Splitter design function and effects. Experience, Design knowledge?
08-18-2009, 06:54 PM
#31
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Beyond that, be very careful of what you believe about aero. The single most significant aspect of how aero works (or doesn't) on a race car, is focused on the concept of laminar vs. turbulent flow. When I read explanations that never mention that, I pretty much discount what they have to say. The web site with the drawings is about 25% right and 75% barking up the wrong tree.
Here is an example. Most amateurs and many pros put helicopter tape on the leading edge of a wing to protect it. I did that for years. Until I met 2 F1 aerodynamicists in a class. In chatting, they told me that wings work by keeping laminar flow on the wing as long as possible (which I knew). What I didn't understand, and they told me is that the tape (from the back edge) creates a sharp break. This causes separation and turbulence earlier and that little, thin tape can cost 10% of the total downforce on a wing. That helps point out how little most of us really know about aero. It also points out how silly it is to try to measure pressures over a wing or other licked surface without F1 level technology.
08-18-2009, 06:57 PM
#32
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I read this discussion and want to point out that the air on the surface of a race track is almost always nasty from the cars that just passed through it.
If the air is already turbulent, all these calculations are a waste of paper. If you have a wind tunnel with good instrumentation, you can get data that applies to track conditions with nobody on the track.
I don't have my wind tunnel, I left it on the dresser this morning........
If the air is already turbulent, all these calculations are a waste of paper. If you have a wind tunnel with good instrumentation, you can get data that applies to track conditions with nobody on the track.
I don't have my wind tunnel, I left it on the dresser this morning........
08-18-2009, 07:04 PM
#33
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Thread Starter
Funny you should mention this. Actually, following a car at 80mph, i didnt get much of a change on net pressure to the splitter core area.
I read this discussion and want to point out that the air on the surface of a race track is almost always nasty from the cars that just passed through it.
If the air is already turbulent, all these calculations are a waste of paper. If you have a wind tunnel with good instrumentation, you can get data that applies to track conditions with nobody on the track.
I don't have my wind tunnel, I left it on the dresser this morning........
If the air is already turbulent, all these calculations are a waste of paper. If you have a wind tunnel with good instrumentation, you can get data that applies to track conditions with nobody on the track.
I don't have my wind tunnel, I left it on the dresser this morning........
08-18-2009, 07:11 PM
#34
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You are right, but you have to think in terms of pressure zones and differential pressuere. Yes, the 928 actualy is nice and round up front, but you are right, the downward part pushes the air down under the car. If the splitter is allowed to match the nose length, which is does now exactly, the air pressure builds in this area and slightly out in front of it as well, and then spills to the sides, up over the car and some under the car.
no car, except the daytona prototypes will have the shape you talk about. a wedge,meeting the ground,basically, but there is a trick to the game.
what you do, and could do with even the 928, is open the front of the car more below the nose and vent it ALL to the top of the hood. It would not spill under teh car or even go to the sides, because those areas are ambient pressure. ON TOP of the hood, is a vacuum area near .08psi at 120mph! So, if vented correcly, the air will go there and add to the downforce, much more than even a splitter can provide if designed correctly. Notice the astonMartin for example in the pics I provided.
no car, except the daytona prototypes will have the shape you talk about. a wedge,meeting the ground,basically, but there is a trick to the game.
what you do, and could do with even the 928, is open the front of the car more below the nose and vent it ALL to the top of the hood. It would not spill under teh car or even go to the sides, because those areas are ambient pressure. ON TOP of the hood, is a vacuum area near .08psi at 120mph! So, if vented correcly, the air will go there and add to the downforce, much more than even a splitter can provide if designed correctly. Notice the astonMartin for example in the pics I provided.I think you are over testing and over thinking a bit. One test is to take a level and hold it straight up and down at the nose of the car. How much splitter is in front of the nose? That is your effective splitter surface area. The splitter area under the nose will not force the air over the top of the car. The knife edge shape of the 928 makes air go over under and around the car. You want over. The splitter will increase the side spill and decrease the amount going under an = amount. You want the air to go over the car. If the rules allow you should reshape the nose into a chisel shape to coax the air over the car not under or around.
08-18-2009, 07:23 PM
#35
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yes flow is important, but we are testing actual pressure values.
If what you said is true, the differential pressure at some part of the wing would be less, and that is not true. Laminar flow is important, mostly for drag. you say the trailing edge of the tape can loose 10% drag? that is just not true. in fact, I can prove it too. I have downforce spring scale that shows the rear wing at 250lbs at 120mph at 7 degrees angle of attack. Ill put a thick painters tape all over the front of the wing and downforce will not go down much, if any. Did you know that most wings in the early days, didnt even have bottoms!! talk about tubulence! (bottom is the top of a race car wing) youcould open it up and make a HUGE bucket there and it would work fine! more drag, but still downforce! icing on an airplane causes problems as most of the surface of the rounded part of the wing needs to be very smooth. (or you guess it, drag will be produced) It acts like a spoiler.
you can even put little vertical bumps on the wing, in the critical area called vortex generators. it causes flow to separate and turbulence to be created. at the small cost of drag, the flow stays attached longer for more air flow over the control surfaces in near stall , at high or low speed, conditions.
Your point is well taken. laminar flow is important for efficiency of the wing. Lift for the amount of drag, for a given angle of attack. But, a strip of tape along the leading edge is not worth 10% of the total lift. I can easly prove and video tape that it is not.
If what you said is true, the differential pressure at some part of the wing would be less, and that is not true. Laminar flow is important, mostly for drag. you say the trailing edge of the tape can loose 10% drag? that is just not true. in fact, I can prove it too. I have downforce spring scale that shows the rear wing at 250lbs at 120mph at 7 degrees angle of attack. Ill put a thick painters tape all over the front of the wing and downforce will not go down much, if any. Did you know that most wings in the early days, didnt even have bottoms!! talk about tubulence! (bottom is the top of a race car wing) youcould open it up and make a HUGE bucket there and it would work fine! more drag, but still downforce! icing on an airplane causes problems as most of the surface of the rounded part of the wing needs to be very smooth. (or you guess it, drag will be produced) It acts like a spoiler.
you can even put little vertical bumps on the wing, in the critical area called vortex generators. it causes flow to separate and turbulence to be created. at the small cost of drag, the flow stays attached longer for more air flow over the control surfaces in near stall , at high or low speed, conditions.
Your point is well taken. laminar flow is important for efficiency of the wing. Lift for the amount of drag, for a given angle of attack. But, a strip of tape along the leading edge is not worth 10% of the total lift. I can easly prove and video tape that it is not.
I would say that ~100 lbs at ~120mph is typical.
Beyond that, be very careful of what you believe about aero. The single most significant aspect of how aero works (or doesn't) on a race car, is focused on the concept of laminar vs. turbulent flow. When I read explanations that never mention that, I pretty much discount what they have to say. The web site with the drawings is about 25% right and 75% barking up the wrong tree.
Here is an example. Most amateurs and many pros put helicopter tape on the leading edge of a wing to protect it. I did that for years. Until I met 2 F1 aerodynamicists in a class. In chatting, they told me that wings work by keeping laminar flow on the wing as long as possible (which I knew). What I didn't understand, and they told me is that the tape (from the back edge) creates a sharp break. This causes separation and turbulence earlier and that little, thin tape can cost 10% of the total downforce on a wing. That helps point out how little most of us really know about aero. It also points out how silly it is to try to measure pressures over a wing or other licked surface without F1 level technology.
Beyond that, be very careful of what you believe about aero. The single most significant aspect of how aero works (or doesn't) on a race car, is focused on the concept of laminar vs. turbulent flow. When I read explanations that never mention that, I pretty much discount what they have to say. The web site with the drawings is about 25% right and 75% barking up the wrong tree.
Here is an example. Most amateurs and many pros put helicopter tape on the leading edge of a wing to protect it. I did that for years. Until I met 2 F1 aerodynamicists in a class. In chatting, they told me that wings work by keeping laminar flow on the wing as long as possible (which I knew). What I didn't understand, and they told me is that the tape (from the back edge) creates a sharp break. This causes separation and turbulence earlier and that little, thin tape can cost 10% of the total downforce on a wing. That helps point out how little most of us really know about aero. It also points out how silly it is to try to measure pressures over a wing or other licked surface without F1 level technology.
08-18-2009, 07:27 PM
#36
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Thread Starter
very few of us ever get to use a wind tunnel, but phil mcClure did with his WCGT vet. they started out with lift in the front and 175lbs of downforce in the rear, and ended up with 100lbs of downforce in the front and 250lbs of downforce in the rear. I measured .32psi pressure on my 300sq-in splitter surface. that translates to about 100lbs of downforce on the surface, but much more than that when considering the real effects of the splitter re-routing the air flow. how much, only the folks at the wind tunnel know for sure.
I can measure downforce in the rear, by the rear wing. that is much more straight forward. 250lbs at 7 degrees at 120mph. cup car GT3 wing.
mk
I can measure downforce in the rear, by the rear wing. that is much more straight forward. 250lbs at 7 degrees at 120mph. cup car GT3 wing.
mk
08-18-2009, 07:45 PM
#37
Lifetime Rennlist Member
yes flow is important, but we are testing actual pressure values.
If what you said is true, the differential pressure at some part of the wing would be less, and that is not true. Laminar flow is important, mostly for drag. you say the trailing edge of the tape can loose 10% drag? that is just not true. in fact, I can prove it too. I have downforce spring scale that shows the rear wing at 250lbs at 120mph at 7 degrees angle of attack. Ill put a thick painters tape all over the front of the wing and downforce will not go down much, if any. Did you know that most wings in the early days, didnt even have bottoms!! talk about tubulence! (bottom is the top of a race car wing) youcould open it up and make a HUGE bucket there and it would work fine! more drag, but still downforce! icing on an airplane causes problems as most of the surface of the rounded part of the wing needs to be very smooth. (or you guess it, drag will be produced) It acts like a spoiler.
you can even put little vertical bumps on the wing, in the critical area called vortex generators. it causes flow to separate and turbulence to be created. at the small cost of drag, the flow stays attached longer for more air flow over the control surfaces in near stall , at high or low speed, conditions.
Your point is well taken. laminar flow is important for efficiency of the wing. Lift for the amount of drag, for a given angle of attack. But, a strip of tape along the leading edge is not worth 10% of the total lift. I can easly prove and video tape that it is not.
If what you said is true, the differential pressure at some part of the wing would be less, and that is not true. Laminar flow is important, mostly for drag. you say the trailing edge of the tape can loose 10% drag? that is just not true. in fact, I can prove it too. I have downforce spring scale that shows the rear wing at 250lbs at 120mph at 7 degrees angle of attack. Ill put a thick painters tape all over the front of the wing and downforce will not go down much, if any. Did you know that most wings in the early days, didnt even have bottoms!! talk about tubulence! (bottom is the top of a race car wing) youcould open it up and make a HUGE bucket there and it would work fine! more drag, but still downforce! icing on an airplane causes problems as most of the surface of the rounded part of the wing needs to be very smooth. (or you guess it, drag will be produced) It acts like a spoiler.
you can even put little vertical bumps on the wing, in the critical area called vortex generators. it causes flow to separate and turbulence to be created. at the small cost of drag, the flow stays attached longer for more air flow over the control surfaces in near stall , at high or low speed, conditions.
Your point is well taken. laminar flow is important for efficiency of the wing. Lift for the amount of drag, for a given angle of attack. But, a strip of tape along the leading edge is not worth 10% of the total lift. I can easly prove and video tape that it is not.
So how did you do this measurement? Was the wing in clean air or was it mounted on your car? You basically call BS on the tape issue but ignore the likelihood that your wing is already in turbulent air, or that the wind design is so bad that it never has laminar flow.
My comments were really for those in this thread who have an open mind and are interested in learning something - you don't fall into that group - as you have shown time and time again.
08-18-2009, 07:58 PM
#38
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Thread Starter
Im surprised of your comments. Now, you talk to a F1 engineer and it sways you to change your wing techniques, but my wing tests are not valid? Hmm, did you say you had an F1 car or a sports car like mine. You were "chatting" with an engineer. I dont know who he was, so I cant comment, but what I can comment on is maybe you didnt understand exactly what he was saying. Could it be that possibly that 10% of lift from a piece of tape was at 220mph and at a specific angle of attack and for a certain air foil shape, placed in a certain place in the air stream?
Can we discuss? Im certainly into having this thread provide a learning experience for everyone. Personally, i do want to learn more.
My wing was roof line hight. not perfectly in clean air
the wing is GT3, which is very close to a NACA numbered wing in my aero books.
I did the testing with 0-8 degrees and the downdraft coming off the car is near 7-9 degrees.
Now, the wing cant be that bad if it is putting down the force readings at the angle of attack values we know or can estimate. I also get pressure readings from top and bottom of the wing.
Could there be a chance that you didnt fully understand what the F1 engineer was saying? much of airplane design is theoretical, thats why wind tunnels and imperical testing is so important. a lot of factors that might not be counted, effect outcome.
So. You heard this and took off the tape because you thought you were loosing 10% of your downforce? was your wing in clean air? was it an efficient wing design? do you know the NACA number it was modeled after?
How about you, do you want to learn something new possibly. Just saying!
Let me know the test you want me to do with the wing and Ill test it. tape, gurney lips, etc. I can test it all.
PLEASE also answer one question. what do you mean that only 25% is correct on the drawing or website and 75% is barking up the wrong tree.
mk
PS, Here is a windtunnel derived chart of the pressure areas of my car before any mods.
Can we discuss? Im certainly into having this thread provide a learning experience for everyone. Personally, i do want to learn more.
My wing was roof line hight. not perfectly in clean air
the wing is GT3, which is very close to a NACA numbered wing in my aero books.
I did the testing with 0-8 degrees and the downdraft coming off the car is near 7-9 degrees.
Now, the wing cant be that bad if it is putting down the force readings at the angle of attack values we know or can estimate. I also get pressure readings from top and bottom of the wing.
Could there be a chance that you didnt fully understand what the F1 engineer was saying? much of airplane design is theoretical, thats why wind tunnels and imperical testing is so important. a lot of factors that might not be counted, effect outcome.
So. You heard this and took off the tape because you thought you were loosing 10% of your downforce? was your wing in clean air? was it an efficient wing design? do you know the NACA number it was modeled after?
How about you, do you want to learn something new possibly. Just saying!
Let me know the test you want me to do with the wing and Ill test it. tape, gurney lips, etc. I can test it all.
PLEASE also answer one question. what do you mean that only 25% is correct on the drawing or website and 75% is barking up the wrong tree.
mk
PS, Here is a windtunnel derived chart of the pressure areas of my car before any mods.
Man, this is a really tough choice. Should I beleive 2 F1 aerodynamicists or Kibort? I hope you don't miss that call from Ferrari to take over their aero program.
So how did you do this measurement? Was the wing in clean air or was it mounted on your car? You basically call BS on the tape issue but ignore the likelihood that your wing is already in turbulent air, or that the wind design is so bad that it never has laminar flow.
My comments were really for those in this thread who have an open mind and are interested in learning something - you don't fall into that group - as you have shown time and time again.
So how did you do this measurement? Was the wing in clean air or was it mounted on your car? You basically call BS on the tape issue but ignore the likelihood that your wing is already in turbulent air, or that the wind design is so bad that it never has laminar flow.
My comments were really for those in this thread who have an open mind and are interested in learning something - you don't fall into that group - as you have shown time and time again.
08-18-2009, 08:10 PM
#39
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08-18-2009, 08:22 PM
#40
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08-18-2009, 08:25 PM
#41
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Sunday, check out this link about aero. I had a great book from school that had a generic air foil chart for a GT3cup type wing and all the data you would want for it. I cant find it, but this link has some great aero info.
I think i posted it on another aero discussion a few years ago.
Here is the chart of airfoils to look at the characteristics your wing might have.
a cup car wing is very simular to a NACA 6215
http://history.nasa.gov/SP-4103/app-f.htm
I think i posted it on another aero discussion a few years ago.
Here is the chart of airfoils to look at the characteristics your wing might have.
a cup car wing is very simular to a NACA 6215
http://history.nasa.gov/SP-4103/app-f.htm
08-18-2009, 08:38 PM
#42
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08-18-2009, 09:05 PM
#43
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I would say that ~100 lbs at ~120mph is typical.
Beyond that, be very careful of what you believe about aero. The single most significant aspect of how aero works (or doesn't) on a race car, is focused on the concept of laminar vs. turbulent flow. When I read explanations that never mention that, I pretty much discount what they have to say. The web site with the drawings is about 25% right and 75% barking up the wrong tree.
Here is an example. Most amateurs and many pros put helicopter tape on the leading edge of a wing to protect it. I did that for years. Until I met 2 F1 aerodynamicists in a class. In chatting, they told me that wings work by keeping laminar flow on the wing as long as possible (which I knew). What I didn't understand, and they told me is that the tape (from the back edge) creates a sharp break. This causes separation and turbulence earlier and that little, thin tape can cost 10% of the total downforce on a wing. That helps point out how little most of us really know about aero. It also points out how silly it is to try to measure pressures over a wing or other licked surface without F1 level technology.
Beyond that, be very careful of what you believe about aero. The single most significant aspect of how aero works (or doesn't) on a race car, is focused on the concept of laminar vs. turbulent flow. When I read explanations that never mention that, I pretty much discount what they have to say. The web site with the drawings is about 25% right and 75% barking up the wrong tree.
Here is an example. Most amateurs and many pros put helicopter tape on the leading edge of a wing to protect it. I did that for years. Until I met 2 F1 aerodynamicists in a class. In chatting, they told me that wings work by keeping laminar flow on the wing as long as possible (which I knew). What I didn't understand, and they told me is that the tape (from the back edge) creates a sharp break. This causes separation and turbulence earlier and that little, thin tape can cost 10% of the total downforce on a wing. That helps point out how little most of us really know about aero. It also points out how silly it is to try to measure pressures over a wing or other licked surface without F1 level technology.
08-18-2009, 09:10 PM
#45
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