Aerodynamic of the reverse tear...

[Prem]

Conestoga wrote:

I wonder if "golfball dimples" and airtabs are creating a similar effect?

The golf ball dimples are removing the boundary layer, making the object "slipperier" in the fluid...the air. The AirTabs create focused vortices, as per the NASA article. Both turbulate (not cavitate* **) the fluid they are traveling in. (But what do I know? I end sentences with prepositions, for Pete's sake!)

*The sudden formation and collapse of low-pressure bubbles in liquids by means of mechanical forces, such as those resulting from rotation of a marine propeller.

**The act of forming vapour bubbles in a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure. [IA near void of much lower pressure.]

Visible turbulance of air

And the visible cavitation of air...not the stargate.
http://en.wikipedia.org/wiki/Sound_barrier

Also see: http://en.wikipedia.org/wiki/Eye_(hurricane)

Happy teardropping,
Prem

[angib]

Hey, I'm vain enough to simply repost the whole of a post I made on this subject exactly a year ago:

A while ago I suggested that it might be possible to build a zero drag trailer - that is, it would use the extra length to improve the drag coefficient of the combined tug-trailer. This was my idea for a trailer for an older CRV (and only that one tow vehicle):



Well, Honda have proved that not only can you have a zero-drag trailer, you can actually have a negative-drag trailer.

The solo Honda Insight has a drag coefficient of 0.26:



Honda built this trailer with flexible panels attaching it to the car's body, so that there is no gap but it can still can turn corners:



The car-trailer combination has a drag coefficient of 0.12 - just less than half the drag of the car alone! There are a few 'fiddles', like enclosing the front wheels, so it's not strictly just a very-close-coupled trailer. The trailer is even sorta teardrop-shaped, though there's not going to be much room inside it.

Anyone interested in aerodynamics might like to visit the web page I stole this from:
A�rodynamique des Vehicules Routieres
Yup, it's in French, so here is a (poor) translation to English
Aerodynamics of Road Vehicles

Happy streamlining
Andrew

PS Dimples would have no effect on a road vehicle - they are used on a golf ball to trip the airflow from laminar to turbulent (note, this is not detached, just turbulent - two very different flows) because the golf ball is so small the airflow doesn't go far enough over its surface to trip itself - but it does in any road vehicle.

[Prem]

Andrew...and any brave soul who is still with us here,

In brief summary then: It's AS important how you take apart the airstream (frontal shape) AS how you put it back together (rear taper to a point); the standard airfoil being the optimal shape.

My current trailer is an aluminum box. I cheat the coefficient of drag equation a bit with AirTabs on the rear. Cheating gets me a free gallon of gasoline about every 100 miles.

This Babel Fish translation from the French was especially curious and simultaneously entertaining:

Convincing example, for those which would doubt it, of the aerodynamic effectiveness of a frayed poop (with the detriment certainly of the obstruction). (Honda Courtesy)

WELL, okay then!

There *are* the nautical terms poop deck---deck over the stern---and to be pooped---have a wave come over the stern---from the Latin puppis meaning stern. (...and ya'll thought it meant something else now didn't ya?)

Toward the bottom of the webpage, there is more detail (and video) of the NASA Dryden Flight Research Center truck tests previously mentioned. GOOD find. Thanks.

Gotta go to bed now. I'm pooped.

Prem

[Conestoga]

I read these fun and informative posts late last night and resolved immediately to build using frayed poop. Surely it could be molded easily, and others would think it was Rhino liner. Or, depending on the amount of frayed fibers added, they might think it was a new type of fiberglass. I could build in elements at the trailing edges to create the counter-rotating vortices, as well as many other cool bells & whistles.

At what temp. does frayed poop need to be fired in the kiln? What types of fibers can be added to the poop so that it does not catch on fire in the process? And last but certainly not least, is it lightweight enough for this application?

[Prem]

Conestoga wrote:

I read these fun and informative posts late last night and resolved immediately to build using frayed poop. Surely it could be molded easily, and others would think it was Rhino liner. Or, depending on the amount of frayed fibers added, they might think it was a new type of fiberglass. I could build in elements at the trailing edges to create the counter-rotating vortices, as well as many other cool bells & whistles. At what temp. does frayed poop need to be fired in the kiln? What types of fibers can be added to the poop so that it does not catch on fire in the process? And last but certainly not least, is it lightweight enough for this application?

OMDog! That's hilarious! My comments below:

Yup. Uh huh. You certainly could. Only 125 degrees F. Asbestos. Yes, super light weight. Please post photos of hands-on process asap!



Prem

[Conestoga]

Please post photos of hands-on process asap!

Ok Prem. I worked hard today. Unfortunately just after I picked up my new trailer, and was grinning all the way down the road, somebody was texting as they went thru the intersection and plowed into the port side of my trailer. Luckily I was able to continue, and I got a load of materials to get started.

I will be changing to a ball hitch. I think the stickers are cool, and will provide a rough surface for the flayed poop to adhere to.

Lots of work to do! Suggestions welcome!

[Ageless]

Make a slurry and use a texture gun to shoot it on

[Prem]

Conestoga,

GREAT start! Add Vermiculite and some Elmer's glue to the slurry and the stuff will be lighter and tougher!

Prem

P.S. I feel sorry for the tike on the trike who was texting when he ran into your trailer. A low, small dent like that means only one thing: It was a Murray.

[Conestoga]

Prem, actually it was the guy who has a lawnmower as his daily driver. He was ok. I was so surprised he was using mobile phone and he didn't even flip me off this time.

Thanks everyone for the good suggestions.

[Prem]

Oh hey, one other thing:

MegC (over on the Cargo Trailer forum) is looking to do a "grunge trailer" and this would be perfect! Drop her a PM asap. She may pay you to build a second one for her!

Prem

[Prem]

It wasn't a flip phone?

Prem

[Conestoga]

Bringing this 'round again to aerodynamics...

http://hackaday.com/2009/12/25/aerodyna ... en-cooler/

[artwebb]

[Prem]

Conestoga,

I was going to do something like that for the back of my cargo conversion before I found AirTabs. But I was going to curve aluminum square tube and rivet light aluminum sheet to it instead of using wood products.

Good find.

Prem

[MegC]

Oh hey, one other thing:

MegC (over on the Cargo Trailer forum) is looking to do a "grunge trailer" and this would be perfect! Drop her a PM asap. She may pay you to build a second one for her!

Prem

Having never worked on a trailer or anything like it, I have no build advice. However... as a dog musher, my friends and I can hook you up with an endless supply of building materials for your project. Come spring time those with alaskans, siberians, mals, and samoyeds blowing coat can also supply more than enough 'fiber' to mix in for structural integrity.

We mushers will recognize you as one of us by smell of course, and you will be instantly welcomed into our fraternity.