Dramatic drag comparison

[sendler]

Originally Posted by RedDevil

Compare this to the old video Darcane posted in this link:
http://ecomodder.com/forum/showthrea...rag-25378.html

From that, at 5:49:

Ten times. That is quite a bit less than the NACA wing shape, but the wing shape used there did not have the concave tail section.
Would that alone make for such a big difference?

Apparently careful design has allowed the much thicker concave airfoil to maintain the same drag as the thinner airfoil in the video which was not necessarily chosen for max efficient width.
.
Can you imagine the extreme efficiency of an electric Vetter style motorcycle with that pure airfoil top view. Even in the current form of the Vetter fairing which has been made to universal and practical application the gas bikes are over 150 mpg in mixed riding and Hershner's electric streamliner is pushing 300 mpgE.

[skyking]

Originally Posted by RedDevil

I already have a wing shaped sleeve over my car's antenna stalk, but it is a bit out of shape.
I'll use this as a template to craft a new one from hard foam and thick alu foil.

Thanks again for your post. you reminded me my truck has two aftermarket antennas in addition to the standard antenna.
I'd like to keep the CB radio, but the one on the roof is no longer in use and of course is the hardest to remove.
I can make some sleeves though.

[Focus-Ak]

For a wire antenna mounted at the front of the roof and angled backward, the airflow would see an ovoid shape. The airflow near the base of the antenna would also have an upward component that would accentuate that effect, although the upper part of the antenna would likely be in free (horizontal) airflow.

[aerohead]

Originally Posted by sendler

Apparently careful design has allowed the much thicker concave airfoil to maintain the same drag as the thinner airfoil in the video which was not necessarily chosen for max efficient width.
.
Can you imagine the extreme efficiency of an electric Vetter style motorcycle with that pure airfoil top view. Even in the current form of the Vetter fairing which has been made to universal and practical application the gas bikes are over 150 mpg in mixed riding and Hershner's electric streamliner is pushing 300 mpgE.

We'd never be able to use a laminar section on a motorcycle.They're only for 'flight' conditions,tens of thousands of feet above ground level where there is zero atmospheric turbulence.
The Earth has a turbulent boundary layer which can be measured in kilometers of thickness.Any 'laminar' airfoil operating at ground proximity would be subjected to this ambient turbulence and immediately transition to a full turbulent boundary layer,destroying its potential for laminar BL performance.
Craig Vetter's fairing design is about as low drag as we can expect in the real world.

[aerohead]

*subcritical Reynolds number drag= Cd 1.2
*supercritical Reynolds number drag = Cd 0.40
The data is cited in Hoerner's book "AERODYNAMIC DRAG",and the actual research is from the German DVL,1934
*With a "optima" fairing (not shown),the drag is as low as:
^ Cd 0.35 subcritical
^ Cd 0.05 supercritical

[sendler]

Originally Posted by aerohead

We'd never be able to use a laminar section on a motorcycle.

Which brings me to another question. Which streamlined shape would be the best compromise for efficiency assuming frequent off axis wind vectors in the real world? A standard NACA airfoil? Or is there another formula that would be better in rough and off axis air?

[freebeard]

Since all your compromise is with functionality, it may be hard to reduce to a formula. Such formula would need a term for 'the front wheel should have open spokes to reduce cross-wind reactions'.

I propose a squircle.

Except unrotated, so the body is narrow at your head and the road surface, and widest through your knees and shoulders.

[sendler]

The front view is not in question and normally turns out to be an oval with a flat truncation under the middle of the bike. But doesn't even have to be vertically symetrical in any way. The top view is the critical consideration for a two wheeled streamliner since most of the air goes around the sides. Unlike a car which has more air going over the top.

[freebeard]

At an equal ride height the flat-bottomed oval will ground strike before the circle when you lean it over. The squircle-based body could lean to 45°.

I would expect the formula to provide asymmetry in all three axes, with a 30/70 split in the top and side views. My open-wheel race car design has that, and a lowered equator.



Because it isn't a leaner, it also has a flat truncation on the bottom as you suggest. Every vertex is geometrically defined to as many decimal places as one cares to use.

[aerohead]

Originally Posted by sendler

Which brings me to another question. Which streamlined shape would be the best compromise for efficiency assuming frequent off axis wind vectors in the real world? A standard NACA airfoil? Or is there another formula that would be better in rough and off axis air?

The lowest drag airfoil is depicted in the center image in the table below.It has a length to thickness ratio of 3.93:1,or 25.5% thickness.

You've got to have the facility to use body English to keep the bike balanced,which means you'll have to lean 'outside' the body at times,like Craig and Allen have been doing.

'Off-axis' would have a specified engineering target.There isn't a one-size-fits-all' solution.
Enclosed bikes are inherently unstable in gust and unless your willing to go to a trike,you'll have to be physically interactive with your riding environment if you're going to survive.
Unless you have a fortune to give the GALCIT folks at Cal Tech University,for design testing and engineering,shoot for zero-yaw streamlining with an eye on your ability to shift your body around.