Renault R31

[marcush.]

renting a windtunnel is a short sentence but in reality the spending starts when you have decided to go to a different facility..
You need to adapt your own windtunnel model to the hardand software supplied by the tunnel ,calibrate etc before you can have any hope of getting useful information...
Also a change in modelsize is not only a windtunnel issue you need a new model as well ..so NO carryover of moulds and bits and pieces wings sidepods etc ...this looks like a major adventure Renault put themselves into and possibly the decision was taken in the aftermath of Kubicas accident .they knew they had no real chance to fight for a championship without him and stopped everything and pushed through the tunnel upgrade and prepare themselves for 2012 maybe ...this would explain why they got themselves into this trouble and now as the summerbreak is approaching they come up with lots of updates ...having lost valuable ground in the championship.For 2012 this is a good decision as all work is done already with the new modelsize and they got a good read on the R31 already with the upgraded tunnel.and a possibility to compare results with their smaller size model ..for correlation purposes.Kubica would have killed them doing this and ruining the 2011 season .

[hardingfv32]

"BTW can you explain how slits are producing more down-force?"

I think the basic idea is that you are blowing a wing shape. The exhaust flow is said to exaggerate the performance of the wing. I question this theory. Why don't we see other examples of this on other cars if it is so effective?

Brian

[ringo]

I don't know about the ferrari, but if the renault had the slits in the tips of the floor, they would effectively have a multi element wing in the middle of the car.

@ Brian, blowing the wing shape at 6 times the speed of the car is like virtually have a full sized rear wing in the middle of the car.

Those "wings" will behave like they were 36 times larger in area, when being blown with the fast moving exhuasts.

remember Lift = 1/2 * rho * Velocity squared * Area* Coeficient of lift.

a factor of six will mean the downforce of the wings will be 36 times that of another car.
Or if we normalize it to the speed, then it's like the area being 36 times bigger.

One thing i ignored is the density. The density will drop to about 1/4 of the value, due to the temperature, so the wings will be effectively 12 times as big.

Imagine the R31 with 6ft wingspan either side of the car. That is what blowing the winglets at front are virtually doing.
Now think of it like a rear wing, and put a slit in it and increase the camber. It should see similar gains to those seen when such changes are made to rear wings.

[hardingfv32]

So why is this technique not seen on any other cars? Was it ever used in the past under a different rule set? Just seems to good to be true.

Brian

[ringo]

Materials technology, regulations, exhuast positition etc.
The other teams can't put wing profiles round the back of the car either.

Referring to the past isn't really a justification for a technology being useful.

modern blown diffusers have similar principles but different execution, the same for pull rod suspension and movable body work.

Air craft have blown flaps, which are well documented. And we also have ejector technology so it's been proven in other fields.

http://en.wikipedia.org/wiki/Blown_flap

[youtube]http://www.youtube.com/watch?v=NclYbrZAnLc[/youtube]

[youtube]http://www.youtube.com/watch?v=k_eDutgh4IU&NR=1[/youtube]

now think of it the other way for downforce. Blow under the wings.

[hardingfv32]

I don't think a blown flap is relevant to the discussion of a blown wing which I believe you have proposed.

Why not just blow the beam wing? Would that not be allowed under the current rules?

Brian

[ringo]

blown flap blown wing, same thing bar the coanda effect. The crux of the argument is the air speed from the exhuast energy, surely you can see that.

The beam wing's profile is controlled by regs and you cant get ground effect from it.

Then there is the issue with balance.


Renaults idea is pretty solid. I just thing they need to exploit it more since they are sticking with it.

It would be amazing if it blew at transonic speeds though. It's quite possible with some sacrifice of power from the engine.

[marekk]

One thing i ignored is the density. The density will drop to about 1/4 of the value, due to the temperature, so the wings will be effectively 12 times as big.

Imagine the R31 with 6ft wingspan either side of the car. That is what blowing the winglets at front are virtually doing.
Now think of it like a rear wing, and put a slit in it and increase the camber. It should see similar gains to those seen when such changes are made to rear wings.

My well known nitpicking: 1/4th of 36 is 9, not 12. So i would say rather winglet then wing

The only reason to use slotted (multielement) wing is to prevent stall at high AoA - other than that, it's always less efficient then clean configuration.

I can't see any seapration problems on this almost flat (due to regulations) part of the floor (not to mention the fact, that turbulent flows, like our exhaust, tend to stick much harder to airfoils surface, and increase critical AoA).

Adding slot and secondary flap would make sense only if they are allowed to position it higher and steeper then main profile (like seen on front and rear wings) - but this is obviously prohibited.

[hardingfv32]

The beam wing has a much better profile than the leading edge to the Renault floor even while being controlled. It is much larger and should provide outstanding down-force numbers under your theory. No concern with ground effect, simply increasing the flow across a wing. So why is it not blown? What could be simpler?

The drivers have lived with the imbalance issue before.

Brian

[ringo]

One thing i ignored is the density. The density will drop to about 1/4 of the value, due to the temperature, so the wings will be effectively 12 times as big.

Imagine the R31 with 6ft wingspan either side of the car. That is what blowing the winglets at front are virtually doing.
Now think of it like a rear wing, and put a slit in it and increase the camber. It should see similar gains to those seen when such changes are made to rear wings.

My well known nitpicking: 1/4th of 36 is 9, not 12. So i would say rather winglet then wing

The only reason to use slotted (multielement) wing is to prevent stall at high AoA - other than that, it's always less efficient then clean configuration.

I can't see any seapration problems on this almost flat (due to regulations) part of the floor (not to mention the fact, that turbulent flows, like our exhaust, tend to stick much harder to airfoils surface, and increase critical AoA).

Adding slot and secondary flap would make sense only if they are allowed to position it higher and steeper then main profile (like seen on front and rear wings) - but this is obviously prohibited.

It's not prohibited. It can be positioned higher. There is 50mm or 100mm height to play with above the reference plane.

The video was not to say that there is seperation. It's there to show what accelerated flow can do, even if the vehicle is moving at a much lower speed.

[ringo]

The beam wing has a much better profile than the leading edge to the Renault floor even while being controlled. It is much larger and should provide outstanding down-force numbers under your theory. No concern with ground effect, simply increasing the flow across a wing. So why is it not blown? What could be simpler?

The drivers have lived with the imbalance issue before.

Brian

Well that has to be investigated.

But a beam wing has to be one element. and the exhuast can't blow all of it.
Neither can it have an end plate.
Neither does it have ground effect which is very very substantial.
Then there is retrictions on the radius of curvature of the profile.

It's probably left to be investigated. But either way would work, but i think the FEE is more effective, as there are other benefits to the floor of the car than just blowing those wings.

[beelsebob]

Can someone clarify. I don't get why ground effect is relevant to the beam wing. No air can escape round the sides of it due to the rear wing end plates... How is ground effect meant to help?

[hardingfv32]

It is not clear to me how the lift is being created by this flap system. Is the exhaust thrust being redirected downward (vectoring?) or is there more lift being created because of the flow over the top of the wing surface.

It seems Boeing considered flow under the wing as well as over the top.

Brian

[ringo]

Can someone clarify. I don't get why ground effect is relevant to the beam wing. No air can escape round the sides of it due to the rear wing end plates... How is ground effect meant to help?

Yes it doesn't have ground effect, on the other hand the leading edge of the floor does.

[n_anirudh]

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