Stability Theory.

[Matt]

I was going to the bathroom when this idea came up(as most do for many, lol.). What if you adjusted the endplates to kick out at the back, would that stabilize the rear of the car under speed? In opposite effect, could you tilt the rear of the endplate in, to create quicker turn in?

Diagram.

[Hitech]

You will notice that all current F1 cars use wing endplates, at least on the front, that taper in towards the rear of the wing. This is both to get the air to go inside the front tyres, and to speed the airflow up to give a venturi effect and extra downforce. At the rear of the car the main aim of the endplates is to help minimise drag, so they are usually parallel and often with bleed slots to help minimise turbulance.
Without the benefit of a wind tunnel you just have to try it to see what the effect is really.

[Al Weyman]

Why not fit a rudder while you are at it

[terence]

It did,nt work!

[trikesrule]

In speedway the Sprinters tried movable wings connected by rams working in conjunction with the steering. Up and down. Up as the car was tossed into the corner and down along the straight aways. The end plates make the wing more efficient in any class. In F1 the end plate size was increased for the Sponsors benefit. In my experience moving the endplates from the straight a head position just increased the drag and gave no benefit to turn in........trikes

[meb]

What might the effect on the wing be if the endplates were cambered, or curved to allow for greater surface area where down force is needed? In front view, the bottom of the wing has less surface area than the top. Might this enable a designer to reduce the frontal area of the wing and reduce drag as well?

[Locost47]

The biggest effect of the endplates on stability is in yawed conditions, where the large surface area acts simply like the tail on a weather vane and attempts to push the back end round - hence effectively turning the nose of the car into the yaw and reducing its effect. The yaw angles adopted on turn-in aren't very big for circuit racers so the effect of the endplates one way or the other is minimal. Applying something similar to toe-in or toe-out to them won't have the same effect as it would on wheels.

The rally guys do tend to play with yawed flow conditions and stability a lot more though, because they can be at more substantial yaw angles and still at high speed.

Fundamentally the endplates are there to limit (or control) the flow attracted towards the lower surface of the wing by the very low pressure you're generating there to get the downforce. In most categories the dimensions of the wing & endplate assembly is tightly controlled so normally you try and get as much surface area as possible on the wing itself and just have flat vertical endplates as big as you are allowed. If you are only allowed very small endplates then you could spend a lot of time looking at the compromise between wider and more elaborate endplate designs and overall width of the wing.

[AU N EGL]

Wing Endplates

"End plates (side fins) are mounted on low aspect-ratio wings to reduce the three-dimensional effects on the wing, by creating a physical bound to the tip flow that would tend to spill from the pressure to the suction side of the wing. Their effect is a function of their size as compared to the wing size.
Some recent developments in Formula 1 have led to the introduction of intermediate fences on the lower side, whose function is to further reduce the three-dimensional effects, by creating a limit to the deviation of the boundary layer flow from the plane of symmetry."


Source: http://aerodyn.org/Annexes/Racing/hlifts.html#plates

[Pat_T]

Originally Posted by Locost47

...The rally guys do tend to play with yawed flow conditions and stability a lot more though, because they can be at more substantial yaw angles and still at high speed.

Fundamentally the endplates are there to limit (or control) the flow attracted towards the lower surface of the wing by the very low pressure you're generating there to get the downforce. In most categories the dimensions of the wing & endplate assembly is tightly controlled so normally you try and get as much surface area as possible on the wing itself and just have flat vertical endplates as big as you are allowed. If you are only allowed very small endplates then you could spend a lot of time looking at the compromise between wider and more elaborate endplate designs and overall width of the wing.

Is that what the fins you see along the length of WRC wings are for? As I have been wondering this for some time?

[Locost47]

Yes, the large fins produce a restoring force when the car is in yaw - it tries to push the back end of the car straight again. The Subaru version is quite extreme though, and i would have thought that the actual wing performance (with respect to pure downforce generation) would diminish substantially because of the shielding effects of the fins. Admittedly, it might help the upper surface of the wing by catching air in the concave 'pockets' formed between each fin but that's not as effective or as efficient as accelerating the flow underneath.

They know what they're doing though, so i guess they've found that, on loose or slippery surfaces, it's better to gain rear-end stability by generating lateral forces directly from the wing, rather than using downforce to amplify the lateral grip of the tyre.