Aerodynamics...

[s15specr]

Hi,

One thing I had been wondering about Gran Turismo 5 Prologue is how do PD get downforce and is it correct?

Take the honda NSX-R, it's the kinda of car where pretty much everything on it is there for performance. The rear wing, in Quick Tune PD say the NSX-R has 0 downforce, yet the wing is carbon fibre, so what i mean is, why would Honda Put a non-functional wing on a car where they removed things to save weight?

Surely on a car like the NSX-R the wing is there for a reason- so why do PD say it has no downforce??

 

[wnffe]

I think PD only gives adjustable downforce for the standard cars, which have that ability IRL. Like RX-7 for example.

 

[ExigeEvan]

Hi,

One thing I had been wondering about Gran Turismo 5 Prologue is how do PD get downforce and is it correct?

Take the honda NSX-R, it's the kinda of car where pretty much everything on it is there for performance. The rear wing, in Quick Tune PD say the NSX-R has 0 downforce, yet the wing is carbon fibre, so what i mean is, why would Honda Put a non-functional wing on a car where they removed things to save weight?

Surely on a car like the NSX-R the wing is there for a reason- so why do PD say it has no downforce??

It's not that the downforce is zero, it's that you can't adjust it.

And the fact it is made of carbon fibre has nothing to do with it being functional.

 

[Obli]

PD should have the downforce figure in there greyed-out, if that is the case. 0 suggest no downforce to me too.

 

[Ardius]

PD should have the downforce figure in there greyed-out, if that is the case. 0 suggest no downforce to me too.

It should really suggest default downforce, thats probably the reason they left it like that and that's what the numbers in quick-tune represent - the default stock settings. So, the default for the NSX is that there is no adjustment of downforce, its as it comes.

The physics for the car will of course taken into account the downforce, its just because you can't adjust it, theres no point in putting a value for downforce because it never changes.

 

[Stevisiov]

The f430 has downforce figures greyed out that are un-adjustable but they are greater than 0. Why PD decided to do this for the 599,f430 and california but not other cars is beyond me.

 

[Exorcet]

The f430 has downforce figures greyed out that are un-adjustable but they are greater than 0. Why PD decided to do this for the 599,f430 and california but not other cars is beyond me.

Yes. And actually IIRC, the 599, Viper, and Z06 have 0 for downforce when they do not in reality.

It kinds of looks like they took a very lazy approach to it, I don't know. Also, what do those numbers even mean? They had units for suspension stiffness in old GT games, but they always used some random number for downforce.

It should tell you pounds of downforce and drag, coefficients, or give you a wind tunnel option by GT5 full.

 

[Stevisiov]

Yes. And actually IIRC, the 599, Viper, and Z06 have 0 for downforce when they do not in reality.

It kinds of looks like they took a very lazy approach to it, I don't know. Also, what do those numbers even mean? They had units for suspension stiffness in old GT games, but they always used some random number for downforce.

It should tell you pounds of downforce and drag, coefficients, or give you a wind tunnel option by GT5 full.

Yes, its nice to see someone else who thinks this is a problem with the GT tuning model.

setting my wing to 35 doesn't tell me much other than I am adjusting imaginary GT units of downforce as far as I can tell. Ideally it should give us figure for stock down force, and tell us the effects of the adjustments we make.

Its a very simplified tuning menu in GT5P hence being called the quick tune. I have hope that it will be in sufficient detail for GT5 though.

 

[s15specr]

I also says the nissan gt-r has 0 - 3. It did on the skyline gtr in GT4 too.

 

[Tired Tyres]

This is a very complicated area as the following link would indicate.

http://en.wikipedia.org/wiki/Downforce

I wonder if PD have a software wind tunnel?

 

[Exorcet]

It's no more complicated than the rest of the physics. And a lot of the formulas just boil down to constants that be taken from manufacturers anyway.

 

[Context]

This is a very complicated area as the following link would indicate.

http://en.wikipedia.org/wiki/Downforce

I wonder if PD have a software wind tunnel?

that would be kick ass if you could change the downforce on cars and then put it in the wind tunnel.

 

[Mad Matt]

I've got a friend who works on wind tunnels, and it really isn't that easy. The effects of changes often go beyond what was intended, or don't work well in cross-winds etc. Often, even after extensive testing, the parts they bring to the track don't do what they expected.

If it was that simple F1 would have the perfect set-up by now and that would be that.

So, you can't say I want an extra 5kg of downforce in a meaningful sense, but you could say I want to change the angle of the rear spoiler by 2 degrees, that might make more sense than GT magic numbers.

 

[Exorcet]

GT is already simplified anyway. There are no variations in the air except for drafting, maybe altitude, but I doubt it.

All they need is a coefficient of lift and drag for each aero part, and an approximate derivative of each of those numbers. That would work much better than what is in place now.

And like I said before, GT can use shortcuts simply by asking manufacturers for info. Your analogy of wind tunnel testing seems a bit off though, there formulas that can predict airfoil performance fairly easily. The hard part is knowing what configuration will make the car fastest, not knowing what the wing will do.

 

[Stevisiov]

GT is already simplified anyway. There are no variations in the air except for drafting, maybe altitude, but I doubt it.

All they need is a coefficient of lift and drag for each aero part, and an approximate derivative of each of those numbers. That would work much better than what is in place now.

I am fairly sure that's what they do already but they don't publish these numbers, instead they give a few figures in their own GT units to tell us how much downforce a car has, which is a bit of a shame.

And like I said before, GT can use shortcuts simply by asking manufacturers for info. Your analogy of wind tunnel testing seems a bit off though, there formulas that can predict airfoil performance fairly easily. The hard part is knowing what configuration will make the car fastest, not knowing what the wing will do.

They will be given drag and lift/downforce figures by the manufactures like you say. I wonder how they calculate it on older cars though.

 

[Mad Matt]

GT is already simplified anyway. There are no variations in the air except for drafting, maybe altitude, but I doubt it.

All they need is a coefficient of lift and drag for each aero part, and an approximate derivative of each of those numbers. That would work much better than what is in place now.

And like I said before, GT can use shortcuts simply by asking manufacturers for info. Your analogy of wind tunnel testing seems a bit off though, there formulas that can predict airfoil performance fairly easily. The hard part is knowing what configuration will make the car fastest, not knowing what the wing will do.

Hmm, with GT5Ps simplification, you may be right, it's not may area of specialism. I wonder if they model increased load on the suspension due to higher downforce, for example?

 

[Exorcet]

Hmm, with GT5Ps simplification, you may be right, it's not may area of specialism. I wonder if they model increased load on the suspension due to higher downforce, for example?

The only way you might be able to test this is setting a car's suspension very high and soft, then crank downforce and power/weight up to the maximum. Take it to Fuji and see if the ride height lowers as speed increases along the straight (I think the camera angle may allow you to see this)

And Stevisiov, you're probably right that they take the coefficient data and convert it, but I'm not sure if they take/estimate the derivative data. I only say this because I never see noticeable drag when I increase downforce on the cars. Even if most adjustable wings are on fake GT tuned cars, they should still act pretty close to similar real life wings.

 

[Stevisiov]

And Stevisiov, you're probably right that they take the coefficient data and convert it, but I'm not sure if they take/estimate the derivative data. I only say this because I never see noticeable drag when I increase downforce on the cars. Even if most adjustable wings are on fake GT tuned cars, they should still act pretty close to similar real life wings.

They do make a difference, but there air resistance model isn't great, it maybe incomplete or it may just be calibrated wrong but it doesn't work the way it should. changing the wing on the f1 car does make a difference on high end acceleration (There isn't a straight long enough to test top speed), but no where near enough to be realistic. Also you would assume the model is wrong because PD's drafting model doesn't work very well either. The drafting is over pronounced, its like every car displaces more air than a truck in its wake

 

[Zer0]

Hmm, with GT5Ps simplification, you may be right, it's not may area of specialism. I wonder if they model increased load on the suspension due to higher downforce, for example?

Yes, since GT1.

 

[Kryz11]

Yeah just because it's set to 0, it does not mean it's not gives any down force.


By the way, some cars do have adjustable wings.
For Example the EVO II Mercedes Benz, you can adjust it, in GT4 you could not untill you bought a wing. I really hope in GT5 this will change for the cars.

 

[SH1FT3R]

I wonder about this as well, for example the Ford GT is another car that doesn't have adjustable down force, but the greyed out value still reeds 20. So it would seem that PD have given the NSX no downforce at all, which would be wrong.

I also wonder a similar thing about the suspension settings, most sports cars have some toe and camber from the factory, but all the cars have the same camber and no toe when you look in the settings. So does a zero toe setting mean zero toe or does it actually mean stock toe settings?

Having proper units for all the settings would help with tuning.

On an interesting side note I remember reading somewhere the NSX-R is designed to produce more downforce going around a bend that going in a straight line.

 

[HUGHS1E]

For gt5 a car set with a zero represents the the downforce on that area is neutral or running the least amount the car/spoiler can, you can not use less than this because this is the shape of the car or the spoiler set to most aerodynamic, then you simply add more downforce via a spoiler, the better the spoiler the greater the adjustments, there is no point gt5 going into figures they would be pointless, drag/downforce is directly proportionate to speed which on most tracks is varriable which means throughout the lap it changes, not to mention air pressure, air density, wind speed/direction, humidity the list goes on!

GT5s 0 values are different for everycar it just states that that car is running the least amout of downforce it can, and if it hasnt an adjustable spoiler thats the max it runs too, hope this helps

Just because an object has a low drag coefficient does not mean it is more aerodynamic (creates less drag), yes it is a more aerodynamic shape! but does it create less drag? that depends!

 

[Exorcet]

For gt5 a car set with a zero represents the the downforce on that area is neutral or running the least amount the car/spoiler can, you can not use less than this because this is the shape of the car or the spoiler set to most aerodynamic, then you simply add more downforce via a spoiler, the better the spoiler the greater the adjustments, there is no point gt5 going into figures they would be pointless, drag/downforce is directly proportionate to speed which on most tracks is variable which means throughout the lap it changes, not to mention air pressure, air density, wind speed/direction, humidity the list goes on!

Yes drag and downforce do vary with speed, but they vary in relation to a constant coefficient. There is no reason for you to not want to know that number as a driver/tuner.

GT5s 0 values are different for everycar it just states that that car is running the least amout of downforce it can, and if it hasnt an adjustable spoiler thats the max it runs too, hope this helps

Just because an object has a low drag coefficient does not mean it is more aerodynamic (creates less drag), yes it is a more aerodynamic shape! but does it create less drag? that depends!

Some cars cannot be tuned to 0 downforce, so I'm not sure that your theory is correct. Cd does not directly relate to drag, but since cars are relatively the same size it can be used as a good estimate.

 

[Stevisiov]

For gt5 a car set with a zero represents the the downforce on that area is neutral or running the least amount the car/spoiler can, you can not use less than this because this is the shape of the car or the spoiler set to most aerodynamic, then you simply add more downforce via a spoiler, the better the spoiler the greater the adjustments, there is no point gt5 going into figures they would be pointless,

Some cars that shape produce downforce are given figure by PD. Take the f430 for example, the undercarriage of the car is designed to give downforce but its not adjustable, PD recognised this. PD don't appear to have acknowledge that cars like the NSX-R produce negligible downforce, suggesting that the rear wing is purely cosmetic. Now I doubt this is how the NSX works in the physics engine, but it does make me wonder why they choose not to publish the figures in their GT units.

drag/downforce is directly proportionate to speed

Actually Drag/downforce is directly proportional to your velocity squared. If you double your speed the drag/downforce increase by 4 times as much

which on most tracks is varriable which means throughout the lap it changes, not to mention air pressure, air density, wind speed/direction, humidity the list goes on!

But thats all moot. The co-efficient of drag takes all those factors out of the equation. The co-effecient works on the bases that all other factors are the same value. Say a car and a truck in a wind tunnel. Pressure same, humidity the same, they both have a set surface area.

I don't have any figures on what standard conditions are when finding out what the drag co-efficient of a vehicle is. But its tested in the same conditions for every car. Once you have the co-efficient of drag for a vehicle it doesn't matter how the pressure changes the co-efficient stays the same (for the sake of argument, although cars deform to an extent all the time but is generally negligible for most cars). The pressure is used to calculate the overall drag the actual amount of force resisting motion as is the square of the velocity as may other factors but they all are multiplied by the co-efficient at the end.

That's in real life when things are tricky too. In Gran Turismo things are a lot simpler, air pressure is the same all the way around (it might not be in the wake of a vehicle, its depends on how PD model it, in real life it would.) All these factors cancel out because PD don't have to worry about it, there isn;t change in weather in Gran Turismo, every day is the same temperature, air pressure add infinitum of variables. The only factors that will affect two different cars drag in Gran Turismo is the speed of a vehicle (squared) and that vehicles drag co-efficient that's programmed. That is unless PD's physics model is more complicated

For example a co-efficient in real life will change on high downforce cars at highspeed, i.e car gets pushed lower to the road lowering co-efficient, wings flex a bit (although only really happens on wafer wings (as I like to call them). I doubt PD's model will simulate that but it could.

GT5s 0 values are different for everycar it just states that that car is running the least amout of downforce it can, and if it hasnt an adjustable spoiler thats the max it runs too, hope this helps

The f430 you will notice has a fixed max downforce value that can't be changed but its given downforce values greater than 0.

Just because an object has a low drag coefficient does not mean it is more aerodynamic (creates less drag), yes it is a more aerodynamic shape! but does it create less drag? that depends!

well its the same as any co-efficient, as long as both cars are in the same part of track side by side going the same speed the the car with the lower drag co-effiencient is subject to less drag, its doesn't depend. The biggest factor is the speed without a doubt, pressure humidity temperature don't make a big difference. The co-efficient can also make a very a big difference can if we are comparing a truck to a streamlined supercar.

Sorry about dismantelling your post, I didn't feel it was entirely accurate so I had to chime in

 

[HUGHS1E]

I am aware that some cars do have different starting aerodynamic numbers for example the f430 is not 0, but at its fixed setting I feel thats what PD feels thats waht the car is like, Maybe PD were not happy with the performance on certain powerfull rwd cars, so instead of going back and changing there code for that car they altered it in the quick tune to make it handle better, this is just what i feel, I do not know how they create or code the data for a game I just think that PD could of done this as a quick fix, keep an eye on that fixed figure to see if it alters after physics updaes, I remember the ford gt been very tail happy then very neutral after updates, maybe they altered this figure and not just tires grip.

In my earlier post I miss understood Exorcet's post "All they need is a coefficient of lift and drag for each aero part, and an approximate derivative of each of those numbers. That would work much better than what is in place now." Here I thought you meant you wanted the cd of the spoiler in terms of how slippy it is which I thought would be pointless because you want a figure for the force it creates not how aerodynamic it was, My bad I'm not the best at english and here once again is an example of how fast I get lost, I think i'll stay out of forums and stick to the track.

I was just making sure people realised that a spoilers performance alters in force depending on the speed so having a fixed number would be like it is now just with value/forces included, as long as you know which way to increase/decrease it I cant see a problem.

I can see the only help of having a value would be so I could set my car up from real life tuning figures, which to be fair would be interesting to see how they compare.

At Stevisiov,
From what I remeber to calculate drag you need the cd and the surface/frontal area, a really large car featuring a big frontal area with average cd will not necessarily create less drag than a smaller car featuring a small frontal area with a higher cd just because its cd is better, there are examples of this in the early days of racing. THE ERA OF BENTLEY BLOWERS I think they called them. But this is off topic now so who gives its a shame you could not correct my post with red font to remind me of the red ink that corrected my work after marking all them years ago

THANKS

 

[SH1FT3R]

Pretty much all car shapes produce lift and therefore have a positive lift coefficient, aero parts (vents, diffusers, spoilers) can be used to add downforce and reduce the lift coefficient of the car, with enough aero one can reduce the lift coefficient below zero. It's important to note that having downforce does not automaticly mean that the car will have a negative lift coefficient, only a reduced lift coefficient.

Ok, you probably all knew that. So I did a little research about some of these cars and this is how I think it works:

All the cars that have a negative lift coefficient in real life have an aero value greater than zero in GT5P. While all the cars with a positive lift coefficient in real life (most cars) have a zero aero value in GT5P.

So my theory is that GT does not simulate the lift forces on a car only the downforces, and only if the car has a negative lift coefficient. So the cars either produce negative lift (downforce) or no lift at all.
I can see why they would do it this way because this is what most people think of when your talking about downforce,
more downforce = more downward force than when the car is stationary


So the NSX-R is actually pretty accurate, as the lift coefficient of the NSX-R is close to zero. But not for the Acura NSX; it's missing a lot of the R's aero gear.

 

[HUGHS1E]

nice work

 

[Zer0]

So my theory is that GT does not simulate the lift forces on a car only the downforces,

 

[Exorcet]

You don't need lift to replicate the video. The theory about lift = 0 in GT doesn't account for the 599, Viper, and Corvette (probably other cars).

 

[SH1FT3R]

The info I found on the 599 and Corvette was that they had positive lift coefficients, couldn't find anything on the viper though, except that the convertible had zero lift.