Monday, February 26, 2007

Wings, not Spoilers

I was thinking that both spoilers and rear wings the same, so the explanation and the pictures given is that of a rear wing.The working of both the same.

The comment at the end is very important.

While I was browsing through the orkut community Vehicle Dynamics, I saw a question on Spoiler.

The Q below…
In books it is given as rear wind spoilers induces -ve lift and because of that road traction is increased. If that is the case a lion share of the reaction obtained should come on the mechanism used for that.But In our commercial cars these things are made of Plastics or some similar thing. By just seeing itself it is possible to say that it will not take much load, definitely a load comparable to weight of a car is not possible to apply on that. so what is the real use of that. any other use other than an aesthetic appeal...?

I gave an answer – MY Explanation to that, is given here. When i was writing about it i was thinking about F1 cars.

We know that a spoiler is given to increase the down force to get more traction. But how does it give the necessary down force?? Then we will analyze the strength required.

Below is shown a F1 car where spoiler is a ‘must accessory’. Also here the spoiler is some what different from the road cars.


And a ‘top fuel dragster’ where the effect is very very important.


ANother of the monster


Now a spoiler


And a rough picture downforce generating flat plates on open-wheel race cars.


From the picture, the spoiler alone is taken out and analyzed. Now see the cross section of it.


Now as air past flow the spoiler we can see that the air will get deflected. The direction and the angle is clear from the picture.

From Newton’s second law, the force is also shown. Resolving the force into two, the vertical force will directly add to the down force.

Is that all?? Will it create enough tractive force to overcome the horizontal force that was created by its presence? I doubt it.

Now it is said that, the spoiler adds advantage mainly to rear wheel drive vehicle. Why? How?

To understand that, take moment of forces about the rear wheel.
(All auto enthusiasts, sorry for the picture... I myself is feeling very bad)


Now Calculating the reaction forces at front wheel, with and without spoiler. We will find that the spoiler reduces the reaction at front wheel, transferring more to rear wheel. That means more traction for rear.

That explains the importance of the horizontal force. By spoiling the smooth air flow it is creating more down force – may be the reason it is named so. Don’t know…

Now to the ‘strength’ part. The force on it need not be that high to create a good enough down force on the rear wheels (because of the offset).

Now how much force the air can give on the spoiler, by the deflection of air??
BIG ENOUGH TO GIVE LIFT FOR AN AIRPLANE!!!

Believe me… The lift of an airplane is like that… not just by Bernoulli’s principle. It is written in the blog topic titled ‘lift’.

But in road cars as I mentioned the spoiler is different… I don’t think it has got something more than an aesthetic function.

The Coanda effect deflects the air below the spoiler in picture. It is also mentioned in ‘lift’. But I am not an expert to comment on it, so a link to a web page is given in the first part of it.

My friend Jay pointed out that there is a mechanism by which downforce is given to the front wheels also in the model Koenigsegg CCX - i dont know about that...

Also I would like to change my own statement – if properly designed and fixed it can aid front wheel drive cars also - not sure… But 4wd for sure...

2 comments:

frag'em'all said...

Do not confuse a spoiler with a rear wing. The rear wing of which you have pictures are opposite to an airplane wing and are there to increase down force albeit at the cost of drag. On high speed F1 circuits like Monza you would find cars with a very shallow wing while at Monaco, top speed not being important, they use a steeply angled rear wing...

spoilers are much smaller mainly just a curved lip on the edge of the boot lid (see the pic of a Ferrari F430)of the car. They do increase down force. cant type in the whole answer but you can read on flow separation, critical angle and pressure drag...

and about increasing the down force at the front, read on air dams.

Vishnu Nair

Spoiler Wings said...

Wow great blog! Thanks for posting!