Design of Adjustable Spoiler to Reduce Drag and Increase Downforce

[CCTENG]

I would like to create an Adjustable Spoiler for an Automobile. My spoiler would be used for street vehicles for the purpose of reducing drag primarily (for fuel economy) and increasing down force (while braking or turning at high speeds)and would be completely automatically adjustable (angle of attack) based on speed.

I was wondering if there is anything you would recommend I could do or whether you could suggest what airfoil I should use and which ones I should look at. I have looked at some NACA and SELIG airfoils but I can't come to the consensus of the final design.


Any help or suggestions would be greatly appreciated. Thank you in advance.

 

[dcasto]

Porche whale tail and the Chrysler Crossfire are both rear spoilers that adjust with car acceleration and speed parameters.

 

[patprimmer]

Tmoose

I agree about chin spoilers and ground effects and rake so long as it is gained by lowering the front rather than raising the rear.

The OP mentions aerofoil shape which does not apply to chin spoilers or even rear deck upturns, but only applies to wing style devices.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evelrod]

Agreed, as to "chin spoilers", diaplanes, flow seperators, whatever...The more air flow that can be excluded from the under carriage and underside of the chassis the better for reduction of aerodynamic drag...With most cars nowadays being FWD, it probably won't upset handling (may even improve?) at high speed. The ultimate if impractical limit is to exclude ALL airflow from under the car to eliminate most of the drag and increase downforce. Was done years back by Jim Hall and the 2-J but ruled illegal by most race organizations...totally impractical for street.

As to wings, a waste of money for street, IMO. For aircraft, I don't recall seeing a plane with a "reverse" empanage lately. I designed a set of wings for a sailplane once a long time ago and the stab was a "full flying" symmetrical airfoil!

Rod

 

[safetydan]

Here is the simple pretty version from a former racer. Wings, or whatever you want to call them, reduce top end speed, and generally at best generate about 300 pound of downforce @ 100 mph. However the drag created by such wing drops your top end speed by about 10 mph, depending on your car. Depending on what you classify as a high speed turn, you are not going to see a significant improvement in performance unless your "wing" is very large, 7 feet across for single element with a high angle of attack. Street car performance is a pretty simple thing, don't worry about the aero effects, just improve your mechanical grip. If you were talking about a purpose built race car, then you can talk about wings and downforce, until then everything else is for show.

 

[SomptingGuy]

If I remember rightly, Porsche produced one vehicle with a rear spoiler that popped up at a certain speed ... a speed higher than the limit in most US states. So the US version had the pop-up speed reduced. What's the point of having useless flamboyant body-kit if you can't show it off.

The really odd thing about the whole business is that it's only men who body-kit their cars. What are they doing? Trying to impress other men?

- Steve

 

[dgallup]

There are a couple of cars with movable front splitters & pop up wings. Always looked like an "arrest me now" flag to me. There are also a couple of high end cars that reduce their ride height at high speeds. That is probably a more useful but more costly solution. At the speeds they activate nobody is worried about fuel consumption.

 

[KENAT]

Sompting. I believe it was the 911 and the speed was 70mph. The joke as I recall it in UK was that if a cop saw one with the spoiler up he'd pull it over.

KENAT, probably the least qualified checker you'll ever meet...

 

[patprimmer]

In my opinion the only real functions of wings and rear deck spoilers on road cars it to attract extra attention from police and to help avoid drivers from being distracted from anything behind them by obstructing such items from view.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[vc66]

Next, they'll be adding speed holes...

That's a Simpson's reference, for those who don't know.

V

 

[Ataloss]

The Porsche Boxster also has a pop up aerodynamic device, I guess spoiler is maybe the best thing to call it. Going from memory its about 60mm across, and extends about 10mm up from the rear at about 100-120kph. It slides out from just behind the rear decklid rather than the 911's pop up wing that is hinged and kind of swings up.

Bob

 

[SomptingGuy]

Anyone else remember "Speed Blocks" painted onto the tanks of old Yamaha bikes (e.g. the FS1E). At least they didn't slow the bikes down.

- Steve

 

[Higgler]

Would changing the back end of a vehicle to make it pointed (cone shaped) improve drag? Isn't that four triangular spoilers.

It would be very Ugly yes. Hey, wasn't the "Pacer" a dull point in the back?

kch

 

[KENAT]

Q: Would changing the back end of a vehicle to make it pointed (cone shaped) improve drag?

A: Simplistically yes but... There are so many other factors that it's not a very practical solution. Also the height of a car compared to it's length means that trying to manage airflow in this way is pretty impractical. Some solar powered cars or those cars that go hundreds of miles on a gallon of gas, typically university research projects or the like, do use a shape a bit like this (essentially some kind of aerofoil/teardrop) though with the driver usually reclined.

http://www.msnbc.msn.com/id/8737930/

Q: Isn't that four triangular spoilers.

A: No.

KENAT, probably the least qualified checker you'll ever meet...

 

[evelrod]

Several race cars of the past have tried the "long tailed" approach. E.g., Porsche's Le Mans efforts of years past. Great theory...totally impractical, even for a race car and completely out of the question for street use. However, you can knock yourself out up on the salt flats...those boys just love looooooong cars.

Rod