Flat Floors - (Custom Parts)

[ZedMan1996]

My cars went faster with flat floors (no other mods) than without.

This is due to the fact that the underside does not corrupt the airflow as its all jaggy and so on.

I dont know why you guys are reporting a lower top speed though. Maybe you're using other mods like spoilers or bumpers?

Anyhow, flat-floors improve speed and cornering, and all-out reduce drag, the reason it gives more downforce is simply because there is less air underneath trying to make the car take off (Just simply wording this) and also the flow in which it is carried out of the car.

It also makes the car more stable.

 

[raytard]

ZedMan, that's not how physics works.

If less air was moving under the car, it would have a lower speed, and a higher pressure, lifting the car (when compared to the air moving relatively fast over the top.) Faster air=lower pressure=lift. That's how a wing works, and it's all relative.

Flat floors make the air move faster. All else held constant, atoms per second, more air is moving under the vehicle with a flat floor. It makes the air velocity under the car fast (relative to the air going over) Fast air=low pressure=vacuum effect to the ground.

Exorcet, you're completely right, but we're saying the same thing from two view points. When I say compress, I'm not referring to density, but velocity (compress may be the wrong term). What's the proper term using energy to take a high volume of air and force it through an area of smaller volume to increase the velocity?

You're right about the ground proximity vs. the curve, but they're two synergistic factors, not mutually exclusive. Two sides of the same coin, so to speak.

The golfball thing, I was referring to it detaching "general" air, which it accomplishes, as you pointed out, by attaching "local" air (basically, a little air buffer between the relatively still car body and fast moving air, as seen from the perspective of the vehicle.) Again, it's a perspective thing.

Moral of the story, downforce is being generated, and that requires energy. As we know from physics, energy is never lost, only converted, but never at 100% efficiency. Converting the vehicle's forward energy into vertical (downforce) energy is the flat floor. Energy comes from the engine, and since that energy is no longer available to overcome air resistance, top speed is decreased.

 

[Exorcet]

Exorcet, you're completely right, but we're saying the same thing from two view points. When I say compress, I'm not referring to density, but velocity (compress may be the wrong term). What's the proper term using energy to take a high volume of air and force it through an area of smaller volume to increase the velocity?

Fair enough. The best way I can think of for explaining what happens to the air is to just say it's accelerated. If necessary add to that that lowering the flow area leads to acceleration because of mass conservation.

Be careful with terms like volume though as volume doesn't really apply to this case.

Moral of the story, downforce is being generated, and that requires energy. As we know from physics, energy is never lost, only converted, but never at 100% efficiency. Converting the vehicle's forward energy into vertical (downforce) energy is the flat floor. Energy comes from the engine, and since that energy is no longer available to overcome air resistance, top speed is decreased.

It is true, by creating a pressure gradient you're accelerating air and putting energy into it. This energy is in the form of linear and rotational kinetic energy. The ground effect heavily impairs the build up of rotational kinetic energy though. Linear kinetic energy is actually returned to the car in the diffuser (the air slows down).

But the big factor being overlooked is this: the open floor is just plain draggy. What little induced and skin friction drag the flat floor makes is far less of a penalty than the drag of an open floor. This is also why airdams are use on cars. The dam will create drag itself, but lower the drag of the car. I was looking for images of total pressure around a vehicle to show how underbody flow management using a flat floor is advantageous because the acceleration of air in that case is reversible, but I happened to find a site detailing a nice project on a Miata

http://hanchagroup.wordpress.com/author/paulwlucas/

Halfway down the page there are 6 configurations for the Miata. Look at numbers 2 and 5. 2 is the base configuration with a CD of .41. 5 is modified with a huge brick of an airdam, but has a CD of .31. That is a huge difference in favor of adding a barn door to the front of the car. It's advantageous because while the airdam is very very draggy, the open underbody of the car is even more draggy. However in this case, the airdam does something that the flat floor does not, which is shield the wheels. A Flat floor design may increase wheel drag. Also specific to this case, the Miata model is simplified. The floor is specifically mentioned as one such simplified area and the simple model of the car was measured with a lower CD than that of the real car.

In the end, you're technically correct in saying that the flat floor create drag. However it is not unreasonable to expect that the floor lowers the drag of the vehicle while creating drag of it own. This goes double when you add a diffuser since the acceleration of the air by the floor becomes reversible.

 

[ZedMan1996]

ZedMan, that's not how physics works.

If less air was moving under the car, it would have a lower speed, and a higher pressure, lifting the car (when compared to the air moving relatively fast over the top.) Faster air=lower pressure=lift. That's how a wing works, and it's all relative.

Flat floors make the air move faster. All else held constant, atoms per second, more air is moving under the vehicle with a flat floor. It makes the air velocity under the car fast (relative to the air going over) Fast air=low pressure=vacuum effect to the ground.

Exorcet, you're completely right, but we're saying the same thing from two view points. When I say compress, I'm not referring to density, but velocity (compress may be the wrong term). What's the proper term using energy to take a high volume of air and force it through an area of smaller volume to increase the velocity?

You're right about the ground proximity vs. the curve, but they're two synergistic factors, not mutually exclusive. Two sides of the same coin, so to speak.

The golfball thing, I was referring to it detaching "general" air, which it accomplishes, as you pointed out, by attaching "local" air (basically, a little air buffer between the relatively still car body and fast moving air, as seen from the perspective of the vehicle.) Again, it's a perspective thing.

Moral of the story, downforce is being generated, and that requires energy. As we know from physics, energy is never lost, only converted, but never at 100% efficiency. Converting the vehicle's forward energy into vertical (downforce) energy is the flat floor. Energy comes from the engine, and since that energy is no longer available to overcome air resistance, top speed is decreased.

All I can say is...

Ooops...

 

[raytard]

Exo, again, I have to agree, you know your stuff. On paper, in real life, in normal situations, flat floors overwhelmingly decrease the coefficient of air resistance compared to an open floor. This holds true even at immense speeds (200MPH+), just look at F1 cars.

In the game, we don't know the coefficient either way, "open floor" may actually have a negligible or non-existant air resistance (which makes sense considering all the "fast" cars in the game, especially at launch). While a flat floor is "lower resistance" than normal, any resistance might be seen as "more than 0" by the game of normal didn't have a resistance to begin with.

At high speeds (150mph+ in the case of my NSX-R, 250+mph on my ZZII), it's certainly reasonable to believe that the drop in the coefficient of air resistance is negated by the added resistance of generating all that downforce. We both agree it takes some amount of energy to create the downforce. More speed means more downforce, which means more parasitic energy loss. At some point (or speed), the energy going into generating downforce must surpass the resistance savings and produce a net increase in resistance, right?

 

[Exorcet]

In the game, we don't know the coefficient either way, "open floor" may actually have a negligible or non-existant air resistance (which makes sense considering all the "fast" cars in the game, especially at launch). While a flat floor is "lower resistance" than normal, any resistance might be seen as "more than 0" by the game of normal didn't have a resistance to begin with.

That's an interesting way of looking at it and might be a possible explanation for what's seen in game. However, if the aero model is that advanced so that the stock car is broken up into parts already, it's strange that the floor would have no drag coefficient. It's also strange that combining the flat floor with a diffuser would not then lead to increased pressure recovery.

I would expect the drag from the floor would be factored into the overall CD which is a number PD would just get from the manufacturer. The floor probably modifies the CD by a fixed amount. This is testable in game as we can calculate the drag ratio from top speeds with and without the floor.

At high speeds (150mph+ in the case of my NSX-R, 250+mph on my ZZII), it's certainly reasonable to believe that the drop in the coefficient of air resistance is negated by the added resistance of generating all that downforce. We both agree it takes some amount of energy to create the downforce. More speed means more downforce, which means more parasitic energy loss. At some point (or speed), the energy going into generating downforce must surpass the resistance savings and produce a net increase in resistance, right?

But they are both drag, so they both grow with V^2. Both the benefit and the induced drag would grow at the same rate, so they would always hold a fixed ratio.

Remember that drag takes energy too. You're turning kinetic energy into heat and also dragging around a wake behind your car. The energy going into that goes up with speed. Also the energy lost in the wake is not reversible. Total pressure drops in the wake. Total pressure is constant under a flat floor and in a non stalled diffuser.

 

[wudy201]

Is there a simple answer for this. What would be the difference in the car with the flat floor. Example, is it faster, slower, corner better, corner worse, handle better or worse overall,
Is it worth installing, is there any real difference, and i'm talking about the video GAME, not real life. Anybody that could answer this without going into the science of it would be greatly appreciated. I am not a good tuner in this game and i've been spending days and putting 800+ miles on some cars trying to tune it and just am not getting anywhere, I've printed out dozens of articles explaining tuning and the parts and what they do I just don't know how to decide what part to tune since it seems like some parts in a way do the same thing.

 

[ryzno]

Is there a simple answer for this. What would be the difference in the car with the flat floor. Example, is it faster, slower, corner better, corner worse, handle better or worse overall,
Is it worth installing, is there any real difference, and i'm talking about the video GAME, not real life. Anybody that could answer this without going into the science of it would be greatly appreciated. I am not a good tuner in this game and i've been spending days and putting 800+ miles on some cars trying to tune it and just am not getting anywhere, I've printed out dozens of articles explaining tuning and the parts and what they do I just don't know how to decide what part to tune since it seems like some parts in a way do the same thing.

Simple answer...
The car will have lower top speed, and slower acceration at high speeds.
It will corner and handle better with the added downforce.

Is it worth it?
For drag racing no. Drifting Im not a drifter but I doubt they want more downforce. Circuit racing I would say yes, but you have to adjust for or accept the slightly lower top speed.
Hope I kept it simple.

 

[Downhill Dino]

I wouldn't even recommend it for circuit racing, especially if you're under a performance point cap, as sacrificing around 30 performance points to it is not worth the added handling ability.

 

[wudy201]

Simple answer...
The car will have lower top speed, and slower acceration at high speeds.
It will corner and handle better with the added downforce.

Is it worth it?
For drag racing no. Drifting Im not a drifter but I doubt they want more downforce. Circuit racing I would say yes, but you have to adjust for or accept the slightly lower top speed.
Hope I kept it simple.

You did and thanks. I can follow your answer and clearly understand the concept.

 

[citycar]

What i find is that with traction control and abs turned on my brother and i put in slower lap times. With 'skid force recovery' its even worse.

On events where skid force recovery was forced 'on' we used to remove the rear wing in an effort to negate the effects it had on our tunes and our driving and we would see improved lap times (compared to skid force recovery 'on' with a rear wing on).

For those experiencing slower lap times and lower top speeds on straights between corners it might be worth experimenting with reducing the number of driving aids or reducing the 'strength' (of said driving aids) and/or reducing the rear wing as it could be having an effect with the flat floor which is negative for you, but positive for others.

 

[Kakti]

ZedMan, that's not how physics works.
What's the proper term using energy to take a high volume of air and force it through an area of smaller volume to increase the velocity?

Essentially what you're describing is compressing air - taking a given volume of a compressible gas and forcing it into a smaller volume, thereby compressing it. If it has an exit (i.e. not in a container) then the velocity will increase per the principle of Conservation of Energy. Two laws that directly apply to this topic are Bernoulli's Principle regarding compressible gasses, and the Venturi Effect. Bernoulli's I believe addresses taking a gas and forcing it into a smaller volume, thereby compressing it and increasing its pressure and velocity. Venturi describes the opposite, a gas entering a lower pressure zone and slowing down.

https://en.wikipedia.org/wiki/Venturi_effect
https://en.wikipedia.org/wiki/Bernoulli's_principle