How much is a "point" of downforce?

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raymondu999
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How much is a "point" of downforce?

Postby raymondu999 » Mon Mar 29, 2010 5:37 pm

I've often heard of downforce quantified in "points." I saw in one of the videos on YouTube of turning the mp4-24 into a race winner that they added "30 points." How much is a point of downforce? For example, in terms of downforce, at x speed, how much more downforce does an extra point of downforce generate?
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Re: How much is a "point" of downforce?

Postby Giblet » Mon Mar 29, 2010 5:41 pm

raymondu999 wrote:I've often heard of downforce quantified in "points." I saw in one of the videos on YouTube of turning the mp4-24 into a race winner that they added "30 points." How much is a point of downforce? For example, in terms of downforce, at x speed, how much more downforce does an extra point of downforce generate?


A point is the same as a click. It's an arbitrary number for us, but a real number to the team. They know what one click is, but you can just think of it as one 'step'.

A click on a Reanault wing is not the same as a point on a Ferrari wing.

They sometimes call it a turn, or half turn of downforce as it's done with a ratchet.
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raymondu999
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Re: How much is a "point" of downforce?

Postby raymondu999 » Mon Mar 29, 2010 5:45 pm

AH. So it's actually just an internal convention on how to quantify it?
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shelly
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Re: How much is a "point" of downforce?

Postby shelly » Mon Mar 29, 2010 10:39 pm

As far as I know in most of the teams 1 point corresponds to 0.000048*(speed in kph)^2 kg of downforce.
i.e @ 250kph 1 point is roughly 3kg of downforce; @ 300 kph 1 point is 4.3kg of downforce
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Re: How much is a "point" of downforce?

Postby Jersey Tom » Tue Mar 30, 2010 12:10 am

shelly wrote:As far as I know in most of the teams 1 point corresponds to 0.000048*(speed in kph)^2 kg of downforce.
i.e @ 250kph 1 point is roughly 3kg of downforce; @ 300 kph 1 point is 4.3kg of downforce


Where did you come across this?
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Richard
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Re: How much is a "point" of downforce?

Postby Richard » Tue Mar 30, 2010 7:42 am

I'm intrigued by the 0.000048. It looks like one of those magic constants that has a simple neat origin.

twoshots
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Re: How much is a "point" of downforce?

Postby twoshots » Tue Mar 30, 2010 8:27 am

Always one of those little things that I wondered about. Not being an aero guy myself.

In fact it cropped up at the weekend with Whitmarsh's comments that Hamilton losing his front wing end plate cost 10 points of downforce. 10 'sounds' like a lot, but without a way to quantify it with units...

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Re: How much is a "point" of downforce?

Postby newbie » Wed Mar 31, 2010 12:09 am

a point of downforce is the same throughout the F1 teams from what I understand. downforce is measured not in Cl (lift coefficient) but in a similar parameter with a similar magnitude. A point is worth 0.01 of this parameter and a unit is worth 0.001. so for example if a hypothetical F1 DID use Cl to quantify downforce and their F1 car has a Cl of 4.000, then adding 30 points of downforce would bring the car up to a Cl of 4.300.

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Re: How much is a "point" of downforce?

Postby Jersey Tom » Wed Mar 31, 2010 12:47 am

Honestly sounds like BS to me. An arbitrary measure. Could be whatever units you want. Pounds, kilos, some dimensionless measure...
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Re: How much is a "point" of downforce?

Postby Mystery Steve » Wed Mar 31, 2010 3:46 am

newbie wrote:a point of downforce is the same throughout the F1 teams from what I understand. downforce is measured not in Cl (lift coefficient) but in a similar parameter with a similar magnitude. A point is worth 0.01 of this parameter and a unit is worth 0.001. so for example if a hypothetical F1 DID use Cl to quantify downforce and their F1 car has a Cl of 4.000, then adding 30 points of downforce would bring the car up to a Cl of 4.300.



I think this is common in general. Simon McBeath's columns in Racecar Engineering magazine use this convention, for example.

shelly
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Re: How much is a "point" of downforce?

Postby shelly » Thu Apr 01, 2010 12:10 am

I agree with newbie and mistery steve.

Downforce=0.5*(air density)*(speed)^2*(reference area)*Cl

Usually you don't work with Cl, but with [reference area*Cl], namely SCl.
SCl has the dimension of surface, i.e. m^2 in SI; typical values are between 2 and 5.

1 point corresponds to SCl=0.01m^2:
if your car improves from SCl=4 to SCl=4.30 it has gained 30 points of downforce.

Working with points is easier because you work with numbers like 5, 7, 30 instead of 0.05, 0.07, 0.30.

If in the formula for downforce you substitute air density=1.22 kg/m^3 and take into account dividing by 3.6^2 (conversion for speed from m/s to kph) and by 9.81 (conversion from N to kg) you get

Downforce=0.0048*(speed in kph)^2*SCl

and finally with 1 point corresponding to SCl=0.01m^2

1 point [kg] = 0.000048*(speed [kph])^2
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newbie
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Re: How much is a "point" of downforce?

Postby newbie » Fri Apr 02, 2010 12:21 am

shelly hit the nail on the head. using SCL rather than CL is advantageous because you dont need to continuously keep track of frontal area.

autogyro
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Re: How much is a "point" of downforce?

Postby autogyro » Fri Apr 02, 2010 12:40 am

Well I think it is just a way to avoid placing an understandable measure on it that others would relate to.
This is to make it difficult for the FIA to define a set maximum for regulation.
An old saying of mine. Bulls--- baffles brains covers it.

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Re: How much is a "point" of downforce?

Postby Pierce89 » Fri Apr 02, 2010 6:39 am

autogyro wrote:Well I think it is just a way to avoid placing an understandable measure on it that others would relate to.
This is to make it difficult for the FIA to define a set maximum for regulation.
An old saying of mine. Bulls--- baffles brains covers it.

If that's the case, why would Mcbeath in Racecar Engineering use points of DF as a reference in articles about modifying 30 year old racecars
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Re: How much is a "point" of downforce?

Postby autogyro » Fri Apr 02, 2010 12:17 pm

Pierce89 wrote:
autogyro wrote:Well I think it is just a way to avoid placing an understandable measure on it that others would relate to.
This is to make it difficult for the FIA to define a set maximum for regulation.
An old saying of mine. Bulls--- baffles brains covers it.

If that's the case, why would Mcbeath in Racecar Engineering use points of DF as a reference in articles about modifying 30 year old racecars


You tell me?




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