Aero Question..........
02-10-2010, 06:53 PM
#76
Rennlist Member
I think I may have found the answer. If you look a the curves for the air foils you can see a wing, for example, that was double in length, would share the same L/D and Cl and Cd. so, that longer wing would have less angle to create the same downforce. If the L/D curve starting out at near 0 AOL, is followed, its my thought that there would be an equal trade off if the curve is at a 45 degree angle on the chart, which is is for wings like we use on race cars. So, there would be no difference, except for the fact that the ends of the wing, being further out could create more downforce, and you would have more angle to play with before max lift was produced.
Is that the answer we are looking for?
Is that the answer we are looking for?
02-10-2010, 06:59 PM
#77
Rennlist Member
interesting. my dad was involved in a lot wind tunnel testing in the 60s at Nasa, and much of their work showed up on the shuttlecraft, 30 years later.
I did some study in that area as well, but cant find any of my notes. What you have sure looks good too.
That text is from the late '70s but im sure it has been only slighly modified since the. I think you need to look at the Virgin Atlantic record holder Canard plane to see what the latest advances have been. Pretty close to what you have.
you can never take empirical testing too far, unless you are going to get a ticket doing it.
mk
Actually, McBeath's testing showed benefits from going as high up as you go down below with straight end plates.
My angled winglets were based on different research:
Source: McCormick, Aerodynamics, Aeronautics, And Flight Mechanics. Wiley, 1979. ISBN: 0-471-03032-5
Of course, you have to invert everything for a race wing. But you can see it in use more and more on commercial aircraft:
And I agree that I sometimes take empirical testing too far.
My angled winglets were based on different research:
Source: McCormick, Aerodynamics, Aeronautics, And Flight Mechanics. Wiley, 1979. ISBN: 0-471-03032-5
Of course, you have to invert everything for a race wing. But you can see it in use more and more on commercial aircraft:
And I agree that I sometimes take empirical testing too far.
02-11-2010, 06:12 AM
#78
Nordschleife Master
Unless you have a windtunnel and a degree in aerospace engineering, you are not going to discover anything new that the F1 teams haven't already.
If you're just doing DE's, focus on your driving instead.
If you're racing and want a competitive wing setup, copy the top3 cars, and focus instead on your driving.
( Unless you're a tinkerer like me and jack olsen and love to try funky looking solutions on your car, partly to satisfy your inner inventor persona, and partly to intimidate everyone else at the track.
)
If you're just doing DE's, focus on your driving instead.
If you're racing and want a competitive wing setup, copy the top3 cars, and focus instead on your driving.
( Unless you're a tinkerer like me and jack olsen and love to try funky looking solutions on your car, partly to satisfy your inner inventor persona, and partly to intimidate everyone else at the track.
)
02-11-2010, 10:29 AM
#79
Rennlist Member
Rich, with over 8000 posts I hope this is one of your less inspiring ones. I have good advice in this thread and yes it pertains to the race group I run with so would you mind not spoiling it?
02-11-2010, 02:55 PM
#81
Addict
Rennlist Member
Rennlist Member
Not trying to spoil the fun, but my approach pretty much agrees with Rich...
When I needed a wing, I bought a big one, similar to what most other folk were running. With a 60" wing you can generate lots of down force by using a large attach angle. Too much rear down force and too much drag were easy to obtain. It's silly to generate a lot of rear down force if it is not balanced by increased down force up front. I've dialed my wing back to the lowest attack angle and I still get a few hundred lbs of down force at 100 mph (and I get a higher velocity at the end of the straights because of the reduced drag). I measure the front and rear down force with shock sensors. I had to add the 'canards' to the front of my car to get any real down force up front while at WOT - and I had to lower the front ride height too (a larger rake).
To me, dreaming about how to design the perfect wing isn't worth the time or effort. I'd rather be looking at my data to see what impact a set up change had in my speed through the turns versus at the end of the straight and what it did to lap times. If I find I can't seem to get what I want with the wing I have, I'd simply consider going bigger or smaller based on what the data points out as a problem.
When I needed a wing, I bought a big one, similar to what most other folk were running. With a 60" wing you can generate lots of down force by using a large attach angle. Too much rear down force and too much drag were easy to obtain. It's silly to generate a lot of rear down force if it is not balanced by increased down force up front. I've dialed my wing back to the lowest attack angle and I still get a few hundred lbs of down force at 100 mph (and I get a higher velocity at the end of the straights because of the reduced drag). I measure the front and rear down force with shock sensors. I had to add the 'canards' to the front of my car to get any real down force up front while at WOT - and I had to lower the front ride height too (a larger rake).
To me, dreaming about how to design the perfect wing isn't worth the time or effort. I'd rather be looking at my data to see what impact a set up change had in my speed through the turns versus at the end of the straight and what it did to lap times. If I find I can't seem to get what I want with the wing I have, I'd simply consider going bigger or smaller based on what the data points out as a problem.
02-11-2010, 03:01 PM
#82
Not trying to spoil the fun, but my approach pretty much agrees with Rich...
When I needed a wing, I bought a big one, similar to what most other folk were running. With a 60" wing you can generate lots of down force by using a large attach angle. Too much rear down force and too much drag were easy to obtain. It's silly to generate a lot of rear down force if it is not balanced by increased down force up front. I've dialed my wing back to the lowest attack angle and I still get a few hundred lbs of down force at 100 mph (and I get a higher velocity at the end of the straights because of the reduced drag). I measure the front and rear down force with shock sensors. I had to add the 'canards' to the front of my car to get any real down force up front while at WOT - and I had to lower the front ride height too (a larger rake).
To me, dreaming about how to design the perfect wing isn't worth the time or effort. I'd rather be looking at my data to see what impact a set up change had in my speed through the turns versus at the end of the straight and what it did to lap times. If I find I can't seem to get what I want with the wing I have, I'd simply consider going bigger or smaller based on what the data points out as a problem.
When I needed a wing, I bought a big one, similar to what most other folk were running. With a 60" wing you can generate lots of down force by using a large attach angle. Too much rear down force and too much drag were easy to obtain. It's silly to generate a lot of rear down force if it is not balanced by increased down force up front. I've dialed my wing back to the lowest attack angle and I still get a few hundred lbs of down force at 100 mph (and I get a higher velocity at the end of the straights because of the reduced drag). I measure the front and rear down force with shock sensors. I had to add the 'canards' to the front of my car to get any real down force up front while at WOT - and I had to lower the front ride height too (a larger rake).
To me, dreaming about how to design the perfect wing isn't worth the time or effort. I'd rather be looking at my data to see what impact a set up change had in my speed through the turns versus at the end of the straight and what it did to lap times. If I find I can't seem to get what I want with the wing I have, I'd simply consider going bigger or smaller based on what the data points out as a problem.
Get a big *** wing, big *** splitter, try to duct your oil cooler/ radiator openings out the top or the sides of the car, make the bottom of the car as smooth as possible and use the adjustment of the wing to balance out the car.
02-11-2010, 03:18 PM
#83
Race Car
Thread Starter
Join Date: Apr 2005
Location: With A Manual Transmission
Posts: 4,728
Likes: 0
Received 2 Likes
on
2 Posts
Where do you guys get these shock sensors and how do they read over time so you know what speed you were going when they were being compressed, or do you just get to a max speed and go by that compression?
02-11-2010, 03:56 PM
#84
Rennlist Member
Well,it all boils down to the original question, and as I posted, large or small wing will have a cross over point to where they would produce the same lift and drag at different AOA's. any other pont and there will be trade offs.
My GT3 cup wing is 55" and puts out 275lbs of downforce at 120mph at 8 degrees set, plus, the all important actual AOA, which is due to the roof line shift in air direction giving a total AOA of more like 15+ degrees. (which is near max for the airfoil based on its NACA #)
as far as the drag as concerned, i dont think 5hp will change your top speed much at the end of the straight, but the right amount of down force could give you an extra 1-2mph off the prior turn exit which would, and even allow for deeper braking into the next turn.
its all part of the tuning quest. Use the theory to understand the trade offs and use the car at the track to emperically test it. It think that is the fun part!
mk
My GT3 cup wing is 55" and puts out 275lbs of downforce at 120mph at 8 degrees set, plus, the all important actual AOA, which is due to the roof line shift in air direction giving a total AOA of more like 15+ degrees. (which is near max for the airfoil based on its NACA #)
as far as the drag as concerned, i dont think 5hp will change your top speed much at the end of the straight, but the right amount of down force could give you an extra 1-2mph off the prior turn exit which would, and even allow for deeper braking into the next turn.
its all part of the tuning quest. Use the theory to understand the trade offs and use the car at the track to emperically test it. It think that is the fun part!
mk
Not trying to spoil the fun, but my approach pretty much agrees with Rich...
When I needed a wing, I bought a big one, similar to what most other folk were running. With a 60" wing you can generate lots of down force by using a large attach angle. Too much rear down force and too much drag were easy to obtain. It's silly to generate a lot of rear down force if it is not balanced by increased down force up front. I've dialed my wing back to the lowest attack angle and I still get a few hundred lbs of down force at 100 mph (and I get a higher velocity at the end of the straights because of the reduced drag). I measure the front and rear down force with shock sensors. I had to add the 'canards' to the front of my car to get any real down force up front while at WOT - and I had to lower the front ride height too (a larger rake).
To me, dreaming about how to design the perfect wing isn't worth the time or effort. I'd rather be looking at my data to see what impact a set up change had in my speed through the turns versus at the end of the straight and what it did to lap times. If I find I can't seem to get what I want with the wing I have, I'd simply consider going bigger or smaller based on what the data points out as a problem.
When I needed a wing, I bought a big one, similar to what most other folk were running. With a 60" wing you can generate lots of down force by using a large attach angle. Too much rear down force and too much drag were easy to obtain. It's silly to generate a lot of rear down force if it is not balanced by increased down force up front. I've dialed my wing back to the lowest attack angle and I still get a few hundred lbs of down force at 100 mph (and I get a higher velocity at the end of the straights because of the reduced drag). I measure the front and rear down force with shock sensors. I had to add the 'canards' to the front of my car to get any real down force up front while at WOT - and I had to lower the front ride height too (a larger rake).
To me, dreaming about how to design the perfect wing isn't worth the time or effort. I'd rather be looking at my data to see what impact a set up change had in my speed through the turns versus at the end of the straight and what it did to lap times. If I find I can't seem to get what I want with the wing I have, I'd simply consider going bigger or smaller based on what the data points out as a problem.
02-11-2010, 04:02 PM
#85
They are part of a data acquisition system (usually Motec or similar). It's a linear potentiometer that you mount on the shock. With the data you will also have speed, so you can correlate speed to spring compression and figure out downforce. However, the shock position data is often very noisy, especially on very stiffly sprung cars so it is sometimes hard to get good measurements of downforce based on this data when taken at the track. If you can find a long, very smooth area to do straight line testing that is ideal. Abandoned runway or something like that, but that's not usually available.
02-11-2010, 04:17 PM
#86
Addict
Rennlist Member
Rennlist Member
Yep, a data system. In my case, MoTeC shock sensors to look at shock compression/rebound to calculate ride height and down force or lift. Then use of MoTeC i2Pro software to calculate various values and analyze the data.
The data are a bit noisy but you can see how the down force changes as you increase speed down the straights. It's a lot harder to look at it this way in the turns because of the changes in the car's attitude due to use of the accelerator (rear squats and front lifts when you slam on the throttle).
You can see differences in speed at the end of the straight and you can see the g's you get at maximum grip in the turns (and how the max g's change with speed) to help figure out what to change in set up to go faster.
You've got to remember that down force is directly related to the speed/airflow and you get no significant benefit in a slow speed turn (<60 mph) but a reasonable benefit in a 100 mph turn.
The data are a bit noisy but you can see how the down force changes as you increase speed down the straights. It's a lot harder to look at it this way in the turns because of the changes in the car's attitude due to use of the accelerator (rear squats and front lifts when you slam on the throttle).
You can see differences in speed at the end of the straight and you can see the g's you get at maximum grip in the turns (and how the max g's change with speed) to help figure out what to change in set up to go faster.
You've got to remember that down force is directly related to the speed/airflow and you get no significant benefit in a slow speed turn (<60 mph) but a reasonable benefit in a 100 mph turn.
02-11-2010, 04:20 PM
#88
Rennlist Member
And, obviously, you have to run the car with no wing over the exact same speed to see what the wing is really producing. what is nice about the simulation programs, you plug in the like NACA number or even rough estimation of shape and you can get most all of your answers there. you can then, compare lengths of an air foil based on what you want for downforce to find the optimum with for your use. I see a lot of overwinged cars that have handling issues, due to more downforce than they need and require for balance.
They are part of a data acquisition system (usually Motec or similar). It's a linear potentiometer that you mount on the shock. With the data you will also have speed, so you can correlate speed to spring compression and figure out downforce. However, the shock position data is often very noisy, especially on very stiffly sprung cars so it is sometimes hard to get good measurements of downforce based on this data when taken at the track. If you can find a long, very smooth area to do straight line testing that is ideal. Abandoned runway or something like that, but that's not usually available.
02-11-2010, 04:24 PM
#89
Lifetime Rennlist Member
Also you should have height sensors at each corner. You can do it with 2, but if there is any roll or sideways pitch or uneven downforce (side to side) you will have errors.
I have only done this on Motec, so I don't know which of the lower cost systems will actually let you do this.
02-11-2010, 04:29 PM
#90
Rennlist Member
Here's a pretty interesting article on the Viper ACR aero package which produces an amazing amount of downforce for a sports car. The sidebar at the bottom about the front end is good too. Note that the winglets are primarily down on the ACR wing also.
BTW Jack - I love the picture of your extended empirical testing - that's inspirational stuff!
http://www.compositesworld.com/artic...stability.aspx
BTW Jack - I love the picture of your extended empirical testing - that's inspirational stuff!
http://www.compositesworld.com/artic...stability.aspx