GTS Wing's Aerodynamics

[rhyary]

GTS Wing's Aerodynamics

Aerodynamics are very difficult to test at home.
The GTS wing is lower and is not at the airstream. From what I can tell, the air comes over the roof and its direction is somewhat slanted downwards rather at the direction of travel.

For a long time my angle of attack was roughly at 0 compares to the direction of travel. That means the winglet is slanted downwards.

You can see the angle in this picture:
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[rhyary]

I mostly based my AOA on this picture:
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[rhyary]

I than thought that zero AOA should actually be one hole upper, based on the winglets angle. So I adjusted the AOA.

Now the Winglets are parallel to the ground, but the wing is pointing a bit upward as related to the direction of the travle.

But if you look to the direction of the wind over the roof, it looks like it is in a neutral position.

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[rhyary]

Wing looks upwards but 0 AOA ?
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[SAMM3Y]

Why do you want to zero out the wing? Looking for efficiency off track? Thanks for the pic of the wind tunnel, I'm setting up a wing for my car and that helps.

[tsk94]

AOA is not based on the end plates. It's based on the airfoil of the wing itself. The car MUST be level to actually measure the AOA.

There's a reason why cars like Schrimer for example, that must run a GTS size wing due to TUV, run 'extreme' angles of attack. These wings are so small and low that a very high AOA is needed to produce any meaningful levels of downforce.

[tsk94]

So, when you have the endplates parallel to the ground at '0 AOA' like in the pictures above, the wing itself is creating lift and drag - not downforce.

[rhyary]

Originally Posted by SAMM3Y

Why do you want to zero out the wing? Looking for efficiency off track? Thanks for the pic of the wind tunnel, I'm setting up a wing for my car and that helps.

The wing at zero produces the most downforce at the least drag. You can get more downforce, but with more drag so it is a balancing act of top speed vs corner speed.

The GTS wing is only adding down force above 200km/h (or 124mph) so it does nothing for public roads.

[tsk94]

Typo above: airfoil not airflow. Damn autocorrect.

[tsk94]

Originally Posted by rhyary

The wing at zero produces the most downforce at the least drag. You can get more downforce, but with more drag so it is a balancing act of top speed vs corner speed.

The GTS wing is only adding down force above 200km/h (or 124mph) so it does nothing for public roads.

Also, you've basically explained the reasoning of high AOA and why they are used with these wings.

The amount of downforce produced at low AOA with these wings is minimal. How many turns are you going through at over 200kph? Probably not many. You want downforce for braking and corner performance. What's the point in running a wing at 0 AOA that produces negligible amounts of downforce unless above 200kph? There isn't any. That's why these people are running them at such aggressive angles, otherwise there is NO point in having on the car other then for cosmetics. Drag will always be a trade off for downforce, but again, the wing is small. So even at high AOA, the drag isn't that extreme but neither is the amount of downforce. If the Schrimer cars are running those AOA on the Nordschleife, then it will be more then adequate for you at tracks with MUCH lower average speeds.

[SAMM3Y]

I didn't want scaffolding on the back of my car so I went with a big foil with relatively low risers and an aggressive aoa. How tall is a gts wing from top of trunk lid to top of foil tuned aggressively? Approximately

[tsk94]

Originally Posted by SAMM3Y

I didn't want scaffolding on the back of my car so I went with a big foil with relatively low risers and an aggressive aoa. How tall is a gts wing from top of trunk lid to top of foil tuned aggressively? Approximately

Yeah, I understand how some people wouldn't want a full size wing on their car - especially if it's street driven as well. The GTS wing fills that niche of a good size wing without being ridiculous. But, like you said, you need to run high AOA for it to do anything meaningful.

I'm sure if you're asking me directly regarding the height. Unfortunately I don't know. I was planning on running a GTS wing but when test fitting it just seemed to small. I stepped up to a full size wing given my application (track only car) instead.

[rhyary]

Originally Posted by tsk94

So, when you have the endplates parallel to the ground at '0 AOA' like in the pictures above, the wing itself is creating lift and drag - not downforce.

First, I don't know. So I am not speaking as if I know the answer.

But my point is that if the air flow goes over the roof and slope down, the angle of the wing has to be in relation to the airflow, not the direction of the airflow above the roof.

I am aware that the AOA is not the end plates. It was just use as a reference point since it shows well in the picture.

p.s. I flew Hang Glider for years and I am well aware how the wing works. My life was dependent on me knowing it.

[rhyary]

Originally Posted by tsk94

Also, you've basically explained the reasoning of high AOA and why they are used with these wings.

The amount of downforce produced at low AOA with these wings is minimal. How many turns are you going through at over 200kph? Probably not many. You want downforce for braking and corner performance. What's the point in running a wing at 0 AOA that produces negligible amounts of downforce unless above 200kph? There isn't any. That's why these people are running them at such aggressive angles, otherwise there is NO point in having on the car other then for cosmetics. Drag will always be a trade off for downforce, but again, the wing is small. So even at high AOA, the drag isn't that extreme but neither is the amount of downforce. If the Schrimer cars are running those AOA on the Nordschleife, then it will be more then adequate for you at tracks with MUCH lower average speeds.

Not exactly.
If you run the wing at sharp AOA, you may stall the wing and produce only drag.

At sharp AOA as in the picture, you turn the GTS into a spoiler, rather than an upside wing.

A wing and a spoiler try to achieve the same thing but in a different way.

A wing is an active device that generate a lift or a down force by creating a difference air pressure on both sides of the wing.

A spoiler is a passive device that aim to spoil the smooth air going over the roof and turns the whole car into a wing that wants to lift off.

Now, because it is all very much dependent on speed and airflow angles, I don't really know how to measure the effectiveness of the wing.

The M3 with out the GTS spoiler and wing generate lift at 200kph. The GTS at best just counter act that lift.

[tsk94]

Originally Posted by rhyary

First, I don't know. So I am not speaking as if I know the answer.

But my point is that if the air flow goes over the roof and slope down, the angle of the wing has to be in relation to the airflow, not the direction of the airflow above the roof.

I am aware that the AOA is not the end plates. It was just use as a reference point since it shows well in the picture.

p.s. I flew Hang Glider for years and I am well aware how the wing works. My life was dependent on me knowing it.

Fair enough, from your original post regarding AOA via the end plates it seemed like you were inferring AOA can be based off the end plate angle.
I just misinterpreted.

Originally Posted by rhyary

Not exactly.
If you run the wing at sharp AOA, you may stall the wing and produce only drug.

At sharp AOA as in the picture, you turn the GTS into a spoiler, rather than an upside wing.

A wing and a spoiler try to achieve the same thing but in a different way.

A wing is an active device that generate a lift or a down force by creating a difference air pressure on both sides of the wing.

A spoiler is a passive device that aim to spoil the smooth air going over the roof and turns the whole car into a wing that wants to lift off.

Now, because it is all very much dependent on speed and airflow angles, I don't really know how to measure the effectiveness of the wing.

The M3 with out the GTS spoiler and wing generate lift at 200mph. The GTS at best just counter act that lift.

That is true. At a certain angle the wing will not produce anymore down force and just more drag and further beyond that you'll lose downforce and gain a lot of drag. I don't believe the angles as shown above, like on the Schrimer cars, are reaching that point yet though. They are a very knowledge team/brand, I'd trust in their ability to setup a car with the GTS wing appropriately.

What exactly are you trying to accomplish? Maximum downforce? Minimum drag?

[rhyary]

Originally Posted by tsk94

Fair enough, from your original post regarding AOA via the end plates it seemed like you were inferring AOA can be based off the end plate angle.
I just misinterpreted.

That is true. At a certain angle the wing will not produce anymore down force and just more drag and further beyond that you'll lose downforce and gain a lot of drag. I don't believe the angles as shown above, like on the Schrimer cars, are reaching that point yet though. They are a very knowledge team/brand, I'd trust in their ability to setup a car with the GTS wing appropriately.

What exactly are you trying to accomplish? Maximum downforce? Minimum drag?

fair question.
I have a specific objective at the moment.

First, most of the weight I took off the car is in the rear.

At NYST i come to ~52-55mph turn doing 132mph. I would like to make the rear help with the braking.

NYST turn 8 left at 102mph, I would like to generate some downforce there.

LRP I come at ~138mph to big bend, I would like the GTS wing to help during the initial braking.

I don't think the GTS makes a difference anywhere else on those tracks.

My theory is, if I am right, that when the winglets are pointing slightly down, the actual wing in relationship to the air flow is actually at a steeper AOA than one would think.

[tsk94]

Originally Posted by rhyary

fair question.
I have a specific objective at the moment.

First, most of the weight I took off the car is in the rear.

At NYST i come to ~52-55mph turn doing 132mph. I would like to make the rear help with the braking.

NYST turn 8 left at 102mph, I would like to generate some downforce there.

LRP I come at ~138mph to big bend, I would like the GTS wing to help during the initial braking.

I don't think the GTS makes a difference anywhere else on those tracks.

My theory is, if I am right, that when the winglets are pointing slightly down, the actual wing in relationship to the air flow is actually at a steeper AOA than one would think.

From the sounds of it, the easiest and simplest solution would be to try different AOA while at a track day. Once you begin to notice a perceivable improvement is probably around where you'd want to stop. You have data so you can see how much top speed is affected. Being supercharged, I doubt that even at high AOA you'd drop much more then 1-2mph at most, but might gain some extra confidence under braking and in the fast turn.

[rhyary]

Originally Posted by tsk94

From the sounds of it, the easiest and simplest solution would be to try different AOA while at a track day. Once you begin to notice a perceivable improvement is probably around where you'd want to stop. You have data so you can see how much top speed is affected. Being supercharged, I doubt that even at high AOA you'd drop much more then 1-2mph at most, but might gain some extra confidence under braking and in the fast turn.

2mph.
Previously I was getting to 130, last track day was getting to 132mph after I changed to "winglets parallel" position.

Did I create lift? did I actually had less drag, was it just right downforce/drag?

who knows, perhaps the 10mph headwind one day, and last time it was tailwind.

[tsk94]

Originally Posted by rhyary

2mph.
Previously I was getting to 130, last track day was getting to 132mph after I changed to "winglets parallel" position.

Did I create lift? did I actually had less drag, was it just right downforce/drag?

who knows, perhaps the 10mph headwind one day, and last time it was tailwind.

Welcome to the world of downforce/drag. You'll have to determine, via data, if the time lost on the straights from a slightly lower top speed is offset by gains in other areas.

If you're hoping to get any noticeable differences in braking or corners, while maintaining the same top speed, it's not going to happen. At least certainly not with that wing. Perhaps with a full size wing that would be much more realistic.

[ThunderMoose]

Originally Posted by rhyary

2mph.
Previously I was getting to 130, last track day was getting to 132mph after I changed to "winglets parallel" position.

Did I create lift? did I actually had less drag, was it just right downforce/drag?

who knows, perhaps the 10mph headwind one day, and last time it was tailwind.

Are you able to see the car height drop via your linear potentiometers as the car increases in speed? You'd need a pretty flat and long straight.

[rhyary]

Originally Posted by ThunderMoose

Are you able to see the car height drop via your linear potentiometers as the car increases in speed? You'd need a pretty flat and long straight.

Yes at LRP, at NYST it is too bumpy at the top of the straight.

I will try to get that data on the 13th

[Redd]

Originally Posted by rhyary

fair question.
I have a specific objective at the moment.

First, most of the weight I took off the car is in the rear.

At NYST i come to ~52-55mph turn doing 132mph. I would like to make the rear help with the braking.

NYST turn 8 left at 102mph, I would like to generate some downforce there.

LRP I come at ~138mph to big bend, I would like the GTS wing to help during the initial braking.

I don't think the GTS makes a difference anywhere else on those tracks.

My theory is, if I am right, that when the winglets are pointing slightly down, the actual wing in relationship to the air flow is actually at a steeper AOA than one would think.

If what you want is more stability under braking you're wasting your time looking at wings. Assuming there is any meaningful downforce from the GTS wing in the first place at the speeds you operate at, that downforce decreases the moment you stomp on the brakes, not increase. If you want more rear end stability on braking, get a proper LSD, not a static wing. A wing/aero helps most on high speed sweepers.

Firstly, a wing's job is not only to produce downforce, but also to reduce lift. Sometimes you may not get any actual downforce produced, but lift reduction results in a nett positive result as well.

A type of drag that is often ignored in these aero conversations is pressure drag. Pressure drag is caused by the airflow curling in on itself behind the vehicle, causing a low pressure area that 'pulls' the car backwards. Sometimes adding a wing - and introducing some lift-induced drag - has the added benefit of moving the low-pressure zone further away from the car to reduce pressure drag.

Aero is a bit of a black art and you need to also look at what happens around the car and not only what happens on the car.