Downforce front and rear balance, distribution?

[Ben_tire]

Hello,

i have a basic question. I try for my self a bit calculation on a basic open wheel Race car concept car. and try to understand some things.

I want to know how much down force i need for a turn with 1,6g. With a my friction coef. and the mass of the car and the The equ.: F=m*a and Fy=Mue*Fz i calculate for example 3500N for Fz is needed.

with the weightransfer calculation in turn with 1,6g i can calculate my Axle/ Tire Loads on front and rear generate form the car:

Fzf: 1388N Fzr: 1680 Fz complete: 3068N

Now: i subtract the 3500N Need downforce minus 3068N = 438N Downforce i need from my wings.

But How can i calculate how much i have to put on the front and how much on rear from the 438N downforce i need?
I think a good aproximation is to take the same amount as the Percent of the Weight transfer? Or the static Weight distribution?

And what about a diffusor? i think the best is that the center of pressure of the diffusor is at the same location as the cg?

I´ve read that 35-40% of the complete downforce is generate by the front Axle? Why this? How much is generate by the diffusor and the rear wing for a general open wheel race car, as a rule of thumb?

I would be great to discuss a few things here.


Thank you

Ben

[Greg Locock]

I suppose one approach would be to apply the downforce so that it is resolved at the contact patch in the same proportion as the static axle loads, so that the balance of the car doesn't change too much.

[Tim.Wright]

Use the often forgotten fact that cornering stiffness is roughly proportional to vertical force to express your vehicle dynamics metrics such as US or stability factor or directional stability etc as a function of aero balance. Choose the balance you want at a nominated low speed, and the balance you want at a nominated high speed and you can then solve for the required aero balance to achieve that. If you don't want any difference between low and high speed, the your aero balance will come out to be the same as the mass distribution.

Then there is a line of thought which suggests that you should put the aero C.o.P. behind the C.o.G. for better stability, however consider that there is no such thing is a single unique aerodynamic C.o.P. Aero forces, like any other force, can act at an infinite number of locations along its line of action.

[Ben_tire]

Hello,

Thank you, for your answer. I have to think about that. Can you please make it visual what you mean with your sentense about the aero C.o.P. ? Do you mean the whole aero C.o.P. oder the C.o.P. of the diffusor?

Is it the normal way to set the aero balance at high and low speed is nearly the same? so like the static weight distribution?

At what situations it is benefit that the aero balance is differnt?

Thank you.

[olefud]

Hello,

Thank you, for your answer. I have to think about that. Can you please make it visual what you mean with your sentense about the aero C.o.P. ? Do you mean the whole aero C.o.P. oder the C.o.P. of the diffusor?

Is it the normal way to set the aero balance at high and low speed is nearly the same? so like the static weight distribution?

At what situations it is benefit that the aero balance is differnt?

Thank you.

Keep in mind that braking and cornering may well benefit differently from total downforce distribution. Braking will always benefit from equal and greater downforce. Cornering ranges from flat out with less-than-max downforce to more downforce yielding faster cornering, the latter being at the expense of greater drag. It even gets tactical in that faster cornering carries into the next straight while braking benefits lap times rather less. But braking probable provides the most effective passing advantage.

[dynatune]

Typically on a wing car you have the possibility to put on top of a mechanical balance (that by itself can be aeroload dependent) the aerodynamic balance that of course will be most significant in the high speed range. It would for instance permit to make a mechanically oversteering car become more understeering at high speed or vice versa. Since there is a close interaction of riding heights and aerodynamics and riding heights and suspension stiffness one can easily oversee or miss some interactions jumping to incorrect conclusions, not to mention Tim's comment on tire cornering stiffness dependency on vertical load too. I have always found great benefit in creating for myself some more or less complex excel sheets to put some numbers next to my ideas but then those sheets started to become more complex and turned eventually complete programs. The deeper you dive the more questions come up. Beware of the danger

Cheers,
dynatune, http://www.dynatune-xl.com