Aerodynamics

[Elumia]

So this should open a can o worms.....

Most new Euro "caravans" are more of a wedge shape than a teardrop. So, that begs the question, is it a better aerodynamic shape or just a matter of practical aspect to fit everything in and be more aerodynamic than a big ole refridgerator box..[/img]

[Chris C]

Maybe Andrew can chime in on this one and help you out.

[Classic Finn]

Practicality is one big factor... as well as the aerodynamics....and Weight...


This is what Ive seen here in Finland and Sweden ....


Classic Finn

[angib]

So, that begs the question, is it a better aerodynamic shape or just a matter of practical aspect to fit everything in and be more aerodynamic than a big ole refridgerator box..

I've still got this graphic sitting in my personal gallery since the last time I answered this question!



Volkswagen did some full-scale wind tunnel tests (I would guess 20 years ago judging by the shape of the Passat they used) which showed that the slope-fronted trailer has substantially better stability. The drag and hitch load (at 50mph) data are given in order below:

Square front: drag coefficient 0.53, hitch load change -75lb
Roof spoiler: drag coefficient 0.45, hitch load change -70lb
Slope front: drag coefficient 0.53, hitch load change +/-0lb

So the slope-front trailer has no less drag than the square front, but doesn't generate any lift on the hitch. As a Yurpeen trailer will typically have a very light hitch weight (7% is recommended but most cars are limited to 220lb or even 165lb), losing 70 or 75lb is very significant for swaying.

It's interesting to see the drag data for the roof spoiler as these were a fashion for trailer towing at one time over here. That 0.08 difference is a 15% reduction, which should provide a 15% improvement in fuel economy.

Andrew

[alaska teardrop]

Andrew - I'm wondering if you or anyone else on the board has access to computer generated computational fluid dynamics. Could be interesting to test some of our teardrop shapes including tow rig. Guinness lists the speed record for a caravan tow at 139.113 mph. I'd bet some folks on T&TTT could beat that! Fred - the worlds' farthest North teardrop builder. Blue sky - 33* below - in need of more [/img]

[Guest]

Andrew - I'm wondering if you or anyone else on the board has access to computer generated computational fluid dynamics. Could be interesting to test some of our teardrop shapes including tow rig. Guinness lists the speed record for a caravan tow at 139.113 mph. I'd bet some folks on T&TTT could beat that! Fred - the worlds' farthest North teardrop builder. Blue sky - 33* below - in need of more [/img]

Fred,
Grant Whipp is building a salt racer...
He should be able to smash that record, should he decide to take a Lil' Bear along for the ride.

[Arne]

Andrew, what is your interpretation of the flat front vs. slope front then..?

Seems like it means rounding the front of a tear is useless...... the rounded part is simply a double slope, one up, one down....

When I chopped my top down, I did gain some measurable mileage, but I also ran the curve further back and made it more gradual.... Now I'm not sure where I gained it, through cutting it down 6" or changing the shape.

My design for no. 2 has a very small radius on the front to keep the least possible flat part to the air.... now it seems it does not matter much.

I may have to investigate some sort of wing to attach to the roof rack of my van.

[bledsoe3]

I don't know how much weight you removed, but that could count for at least some of your mileage.

[Arne]

Don't think so, as I added (as in 'appended') a galley to the back, extending the tear by 19", from 104" to 123", and adding a microwave, etc..... I think the weight actually increased... indeed, I'm sure of it...

So, it has to be the 6" drop in height or the change to the front contour......

See pics at:

http://www.freewebs.com/teardrop-stuff

[bledsoe3]

I forgot you extended it. I even followed you progress at the time. My CRS must be acting up again. It must be the height then.

[wa_flyfisher]

http://www.cfd-online.com/Wiki/Fluid_dynamics

Did someone say Fluid Dynamics?

[angib]

Andrew - I'm wondering if you or anyone else on the board has access to computer generated computational fluid dynamics.

Even now, I think CFD is pretty serious stuff - finding someone with access to an academic institution's CFD would be the only way to get it free/cheaply, I would think.

Building a detailed enough model to accurately represent a car-trailer combination sounds quite complex and the results would only apply to that particular tow vehicle. It sounds like way too much work to get very limited answers to me.....

Andrew

[angib]

So, it has to be the 6" drop in height or the change to the front contour......

I'd say the 6" drop in height came first, second and third in the list of important factors....... I should stress that this is for your case, where the trailer used to stick up out of the 'wind shadow' of your minivan*.

There is nothing as good for low drag as not having so much vehicle!

Andrew

* PS I hope your vehicle is what you call a minivan - this is what I think a minivan looks like:

[Arne]

Andrew, go here and take a look at the last two pictures. The original tear was 6" taller and the frame 4" higher off the ground.

http://www.freewebs.com/teardrop-stuff

I may take a model and mount it on a spring loaded arm and drive down the road at 30 mph and see what the spring tension is, then change the model with a different front (flat) and see that the spring tension is....

One thing that has always intrigued me is that a boat with a bulbous bow has less resistance than one with a knife sharp bow.....

[goldcoop]

Hey all!

Here's a great Aero cargo trailer!

http://tinyurl.com/7hazv

Cheers,

Coop