Tear Drop shape...why?

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Re: Tear Drop shape...why?

Postby NorthEGPhoto » Tue Aug 07, 2018 7:47 am

You know, as someone who basically built your wedge shaped trailer (but not as extreme) - I have to say, making things square is a lot harder than you might think starting out as a novice. After seeing just how easily the plywood will bend- frustratingly while trying to install it, I think if I ever build again after this time I'll be adding rounded elements. plus, it adds strength while removing weight.

I honestly think maybe next time, i will look at a design more like This: /_D

My tow vehicle has a big problem with backdraft. you can see the results of it after driving down any dusty dirt road. the front 7/8 of the vehicle will be completely clean, leaving the back gate and rear covered in dust. Having the front of the trailer slightly slanted will hopefully allow that backdraft a place to 'smooth out' and flow down the back of the trailer.. possibly even improving fuel economy.
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Re: Tear Drop shape...why?

Postby Louisd75 » Tue Aug 07, 2018 10:50 am

NorthEGPhoto wrote:You know, as someone who basically built your wedge shaped trailer (but not as extreme) - I have to say, making things square is a lot harder than you might think starting out as a novice. After seeing just how easily the plywood will bend- frustratingly while trying to install it, I think if I ever build again after this time I'll be adding rounded elements. plus, it adds strength while removing weight.

I honestly think maybe next time, i will look at a design more like This: /_D

My tow vehicle has a big problem with backdraft. you can see the results of it after driving down any dusty dirt road. the front 7/8 of the vehicle will be completely clean, leaving the back gate and rear covered in dust. Having the front of the trailer slightly slanted will hopefully allow that backdraft a place to 'smooth out' and flow down the back of the trailer.. possibly even improving fuel economy.


I think that your best bet would be a vertical front trailer with the shortest tongue that you can get away with. And match the trailer roof height to the tow vehicle roof height. I recall Camp Inn looking into this. They're pretty big into general aviation along with trailer building. They found that at they took a bigger hit to mpg towing their teardrop shaped trailer vs their raindrop shaped trailer even though the raindrop is bigger (the aft end of both models is the same). The vertical front minimized the space for turbulent air to collect, improving mpg and causing less dust to swirl around. I do know that I get far less dust on the back of my truck when towing the raindrop than I do when I'm not, but I have no experience towing another shape to compare my results. Maybe Tony will chime in, I've got a hunch he's spent some time on dirt roads.
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Re: Tear Drop shape...why?

Postby GPW » Tue Aug 07, 2018 10:57 am

Plus there’s that bit of Nostalgia where some want a trailer like grandpa had back in the old timer days … :)
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Re: Tear Drop shape...why?

Postby tony.latham » Tue Aug 07, 2018 12:00 pm

Maybe Tony will chime in, I've got a hunch he's spent some time on dirt roads.


We do... this fifty-six-mile traverse quickly went from gravel to dirt two weeks ago.

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If you look at this pic, you'll see little or no dust coming from the 4' gap:

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What I haven't done is paid attention to the dust buildup on my truck bumper after a tow through the dust. Next weekend. Dust does accumulate behind my vent fan and hurricane hinge.

In thinking about this... freight trains are closely stacked. Bullet trains have no gap.

:thinking:

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Re: Tear Drop shape...why?

Postby Dan242 » Tue Aug 07, 2018 12:40 pm

My wife did not want a door on the side. I wanted to still be able to haul 4x8' sheets of material if needed. I did not need a big kitchen. I did not build a tear, but wanted aero. I wedged the front and made a smaller version of the aero aids you see on semis. I have a rear "porch that is great for sitting on and provides additional storage. This is the design I created. I towed it 2 k miles this summer, pulled easy, never had a problem with it not tracking or moving around. Its not as pretty as a tear maybe, but I lived in it for 2 months and loved it. I did have some paint issues on front where it curves, filled it in with marine epoxy and repainted, issue seems to be solved. My .02
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Re: Tear Drop shape...why?

Postby GPW » Tue Aug 07, 2018 12:51 pm

Nice streamline alternative Dan242 Great job !! 8) :thumbsup:
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Re: Tear Drop shape...why?

Postby timm » Thu Aug 30, 2018 12:45 pm

The rounded teardrop shape is slightly better aerodynamically than a box.
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Here's a CFD simulation of my car. About 265 N of drag force

Now compare this with the same car pulling a 5x8 enclosed box trailer.
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Now the drag force is up to 820 N, that's a 210% INCREASE in drag force over just the car.

Compare this with a standardish teardrop.
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The drag force is up to about 710 N, which is still a huge 167% increase, but considerably less than the box trailer.

Now compare this to a trailer that has been designed specifically to be aerodynamic.
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This is my current design, it's a hard shell pop up with MORE internal space than the rounded teardrop above, yet the drag force is a mere 444 N, only a 67% increase in drag compared to the car. Literally 100% less drag than the normal teardrop.

Here are all the numbers:
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Re: Tear Drop shape...why?

Postby Homebrewer25 » Thu Aug 30, 2018 1:13 pm

Hey Timm,
That's some pretty cool stuff.

what is the software that does that? is it online?
Could any of us input their trailer design and see what the drag force is?

It would be great to know what the drag force would be before you build it.
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Re: Tear Drop shape...why?

Postby timm » Thu Aug 30, 2018 1:35 pm

Thanks, it's been fun running these simulations.
The program is Autodesk's Flow Design, I have access to it with an education license. You might be able to get it with a hobbyist license but I'm not sure.

You'd need an accurate 3D model of your tow vehicle and the trailer, but yeah you could see what the drag force is.
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