Gurney Flap?

[ValidusVentus]

So I'm toying around with the idea of putting a gurney flap on the trailing edge of my sport spoiler. At the moment I am not buying a wing. Anyway, I was going to go with something modest, say 2.5% of the cord length (which I'm not sure really applies since it is just a spoiler) so I was thinking probably just .5-.75" Thing is, I'm not sure of how much benefit it would actually be seeing as how there is no airflow under the spoiler, negating a lot of the normal effects of a gurney flap. So I am still in the thought process on this and looking for any well thought out input. One example would be the gurney flap on the back of the spoiler on the new C7 vette, especially the Z06.

I was also thinking of flipping whatever "L" shaped material I may end up using and applying it to the underside of the leading edge of the chin spoiler/splitter on the Stillen front end since it has no air dam and putting one in the stock location would be way back from the leading edge. Nothing major, maybe an inch, and I'd obviously have to make it out of something a bit flexible.

[ResIpsa]

I thought about doing the same thing a couple years ago. I purchased a piece of angle aluminum tried to bend it to shape and gave up. Unless you have a way of making smooth bends it is going to be difficult and ugly.

However, I think it should have some small benefit. Both BMW and Audi use thin spoilers that are in effect a gurney flap.

[Chuck33079]

I can't imagine arbitrarily slapping a gurney flap on the sport spoiler would have any effect whatsoever. Usually when I see one on a car it's seen some wind tunnel testing and the flap was part of the overall plan, not an afterthought put on later.

[GSS138]

I'm on the fence, lots of guys at track build their own splitters, but I don't see too many custom wings. Not even sure if it will work on a spoiler since the spoiler is really just to add good flow to the aero and keep the airflow from disrupting until it is behind the car.

I like the idea, but would have to give it a thumbs down. It's creative, but I think aero needs to be tunnel tested or it isn't going on my car.

[kenchan]

i thought mr.gurney was going airborne. wheew.

[BGTV8]

You need a proper wing to provide down-force .. the OEM stuff is simply cosmetic and marketing-driven bull-tish

Could give serious bling-factor though.

If you install a wing, then a splitter is also required because the last thing you want is the equivalent of a 100 or 150kg bag of sand in the boot/trunk which will only serve to lift the front and let more air underneath it.

Usually, first is the splitter at the front then when you have that under control, add wing - or do both as a package.

Remember also, if the splitter is generating 80-100kgs of downforce, you are going to need to have it securely mounted - my race car splitter/airdam is mounted to the chassis with 6 x 8mm bolts for precisely this reason. Where the bolts go thru the fibreglass it is reinforced with some ali plate as well - it needs to be "robust".

[kenchan]

Originally Posted by BGTV8

You need a proper wing to provide down-force .. the OEM stuff is simply cosmetic and marketing-driven bull-tish

Could give serious bling-factor though.

If you install a wing, then a splitter is also required because the last thing you want is the equivalent of a 100 or 150kg bag of sand in the boot/trunk which will only serve to lift the front and let more air underneath it.

Usually is splitter at the front then when.

Remember, if the splitter is generating 80-100kgs of downforce, you getting have it securely mounted - my race car splitter/airdam is mounted to the chassis with 6 x 8mm bolts for precisely this reason. Where the bolts go thru the fibreglass it is reinforced with some ali plate as well - it needs to be "robust".

we see that you stick very well to the earth driving up-side-down all the time down there in australia.

btw, the factory spoiler is there to provide zero lift.

[ValidusVentus]

Thanks for the input, even the negative input.
I will be doing more research into this. Just received my copy of "Competition Car Aerodynamics" in the mail today (to go with my much read "Competition Car Suspension"). I hope to be better able to analyze the airflow over the car with a bit of reading.

[Dwnshift]

You would be better off installing a LARGE front sway bar.

[ValidusVentus]

So after doing some more research I do think a larger spoiler (rather than just a gurney flap) put at an angle would be of benefit to our car, especially if I cover some of the gaps in the underbody in front of the rear bumper. For the same reasons they are able to produce downforce on NASCARs they should work for our vehicle. For our car it should create a larger static high pressure area on top of the rear hatch as well as directing the airflow coming off the back of the car in a bit of an upwards direction, which due to newtons second law of motion will also produce some downforce. It also creates a more "intense" low pressure area behind the car -yes, adding drag- which helps to pull air more actively out from under the rear end, -this would be a huge benefit for anyone with a functional rear diffuser - reducing static pressure beneath the car (contributing to downforce). This low pressure area also acts on the underside of the spoiler. Seems like with the design of our rear hatch the boundary layer should be staying attached pretty well as it comes down from the roof and we should be getting pretty good airflow over the spoiler area.

Also looked into the effects of a front chin spoiler extension / air dam. It should create some front downforce (with a very slight increase in rear lift- but a net overal gain in DF) via creating a low pressure area directly behind it which acts on the underbody of the car. If I ever put a front splitter on the car it would increase the DF generated by the splitter as well (even higher pressure on top, even lower below it). It will also cut drag by reducing the flow of air over the relatively rough underbody. This lower pressure below the engine compartment also helps pull air through the radiator and out of the engine bay, as well as through the wheel wells. This should obviously help with engine cooling (which isnt really an issue for us) but the lower pressure in the wheel wells coupled with higher pressure seen by the front end could possibly help with pulling air though the brake ducting - which is an issue.

I didnt completely explain everything here, that would take a while and people can look it up in more detail. The trick will be finding a way to make a rear spoiler that doesnt look completely ugly lol. I prefer functional over form in most cases but I cant put sometihng on my car thats straight up unattractive.

[ResIpsa]

Here is some of the custom aero on my ride. The splitter you see is plywood wrapped in fiberglass (+/- 10 lbs) with custom attachments to the crash bar and chassis. I recently fabricated a carbon fiber splitter which shaves off around 5 lbs.

The diffuser is aluminum covered with fiberglass which I have been fabricating/developing/changing for the past 4 years.





And currently under fabrication... More wing please!

[ValidusVentus]

Yeah, thanks for sharing the pics ResIpsa. Impressive work! How did you support the underside of the hatch area under wing?

The splitter looks like it could stand to extend a bit further. Its easy to make them too long in the case of most cars but with the/your 370 front end, it doesnt appear to extend noticeably past the front overhang. This means the high pressue area acting on the top of the splitter is also acting on the underside of the front overhang and probably negates most of its effects.

Also if you were to move the wing rearward I think it might be more effective. For one, just due to the better leverage. But less obviously to enhance its interaction with your diffuser. You probably considered putting it further back already and didnt want to mess with the spoiler, and maybe the wing wont even mount to the curved area there. I dont think there would be a large interaction between the spoiler and the wing due to the spoiler having basically no angle of attack.

Just a couple of constructive suggestions you may want to look into if you hadnt already thought about them, not trying to be negative or pick things apart. I just enjoy analyzing engineering/physics related stuff. Do you have any thoughts on any of that?

PS: Obviously you run the wing with endplates?