Video: clever, simple demo of teardrop shape -pointy end first vs. blunt end first - Fuel Economy, Hypermiling, EcoModding News and Forum

MetroMPG · 07-11-2008, 11:53 AM

Says veteran motorcycle ecomodder Craig Vetter:

Quote:

I am always astonished to discover that most people simply do not understand what streamlining is.

When shown a teardrop shape, most people (including his brother) incorrectly assume it will slip through the air better going pointy end first.

To demonstrate the difference between "pointy end first" vs. "blunt end first", his brother made up a brilliantly simple demonstration using a shop vac exhaust, a clear tube (the wind tunnel) and a model teardrop car.

car:

"windtunnel":

He compares the amount of time it takes the car to be blown out the tube depending on which way the pointy end is facing.

From: Craig Vetter's site: What is streamlining (the Quicktime MOV video is linked at the bottom of that page)

Direct link to the movie (.mov) file: http://www.craigvetter.com/Movies/Streamlined_test.mov

Daox · 07-11-2008, 12:04 PM

Fluid dynamics isn't in your average high school or college curriculum. I wouldn't expect many people to know about it. Cool video and test though.

cfg83 · 07-11-2008, 12:22 PM

MetroMPG -

That is a fantastic video! I wonder how much it would cost to make that?

CarloSW2

hypermiler01 · 03-09-2009, 06:46 PM

The only thing this proves is that a pointy tail alone is more effective than a pointy nose alone. Now how about a test with both ends pointy?

NeilBlanchard · 03-09-2009, 11:34 PM

Hi,

I think that you'll have to trust that two pointy ends would not be as good as the bunt end first. There is a reason that the Schlor "Pillbug" looks like this:

The drag coefficient of the Pillbug is just 0.13, which is lower than anything I have heard of, except the Aptera Typ-1 at 0.11. An early scale model of the Mercedes Boxfish had a Cd of 0.06 -- and it is decidedly blunt!

Just about every airplane wing also shows that the blunt end is better/lower drag.

winkosmosis · 03-10-2009, 01:37 AM

I think most people don't visualize what happens with the rounded rear which is air separating is a messy way.

Frank Lee · 03-10-2009, 01:43 AM

Next up: a rational discussion of politics and religion!

winkosmosis · 03-10-2009, 01:49 AM

Next, make a cone and test it both ways.

aerohead · 03-12-2009, 08:30 PM

Quote:

Originally Posted by hypermiler01

The only thing this proves is that a pointy tail alone is more effective than a pointy nose alone. Now how about a test with both ends pointy?

According to the big dogs,below 250 mph the nose won't effect drag reduction,and can actually increase drag due to increased skin friction.

Coyote X · 03-12-2009, 08:59 PM

Making your own wind tunnel is not that hard or expensive. You just have to get a bit creative with finding parts.

Make - Volume 15

If that link works it shows a really simple but very nice repeatable setup.

Talking about theory is fine but sometimes testing ideas out for yourself is what really gives you the best understanding. A nice small scale tunnel could be built for easily under $100 and would let you test pretty much any idea you might want to try.