Attached vs detached flow?

[Evl]

Hi All,

Looking at the bottom of my front wing after a rain race I see an interesting pattern. Near the front of the wing you see nice little streaks from the water/dirt. Farther back, the streaks widen and dissappear:

-----------  <--- leading edge
   ||   ||
   ||   ||
  /  \ /  \


-----------  <- trailing edge

[not to scale]

Does that indicate that the flow is detaching (which I assume means stalling, more drag, less downforce), or is it just the transition from laminar to turbulent but attached flow? (If it isn't already obvious, I know very little about aerodynamics, beyond the 3 paragraphs in tune to win, which only show the dirt streaks on the top of the wing, not the bottom.)

Interestingly, for the portion of the front wing that has flaps, the streaks continue all the way to the trailing edge.

Thanks for any illumination you all can provide,

-Chris

[brownslane]

Chris, you are correct. The air is stalling. Often the addititon of a small gurney at the rear of the wing (wickerbill) will correct the problem.

I use WD-40 to create the same traces that you saw as a result of the rain water. It is a good (and inexpensive) way to check these sorts of things. I do it every weekend, as I adjust the aero on the car.

Good Sleuthing, Chris!!

Best, Tom

[iamuwere]

So on a car with a spec part--how do you do that?

[brownslane]

For spec cars, first make sure that a gurney is allowed. Normally, they are, but check your rule book.

You can source gurneys at your local hardware store. They call it aluminum angle. usually available in 1/2 by 1/2, all I would do is cut one side down to 1/4, drill a few 1/4 holes in the wider side (the base) and match drill the trailing edge of the wing. Then install with 1/4 round headed machine screws (also usually available at the hardware store) with the rounded heads under the wing and the little nylok nuts on top.

I would build three sets. 1/4 inch for low drag, 3/8 for more DF and 1/2 for even more.

Be sure and get the round headed bolts (machine screws) and make sure they are installed facing up. Otherwise you will create a lot of drag on the underside of the wing...that is a big deal.

Best, Tom

[Ivinsea]

Stohr makes gurneys from plastic corner molding like what Home Depot and Lowes sells to protect drywall corners and tapes it to the wing. Might be good for testing before drilling holes....

[Dennis Valet]

Stohr makes gurneys from plastic corner molding like what Home Depot and Lowes sells to protect drywall corners and tapes it to the wing. Might be good for testing before drilling holes....

DRILL BABY DRILL!!!!





Couldn't resist

[AndrewR]

All FE front wings I've seen get a big separation bubble in the central two thirds. Can't really do anything to the wing, but adjust the angle (which is a small angle). Which doesn't do much for the condition or down force.

[Jon Horgas]

It has been my experience to tape them on the top back edge of the wing with 'heli' tape instead of using duct tape. The 1/2" base is sufficient to hold them on,at all speeds, providing everything is clean. Sometimes you can get away with less wing, and a larger Gurney to make the bottom of the wing more efficient, and keep some of your straight line speed by using a smaller 'attack' angle of the airfoil.