Aerodynamics!

[hsutton]

Does anybody know where i might find aerodynamic drag figures and frontal areas for the 68-72 Novas and other late 60s muscle cars? Some of the newer cars have that information in Car & Driver magazine but the old cars aerodynamic's aren't listed anywhere i've seen to date.

[Noob]

with a tape measure, a stop watch, and this book

http://www.amazon.com/Race-Car-Aerodyna ... 358&sr=8-1

you can do a couple of high speed runs and coast to a stop. There are formulas included that will calculate your aerodynamic drag value which is more important than cD given in magazines. You will still need a tape measure to calculate your cars total frontal squarefootage.

So it doesn't matter if you've got a cD of like .18 if you've got the frontal area of a semi. or drag number of .45 if you've got the frontal area of a prowler. cD numbers are just that. numbers.

[David Redszus]

It might be useful to remember that any coastdown measurements will always include rolling resistance as well as aero resistance.

Aero resistance will be a function of CdA and air density.
The frontal area (A) can be measured directly.
The Coefficient of Drag (Cd) can be calculated but the rolling resistance must be removed.
The air density can be calculated from barometric pressure and temperature.

[Cammer]

Go here and scroll down to aero section:

http://purplesagetradingpost.com/sumner ... elinks.htm

[hsutton]

with a tape measure, a stop watch, and this book

http://www.amazon.com/Race-Car-Aerodyna ... 358&sr=8-1

you can do a couple of high speed runs and coast to a stop. There are formulas included that will calculate your aerodynamic drag value which is more important than cD given in magazines. You will still need a tape measure to calculate your cars total frontal squarefootage.

So it doesn't matter if you've got a cD of like .18 if you've got the frontal area of a semi. or drag number of .45 if you've got the frontal area of a prowler. cD numbers are just that. numbers.

Thank you all for your help. I'd probably need a get out of jail free card too if i were to attempt a top speed run on any public road. Some chassis dynos, (Superflow i think), have the coast down horsepower feature from what i've read.

[Eric David Bru]

...Some chassis dynos, (Superflow i think), have the coast down horsepower feature from what i've read.

This will not work for aero since it is stationary...

EDB

[nos-stang]

My desktop dragstrip program has the 69 Nova listed as 23 sqft and drag coef of 0.42. It also has a list of quite a few 50's -80's cars. hope this helps.

[Noob]

yes the coast down is in there as well and there are ways in there to show how to eliminate "rolling resistance". It will be all subject to how close you perform the lab. I'd say nos-stang's numbers are close.

[David Redszus]

For anyone really interested in determining the Cd and rolling resistance of their car, send me an email and I'll send an excel program that will calculate Cd, rolling resistance and power required (at any speed).

[Ed-vancedEngines]

By coincidence this is something Big Joe and others and I were just talking about in another thread about the inner fenders.

We were not actually doing any Coeffient's of drag or anything though. Just off the cuff home brew tricks.

https://www.speed-talk.com/forum/viewtopic.php?t=8430

Ed

[hsutton]

Thanks nos-stang, that is what i was inquiring about. The Chevelle is near 25.5 frontal area with about 420 Cd and Camaro is a little slicker but has more frontal area. Thank you also "Ed". I have a magazine that has an article about Joe's "Mean Green" '70 Chevelle. It seems as though it had a tunnel ram on top of a 454-468 the best i can remember. It was very fast, even now it is still impressive.

[jacksoni]

My third gen (86) firebird is 21.4 sqft. ( have measured it ). Generally you can get pretty good estimate taking widthxheightx0.85. Taking of mirrors, getting it low, blocking off flow through grill/radiator (if legal), keeping air from under the car etc can go long way it improving Aero Drag.

[maxracesoftware]

i'm writting a Program that includes calculating
Drag Coefficient Cd from 2 methods=>
1-Coast Down Method

2-newer Method from DragStrip ET Slip

the 2nd Method is very accurate,
but only as accurate as your Inputs are

i need the following Info

1- HoodScoop Yes or No (this will later be changed to a PerCent for
greater accuracy instead of Yes/No)

2- Density Altitude in Feet at Time of Run

3- 1/4 Mile ET Time

4- 1/4 mile MPH speed

5- Car Weight in Lbs w/Driver included

6- Frontal Area in Sq.Feet based off of .85% PerCent of Area
example=>

Square Feet = CarWidth_inches * CarHeight_inches * .0069444 * ShapeFactor

Normal ShapeFactors: Rectangle= 1.000 Circle= .7854 Triangle= .500

Society of Automotive Engineers SAE J1263 recommends = .800 ShapeFactor

i need you to use => .850 = Baseline ShapeFactor

7- Peak Engine Dyno HP measured at 600 RPM/SEC accel Rate


Equation is dead-on accurate, but only as accurate as your inputs
like if your Dyno reads the same as my Dyno and are both at
600 rpm/sec test rate

i'll run a few simulations if some of you want to compare results

[David Redszus]

Max
Having written a program to compute Cd and rolling resistance from very accurate coastdown data, I would be very interested to see how you approach the subject. I look forward to seeing your results.

I do have a few minor questions.

How does your approach compensate for changes in engine power due to changes in air density?
Do you correlate delta air density to delta power?
Do you consider the effects of air viscosity?
If acceleration and terminal velocity are critical inputs, then how do you compensate for variances in tire adhesion?
While frontal area and shape are considered inputs, what value is placed on undercar turbulence and drag?

And, the nagging problem of all simulations--how does one validate the results?

[maxracesoftware]

For anyone really interested in determining the Cd and rolling resistance of their car, send me an email and I'll send an excel program that will calculate Cd, rolling resistance and power required (at any speed).

can you email me a copy to
maxracesoftware@yahoo.com
thanks