NoGripRacing.com
Old 21 April 13, 15:15   #1
poet
 
poet's Avatar
 
Join Date: Jan 2013
Location: t'north
Default Downforce?

Is there a point at which downforce fails?

I know the basic principles (air-pressure differences/upside-down plane etc), but always thought the faster you go - the more downforce you have, seems to make sense.
But is there a point that becomes no longer true? And if so, what causes the downforce to drop, or is it something like friction/air resistance overcomes the beneficial effects of downforce?

Reasonably simple answers please, its Sunday.
poet is offline   Reply With Quote
Old 21 April 13, 15:22   #2
Roger
TT/3
 
Roger's Avatar
 
Join Date: May 2003
Location: England
Age: 55
Default

I think the answer is pretty much 'supersonic' - we have to assume that the flow remains attached at the higher speeds to answer your question.
Roger is offline   Reply With Quote
Old 21 April 13, 15:38   #3
MickeyMouse
 
MickeyMouse's Avatar
 
Join Date: Jan 2007
Location: Ohio, USA
Age: 27
Default

Downforce would presumably keep increasing until when near supersonic speeds. When shock waves start to form, the airflow around the wings change considerably and would have to be accounted for. Aircraft wings for supersonic and subsonic planes are quite different, for example.
Of course, an F1 car could never go that fast, so it's a rather moot point. In practical terms, downforce (and drag) will keep getting stronger the faster you go.
MickeyMouse is offline   Reply With Quote
Old 21 April 13, 15:48   #4
poet
 
poet's Avatar
 
Join Date: Jan 2013
Location: t'north
Default

Quote:
Originally Posted by MickeyMouse View Post
Downforce would presumably keep increasing until when near supersonic speeds. When shock waves start to form, the airflow around the wings change considerably and would have to be accounted for. Aircraft wings for supersonic and subsonic planes are quite different, for example.
Of course, an F1 car could never go that fast, so it's a rather moot point. In practical terms, downforce (and drag) will keep getting stronger the faster you go.
That's what I thought.


I asked, because I notice in a lot of Formula based titles or games with F1/F3000 in, that it seems that downforce drops off when you approach the cars top speed, and they start sliding about on the track more (take the F3000 in GTRE for instance.).

But could that not be a factor of the increased downforce putting too much force on the tyres, and the rubber not being able to cope?
poet is offline   Reply With Quote
Old 21 April 13, 15:50   #5
Roger
TT/3
 
Roger's Avatar
 
Join Date: May 2003
Location: England
Age: 55
Default

Two possible answers (I think)

1. Does the flow become detached and then stall the wing? Not very likely in a sim

2. You are right about tyres - they can become saturated
Roger is offline   Reply With Quote
Old 21 April 13, 16:17   #6
MickeyMouse
 
MickeyMouse's Avatar
 
Join Date: Jan 2007
Location: Ohio, USA
Age: 27
Default

Quote:
Originally Posted by poet View Post
I asked, because I notice in a lot of Formula based titles or games with F1/F3000 in, that it seems that downforce drops off when you approach the cars top speed, and they start sliding about on the track more (take the F3000 in GTRE for instance.).
I can't say I've really noticed that in sims (I'm not familiar with GTRE). Of course, there is a difference between turn rate and turn radius. The car can pull more lateral Gs at higher speeds, but your turn radius will increase as well. Naturally, the balance of the car will also change (sometimes considerably) depending on speed and the setup.

Quote:
Originally Posted by poet View Post
But could that not be a factor of the increased downforce putting too much force on the tyres, and the rubber not being able to cope?
Tire forces increase with the load, increasing the amount of grip the tire can generate, with no (practical) limit. But again, the momentum and kinetic energy of the car also increase, requiring more tire forces to generate the same turn radius.
MickeyMouse is offline   Reply With Quote
Old 21 April 13, 17:13   #7
poet
 
poet's Avatar
 
Join Date: Jan 2013
Location: t'north
Default

Quote:
Originally Posted by MickeyMouse View Post
Tire forces increase with the load, increasing the amount of grip the tire can generate, with no (practical) limit. But again, the momentum and kinetic energy of the car also increase, requiring more tire forces to generate the same turn radius.
I'm not sure if its turn radius I'm experiencing, and its not just GTRE I've noticed it in, other sims/games too with cars that are more geared towards downforce (Zonda R in Shift series for example)

Say in GTRE going down Nords in an F3000.
You can tell as you pick up speed that downforce increases, and its much easier to handle round corners.
But going down the back-straight, its like the downforce drops off as you pick up towards top-speed, so the tiniest left or right adjustment and the car just starts drifting off to the side, almost like its on ice, like the downforce is no longer holding it to the road as much.

Of course it could be just game mechanics, then, sorry if this thread is in the wrong section, but then its odd that I've noticed in a couple of games (at least), and so I wondered if it was a real-world effect of friction or tyre limits etc.
Sorry, I'm not the best at describing these things.
poet is offline   Reply With Quote
Old 21 April 13, 17:27   #8
David Wright
 
David Wright's Avatar
 
Join Date: Jun 2006
Location: UK
Default

The ISI physics engine works on increasing downforce with the square of velocity. So the wings will not lose downforce at high speed.

Tyre grip increases with vertical load, but if you double the load you don't get double the grip. This is why a light car will corner faster than a heavy car on the same tyres. However, it is a gradual effect, and grip will not fall away, it just won't increase as fast as the downforce does.

There are a couple of unknowns.

1. Downforce can result in you hitting the bump-stops which might give unwanted results. When you hit the bumpstops you tend to loose grip. On a low car like the F3000 you might even hit the skid plates at the bottom of the car in which case you will lose grip.

2. The diffuser depends not only on velocity but also the ride height and pitch of the car. Its possible the diffuser could be losing downforce at high speeds if the set-up isn't optimal.

EDIT - the last thing to remember is you need a great deal more grip to corner at high speed. The grip you need varies with the square of your speed. So to go round a corner at 200 mph requires four times the grip than going round it at 100 mph.

Last edited by David Wright; 21 April 13 at 17:39.
David Wright is offline   Reply With Quote
Old 21 April 13, 18:07   #9
MickeyMouse
 
MickeyMouse's Avatar
 
Join Date: Jan 2007
Location: Ohio, USA
Age: 27
Default

Yeah, we'll probably need more information to explain your specific situation. Videos, setups and telemetry, for example. But in the general case of "in reality, does a high downforce car lose grip and slide at high speeds?", the answer is no.
MickeyMouse is offline   Reply With Quote
Old 21 April 13, 19:27   #10
jgf
 
jgf's Avatar
 
Join Date: Nov 2005
Location: Columbus, OH
Age: 60
Default

Quote:
Originally Posted by MickeyMouse View Post
Yeah, we'll probably need more information to explain your specific situation. Videos, setups and telemetry, for example. But in the general case of "in reality, does a high downforce car lose grip and slide at high speeds?", the answer is no.
You've obviously never watched Indycars. I haven't checked modern specs but in the CART days Indycars generated downforce equivalent to roughly three times the cars' actual weight; at speed they could have literally run "on the ceiling". And they would slide. Whenever lateral force exceeds the tires' grip, regardless of downforce, the car will slide.
jgf is offline   Reply With Quote
Old 21 April 13, 19:38   #11
poet
 
poet's Avatar
 
Join Date: Jan 2013
Location: t'north
Default

Quote:
Originally Posted by MickeyMouse View Post
Yeah, we'll probably need more information to explain your specific situation. Videos, setups and telemetry


(*busy off looking for telemetry software)
poet is offline   Reply With Quote
Old 22 April 13, 11:03   #12
MickeyMouse
 
MickeyMouse's Avatar
 
Join Date: Jan 2007
Location: Ohio, USA
Age: 27
Default

Quote:
Originally Posted by jgf View Post
You've obviously never watched Indycars. I haven't checked modern specs but in the CART days Indycars generated downforce equivalent to roughly three times the cars' actual weight; at speed they could have literally run "on the ceiling". And they would slide. Whenever lateral force exceeds the tires' grip, regardless of downforce, the car will slide.
I think you're making some terminology mistakes there.
MickeyMouse is offline   Reply With Quote
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 08:43.


Powered by vBulletin® - Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.

www.nogripracing.com 2003 - 2014
Page generated in 0.12701 seconds with 10 queries