Teardrop aerodynamics... in reverse!

[hypermiler01]

BTW, that doodle bug thing was clearly designed for low speed operation. The angle of the back is much too steep to maintain attached flow at higher speeds, and another flaw in it's design, besides having too high of a stagnation point in front, is the the back ends in a radius, when it should end either in a point, a sharp edge, or a sudden, sharp-edged cut-off. The blunt rounded tail will cause turbulence behind it at higher speeds.

[Frank Lee]

Yes, clearly. Why I can see all that by looking at it.

[winkosmosis]

Originally Posted by hypermiler01

The reason that the noses and wing edges of airplanes are not razor sharp is not because it wouldn't be more efficient, but because they are frequently subjected to gusts and angles where the leading edges are not in line with the oncoming air, and the air would shear at the edge and stall, rather than following the curvature around to the top wing surface.

But the radius of the leading edge is kept as small as possible to avoid pushing air while being large enough to do the job of maintaining attached flow at the necessary range of pitch and yaw.

Also though, a wing must be at an angle in order to generate enough lift to support a plane. Contrary to what they teach in grade school, the vast majority of lift comes from redirecting airflow downward, and a tiny fraction from the Bernoulli effect.

[hypermiler01]

Originally Posted by Frank Lee

Yes, clearly. Why I can see all that by looking at it.

Yes, of course you can.

But just in case you couldn't, here's a picture.



Not only does this show the air tearing apart behind it, but it also shows how the air is disturbed several feet ahead of it. The snowflakes begin seperating where the blue line on the ground is destroyed.

Meanwhile, the pointy nose, under the same test conditions, has absolutely no effect on the air even just a few inches ahead. The blue line on the ground continues almost completely undisturbed, and both the blue and pink lines on the object maintain attached flow, and reunite behind the vehicle almost as though it was never there.

[MetroMPG]

You can't model flow around a 3d shape with that program, so your conclusion is flawed.

[NeilBlanchard]

Hi,

I think this recent EM thread has direct relevance:
http://ecomodder.com/forum/showthrea...nose-7131.html
This shows that blunt is better for the front.

[hypermiler01]

Originally Posted by NeilBlanchard

This shows that blunt is better for the front.

Looks to me like it shows that longer, lower, and pointier is better. Unless faster and more efficient is a bad thing.

I guess you mean that the radiused transition to the top surface is good. Yes, when there is a vertical surface below it, but most of the gain came from lowering the stagnation point, making the vertical surface smaller, and covering the headlights.

[hypermiler01]

Originally Posted by MetroMPG

You can't model flow around a 3d shape with that program, so your conclusion is flawed.

No, sorry, I don't think it is.

But I am sure that everyone here, including yourself, is already well aware that the required angle of taper is not the same for all speeds, but varies in direct proportion to speed, and that what I said about faster speeds needing a longer, more gradual angle to prevent detachment is the truth.

And I am sure that everyone here also knows that it is just silly to radius the trailing edge, as that causes turbulence in the flow.

[NeilBlanchard]

Hi,

The angle of the back of the Pillbug looks like it is pretty similar to the Aptera.

The 240Z 'G' nose has a lower stagnant point, and the the leading edge is blunted, and the headlights are covered. The length is changed because that is the angle of the hood they are working with, but the frontal area is the same (ignoring the wheel well flares), so the length is irrelevant for this discussion.

I think that if the Pillbug had a abrupt truncation it might help the Cd a bit -- the Aptera and the VW 1L have this; but then both of those have higher drag. Actually, the Aptera Typ-1 beats the Pillbug 0.11 vs 0.13, but the Aptera 2e is 0.15.

Lets not forget about the Maybach with it's 0.14 Cd (with a curved windshield) and 0.16 Cd with a flat windshield -- another example of a blunt nose on a low drag vehicle. This car went 150mph with only a 150HP engine.

We have the Aptera Typ-1/2e, the Pillbug, the Maybach, the VW 1L, the EV-1 -- all very low drag street cars; all with blunt noses. Do you have any examples of street cars with pointed noses, with a lower drag coefficient than any of these?

[hypermiler01]

Simply being longer isn't what is important, but it's the way that the additional length is used to adjust the angle of the nose. That angle has a direct effect on the behavior of the air flowing both over and under the nose (as can be seen on page one of this thread, and in my picture above), and on the pressure of that air.

My argument is supported by hundreds of thousands of cars specifically designed for reduced drag, and the only reason that you don't see more of them on the street is because of ground clearance, speed bumps, dips, etc.

Basjoos's car is an example, and so is the one in my garage. Most of the others cost more than a house.