Aerodynamic lift- A real problem

[Christ]

So the glider really works, eh?

I just watched (fell asleep watching) a show on Science Channel last night where they built a DV glider to his original specs, including soaking and bending bamboo for the frame, and using period canvas for the covering. Not sure if it flew, as I entertained myself checking for leaks in my cranial photo-energy seals.

[EngineeringStudent]

looks like getting any real data will be next to impossible for skeptics like frank lee. i guess that every expert on the planet saying lift hurts stability isn't good enough for some people.. lol

"Despite their widespread use (effectively universal in the case of new cars), wind tunnels tend to keep their secrets. Sure, some data is released, but manufacturers are notoriously wary of releasing any information that might cast a negative light on their models. The Audi TT, for example, wasn't heading for the new car showrooms at the same time as tech journals were full of rear lift co-efficient data for the car... And when successive models go backwards in their aero behaviour, you'll never hear anything of that!

So finding good wind tunnel pictures of a model showing both smoke-streaming and wool-tufting is difficult; finding detailed numerical data on drag (eg with a cross-wind component as well as the more common zero yaw angle), front and rear lift coefficients - and so on - is nearly impossible. The MIRA research facility (based in the UK) has excellent aero data collected on a variety of models in their own wind tunnel- but unfortunately you need to pay big bucks to get the info."

http://autospeed.com/cms/A_108677/article.html

no wonder i'm having such a hard time finding raw data.

[Nerys]

I think what frank is saying is that for most cars the amount of lift generated is MINIMAL in its impact on the stability of cars. Now where I do disagree with frank is that this is universal. I have driven cars that got "light" in high winds. Not dangerous but I could SEE conditions existing where that WOULD become dangerous.

Think bridge high winds a gust of cross wind and as you hit the gust you hit a small slick of oil. the lift being JUST enough to break traction on that slick and your car turns sideways even just a few degrees. If your not on your toes this is going to get VERY ugly. ie you treat it like a spin and turn INTO it slightly so when those tires regrip they are at least somewhat pointed in the right direction :-)

Frank. have you ever used ONE FINGER to unstick a car in the snow? I have. get the wheels spinning on a level surface icy with snow and on a smaller car you can take one finger and PUSH the front or rear of that car (FWD or RWD dictates) I am not talkin mad spinning. 5mph just SPINNING on ice without moving the car ie stuck.

you can easily "push" that car sideways even with one finger under the right conditions.

so it really would not take much lift under the right conditions with the wrong car to cause some serious trouble.

NOW I do agree with frank that in all likelihood this is very unlikely to be an issue on modern cars unless the manufacturer was a moron :-)

so while no raw data I do have real actual observed data and thats enough for me. Reality trumps "existence of data" every time :-)

Does not appear to be a problem with my metro thankfully. I thought my metro was BAD in wind as it was all over the road (compared to normally) I was getting shoved around pretty good. but the front end never got light or loose or anything it was just physical shoving around.

then I got to the toll booth and had to open the door (window broken) and the 50-60mph gusts of wind nearly tore the damned door out of my hand!! I did not realize the wind was quite so high.

I was impressed with how well it handles in the wind once I realized what kind of wind I was dealing with and its a 94.

The winds were strong enough and CROSS WISE as well to tear down billboards :-)

now where I WOULD worry about aero lift is if you start to AERO MOD your car. There is not much we can do about it without wind tunnels and massive computer systems and engineers but it does mean BE ALERT and watch and feel for the warning signs of a potential problem.

[EngineeringStudent]

i found something that could work for everyone. it's a deflector thats in the wheelwell and changes the pressure zones, resulting in less lift without having anything interrupt the outside airstream:

Patent US6712425

[Christ]

Did Hermie come back from Banlandia?

Noone is coming right out and saying that lift can't be a significant factor in performance (though a good number of us are thinking it ) of a vehicle.

What we're saying is that with the available specifications, the math just doesn't support that the lift created by a vehicle under normal operating conditions will have enough power do really cause any problem.

Nobody to date has proven otherwise, unless you consider opinion (data which is not recorded, quantified, or otherwise inspectable is not, and can not be considered fact.) something to go by. If you do, you're in the wrong place.

Opinions are like anii. Everyone has one, they all stink.

[Frank Lee]

Originally Posted by EngineeringStudent

looks like getting any real data will be next to impossible for skeptics like frank lee. i guess that every expert on the planet saying lift hurts stability isn't good enough for some people.. lol

Hi Mikey-

I've provided the best data I could find. If you have something better, show it.

[Christ]

Has it occured to anyone else that Hermie was from Oregon State, and this "Enginnering Student" person showed up exactly the time Hermie was given a one-way to Banlandia... and has a link to Oregon State U's Beaver Formula Racing Team?

I think an IP check is in order... Sorry if I'm wrong about this, but I'm guessing we're being haunted here.

[NeilBlanchard]

Hi,

Originally Posted by EngineeringStudent

i found something that could work for everyone. it's a deflector thats in the wheelwell and changes the pressure zones, resulting in less lift without having anything interrupt the outside airstream:

Patent US6712425

From my reading of Hucho, drag inside the wheel well -- is still drag on the vehicle. Just like drag inside the engine bay, all air movement around, or through the engine bay and through the car, or under the car -- it all contributes to drag.

And, those patent drawings are pretty awful! They look like a 2nd year drafting student did 'em. The first drawing shows the front wheel well passing through the car!

[Frank Lee]

Of course it's Hermie.

I would suggest to him that he show this thread to one of his engineering professors.

I ain't scared of anything I've put in here.

[Nerys]

"normal operating conditions" don't scare me or concern me.

"abnormal operating conditions" are what worry me :-)