Aerodynamic lift- A real problem

[ncs]

The 7th gen Celica was only offered without a spoiler for one year. The spoiler became standard equipment after high speed stability problems were found without it. The spoiler blocks half the view out the rear windows.

VW also added a spoiler to the current Beetle for similar stability reasons.

In both cases, the handling problems were only apparent at speeds above 75mph. Wind speeds we'd only legally see driving into a head wind.

Here's some second or third hand info on two modern cars.

euro spec evo IX and 06 STI
The red arrow represents lift at air flow of 40m/s (around 144km/h or ~90mph), the blue – at 55m/s (approximately 200km/h or 124mph). The lift is measured in newtons. One newton equals roughly 0.22 lbs.

On my car, I removed the hood scoop and the steering became slightly heavier.

[Hermie]

From another thread: http://ecomodder.com/forum/showthrea...tml#post120492

The Audi TT in question was notorious for high speed lift-off snap oversteer due to the style-over-function design. After that incident (not the only one), the optional rear spoiler was installed on all of them by the factory.

My 1983 Subaru GL sedan was a similar style car to the Tempo with a likely comparable drag coefficient. I had few stability issues until it was topped out at "P" (the P in MPH at the bottom of the 85 mph speedometer), which worked out to be around 110 going by the tachometer. At that point, it would move around a little in crosswinds, but could still keep in a lane sawing the wheel like a '50's movie racecar driver. Where it bothered me was on on-ramps at speeds over 80, with significant understeer, so I added a front airdam. Got slightly better mileage which was probably within a margin of error, but it did add straightline stability and cured the understeer (at least the lift-induced understeer). What it also did (besides scrape the occasional driveway when I forgot to enter at an angle) was increase oversteer to a level that was fun in the dry and a little hairy in the wet. A tree fell on it while I was driving down the street, so I never got to put an adjustable rear spoiler on the trunk.

Other members here have had direct experience in the negative aspects of lift.

On my car, I removed the hood scoop and the steering became slightly heavier.

That's because you reduced front-end lift from reducing the pressure buildup under the hood.

Also, the "apparent" dangers of lift can be seen even at slower speeds during sudden manuvers- eg., swerving to avoid an accident.

[Frank Lee]

Originally Posted by Hermie

Probably closer to 700. I don't think the rear wheels have just 300 pounds each (which they would with your numbers)... That would make it EXTREMELY unbalanced.

You have a 2000 pound Tempo that drives itself down the road empty? Tell me more about that Mr. Real World.

[user removed]

The early Datsun Z cars had so much lift, at 100 MPH the front wheels looked the same as they did when you pulled the engine out of the car.

Air dams were the solution.

regards
Mech

[Nerys]

This old data is more important than we might think. consider "factory fixes" for aero issues goes out the window with our cars when we start messing around with the aero IE kambacks air dams grill blocks boat tails skirts all ALTER the aero of the car and may introduce some of the problems the OEM designed out of the cars :-)

Just something to think about.

[MadisonMPG]

Originally Posted by Nerys

This old data is more important than we might think. consider "factory fixes" for aero issues goes out the window with our cars when we start messing around with the aero IE kambacks air dams grill blocks boat tails skirts all ALTER the aero of the car and may introduce some of the problems the OEM designed out of the cars :-)

Just something to think about.

In all honesty, at the speeds we drive, it doesn't matter. If it was increasing lift a lot, it wouldn't help gas mileage.

[Hermie]

Originally Posted by Frank Lee

You have a 2000 pound Tempo that drives itself down the road empty? Tell me more about that Mr. Real World.

Tempos weigh about 2600 pounds. If they had 1000 on each front wheel, as you said, that would only leave 300 per rear wheel.

Consider that the Tempo front wheels probably have 1000 lbs on em each.

Your numbers are off, and learn how to read.

[Frank Lee]

Tempos weigh about 2500 lbs empty. Add two guys in the front seats at 200+ lbs each and 15 gallons of gas at about 90 pounds and you have a 3000 lb unit for a typical load. Then know that 2/3 the weight of Tempos is on the front wheels and you have 1000 lbs on each front wheel, and 500 lbs on each back wheel.


I've been a gearhead since before you were swimming around in your Dad's shorts, ya punk. Put your car on a scale and get back to us.

[NeilBlanchard]

Hi Hermie,

Can you explain your apparent fixation on lift, please? When has it actually affected you?

[MadisonMPG]

Originally Posted by NeilBlanchard

Hi Hermie,

Can you explain your apparent fixation on lift, please? When has it actually affected you?

The dynamics of the flow of the air particles may produce an effect at 300 miles and hour that would create a force upon which would lift the tires off of the ground enough to cause adverse handling when trying to swerve/take evasive action on a rain soaked hill.

But seriously, tell us why.