Setting wing angle

[Magpie]

How should you set your wing angle? The rear wing angle is dynamic, as when the rear suspension is compressing (and the front remaining unchanged or operating in the opposite direction to the rear) the wing angle will change. Think of a see-saw and on one end is the wing fixed at one angle.

Do you set the AOA when the car is at rest? With the drivers weight? When the car is level? Do you take it from the middle of the wing? Do you use the endplates?

As a side project on Sunday and since I had the car level (on jack stands) decided to set the wing angle (again). The car being level means that rake had been taken out of the equation. Further decided to make sure an edge of the endplates was level so that there was a reference point. When the car comes off the jacks I will retake the angles to see if there was a difference.

For those people with APR wings don't forget to loosen off the pivot points for the bottle screws as you can easily damage the aluminium adjusters.

Wing in the middle. This is hard to do because of the gurney flap, however adjustments are made relative. As long as the same place is used then changes can be measured. The wing was adjusted to 0° after the photo.
DSCN3064 by Eipeip, on Flickr

Bottom edge of endplate
DSCN3062 by Eipeip, on Flickr

Top edge of endplate. Was surprised that it was not level with the bottom. In fact none of the edges are the same angle!
DSCN3063 by Eipeip, on Flickr

[zossy1]

My understanding is that AoA is set using the plane from the centre of the front of the chord of the wing to the rear (ignoring the gurney). I'm talking 2D wings here - 3D, I'm not so sure.

The way to do this is to remove an end plate and mark the centre of the front chord, and then measure the angle placing the level along the exposed profile of the wing (along that line - the "chord line"):

https://encrypted-tbn3.gstatic.com/imag ... d2ZSZVXL0g

You can then either adjust, or otherwise, set the level up on top of the wing (chocked to the same angle as the AoA measured from the exposed profile) and then adjust.

The end plates from Singlular, as I understand it, are NOT intended to run flat/level. Ryan should have noted that in the instructions. I understand why he may be cagey about this setup stuff because, whilst it is possible to copy a singular end plate from pictures, it is not possible to duplicate the setup of the end plates.

If you are a genuine singular customer (as you are), I'd email Ryan about end plate angle.

[Magpie]

zossy1 thanks, there were no setup instructions, will email Ryan.

[madjak]

The end plate angle shouldn't matter that much, it's where the cutout on the backside of the plate sits against the wing that is more important. Because of the way the endplates mount, changing the cutout changes the angle.

As for AoA on a 3D wing like the APR... there are basically two. One at the center of the wing, one on each end. Really AoA is onoy useful for initial setup as the direction of the airflow over the wing will change from car to car depending on the height of the wing, rake of the chassis, roof, front aero, etc

I would just get it ball park and then tweek subject to how taily the car is through big sweepers. Record what holes you use to mount t and iteratively refine it. For record keeping I measure my wing on the top face just because it's easier.

[madjak]

The end plates are stopping the high air pressure on the top of the outer edges of the wing from leaking around the sides to the low air pressure below. If you have no end plate then a good part of the length of the wing is less effective as the high pressure and low pressure air can mix effectively losing that force downwards on the wing. Add a well designed end plate and you can keep the pocket of high pressure on the top and low pressure on the bottom from mixing.

The end plate also forms a nice little vortex swirl where the laminar flow along the side of the car mixes with the deformed air from the wing which reduces drag a lot. So a well designed end plate not only increased downforce but reduces drag at the same time.

I think the claim of 25% might be accurate if you think of it at 12.5% increased downforce on each tip of the wing.

the whole 3D wing thing is only useful because the air coming over the rooftop is heading downwards over the boot, whilst the air that skips around the side of the roof is near horizontal. A good designed 3D wing is keeping the airflow over the wing more consistent over the length of the wing. The idea being that you can prevent the middle section going into stall if the AoA is too steep. If you put a 3D wing high enough though it will be worse off than a 2D wing as the airflow high is flatter. So generally, low wing mount = 3D wing, high wing = 2D.

Edit: I was responding to Dan's post which is now gone.

[Dan]

Edit: I was responding to Dan's post which is now gone.

Sorry, I realised I posted it in the wrong thread, I reposted it in the endplate thread here

viewtopic.php?f=30&t=71321

[madjak]

Edit: I was responding to Dan's post which is now gone.

Sorry, I realised I posted it in the wrong thread, I reposted it in the endplate thread here

viewtopic.php?f=30&t=71321

Thanks Dan, I found it after I posted... Lets move the discussion to the other thread.

[Dan]

Thought I'd upload these for people to use.

I did a bit of a comparison of APR wings/angles before I brought my wing as I wanted to make sure it would still be useful after I upgraded to a supercharger and after one of the BYP guys suggested that a GTC wing might be a mistake suggesting I should consider a GT series wing (low speed drag does look good on the GT wing but I thought it was a bit silly driving a wing that's high enough to be in free air on the road ).

The problem with comparing on the APR site was some of the charts uses newtons and others lbf so I converted them all to lbf and put them in excel. If anyone wants it I can upload the spreadsheet.

Since APR engaged two seperate firms to do the analysis for them there might be some difference in how these are modelled but it is never going to be 100% accurate anyway, it'll just give you an idea.

I was mainly tossing up which way to go if I wanted to go bigger than a GTC-200 and that's why I compared the GTC-300 to the GT-250 and GTC-500

GTC-200 vs GTC-300



GTC-300 vs GTC-250



GTC-300 vs GTC-500

[madjak]

I read somewhere that for every 20lbs of drag it's roughly equivalent to a loss of 2 hp (approx). So the GTC200 @ 10 degree and 100mph gives you 160lbs of downforce for the loss of 2hp.

That statement is up to 100% correct or more!

[Magpie]

The force of aerodynamic drag (Fd) regarding an auto is the product of the drag coefficient (Cd) times the frontal area (A), multiplied by the square of the velocity. Overcoming Fd requires a propulsive force rising as a cube of velocity. An ordinary car traveling at 40 mph may require 20 horsepower to overcome aerodynamic drag, but this would rise to 160 hp at twice the speed (80 mph).
http://www.rmi.org/RFGraph-Horsepower_overcome_aerodynamic_drag

Drag depends on speed.

The issue would be having a wing that produces TOO much downforce as you only have limited HP and what should it be used for? Speed or overcome drag?

[Dan]

I mainly use the numbers to do relative calculations e.g. if I have a wing with X angle what angle would that correlate with on a different wing in terms of efficiency/downforce rather than worrying about the exact numbers being given.

For the most part with APR you should have a pretty good idea of what size wing you need for your car based on others experiences with similar power and who drive on similar tracks.

Talking about drag and speed, one thing that surprised me looking at the calculations that APR have on their site was comparing the GTC-300 and GTC-500 numbers, the same guy did the analysis a few months apart and initially I thought he got something wrong with his calculations as the GTC-300 numbers were higher than the GTC-500...

But I think the reason I think the GTC-500 has less downforce than the GTC-300 at lower speeds is because it's optimised for higher speeds - One thing they did which is obvious is change it to have only 10 degrees of twist on the GTC-500 rather than 15 degrees on the GTC-300.

Here's the drag numbers for the GTC-500, you can see the gain in drag at higher speeds:


Here's downforce for the GTC-500 (180mph = 584kg @ 0AOA):


Also my numbers were wrong in my GTC-300/GTC-500 comparison as the 500 was in newtons (I think I must of tried to recalculate my numbers at one point as I was in disbelief about them being less and forgot to fix it), here's the corrected one:

[madjak]

The force of aerodynamic drag (Fd) regarding an auto is the product of the drag coefficient (Cd) times the frontal area (A), multiplied by the square of the velocity. Overcoming Fd requires a propulsive force rising as a cube of velocity. An ordinary car traveling at 40 mph may require 20 horsepower to overcome aerodynamic drag, but this would rise to 160 hp at twice the speed (80 mph).
http://www.rmi.org/RFGraph-Horsepower_overcome_aerodynamic_drag

Drag depends on speed.

The issue would be having a wing that produces TOO much downforce as you only have limited HP and what should it be used for? Speed or overcome drag?

The general rule of 2hp per 20 drag still applies though. So as the speed moved up the drag will increase. So the 20 will turn to 40, then 80 and so the power the wing saps goes from 2hp to 4hp to 8hp and so on.

A wing only contributes a small proportion of the car's drag.

And Dan, yes the different wing profile shapes effect where the wing is efficient. The COT wing that alot of the US guys put on their cars is optimised for higher speed as it is designed for Nascar. If you look at the profile it has a hollow at the rear almost like the curve is in the wrong direction. The good thing is the wing has very high L/D ratio so it's efficiency is in the 10-12% range as opposed to the APR wings which sit in the 6-8% range. The AoA must be shallow however as the hollow can cause a stall point if the angle steps up too high. So it's optimised for a specific downforce rate at a certain speed and has less adjustability range than a more generic APR profile.

The wing I designed has some of the COT wing aspect but no where near as severe... It is more tailored to slower speeds in the 100-180kph range. In theory I think my wing should be more efficient than an APR at those speeds but if I start getting over 200kph or I increase the AoA too far, the wing will start to generating far more downforce with the drag going up exponentially. So it's ideal for the tracks I run at as I'll never hit over 200kph and it operates at very low drag which is ideal for my 200whp but if I ran it at Bathurst or PI I'd lose lots of top end speed due to the drag.... Not that my diff gearing would let me get that far.

COT wing:


My Wing: (you need to turn your screen upside down)


Can someone post a pic of the end of an APR wing? It should be a more standard profile.

[Magpie]

[greenMachine]

I assume people here are also reading the other thread, so I will not repeat that. All I will say here is

1. Precise measurement of the chord line implies you know the airflow in front of the airfoil, otherwise you are just guessing the AoA angles.

2. You really want an AoA reading that is repeatable and reliable, accuracy is secondary, because you want to be able to assess the effects of AoA changes, and determine airfoil positioning accordingly. For example, fastest setting at track 'x' is at setting 'y'. This might be -10 on your gauge, but the true AoA number may be quite different but it is irrelevant as all you want to correlate is lap time with your readings, and be able to go back to exactly that reading every time you visit that track.

3. Changing rake will affect AoA numbers, though I doubt there would be a big effect unless the rake change was quite extreme - but someone might correct me on this.

4. 3D wings would be (I think) treated the same way, ie experimental approach correlating lap times and airfoil angle - doesn't matter how you measure AoA, just do it in the same place, the same way, every time.

Performance data is great for choosing one airfoil over another, but that is about the end of their practical benefits. Having chosen the shape, getting it to work is largely an exercise in experimentation.

My 2c.

[Magpie]

Angle of attack (AOA) is the relationship between the wing's chord line and the air through which the wing is moving http://ehfc.net/angleofattack.pdf

Agreed. Keep a notebook and note changes (and the effects) so that changes can be wound back if needed.

You will not only need to record the angle of the wing but another surface as well. It would be pointless to record an angle of 5° yet the car was sitting on a 5° incline! You could record the angle of the frame rails or pinch welds and the wing angle relative.

I could test impact of changes in rake on the wing angle on the weekend if there is enough interest