving range when towing, but she said it had been more like a 35/40% loss and it was getting a little 'iffy' between charging stations (this was one of the early Tesla's)
Earlier this this year just a few month's ago, when I was at one of my local RV trailer lot's, I spoke to a guy with one of the new 'smaller' Tesla 3's towing a bigger/standy version 'TAB' trailers and he said it was doing just fine towing. He said he was able to go something like 160/190 miles towing with it and had been fine going between charging stations.

[kmack67.km]

SNIP

I guess it's something to keep in mind as more and more EVs come on the road and especially as this next year a lot of the new EVs are going to be in the CUV category. Aerodynamics so far may only mean saving a lot of money if you're dealing in economies of scale because you own a large trucking company. If you have a gas-powered vehicle you're saving pennies but with an EV these days it could mean needing to call a tow truck if you're towing a camper into a headwind.

I know this seems to fly in the face of EVs, but have you considered including a gas or propane powered generator in your TD, effectively making it into a tender? Yes, you would be using gas and emitting CO2 while on long trips but if that means you can continue to drive your EV the other 95% of the time, you are still saving money and emitting much less per year than if you used a gas vehicle instead.

Just a thought,
Kevin

[trevize1138]

I know this seems to fly in the face of EVs, but have you considered including a gas or propane powered generator in your TD, effectively making it into a tender? Yes, you would be using gas and emitting CO2 while on long trips but if that means you can continue to drive your EV the other 95% of the time, you are still saving money and emitting much less per year than if you used a gas vehicle instead.

Just a thought,
Kevin

Well, over time the range hit issue and distance between fast chargers gets better. Three years ago there were 600 Tesla Supercharger locations worldwide and today there are about 1600 and the rate of construction is accelerating. VW has their own fast charging network that's being built rapidly and hopes to surpass Tesla's by 2021. And if we're stopping to camp along the way for a road trip often that's going to be at a KOA or other place that has electrical hookups that work just fine for overnight charging an EV.

I'm not at all morally opposed to a propane or gas generator. I didn't really get an EV out of environmental activism but because I'm in IT and I love elegant solutions. Part of why I never even considered a hybrid or PHEV. Because of that I'm more apt to spend money on rooftop solar panels for the TD even though it'd be more expensive than a generator just for the whole techie/elegance of the thing. And in a few years I hope to replace our Outback with a 2nd EV that will be more in the CUV size range with even more range.

[kmack67.km]

A solar panel tender / teardrop would be an elegant solution for sure. I imagine you will need a lot of panels, and batteries to smooth out the demand, but it would be cool if you can make it work.

[rjgimp]

A solar panel tender / teardrop would be an elegant solution for sure. I imagine you will need a lot of panels, and batteries to smooth out the demand, but it would be cool if you can make it work.

Seems a bit Rube Goldberg-ish to me, but each to their own!

[trevize1138]

A solar panel tender / teardrop would be an elegant solution for sure. I imagine you will need a lot of panels, and batteries to smooth out the demand, but it would be cool if you can make it work.

I wouldn't use the solar panels to charge the car at all just for the trailer. Yes, to at all reasonably charge the car with solar you'd need to abslutely carpet the entire campsite with panels!