Downforce - how much?

[marcush.]

thank you reca ,
even F1 one so called experts like Niki Lauda do not know what a diffuser
does do.....
funny enough a badly designed big diffuser does not provide any thing in terms of download,as well as a floor not run in rake (nose down)or too far away from the ground.
about those flexing parts:things that flex tend not to transfer forces to the main body very well ,in extreme cases if the part would make contact with the trackthe download would decrease ....if the flexing is within limits ,downloads level out with increasing speed ,so one might run a little more angle of attack and gain some downforce at lower speeds without sacrifying topspeed.

[Reca]

I’m pleased that you agree with me about the diffuser but I really don’t understand your explanation about flexing elements (especially the part “things that flex tend not to transfer forces to the main body very well”). I agree with the conclusion (more downforce at low speed without sacrificing top speed) but the way I read your explanation hmm... maybe I don’t understand it in the right way, could you please add some details ?

[Monstrobolaxa]

Hummm......well....I think I understood the flexing things......well in 1993 Jordan had a problem with the difuser....it flexed at high speeds which reduced the downforce that it created.....what I think marcush meant was that the flexture of materials might bring some problems to the amount of downforce produced.

[marcush.]

yep that was what I wanted to say.
The force needed to flex aerodynamic surfaces will have to be subtracted
from the downforce ,and the question is :is the newly created surface the shape that brings the best downforce?
It is quite complicated to understand ,I know.
Did someone actually see the vibrations of the williams Frontwing assembly in the last race? The Thing seems to suffer buffetting or something else at speed ..if i observed correctly ,the Flap is vibrating quite a bit and the whole Frontwing assembly seems to move from side to side under braking(?) ,or maybe this is the front suspension (twinkeel...) moving relative to the rest of the car ...I´m not sure....

[Reca]

I do understand the correlation between aero load and deformations (I hope the hours I’ve spent studying Aeroelasticity aren’t just wasted...), what I don’t understand is this part :

things that flex tend not to transfer forces to the main body very well

and now, coupled with :

The force needed to flex aerodynamic surfaces will have to be subtracted from the downforce

Are you saying that not the total amount of downforce generated by the wing, while flexing, is transmitted to the body, but a part is somehow “absorbed” in the deformation ??

[marcush.]

Well it depends off course.But I would bet a lot of non correlation comes from the fact that parts aren´t stiff enough .Having elastic deformation you just add another variable to the equation ,as the deformed part of course has different flow characteristics.
For example ,a bending rear floor could reduce your rake considerably ,reducing downforce ,so you would have to compensate with stiffer springs or more ride height at the rear...

[Reca]

Putting aside for the moment the part about load transfer (think about it), it seems to me that there’s a misunderstanding on an higher level here because we are talking about different things. You are considering the flexing only as a bad thing that must be avoided because could lead to a difference between aerodynamic characteristics computed/measured in wind tunnel and the real behaviour on the car, that was a problem in the past, nowadays I hope not.
What I’m saying is the opposite. The designers wants the part to deform, but they want it to deform basically in a “programmed” way, with a sort of control on aerodynamic coefficients with speed. That’s what Seymour was referring to. On the Ferrari Enzo (and on the first cars with aero device in late 60s) this control is very precise because it’s made via movable devices (with rigid degrees of freedom), clearly that's not allowed by rules.
A little different function have the movable devices on most of production cars (for example on the Porsche Boxster and 911), aimed to correct a design that otherwise would generate too much lift (often with uneven variation on the front and rear) causing instability at high speed.

[marcush.]

well,next try:
You said ,the elastic deformation is wanted and as long as the part does what it is designed to do I do agree .

And obviously a movable device was not part of our discussion.

You would agree ,that a floor that is sucked down to the ground bending instead of pulling the car down is a bad thing,and that was my point.

As for the bending wings we saw some years ago,I would conclude these could give higher downforce at lower speeds without sacrifying top speed.

the vibrating flaps we frequently see ,is this designed or just ,random event with no consequence?

[Monstrobolaxa]

Random event.....with some consequency but not VERY VERY important....you do lose some downforce but not as much as the difuser bending....(the following numbers are an example) if the difuser bends you could lose almost 100% of the downforce but to giva an idea lets say 90%.....and the wings vibrating....well it could go up to 10% at the most. (personal opinion not based on any calculations).

[marcush.]

I`m with you totally.
I actually did some testing with all sorts of diffusers and had at one time a monster diffusser under the car with three really big tunnels,but if you removed it from the car and ran without the device ,their was NO change
at all.So clearly it did nothing to the downforce.
Increasing Bottom stiffness thru Honeycomb Sandwich and a full floor running from the front axle to the rear with something like 20 mm rake
and a very very basic diffuser showed huge gains....
So in that crude area I´m at home (no Tunnel ,no CFD) STIFF works better than hoping of things bending in amanner that could perhaps increase downforce,err boundry layer control I wanted to say.
By the way ,the full width Diffuser was a total flop,a narrower one with feet (horizotal plates matetd to the outside was much more efficient,as was closing all holes in the floor and trying to capture the air for engine compartment from the front of the car.

[Reca]

Marcush, I see that in my previous posts I was unable to show to you what I don’t understand in your comments. Hope you don’t mind if I try again.
You wrote :

- "things that flex tend not to transfer forces to the main body very well"
- "The force needed to flex aerodynamic surfaces will have to be subtracted from the downforce"
- "a floor that is sucked down to the ground bending instead of pulling the car down"

Now my question, the same as before.
Assume you have a bending rear wing that, at a certain speed and in the final deformed shape generates 1000 N of vertical aero force. Is that force, 1000 N, entirely transferred to the car body or from the 1000 N you have to subtract the force needed to keep the new shape and so only a part, say 800 N, is transferred to the car body ?

[EAKMotorsports]

great topic..If someone knows how much the ´93 F1 generate I´ll be happy.

[Belatti]

great topic..If someone knows how much the ´93 F1 generate I´ll be happy.

1216,3 Kg at 281 Kph.

[xpensive]

great topic..If someone knows how much the ´93 F1 generate I´ll be happy.

1216,3 Kg at 281 Kph.

That's most affirmative, but I wouldn't use the decimal without knowing the air-density with five digits.

[marcush.]

downForce should be in Newton , as I was instructed by some swedish tribologist....thanks for : Me not being the only one getting squared up with my
units at times...