NineLivesRacing Gurney Flap Question

I have been reading about gurney flaps an intrigued. I'm curious why every wing DOESNT come with them. Is there a downside?

Question 1

Also...without having completed testing, is it premature to buy the medium flap now?

Question 2

Will Johnny be at Hyperfest again this year?

Question 3

Any chance you would have a flap in stock I could buy and install there?

Gurney flaps, wickers, whatever you want to call them. They do push a wing at the limit of angle (stall) into a bit better downforce by accenting the low pressure near the bottom surface trailing edge.

The reason all wings don't make use is they can be more draggy than increasing angle, unless you are up against stall. If you are not drag limited (plenty of power) then a wicker is an option. If you are power limited, the drag increase can be bad enough to reduce total lap times (due to increased drag).

In reply to jh36 :
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let's get those questions in order but first an explanation. 
Gurney flaps or "wickers" are a little 90* tab at the trailing edge of a wing.  this little part trips the air leaving the wing and makes "eddies" (circled in yellow) this little air disruption helps extend the theoretical chord. aka it make the wing act like a bigger wing. all good right? well no. The bigger the wicker the more downforce but also the more drag.  https://9livesracing.com/pages/cfd-testing if you follow this link to our CFD testing you can see the .75" gurney drops our normal 15:1 lift to drag ratio down to 7.9:1. you do get a drag hit. 
How i use wickers are mostly on endurance teams. champ/lemons/wrl. they install quickly and can make for very quick downforce changes that could be done in the pits. example: lets say your driver is hit and the car now wants to rotate, easy toss in a .75" gurney and send him back out. the wing can make up for poor suspension. also lets say the front tires are starting to age quickly. pop into the pits pull the gurney out and keep going.   
 
I have been reading about gurney flaps and intrigued. I'm curious why every wing DOESNT come with them. Is there a downside?
integrated gurneys are not a good idea. as stated they do hurt lift to drag ratios. and most cars out there running now can find plenty of downforce with the wing alone. 
 

Question 2

Will Johnny be at Hyperfest again this year?
I won't :( shop has been nuts we have over 200 open orders. i gotta stay here and weld weld weld. 
 

Question 3

Any chance you would have a flap in stock I could buy and install there?
we have them in stock. be happy to ship you some. 

Ok, so it seems they are not the magic elixir I thought. I am running your wing fairly conservatively (I think) and the thing feels pretty planted. Perhaps I will hold off until I reach limits and have a better feel for my needs. I appreciate the complete answer. The wing continues to be great. I'm glad the business is hopping!

When I crewed for IMSA teams we used them for tuning.   We had them in the pits in 1/8",  1/4",  3/8" and 1/2".    And some were not as wide as the whole wing.  The engineer would call for a certain set during a pit stop and we would tape them on fast.   Because we would test in the wind tunnel the engineer already knew what the resulting change would be.

In my FC car we always tried to get the most efficient airfoil shape, and run as low an angle as possible.  Within that situation a wicker could increase downforce without too much drag increase.

Aero is complicated.  Its not about how cool it looks, its about how well it works.