Veloce Raptor

Mark, ENOUGH with the pedantic lectures, please.

I stated I had pointed out aero earlier. You said I didn't. I posted proof in post #63. Please, leave the FACTS at that, OK?

Good grief.






Professional Racing and Driving Coach

Circuit Motorsports

It's still not a reasonable question.

How efficient is the wing?
How much air is actually getting to the wing? Is it on the decklid, spaced up, way up high?
Where is the force measured? At the wing or at the rear suspension?

mark kibort

I see, you are just making a general statement of why, not a discussion.

Its not a lecture, its a forum to discuss why. I contend that the trade off of the hole the 911 makes in the air, is offset by its HP to accelerate its mass so that there is no NET advantage over a Viper or Vet as far as aero drag to HP ratio.
This then would give a slight advantage to the 911 for its pure lower weight.

Thats all, just a theory. How about that torque off the turns VR! hmmm, 911 has half that of the viper, yet it stays pretty close on all corners. . Wonder why? rear wheel torque or engine torque??

enjoy!

mk

mark kibort

Its a very resonable question, when i ask the answer to be approximate.

I'm asking for the answer based on the force generated by the wing. Sure, you are right in asking the question to clarify where the force is measured, because it would change one where it is located on the chassis . Its efficiency is not that important in terms of the purpose of the question. Make it as effecient as you want , or dont want, but keep it in a reasonsable range. you look at all the NACA numbers available give me a general figure for a wing that most of use would use on a car. I'm surprised you didnt ask the angle of attack. (another form of maybe where the wing was located on the rear of the car)
The key point is to show what the effects of drag are on the total available forces for acceleration.

So, any guesses?

Veloce Raptor

Mark, I mean no malice when I say this...but there is no discussing with you. There is your way...........and everyone else. And when someone disagrees with you, or proves you wrong, you launch another lecture and change the subject. Perhaps this is why so few people respond to you anymore. I am frankly not sure why I am still among them.

Watching that race, it appeared the Porsches carried more speed into the corner, preserved it at midcorner where it is critical, and thus got bettter launches than their dyno numbers would predict. And then DUE TO BETTER AERO, they were able to keep that velocity....and win the race.






Professional Racing and Driving Coach

Bob Rouleau

Mark, I get riled reading this thread. You go on and on and on. You ask questions that cannot be answered. How much drag does a wing induce. Unless you are an aeronautical engineer, I suggest you stop playing one. As Circuit Motorsports has stated, the question you have posed cannot be answered even in theory without knowing the precise details of the wing itself. At that fluid dynamics would produce at best a theoretical outcome and would have to be verified with testing. No guess can tell you about how efficient the wing is and how much drag it produces. There are too many other factors like turbulence, laminar flow etc. which are unknown. Aero engineers work very hard with exotic tools to make airplane wings as efficient as possible, lift/drag ratios are crucial, yet they are a compromise depending on the angle of attack, density of the air and a number of other factors. That's why airplanes have movable surfaces, like slats and spoilers.

Further relating that to your rear wheel torque number just complicates things needlessly and provides you with an excuse to start that mind numbing thread all over again.

Please do not assume that those of us who frequent this forum are not aware of HP/Weight, and HP/Drag. You take VR to task because he said "aero is huge at RA". His statement is backed up by other experienced racers yet you chose to interpret his words differently than the rest of us. Worse you then throw a bunch of pseudo science at us.

If you get the impression that I am getting fed up of this nonsense you are correct. ASk questions, provide meaningful inputs but stop derailing threads with your attempts to "school us".

How about you stick to the topic and I apologize to the rest for this off topic post.

Regards,

mark kibort

Carring more speed in the corner would be due to a lighter car with more stick.
that would give a better launch, but that mid corner speed preservation would be more a function of handing, or if aero, downforce. (which would be more drag) Now, your last point seems to totally ignor force to drag ratios that I contend would be near idential for the porsche vs the larger cars, regardless of the size of the hole they punch in the air.

Now, we can discuss that without getting too personal, cant we?

I only posed the question to give a value of drag to the equation that you are guessing at.

mk

And by the way, if folks were not interested, this wouldnt be going on for 7 pages already , without your cheap shot japs. that usually takes the discussion needlessly out to 20+ pages. many are involve in the splitter discussion as well.
Instead of just bashing everything, why dont you just sit back and try and learn something. heck, it might even help you in your driving business!

DAVE SAID :
Perhaps this is why so few people respond to you anymore. I am frankly not sure why I am still among them.

mark kibort

I asked the question to get the thought process going in the direction that uses the forces that some might not realize and to open the discussion. I dont bring it up to "school " anyone, excecpt VR. (kidding) but to start the discussion and to learn something we all might not know . Hey, on the splitter discussion, there are a lot of smart folks here. the discussion is interesting. Im learning a lot there, and its sparking new ideas in testing and design. I guess if this kind of discussion is not interesting, you dont really have to join in.

Ill answer it for you so that it can stop here.

Generally, a wing has a near 10:1 lift to drag ratio at moderate angles of attack (most wings, especially the ones that we are familar with in racing)

If a wing puts out 200lbs of downforce, 20lbs of that would be near the drag figure. The point was not to look at exact numbers, but to see how it relates to the overall accelerative forces. Rear wheel torque if you wish.
The actual values, Standard day pressure, temp, are not needed. designers of wings usually use one of many NACA numbered airfoil designs. efficiency also is more of a rounding error for our discussions, but brings up other factors that are interesting, such as gurney flaps, angle of attacks, wing height, turbulence, vortex generators, etc.

If its 20lbs of drag, on a 24"diameter tire, and at 100mph, its near 4hp at the engine that you just lost . Thats just the wing, at near full drag for most race speeds.

It kind of keeps things like this in perspective to see the actual values as it relates to engine torque.

Bob Rouleau

Mark on my home track setting my RS wing to maximum angle of attack (about 8 degrees) results in a 10 MPH drop in top speed. Maximum speed with the wing in the lowest position (normal) is 238 KPH, with max angle and perhaps although it is not certain, downforce) the top speed is 223 KPH at the end of the straight. Is that 4 HP? I doubt it. Drag increases exponentialy with speed which is why you need a lot of HP to increase speed significantly once you hit the aero "wall". You have posted on this subject before. Note that the RS wing is similar to the cup car in size and shape.

mark kibort

Here is a porsche carrera vs a porsche 928 as far as frontal area. the Vet and viper are close to the same frontal area of the 928, so I posted it. point is, there is about a 10% lower frontal area and drag coefficients will be the same I would imagine. want the total drag? just multiply out the Cd and he the frontal area and you can get the drag forces. This can put in perspective any advantage or disadvantage based on rear wheel hp/weight at any speed.

Porsche 911 Carrera
0.38 - 0.39 drag coef. Cd
19.15 frontal area

Porsche 928 S
0.30 - 0.40 Drag coeff
21.09 frontal area

mark kibort

Now, wait a little bit here Bob.

Lets go on the facts. 238kPH is 148mph. and I assume you are going from 0 angle (level) to max angle 8 degrees.

If it is 4hp at 100mph, then because the power to drive the drag goes up with the cube of velocity, that 4hp goes to 18hp at 148mph. can 5-18hp from 100 to 148mph cause a 10mph drop in top speed over a set straight? I dont know. Id have to see the data aqu. output to really see. remember brinkely's discussion. it was tires tires tires for 5mph, diff, and ended up being driver style.
9mph is a lot.

BUT, almost missed the main point. the 4hp is the drag at 100mph and the drag force of near 4lbs. on my car that is near 4hp. however, the downforce goes up with speed^2 as well. so, at 148mph, (if 200lbs at 100mph)downforce is 440lbs, or 44bs of drag. at 148mph, the power associated with that would be near 18hp.

There is no aero wall, but the forces do go up with the square of speed, and power to push through it requires cubed!

Also as a note, we both have or wings set at 8 degrees, but how the air travels back to the wing changes that angle of attack number. (unless it is way up in clean air) . Here is something to think about. If your "deflection" angle is more than 9 degrees, you will be operating the wing at 18 degrees AOA (angle of attack) if so, drag goes through the roof, while downforce doesnt change much.
I think the 911s get more of a deflection down off the rear deck, so that the AOA is greater than just the angle measured from level.

mk

Veloce Raptor

Incorrect.

Incorrect.

And incorrect.






Professional Racing and Driving Coach

mark kibort

I always love to discuss with folks that just say "wrong".

If those points are wrong, back it up. Can you explain why?

Seriously, I really want to know.



Its a great topic!

You said:
Watching that race, it appeared the Porsches carried more speed into the corner, preserved it at midcorner where it is critical, and thus got bettter launches than their dyno numbers would predict. And then DUE TO BETTER AERO, they were able to keep that velocity....and win the race.

1. porsche carried more speed into a corner.
comment: doesnt that mean it has better road holding abilities. sounds like handling to me, which could be downforce, or just lightweight, and lower C/g to create greater g's in that corner

2. preserving mid corner speed.
comment: define "preserving" carried more speed, was faster through the corner, faster out of the corner??

3. better launch off the corner.
comment: if two cars are going the same speed exiting the corner, and one gets a better "launch" assuming "launch" means acceleration, then one will have more available hp/weight at the exit.

mark kibort

http://www.a2wt.com/APPENDIX.htm

VR, a great site to actually calculate anything related to your beliefs.

Corvette is frontal area 21 sq-ft / 2.04sq-m
porsche GT3RS is 21.95 sq-ft / 1.95sq-m

Hmmm, looks like the vet is actually smaller than the porsche, but that doesnt look right.
Certainly, with wings and flares, things change, but they are not that different at first glance. I say, even if you go off a 10% difference, what is the real differnce on the track, based on known HP values.


HERE YOU GO VR a full chart. This is square feet of the frontal area of a car, multiplied by its coefficienit of drag. This gives the TOTAL drag of any car. You say that the 911 punched a smaller hole through the air? dont think so. If Im wrong as you say, what is wrong with these numbers below? These are Facts!
pretty close comparisons. in which case, the higher hp cars would have an aero drag vs HP advantage at highs speed, wouldnt they??
Case in point. Remember the RS6 audi 4 doors??? sure you do. 2:14 at Road america and WITH 3500lbs !! not very aero now were they?


CdA ft² / Vehicle

2.11 2009 Aptera 2 Series
2.50 1986 Twike
3.38 1992 AeroCivic
3.95 1996 GM EV1
5.10 1999 Honda Insight
5.40 1989 Opel Calibra
5.71 1990 Honda CR-X Si
5.74 2002 Acura NSX
5.76 1968 Toyota 2000GT
5.80 1986 Toyota MR2
5.81 1989 Mitsubishi Eclipse GSX
5.86 2001 Audi A2 1.2 TDI 3L
5.88 1990 Nissan 240SX hatchback / 200SX / 180SX
5.92 1994 Porsche 911 Speedster
5.95 1990 Mazda RX7
6.00 1970 Lamborghini Miura
6.08 2008 Nissan GTR
6.13 1991 Acura NSX
6.17 1995 Lamborghini Diablo
6.24 2004 Toyota Prius
6.27 1986 Porsche 911 Carrera
6.27 1992 Chevrolet Corvette
6.35 1999 Lotus Elise
6.40 1990 Lotus Esprit
6.54 1991 Saturn Sports Coupe
6.57 1985 Chevrolet Corvette
6.63 2001 Audi A2
6.66 1996 Citroën Saxo
6.77 1995 BMW M3
6.79 1993 Toyota Corolla DX
6.81 1991 Subaru Legacy
6.90 1993 Saturn Wagon
6.93 1982 Delorean DMC-12
6.96 1988 Porsche 944 S
6.96 1995 Chevrolet Lumina LS
7.02 1992 BMW 325I
7.04 1991 Honda Civic EX
7.10 1995 Saab 900
7.14 1995 Subaru Legacy L
7.34 2001 Honda Civic
7.39 1994 Honda Accord EX
7.48 1993 Chevrolet Camaro Z28
7.57 1992 Toyota Camry
7.69 1994 Chrysler LHS
7.72 1993 Subaru Impreza
8.02 2005 Bugatti Veyron

Veloce Raptor

Why bother, Mark? Seriously....why bother? Oh, and thanks for barraging us with boolsheet on a 1986 Porsche and a 1992 Corvette. Relevance to 2009?????

1. more likely better braking & transition characteristics, as well as a driver who is better skilled at using his car's strengths & avoiding its weaknesses

2. everyone here understood it except you

3. nope, as I made clear, the Porsche was consistently just a shade faster mid corner, and thus carried that speed at exit and all the way down to the next corner, thus winning the race....it has nothing to do with HP or torque, so PLEASE (as Bob already asked you nicely) do NOT drag us back down that rathole of yours.






Professional Racing and Driving Coach