Johninrsf

Jack,

You are one incredibly ingeneous guy!!!! Well done!!

mark kibort

Scot, remember? similar sized wings?????
Anyway, there inlies the rub. 8.8:1 at 120mph but downforce of 345lbs at 0 AOA. so, what if 345lbs of downforce is too much and you want more like 250lbs? that could be an issue. sounds like a very high lift airfoil. (and its much larger, near 70" which is much wider than the Cup car wing. (near 50% larger)
anway, I dont think we are talking about the same size wing are we, so its hard and senseless to compare, but if you could back it down to 250lbs of downforce, it might be the same L/D.

Now, if you get a GTC-200 wing that is 59" in span, vs my 50" cup car wing, guess what the values are? it barely gets to the same downforce at 120mph even at max AOA, and if you noticed, the adustability is pretty senstitive. (stall angles). the GTC -200 has only 228lbs of dowforce at 120mph and at 10degrees AOA and 31lbs of drag (7:1 L/D) It is "MUCH DIFFERENT" than the cup car wing too, regarless of the AOA . So, in the smalller widths, the cup car seems to have some advantages.

http://www.aprperformance.com/index....sk=view&id=183

95m3racer

Understood, and thats good that you are spending on both, best way to go

What suspension are you running? Dynamic, Ohlins or Sachs?

See, now that is where you have a problem in your theory...just having CFD does not do anything for you if its bad data. In fact, if its totally irrelevant CFD data it could steer you in the total opposite direction of what you should be doing to get the setup your car needs. This is not like a blood test where it shows a 99% confident result. The only way to validate the CFD data is to take physical readings and/or get wind tunnel time (which is getting cheap btw).

Best bet is to just get a well proven wing from physical testing, or better yet go get some wind tunnel time. Then tune the hell out of the car, thats where the speed will come in. Get it as high and far back as you can within the rules and you'll be good to go.

stownsen914

Interesting ... I would venture a guess that the rule may have stated something about the wing had to be contained within the silhouette of the car when viewed from above, or something like that. So with the banana wing they could mount the wing all the way back at the tail and still have it be the full width of the car.

Scott

onefastviking

So do you still stand behind this statement then Mark ?
"I said that the differences of wings are slight due to the closeness of lift to drag ratios of the wings most likely used by a someone putting it on a race car."

Or do we agree that similiar sized wings can be much different ?

mark kibort

And this is where i see the problem too. how much downforce are you going to get. what does your car need? are you adressing front end downforce with splitters, dive planes, etc. if you are looking at to reduce the drag due to lift (or downforce) why not put some covers underneath the car as that is a big source of drag, as welll as the exit are of the air in the rear.

I actually like that my competitors go crazy with wings. It probably gives me a little advantage

mark kibort

Yeah, I kind of do stand behind what I said. When I first saw Scott's link to the wing spec's, i started to think, "wow, these wings are much different in lift". But then, after closer examination, i found that we were not talking about similar sized wings at all, (huge differences in size) which was my point. BUT, to your point, I imagine, when I came back with an even still larger wing with less lift at more AOA, but at near the same L/D, I was starting to think, yes, some of these wings can be much different as far as L/D, and that the Cup car wing is pretty darn good. BUT, even with the differences of the cup car wing and the GTC200 which is larger, what is the net net difference when you produce the same amount of downforce?
(i.e. 230lbs as the GTC200 produces at 120mph). Its 7:1 L/D and the cup car wing is near 10 to 15:1 L/D. same down force, cup car has less drag, but how much less? well, 10:1 is 23lbs and 15:1 is 15lbs, while 7.1 is 32lbs. we are talking about a potential spread of 15lbs of drag from two vastly different wings. Now I ask you, is 15lbs of drag at 120mph that much to write home about? that would be like 1.5 hp effects on acceleration. Keep in mind that at lower speeds the differences would be almost unmeasurable.

So, do different wings produce noticible differences at the tracks we visit? If so, how. Im curious if im missing something or leaving something out here.

From the racing Ive done and the things Ive seen, i would bet most of the race cars are "overwinged" and there is nothing they can do about it, besides putting a smaller one on. With a lot of testing or wind tunnel time, you will know for sure. The nice thing about the specs, is that it gives you a starting point. with our 928, we have the wind tunnel specs on the car and some flow information to get a decent grip on the angles of the air flow off the roof line. this is a pretty important big of information to start setting wings with.

So, when YOU say that similar wings can be much different, what do you or anyone mean, really?

Mark

winders

First of all, it's Scott.

Second, I don't recall suggesting the APR GTC-300 was the same size as the Cup wing you keep mentioning. The simple fact is that the image of the data you posted is pretty much unreadable and I have not seen where you have posted the width or chord dimensions for the Cup wing. You have not forgotten that wings are measured in area, not just width, have you? Are we all supposed to magically know all the specs of the "Cup" wing you run???

Scott

mark kibort

Sorry, "Scott". (my race buddy's name is Scot, and dont know why he has only one "T". )

Let me remind you :

you said:The APR GTC-300 wings has 345 lbs of down force and 39 lbs of drag (8.8:1) at 120 MPH with a zero degree AoA. At 5 degrees AoA, the downforce is 419 lbs while the drag is 52 lbs (8:1).

That's much different than the Cup wing if the downforce is 250 lbs at 120 MPH, whatever the AoA.

Scott


Now, I thought we all knew the cup car wing specs as they are so prevelant.

Its a CF wing from a GT3 cup porsche ('05) and it measures 13" wide and 51" long. (about 660sq") the air foil shape is very very close, especially for comparison, to the graph I show.
as far as the readability of the graph. you can see that the L/D curve is pretty clear and it characteristics has a peak of 21:1 and you can see the shape of plot. on the bottom is the angle of attack in 4 degree increments. Its clear enough to get out of what we need. I have been tearing my house apart to find that book again to take a better pic, and cant find it I have others with this kind of information, but that one had a great section on all sorts of wing shapes and this kind of graphing of information.)

Anyway, im still trying to figure out what we are looking for when comparing wings. Im noticing a major difference in L/D ratios and of course, there are larger wings with much more lift (downforce ) available.
But, im trying to understand what other factors are coming into play when looking at the CFD data, or other information when selecting a wing, AND what are you looking to improve on if you already have a wing. personally, i put on a real wing to just get more downforce and i knew as a bonus, a little power would be saved due to a better L/D ratio.

winders

Mark,

Here you go again. That text of mine you quote does not say anything about wing size.

The GTC-200 wing, the wing you are using for comparison, is 59.5" wide and has variable chord length from 6.75" to 8.5". Let's pick the big number: 59.5 x 8.5 = 505.75 square inches. So yes, let's compare wings of the same size.....your "Cup" wing has 30% more wing area.....

Geez....

Scott

winders

Mark,

The GTC-300 at 67", with its variable chord width (12" Inner/8.75" Outer), is probably a close wing area match to your "Cup" wing.

Scott

mark kibort

Great point and this is what a discussion is all about. Now, the total area doesnt tell all the story, as like on airplanes, the outer 3rd provides most of the lift. I imagine the outer 25% produces most on the car's wing, but thats a guess.

Eitherway, you are probably right. the 67" GTC wing is near the same size as the cup car wing in area. If you average the cords you get 690sq" area vs the gt3cup 676sq". (edit) Also, to my next post point, cord doesnt have the same effect as wing width.

So, very different wings, yet making dramatically different downforce at near the same AOA. But in the end, the real difference of the L/D at that downforce is near 10:1 a difference between the two, hardly measureable in performance impact, aside from the fact that the more traditional cup car wing is more predictable and adjustable due to its, propably, more linear L/D ratio plot.

This is the point. Am I missing something , or is there something else that the wing provides when comparing two very different wings and making a selection

which wing would YOU choose knowing a few of the facts we know now? Or, does it really matter or if it does, what are the concerns. Looks, adjustability, mounting ease, etc etc??

Mark

mark kibort

exactly! it didnt, but yet we all know it was a poke to show that these two wings were very different, yet they were very different because they were not near the same size.

Now if we are talking area, then we talk about the wings ability to provide lift. one might be better at providing more total lift, vs another and is that the main qualifier to look at? If so, then you also ignor some of the tunibilty capabilities of each wing. I guess the L/D plot being linear might be a good choise for my needs. I dont keed much downforce at this point, and small changes make small downforce changes. with this GTC wing, it looks like small changes make some pretty big downforce changes. certainly its width is bigger, but area near the cup car wing. it does have the capability of producing much more downforce which might be desired.

BTW, my cup car wing is 11.75 x 55 and is 2.5" thick at its highest point. 645sq"

mark kibort

here is a good general wing simulator to see the effects of changing major attributes of a wing design.
for compound designs, you can take sections and then add the results together (if there are 3 sections with different profiles or cords for example.)

http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html

edit: I forgot some of my basic Aero. Looks like cord has the same effect as length or width, so i might stand corrected on that point. So, area is the best comparitive metric.

JackOlsen

You wouldn't have thought so if you were the guy behind me, probably.

(Nice -- briefly -- meeting you last time at Willow!)