COEFFICIENT OF DRAG

[Toad]

Probably one of the best examples of the chopped off rear would include the Kamm tailed Alfa's from the late 50's early 60's as well

Jeff

[ZAMMY1]

drag, schmag, you don't have broads hanging out of the windows taking cellphone pictures of corvettes!

[carlover]

Originally Posted by xtn

The 100lbs of downforce at 100mph for the Exige is no more draggy that any number of cars that produce 100lbs or more of lift at the same speed. It's just a lumpy, scoopy shape people.

Now THIS is how you go 280mph on 200hp or less:

Doesn't generate much downforce does it?

[Bane]

Originally Posted by carlover

Doesn't generate much downforce does it?

Turn it upside down and it will

So what is the official Cd for the Elise? I saw 0.36 and 0.407 in this thread.

[sanchez]

Originally Posted by ZAMMY1

drag, schmag, you don't have broads hanging out of the windows taking cellphone pictures of corvettes!

And no one has ever written a song about a lotus.

In any case I hope the OP gets the info he is looking for.

I don't think I would be too concerned with how much drag the Elise and Exige are making. They are primarily, at least I think, for smaller tracks where their light weight and superior handling are exploited. On the front straight of a track like Road America a 1.8L cycl is not going to keep up with a large displacement V8.

Doesn't make it bad or worse, just different.

[xtn]

Originally Posted by carlover

Doesn't generate much downforce does it?

In straight and level flight it generates about 680 pounds of lift. The vector is pointed at the sky instead of at the ground, but downforce or lift is all the same as far as drag goes.

Originally Posted by bane

Turn it upside down and it will

Even when upside-down, in straight and level flight it generates 680 pounds of LIFT. Sure, the vector is pointing out the belly of the airplane, but it's still pointed at the sky.

Oh and by the way, I'll say it here instead of editing my previous post:
That's 280mph on 100HP !!!!!!!!!!!!!!!!!!!!!!!!!

Now that's a low drag design.

[Beanie]

'Calculate HP including that needed to overcome aerodynamic drag
' rho = density of air in kg/m^3
' Cd = coefficient of drag which is unitless
' FA = frontal area in m^2
' V = car velocity in m/s
Pd = 0.5 * Cd * rho * FA * V * V * V
' Pd = Power to overcome aerodynamic drag
' a = acceleration in m/s^2
' MkG = mass in kg
PinW = (MkG * a) + Pd 'power in Watts
HP = PinW / 745.699872

[sonza68]

Ahhh...the metric units are hurting my head.

[climb4fun]

Originally Posted by Beanie

'Calculate HP including that needed to overcome aerodynamic drag
' rho = density of air in kg/m^3
' Cd = coefficient of drag which is unitless
' FA = frontal area in m^2
' V = car velocity in m/s
Pd = 0.5 * Cd * rho * FA * V * V * V
' Pd = Power to overcome aerodynamic drag
' a = acceleration in m/s^2
' MkG = mass in kg
PinW = (MkG * a) + Pd 'power in Watts
HP = PinW / 745.699872

What's exactly your formula?
* =What's that???

[Conan]

Originally Posted by climb4fun

What's exactly your formula?
* =What's that???

'*' is typically the charcter used to denote multiplication.

[Lancia]

Who needs the metric system?
My car gets forty rods to the hogshead.

[Beanie]

The units don't have to be metric, but they do have to be consistent.
That's Visual Basic source code... part of my program for tuning an Apex'i Power FC. I can see a graph of HP and torque and... (see below)... as I drive and/or replay it later. HP calculation takes drag into account. I got the Cd by doing a coastdown test from 80MPH and someone analyzed the results using some math tool I don't have. BTW, someone gave me the algorithm and I believe it's good.


NOTE: Wheel HP

At some point the program *could* (with absolutely minimal user input) just try different combinations of AFR, ignition timing, and VVT timing until it finds the max power for every possible condition. It just takes a lot of time to write all this code.

[holmz]

Originally Posted by Conan

No. You are talking about two different concepts simultaneously. Drag and lift. The TT has very low drag. The round egg shape is very aerodynamic from a standpoint of low drag. However, it is lift that causes instability at high speeds. The prius and insight are probably very unstable at high speeds because they doubtfully have anything in their design to generate downforce. The reason you don't hear about them as being unstable is because no one drives them at 100 mph.

There is never a no one or a never.
Actually the prius does feel unstable at 100MPH - which is easy to get to if you aren't using cruise control.
If you look at the back - you can actually see a little diffuser... (Surprised it doesnt have a smoother underbelly).

But yeah I wouldn't say it generates downforce - it is slippery though. (and sippy too).

[apexdc]

There is an excellent British publication called "Racecar Engineering" that just started a very comprehensive aero analysis of the Exige.

First article is August 2007. The magazine is usually available at places like Borders, Barnes and Noble, etc.

This month they are comparing a box stock Exige with a Hanger 111 racing version. Very interesting stuff.

If you think our cars are bad on drag, check and see what a current Formula One car is. About the same as a barn door!

[Andrikos]

Originally Posted by Lancia

Who needs the metric system?
My car gets forty rods to the hogshead.

LOL! That was really funny.

[Lancia]

Thanks.

[yacoub]

the newest model Civic that started in MY06 has a pretty good Cd. Helps hit those higher mpg ratings too! =)

[Westrock]

Originally Posted by climb4fun

What's exactly your formula?
* =What's that???

LOL...not used a calculator/keypad much?

[Westrock]

Originally Posted by gogogo

Ok, maybe my TT point was a bad example but Prius, Insight has excellent Cd. Figures.

Yes, once when I was trying to figure out what the actual differences were between fastback and hatchback and such. I came upon some of the lesser know styles and the Prius and Insight are part of the Kammback design....which is supposedly one of the best.

Very cool stuff for sure....a balance of art and science I guess.

I remember a couple years ago one of the major car mags did a comparision of the, then, new Z06 versus the Viper to see which was fastest. I believe it turned out the Vette was as fast if not faster flat out then the Viper despite the 150HP definciency. As it turned out the Viper was horribly unaerodynamic, like a Cd of 0.4x while the Vette as mentioned was around 0.28.

[Bavarian Motorist]

Originally Posted by Westrock

I remember a couple years ago one of the major car mags did a comparision of the, then, new Z06 versus the Viper to see which was fastest. I believe it turned out the Vette was as fast if not faster flat out then the Viper despite the 150HP definciency. As it turned out the Viper was horribly unaerodynamic, like a Cd of 0.4x while the Vette as mentioned was around 0.28.

It's Dodge's design elements. Too boxy!


Not that it matters, but the current Z06 has a cd of approximately .34 as opposed to the regular C6. I just hope it's purposeful drag and not just appearance-induced drag.