Wing Shapes

THR · 25 Jun 2002, 20:12 (Ref:321513)

We would like to try a new front wing, as we are getting understeer and thats about all there is left to try to get rid of it...

we know the front wing currently used isnt exactly perfect.. and didnt come from orginal the car as built, hence we have no idea where it came from! looking round the paddock, it also looks very different, so it was probs just a guess by the previous owners.

so the question is, does anyone know where i can get, or have dimensions for a wing profile?

its no problem making the wing, thats the easy part

the hard part is actually getting a profile that is known to work. as a lot of the ones sold are for two plane front wings, and we are only allowed one plane, a 2 plane one would have been designed differently simply taking the 2nd plane off wouldnt be the most effiecent wing i feel.

Tony_Simpson · 25 Jun 2002, 20:54 (Ref:321540)

If you want some wings (admittedly aircraft ones) then have a look at: http://amber.aae.uiuc.edu/~m-selig/a..._database.html

It gives you the points for a wing section, which you can make up/look at in say AutoCAD. A little trial and error might be needed, but it a start.

Hope that helps a bit.

boyracer · 26 Jun 2002, 01:05 (Ref:321713)

If you are designing wings at all may I recommend a book...
"Competition Car Downforce" by Simon McBeath (I know I've got the author right not so sure about the title)
It is an excellent book for the type of thing you're attempting as it explains what effect aspect ratio and the position of camber within the wing have on stall, drag and downforce.
Most wing shapes for aeroplanes are classified by the NACA system (also described in the book) so it is worth searching the net for any reference to that. I found a freeware program called "NVFoil", unfortunately I forget where I got it from. Admittedley it is for analysing wing profiles for aeroplanes but all you need to do is stand on your head and it becomes the right way for downforce. The program has a database of NACA wing profiles and allows you to create your own (not sure ??) but then it also gives drag and lift co-efficients for varying angles of attack of the wing.
If you need more info e-mail me and I'll scan the articles and pull up a copy of the program for you.

Tony_Simpson · 26 Jun 2002, 08:16 (Ref:321854)

The Competition Car Downforce, is a good book but like all books it does not list the wing points. They do have a data in them on lift and drag coefficients, and referances to other books.

Some of the best ones I have found are:

BARNARD R.H. Road Vehicle Aerodynamic Design, second edition, Mechaero Publishing, England, (http://www.mechaero.co.uk/)

KATZ J. New Directions in Race Car Aerodynamics, Designing for Speed. Bentley Publishers, USA,

and also the McBeath book, from Haynes publishing.

By the way THR, what car are you building the new wing for???

Tony_Simpson · 26 Jun 2002, 08:20 (Ref:321856)

Just found the nvfoil site for you all: http://www.geocities.com/CapeCanaver.../nvfoilen.html

THR · 26 Jun 2002, 10:51 (Ref:321974)

Thanks for all that...
however im not entirely sure that plane wings are any good for racing cars... they must average at wot... 200mph? were as we average 90mph.
also there is the ground effect to consider as they are only 50mm off the floor.

Its a Formula Renault single seater...

that book is good.. and Simon is a nice guy, helpful.

any more!!??

Tony_Simpson · 26 Jun 2002, 12:14 (Ref:322032)

For my dissertation I tested the GA(W)-1 wing section in a motorsport application (to generate downforce), and at a ride height of 40mm, it produced a lift coefficient of around -1.6, and drag of around 0.09. This is with a chord length of 200mm and angle of attack of 4degrees, and air velocity of 50m/s, 110mph or so. This wing is a low drag wing, but was one of the first ones developed by NASA, there are alot more and better wings out there.

Just look at the data in the back of the McBeath book (Apppendix 1) as it has alot of info for airplane wing sections.

Unless you have a CFD package and know how to use it properly or are able to do some wind tunnel testing then using an aircraft wing is the only real option, as you can find the lift and drag coefficients for it. This makes the nvfoil program important as you can test and find the lift and drag coefficients and you will know that with a bit of ground effect on the wing will only improve the values. You only need then to be wary of pitch sensitivity, etc, etc.

By the way what do the Formula Renault rules say for the series, max chord length etc etc. And I guess you know that a low drag wing is needed as you do not really have the power to compenste for the drag produced. Have you thought much about end plate design, etc, etc???

Flatjack · 26 Jun 2002, 12:53 (Ref:322075)

The differences in racecar wings and aircraft wings are not great. If I remember correctly the low-pressure side of the wing (facing the ground) is slightly flatter as this takes more from the ground effect. A bit of theory the smaller the gap between the wing and the ground the faster the airflow has to travel and so the lower the pressure. If you have a wing that curves down causing a smaller area then stays there the low pressure will be over a larger area and thus more of a force is acting on the front wing as force = pressure *area.

Another thing that has to be considered is the pressure recovery if pressure has to change from very low to high then it will reach a point that it separates and you will lose pressure and increase drag.

So at the end of that ramble I suggest you use an aircraft wing upside down and maybe flatten the low-pressure side slightly.

Also I have seen a book called Wings it is written by Enrico Benzing and is bilingual (Italian and English) I have only been able to find one copy in the whole of England and that is in the British Library. I have not been able to buy it nor have I been able to get it from anywhere else for example the I Mech E don't have it. Good luck in your search.

THR · 26 Jun 2002, 13:11 (Ref:322091)

Fairly sure that the actual wing for the front is only limited for the width.
End plates are free, so ive made some largish ones.

yea its gotta be low drag aint it... which is y i really want to run very little attack on it, which is why the actual shape of the foil is important. the current wing we use seems to not let the air on the underside reach the trailing edge, it breaks away b4 it gets there. (by looking at the rain and muck stuck to the wing).

in that proggy then... Cd is coeff of drag, i want a tiny number...
Cl, i want a big number
but wots Cm?

Flatjack · 26 Jun 2002, 15:03 (Ref:322187)

cm is the pitching moment. Hmmm what is the pitching moment well er I think you could say it is the amount force is distributed thus making it pitch example if you have a beam on a pivot and put more weight in front than behind then it will pitch forward. Not the best explanation. I will come back on that.

If the underside of the wing has a high angle of attack then it will separate. As I was saying earlier about the pressure recovery it is trying to change from a low pressure to a high pressure quickly then it will separate have you tried reducing the angle of attack?

Any of the books prevously mentioned will explain Cm. When i get home i will have a look at let you know

Flatjack · 26 Jun 2002, 15:42 (Ref:322227)

ok pitching moment for a car is Pm = Cm*q*A*WB where Cm is coefficient of pitching moment, q =0.5*density of air * velocity squared, a is frontal area and WB is wheelbase

This can be related to the wing by A being the surface area and WB being the chord.

oh yeah PM is positive when the nose rotates upwards.

Does that help you?

THR · 26 Jun 2002, 16:09 (Ref:322258)

yea i understand it now

currently the wing is at 0 deg. when the car is flat and a piece of wood is rested on top of it.having a negative value on it may increase the downforce yea.. but it wouldnt be all that effeicent would it?

Flatjack · 27 Jun 2002, 09:19 (Ref:322747)

You said earlier that "the current wing we use seems to not let the air on the underside reach the trailing edge, it breaks away b4 it gets there. (By looking at the rain and muck stuck to the wing)."

Do you remember how far before the end it broke away? In terms of chord length. also what angle of attack was it running at?

I said earlier that the angle that you need to keep an eye on is between the ground and the last section of the airfoil. Defiantly should not be above 15 degrees. As this will promote the stalling of the wing.

THR · 27 Jun 2002, 11:35 (Ref:322819)

yea... the angle of attack is 0, but the actual angle of the trailing edge to the ground is quite steep, probs is greater than 10deg, ill have to measure it.

the wing chord is about 300mm, and it breaks off about 120mm from the trialing edge. (looks a long way!)

Flatjack · 27 Jun 2002, 12:13 (Ref:322834)

So that is just over half way from the noes to the tail?. you are loosing a massive amount of downforce and creating a massive amount of drag.

i take it that the camber of the airfoil is very high then. Do you have a picture of it.

If you can't find any profiles then I could send you one just let me know the format that you would like it in.

THR · 27 Jun 2002, 12:40 (Ref:322864)

yea thats right.. its pants!
ill take a pic of it in the next few days.

the reason why they made it so big is cos they were picking up understeer, but to me it looks like they have gone way to far!

mdp · 6 Jul 2002, 14:20 (Ref:328188)

I presume the wing you are using is the one on your clubs website for car 66/24??
The front wing on a racing car doesn't just provide downforce. It is used to split the air. if the wing you are using is the same one as for the photos on your website then it would apear you are limited in angle of attack due to the nose. Who ever built this wing was trying to produce a wing with a large degree of camber because you say you cannot use multi foiled wings. The photos are pretty bad but are you using a gurney on the wing? If not try it. If you ever do testing smeer some oil on the underside of the wing. this will show you where you are getting seperation on the wing for days that it doesnt rain!

Go have a look at this web page it may help you.
http://www.insideracingtechnology.com/techstart.htm

THR · 6 Jul 2002, 18:04 (Ref:328275)

heres a scan of the shape of the aerofoil at the moment...
we have run this at various angles... between -2 and +3 deg, measured by placing a piece of wood on top the wing and measuring the anlge of this bit of wood to the floor.

it is...400mm long and the thickness is 70mm (the pic doesnt show how big it is very well)

the mark on the pic shows where the air is breaking off (measured by the practice MDP just described)

A gurney can be used.. but this would still not make the wing work properly. like you say.. the nose gets in the way.. but it doesnt anymore, cos weve sussed that

tis a bit of an old piccie.

as you can see on the pic the tail of the wing is fairly steeped, and looks more than the 15deg you mention flatjack

if you could email me that aerofoil pic you have id be most greatful paul@teamhobbit.com

for the size of the new foil. i was thinking more like 250mm long (looking at other wings).

hope the pics work

THR · 13 Jul 2002, 16:31 (Ref:333284)

anybody got any comments on it?

Flatjack · 15 Jul 2002, 12:22 (Ref:334197)

A few comments. it is not really all that thick (17% chord) i would go for somthing like 15%.
I do think this type of wing would work much better with some angle of attack.

another questions how close to the ground are you runing it? i ask this because a wing will work best in the range of 15% chord above the ground, in terms of lift to drag. Due to ground effect you will lose all downforce at 7% chord above the ground. however at 15% your wing will be very pitch sensitive.

I can send you a graph on the ground effect curve if you like and i will try and put the wing pictures on tonight.

THR · 15 Jul 2002, 13:09 (Ref:334238)

graph would be good....
im not entirely sure how u mean 15% above the ground. if the chord is 70mm.. 15% is only 10.5mm

its about 50mm off the ground at the moment.. hadnt thought about it being too low.. guess it could be?

i was also reading that a gurney flap might also let the air go to the tail of the foil, preventing it breaking off so much.

Tony Harman · 16 Jul 2002, 08:55 (Ref:334787)

Hi Hobbit. Loads of good stuff above, especially if you are making the wing yourself. If you want a wing made THE man to go to is Haggis down in Bournemouth. He was responsible for the Haggispeed Clubmans cars fo the 70's but is now known for his aerodynamic work, does loads of wings for people. If you want more info PM or mail me. TH

Flatjack · 18 Jul 2002, 12:31 (Ref:336466)

The chord is nose to tail and you said that is 400mm so 15% is 60mm. if you say your wing is 50mm (12.5% chord)from the ground then that is proberly what is causing all of the seperation. however a new wing may help.

you are right about the gurney flap what it does is create a low pressure area that helps to suck air under the wing.

sorry i have not got around to putting the profil on yet. been busy. should do it over the weekend though.

THR · 18 Jul 2002, 14:08 (Ref:336525)

ahh thats part of the problem then id guess. bit higher would be better. altho i think it will hit things if i move it up a bit! lol...bit of redesign there to do!

hmmm interesting tho!!!

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