mark kibort

I think the point I have been trying to make, is that its easy to get a wing to make downforce, because thats what they do. tuning, will happen, regardless of what wing you select. (i.e. how much downforce do you want) at the speeds we run (at most tracks, besides the RA, RA, VIR, and Willows) the drag considerations are minimal, so the "sweet spot" reaching goal is a little devalued. What this means, is if I bliindly pick a wing. set it at some AoA, and eventtually set it to the downforce i need to balance the car, (or find out I need a better splitter, hood vent, or other aero up front to match the rear downforce), the difference in the different types of wings will be minimal. in a wide range, these L/D ratios will be from 8 to 12:1 at some particular setting.

so, if what you are searching for, is to reduce the drag for a given lift by 50%, the power ramifications, since they are relatively small to begin with, will be even smaller. In otherwords, if the HP loss to wing drag is 15hp at some high speed, we are really searching to save 7hp by all this discussion.
In otherwords, this is a 7HP discussion in its most extreme form

since we are optimizing all the time with everything we do in racing, this is not a bad thing and makes the sport fun. But, its always great to level set the expectations.


edit: one of the things that I noticed with the Race car Eng. article, was that the wing change did offer about 15% more downforce in the rear witi the new wing, but reduced the frontal downforce by near 30%. drag went down over all 9% or so for a given lift comparitively. The problem is that the extra downforce may unbalance the car, or need to be matche with more front downforce . if splitters and hood vents are already used, dive planes and other bolt on devices will need to be added to bring back balance, and certainly increase the drag values. yes, this discussion validates that different wings can make more or less lift for a given size. (thats the concept of high lift airfoils vs others) you certainly dont want to max out a wing at 15 to 20 degrees to get the lift you want as this will kill the wings L/D ratio and possibly not give you the downforce (lift) you need. thats when going to a radical high lift air foil is required. forget about the camber shape, think of drawing a line from wing leading edge to trailing edge. that really becomes the shape of the wing, in essesnce. (high lift wings have big arcs on thier rounded low pressure side.)

The interesting thing thing here is I went through all the trials and tribulations on the track with a wing. some of you saw my first race with a wing with 50% more downforce at half the wing angle vs my original wing. the car was near undriveable. (very pushy to say the least)
Then, with a splitter( and different variants of it) , hoodvents, dive planes, the car became near perfect as it stands today.

333pg333

So to paraphase Mark, are you suggesting that as there is very little negative drag at our speeds that we should therefore use the wing at max angle?

mark kibort

Not exactly. you should use the wing and angle it such that it provides the appropriate downforce. based on our cars shapes. (yours, not so much mine) the roof line flow will in effect, give a greater angle of attack than what is indicated by a level. SO, going beyond 10 degrees of wing angle and further, will give slightly more downforce, and a lot more drag.

the point is, if you want more downforce for purpose of increasing handling, you give the wing more angle until its maxed out (where the drag starts to rise and no more lift or downforce is provided) THEN, you need to change the wing to a different shape if you want more downforce. the gains there is optimizing lift to drag, and this will be determined by the shape and size of the wing. its shaving hairs for most of our use on the track. again, the range of lift to drag is 8 to 12:1, so drag is near 10% of the lift value. at speed, over 120mph, its a very small factor, but still a factor to consider, if you are halving the drag for the same lift or downforce . its a 3-6 hp discussion to optimize, best case. still, i will kill for this kind of benifit, but you have to be sure you are going to get it before investing in a very expensive wing vs what you are runnining today.

Cory M

Just an update. I talked to Mike (Kognition) and he was very dismissive. No interest at all in selling wing elements without the uprights and of course he doesn't make any uprights that would work for a 911 tail. He said said he wouldn't sell the wing seperate because "the adjustment design is very specific". the adjustment seems very simple to me so I am assuming he makes decent margins on his complete kits and doesn't want to give people the option of making their own uprights. He must not need the business. It appears that he just has the one profile with a 10" chord, which isn't very big for a car with open aero rules. So anyway, it looked promising but it's a no go.

winders

Yes, I pretty much got the same response to an email I sent them. At this point, I am sticking with the Predator from GT Racing since it is a well know product by my chassis builder and the is most common wing on cars like mine in my area.

If I find that I cannot get the downforce I need with the Predator to match what I can get out front, I will look again for other solutions.

I will say that the downforce to drag ratios look great on that Kognition wing. If we could get him to make one with a 12" cord and let us figure out the mounting, that would be great.

Scott

mark kibort

sounds like you just need to bolt on a gurney flap to the wing you got to get close to the lift to drag he has advertised.

333pg333

Well just to digress slightly and also sort of go against my own question about why would you go looking outside of the US...I've been dealing with Simon McBeath in Cory's post# 122 of DJ engineering. Very helpful guy who builds a very effective product from what I can gather. (Not just from him of course!) Looking pretty much like I'm going to go with one of their wing setups which will allow me to run a single element wing in the classes that limit it to 1 and a twin element version for the more Open classes. Merely a case of taking off the end plates and affixing the 2nd element. The theoretical downforce is in the vicinity of over 500lbs. Probably the biggest job apart from mounting it, will be balancing the front with splitter and perhaps canards to apply commensurate frontal downforce. Should be interesting.

winders

Patrick,

I would love to hear more details. What product are you getting and, if you don't mind answering, how much is it going to run?

A PM works if you prefer....

Scott

333pg333

PM sent Scott.

mark kibort

At what speed are you looking to get 500lbs of downforce?

Thats a lot, and with a 911 and its lighter front end, its tough to match it with dive planes up front, unless you use a lot of them. A heafty splitter, (large) and lowering the car up front will do most of it. do you have the ability to do a hood vent? that is the latest thing that most all the high downforce designs are going too. even some of the porsches have this going on now. In tests I was amazed of the flow out the hood into a very low pressure zone venting the air over the car vs letting it go under the car through the nose inlets.

I know scott cringes when I bring up the GF information, as that was actually a good thread with a lot of great info, but the main product of that discussion was realizing that a GF can add near 50% more downforce for the same angle of attack. (a 5% GF which is common and works out to be .5" high)

As a side note, i was watching the supercup series the other night. I wonder why those guys run a pretty neutral setting for their wing and no GFs. (looked to be near 3-5 degrees max) there might be a rule agaist GFs, or they might get all the DF they need with the stock cup car wing. 2- or 3 of the leaders showed almost a neutral setting on a track that was pretty turney. Just an observation.

AussieRacer

Hi all,

Found this thread via Google in my research on wings for my car.

Yeah a lot of the upper level time attack cars run large hood vents - it's a standard thing to do in that kind of racing.

The top time attack teams put a lot of focus on aero.

Like 333pg333 I've been looking at the Simon McBeath DJ Engineering wings. It's for a time attack car I'm building, and I know a number of other guys building cars for the World Time Attack Challenge are looking at them too.

In answer to your question Mark about "what speed are you looking to get 500lbs of downforce?", the CFD data test results for the Simon McBeath DJ Engineering high downforce dual element wing is that with a span of 1380 mm, the wing makes 1502 Newtons of downforce at 100 mph, but I'll be running a wider span than 1380 mm - we'll likely run the 2100 mm span version which is just over 82.6 inches wide.

At that width of 2100 mm we are looking at projected downforce of approx 513 lb force @ 100 mph, based on data from CFD testing done by Simon McBeath using Ansys, and then running the numbers through the formula below.

http://www.tunersgroup.com/Products/wings.html reads ...

The McBeath DJ Engineering wings have also been tested in a full scale wind tunnel, so it's great to see full scale wind tunnel testing as well as CFD data ...



I like testing and data

Info is here with data, drag and downforce charts etc ...

http://www.tunersgroup.com/Products/wings.html

If we're running at an event whose rules limit front aero it gives us the option to run the rear wing at a relatively conservative angle of attack (to balance the front to rear aero) ... with plenty of adjustment left to adjust the rear wing for more downforce for different aero configurations etc like when we run at World Time Attack Challenge where we can run more aggressive front aero.

There is an article here titled "An Introduction To Racecar Aerodynamics & How Aero Can Improve Your Laptimes" which talks about the front to rear aero balance and includes some info about how the aero was balanced on the original 911 RS ...

http://www.tunersgroup.com/engineering/aero_intro.html

In time attack racing we are going after a lot of downforce, so we'll run the rear wing with a big front splitter and canards / dive planes etc to balance the aero front to rear - similar to what 333pg333 mentions above with the wing on his car.

- Rob

AussieRacer

What a cool idea to use ride height sensors from a Lincoln Continental - might try this at the track !

- Rob

AussieRacer

The first thing to remember is that the lift to drag ratio is a relative measurement for a particular wing in that it compares how much lift / downforce that individual wing makes to how much drag that individual wing makes.

So it's a measure of how much drag an individual wing creates for each pound of downforce / lift an individual wing creates. The lift / drag ratio can also vary at different speeds.

But the point is that if you simply select a wing based solely on the lift / drag ratio, you can end up with a wing which has what looks like a great lift / drag ratio but which simply does not generate as much downforce in pounds as a wing on a competitors car.

Think about the "hp per cubic inch" calculation ... for example a competitor may have an engine that produces a high amount of power per cubic inch, but if that engine only produces 200 peak horsepower and another car has an engine with a lower "hp per cubic inch" number but makes 250 peak hp, which engine do you want in your racecar ?

If you are racing in a series where outright power is an advantage, the outright horsepower number is arguably more important than the "hp per cubic inch" ratio.

So instead of looking purely at Lift to Drag ratios when figuring out which wing to get, I also looked at how much downforce each wing makes in pounds, as well as how much drag it makes in pounds.

This way I could get an idea of how much downforce each wing would make in pounds, and how much drag each wing would make but in pounds instead of as a ratio.

That data is essential to me when selecting a wing, because if I am looking at two different wings (let's call them "wing A" and "wing B"), though the lift to drag ratio gives an indication of how efficiently a wing generates downforce relative to how much downforce it makes, I need to know how much downforce and drag in pounds that wing A or wing B makes at the physical size it is supplied in, so that I can say "OK - wing A generates _ pounds of downforce and _ pounds of drag, and wing B generates _ pounds of downforce and _ pounds of drag".

You need the downforce data and drag data from the wing manufacturer to do that comparison, which is why it is important to deal with a wing manufacturer that provides drag and downforce data for their wings, and it's also important to deal with a reputable wing manufacturer whose data is accurate.

Once you have the data it can be very useful for comparing wings ...

Here is a downforce chart from the CFD testing for the 1380 mm span versions of the dual element McBeath DJ Engineering wings ...



If you grab some graph paper (I'm old school) or have a graphing application on your computer, you can can plot the downforce for different wings at 100 mph on a downforce chart like the one above, so that you can compare downforce numbers from different wings in pounds.

I plotted the downforce of a few different wings from different manufacturers at 100 mph at the widths they are supplied in, all on one chart so that I could easily compare the numbers for different wings. I put angle of attack on the X axis on the chart and downforce in pounds on the Y axis on the chart. I used a different colour for each wing's line on the graph, so I had labels for each line on the chart of "wing A at x inches span", "wing B at x inches span" etc.

As for why the downforce numbers in pounds are so important, http://www.tunersgroup.com/engineering/aero_intro.html reads ...

For time attack racing where we are focusing on downforce we focused on finding a wing that produces a lot of downforce and which does not create excessive drag.

The right wing for a given car depends on things like what tyres are used, how much power the car has, series rules and other factors etc, but purely looking at the drag to downforce ratio is looking only at a relative measurement, a ratio ... when what matters most to me in aero data terms is the amount of downforce and drag a wing makes in pounds, at the physical size that wing is supplied in. And of course a properly engineered wing that is built with high quality materials and engineered to handle the forces at play is also very important.

- Rob

333pg333

Rob, have I seen your build on Performance Forums? Which car are you building up?
Oh and thanks for posting all the above info. I was going to post similar. You saved me the hassle.

SundayDriver

There is some other, very cool, stuff you can do with this data.

If you have decent math channels, input the spring rate and let the system have wheel rate as a channel (assuming you know or will measure motion ratio). Then you can use the ride height change (zero it at rest) to calculate front and rear downforce. Add another math channel to calcualte center or pressure and you can see what your changes do to aero balance.

Chart all that as all the little bumps on the track bounce the calculated downforce all around so you want to look at the trace to see what the real downforce component is.

Also fascinating to see (in terms of downforce to weight) what happens over even the smaller rises on the track and how much grip you lose there.