Aerodynamic drag help

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Re: Aerodynamic drag help

Postby gudmund » Sat Jun 08, 2019 1:55 am

158348 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 :thumbsup: 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..................... :roll:
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Re: Aerodynamic drag help

Postby jimbo69ny » Sun Jun 09, 2019 7:53 am

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
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Re: Aerodynamic drag help

Postby Socal Tom » Sat Jun 15, 2019 9:46 am

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.
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Re: Aerodynamic drag help

Postby gudmund » Thu Sep 26, 2019 12:33 pm

158348 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............................. :thinking:
Last edited by gudmund on Sat Sep 28, 2019 10:13 am, edited 2 times in total.
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Re: Aerodynamic drag help

Postby Sparksalot » Thu Sep 26, 2019 9:00 pm

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.

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The Compass Rose build thread: viewtopic.php?t=23213

Inspiration: http://tnttt.com/Design_Library/Trailer%20for%20Two.htm

It's got a cop motor, a 5.3 LS plant, it's got cop tires, cop suspensions, cop shocks. ~ Elwood Blues
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Re: Aerodynamic drag help

Postby Aguyfromohio » Fri Sep 27, 2019 12:25 pm

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...
:lol:
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Re: Aerodynamic drag help

Postby Pmullen503 » Fri Sep 27, 2019 2:14 pm

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.
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Re: Aerodynamic drag help

Postby gudmund » Fri Sep 27, 2019 8:13 pm

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...................... :thinking: :thumbsup: :applause: :beer: 158347
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