Trebuchet03's JettKamm

[trebuchet03]

Originally Posted by Ernie Rogers

I am coming in late on this topic, I think-- Do you have any Cd numbers? If so, how do the modifications compare to the original shape?

VW Factory cD is something between .30 and .33 - it's already fairly low for a 2000 notch back.

I have lots of numbers from my own work... But I am purposely not reporting them. I don't like the numbers, they're too low, so I'm rejecting their validity. That's science for ya I have, however, been using them barometrically.

It's my goal to attempt empirical measurements in an ABA fashion - but not using a ScanGauge. Ideally/Dangerously, I'd like to tow the vehicle with a force gauge inline. Tow at slow velocity for mechanical losses and at high velocity for aero measurements... I've done this with great success with HPV's - but cars are a very different animal with much higher velocities o.0 I forgot to mention, recently I've got access to a VAG-COM

[JasonG]

Long time lurker, first time poster.
Robert Riley has a nice write-up on foam fiberglass one off work at rqriley.com
Basically the way Tre stated he was going.
I talked to an aviation friend that stated the optimal angle of convergence depends on the velocity (and fluid density of course). The often quoted 14 deg angle is optimal for 110 MPH (IIRC) in air @ sea level. You may find when you increase your air speed that you will need to lower your angle to prevent seperation.
Basjoos put his exhaust and cabin air exit in the tail to help with filling the air void. Perhaps he can weigh in on any benefits. Motorcycle racers have found that the angle and location of the exhaust plume makes a fair difference in air drag. A change from a straight tip on the muffler to a rotated one can subtract a few hundredths off lap times.

Just my $0.02

Awesome job, keep up the good work.

[johnrobinson]

howdy, I just purchased a 2008 hyundai accent that I plan on modifying for aerodynamics on a long term basis. first a 250 mile baseline recording with a scangauge, then wheel discs, rear wheel skirts, belly pan, then the big one, an extended tail section. I see there are arguments concerning photos and distortion of size while using those measurements/outlines in your program. would taking a floor lamp with a heavy base, attaching a horizontal member above the car and draping a cloth marked in 12 inch (6 inch better?) squares down the center line help alleviate some or all of the problem? I plan on taking photos of just the aft section of the car, as the front I am not going to change. I'll send a photo of the base line carbody for you to use if you want / need. throw it into a data base ifn you want. (although it will take several days until I get a photo etc, as I am still hobbling on crutches from a motorcycle crash...) prolly do it this weekend.. anyway take care and drive careful.

[johnrobinson]

Howdy,
bonneville salt flat streamliner body builders use 11 degrees as the number to use for rear of car angles to keep separation to a minimum..
I hold a record at the Salt in a dodge colt 144 mph.... and keep up with the discussions about all aspects there... which is where that came from..

[johnrobinson]

Also, a book or two on aerodynamics
race car aerodynamics by katz isbn 0-8376-0142-8
and especially for low speed aero
the leading edge of ultra streamlined land vehicles by tamai isbn 0-8376-0860-0

about $35 each or so....