Aerodynamics for beginners

[AMMO]

Arnie

 

You can hire the wind tunnel at MIRA Ltd. (0247 635 5000) for £3,460.00 + VAT for an 8 hour session. You get an operator and senior technician thrown in at this price.

 

Peter

 

Enclosed bodywork has got to be the way to go for less drag. Regarding top speed if we can get hold of the neccessary equipment it might be fun to get a few fast cars at Bruntingthorpe or Woodbridge and see how fast the top cars really are. Bruntingthorpe I think has a 2 mile straight, Woodbridge possibly longer.

 

I've been involved in a couple of speed challenges for motorcycle magazines and had a very enjoyable time. Shouldn't cost too much to organize. Anyone interested?

 

AMMO

[Lennie]

Flared wings do not give lift, all the air bleeds out the side of the car and due to there shape do actually give downforce. They also reduce unsprung weight.Cycle wings actually give lift if you look at a racer with the wing off the back i.e bottom wing stay fixing the wing is actually sucked in the air.

[EFA]

Er typo, distance should have read 10m.

 

 

My point ws that tyre slip (as Peter points out on an undriven wheel) is linear if it exists at constant speed.

 

So if I cal the stack at a steady 30 mph using the GPS as reference, then accelerate to 120mph on the GPS and let the car settle at this speed, guess what - the Stack also reads 120mph. Not 119, not 121.

 

So if there is slip, it must be a linear percentage, or slip does not exist at constant speed.

 

I don't understand how you can increase pressure above the wing on an F1 car and not on a Seven Cycle wing. Surely moving the (Seven) wing forward must increase the downforce effect.

 

Also, the position of the leading edge must reduce lift when it is such that airflow is not driven up between the wing and tyre? (i.e. if the front cycle wings were fitted so the leading adges was at the 3 o'colck position??)

 

I still think that although the front of the clamshell may create downforce Len, the rear section has to create lift to a greater extent.

 

 

 

Oh and that wind tunnel is far too expensive.....

 

 

 

 

 

 

 

 

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

See the Lotus Seven Club 4 Counties Area Website hereid=green>

 

 

Edited by - Fat Arnie on 15 Oct 2001 19:30:21

[Red SLR]

Having spent a couple of years of my boring student life working out things like lift I would have to agree with Len. The shape of a clamshell is nowhere near an aerofoil and is not likely to produce lift with the car running in the horizontal position, however if your car was to pivot about the rear, ie raise the front end up, then you will soon learn that the air pressure at this speed acting on a flat object with "cup" shaped wings would soon "lift" it alright! I would bet that this would flip the car over. So all you have to do is remove your wings and re-install them at an angle of about 30deg, then you will fly!(well maybe feel the frot going light, I am sure Arnie will try this out for us!) But I think you would have to reach over 130mph for this to happen.

 

I think the Lambo Mioura question.gif had this problem!

 

 

 

 

X777CAT

[Morls]

Somewhere recently on Blatchat people were disscussing scale model sevens. These were available with both cycle and proper wings and would fit in a small, (university?) wind tunnel.

 

Although this would mean admitting to playing with toy cars it would cost less than the MIRA facility.

 

Given that all the theory is just that, has anyone compared lap times or terminal speeds with no change other than wings on - wings off?

 

 

 

Mark

[Miraz]

The lift or downforce is generated by the difference in pressure on either side of the wing.

 

The F1 aerofoil achieves this by accelerating the airflow along the longer, lower surface and hence lowering the pressure of the lower flow.

 

The cycle wing has a high-pressure zone below the wing surface created by the meeting of the turbulent airflow on the tyre surface meeting the oncoming airflow coming under the leading edge.

 

If you moved the wing round the wheel to the 3'o'clock position as suggested then you will probably managed to create a low pressure cell behind the wing and the required pressure gradient, however as the surface would be 'stalled' it would only create drag.

 

The key to creating effective downforce is not the high-pressure above the surface, but the low-pressure below it. This can be achieved in two ways - by acceleration of smooth air, as demonstrated by aerofoils, diffusers, etc...or by leading edge containment of incoming air using air dams, spoilers and side-skirts.

 

Miraz

[Miraz]

Just found this to play with....http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html

 

A virtual windtunnel website - if you play with the shape (ellipse) and camber controls then you can create something a little like a cycle wing. If you play with the aerofoil shapes with negative camber then you get some interesting representations of what shapes create most downforce.

 

Now we can draw our own (probably unique) conclusions!

 

Miraz

 

Edited by - Miraz on 15 Oct 2001 23:03:38

[paul.davis]

Flared = drag and very slight lift - barely enough to affect high speed understeer in my experience. Drag is the greater impact - removing them is one of the cheapest performnec upgrades you can buy, along with Brooklands screens - add 10mph for these two and much more viatility on acceleration above 80 mph.

 

And before anyone tries this argument - full screens do not create any downforce but do create mega drag . . . . and the byproduct of horrible side draughts (without side screens) that you do not get with Aeros.

 

Paul

 

Zeeeeeeetec . . .

[Asklepios]

So,all you high speed daredevils,do screens by reducing drag permit a higher top speed? As you are all doing nutty MPH without front wings,this experiment must have been done. Did you then try with the hood up as intuitively this must be the least draggy .

Please share the fruits of your experimentation with your fellow Blatchatters.

[Stijn LUYCK 1]

I can not give you any figures for Aero screens and half sidedoors but for my car, a 1.66SS with 13inch-032R's I get:

 

193kmh with screen and doors

184kmh with screen and no doors

 

Both these where measured on the same long stretch of Belgian highway. I never took the car flatout with the roof on so I have no top-speed data. Last month however I got a higher end-speed on the Kemmel straight at SPA with the roof on compared to without the roof ...