F-duct made with exhaust gases

[okibcn]

The current regulation forbitds any aerodynamic action done by movements of the pilot but... the exhaust gases could be routed to any wing of the car that makes downforce as default. But at high speed thus high rpms and increased gas flow in the exhaust, with a clever design, the gases could be routed to the front of the wing so the airstream around the wing is minimized or deviated in order to minimize or even neutralize the downforce action of the wing and then minimize the drag.

Hot gas is a low density gas and it can change the laminar flow of a wing into a more turbulent flow thus reducing the drag of the leading edge and reducing the downforce.

It is like a F-duct but activated by the hot gas flow and not by a pilot movement. This could be a boost in all the straights since the use of the ARW is very limited by the 2011 regulation.

This could be the principle of the solution applied by Renault but front exit exhaust are not the ony way to apply this technique since there are, or could be, other wings to apply to...



And now I remind the early drafts of the F150 with additional sidewings on the engine cover, a place very close to exhausts...



This could be even applied to the Rear Wing as the traditional F-duct.



What do you, gurus think about this?

Regards

Oki

[tommylommykins]

How much of a link is there between exhaust gas volume and the need to cut drag (and coincidentally reduce downforce)? I would assume it's in the teams' interest to run the engines hard at any point when the car is trying to go faster. This would include when a driver is accelerating out of a corner... As soon as they put their foot down, this exhaust-f-duct would activate, and depending on whether it worked on the front or the back, the car would either understeer off the track, nose first, or oversteer off, arse first...

That's an advantage of any driver controlled system over a passive one. You get to let the driver choose sensible times to turn it on, instead of having some complex mechanism to stop it turning itself on at some time when you don't want it on.

[okibcn]

The F-duct and the proposed Exhaust Controlled Aerodynamics both only work when the car runs at a given speed, so the design includes speed into the function. The curve of the drag/downforce vs. speed can be fine tuned so the exhaust can be useful only when the speed is over a threshold so the oversteering problem could be minimized.

In other words, the downforce is a function of speed and hot gas volume. With a clever design, this 2D function could be adjusted to custom thresholds of speed and gas volume.

Even more, the understeer/oversteer due to the mentioned downforce unbalance problem can be workarounded. Renault is acting on the sidewings under the sidepod intakes, more or less in the middle of the car. This is a way to reduce the dowforce near the CoG, so the head/aft aerodynamic downforce is barely unbalanced due to this technique.

From the point of view of the pilot is like when you press too much the gas pedal. Is tricky if you are not used to it but this system would increase the tyres life, it would increase the top speed and it also would reduce fuel consumption...

There isn't a perfect system, but this would give a lot of benefits with only a single drawback, it would need a skilled pilot able to handle the car properly when accelerating after a high speed curve.


Regards,

Oki

[raymondu999]

Problem is, straights are flat out, and there are flat out corners. And you need to be hard on the throttle, and on full throttle as fast as possible on the traction. Besides the drag vs traction would be too throttle dependent, very sensitive on and off throttle.

[okibcn]

Same could be said about the double decker front wings in 2007 season that were used by most of the teams:



They had to be fine tuned in deformation vs. speed in order to remove the downforce of the car in the straights and not in slow corners. The result was improved front-end sharpness to the car's handling in both fast and slow corners.

No one said it was easy, I just said that Exhaust Controlled Aerodynamics is possible and not forbidden this year.

Regards,

Oki

[Ian P.]

There is loads of discussion on the interesting topic of exhaust blown floors, diffusers, turning vanes, F-Ducts ........etc.
From what we have seen of the Renault forward exhaust it doesn't look to me like it is being used to trigger or direct flow in any specific manner.
If the exhaust flow is being used to raise the temperature of the air hitting the rear tyres, it could have a significnat effect.
Drag and lift from the tyres is directly proportional to air density. Raising the temperature 10 deg C will cut both drag and lift 3%. This is would be a big boost as the wheels are a major lift inducer and create significant drag. To cap it off, lift from the wheels is sprung lift, even more incentive to try to cut the effect..

[okibcn]

This is exactly what I am saying. High hot gas volume in the leading edge of any part will reduce the drag as well as the aerodynamic force: lift or downforce. So I totally agree with you on this:

Drag and lift from the tyres is directly proportional to air density. Raising the temperature 10 deg C will cut both drag and lift 3%. This is would be a big boost as the wheels are a major lift inducer and create significant drag.

Anyway heating the air in front of the tyres shortens their life and may affect the braking system too. If this is the trick, then Renault has found a good way of neutralize part of the wheels drag and lift.

Regards,

Oki