Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
(OP)
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.





RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
I see the need to improve fuel efficiency but I would have thought changing the profile of the car itself would be more beneficial than putting a wing on it.
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Adjustable wings are not new. Porsche did one on the 911 about 1990 I think and Chaparrel did one on on their sports prototype race cars in the 70s. The concept was banned in racing due to fears of failure leading to crashes due to sudden loss of drag and down force, and due to fears of detached wings impacting crowd and other cars.
I think most OEM body engineers consider wings a styling aid with zero or less than zero technical merit.
Regards
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RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
I understand that there is no dramatic need for down force on street cars. I was looking towards implementing a spoiler even simply for long term effects (i.e. reduce drag to save fuel). I understand that it would be hard to create a generic spoiler for multi-vehicle purpose, but perhaps I would have to check to see a small list of vehicles that have large Drag Coefficients and implement my spoiler on those.
My spoiler should be controlled entirely autonomously via on-board sensors that would detect speed and change angle of attack; as well as detect traction control or slip and engage max down force at that time.
What my primary concern is to pick an airfoil design that would help me achieve this. How would I know which one would give me the least drag at different angles of attack for typical driving speeds?
Thanks for all your help again.
Regards,
Cumbysis
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Mike Halloran
Pembroke Pines, FL, USA
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Mike is correct.
SPOILERS DO NO REDUCE DRAG.
It is a basic law of physics. The energy to create the down force comes from drag
Regards
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RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Regards
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
The number of production cars with movable aerodynamic surfaces can be counted on your fingers, maybe only one hand's worth of them.
Think about that for a while.
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
- Make your car a target for kids to steal.
- Increase your fuel consumption.
- Reduce you maximum speed.
- Make your rear view mirror useless (unless you were thinking of roof-mounting it (!).
- Steve
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
In the UK it would probably invalidate your insurance, since the insurance drones would see it as a "performance enhancement modification".
- Steve
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Regards
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RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Originally I was with the "SPOILERS DO >>>>NOT<<<< REDUCE DRAG." crowd but then recalled something from Aero at School.
CCTENG are you talking about an aerodynamic device to energize the flow so that it follows the car body shape at the rear? Hence reducing the low pressure area behind it and hence drag?
At university my Prof was doing research on how this effect could be applied to the Engine pylons on airliners. I think they called it a trip wire or something. Basically a feature a bit before the end of the pylon that upset the boundary layer making it more turbulent. The extra energy in the airflow causes it to actually follow the sharp drop off of the pylon at the rear, at least partially, actually reducing drag.
I don't know enough about it to give you any more specific advice. My university was Southampton, Aeronautical department, the prof was either Dr Tutty or maybe Graham Bull, can't recal which as I had aero classes from both.
However, given what you're trying to achieve, a conventional aerofoil shape may not be what you need.
I do recall a TV show some time back with some guy working on stock cars or something and in his league or whatever wings were banned but he but a 'box' on the rear and it actually worked, can't recall details though.
Then again, the fact you also talk about down force makes me doubt you were thinking along these lines.
KENAT, probably the least qualified checker you'll ever meet...
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
But... the car manufacturer has altready optimised the shape of the tail within their constraints.
Cheers
Greg Locock
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RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
As soon as I posted I realized that the shape of the rear of some vehicles was probably designed at least partially for this purpose.
I'm not sure that an adjustable feature for this purpose would make sense, haven't really thought about it though.
Plus like I said, that fact the OP talks about down force makes me think this may not be what he was talking about.
KENAT, probably the least qualified checker you'll ever meet...
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
From SAE Progress in technology series No 18 PT-18 - "Automotive fuel economy part 2" published ~ 1979.
VW engineers Hucho, Janssen and Emmelmann published "The optimization of body details - A method for reducing the aerodynamic drag of road vehicles" All the test results quoted in this report were obtained in VW's wind tunnel using full scale models and actual vehicles with suspension unlocked and cooling airflow flowing . Their Stated Cd undertainty is +/- 0.002 to 0.003.
Bottom line, There are front and rear "spoilers" dimensions that reduce lift and drag. This squares well with some of the info in the Chevy Power books making claims that a chin and rear deck "spoiler" dimensions (and even modest vehicle rake) can reduce lift and drag.
I think this is because there is little about automotive aerodynamics that involves airfoil theory. Perhaps It is all ground effects (some sources say is max when the "wing" is 1/2 span off the ground, or when my car has 24 inch ground clearance), or maybe because even swoopily styled cars are basically bluff bodies, so "drag" and "lift" are the result of pressure creeping around and influencing any surface they can.
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
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
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RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
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
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
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
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
KENAT, probably the least qualified checker you'll ever meet...
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
That's a Simpson's reference, for those who don't know.
V
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Bob
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
- Steve
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
It would be very Ugly yes. Hey, wasn't the "Pacer" a dull point in the back?
kch
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
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...
RE: Design of Adjustable Spoiler to Reduce Drag and Increase Downforce
Rod