Wickerbills

[Rick Iverson]

Fellas;

We can thank Doug for this. Bud, an ice COLD Rolling Rock is on me.

Now, here is a topic that I have considered for some time, although I have yet to see any practical application on the track. I am going to make a few wickerbills of varying angles and heights, but am hesitant to apply the slots. Thoughts?

VR

Iverson

[nulrich]

Is this for an FC car? If so, you don't want to run Gurney flaps of any style UNLESS you are already running your wings at their max downforce setting. That's unlikely at most tracks I know.

Gurney flaps do make downforce, but not very efficiently. You're better off increasing your wing angle of attack assuming you aren't approaching stall.

They do look trick, though .

Nathan

[Rick Ross]

Hi Nathan,

How about the case where the existing wings on the car are not optimized for the desired CL range at the operating Reynolds numbers? I would agree that it is possible to utilize airfoil sections that would make Gurney flaps undesireable, but most club racers are stuck with whatever wings came with their cars. Sometimes these wings are spec designs from the 90's (or older), and they are definitely not the most efficient avalilable. In such cases it would seem to me that a Gurney may offer an improvement if the goal is to incease maximum downforce available.

Gurney flap performance depends on many variables, including Reynolds number, flap height, flap angle, wing angle of attack, etc. In general, they allow for significantly increased CL max, although with a corresponding drag increase. Still, in some cases the L/D ratio is actually improved, depending on the specific airfoil sections involved. Drag from Gurney flaps is relatively sensitive to flap height. Based on the limited data that I have seen, Gurney flap heights in the range of 1% to 3% of wing chord normally offer the best compromise between lift and drag. Flap heights of greater than 5% wing chord would rarely be optimal.

I have not seen any data on "saw-tooth" Gurneys, but I have seen wind tunnel data on other alternative Gurney shapes. The data in these cases did not indicate any particular advantage over a "standard" Gurney. In my opinion, the saw-tooth Gurneys that you see on some cars do not necessarily offer any measurable improvement over a conventional design.

Just my 2 cents.......

Rick

[nulrich]

Hi Rick:

All true. Two points, though.

Many FC cars run older rear wing designs, but in general, the most common two-element upper rear wings aren't too bad. I think they were originally the spec wing for the Cooper series? They are a little bit draggy for the lift produced, but nowhere near as bad as some of the wide chord designs out there (the ones that look like FA wings). It's unlikely a Gurney will improve L/D for these wings in the C_L range most commonly run in FC.

That said, and the caveat in my message above, if you are running one of these wings at very high angles of attack (say 12 degrees or more) then you might benefit from a Gurney, which would allow you to lower the angle of attack a bit and possibly be more efficient.

The second point is that FC cars generally do better at low downforce/drag levels, at least at the tracks with which I'm familiar. There are exceptions (like possibly Mid-Ohio), but with the limited power available it's hard to pass if you are carrying too much wing down the straight.

Your point about Gurney height is absolutely correct. I've seen some Gurneys run on FC rear wings that had to be nearly an inch tall! Our pet name for that is a "DPD" (Drag Producing Device).

Nathan

[Rick Ross]

Nathan,

Good info......I did not realize that FC's tend to operate in the low-downforce area of the aero map.

My comments were obviously very general in nature. Many folks are surprised that in some situations a Gurney can actually improve the L/D ratio......a real win-win situation. This was certainly the case when Dan Gurney originally applied these flaps to the wide wings on his Indy cars!

Rick

[Rick Iverson]

Is this for an FC car? If so, you don't want to run Gurney flaps of any style UNLESS you are already running your wings at their max downforce setting. That's unlikely at most tracks I know.

Gurney flaps do make downforce, but not very efficiently. You're better off increasing your wing angle of attack assuming you aren't approaching stall.

They do look trick, though .

Nathan

Sir,

I am using stock Van Diemen wings, both fore and aft, on my RF 94/95 FC. But that is why this category is going to be a boon for the aerodynamically challenged, such as myself.

Fellas;

Ain't America great, or what?

VR

Iverson

[Brands]

We did all sorts of gurney testing at Williams. The max we ran was 6mm model scale (half scale) on the rear wing and maybe 8mm on the front wing flap. Of course this varied race to race, wing to wing and flap to flap. We mostly ran 3mm on the rear wing upper flap and on the the t/e of the RWEP. I don't think we ever ran a full span gurney on any wing. As a rule they were 75% span including a 30mm taper to zero (I still only talk in model scale!). Every time we tried 100% gurney it was only an increase in drag which is why I only ever run 75% on my cars. Every now and then a fresh faced aerodynamacist would come into the tunnel for his first test with a saw tooth gurney. We'd just smile and let him get on with it! Needless to say they never did anything. At best invisible.

It was always a standing joke in the tunnel if a part wasn't working - stick a gurney on it! Actually they are pretty cool little devices and can be used in all sorts of applications. When I was there we were the only team that didn't run barge boards. We had a fairly complex guide vane assembly just behind the front wing. We were at the end of a test and decided to stick a gurney on the t/e of one of the turning vanes to see if it might take more camber. It was immediately a 15lb gain (we would make a part for anything above a repeatable 5lb gain) and led us down a new avenue which resulted in a much bigger gain. I can still remember the disappointment when a driver went through the gravel and a guide vane came off. I knew just how much performance he had just lost!

[dereklola]

Every time we tried 100% gurney it was only an increase in drag which is why I only ever run 75% on my cars.

Is this the central 75%?
And in simple terms why do the outer ends not benefit, or not benefit as much, from the Gurney?

[nulrich]

I am using stock Van Diemen wings, both fore and aft, on my RF 94/95 FC.

When we tested a late model VD (an '02, I believe, FWIW) in the wind tunnel, the stock Van Diemen wings were the second best performing after the Radon parts, substantially better than a few aftermarket pieces we tried.

That said, aerodynamics is a little tricky. What works well on one car won't necessarily work well on another. The shape of the nose, the sidepods, roll hoop, and even suspension wishbones can strongly affect the behavior of wings and diffusers.

To get good correlation in our CFD models, we've found that we need a fairly detailed model of the suspension wishbones, upright, brake disk and wheel (which, of course, is modeled as rotating) not just a simple tire. The flow through the sidepods and radiators is also critical.

And the 94/95 VD is shaped quite a bit differently from the later models.

That said, I believe the basic aerodynamic behavior of all current FC cars is very similar. And with only 150 hp, it's all about aerodynamic efficiency!

Nathan

P.S. Ben, in F2000 we would give away our first born for 5 lbs of downforce and commit multiple homicide for 5 lbs less drag .

[Rick Kirchner]

Cal speedway, willow springs, and long buttonwillow variants are my tracks - all pretty high speed. with pretty flat rear wing and front mainplanes (flaps are run pretty steep) When I first got the car (94 VD with later model rear wings) I insisted in running gurneys. Pete West told me to take 'em off. Even my slow a$$ could feel a significant difference on the straights.

[dereklola]

I don't think we ever ran a full span gurney on any wing. As a rule they were 75% span including a 30mm taper to zero (I still only talk in model scale!). Every time we tried 100% gurney it was only an increase in drag which is why I only ever run 75% on my cars.

Ben
Does this mean I should consider shorter Gurneys on my vintage cars? (1976 Atlantic, 1980 CanAm, 1991 F3000.) I assume the 75% is the centre bit (special spelling just for you!) - so maybe no Gurney for about 6" at either end of the wing(s)?
Thx - Derek

[Brands]

Yeah, I think so, worth a try. As I say my only experience is on 50% and 60% wind tunnel models and we always ran our gurneys at 75% of the total width (in the centre). Full width was only ever extra drag. That extra drag was only a few lbs (in 900lbs ish total drag), so not dramatic at all. Every little helps though! Of course this is aerodynamics and what works on a F1 rear wing may not work on vintage stuff. That said I don't ever remember running a full span gurney on any wing from a Hockenheim/Monza wing package to an 8 element Monaco wing (I think Ferrari crammed 10 elements in one year!)
Ben

P.S. Is it 'special' spelling when you guys spell it correctly? : )

[dereklola]

Actually the British spelling was 'center' until about the same time as Americans declared independence!

[Brands]

Fair enough!

[Ranald]

"It's not what they've done to the English King, it's what they've done to the King's English!"

[Becker Motorsports]

Gentlemen, We run a 95 VD FC also at Willow Springs, Cal Speedway, Butonwillow, ie; high speed tracks, and generall we run the front wing and lower rear wing At zero degrees, the rear endplates [mfg. unknown] have gurney's on the them. Other the stiffening the end plate what effect could they have? I have just made new Alum. end plates and qustion as to whether or not I shoud add Gurney's. Thank for any imput, ernie

[kea]

The "Gurneys" you have on your outer, rear end plates, besides stiffening the end plate, will contribute to keeping more air pressure across the entire width of the wings. Without them, the pressure narrows the further back along the wing it goes.
The treatments that the F-1 crowd has done to the upper portion of their rear wing end plates, is for the same thing, but with I'm sure, less drag consequences.

[Becker Motorsports]

Thanks Keith, I shall add the gurneys Ernie

[Paul LeCain]

there's an article here that discusses a lot of this, plus t-strips:

http://www.aoe.vt.edu/~mason/Mason_f/AIAA2007-4175.pdf

[Becker Motorsports]

Thanks for the article, looks to be good reading,

[M.Sauce]

There was an article written by the engineering dept. at MIT about 8-10 years ago..It was very informative.Wickers used correctly help create more downforce but used incorrectly like the front of the mustche wings on later Van Diemans create more drag than downforce.Wing technology is some real amazing stuff.Racecar manufacturers of lower formula cars rarely do it right.Most all the technology is for high downforce cars with alot of horsepower.When you put a wing on a car that has 150hp it must be the right profile to accomplish the downforce numbers versus the drag created.One wing profile for a FC does not work for all speeds regardless of what wicker you use.

[openwheeler37]

I'm thinking about messing around with some different wickers but dont know where to start. Height, angle, and wing angle of attack. Can someone please correct me in any areas I may be wrong in ... I should have the wicker span 75% of the wing (from the center out) and the wicker height should be 1-3% of the wing coard depth. From some other forums/links I have seen that about a 10% wicker angle seems to be optimal. Also, what is the range of wing AOA that the wicker will be effective before drag is to high? oh yeah, im sure it helps to know i'm running a RM02A Speads with the updated "high downforce" wings.

Thanks for any help and suggestions!

Grant

[brownslane]

Grant, use Gurneys only when they are needed. (sounds simple doesn't it?).

A simple way to field test for wing efficiency is the use of WD-40 sprayed on the leading edge of the wing(s) before a session. When you are back in after the session, you can read the underside of the wing for flow patterns. You are looking for nice, straight lines running in the direction of travel starting from the leading edge. The key is looking to see the flow lines continue to the very end of the wing (within a half inch)....if they do, the wing is working without stall and in (reasonably) clear air. If the flow patterns "stop", or seem to reverse direction, then you have a stalled wing and need to make changes. A simple gurney addition at this time will correct the stall. I carry three sizes for my cars; 1/4, 3/8, and 1/2 inch. Hardly EVER use the 1/2 inch, but the 1/4 inchers get worn out from use. Mount the gurney on the top of the wing, not underneath...mount in a way that you minimize any protrusion into the air flow under the wing. At a minimum you can mount the gurneys using button head screws with the jet nut portion on the top of the wing.

I usually WD-40 my wings at every track in practice sessions, but always if I am at a new track, or have changed the AOA. It is amazing how much you can learn about airflows with this simple tool (for a simple guy like me). F-1 guys have this cool flourescent stuff that probably costs hundreds of bucks a can...mine is a bit cheaper but works fine.

Oh ya, the gurneys I make/use are 90 degree angles. No funny saw-tooth ones. I make 'em from carbon fibre cause they are cool, but hardware store 16 gage aluminum angle works fine.

Regards,

[openwheeler37]

Thanks a lot Tom. I will use the WD-40 trick first. Will this also help show me if i'm at the right AOA on my wing?

[brownslane]

WD 40 will not indicate appropriateness (is there such a word?) of AOA. Testing with sector times (or overall lap times) with different setups will tell you that.

Back "in the day" I built a series of bike-powered cars called F-4. Powered by 750 cc engines, these small, light and (relatively) underpowered cars ran FC lap times. You would think that small low force (and low drag) wings would be the way to go? Out testing with FA wings actually DROPPED lap times at Mosport by well over a second a lap! Sometimes your best guess is just that; a guess! Of course, df is addictive as well.

A big setup objective is to develop a wing setup that provides a consistent centre-of-pressure that stays both consistent with CofG and that stays relatively positioned throughout the speed range at the track being used....AOA and wing size allows you to setup a car to these requirements.

Oh ya, some wings actually work better at zero degrees incidence (especially front wings where ground effect is greater) than if they are angled up....I have a couple of rear wing profiles that actually install with a negative incidence...in other words, install with a nose-UP AOA


Also, remember the first rule of turbulence/drag.....if it has to happen, make it happen as far back in the car as possible.....turbulence created at the front of a car will influence virtually everything behind it.... so pay attention to things like bolt heads, radio antennas, etc.....think about the shape of a wake behind a boat.....the further away from the source of turbulence, the wider the area of influence....

Best,

[Rick Ross]

The research that I have seen indicates that gurney flaps are most efficient (best L/D) when mounted at a 45 to 60 degree angle to the wing. However, I have never seen this done in club racing, and it is easier to fabricate 90 degree gurneys. You probably want to keep your gurney heights at less than 3% of the wing chord.

Also, the drag "penalty" from using gurney flaps is most pronounced at low to moderate wing angles of attack. At really high AOA the gurneys do not add a lot of additional drag....the wing is producing plenty of drag on its own at that point.

Finally, when adjusting wing angles it is important to keep the aero balance correct.....usually somewhere near the static weight distribution. So if you add downforce in the rear, you will usually want to do the same in the front (assuming your car was handling OK before the change). The problem is that it is almost impossible to know how your aero balance has changed unless you have data acquisition that allows you to measure the front and rear downforce on the car. So without damper pots (or strain gauges), it is difficult to maintain the desired aero balance when changing wing angles, adding gurneys, etc.

[Steve Demeter]

Read Carroll Smith's books.

Air still works the same way. Wing design has changed a bit since then, but you still have to experiment to find what works best for you at any particular track.

The WD-40 will tell you if you have too much AOA as it will show a stall condition and if a flap does not correct it, then the AOA should be looked into.

One thing to do is to look at what others with similar cars to yours are running for a starting point.

[openwheeler37]

Can anyone share some pictures or input of how they attached their Gurney flap / wicker bill? I'd like to make sure i'm doing it right before I destroy my rear wing element.

[Jerry Kehoe]

Mount it on the top surface of the wing, use small buttonhead screws with the nuts on the top side.

[racerdad2]

Jerry has it right. Pretty straight forward. Many Thx for all the great info. My CFC came with a full width 90 degree wicker across the rear wing. I'll be replacing it with a 60 degree 75% width unit, after I WD the wing to check the stall... They do look cool ,)

[brownslane]

Kirk, I am interested in why you would install a gurney that is only 75% of the wing width? There will be added drag created at the ends of the gurney flap....

Thanks, Tom

[dereklola]

- - - - 75% of the wing width?

Wasn't that a comment from the guy who used to work on Williams F1 aero?
Something about same df, less drag?
- but no doubt lots of caveats.

[racerdad2]

As a new guy, I'm just trying out new stuff. Seems that 75% rule may work. Although, on my CFC, It may not be noticable, especially with me driving I won't be racing til next year & I am not an 'all or nothing' racer. I've discovered that I have much less stress & much more enjoyment if I don't go for wins ,) That said, I'm already prepping my car far beyond what I promised myself when I bought her 99% of the guys here on Apex have far more experience & knowledge than I. Thanks for steering me in the right direction !

[Steve Demeter]

In general, I would respectfully suggest that you prep the car to the max level possible.

If you only use 95% of the car, a car that has whatever aero aid for example will be 95% of a bigger number and still maintain that comfort level.

That particularly applies to anything that improves safety and or reliability. YMMV

[racerdad2]

Thx ! The more I work on her, the more I find to fix, adjust, tweak, check, safety wire, etc. I'm getting close. I've made rib & side head protection with SFI foam & Nomex fabric. I've repaired all the body panels & replaced fasteners, etc, etc. Honestly, I didn't think I'd get this involved, this intrigued & this much enthused about working on and tuning this old girl. 89 CFC Reynard. A big Thx to all on Apex & a special thanks to Jim @ Westroc & Keith @ Racing-Stuff !!! Without all of your help & advice, I'd be in deep doo-doo...