Why Is The Prius Such A Drag?

[Rangerdavid]

Actually I understand that Honda has discontinued the Insight as well, so there can be no more new purchases of those made either.

[qbee42]

<div class='quotetop'>QUOTE(Tideland Prius @ Aug 11 2006, 09:31 PM) [snapback]301851[/snapback]</div>

What about the Saturn GM EV1?
[/b]

Or the Saturn V for that matter.

Tom

[Weinerneck]

<div class='quotetop'>QUOTE(daniel @ Aug 11 2006, 09:27 PM) [snapback]301848[/snapback]</div>

The Prius could have had a lower CD if it had been a lower car. Do you want to give up a foot of head room to reduce the drag a bit? Or do you want to sit with your butt 6 inches off the pavement and have to struggle to get out of the car? The point of the Prius is that it achieves phenominal mileage and cleanliness without sacrificing comfort or performance!
[/b]

My thought's exactly.......... I would focus on some of the little things that drive people nuts. I don't want a Prius that's like a Neon, laying on the road (fall in, crawl out) is not for me.

[donee]

<div class='quotetop'>QUOTE(Weinerneck @ Aug 12 2006, 09:35 AM) [snapback]302066[/snapback]</div>

My thought's exactly.......... I would focus on some of the little things that drive people nuts. I don't want a Prius that's like a Neon, laying on the road (fall in, crawl out) is not for me.
[/b]

Hi Wiener... and Daniel,


The reduction in drag from "a lower car" is due to a reduction in the air that would flow under the car. One might rig a deployable front skirt to get nearly this improvment at highway speeds.

I think what Toyota figured out that at speed, the Air is bouncing up off the front to the car as high as Prius cabin is. Filling in that void with the high cabin reduced turbulence as the air went over the top of the car. Making the front of the car sloping like it its probably reduces how high the air jumps after hitting the front of the car which, allows the car to be shorter and obtain the turbulence reducing effect. The Dymaxion and to some extent the Puffer Fish Mercedes Van have the full bluff body treatment in the front. Which addresses this issue right off the bat.

So, making the car lower in body thickness (not lower between the bottom of the car and the ground) probably wont improve the Cd and might actually reduce it. Unless you made the car narrower as well as lower. Thus maintaining the overall shape.

Where Cd might be improved I think, is to do something like Ernie Rodgers did. Not the horizontal portion of his Beetle spoiler. The Prius already has that integrated in. But vertical triangular shaped strakes down the side of the hatch. Styling wise this would be reminiscent of a strakes on a F/A 18, although functionally different. Ernie Rodger's Beetle spoiler has those large side panels, which I think is to keep the air off the roof running straight down the steep tail of the Beetle. The strakes on the Prius might help improve the laminarity of the flow down the hatch, and reduce the turbulent cross-section off each side of the car that might be caused by the air spilling over the sides from the hatch flow zone. Keeping the air on the sides of the car from going turbulent would decrease the boundary layer layer cross section area of the car.

Oh, I am not an aerodynamicist. Anybody who might try this needs to carefully test it to see if it actually improves fuel economy! The improved laminarity would increase friction drag, which might offset the gains due to reduced side air cross-section. A strake has friction drag too. That drag might be enough to offset any gain, too. Ernie Rodgers experience seems to indicate its worth a try though. Then again, the Prius is significantly different from a Beetle. The strakes would increase tail end sideways cross section and might upset the car in cross wind conditions, too. So it would be prudent have the strakes feild removable.


Now, thee is a school of aerodynimc thought that says turbulence can actually be used to reduce the boundary layer cross section at the air-speeds and vehicle sizes of cars. Introduce some turbulence in the right place and the overall drag gets less.

This really needs to be empirically evaluated!

The tall body on the Prius is probably advantageous to the Cd, which probably makes it a wash for the overall drag. So, why not make the car tall, especially if you need to seat 6 foot plus people in it? I think that is the design decision that was made. Make the car more versatile without any additional losses over previous cars. A shorter car of the traditional form would not be able seat a tall person, would have worse Cd and similar aerodynamic drag.

[wstander]

For one thing, you will note the absence of large side mirrors on the Tatra T77; the undercarriage also was smoothed and quite clean. The use of a belly pan helps immensely.

Ferdinand Porsche adopted some of Ludwinka's ideas from the Tatra to incorporate in to his design 007 and before that, the VW.

[rufaro]

I am not a physicist/aerodynamocist, nor do I play one on tv...BUT, do not the two grooves on that high roof of the Pri add to (or rather, subtract from) its cd #? (By the way, in arguments w/ dh & ds about cd of our respective cars--dh's is an '02 beemer --I stated that I had seen a list that showed the PRI to be one of the TWO best PRODUCTION cars (though the '02 beemer does not do too badly on that scale, all things considered--and Insight had not then been officially discontinued). Even 18yo ds hadda give me that one.

We would ALL love to have Bucky Fuller's car...but it is not now, nor has it ever been, a PRODUCTION model. Not CONCEPT. Not NO LONGER AVAILABLE. BUYABLE *NOW*. They BOTH agreed. And, ya gotta understand...it is REALLY hard to win ANY argument with an 18 yo male about cars! :P

[darelldd]

<div class='quotetop'>QUOTE(Godiva @ Aug 11 2006, 07:45 PM) [snapback]301907[/snapback]</div>

Let's get practical and only list cars it's possible to buy. [/b]

But the point of the thread, as I read it, is what is *possible.* And while all the prototype vehicles may not count, the EV1 certainly should. It was produced, and driven. Many millions of miles on EV1s! There's a Cd that is entirely possible in a vehicle that was designed in the late 80's! Just because we can't buy something doesn't mean its past reality should be ignored! I mean unless you're GM.

I'm talking about what is available now. What I can go out and buy and drive. Otherwise, what is the point? [/b]

The point... or the question in this case, is, "Why have we gone backwards in some areas?" If we could build the EV1 (here in America, mind you) with such awesome aerodynamics, why don't we continue to improve on that model instead of throw it away and get back to business as usual? The EV1 was the most efficient full-function car ever produced. And that was with it's old, inefficient inverter and lead batteries. Imagine what we could do today! The EV1 held about half the battery energy as my Rav4EV does... and the two cars had the same range on a charge!

[windstrings]

<div class='quotetop'>QUOTE(daniel @ Aug 11 2006, 06:27 PM) [snapback]301848[/snapback]</div>

The Prius could have had a lower CD if it had been a lower car. Do you want to give up a foot of head room to reduce the drag a bit? Or do you want to sit with your butt 6 inches off the pavement and have to struggle to get out of the car? The point of the Prius is that it achieves phenominal mileage and cleanliness without sacrificing comfort or performance!
[/b]

Agreed, whats the point if you have to crouch down in a cock roach car?

You could make it like a bullet cylinder and lay down in it and get even better.... but every person has to decide where to draw the line.

The prius gives best of all worlds.....

And whats funny, is most of those cars get much worse gas mileage!

[ChuckKtoo]

Damlier's Boxfish concept - .19 drag coefficient. Pretty Good!! Now, where do the fins go...

[Doc Willie]

Originally Posted by Godiva

Seems to me I see a lot of 'concept' and 'prototype' on that list.

Mind reducing it to cars that exist that you can acutally buy? (That eliminates the EV1 right off.)

If you are talking new:

Toyota Prius

Done.