Most Effective Wing?
03-20-2011, 09:50 AM
#151
Addict
Rennlist Member
Rennlist Member
Acura MDX's and plenty of GM cars (Corvette, Cadillac) have height sensors too - just look for cars with MR suspensions. 
I still need to chase some down and implement on my car...
I still need to chase some down and implement on my car...
03-21-2011, 01:15 AM
#152
Rennlist Member
Thanks Rob. Good info.
Yep , i get the L/D ratios, but my question was about some of the outrageous wings that make huge amounts of downforce but dont seem to have the L/D of wings that might make a little less. So i guess if more is better, than the answer is simple. Also, if you notice, the pics have the wings extended rearward, which will throw off the downforce numbers if measured at the tires due to the moment lever.
I think you are right about making as much downforce as possible. my goal is to fully utiize my cup car wing, with only a few options left for front end DF to match higher rear DF values. slightly larger front splitter, lowering the splitter and of course dive planes. dive planes are probably equal drag to downforce, while most wings are generally in the 10:1 range. the drag itself is not that much for a lot of downforce as I have translated back to reflect its effect on engine Hp or torque, so it might make sens to figure it out, like the time trial guys do, to take advantage of it. Until i find a way to fix the front lack of equal downforce, im kind of stuck. too much rear downforce makes for a real crappy driving car with a ton of push. Im stuck at near 50% of the max angle for my cup car wing, and I bet for the same reasons that the supercup cars in europe dont use much angle on their cars either. even the '11 cup cars had very litle angle. I found that interesting.
Yep , i get the L/D ratios, but my question was about some of the outrageous wings that make huge amounts of downforce but dont seem to have the L/D of wings that might make a little less. So i guess if more is better, than the answer is simple. Also, if you notice, the pics have the wings extended rearward, which will throw off the downforce numbers if measured at the tires due to the moment lever.
I think you are right about making as much downforce as possible. my goal is to fully utiize my cup car wing, with only a few options left for front end DF to match higher rear DF values. slightly larger front splitter, lowering the splitter and of course dive planes. dive planes are probably equal drag to downforce, while most wings are generally in the 10:1 range. the drag itself is not that much for a lot of downforce as I have translated back to reflect its effect on engine Hp or torque, so it might make sens to figure it out, like the time trial guys do, to take advantage of it. Until i find a way to fix the front lack of equal downforce, im kind of stuck. too much rear downforce makes for a real crappy driving car with a ton of push. Im stuck at near 50% of the max angle for my cup car wing, and I bet for the same reasons that the supercup cars in europe dont use much angle on their cars either. even the '11 cup cars had very litle angle. I found that interesting.
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
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
03-21-2011, 12:36 PM
#154
Race Car
It's pretty common to find the Lincolns and Range Rover systems pulled off to be replaced by a more conventional suspension. I got mine for $4 each on Ebay. They're linear-type potentiometers. Some ride height sensors use a rotating pot. I suppose either would work. I simply zip tied mine to convenient points on my suspension. I was able to calibrate them by setting bags of sand on the front or rear of the car.
03-21-2011, 12:42 PM
#155
Addict
Rennlist Member
Rennlist Member
Thanks for the info, Jack - sound even better than the rotary pots!
03-21-2011, 12:58 PM
#156
Three Wheelin'
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.
Actually a hood vent can be very efficient at cooling the car, but apparently is not so good for downforce. Putting hot air over the top of the car means that your rear wing will get warmer, lower-density air. This is bad for downforce.
You could also argue that this might be offset by the fact that with a hood vent you might get some downforce by virtue of the upward flow of the air as it exits the vent. The shortcoming here is that the flow through the radiator, snaking around the engine, etc, slows down the air enough that for the purpose of adding downforce, it winds up essentially useless. Good enough to cool things, though, which is the vent's primary purpose.
the "other" Scott
03-21-2011, 01:25 PM
#157
Drifting
The hood vent also keeps some of the air from going under the car and creating lift. I doubt that the increased temp of the air makes too much of a difference at the rear wing, we are talking about pretty low temperatures and it mixes with plenty of ambient air before reaching the wing.
Every ALMS GT car running at Sebring this weekend was venting air through the front hood (Porsche, Ferrari, BMW, Corvette, Ford, etc) regardless of front/mid/rear engine location so the positives must outweigh the negatives when done right..
Every ALMS GT car running at Sebring this weekend was venting air through the front hood (Porsche, Ferrari, BMW, Corvette, Ford, etc) regardless of front/mid/rear engine location so the positives must outweigh the negatives when done right..
03-21-2011, 01:43 PM
#158
Lifetime Rennlist Member
Trade offs. You don't really want airflow over the hood and top of car as that creates lift. But high pressure under the floor or hood is even worse. So the current designs seem to favor venting out the top. IMO, the hot air is not the big a deal in terms of wing efficiency.
But if you look at current prototypes, they mostly have moved to a pontoon style front fender arrangement to vent air out the side but production based cars don't have that design ability.
But if you look at current prototypes, they mostly have moved to a pontoon style front fender arrangement to vent air out the side but production based cars don't have that design ability.
03-21-2011, 02:11 PM
#159
Three Wheelin'
It was actually Joseph Katz who wrote about warmer going over the top of the car is not ideal. As SundayDriver notes above, there may be something to it since prototypes, which have more design freedom re: venting, usually do it out the side.
Scott
Scott
03-21-2011, 02:46 PM
#160
Rennlist Member
No, that is not correct at all.
you DO want to add to the flow, as it is the differential pressure from the bottom to the top of the car that determines the downforce.
air flow from the lower front of the car , that would normally be going under or around the car, will actuallly RAISE the pressure on top of the car if the air is fed there.
you DO want to add to the flow, as it is the differential pressure from the bottom to the top of the car that determines the downforce.
air flow from the lower front of the car , that would normally be going under or around the car, will actuallly RAISE the pressure on top of the car if the air is fed there.
Trade offs. You don't really want airflow over the hood and top of car as that creates lift. But high pressure under the floor or hood is even worse. So the current designs seem to favor venting out the top. IMO, the hot air is not the big a deal in terms of wing efficiency.
But if you look at current prototypes, they mostly have moved to a pontoon style front fender arrangement to vent air out the side but production based cars don't have that design ability.
But if you look at current prototypes, they mostly have moved to a pontoon style front fender arrangement to vent air out the side but production based cars don't have that design ability.
03-21-2011, 04:52 PM
#161
Three Wheelin'
Mark -- when you say that all the ALMS cars vent over the top now, are you including prototypes? The Peugot as an example has large openings behind the front wheel pods. I assumed that this was for exhausting air from the radiators and front diffuser. I don't seem much coming out the top of the car aside from the fender louvers.
The Joseph Katz source I quoted in my earlier post is the book he wrote, Race Car Aerodynamics.
Of course I have been wrong before ...
Scott
The Joseph Katz source I quoted in my earlier post is the book he wrote, Race Car Aerodynamics.
Of course I have been wrong before ...
Scott
03-22-2011, 09:51 AM
#162
7th Gear
Join Date: Mar 2011
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
Trade offs. You don't really want airflow over the hood and top of car as that creates lift. But high pressure under the floor or hood is even worse. So the current designs seem to favor venting out the top. IMO, the hot air is not the big a deal in terms of wing efficiency.
Have a look at how much the hood moves on this time attack car as it runs down the main straight. Bear in mind that this car does have a hood vent ...
[youtube]D1fyG4yGA9E[/youtube]
- Rob
03-22-2011, 10:28 AM
#163
Lifetime Rennlist Member
Clearly venting the high pressure is better and results in a net reduction in lift. This has been proven over and over with fender vents and the fact that it is being widely used by production car teams, with wind tunnel access, tells us that is true for hood vents too.
One of my points is that the best is if it can be vented out the side - then you do not increase lift on top of the hood. But production car rules limit what you can do with the body, so it appears this is really not possible to properly vent to the sides.
03-22-2011, 11:08 AM
#164
Rennlist Member
again, that is not exactly true. venting through the hood tends to raise the already very low pressure. its a common misconception that more air over the top of the car is a bad thing. its a good thing because that air is normally going under the car. if you can add it to go over the car, its a good thing too, because it also gives more air to the rear wing in the back of the car.
remember is differentital pressure from the bottom to the top of the car we care about. if you vent to the side, you do nothing to change the lower pressure on top of the car, and that is creating lift.
remember is differentital pressure from the bottom to the top of the car we care about. if you vent to the side, you do nothing to change the lower pressure on top of the car, and that is creating lift.
Exactly! There is high pressure under the hood, creating lift. The option is to vent the high pressure which reduces the lift on the underside of the hood, but the compromise is that it lowers the pressure on top of the hood with increased flow and creates lift. Which is better?
Clearly venting the high pressure is better and results in a net reduction in lift. This has been proven over and over with fender vents and the fact that it is being widely used by production car teams, with wind tunnel access, tells us that is true for hood vents too.
One of my points is that the best is if it can be vented out the side - then you do not increase lift on top of the hood. But production car rules limit what you can do with the body, so it appears this is really not possible to properly vent to the sides.
Clearly venting the high pressure is better and results in a net reduction in lift. This has been proven over and over with fender vents and the fact that it is being widely used by production car teams, with wind tunnel access, tells us that is true for hood vents too.
One of my points is that the best is if it can be vented out the side - then you do not increase lift on top of the hood. But production car rules limit what you can do with the body, so it appears this is really not possible to properly vent to the sides.
03-22-2011, 11:14 AM
#165
Rennlist Member
The wheel openings vent air rearward as well. remember,we also have to look at drag that is created from air moving over the car too. but the main reason the wheel pods are rear ward, is because in that area, its in a spot where venting straight up will be venting to a high pressure zone. you have to realize that the low pressure zone is in a narrow area just passed the front bumper to about mid hood on most cars. after mid hood , the pressure rises significantly. almost as much as the nose pressure, and then it goes to the low pressure again as the air travels over the windshield and roof line. Its all a balacing act of flow and pressure control.
on my car for example, if i vented upward, at the rear of the wheel well, air would be forced in and wouldnt relieve its pressure as great as the sides would.
this is for drag reduction,not downforce obviously.
as far as Katz. I havent seen that study, so I cant comment on what he is talking about, but more air, even warm would be better and more effective for downforce and rear wing effect if it came originally from the under the car and through the hood. its adding to the mass air flow going over the car, AND, its releaving the negative pressure (think kind of vacuum) of the air over the car as well creating downforce. It could have been mentioned in a different context I would imagine. Plus, a lot of the concepts of downforce and air flow in regards to race cars is still a little black art, unless you are testing everything with sensors everywhere, or have a wind tunnel or incredible computer simulators.
mk
on my car for example, if i vented upward, at the rear of the wheel well, air would be forced in and wouldnt relieve its pressure as great as the sides would.
this is for drag reduction,not downforce obviously.
as far as Katz. I havent seen that study, so I cant comment on what he is talking about, but more air, even warm would be better and more effective for downforce and rear wing effect if it came originally from the under the car and through the hood. its adding to the mass air flow going over the car, AND, its releaving the negative pressure (think kind of vacuum) of the air over the car as well creating downforce. It could have been mentioned in a different context I would imagine. Plus, a lot of the concepts of downforce and air flow in regards to race cars is still a little black art, unless you are testing everything with sensors everywhere, or have a wind tunnel or incredible computer simulators.
mk
Mark -- when you say that all the ALMS cars vent over the top now, are you including prototypes? The Peugot as an example has large openings behind the front wheel pods. I assumed that this was for exhausting air from the radiators and front diffuser. I don't seem much coming out the top of the car aside from the fender louvers.
The Joseph Katz source I quoted in my earlier post is the book he wrote, Race Car Aerodynamics.
Of course I have been wrong before ...
Scott
The Joseph Katz source I quoted in my earlier post is the book he wrote, Race Car Aerodynamics.
Of course I have been wrong before ...
Scott
Last edited by mark kibort; 03-22-2011 at 02:12 PM.