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I just read a aero test on the Dallara F312. The testers had some time left in their wind tunnel session, so they remove some of the new aero features on the car, one at a time, to see what their benefit were. They found that the vertical flow deflector on the outside of the side-pod near the cool duct entrance improved down-force with a small drag penalty. What was strange to me was that the down-force balance was shifted to the front! Why would that be the case?

The deflector look just like the white ones on this Williams.

Brian

Do you mean shifted the CP forward. That would only make sense as you are adding drag surfaces to FWD part of the car.

Yes, the CP moved forward.

Brian

So after removal of these deflectors the CoP moved forward?

These podvanes(as I'd prefer to call them) are there to clean the air from the tire wake of the front tire, and with that shape the flow to go around the sidepod, and by doing so increases rear downforce.

hardingfv32 wrote:Yes, the CP moved forward.

It's not unknown for different wind tunnels & even CFD to generate contrary results (assuming that Dallara actually tested the additions).

I would prefer the on/off comparison to be made on track.

The data is from the Oct 2012, Aerobytes feature by Simon McBeath in Racecar Engineering. I noticed it as I sample the copy on line. You are allowed to read three pages of each issue. They were using the MIRA Tunnel. A very simple test, just removing the part with no other adjustments.

Data with the deflector or fenders (term used in the article) MOUNTED:

Delta: DC +10
CI +31
CLf +27
CLr +4
%Front +1.1
L/D +11

Brian

hardingfv32 wrote:They were using the MIRA Tunnel.

Exactly....

I wonder why moving ground plane tunnels are considered so important?

Not unusual, but we need to see the entire sheet and make a comparison. The aero balance shift would depend on the whole car config, not just synthetic measurement and thus inference.
The shift is actually quite small ...

P.S. Simon and MIRA have longstanding partnership, so ..

I view these test results as a challenge to the conventional theory, on this forum, of how these deflectors/fenders function. I do not believe we have any other data on the subject. The MIRA tunnel seems well used and developed. I would think that the tunnel's limitation are well understood and when possible, properly compensated for.

So, do we cling to the common theory of how these deflectors /fenders function or can we explore what these test results are indicating?

Brian

Rear downforce is decreased due to sidepod panel removal while the downforce generated at the front remains at the same level , thus CP is shifted forward . Sidepod panels ( or Sidepod vanes ) were introduced by Jordan team in 2005 and later copied by Toyota . Development over years revealed that the more efficient the rear end becomes the more complex the front wing becomes either.

bar555 wrote:Rear downforce is decreased due to sidepod panel removal while the downforce generated at the front remains at the same level , thus CP is shifted forward .

I do not think that is what the data posted above is indicating. With the deflectors/vans/fenders in place, BOTH CLf & CLr increased. CP shift forward because of a greater gain in CLf.

Brian

hardingfv32 wrote:The MIRA tunnel seems well used and developed. I would think that the tunnel's limitation are well understood and when possible, properly compensated for.

I'm sure you are correct - for road vehicles. I am just not sure how one would set about compensating for a ground plane effectively moving froward at the same speed as a ground effect vehicle.

DaveW wrote:

hardingfv32 wrote:They were using the MIRA Tunnel.

Exactly....

I wonder why moving ground plane tunnels are considered so important?

Because F1 has a great deal of ground effect going on and having the air come into the model at a high relative speed to the ground (with a boundary layer formed already) twists everything of the scales. Racing cars on clean air face the air standing still aboove ground ( or at least moving at very slow speeds compared to the car).

CofP moved forwards because the pod vane directs better airflow to the rear, by shifting the front tyre wake outboard. Without it the rear aero is less effective, but the front aero remains the same, hence the forward shift.

The tunnel data are intriguing; but is there any significance without track confirmation?