A question about wing settings....

[Knowlesy]

hello all.

I have a simple question relating to wings on race cars. it is so simple, I don't know the answer.

My question is this:

Wings, when set steeper, create more downforce. This downforce increases as the wing angle steepens further.

But can a wing be set too steep, and be totally ineffective? Is there a limit to how steep they can be set before the downforce levels begin to tail off?

Sorry if my question is rather elementary to you folk, but I'd like to know!

[Adam43]

Yes it can be too steep. As the angle increases eventually the drag increases far more rapidly than the downforce does. Tilit it even more and then the downforce will reduce.

Let us consider the extreme: Think of a flat (horizontal) wing. It produces soem downforce because of the same. Rotate (tilt) and you can increase the downforce. Rotate it 90degrees and it is vertical - lots of drag and no down force. Rotate it 180degrees and it is upside down (for a car) and it will produce lift!

[Russfeld]

In the Indy500, especially qualifying, they actually have laid the wings so far back the rear of the wing is lower than the front...

[Knowlesy]

Thanks for clearing that one up!

[imull]

thats not the main reason.

eventually if you keep increasing the pitch of the wing, it will cause separation on the underside, which will rapidly/hugely increase the drag and simultaneously slash the negative lift...

That is why some racers with multi element wings can actually run at a pitch of over 90 degrees (ie air flow actually travelling forward when leaving the 'trailing edge'.

message me your email address and I will send you an aero assignment i did last year that has all teh diagrams and a better explanation if youwant...

[dtype38]

Knowlesy, Adam... Imull is correct, downforce will be lost well before your drag/downforce calcultion would suggest because before that the wing will reach its "stall angle". At that point, like with an aeroplane, the angle of attack is too steep for the air to remain attached to the wing and will separate, destroying the aerofoil effect. It is possible to correct this, but as Imull says, it needs multi-element wings/

[Adam43]

Oh yes, definitely. My answer was only sufficient for the question in hand. On a superficial and first order effect it is clear that there is not a continuous gain.

As for an aeroplane you can't just demand any angle of attack.

imull, I'm interested in your assignment. I'll email you and perhaps we can chat more.

[greenamex2]

From all the books I have read it seems that the maximum angle for a single element wing is around 12-16 degrees to the airflow.

The wing I bought from DJ Racecars for my track day kit car bears this out by only having adjustment holes up to 14 degrees.

The differences between the wing being flat, being half way angled and being fully angled is quite dramatic.

The Simon McBeath book on aerodynamics (published by Haynes) is probably the best all round reference on the subject for laymen and isn't very expensive.

[Knowlesy]

I've PM'd you Imull!

[imull]

email on way. will take a calendar month to upload though forgot how many pics are in it lol

[imull]

splitting it into sections and sending on...

yahoo mail wont allow it in one chunk...

[Knowlesy]

imull....did you send it?

I haven't received it, so it is quite possible that it doesn't fit my puny little wanadoo inbox. I'll give you another e-mail address if needs be!

[Ntrprise]

Without meaning to over simplify this.... a too steep wing will cause it to stall..... meaning to lift / downforce.....

..... I think........

hrug:

[Red Dog]

Yes Ntrprise.

As the wing angle of attack increases, the lift (meaning downforce here) will increase but so will the drag. At a given point, determined by the profile of the wing and generally between 12 and 16 deg, the air will prematurely detach from the underside of the wing and lift (downforce) will decrease. This is the stall condition.

Two things to note:
1) To measure the angle properly the true chord line of the wing must be found. This is from the centre of the leading edge radius to the top edge of the trailing edge (ignore any gurney strip) From this you will see that a wing that looks to be at zero degrees is actually at 3 or 4 degrees already.
2) Unless you have an excess of power or are not expecting to get above 80 mph you do not want to run your wing at anything approaching stall speed as the drag penalty is too big. I would say 8 or 9 degrees is about it.

I have seen people who should know better run silly wing angles and wonder why they didn't go quicker and in any case it is very important to keep the car balanced. Lots of rear downforce will tend to lift the nose unless you add downforce there too. How big is your testing budget??!!

[imull]

been away at the RAC knowsley.

its about 9meg with all the pics in it so does take a bit of space up...

will do it in teh next day or so. knackered after 1500miles and 6 hours sleep over the course of the event

[R59]

That's why NASCAR use such high angles on their lips to slow the cars down via drag, not so much as for downforce.

I'll agree with my learned collegue in tintops that 16deg is probably the most you want to go to, before you gain no more downforce, just adding to drag.

However, when you look at F1 wings, you'll see mahousive amounts of (rear)wing on some circuits, looks like they are running as much as 60deg!! Shurely shome mishtake when you study the books.

Rob

[1200Datto27]

No, because the 16 degree is for a single plane wing. If you have multiple planes, then each plane act on the next, keeping the boundary layers attached, and allowing for greater wing angles than with a single.

[R59]

Ahhh, I see. That makes sense. Damn books never tell you this! (not the one's I've read, they only talk of single element/plane wings!)

Rob.

[Chucky]

Ever seen the flaps come down on a 747? That's a good study in how steep an angle of attack can be with a multi element wing.

[imull]

Competition Car Downforce and Race Car Aerodynamics advertised here are also well worth a read if you want to know more...

Knowsley and pitcrew might recognise a few of the pictures in it...

BOth well worth getting for anyone remotely into F750 or even kit car building as it will give a lot of ideas on how to alter the design and improve in a new way...

Once you understand these, Flightwise is worth getting but it is more in depth and heavy going!


Did you get the emails Knowsley? they werent bounced back to me