Splitter design function and effects. Experience, Design knowledge?
08-18-2009, 12:08 AM
#17
Administrator - "Tyson"
Lifetime Rennlist
Member
Lifetime Rennlist
Member
08-18-2009, 12:19 AM
#18
Drifting
Join Date: Jul 2006
Location: ..."RECALCULATING"
Posts: 3,496
Likes: 0
Received 0 Likes
on
0 Posts
I'm not sure that's really the way a splitter "works". Splitters do act as a wing, by creating a low pressure area underneath and a high pressure area on top. Some good basic info here:
http://www.e30m3project.com/e30m3per...r/splitter.htm
http://www.e30m3project.com/e30m3per...r/splitter.htm
I tend to use the same analogy for splitters but I still believe it is an effect that is created for the nose of the car as a unit. By pushing more air upwards the nose of the car is pushed downwards. I still don't believe all that force is focused primarily on the splitter as much as it is with a rear wing. It changes the aerodynamics of the nose of the car as a whole. Sure the airfoil itself imparts a downward force to the car were it is attached, but I would wager it is not as much as people think.
08-18-2009, 12:29 AM
#19
Drifting
08-18-2009, 01:54 AM
#20
Rennlist Member
Thread Starter
I agree again.
Yes, there is that debate in the aero camps, but they in essesnce are both saying the same thing. its easier to conceptualize the wing or car imparting a negative momentium to create lift or downforce, but they get themselves in trouble when you look at a car and find out that the slanted nose and rounded top actually create negative downforce, but it would apear that the air is "hitting" the hood and windshield and pushing on the car. Thats when Bernoulli comes in . the car is just like a wing. flat bottom and rounded (for the most part ) top, causing air moving over and under it, in order to meet at the rear, have different speeds. the faster speeds, create lower pressure.
under the car is ambient. very little can be done about this. (we can talk about ground effects and defusers later). no mater what you do, even the wedgy car will get lift , just see the ALMS GT1 that flipped at 170mph. :
with airdams, you are limiting the air that gets under the car, by routing it to the sides of the car and/or over the top. The concept is the even if you have more air moving over the top of the car at the same speed, the pressure differential will be different.
Lets cut to the results of the pressure tests.
at 120mph, the under splitter pressure was ambient just after the end of the splitter area. in the middle of the splitter bottom, the pressure was slightly low. .04psi
at 120mph, the pressure at the nose, splitter, in front of the radiator, and base of the windshield is .28psi. at 130 it went up to near .32psi.
Just in front of the hood vent, the vacuum was around .08psi at 120mph.
I also put a probe under the mid section of the car. still ambient pressure.
sure, the differential pressure on the splitter at .3psi at 130mph, and around 300sq-inches, you can see the downforce on the splitter itself is about 100lbs. But, what is the effect of the air that is vented to the hood and routed to the sides of the car. Im sure that might be equal or greater than the pressure on the structure itself. again, its not a wing, its a splitter. The wing in the rear, puts down more than 275lbs of downforce (I have the pressure differential readings somewhere, but not handly expected for that known quantity)
So, the last factor, is the effect of ground effect on the under car air flow, and exit air out the back of the car. this is the part I have the hardest part understanding. you would think that a car wtih a rounded nose like a 928, that the air would spill down under the car, increasing the velocity, due to the venturi effect and would have a lower pressure. with a splitter, this air does not go under the car (air that rolls downward off the nose mid point). does the downforce go up becaue that air is better routed to the sides with the under car air flow, with less mass flow and speed at ambient pressure? Then, if you take that air and route it to the hood vent, you neutralize the over car air mass flow. certainly raising its pressure and increasings its mass flow over the car.
Think differnetial pressure and air mass flow speed.
Couple all that with , ground effect, venturi tunnels, and defusers and you get a pretty complicated model.
The BMW splitter link has some issues. the drawings, though a little comical, are pretty correct.
Yes, there is that debate in the aero camps, but they in essesnce are both saying the same thing. its easier to conceptualize the wing or car imparting a negative momentium to create lift or downforce, but they get themselves in trouble when you look at a car and find out that the slanted nose and rounded top actually create negative downforce, but it would apear that the air is "hitting" the hood and windshield and pushing on the car. Thats when Bernoulli comes in . the car is just like a wing. flat bottom and rounded (for the most part ) top, causing air moving over and under it, in order to meet at the rear, have different speeds. the faster speeds, create lower pressure.
under the car is ambient. very little can be done about this. (we can talk about ground effects and defusers later). no mater what you do, even the wedgy car will get lift , just see the ALMS GT1 that flipped at 170mph. :
with airdams, you are limiting the air that gets under the car, by routing it to the sides of the car and/or over the top. The concept is the even if you have more air moving over the top of the car at the same speed, the pressure differential will be different.
Lets cut to the results of the pressure tests.
at 120mph, the under splitter pressure was ambient just after the end of the splitter area. in the middle of the splitter bottom, the pressure was slightly low. .04psi
at 120mph, the pressure at the nose, splitter, in front of the radiator, and base of the windshield is .28psi. at 130 it went up to near .32psi.
Just in front of the hood vent, the vacuum was around .08psi at 120mph.
I also put a probe under the mid section of the car. still ambient pressure.
sure, the differential pressure on the splitter at .3psi at 130mph, and around 300sq-inches, you can see the downforce on the splitter itself is about 100lbs. But, what is the effect of the air that is vented to the hood and routed to the sides of the car. Im sure that might be equal or greater than the pressure on the structure itself. again, its not a wing, its a splitter. The wing in the rear, puts down more than 275lbs of downforce (I have the pressure differential readings somewhere, but not handly expected for that known quantity)
So, the last factor, is the effect of ground effect on the under car air flow, and exit air out the back of the car. this is the part I have the hardest part understanding. you would think that a car wtih a rounded nose like a 928, that the air would spill down under the car, increasing the velocity, due to the venturi effect and would have a lower pressure. with a splitter, this air does not go under the car (air that rolls downward off the nose mid point). does the downforce go up becaue that air is better routed to the sides with the under car air flow, with less mass flow and speed at ambient pressure? Then, if you take that air and route it to the hood vent, you neutralize the over car air mass flow. certainly raising its pressure and increasings its mass flow over the car.
Think differnetial pressure and air mass flow speed.
Couple all that with , ground effect, venturi tunnels, and defusers and you get a pretty complicated model.
The BMW splitter link has some issues. the drawings, though a little comical, are pretty correct.
I think we are actually saying the same thing...I just over simplified. There is a great debate about "airfoils" and high and low pressure above and below and thus lift is created when in fact the lift is a function of the movement of the airmass downwards (on an aircraft wing). I tend to like Newton more than Bernoulli on such things.
I tend to use the same analogy for splitters but I still believe it is an effect that is created for the nose of the car as a unit. By pushing more air upwards the nose of the car is pushed downwards. I still don't believe all that force is focused primarily on the splitter as much as it is with a rear wing. It changes the aerodynamics of the nose of the car as a whole. Sure the airfoil itself imparts a downward force to the car were it is attached, but I would wager it is not as much as people think.
I tend to use the same analogy for splitters but I still believe it is an effect that is created for the nose of the car as a unit. By pushing more air upwards the nose of the car is pushed downwards. I still don't believe all that force is focused primarily on the splitter as much as it is with a rear wing. It changes the aerodynamics of the nose of the car as a whole. Sure the airfoil itself imparts a downward force to the car were it is attached, but I would wager it is not as much as people think.
08-18-2009, 02:05 AM
#21
I didn't stay at a holiday inn express last night - but I do have a couple of engineering degrees and do CFD everyday...
Bernoulli's equation is derived by integrating Euler's equation along a streamline. Euler's equation is the conservation of momentum neglecting fluid viscosity. Euler's equations also tell us the relationship between streamline curvature and pressure - a point most often missed and waaay over simplified when looking only at bernoulli equation. Euler-N equation says that the pressure increases in the direction of streamline curvature. This explains the low pressure over the greenhouse of a car and the high pressure in front of the windshield. At the windshield area, the streamlines are curving up with the radius of curvature pointing in the direction of the windshield. Pressure is increasing in this direction. Since there is atmospheric pressure far away from the car - there is high pressure at the base of the windshield. The opposite is true as the flow goes over the roof and down the rear window. Radius of curvature points away from the car....
Now - about the Mercedes GT1 flips. That is a direct result of ground effect. An airfoil operating in ground effect is extremely sensitive to angle of attack. Ground effect works for both lift and downforce producting wings. I am probably already getting too technical - but basically ground effect makes the flow much more 2 dimensional which greatly increases aerodynamic efficiency. As the GT1 cars crested the hill and the "angle of attack" of the car turned from negative to positive and you go from a highly efficient downforce producing body to a highly efficient lift producing body.
Also, be careful with pressure readings. Getting good surface pressure measurements in the kind of environment we are talking about is NOT trivial....The data, nonetheless is interesting.
AND PLEASE I do not mean to start an argument but: The notion that the 2 air particles have to meet at the trailing edge is RIDICULOUS and completely wrong. Yes, you will find this in "textbooks" and on the internet. But it is utterly not true. I have seen the experiments with dye traces. The fact of the matter is that on a lifting wing (upper surface = low pressure = higher speed) the particles on the upper surface will frequently reach the trailing edge first, even though they have a longer distance to travel.
Bernoulli's equation is derived by integrating Euler's equation along a streamline. Euler's equation is the conservation of momentum neglecting fluid viscosity. Euler's equations also tell us the relationship between streamline curvature and pressure - a point most often missed and waaay over simplified when looking only at bernoulli equation. Euler-N equation says that the pressure increases in the direction of streamline curvature. This explains the low pressure over the greenhouse of a car and the high pressure in front of the windshield. At the windshield area, the streamlines are curving up with the radius of curvature pointing in the direction of the windshield. Pressure is increasing in this direction. Since there is atmospheric pressure far away from the car - there is high pressure at the base of the windshield. The opposite is true as the flow goes over the roof and down the rear window. Radius of curvature points away from the car....
Now - about the Mercedes GT1 flips. That is a direct result of ground effect. An airfoil operating in ground effect is extremely sensitive to angle of attack. Ground effect works for both lift and downforce producting wings. I am probably already getting too technical - but basically ground effect makes the flow much more 2 dimensional which greatly increases aerodynamic efficiency. As the GT1 cars crested the hill and the "angle of attack" of the car turned from negative to positive and you go from a highly efficient downforce producing body to a highly efficient lift producing body.
Also, be careful with pressure readings. Getting good surface pressure measurements in the kind of environment we are talking about is NOT trivial....The data, nonetheless is interesting.
AND PLEASE I do not mean to start an argument but: The notion that the 2 air particles have to meet at the trailing edge is RIDICULOUS and completely wrong. Yes, you will find this in "textbooks" and on the internet. But it is utterly not true. I have seen the experiments with dye traces. The fact of the matter is that on a lifting wing (upper surface = low pressure = higher speed) the particles on the upper surface will frequently reach the trailing edge first, even though they have a longer distance to travel.
08-18-2009, 06:39 AM
#22
Rennlist Member
yes, the highest pressure on the car will be right at the nose. try and guess what I measured as far as pressure in the nose area,
yes, the pressure builds in all directions and moves to differnential pressure. If there is a nose vent, it will vent to the engine bay, and then under the car if that is its next lower pressure. However, if you have hood vents and ducts, the pressure OVER the car as bernoulli shows, is the lowest pressure in the flow. mid hood and the roof. if you have a hood vent at the mid hood area, as you can see from the pics of the daytona or GT race cars, that air goes out the hood and not under the car, or even to the sides of the car. (ideal) the pressure on the splitter is a side benefit, as the air it now routes over or to the sides creates the most change in pressure over the car. the air that goes under the car from the nose is mayb 3-4 ", the air that goes over the car goes 1 or 2 feet. that both maybe below ambient, but the air over the car is FAR under ambient. I have the data to support it too.
Now, ground effects are also something to look at. I think the entire concept there is to channel the air so that it speeds up under the car, with tunnels and then opens out into the defuser where the pressure suddlely raises behind the car for lower drag and greater downforce in the rear. facinating concepts for sure. Im still not confortable with the ground effects and flow under the car. I believe that without the duct work or flat pannels, you end up with a lot of drag and some stagnation points to raise pressure slightly, but not by much. mostly drag I would imagine.
The proof in downforce that the splitter actually contributes is in the think aluminum I used. its 1/16" aluminum sheet with rivets. Maybe there is 100lbs of downforce due to the differential pressure. (on top vs under the splitter)
yes, the pressure builds in all directions and moves to differnential pressure. If there is a nose vent, it will vent to the engine bay, and then under the car if that is its next lower pressure. However, if you have hood vents and ducts, the pressure OVER the car as bernoulli shows, is the lowest pressure in the flow. mid hood and the roof. if you have a hood vent at the mid hood area, as you can see from the pics of the daytona or GT race cars, that air goes out the hood and not under the car, or even to the sides of the car. (ideal) the pressure on the splitter is a side benefit, as the air it now routes over or to the sides creates the most change in pressure over the car. the air that goes under the car from the nose is mayb 3-4 ", the air that goes over the car goes 1 or 2 feet. that both maybe below ambient, but the air over the car is FAR under ambient. I have the data to support it too.
Now, ground effects are also something to look at. I think the entire concept there is to channel the air so that it speeds up under the car, with tunnels and then opens out into the defuser where the pressure suddlely raises behind the car for lower drag and greater downforce in the rear. facinating concepts for sure. Im still not confortable with the ground effects and flow under the car. I believe that without the duct work or flat pannels, you end up with a lot of drag and some stagnation points to raise pressure slightly, but not by much. mostly drag I would imagine.
The proof in downforce that the splitter actually contributes is in the think aluminum I used. its 1/16" aluminum sheet with rivets. Maybe there is 100lbs of downforce due to the differential pressure. (on top vs under the splitter)
ps with those cable ties I think your Shark is starting to look more like a Catfish Mark. lol No offence intended.
08-18-2009, 06:40 AM
#23
Rennlist Member
08-18-2009, 01:06 PM
#24
Drifting
Join Date: Jul 2006
Location: ..."RECALCULATING"
Posts: 3,496
Likes: 0
Received 0 Likes
on
0 Posts
I didn't stay at a holiday inn express last night - but I do have a couple of engineering degrees and do CFD everyday...
Bernoulli's equation is derived by integrating Euler's equation along a streamline. Euler's equation is the conservation of momentum neglecting fluid viscosity. Euler's equations also tell us the relationship between streamline curvature and pressure - a point most often missed and waaay over simplified when looking only at bernoulli equation. Euler-N equation says that the pressure increases in the direction of streamline curvature. This explains the low pressure over the greenhouse of a car and the high pressure in front of the windshield. At the windshield area, the streamlines are curving up with the radius of curvature pointing in the direction of the windshield. Pressure is increasing in this direction. Since there is atmospheric pressure far away from the car - there is high pressure at the base of the windshield. The opposite is true as the flow goes over the roof and down the rear window. Radius of curvature points away from the car....
Now - about the Mercedes GT1 flips. That is a direct result of ground effect. An airfoil operating in ground effect is extremely sensitive to angle of attack. Ground effect works for both lift and downforce producting wings. I am probably already getting too technical - but basically ground effect makes the flow much more 2 dimensional which greatly increases aerodynamic efficiency. As the GT1 cars crested the hill and the "angle of attack" of the car turned from negative to positive and you go from a highly efficient downforce producing body to a highly efficient lift producing body.
Also, be careful with pressure readings. Getting good surface pressure measurements in the kind of environment we are talking about is NOT trivial....The data, nonetheless is interesting.
AND PLEASE I do not mean to start an argument but: The notion that the 2 air particles have to meet at the trailing edge is RIDICULOUS and completely wrong. Yes, you will find this in "textbooks" and on the internet. But it is utterly not true. I have seen the experiments with dye traces. The fact of the matter is that on a lifting wing (upper surface = low pressure = higher speed) the particles on the upper surface will frequently reach the trailing edge first, even though they have a longer distance to travel.
Bernoulli's equation is derived by integrating Euler's equation along a streamline. Euler's equation is the conservation of momentum neglecting fluid viscosity. Euler's equations also tell us the relationship between streamline curvature and pressure - a point most often missed and waaay over simplified when looking only at bernoulli equation. Euler-N equation says that the pressure increases in the direction of streamline curvature. This explains the low pressure over the greenhouse of a car and the high pressure in front of the windshield. At the windshield area, the streamlines are curving up with the radius of curvature pointing in the direction of the windshield. Pressure is increasing in this direction. Since there is atmospheric pressure far away from the car - there is high pressure at the base of the windshield. The opposite is true as the flow goes over the roof and down the rear window. Radius of curvature points away from the car....
Now - about the Mercedes GT1 flips. That is a direct result of ground effect. An airfoil operating in ground effect is extremely sensitive to angle of attack. Ground effect works for both lift and downforce producting wings. I am probably already getting too technical - but basically ground effect makes the flow much more 2 dimensional which greatly increases aerodynamic efficiency. As the GT1 cars crested the hill and the "angle of attack" of the car turned from negative to positive and you go from a highly efficient downforce producing body to a highly efficient lift producing body.
Also, be careful with pressure readings. Getting good surface pressure measurements in the kind of environment we are talking about is NOT trivial....The data, nonetheless is interesting.
AND PLEASE I do not mean to start an argument but: The notion that the 2 air particles have to meet at the trailing edge is RIDICULOUS and completely wrong. Yes, you will find this in "textbooks" and on the internet. But it is utterly not true. I have seen the experiments with dye traces. The fact of the matter is that on a lifting wing (upper surface = low pressure = higher speed) the particles on the upper surface will frequently reach the trailing edge first, even though they have a longer distance to travel.
In essence I think Bernoulli's equation does a great job of describing a 3-D process in 2-D form theoretically. However, what is actually happening, physically, is much better described by Newton's third law....IMHO.
They come up with the same answer...just represented differently.
08-18-2009, 01:29 PM
#25
Rennlist Member
Thread Starter
Now, I dont stay in Holiday Inns any more, but I do bring my tent to the track now to save money for race gas. 
Yes, agreed as well. Not getting too technical. good information. I have stacks of aero books from college, that not only can I not remember what was in them, but I cant even remember where they are!
as far as my comment regarding the meeting of the air flow at the rear,I was being very general. Ive seen those smoke test results too, over wings though.
Same thing with the flipping GT1. just like a wing that usually provides lift at 0 angle of attack, can produce trememdous negative lift (downforce) if a slight chnage in angle of attack is made. I think the changes made to hood venting might have mitigated this effect. more down force, plus, if the nose does get raised, some of the lift is spoiled as it is venting through the hood on top of the car. Just an observation, as cars these days have this added feature.
as far as pressure tests go. I use some tufts and a very sensitve guage, and did tests at the surface level, 1" higher, and to the front and rear of the surface. all were pretty consistant. as we know, max flat plate pressure is about .11psi at 80mph, and near .44psi at 160mph. Hard to increase that pressure value on the surface itself, but the differential pressure is what Im leaning to understand more. 0 on the underside, maybe lower if you have tunnels ( venturis laterally) and a venturi vertically, (ground to chassis vs incoming air or air rolling off the nose). the pressure on the splitter, and the vacuum on the center of the hood provides downforce in the front, but as you mentinoned, there is the largest area of vacuum (lift) on the top of the passenger compartment. Then, we negate this with a nice wing setting in the rear.
Yes, the car seems to be much more well mannered in the sweepers, but still fighting a push that i think it is a function of rear alignement toe settings.
Claykos, can you explain what is happening in Ground Effect? is it the venturi effect or something else that is lowering the pressure under the car , or airplane at certain heights above ground at speeds?
Yes, agreed as well. Not getting too technical. good information. I have stacks of aero books from college, that not only can I not remember what was in them, but I cant even remember where they are!
as far as my comment regarding the meeting of the air flow at the rear,I was being very general. Ive seen those smoke test results too, over wings though.
Same thing with the flipping GT1. just like a wing that usually provides lift at 0 angle of attack, can produce trememdous negative lift (downforce) if a slight chnage in angle of attack is made. I think the changes made to hood venting might have mitigated this effect. more down force, plus, if the nose does get raised, some of the lift is spoiled as it is venting through the hood on top of the car. Just an observation, as cars these days have this added feature.
as far as pressure tests go. I use some tufts and a very sensitve guage, and did tests at the surface level, 1" higher, and to the front and rear of the surface. all were pretty consistant. as we know, max flat plate pressure is about .11psi at 80mph, and near .44psi at 160mph. Hard to increase that pressure value on the surface itself, but the differential pressure is what Im leaning to understand more. 0 on the underside, maybe lower if you have tunnels ( venturis laterally) and a venturi vertically, (ground to chassis vs incoming air or air rolling off the nose). the pressure on the splitter, and the vacuum on the center of the hood provides downforce in the front, but as you mentinoned, there is the largest area of vacuum (lift) on the top of the passenger compartment. Then, we negate this with a nice wing setting in the rear.
Yes, the car seems to be much more well mannered in the sweepers, but still fighting a push that i think it is a function of rear alignement toe settings.
Claykos, can you explain what is happening in Ground Effect? is it the venturi effect or something else that is lowering the pressure under the car , or airplane at certain heights above ground at speeds?
I didn't stay at a holiday inn express last night - but I do have a couple of engineering degrees and do CFD everyday...
Bernoulli's equation is derived by integrating Euler's equation along a streamline. Euler's equation is the conservation of momentum neglecting fluid viscosity. Euler's equations also tell us the relationship between streamline curvature and pressure - a point most often missed and waaay over simplified when looking only at bernoulli equation. Euler-N equation says that the pressure increases in the direction of streamline curvature. This explains the low pressure over the greenhouse of a car and the high pressure in front of the windshield. At the windshield area, the streamlines are curving up with the radius of curvature pointing in the direction of the windshield. Pressure is increasing in this direction. Since there is atmospheric pressure far away from the car - there is high pressure at the base of the windshield. The opposite is true as the flow goes over the roof and down the rear window. Radius of curvature points away from the car....
Now - about the Mercedes GT1 flips. That is a direct result of ground effect. An airfoil operating in ground effect is extremely sensitive to angle of attack. Ground effect works for both lift and downforce producting wings. I am probably already getting too technical - but basically ground effect makes the flow much more 2 dimensional which greatly increases aerodynamic efficiency. As the GT1 cars crested the hill and the "angle of attack" of the car turned from negative to positive and you go from a highly efficient downforce producing body to a highly efficient lift producing body.
Also, be careful with pressure readings. Getting good surface pressure measurements in the kind of environment we are talking about is NOT trivial....The data, nonetheless is interesting.
AND PLEASE I do not mean to start an argument but: The notion that the 2 air particles have to meet at the trailing edge is RIDICULOUS and completely wrong. Yes, you will find this in "textbooks" and on the internet. But it is utterly not true. I have seen the experiments with dye traces. The fact of the matter is that on a lifting wing (upper surface = low pressure = higher speed) the particles on the upper surface will frequently reach the trailing edge first, even though they have a longer distance to travel.
Bernoulli's equation is derived by integrating Euler's equation along a streamline. Euler's equation is the conservation of momentum neglecting fluid viscosity. Euler's equations also tell us the relationship between streamline curvature and pressure - a point most often missed and waaay over simplified when looking only at bernoulli equation. Euler-N equation says that the pressure increases in the direction of streamline curvature. This explains the low pressure over the greenhouse of a car and the high pressure in front of the windshield. At the windshield area, the streamlines are curving up with the radius of curvature pointing in the direction of the windshield. Pressure is increasing in this direction. Since there is atmospheric pressure far away from the car - there is high pressure at the base of the windshield. The opposite is true as the flow goes over the roof and down the rear window. Radius of curvature points away from the car....
Now - about the Mercedes GT1 flips. That is a direct result of ground effect. An airfoil operating in ground effect is extremely sensitive to angle of attack. Ground effect works for both lift and downforce producting wings. I am probably already getting too technical - but basically ground effect makes the flow much more 2 dimensional which greatly increases aerodynamic efficiency. As the GT1 cars crested the hill and the "angle of attack" of the car turned from negative to positive and you go from a highly efficient downforce producing body to a highly efficient lift producing body.
Also, be careful with pressure readings. Getting good surface pressure measurements in the kind of environment we are talking about is NOT trivial....The data, nonetheless is interesting.
AND PLEASE I do not mean to start an argument but: The notion that the 2 air particles have to meet at the trailing edge is RIDICULOUS and completely wrong. Yes, you will find this in "textbooks" and on the internet. But it is utterly not true. I have seen the experiments with dye traces. The fact of the matter is that on a lifting wing (upper surface = low pressure = higher speed) the particles on the upper surface will frequently reach the trailing edge first, even though they have a longer distance to travel.
08-18-2009, 01:32 PM
#26
Rennlist Member
Thread Starter
So embarrasing to do this to a porsche, But, at 50ft and 100mph, you can barely see it.
Hey, at least it didnt look like this:
Hey, at least it didnt look like this:
There is a difference between a splitter and the old air damn which was a crude way of providing downforce. All splitters seem to run parallel to the ground now rather than downwards. I think you should see some definite improvement. Does this help your turn in?
ps with those cable ties I think your Shark is starting to look more like a Catfish Mark. lol No offence intended.
ps with those cable ties I think your Shark is starting to look more like a Catfish Mark. lol No offence intended.
08-18-2009, 02:05 PM
#27
Ground effect....
For an airfoil type shape (inverted or not) as it gets in close proximity to the ground the flow is forced to become much less 3 dimensional (less spanwise flow). Because the flow is 2 dimensional the wing acts more like a wing with infinite span than a finite wing. Effectively creating more lift. Basically, it's like having a wider wing. It works for both positive and negative lift devices. Running a flat bottom at angle of attack with a rear diffuser is basically turning the bottom of the car into a crude airfoil shape and taking advantage of ground effect. The old IMSA GTP cars with full body length tunnels were just a more refined version of this. The downside is that, a real airfoil shape (like the old GTP cars) running within inches or less is SUPER sensitive to angle of attack. A change of fractions of a degree will change downforce by hundreds of pounds. This is why these cars were outlawed - just too dangerous to have a platform that goes from glued to the ground and you hit a bump and lose 30% of your downforce!
Now the "venturi" effect for a race car is a bit different and really only works for a VERY low car that has VERY low side skirts. The idea is to create a channel between the car/ground where the flow is accelerated.
Back in WWII damaged bombers with engines out used to fly very low over the ocean and be able to make it back to base even though they should not have had the power to stay aloft.
PS: Mark - pressure taps? tufts?? Maybe you should spend some of that time/money on replacing your 12 year old bushings.
For an airfoil type shape (inverted or not) as it gets in close proximity to the ground the flow is forced to become much less 3 dimensional (less spanwise flow). Because the flow is 2 dimensional the wing acts more like a wing with infinite span than a finite wing. Effectively creating more lift. Basically, it's like having a wider wing. It works for both positive and negative lift devices. Running a flat bottom at angle of attack with a rear diffuser is basically turning the bottom of the car into a crude airfoil shape and taking advantage of ground effect. The old IMSA GTP cars with full body length tunnels were just a more refined version of this. The downside is that, a real airfoil shape (like the old GTP cars) running within inches or less is SUPER sensitive to angle of attack. A change of fractions of a degree will change downforce by hundreds of pounds. This is why these cars were outlawed - just too dangerous to have a platform that goes from glued to the ground and you hit a bump and lose 30% of your downforce!
Now the "venturi" effect for a race car is a bit different and really only works for a VERY low car that has VERY low side skirts. The idea is to create a channel between the car/ground where the flow is accelerated.
Back in WWII damaged bombers with engines out used to fly very low over the ocean and be able to make it back to base even though they should not have had the power to stay aloft.
PS: Mark - pressure taps? tufts?? Maybe you should spend some of that time/money on replacing your 12 year old bushings.
08-18-2009, 02:23 PM
#28
Rennlist Member
Thread Starter
Thanks!! 
as far as 20 year old bushings and blown out shocks, flexed to death chassis, and bump stops. They are all part of a highly refined and optimized suspension set up. If I replace anything, it might really mess things up.
as far as 20 year old bushings and blown out shocks, flexed to death chassis, and bump stops. They are all part of a highly refined and optimized suspension set up. If I replace anything, it might really mess things up.
Ground effect....
For an airfoil type shape (inverted or not) as it gets in close proximity to the ground the flow is forced to become much less 3 dimensional (less spanwise flow). Because the flow is 2 dimensional the wing acts more like a wing with infinite span than a finite wing. Effectively creating more lift. Basically, it's like having a wider wing. It works for both positive and negative lift devices. Running a flat bottom at angle of attack with a rear diffuser is basically turning the bottom of the car into a crude airfoil shape and taking advantage of ground effect. The old IMSA GTP cars with full body length tunnels were just a more refined version of this. The downside is that, a real airfoil shape (like the old GTP cars) running within inches or less is SUPER sensitive to angle of attack. A change of fractions of a degree will change downforce by hundreds of pounds. This is why these cars were outlawed - just too dangerous to have a platform that goes from glued to the ground and you hit a bump and lose 30% of your downforce!
Now the "venturi" effect for a race car is a bit different and really only works for a VERY low car that has VERY low side skirts. The idea is to create a channel between the car/ground where the flow is accelerated.
Back in WWII damaged bombers with engines out used to fly very low over the ocean and be able to make it back to base even though they should not have had the power to stay aloft.
PS: Mark - pressure taps? tufts?? Maybe you should spend some of that time/money on replacing your 12 year old bushings.
For an airfoil type shape (inverted or not) as it gets in close proximity to the ground the flow is forced to become much less 3 dimensional (less spanwise flow). Because the flow is 2 dimensional the wing acts more like a wing with infinite span than a finite wing. Effectively creating more lift. Basically, it's like having a wider wing. It works for both positive and negative lift devices. Running a flat bottom at angle of attack with a rear diffuser is basically turning the bottom of the car into a crude airfoil shape and taking advantage of ground effect. The old IMSA GTP cars with full body length tunnels were just a more refined version of this. The downside is that, a real airfoil shape (like the old GTP cars) running within inches or less is SUPER sensitive to angle of attack. A change of fractions of a degree will change downforce by hundreds of pounds. This is why these cars were outlawed - just too dangerous to have a platform that goes from glued to the ground and you hit a bump and lose 30% of your downforce!
Now the "venturi" effect for a race car is a bit different and really only works for a VERY low car that has VERY low side skirts. The idea is to create a channel between the car/ground where the flow is accelerated.
Back in WWII damaged bombers with engines out used to fly very low over the ocean and be able to make it back to base even though they should not have had the power to stay aloft.
PS: Mark - pressure taps? tufts?? Maybe you should spend some of that time/money on replacing your 12 year old bushings.
08-18-2009, 03:58 PM
#29
Mr. Excitement
Rennlist Member
Rennlist Member
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.