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Old 06-16-2011, 07:31 PM   #21
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OK we can agree that for any wing/spoiler, the optimal angle, etc. will vary depending on a multitude of variables. But I think that's besides the point. You're talking about using a wing outside of its normal range of angle of attack.

Basically, you're suggesting a third version of a downforce-creating airfoil - one which does not operate as either a wing or a spoiler. Whether it's 25* or 45*, it is in "stall" because it is outside of the range in which is can operate as an airfoil.

Mainly what I had a problem with was in post #12 where you claimed that the proven effects of a spoiler somehow translate into proof that a wing at a steep angle will provide positive effects - which makes no sense if you understand how a spoiler creates downforce, which is what prompted my "wall of text".

Now, if you're suggesting that a steeply-angled wing creates downforce in a way unlike an airfoil and unlike a spoiler, then that at least is a possibility worth discussing.

So, let's discuss that possibility:

You've still not offered any reason that your suggested wing angle would work.

The equation you posted is correct, but that does more to suggest that you are wrong about a steep wing being beneficial than right.
1) As you stated, CL depends on the angle of attack - but what does that mean if you have a steep wing? Answer: CL drops off towards zero as the angle of attack gets steeper outside of the wing's normal working range. Therefore L falls off towards zero. This means no lift (no downforce)
2) This is an equation for how much lift a wing produces when operating like a wing. It actually doesn't even apply to a stalling wing. CL is too low (nearly zero).

You claim arbitrarily that a greddy'd miata can overcome the drag caused by a steep wing. Sure, the car can still get down the straight away, but by some measure slower - drag is a big deal - and the fact that the miata already has a high coefficient of drag is not an excuse to unnecessarily add more drag - in fact I argue it's a better reason to try to minimize drag as much as possible. If L is falling off towards zero with a higher angle of attack, you're getting less downforce from your wing, and you're creating more drag.

Quote:
Originally Posted by BenR View Post
I based this on actual experience seeing various ebay wings at the track, they often don't mount to the miata trunk with a high enough angle of attack.
This sounds like you're saying that you see other cars at the track using eBay wings, and in your opinion, they are not mounted steep enough. This isn't proof of anything other than that you have a theory that a steep wing would work, which is exactly what I disagree with.

I think, instead of me explaining why a wing does not work like an airfoil when it's too steep and why a steep wing does not create the same effect as a spoiler, we should approach this from a different angle:

Please explain why exactly you think a wing that is in stall will create downforce - and enough of it to justify the unavoidable drag that such a wing will create.

Last edited by ThePass; 06-16-2011 at 07:46 PM.
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Old 06-16-2011, 08:02 PM   #22
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Here's some stuff from NASA. The specific data does of course change with wing design and many other elements, but it does the job to demonstrate why I don't buy what you're trying to sell:

Significant drag:


Drastic drop off in lift as you move into stall angle:


But again, if you have some sort of explanation as to why you think it actually would work, I'm game - please explain.
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Old 06-16-2011, 08:06 PM   #23
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Quote:
Originally Posted by ThePass View Post
This sounds like you're saying that you see other cars at the track using eBay wings, and in your opinion, they are not mounted steep enough. This isn't proof of anything other than that you have a theory that a steep wing would work, which is exactly what I disagree with.



A steep wing can and will work depending on what the L/D ratio is based on the airfoil shape. Is a gurney flap being used?

You should use that equation, you'll see, you can produce some good downforce at pretty extreme attack angles. Sure you also increase drag, but it's not exactly like the miata is a low drag design.

If we are talking about a wing for something like cali speedway the suggestion would be entirely different. But for a low to medium speed track where the trade off for drag down the straight can be made up for by earlier throttle, or in some cases not lifting, my opinion still stands that it's probably worth a $100 risk.
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Old 06-16-2011, 08:08 PM   #24
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Quote:
Please explain why exactly you think a wing that is in stall will create downforce - and enough of it to justify the unavoidable drag that such a wing will create.

Just as soon as you explain why a wing past stall produces 0 downforce/lift.
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Old 06-16-2011, 08:48 PM   #25
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Quote:
Originally Posted by BenR View Post
You should use that equation, you'll see, you can produce some good downforce at pretty extreme attack angles. Sure you also increase drag, but it's not exactly like the miata is a low drag design.
Again, I feel that the fact that the miata is already drag-challenged is more of a reason to be cautious about adding even more drag, than a means to justifying even more drag, unless it is very worth it.

But, OK let's assume we are using this theoretical setup on a low-mid speed track only... although even on a track that fits that description, like Chuckwalla, even I was over 100 mph more than once..

So far you've been talking about using a generic, eBay wing at a steep angle to hopefully create downforce, despite the accepted large amount of drag associated with such a setup. The problem though, is that the variables in the equation you referenced change drastically depending on the wing's shape. Could some sort of wing work at a steep angle and relatively low speeds? Yes. Could a generic eBay wing do so? hmmm...

Check this out:
http://www.scribd.com/doc/57867238/A...high-L-D-Ratio

Those guys found a shape that works to create good downforce at low speeds using a steep angle, but the wing shape they came up with is nothing like a generic wing. So a wing shape intended for normal angles - as a generic wing would be - is not going to have the properties necessary to create force downwards when angled steeply, the shape needs to be drastically different.

So, yes, there is a wing shape out there that can achieve what you're suggesting, but since we are not talking about fabricating your own wing, that's a moot point.
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Old 06-16-2011, 09:02 PM   #26
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Go out to your car and look at the slope of your trunk. Then take a look at how most of the ebay wings mount, including the one in the op. They're typically designed for a flat mounting surface. Tell me that wing isn't going to have a 0 or negative angle of attack. Until you add higher angle of attack.

I agree with you on the differences between a spoiler and a wing. You are 100% right. What I failed to do with the picture of moti was convey that in actual application the drag created by a giant spoiler or a wing at extreme angles of attack are not significant enough to offset the gains in downforce and therefore lap times at a slow to medium speed track.


We are not talking about the perfect airfoil for 100mph here, we're talking about making a car go faster for $100.
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