Teardrop aerodynamics... in reverse!

[hypermiler01]

Originally Posted by Bicycle Bob

If you want to see how much engine men think about airflow, just try to find a streamlined roll bar. A bit of cardboard and tape can halve the drag on those, and proper fairings are far better than that.

Roll bars' purpose isn't to be aerodynamic. If the tubing had a teardrop shape, it would have very poor resistance to lateral bending loads.

[hypermiler01]

A previous thread here on the subject had some good info on page 3 and 4.

http://ecomodder.com/forum/showthrea...ds-2914-4.html

http://en.wikipedia.org/wiki/Fineness_ratio



This image matches the pink smoke trail from page 1.

As was brought up in that thread, turbulence isn't the only thing that makes resistance to motion. Visualize an open door flapping in the wind. A very small air pressure difference on one side will slam it around very hard by causing many pounds of force over the area of the surface.

Making the nose more pointed reduces the pressure in front of the car, eliminating many pounds of force that would be pushing backwards.

[hummingbird]

The blunt front end of a tear drop has nothing to do with aerodynamics - it is constrained by surface tension to minimize the surface area of the drop. Low pressure at the back end of the drop pulls the envelop to form the teardrop shape. Just because a teardrop is naturally that way does not mean that automobiles should be subjected to the same rules... Is there an equivalent of the surface tension constraint for automobiles?

Making the nose more pointed reduces the pressure in front of the car, eliminating many pounds of force that would be pushing backwards.

Couldn't agree more there!

[NeilBlanchard]

Hi,

The nose of the Aptera is blunt -- there's not an edge in sight!

[Frank Lee]

.13 Cd:



.19 Cd:



.20 Cd:



.24 Cd:



.25 Cd:



.199 Cd:

I got to talk to an aerospace engineer once when I was a kid, and I asked how a rounded shape could be as aerodynamic as a cone shape (I think I said "more pointy" at the time) on the nose of model rockets. His response was that the round shape presented the same amount of area to the oncoming air as the pointy one, and slower than the speed of sound, they both did about as well to push the air to the sides of the rocket body.

It is spelled out in text that in subsonic flow,all streamlining basically occurs at the rear of the body(presuming flow is attached in the fore-body).At MACH 1 or higher,everything has to do with the nose.A convex hemisphere nose is considered more than adequate to guarantee fore-body attached flow in subsonic flow,and the air prefers the acceleration profile it provides over that of a straight walled conical nose section.Hucho's book demonstrates how little smoothing of leading edges is necessary for attached flow in the VW Rabbit development.A few chips off the ol' block is all that's necessary.

YouTube - Wind Tunnel Testing

This:



Not pointy like this:



Because further pointiness is pointless for it!

Perhaps some definition is in order? Such as what should be called blunt and what should be called pointy? http://ecomodder.com/forum/showthrea...ar-6982-4.html

You're welcome.



All the above are recent entries on this forum..

[hummingbird]

Originally Posted by NeilBlanchard

Hi,

The nose of the Aptera is blunt -- there's not an edge in sight!

Neil... Look at post 29, not 37...

By pointy we don't mean needle sharp. Not even Fighter Jets are needle sharp in their nose. Just that parting the air in a systematic way helps.

[winkosmosis]

Note that the nose of the jumbo jet is not a dome like a teardrop. It's pointed like a parabola or ellipse.

The nose of that Mercedes fish car is also pointed. It's not cylindrical or globular anywhere

[winkosmosis]

More pointed noses







It's simple physics. The more angled the sides of the nose are, the easier it is to part air. The negative ideas about pointy noses probably comes from the fact that a cone stuck onto a cylinder is not very aerodynamic because airflow fans outward thanks to the lack of a gradual transition.

[Frank Lee]

[winkosmosis]

Frank, when are you going to post a picture of a plane with a dome shaped nose?

Edit: I scrolled back up and saw that you said that further pointiness is pointless. You're right. At some point, for a certain speed, more pointiness is past the point of diminishing returns