57 replies to this topic

[smiley]

A german mag did some testing and it increases drag and down force on the VX, there is a post about it by SpeedyK from years ago but I CBA trying to search for it.

[Andrew aka Stuwy]

i have just read this with an attempt to understand.. so far i have: you have more down-force with the roof off (does this explain my shopping list getting sucked out the car). diffusers decrease the rear lift at speed. a spoiler with the correct angle will add down-force to the rear by creating a vacuum behind it and the air hitting the top, it is best effective higher then the roof and with large end plates. side skirts will help prevent the air from the side of the car getting sucked under, to stop it lifting the rear. Canards deflect the air flow to help do the same as the above, while also adding down-force to the front. louvres stop the front wheels creating pressure in the arch and lifting the front of the car. if you cut holes in the front clam where the fogs are, could you vent this air through the louvres too? thus reducing drag and increasing down-force? please treat me kindly i'm learning (no jokes about my spelling please)

[davemate]

you have more down-force with the roof off (does this explain my shopping list getting sucked out the car).
diffusers decrease the rear lift at speed.
a spoiler with the correct angle will add down-force to the rear by creating a vacuum behind it and the air hitting the top, it is best effective higher then the roof and with large end plates.
side skirts will help prevent the air from the side of the car getting sucked under, to stop it lifting the rear.
Canards deflect the air flow to help do the same as the above, while also adding down-force to the front.
louvres stop the front wheels creating pressure in the arch and lifting the front of the car.


if you cut holes in the front clam where the fogs are, could you vent this air through the louvres too? thus reducing drag and increasing down-force?

please treat me kindly i'm learning (no jokes about my spelling please)

my attempt at a logical reply:

a roof off will create drag. drag and downforce on a wing/car/whatever is a balance, imagine putting your hand out the window of a moving car, tip it directly into the wind and it just gets pushed back, which will leave a hell of a mess in the airfolow behine and thusly suck out any old tesco bills for tesco value vodka...

spoiler and wing are actually different things, a spoiler changes the airfolow around the car and a wing is there to create a difference in pressure. when the air flows over a wing it creates low pressure undreneath (in the case of a car) and thusly in pulls the car down. too much of an angle on a wing and it just makes drag as the air can not flow cleanly around the wing (which is like stalling an airplane).

cannards are there as wings or spoilers for the front of a car as a big wing on the back will potentially unbalance the car, changing the weight distribution. eg downforce on a F1 car a 86 mph doubles the cars weight, at 120 mph is is three times the weight. imagine just doing this to the back of the car.

splitters are little spoilers at the front which flows the air underneath the car and away from under the front wheels (i believe).

holes where the fogs are would be better used to cool the brakes, in my opinion. as with all tuning there is a balance, you could save weight and have no brakes at all, you could have a car that produces a really high amount of HP but it would end up in a very narrorw power band for example.

i would be really interested to look at the differences that the different mods make on the car and which actually have a desired effect, eg short splitters do add weight, but i cant imagine they do much for air flow. some little cameras and some string and looking at the different options would be a really interesting project. although the design of the vx is somewhat flawed for aerodynamics with it's big flat and fat front end, in my opinion, the exige seems to have a much better aerodynamic shape which would flow the air much better.

louvers are designed (when designed for a car with proper wind tunnel testing) to disrupt the airflow over an object and create lots of little vortices which creates little waves of downforce, hopefully, on the car. with holes cut in them it can also have the effect of changing a high pressure area to allow the air to escape.

[FLD]

Competition car aerodynamics is a good read to start you off.

[Aerodynamic]

Anyone who can explaine with a picture or a sketch what they mean with "As 8 plus extended outer diffuser vanes to shroud of rear wheels" Thank you, Per

[Aerodynamic]

As I have understood this Reviere wind tunnel testing, this is the way to go

And the picture in the bottom shows the result of the wind tunnel testing with the real wide diffuser just behind the rear wheels?

Edited by Aerodynamic, 15 September 2011 - 07:24 PM.

[FLD]

Yes, I'd expect that is a good way to go.

[Aerodynamic]

I wrote "sharp angle change without radius" What I ment was it is a sharp angle changes without radius now and wouldnt it be better to put a radius in the begging of the diffuser (where the diffuser meets the floor) to avoid the air releasing from the floor. BR, Per

Edited by Aerodynamic, 15 September 2011 - 08:26 PM.

[FLD]

I write "sharp angle change without radius"

What I ment was it is a sharp angle changes without radius now and wouldnt it be

better to put a radius in the begging of the diffuser (where the diffuser meets the floor) to avoid the air releasing from the floor.
BR, Per

Possibly but it is quite a small angle. I'm not sure if laminar flow would be maintained on this. You need someone a bit cleverer than me for that. Winstar perhaps would know.

[smiley]

Thorney who has also done some (alledged) windtunel testing, claimed that the diffuser required to be quite long to actually work, like on their brittcar.

[Crock]

Although these are now being discontinued and are expensive, there is a little bit of information to help with decisions. http://www.carbonmod...__CMBC4001.aspx

[The Batman]

nice find, i will update a picture tomorrow of the canards i now have and they look pretty good at first glance and offering them up to the car but i will stick them on so i can take a picture for you lot

[techieboy]

Although these are now being discontinued and are expensive, there is a little bit of information to help with decisions.

http://www.carbonmod...__CMBC4001.aspx

I had a pair of those. Didn't fit the profile of the VX so flogged 'em on eBay.

[Crock]

Although these are now being discontinued and are expensive, there is a little bit of information to help with decisions.

http://www.carbonmod...__CMBC4001.aspx

I had a pair of those. Didn't fit the profile of the VX so flogged 'em on eBay.

OK thanks for the heads up. Don't think I'll splash the cash on those then.

[TheRealVXed]

This is fairly acedemic. The blunt front end may look like it would be shocking aerodynamically but it is not as catastrophic as you may imagine, plus its surface area is relatively small. Joe are you going to be having these along with splitter/spoiler and wing? If you are separeating he air at a 30 deg angle at the front be cautious of taking airflow away from the rear grills/ears. In theory however is should direct more air toward a rear wing as the shape of the rear clam above the grills/ears lends itself to create a central channel of air over the middle and most effective part of the wing. Sticking points: Tacking bits on may (or may not) noticibly increase downforce at the expense of top speed. Horror show scenario is that they detract from the natural downforce created by the body shape/thus providing decreased stability at speed. Placement/symmetrics need to be spot on to avoid left to right imbalance (assuming they are even effective) Greater effect can be found fiddling with the "clean" airflow under the car. Speed that up and more downforce is created (smoothing of joints, bolt heads etc). Effective splitter (lenght reason is as the air coming from above/round the sides of the car fills the "hole" in the air the car has made it is travelling in the same direction as the car. Moving the splitter exits rear-ward takes it into "stationary" air (i.e the effective air exit speed from the splitter = or > air entry speed under the car) Hope this helps you guys a bit. IMO canards are barking up the wrong tree.

[VXTyrant]

That looks amazing

[Andrew aka Stuwy]

joe is this what your aiming for??

[The Batman]

I wish I have decided to maybe not use the canards and cut holes in the front clam to vent through the louvres