Angle of the attack of a wing on a Z?

[heavy85]

After a couple track events I realized that over 100 MPH the rear end is not as planted as I would like. So I was going to add a simple sheetmetal spoiler but then came across this for cheap and couldn't pass it up.

 

 

I was looking for an ARP after seeing that's what the fast guys were using. The really nice ones are CF and are about $685. This aluminum one is normally $285 but I got it off ebay new for $90 which is about what a sheet of aluminum would have cost anyway. Now I'm rambling so to get to the point I'm a little confused how the wing should be angled. Currently it's at the highest angle and the front edge is still higher that the rear edge. This has me wondering if the angle of attack is relative to the world or relative to the slope of the roofline? This basic set-up looks similar to the wind tunnel wing and I cant see any spacers from the picture although that was a bi-wing and mine is a single plane. I have yet to test this and want to be prepared for the next track day if I need to make and bring some spacers.

 

Thanks

Cameron

[Filmjay]

You can calculate downforce as follows....

 

Aerodynamic forces have the following form: F = 0.5 * A * coeff * ro * v^2.

Here, F = force, A = area of application (for example the total area of the front of the car, as viewed from the front), v is the speed of the car (in m/s), ro is the air density (1.225 at 15 degrees Celcius is a default value), Furthermore, 'A' can be split for wings into span and cord (width and depth), where A = span * cord.

For wings, you can also (for the linear region) add the angle (in radians) into this, so you get:

F = 0.5 * span * cord * angle * coeff * ro * v^2

 

 

http://www.racer.nl/tutorial/wings.htm -link to original

 

 

 

...but it ca be pretty tricky to accurately figure due to variables like air density. But, I guess a rough estimate is better than none.

[mark]

Is the wing mounted to the brackets backwards? Looks like you need to point the rear of the wing toward the front of the car. Leave the brackets on the car and turn the wing around.

[Roggaman]

Is the wing mounted to the brackets backwards? Looks like you need to point the rear of the wing toward the front of the car. Leave the brackets on the car and turn the wing around.

 

Looks to me he has to make new bracket since these seem to be made for a sedan!

The wing itself seems to be pointed in the right direction.

[Filmjay]

Is the wing mounted to the brackets backwards? Looks like you need to point the rear of the wing toward the front of the car. Leave the brackets on the car and turn the wing around.

 

HAHA! You're right. It DOES look like it's backwards.

 

But, I think it's because those wings are meant to be mounted on a flat deck lid instead of an angled hatchback.

[johnc]

Wing angle of attack is relative to the ground unless you have some airflow data to show otherwise (pretty rare). You'll need to know where the wing stalls (usually provided by the wing manufacturer or you can find the calculation on the internet) and then set the angle of attach just below, that. Then, during testing at each track, you reduce the angle of attack to get the best compromise between top speed and downforce.

 

Most standard wing brackets won't work on the rear hatch of a 240Z.

 

Oh, and yes, the wing is mounted backwards.

[junglist]

Oh, and yes, the wing is mounted backwards.

 

 

First thing that I thought when I opened the thread and saw that picture.

 

$90 for that wing is a pretty good deal! APR makes very nice stuff, I have a set of their universal CF mirrors and love them. I wish I could afford one of the CF wings also, was it an ebay store that you got this wing from or did the seller just have one?

[Slow_Old_Car]

yep, that wings not being a wing right now, it's being a lunch tray.

[heavy85]

Sorry to bust your bubble guys but but I'm not a total idiot. The wing is mounted correctly.

 

I guess I'll plan on making some extensions but still wonder about the wind tunnel wing as I dont see any extra adjustment or spacers used there and the wing was quite effective.

 

Cameron

[Challenger]

I looked at one of these arp wings at a local snows auto (performance/audio/etc) and it was mounted "backwards" on the display stand.. I think the small tip of the vertical planes points forwards.

 

Have you looked at vg's? From what I read on the wind tunnel testing that was a good pair. (aluminum wing and vgs)

[yellazed]

Sorry to bust your bubble guys but but I'm not a total idiot. The wing is mounted correctly.

 

I guess I'll plan on making some extensions but still wonder about the wind tunnel wing as I dont see any extra adjustment or spacers used there and the wing was quite effective.

 

Cameron

 

It is mounted "correctly" in that it is facing the right way. It needs different/modified mounts. As Filmjay said - the ones you are using are designed for a flat deck lid, not one at 30 deg to horizontal.

 

 

 

You have it laying back so far it is creating lift.

 

Btw: it is APR - not ARP.

 

(Edit) After another look: If you can turn it around to face the other way it might alter the attack angle enough to create some downforce. (And swap the endplates around so it looks right). Might be worth a try.

[Challenger]

Yeah arent the ends removeable? Sounds like a good plan.^

[heavy85]

Uhhh this is an airfoil not a spoiler ... you dont just spin it around the other way ...

 

Anyway I made some new brackets so the top is now about flat to the world at the lowest setting. Unfortunately it'll have to wait for next year to see if it does any good. I doubt I'll tell the difference at the autox this weekend.

 

 

Cameron

[JMortensen]

What is the chord length on that wing? It looks small, but that may just be pictures at angles, etc. How hard do you think it would be to adapt a Gurney flap onto it? That would probably make it quite a bit more effective. Any hardware that sticks out should be on top where the airflow isn't as critical.

[heavy85]

What is the chord length on that wing? It looks small, but that may just be pictures at angles, etc. How hard do you think it would be to adapt a Gurney flap onto it? That would probably make it quite a bit more effective. Any hardware that sticks out should be on top where the airflow isn't as critical.

 

It's this: http://www.aprperformance.com/index.php?option=com_content&task=view&id=55&Itemid=44

 

Look at the far end up against the side plates. The top is flat then at the back turns up sharply similar to a gurney flap. Or better yet here it is:

 

 

Cameron

[JMortensen]

You could still add a flap to that wing. In fact, in some of the formula car multi-element wings the gurney actually faces forwards on the very top element. The hard part would be mounting the flap without screwing up the airflow too badly.

[capt_furious]

A simple extruded aluminum L-angle piece with the forward edge ground to a knife point, then flush-riveted with countersunk holes to the trailing edge of that wing would probably be fairly inexpensive - about 30 minutes worth of work at a sheet metal shop. There's enough 'meat' at the trailing edge to drill and countersink the required holes(underside on the wing, topside on the angle), having them flush riveted and the forward edge of the angle ground down would likely give you the cleanest installation possible. Granted, you'd have to drill it out to remove it, so you'd want the proper height of the angle calculated beforehand.

 

 

Edit: Forego the rivets and countersinking on the wing itself. Have the angle countersunk and the holes drilled in the wing threaded, and use countersunk screws. Easy to change the flap height if needed.

 

The Gurney flap, from the source.

[JMortensen]

I was actually looking at the APR site again this morning and it says this wing maxes out at 120 mph. I'm wondering if the aluminum extrusion can't handle the downforce that it would create at speeds above 120. If the flap made the wing a lot more efficient, that might stress the wing even more. Not to mention there is a limit to what the hatch can take.

[heavy85]

I was actually looking at the APR site again this morning and it says this wing maxes out at 120 mph.

 

Look again Jon it actually says:

 

Average Track Speed:

Less than 120mph (193kph)

 

So that said to me it is designed for AVERAGE speeds not that it could not handle going faster than that. For the tracks I will most likely run at this should be adequate because they are < 130 MPH.

 

Edit: This was a bit of an impulse buy since the price was so good. Therefore I did not do the homework I would have normally done to say definitively.

 

Cameron

[JMortensen]

Look again Jon it actually says:

 

Average Track Speed:

Less than 120mph (193kph)

 

So that said to me it is designed for AVERAGE speeds not that it could not handle going faster than that. For the tracks I will most likely run at this should be adequate because they are < 130 MPH.

 

Edit: This was a bit of an impulse buy since the price was so good. Therefore I did not do the homework I would have normally done so say definitively.

I would have bought it too. I'm impressed with the airfoil shape, and it squeezes in just under Solo II regs for XP. I'm just wondering what the weak part is in the assembly, and if you put a Gurney on there and it brought the total downforce to 500 lbs is it going to tear the thing apart at an inopportune time...