[g6civcx]

Let's look at what I said:

Originally Posted by g6civcx

If you want your wing to truly be effective, the rear wing needs to be higher than the roofline! This is because airflow will not drop down at the rear windshield enough to make the wing work, regardless if you have VG or not. This is worsen as speed increases. To counter this, you need a large rear wing sticking up above the roofline to be in the line of airflow.

Merriam-Webster defines "truly" as "in a proper or suitable manner".

You said:

Originally Posted by Def

As far as your wing needing to be above the roofline - totally false. The flow is not separated from the roofline back when looking at a velocity plot. Yes, a wing 2" off the decklid will not work well, that's common sense and a simple tuft test could tell you that. Once you get about 12" off the deck you're probably going to be in "mostly" clean flow, and above 14" on our cars it's probably going to be almost completely linear and horizontal flow.

Question: is the roofline higher than 14"? If no, then my statement is false. If yes, then my statement is true.

You do not need a wing that high, but a) would a wing that high work, and b) would a wing that high work better than a 14" high wing?

You don't need $200 to buy a $100 item, but would going to the store with $200 to buy the $100 item be "in a proper or suitable manner"?

Based on your asserted experience, you should know that in order for an airfoil to achieve the desired effect at lower air speeds, the wing needs to have a larger angle of attack and larger size = picnic table wing. You can probably explain that better than I can.

I said:

Originally Posted by g6civcx

I say the best way to test the theory is to build a model and make your own wind tunnel with a big fan and a smoke machine Or if you're a computer genius you can run a simulation.

You said:

Originally Posted by Def

You do not need a wind tunnel to do aero work.

Merriam-Webster defines "best" as "excelling all others".

Question: is the wind tunnel, even a mini one, the "best" way to measure aero data? If no, then my statement is wrong. If yes, then my statement is right.

Originally Posted by Def

In fact, some simple tools like a manometer/inches of water pressure gauge, some wool tufts plus tape and a little knowledge will go a LONG way towards helping out aero on your car.

I do not disagree at all about what you said. I specifically said that you can also do a computer simulation. This means that I said that there are other ways to do aero testing other than using a wind tunnel. My experience is in computer simulation so I bring that in. Anyone else with more mechanical experience can bring their experience to the table.

Originally Posted by Def

I'm betting most people who say you absolutely must have a wind tunnel to do any aero work on a car have never even stepped foot inside a wind tunnel, or have an idea of what really goes on inside one. I use 'em all the time, and I'm saying large general changes are easy to make without analyzing things within a gnat's ass. It's called back of the envelope engineering, and it's more common than you think, and the GOOD engineers can make absolutely amazing observations with some observations and a few simple calculations about what needs to happen(in some cases).

As far as I know, nobody in this thread suggested that you "absolutely must have" a wind tunnel to do aero work.


I don't mind getting slammed when I deserve it, but please at least have the decency to address what I'm actually saying, not what you think I said. For someone with your asserted knowledge, you should be helping instead of slamming other "engineers".

Are there any professionally certified engineers around here? Yes, there are a few.

Engineers are supposed to be free thinkers and not be constrained by conventional wisdom. Most discoveries are made by accident when people play around and experiment with stuff. Yes, you have to understand the basic fundamentals, but as far as engineering design goes, your mind should be free to play with the full range of natural phenomena around you. Even our Founding Fathers acknowledged this when they set up our legal system. Our patent laws reads "Patentability shall not be negatived by the manner in which the invention was made". My favourite inventor is Thomas Jefferson, and he promoted this concept.



Back to topic, please.

It's futile to discuss this further without trying to figure out what you want to do.

What speeds will you be using the vehicle for? Short or long roadcourse? Do you want to reduce drag or do you want high downforce? Some combo of both?