tuft testing, Aerodynamics and Lift

ChippedNotBroken · November 28th, 2009, 05:20

While I know no-one here would ever drive over 100 MPH on public roads, I am sure there are legal ways to do that on race tracks (cough, cough). Ahem, that said ...

The look of most modern streamlined cars looks alot like the wing of a aircraft. Those wings are designed to lift lots of weight up into the air. I have heard of tuft testing to improve aerodynamics and was wondering if anyone had done any serious work on improving the areodynamics of their Jetta to improve handling at high speeds.

After all, what good does it do to have a car that can go over 130 MPH if it is going to get SCARY over 100 because of areodynamics?

KROUT · November 28th, 2009, 05:52

My golf is fine at 135 with better spring,struts, and swaybars.

ChippedNotBroken · November 28th, 2009, 06:04

Quote:

Originally Posted by KROUT

My golf is fine at 135 with better spring,struts, and swaybars.

Is that in a line on a flat road or a curved track?

How much lift are you feeling at that point?

Still interested to hear if anyone has improved upon the aerodynamics, not just proved you can go there and live to tell about it.

GoFaster · November 28th, 2009, 06:54

Lift is a serious design consideration at the OEM level. The top of the car acts like a wing, but if it's designed right, the bottom of the car counteracts that. Take a look at the plastic shielding underneath a lot of late model cars to control airflow underneath.

TDIJetta99 · November 29th, 2009, 19:27

My Jetta is fine with the rear sway bar and 16's.. I've seen well over 140 with mine and it still felt pretty decent for it having stock springs and struts..

shizzler · November 30th, 2009, 09:31

This isn't exactly an issue of "power enhancement" but I could see having trouble trying to choose what forum to ask this in, and still get a decent number of views. FYI, "tuft-testing" does nothing to improve aerodynamics itself, it's only a method to analyze the visual effect of airflow detachment on a surface.

I have fairly extensively aero-modded my TDI. I did it all in the name of fuel efficiency (now 55 mpg at 75 mph) but the benefits of enhanced stability at higher speeds also apply. The relationship between reduced drag and lift/downforce is not always clear. I suppose all the drag reduction I have done to my vehicle is a form of power enhancement though. At 100mph I am theoretically saving 4 or 5 HP of wind drag; = 5 more HP for acceleration.

Grill blocks - The amount of stock cooling air flow capacity can support wide open runs through death valley with the A/C blasting. I live in Michigan, so I blocked it down to about 10%. just watch your scan gauge coolant temp. Also seal up your hood and other front panel gaps.

Vehicle Lowering - I am down about 2.5". This saves around 35 sq. inches of frontal area, and lowers the amount of air that can get under the car and create turbulence. A little bit of positive rake adds some downforce, too.

Additional drag reduction - removed passenger side mirror, stubby antenna

Rear belly pan and diffuser - These mods helped high speed stability the most. I fit a 3 x 3' sheet of aluminum under the rear axle which transitions into a plastic rear diffuser tapering up at about a 10° angle out the middle of the rear valence. Air flow leaving the car at the rear is greatly calmed and guided to reduce the turbulent rear wake. Also a tangible mileage gain from this mod alone.

Vortex Generators - Some people dismiss these as a waste of time. I can only prove that they are altering the airflow over the rear glass and trunk lid (tuft tested). But fuel economy or downforce changes were mostly imperceptible.

http://ecomodder.com/forum/showthrea...rear-8839.html

I would really like to get into using flowworks or similar CFD to analyze the theoretical effects on both drag and lift/downforce for various vehicle mods. Maybe someday.

GoFaster · November 30th, 2009, 14:25

shizzler, I'd say you are on the right track as far as controlling the airflow through the grille and under the vehicle. I wouldn't recommend the right-side outside mirror removal myself, though. If you are extremely diligent with shoulder checking then maybe it's not a big problem, but I'd rather have every item of safety equipment available and certainly the average non-shoulder-checking driver should leave that mirror in place ...

ChippedNotBroken · November 30th, 2009, 14:40

http://www.docstoc.com/docs/5108044/vortex-generator

Link above may explain why your vortex generators aren't working better.

Tuft Testing is a tool, much the same as a wrench or a screwdriver. Did not mean to imply that they would in and of themselves do anything to improve aerodynamics any more than putting a wrench in your car will make it run better. your belly pan and attachment, while crude appear to be effective, I wonder what it would take to make a lightweight single piece unit. Would not have to be that durable, just strong enough to hold it shape and weather resistant.

Flying Kasper · November 30th, 2009, 16:18

you would want a low pressure system under the carriage so it will stick to the surface better.

I would think, if you would try to create low pressure on the top of the car, it would lift it. Causing less traction and control.

On a real airplane Vortex Generators. Help, right with wing fences and wing tips or triplets.

But honestly, a stock TDI design is quite good for 135 mph. Once you get over 250 km/h, you start looking at body kits that would provide more traction.

Go to Germany, and tell me how many auto bahn drivers bother with anything to do with aerodynamics. pedal to the metal.

A trunk wing will improve traction, simple and cheap, but looks rice. A trunk wing is just a reversed airfoil.

Also you can put on bumper wings, ( i dont remember proper name ), to provide more down force.

Best place to look for examples or aerodynamic engineering on cars would be Formula 1.