Red Bull RB7 Renault

[wesley123]

no offence marekk but that is rubbish, would mean this was linear, which it obviously is not.

At one point the ground effects for the whole floor is gone(of course these are there but higher rake would reduce this) and the front wing will also run closer, at one point this will stall, reducing downforce. Of course designing your car around this could reduce this, but it will still happen at some point.

[marekk]

no offence marekk but that is rubbish, would mean this was linear, which it obviously is not.

At one point the ground effects for the whole floor is gone(of course these are there but higher rake would reduce this) and the front wing will also run closer, at one point this will stall, reducing downforce. Of course designing your car around this could reduce this, but it will still happen at some point.

Rubbish ? Obviously not linear ?



Ground effect is downforce/lift increase when ride height over ground is less then wingspan. If it's less then aprox quarter of chord, this increase starts to seriously roar. At 10% chord - lets say 140mm for F1 car, it's more then 50% bigger then out of ground effect.

And due to stepped floor, you can't stall it by chocking the inlet, and if running rake less then 10 degree, there is no risk of stalling the flow along its way to diffuser.

[PlatinumZealot]

a WHOLE car is not so simple. NEither is a multi element wing. So Yes you cannot make those simple assumptions. For all we know downforce increases all over. Because the rear winds would also have a higher angle of attack with more rake as well. THe boundary layer under the car also disrupts less the diffuser.

[wesley123]

no it isnt liniar as you can see.

The blue line might look liniar, but it is not. 0.5 lift coef. at aprox. 3AoA, if it is liniar that would mean at 1.0 lift coef the AoA is 6 It is not. It looks light a straight line yes, but that is due to the small steps. Also, like i said at a point this rake stops giving additional downforce, which you also see in the blue line. And what you take is a flat plane, nowhere near what is done on a F1 car.

[marekk]

no it isnt liniar as you can see.

The blue line might look liniar, but it is not. 0.5 lift coef. at aprox. 3AoA, if it is liniar that would mean at 1.0 lift coef the AoA is 6 It is not. It looks light a straight line yes, but that is due to the small steps. Also, like i said at a point this rake stops giving additional downforce, which you also see in the blue line. And what you take is a flat plane, nowhere near what is done on a F1 car.

According to thin airfoil theory it's perfectly linear.
In real world it's not that perfect, but for small angles off attack wind tunnel data for common airfoils is very close to linear.

At a point this rake stops giving additional downforce, but this point is near stall angle of attack, which is as you can see > 15 degree. And we are apeaking about 2-4 degree.

@n_smikle: As said, real numbers for F1 car will be different, but still significant (even if you take into account only floor parts not covered by bodywork), and i can't imagine any team would simply ignore this in car's design.

Interesting implication of RB7 rake-centric design (my speculation):

Knowing that both rear wing and diffuser work at the very edge of the stall, if they setup the car softer on front axle or/and initiate front dive by flexing/pivoting front wing, car rake increases, so will diff's and rear wing's angle of attack, possibile over the point of maximum Cl. Once on the other side of Cl curve, downforce on the rear decreases, rear suspension goes up, increasing AoA further, and so on up to the point predefined by rear suspension's setup. This way they could pivot the car around the axle situated somewhere between front and rear wheels.

Almost impossible to control, lots of additional drag and quite sudden change of car balance, but maybe could bring nett gain ?

[PlatinumZealot]

Ok, a little riddle again, how much degrees of rake do you think the redBull has over the Mclaren?

Then think of how much mm at the rear is the redBull higher than the Mclaren and how much mm at the front...

See what I'm getting at?

The change in rake is probalby a 1/4 of a degree the most. Now match it on your graph - (though it's not relevant for the whole car lets say the Front wing/rear wing). However the change in ride height at the back/ or front can be up to 1 cm or more as seen on the RedBull 7.

So we can deduce, the extra Downfroce from angle of attack by increasing the rake is not as significant as the change in heights of front and back in respect Downforce from ground effects.

[PaulB]

Sorry, that's off-topic, but i had to laught when i read that. Who the hell said that sentence in n smikles signature?

"Hamilton is the car behind. Hamilton is the car behind. We are going to have start defending like no tomorrow."

[kalinka]

Not so much revealing, but a little more info about RB7 KERS problems :

http://www.totalf1.com/full_story/view/ ... 7__report/

[tok-tokkie]

no it isnt liniar as you can see.

The blue line might look liniar, but it is not. 0.5 lift coef. at aprox. 3AoA, if it is liniar that would mean at 1.0 lift coef the AoA is 6 It is not. It looks light a straight line yes, but that is due to the small steps. Also, like i said at a point this rake stops giving additional downforce, which you also see in the blue line. And what you take is a flat plane, nowhere near what is done on a F1 car.

You are confusing linear with proportional. If it was 0.5 at 3, 6 & 9 it would be perfectly linear. So too if it was 0.5, 1 ,1.5 at those AoA.

[mep]

no it isnt liniar as you can see.

The blue line might look liniar, but it is not. 0.5 lift coef. at aprox. 3AoA, if it is liniar that would mean at 1.0 lift coef the AoA is 6 It is not. It looks light a straight line yes, but that is due to the small steps. Also, like i said at a point this rake stops giving additional downforce, which you also see in the blue line. And what you take is a flat plane, nowhere near what is done on a F1 car.

It is a line your calculation is wrong.
Did you notice that the blue graph does not cross Y-Axis at zero?
The formula for a line is:
y= mx + b
You left out that b.
b is around 0,35

let’s take two points to prove its linear.
(5/0,7) and (10/1,05)

Let’s calculate m with first point:
0,7=m*5+0,35
m=0,07

Let’s check now if second point is located on that line.
y= 0,07*10+0,35=1,05
You see it fits very well.
Therefore it’s a line.

[SiLo]

Back on topic...

If they have to move around all the KERS pieces, do we think they will have an even longer time trying to get it right over just fixing it where it is?

[beelsebob]

no it isnt liniar as you can see.

The blue line might look liniar, but it is not. 0.5 lift coef. at aprox. 3AoA, if it is liniar that would mean at 1.0 lift coef the AoA is 6 It is not. It looks light a straight line yes, but that is due to the small steps. Also, like i said at a point this rake stops giving additional downforce, which you also see in the blue line. And what you take is a flat plane, nowhere near what is done on a F1 car.

It is a line your calculation is wrong.
Did you notice that the blue graph does not cross Y-Axis at zero?
The formula for a line is:
y= mx + b
You left out that b.
b is around 0,35

let’s take two points to prove its linear.
(5/0,7) and (10/1,05)

Let’s calculate m with first point:
0,7=m*5+0,35
m=0,07

Let’s check now if second point is located on that line.
y= 0,07*10+0,35=1,05
You see it fits very well.
Therefore it’s a line.

Absence of evidence is not evidence of absence. Simply saying "I tried a data point and it looked close enough" is not final evidence that all data points are exactly (or even roughly) right.

[shelly]

What the rake really does is compensate for the boundary layer build up.
Too much may lose the effect of creating high velocity air under the car.
Having the rake just about offset to the boundary layer gradient is the right angle to have.

ringo you are wrong. Rake gives you front downforce and overall downforce gain

ok. care to explain how you get those front downforce and over all gain ?

other members have already offered some expalinations

[PlatinumZealot]

Absence of evidence is not evidence of absence. Simply saying "I tried a data point and it looked close enough" is not final evidence that all data points are exactly (or even roughly) right.

Yeah it is a fair assumption of linearity in those prescribed limits. That is a very, very sound assumption. A lot of engineering purposes you can get away with doing that. Like the Life cycle graphs for steel. So marek is right for that particular wing profile. I won't argue that.

BUT!!! He has simply a poor application of the graph because:

1. The graph is only for a single wing profile not for the RedBull RB7 car.
2. The change in angle of attack due to rack is miniscule compared to the x-axis range of his graph. Which is over 40 degrees when the difference in rake between RedBull and Mclaren is around 0.00625% of his graph.

Morale of the story is that proper interpretation is what is important. From looking at the graph the rake difference will increase the DF a tiny bit, but the real influence is the increase in ground effects. A graph of the ground effect vs rake angle is what is required for this problem.

[marekk]

Absence of evidence is not evidence of absence. Simply saying "I tried a data point and it looked close enough" is not final evidence that all data points are exactly (or even roughly) right.

Yeah it is a fair assumption of linearity in those prescribed limits. That is a very, very sound assumption. A lot of engineering purposes you can get away with doing that. Like the Life cycle graphs for steel. So marek is right for that particular wing profile. I won't argue that.

BUT!!! He has simply a poor application of the graph because:

1. The graph is only for a single wing profile not for the RedBull RB7 car.
2. The change in angle of attack due to rack is miniscule compared to the x-axis range of his graph. Which is over 40 degrees when the difference in rake between RedBull and Mclaren is around 0.00625% of his graph.

Morale of the story is that proper interpretation is what is important. From looking at the graph the rake difference will increase the DF a tiny bit, but the real influence is the increase in ground effects. A graph of the ground effect vs rake angle is what is required for this problem.

1. This graph is just to show the linearity of lift = f(angle_of_atack) function. But as mentioned in prevoius post, linearity assumption is valid for almost every airfoil.
2. No idea where this McLaren comes from.
3. My point one more time - even if the rake is only 1 degree, downforce from the floor rake alone is worth tens of kilograms and every team on the grid knows that, and considers it significant in car's design phase. None of them even try to run CFD and wind tunnel without some rake. RB7 just has a little more then the others.