[ANSWERED] What are the aerodynamic properties of the various C7 models
04-19-2016, 04:30 PM
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[ANSWERED] What are the aerodynamic properties of the various C7 models
Original question is here.
descartesfool asked:
In order to better understand the performance differences and goals of the C7 models, could you detail the values for the lift and drag coefficients and frontal areas for the base, Z51 and various Z06 versions and front to rear downforce ratios and total downforce at speeds, Lift/Drag ratios, and why they were chosen?
In order to better understand the performance differences and goals of the C7 models, could you detail the values for the lift and drag coefficients and frontal areas for the base, Z51 and various Z06 versions and front to rear downforce ratios and total downforce at speeds, Lift/Drag ratios, and why they were chosen?
Tadge answered:
The standard Stingray has a drag coefficient of .30. Its frontal area is 2.02 square meters and has a lift coefficient of .20. Generally speaking, as you move up the Corvette model range, frontal area and drag go up and lift goes down. This is not just true of Corvette, but virtually all performance car lines. Frontal area goes up because tires get wider and you have more aggressive aerodynamic features. The aerodynamic aids that create downforce tend to disturb the air in such a way as to add drag. Directing air through heat exchangers and towards brakes to cool them also creates drag. As engines make more power, more energy needs to be dissipated in all cooling systems including coolant, oil, trans and differential lube, and in the case of charged engines, intake air.
Race cars have a lot of drag by street car standards, but they produce a lot of downforce. Race teams spend a lot of time optimizing this tradeoff for a given track. They also have to make sure the drivers like the way the car handles. It is no different for street cars, we are always looking for ways to improve down force at the minimum drag penalty. The Z51 option on the Stingray adds cooling content, a rear spoiler and modifies the aero panels under the nose of the car. It's Cdx moves up to .35 but lift drops to .03, which is very close to a zero lift car. Actually, we have tested Z51 cars with negative lift coefficients, which means those cars are producing true downforce.
The Z06, with its wider tires and flared body panels has a higher frontal area (up to about 2.1 square meters) and the standard car has drag and lift numbers similar to the Z51. The Z06 has available Stage 2 (CFZ or CFV Carbon Fiber Ground Effects) and Stage 3 (Z07 Performance package with the large end plate on splitter and the center bridge "wicker" on the rear spoiler) aero packages that further trade drag for additional downforce. Stage 2 has a "lift" coefficient of -.152 and stage 3 is -.279. The minus signs mean negative lift or down force. The trade off in drag means those coefficients move from about .40 to .50. In other words, the cars are starting to approach race car numbers. In our testing on many tracks, the improvement in corner speeds more than offsets the straight line speed loss from the higher drag. Depending on body style, our aero packages have lift to drag ratios ranging from 2.6 to 3.6. We consider anything over 2.0 (2 counts of lift reduction at the cost of a single count of drag) an efficient tradeoff.
You asked about front to rear down force ratios or what we call "Pitch moment". We have strict criteria for pitch moment. The ratio needs to be held within a fairly narrow range so that the vehicle handling remains consistent. Too much down force on the rear and the car will understeer at higher speeds. Too much on the front and the car will oversteer. We tune all our cars to maintain neutral handling biased slightly towards understeer.
I am sharing these specifics with you quite reluctantly. The reason is that there are many ways aero performance can be quantified. No two wind tunnels are exactly the same. Some have moving ground planes, some do not. Many correction factors are used because none of them replicates exactly what happens in the real world. They have finite test spaces while the world is far more open. Computation fluid dynamics (CFD) is getting so good, it is used widely and surpasses physical testing in some ways. Bottom line is that with so many ways to predict them, numbers from one manufacturer are only roughly comparable to another. In addition to the number of ways to measure, the cars themselves can be variable. Small changes in standing height or pitch (relative height of the front to the rear) can have a big effect on measured numbers. Thank you for the question. I have tried to keep the answer to a level everyone can understand. Aerodynamics can very quickly become a complex technical discussion.
The standard Stingray has a drag coefficient of .30. Its frontal area is 2.02 square meters and has a lift coefficient of .20. Generally speaking, as you move up the Corvette model range, frontal area and drag go up and lift goes down. This is not just true of Corvette, but virtually all performance car lines. Frontal area goes up because tires get wider and you have more aggressive aerodynamic features. The aerodynamic aids that create downforce tend to disturb the air in such a way as to add drag. Directing air through heat exchangers and towards brakes to cool them also creates drag. As engines make more power, more energy needs to be dissipated in all cooling systems including coolant, oil, trans and differential lube, and in the case of charged engines, intake air.
Race cars have a lot of drag by street car standards, but they produce a lot of downforce. Race teams spend a lot of time optimizing this tradeoff for a given track. They also have to make sure the drivers like the way the car handles. It is no different for street cars, we are always looking for ways to improve down force at the minimum drag penalty. The Z51 option on the Stingray adds cooling content, a rear spoiler and modifies the aero panels under the nose of the car. It's Cdx moves up to .35 but lift drops to .03, which is very close to a zero lift car. Actually, we have tested Z51 cars with negative lift coefficients, which means those cars are producing true downforce.
The Z06, with its wider tires and flared body panels has a higher frontal area (up to about 2.1 square meters) and the standard car has drag and lift numbers similar to the Z51. The Z06 has available Stage 2 (CFZ or CFV Carbon Fiber Ground Effects) and Stage 3 (Z07 Performance package with the large end plate on splitter and the center bridge "wicker" on the rear spoiler) aero packages that further trade drag for additional downforce. Stage 2 has a "lift" coefficient of -.152 and stage 3 is -.279. The minus signs mean negative lift or down force. The trade off in drag means those coefficients move from about .40 to .50. In other words, the cars are starting to approach race car numbers. In our testing on many tracks, the improvement in corner speeds more than offsets the straight line speed loss from the higher drag. Depending on body style, our aero packages have lift to drag ratios ranging from 2.6 to 3.6. We consider anything over 2.0 (2 counts of lift reduction at the cost of a single count of drag) an efficient tradeoff.
You asked about front to rear down force ratios or what we call "Pitch moment". We have strict criteria for pitch moment. The ratio needs to be held within a fairly narrow range so that the vehicle handling remains consistent. Too much down force on the rear and the car will understeer at higher speeds. Too much on the front and the car will oversteer. We tune all our cars to maintain neutral handling biased slightly towards understeer.
I am sharing these specifics with you quite reluctantly. The reason is that there are many ways aero performance can be quantified. No two wind tunnels are exactly the same. Some have moving ground planes, some do not. Many correction factors are used because none of them replicates exactly what happens in the real world. They have finite test spaces while the world is far more open. Computation fluid dynamics (CFD) is getting so good, it is used widely and surpasses physical testing in some ways. Bottom line is that with so many ways to predict them, numbers from one manufacturer are only roughly comparable to another. In addition to the number of ways to measure, the cars themselves can be variable. Small changes in standing height or pitch (relative height of the front to the rear) can have a big effect on measured numbers. Thank you for the question. I have tried to keep the answer to a level everyone can understand. Aerodynamics can very quickly become a complex technical discussion.
Last edited by jvp; 04-19-2016 at 04:31 PM.
04-19-2016, 07:15 PM
#2
Thanks Tadge, that offers a fabulous insight into the aerodynamic properties of the C7, from base to Z07 variants, and shows the rather large range of drag, downforce and L/D ratios. Couldn't have asked for a better answer. Few people know how aero dominates race car performance, and how high performance street cars have moved closer into the race car performance arena.
04-19-2016, 08:14 PM
#3
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Thanks for a good answer. It's true few of us have a PhD in engineering, but we're not stupid, either. I appreciate people who really do have advanced knowledge not talking down to those of us who are really interested.
04-20-2016, 01:49 AM
#4
Thanks Tadge.
As aircraft aero is my trade so to speak, I quite appreciate that CFD is indeed one of the greatest tools a designer has these days.
One added point I'd be asking Tadge, if and when the opportunity avails itself through Jvp, is whether active aero is something the Corvette Design Team is looking into for the future.
An interesting subject indeed.
As aircraft aero is my trade so to speak, I quite appreciate that CFD is indeed one of the greatest tools a designer has these days.
One added point I'd be asking Tadge, if and when the opportunity avails itself through Jvp, is whether active aero is something the Corvette Design Team is looking into for the future.
An interesting subject indeed.
04-20-2016, 02:24 PM
#5
Pro
This very well may be one of the first Ask Tadge segments that he gave a no BS straight up factual and well explained answer, showing numbers and not making general statements or vague comments. I'm very content with this!
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daleong (06-05-2019)
04-20-2016, 03:28 PM
#6
04-20-2016, 09:19 PM
#7
Safety Car
I read the first sentence and I knew this was going to be chock full of good info.
There are two surprises for me in the response. The CDx is the same for Z51 and Stage 1 Z06. I mean wow, how did they do that? I was working with the suspicion that the rear fender scoops increase drag a lot. Is that additional drag not included in these calculations?
The CDx sky rockets for the Z07 pack. I'm not sure I've seen one in the .5 range. Makes sense why I couldn't get the car to pull over 184mph with full aero. I do believe Tadge when he says the tradeoff is worth it.
There are two surprises for me in the response. The CDx is the same for Z51 and Stage 1 Z06. I mean wow, how did they do that? I was working with the suspicion that the rear fender scoops increase drag a lot. Is that additional drag not included in these calculations?
The CDx sky rockets for the Z07 pack. I'm not sure I've seen one in the .5 range. Makes sense why I couldn't get the car to pull over 184mph with full aero. I do believe Tadge when he says the tradeoff is worth it.
04-21-2016, 11:15 PM
#8
Le Mans Master
Wow, what a straight forward easy to understand response to a very complex question. Sign of a truly brilliant man.
I alway look for to the questions forum members submit and the subsequent responses from Tadge. They are always informative and insightful.
I want to extend high regards to Tadge for taking time out of his hectic schedule each month to get back to us. It demonstrates his continuing love for the C7 and respect for us, the owners of the awesome sports car.
Thank you members for the great questions and to our monitor for his great work!
I alway look for to the questions forum members submit and the subsequent responses from Tadge. They are always informative and insightful.
I want to extend high regards to Tadge for taking time out of his hectic schedule each month to get back to us. It demonstrates his continuing love for the C7 and respect for us, the owners of the awesome sports car.
Thank you members for the great questions and to our monitor for his great work!
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plasboy (04-26-2016)
04-22-2016, 11:27 PM
#11
I'm really surprised that nobody has tried to take these numbers and convert them to lbs of downforce at 100 or 150 MPH. We keep hearing about how many lbs of downforce the Viper ACR has and how great that makes the car.
04-23-2016, 08:46 AM
#12
Drifting
I believe these links have been posted before, but if you haven't seen them:
And for you mathematical types , there's always this...
I'm being a little self-indulgent - this last link happens to be my area of specialty. I know they perform similar simulations for the C7, but that type of information is usually proprietary.
In the CFD simulation - you get everything! Pressure & shear stress (every 10 mm), drag, upward force and downward force, etc.
The Supercomputer is the ultimate Sledgehammer of Engineering.
And for you mathematical types , there's always this...
I'm being a little self-indulgent - this last link happens to be my area of specialty. I know they perform similar simulations for the C7, but that type of information is usually proprietary.
In the CFD simulation - you get everything! Pressure & shear stress (every 10 mm), drag, upward force and downward force, etc.
The Supercomputer is the ultimate Sledgehammer of Engineering.
Last edited by Dougs63; 04-23-2016 at 08:49 AM.
04-23-2016, 12:00 PM
#13
Thanks for posting, I've sure missed these before.
CFD can produce all sorts of scenarios, I'd imagine that Tadge and GM are a bit coy about releasing data, which is surely relevant to the racing program as well?
CFD can produce all sorts of scenarios, I'd imagine that Tadge and GM are a bit coy about releasing data, which is surely relevant to the racing program as well?
04-26-2016, 01:37 PM
#15
Drifting
Car and Driver used to do coast down meansurements for aero drag and frictional forces, one of the best ways to demonstrate how efficient a chasiss is... and excellent for comparative results... I recall how the 1982 Trans Am was more efficient than the Z28. 0.5 hp @ 50mph was pretty significant at 50mph. The same can be done with the various levels of Corvette to actually show the differences. Aero used to be for fuel economy, now, above 100mph, it's for handling.
I do think that active aero, as mentioned in previous posts, is the way to go for the future... kinda like flying a swing wing F-14.
I do think that active aero, as mentioned in previous posts, is the way to go for the future... kinda like flying a swing wing F-14.
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JerryU (04-27-2016)
05-09-2016, 04:59 PM
#19
This is awesome - great response.
It also highlights why I'm always reluctant to muck around with things the designers could have changed but didn't. I assume they made smart tradeoffs and unless I understand them I might not be making good ones. I also worry the traction control computers are tuned for certain assumptions that aftermarket modifications might invalidate. I appreciate how effective the computers are at keeping me from killing myself and don't want to break that.
It also highlights why I'm always reluctant to muck around with things the designers could have changed but didn't. I assume they made smart tradeoffs and unless I understand them I might not be making good ones. I also worry the traction control computers are tuned for certain assumptions that aftermarket modifications might invalidate. I appreciate how effective the computers are at keeping me from killing myself and don't want to break that.
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quick04Z06 (06-20-2016)