Teardrop aerodynamics

[loaderman]

Looking at building a 5 foot wide by 8 foot long teardrop.
Wondering if a rounded front slopeing down to the rear, is much more aerodynamic and how much feul will it save over a sloped front and slopeing down to the rear.
Thanks for any help.

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[GTS225]

Do a Google search for the "Clark Y" airfoil pattern. That is a classic airfoil shape that was used for many decades for good lift, on a (relatively) low speed airplane wing design. That should answer your question quite nicely.

Roger

[Sparksalot]

I've towed Rose with 4 different tow vehicles. I can honestly say I've not seen any difference in mileage on most terrain. When I get into the mountains, there is a difference, but that's most likely the 1,500# loaded weight.

You can see Rose in my album, but she's a very classic trailer for two teardrop profile.

[booyah]

For what they are most tears arent really that aerodynamic, the exception is he CLC TD.

Mine towed by a Scion XD 1.8l 4 cyl cut my gas mileage by about 23% (about 35 to about 27)
Towed by a Kia Sorento V6 its cut also by about 23% (22 to about 17)

This is for an 8x5 benroy profile weighing in at under 900lbs.

I'lll be honest I feel the 23% on the kial a lot more than I felt the 23% on the scion :-) 27 is so much nicer than 17....

That said it kills my friends with the 23ft travel trailer who are lucky to get 8MPG with their expedition while towing.

[tony.latham]

The classic teardrop is reasonably aerodynamic. At least compared to a big fat Jayco.

And they are efficient to use. If you modify the shape to get better mileage, you'll decrease the camper's livability. Everything has its price. The galley won't be as functional (the countertop will be hard to reach) and there will probably be issues with the cabin area.

Having owned a four-wide teardrop, I can testify that width does matter when it comes to towing. But having owned a five-wide for six years, we're not going back.

But you could build a little 3' wide teardrop-shaped camper. It'd tow like a dream. It just wouldn't work well when you got to camp. Trade-offs.

Tony

[Tyrtill]

You are probably concerned about fuel economy and what seems to make the most difference is fitting the trailer into the "shadow of the vehicle". As long as you don't make the trailer too tall the aerodynamics won't make a gigantic difference. However once you get outside the "shadow" the rounded shape does help quite a bit. Notice how in the large version of the trailers there is a flow around the teardrop but it "slams" into the squaredrop. I can confirm this slamming because the top foot of my camper gets coated in bugs.

EDIT: YES width does make a difference in seeing behind you, aerodynamics, and comfort. However most of us are stuck with certain widths mostly due to the comfort factor and or layout.

Also keeping the trailer close to the TV can help too.

I use an app called wtunnel free on iphone to whats what's going on take everything here with a grain of salt
Sorry for the large image

[loaderman]

Yes having it useable for 2 people, and I am 6 foot tall and 250lbs, does really mean a 5 wide.
In doing some research it seems many teardrops actually taper off to much to the rear and that loses the aerodynamic effect.

Not only is the rounding of the front important but also the proper taper to the rear. An 8 foot long teardrop tapers to quickly.
A better design seems to be what is called a Kammback. Rounded front, roof slopes down to the rear then the rear is verticle.
This is used in the auto industry.

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[Tyrtill]

If the app is accurate it's actually more important to round the rear than the front.

[loaderman]

If the app is accurate it's actually more important to round the rear than the front.

From what I read roundingbthe front is important too.
The taper to to rear allows the air you displaced to in a sense push down and squeeze you forward. No angle or too much and you lose this.

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[friz]

For what they are most tears arent really that aerodynamic, the exception is he CLC TD.

Mine towed by a Scion XD 1.8l 4 cyl cut my gas mileage by about 23% (about 35 to about 27)
Towed by a Kia Sorento V6 its cut also by about 23% (22 to about 17)

This is for an 8x5 benroy profile weighing in at under 900lbs.

I'lll be honest I feel the 23% on the kial a lot more than I felt the 23% on the scion :-) 27 is so much nicer than 17....

That said it kills my friends with the 23ft travel trailer who are lucky to get 8MPG with their expedition while towing.

I have had the same results with mine. My best mileage towing behind my Focus was 29mpg. Cheap vacation.

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[alaska teardrop]

Not only is the rounding of the front important but also the proper taper to the rear. An 8 foot long teardrop tapers to quickly.
A better design seems to be what is called a Kammback. Rounded front, roof slopes down to the rear then the rear is verticle.

Agreed. Pictures & quote from Northern Lite Traveler build thread:



Aerodynamics: The lower front wall really doesn't matter, because that portion of the front is always within the slipstream of the tow car. The only way to improve this would be to round the front corners & blend them in to the curve of roof with compound curves.
As the tow car & trailer move through the air, the trailer strikes the air coming off the top of the tow car. The more rounded the top front, the least the resistance.
The blue line represents the boundary layer of that air. As the roof slopes down at the back, the boundary layer is released creating a vacuum that causes drag & lowered efficiency. By keeping that slope at a shallow angle, the boundary layer doesn't release until the very back.
At that point the flip up at the back strikes the boundary layer & turns it under, helping to break the vacuum & drag, increasing efficiency.

The flip up is my version of the Gurney Wicker. So called because it was developed by American racing driver & Indy car builder, Dan Gurney.
Of course, I have no way of testing my theories other than towing the trailer down the road at high speed (which I have ). However, combined with a suspension matched to the load of the trailer & the large radial tires rated at 1356# & run at 21 psi., the trailer rides smoothly & handles well at speed.

Northern Lite Traveler design: viewtopic.php?f=27&t=51991

[Modstock]

In NASCAR terms. You'll draft easier and go faster.


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[DaddyJeep]

My research tells me that the front surface(s) are much more important than the rear. If you can hide your trailer in the shadow of the TV the only significant efficiency penalty will be the weight. My camper can not hide in the shadow so I have added as much radius to every edge that I can. My TV is a big block 1 ton that gets 8 mpg so I want to do what I can to not lose more.

[loaderman]

My research tells me that the front surface(s) are much more important than the rear. If you can hide your trailer in the shadow of the TV the only significant efficiency penalty will be the weight. My camper can not hide in the shadow so I have added as much radius to every edge that I can. My TV is a big block 1 ton that gets 8 mpg so I want to do what I can to not lose more.

My trailer will be wider and taller that my chevy cruze.
Rounded front us important from what I read.
So is a gentle slope to the rear a Kammback design.

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[Cosmo]

Great topic! I am wondering about the wings I see sticking out of the back of truck trailers these days and the panels down low on the sides of trucks at the side space between the front and back wheels. I have to assume these devices are helping fuel economy. Not sure how extending the trailer on the rear cuts drag (unless there is suction there that is moved away from the trailer. On that note I have seen many drivers drafting off the truck in front of them so I tried it for a short distance and I could see my mileage go up when I was close.