Wickers & Gurneys

[Jorma]

Does anybody know where there is any discussion or documentation of the use of wickers (Gurney)? Is there an optimum height? Why are they always 90 degrees, does 45 or some other angle not work? I'm sure somebody has done the research.
Mike M.

[EricP]

Carroll Smith's book(s) talk about it. I don't have my copies in front of me...

[tonychilton]

Does anybody know where there is any discussion or documentation of the use of wickers (Gurney)? Is there an optimum height? Why are they always 90 degrees, does 45 or some other angle not work? I'm sure somebody has done the research.
Mike M.

[EricP]

The legend in the first graph... is that percentage of cord length? And if so, when does it fall off (start producing significant drag)? Why not have a 12" tall wicker?

[2BWise]

There are quite a few technical papers on the subject. One I've referenced in the past is AIAA2007-4175 - Wind Tunnel Test of Gurney Flaps and T-Strips on an NACA 23012 Wing. Type the paper number into the google to find it. Should be the first or second entry.

[JerryH]

The previously posted wicker data is well documented....and I have personally tested it in wind tunnels.

Keep wickers down to 4% or less of chord length......preferably less. The drag goes up dramaticallly over 4%. Above that the gain in downforce is not worth the drag increase.......and at some point even the downforce gains go away.

I typically use 1/4 inch on race car wings.....on rare occasion 3/8 inch ( very large chord wings). 1/2 inch works well on diffusers.

I have them bent from 032 aluminum.......and tape them full length on.the top surface. (a few pieces of tape on the rear going under the wing are needed to keep it down). I make the lower portion where it lays on the wing no less than 1/2 inch. 3/4 is better.,

The tape is much faster to get off if I want to make a quick change in a test session.

In a pinch you can buy alum angle from hardware stores....but it is usually .065 thick.....and anything less than 1/2 is hard to find.
I have found 3/8 x 3/4 at farm and fleet.

On the rear......Put one on if you need a high angle of attack.....or if the wing profile needs it (lower VD F2000 ) and adjust the wing angle to balance the car. Playing with to many sizes is a waste of time.

On the front......use one on the flap......and maybe the center of the wing......then adjust the flap angle to balance the car. Again.....don't waste time playing with multiple wicker sizes.

Wickers can also be used instead of wing angle increases......and they do make the wing start working at slightly lower speeds.....but the gains are not as great as wing angle adjustments.

If you are running a large oval.....then tiny wicker changes are a good tuning tool.....often on a trimmed out wing.....because wing angle and/or flap changes may be to much of a change.

Jerry Hodges
JDR Race Cars

[S Lathrop]

I will add something that was popular years ago. It was called "Sliders". it was wickers that could be adjusted to increase the cord of the wing. It was a way of getting an incremental change in down force without a significant increase in drag. They were wickers with elongated holes where they mounted to the wing. If you wanted a small increase in down force, you could slide the wicker to lengthen the wing.

[Steve Demeter]

My old Lola had that. A slider to increase the chord and we mounted a wicker on the trailing edge. Worked like a dream. LIsten to Steve.

[Joefisherff]

I've seen them on the top of diffusers - same function there? Thanks

[DaveW]

I've seen them on the top of diffusers - same function there? Thanks

Exactly.

[Jorma]

Wouldn't you want it to be on the bottom of the diffuser exit?
Mike M.

[DaveW]

Wouldn't you want it to be on the bottom of the diffuser exit?
Mike M.

It needs to be on top to accelerate the air coming off the top off the diffuser and keep the air underneath the diffuser attached to it. Similar to a wing where the wicker is on top to keep the air underneath attached.

[Phil Creighton]

We took off a 1/8 wicker on a 6 liter Riley and Scott at a Mid Ohio test as we thought it probably wasnt doing much as a quick change and completely destroyed the balance of the car - didnt make a flying lap before returning to tell us to put it back on. Used naughty language too!

[DaveW]

We took off a 1/8 wicker on a 6 liter Riley and Scott at a Mid Ohio test as we thought it probably wasnt doing much as a quick change and completely destroyed the balance of the car - didnt make a flying lap before returning to tell us to put it back on. Used naughty language too!

What that tells me is that the wing at that attack angle was stalling w/o the wicker, adding drag and causing a big loss of downforce. The wicker kept the air attached under the wing and thus markedly increased the downforce.

[Steve Demeter]

Exactly.

Also they stiffen the trailing edge of the diffuser

[Phil Creighton]

What that tells me is that the wing at that attack angle was stalling w/o the wicker, adding drag and causing a big loss of downforce. The wicker kept the air attached under the wing and thus markedly increased the downforce.

Dave
If you look at the R & S rear WSC wing its pretty aggressive. The surprise was that such a small wicker did so much to re-attach the air flow. Scared the heck out of our test driver who was very experienced (Lemans, IMSA etc). We knew why but the difference was drastic
Phil

[DaveW]

Dave
If you look at the R & S rear WSC wing its pretty aggressive. The surprise was that such a small wicker did so much to re-attach the air flow. Scared the heck out of our test driver who was very experienced (Lemans, IMSA etc). We knew why but the difference was drastic
Phil

Sometimes it IS surprising how such a small thing can make a huge difference.