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Sure I do. But I am much more a practical person than I am theoretical. All the math in the world does not trump what actually works in the real world. I suspect that the teams racing sports cars with significant aero packages have either tested various wing angles with and without wickers in place or rely on data from others that have. This data may be wind tunnel results or reliable empirical data gathered doing on track testing. But I suspect most put the most weight on actual track testing.
Wings don't operate in a spreadsheet. There are real world variables that the spreadsheets don't take into account.
You missed my jibe dude, but all is well. I was kidding.
Of course I value empirical (ummm, anecdotal evidence) and real results.
Real world, what this is all beginning to mean to me is the fact that I may be able to reduce wing angle, add a GF and decrease drag...a boon for lower hp cars.
You missed my jibe dude, but all is well. I was kidding.
Of course I value empirical (ummm, anecdotal evidence) and real results.
Real world, what this is all beginning to mean to me is the fact that I may be able to reduce wing angle, add a GF and decrease drag...a boon for lower hp cars.
Sorry.....my humor detector obviously failed big time.
I go for empirical evidence myself. My race car has a Gurney flap on its wing because it has proven better that way by testing done by someone I trust.
You missed my jibe dude, but all is well. I was kidding.
Of course I value empirical (ummm, anecdotal evidence) and real results.
Real world, what this is all beginning to mean to me is the fact that I may be able to reduce wing angle, add a GF and decrease drag...a boon for lower hp cars.
ONLY if you are operating the wing currently over the max lift of the wing, which is a distinct possibility.... do you not agree.
What it means to me, real world that is, is that many of us might be underestimating the max lift angle based on this discussion. for me, for sure, and it might mean backing down the wing, and putting on a gurneyflap. OR it might just mean backing down the wing angle. do you see the difference and reason??? we are trying to talk about this intelligently here..... and the discussion is good. the graphs are good. don't look at the empirical tests and discount the actual measured wing data. you have to look at both .... would you not agree.... I certainly am.
and yes, empirical testing, without statistical significance, is anectdotal... ...... ahchem... by definition.
let me give you an example...... I wash my race car before the race and I win and have faster lap times .... even several times...... so, washing the car must make me faster.
Sure I do. But I am much more a practical person than I am theoretical. All the math in the world does not trump what actually works in the real world. I suspect that the teams racing sports cars with significant aero packages have either tested various wing angles with and without wickers in place or rely on data from others that have. This data may be wind tunnel results or reliable empirical data gathered doing on track testing. But I suspect most put the most weight on actual track testing.
Wings don't operate in a spreadsheet. There are real world variables that the spreadsheets don't take into account.
the data is the data! you are discouting it...... I totally agree. put the car in the wind tunnel and do the tests. they don't contradict the data.. they cant
BUT, as an engineer, it can give solid evidence to what might be happening and why its happening.
for example, IF you can put a gurney flap on a flat wing and it produces less drag than the same wing at an angle giving the same downforce...... the wing MUST have been at near or over max lift at that angle....... its clear from the graphs that this must be the case. AND, it proves that the wing might be getting an AoA from the roof line flow deflection that is giving an angle that provides a higher than max Cl value. Can you explain why that is not a distinct possibility?
im toiling with it right now. I have the cup car wing. I have less deflection than a 911 or cayman. BUT, we know from the graphs the max lift is at 10 degrees.... anymore AoA and the wing has increased drag for the same lift.
so, if I don't need more lift, back it down to max Cl. by putting a gurney flap at that same downforce, EVEN near max Cl.... drag doesn't go down. its near the same at that point in All of the actual tests and simulations.
I just measured the angle of the 911 roof line flow effect as it hits the wing.
drum roll please..................................
12.5 degrees. based on the info we have currently from the wind tunnel experiements as well as calculated information.... that's about 1 degee over max lift for the GT3 wing.
16.5 degrees for the roof line itself.
(Ferrari 458 is near parallel, flat, no angle as measured at the point where the wing would attach.)
its all making sense ...........slowly
EDIT: IF you have the wing installed at 3 degrees angle of incidence...that's 15.5 AoA. according to a very simiar wing, that's well above max Cl.... he drag is near .27 for a lift of near 1.3 Cl
with a gurney flap, the same lift can be achieved at 1-2 degree AoA and a drag of .12. ...... but to get 1-2 degree AoA, the wing needs to be negative angle of incident of 10 degrees.
Here is the part you need to grasp.... at that point, you could also back the wing off to 10degree AoA, meaning negative 2.5 degree angle of incidence. that gives the same downforce, BUT, only a drag of .1...... the gurney flap at that same downforce has a drag of .12 as mentioned. THAT is what im talking about.
This is why this discussion can be so interesting. its why the windtunnel can be so confusing and challenging. if you don't test over the full range, you don't know if you could have the same downforce at a much lesser angle.. if you are operating over the max lift of the wing. Ive done enough testing back in the day, to attest this is easy to do (get misled by results) .. especially by folks not that experienced in wind tunnel testing.
I've added the graphs for reference of a high lift wing with a similar max Cl AoA. (the cup car GT3 wing is even more aggressive than this wing)
Last edited by mark kibort; 11-03-2014 at 09:05 PM.
Sure I do. QUOTE]
Real world, what this is all beginning to mean to me is the fact that I may be able to reduce wing angle, add a GF and decrease drag...a boon for lower hp cars.
I was going to make a Venn Diagram to explain the overlap of the real world, your world, and Mark's world, but it's taken too much effort. I'm sure you could picture how it would look and which two circles are concentric and which one stands alone.
Do not forget that not all of the wing is exposed to the same effective AoA. For example, I run a 997.2 cup wing which is signifcantly wider than the 997.1 wing (but has the same profile), and therefore has much more of the wing width exposed to a shallower AoA. The RSR wing shape is likely evidence of this.
by running the wing at its original, more neutral AOA and simply adding a wicker, we had the same measured down force with far less of an increase in drag.
This matches all of my experience with GT and sports racing cars...
__________________ -Peter Krause www.peterkrause.net www.gofasternow.com
"Combining the Art and Science of Driving Fast!"
Specializing in Professional, Private Driver Performance Evaluation and Optimization
Consultation Available Remotely and at VIRginia International Raceway
I was going to make a Venn Diagram to explain the overlap of the real world, your world, and Mark's world, but it's taken too much effort. I'm sure you could picture how it would look and which two circles are concentric and which one stands alone.
matt, when you go fast enough to worry about downforce, come back and chat. until then, enjoy living in "your world " where 10 degree temp drop hurts top speed down WG straight by 5mph.
spend this time watching your videos! you might find a lot of time there... (based on what we all saw from your data)
Originally Posted by Krokodil
Mark,
Do not forget that not all of the wing is exposed to the same effective AoA. For example, I run a 997.2 cup wing which is signifcantly wider than the 997.1 wing (but has the same profile), and therefore has much more of the wing width exposed to a shallower AoA. The RSR wing shape is likely evidence of this.
Cheers,
I was just driving and thinking of that. good point. even my GT3 wing is wider than my car, but not by much. with the wide wings, there might be 20% of the wing with an entirely different AoA. I guess we need to average it out. Don't forget in the turns...... the roof line wont be effecting the on coming air as much as well, right?
Originally Posted by ProCoach
This matches all of my experience with GT and sports racing cars...
Oh brother.... do you even understand what we are discussing. The point clearly is, that even if it worked and was valid for the Cayman, their is a 12 degree difference of AoA vs the Ferrari based on roofline deflection.
5 degree off my 928 deflection
the point of all this is to think about what is actually going on. you might be on the track and find what works, but isn't it possible its working, but working with higher drag than what can otherwise be found? clearly, in the case of the Ferrari, if the high lift wing graphs are remotely applicable, there can be significant drag associated with the GF in low wing angles vs no GF at the same downforce setting.
Another point here is we wont be able to validate anything unless we know what that "more neutral" point of his wing setting was before the gurney.
Keep in mind, the 911 roof line, like the cayman is 15.3 degrees and the air defection is 12.5 degrees
Its 8 degrees for the 928 based on windtunnel tests. with a roof line of 13.3 degrees.
what happens in the turns??? that air isn't following the roofline anymore...... was the car tested at different Yaw angles?? if not, that's a HUGE deal and I bet it was not which kind of defeats the purpose of the test of downforce, as the majority of the use of downforce , besides braking and stability, its for turning grip. during the turn the cord is effectively lengthened, and the width of the wing appears shorter. changes all sorts of charactistics of the wing.
Well I guess I have to admit I was wrong, I did a bunch of runs with my test rig... I ran a series of angles with my gurney and added all kinds of wickers which was just proved to be a drag. I couldn't go far because I only had a 20ft extension cord so the fan would quit when I got up to speed, haven't figured that out yet but I'm thinking a 50 footer will get er done.
I'm still trying to make a chart but I can't find a sharpener for my crayolas, you know the box with the sharpener in the back? love that box, all 64 colors and all, last one I set too close to the exhaust while I was setting up my dyno to get some pulls, I was trying to figure out how many RPM there are in a torque, more on that later.... anyway here's my test rig, it is optimized with a NONO 362436 airfoil its optimized for the vinyl boundary layer...The more wicker I add the slower it goes.
11-03-2014, 06:35 PM
