74 replies to this topic

[siztenboots]

I would concur, even a modest front splitter made the steering feel load up at speed , which in wet weather gave me a lot more confidence.

[xco]

The problem in the Speedster is the rear lift not in front. http://www.sportcarc...hp?f=24&t=10800

Edited by xco, 04 April 2014 - 11:22 PM.

[jameso]

Yep. IMO you shouldn't add front down force to the vx unless you fit a rear wing or a coupe back

[robin]

Jameso have you even fitted any wings or splitters To your car? I see in your profile your running a stage 4 So you no doubt must drive it at high speeds. Reason i ask is i run my car with a front splitter and no rear Wings and run standard suspension and regulaly drive at 100 mph plus and never have felt the need for a rear wing ( i do have a wing Available to fit but not bothered) I get no rear lightness or the back moving around. I do however feel a lot more positive about the front with It feeling a lot more positive and not moving around at 120mph Plus as it does without a splitter. As said before im no racing driver but imo fitting a front splitter Of any size does help the car even with out a rear spoiler.

Edited by robin, 05 April 2014 - 08:16 AM.

[FLD]

A rear coupe will add lift to the rear.  Again consider the airflow over the whole car, its one big curve so will generate lift.  A coupe smooths it out more so I'd expect more lift.  What a coupe will do is smooth the flow to a rear wing making the wing more effective.  Some bedtime reading for you.

[paulk]

Presume most people have seen this for a vx tested at 200Km/h

 

[color=rgb(40,40,40);font-family:helvetica, arial, sans-serif;]Downforce Front closed softtop: 221 Nm[/color]

[color=rgb(40,40,40);font-family:helvetica, arial, sans-serif;]Downforce Rear closed softtop:- 186 Nm[/color]

[color=rgb(40,40,40);font-family:helvetica, arial, sans-serif;]Downforce Front open: 254 Nm[/color]
[color=rgb(40,40,40);font-family:helvetica, arial, sans-serif;]Downforce Rear open: -142 Nm[/color]
 

Splitter will help but only at reduced ride height ride height (as Nev has already pointed out). 

 

[mbes2]

Just read over this thread from 2007 .... its the same as this one 

 

http://www.vx220.org...ce-and-the-vxt/

 

Post 15 is shocking... 

[jameso]

Jameso have you even fitted any wings or splitters To your car? I see in your profile your running a stage 4 So you no doubt must drive it at high speeds.

 

I am a very average driver Robin so am sure people like jimmy, cliffie, 5oc, darren wall who all raced competitively are much better equipped to answer this - but yes do high speed on track.

 

Front: I had a robin splitter (which got obliterated at bedford) and now just run a leon splitter - which are both airdams.

Rear: Exige wing - which I removed in the winter (to save fuel lol?) as I was running it as my daily driver for a short period

 

The car is noticeably better planted at the rear at speeds as low as 80mph (obviously most noticeable under braking and high speed cornering) with the wing fitted.

 

Interestingly I think George said Darren ran with and without that exige wing at one of the TA circuits and did the same lap time with and without - saying he felt much less confident on the brakes when they took the wing off. This partially demonstrates that he was almost certainly faster in the corners/braking zones as my car is definately slower in a straight line when i have the wing on.

 

A rear coupe will add lift to the rear.  Again consider the airflow over the whole car, its one big curve so will generate lift.  A coupe smooths it out more so I'd expect more lift.  What a coupe will do is smooth the flow to a rear wing making the wing more effective.  Some bedtime reading for you.

 

Don't disagree with the the general wing shape aero fld - but thats mostly over the whole car - the reason the rear specifically creates lift relative to the rear though (see the thread with the wind tunnel work mbes linked) I think is because of the void behind the rear screen? Like I say winstar will defo be able to set us straight and explain this better than pretty much any of us. But to me that wind tunnel data suggests you dont really need to worry about front downforce and if it were me I would not be adding any more front end grip without adding to the rear too.

 

The other option here would be to add more mechanical grip to the rear with geo, but then you create a balance issue where because as you go faster the aero effect becomes larger you can only be balanced at either low or high speed - so it seems better to me to balance your aero (or at least try?) front and rear so you get similar balance at low speeds and high speed.

 

Reality is it probably doesn't make a huge difference and only a handful of us are good enough to really find it makes a difference to our track experience, and even less so to our road experience (cos of speed obviously), and it may just be a bit of placebo?

[FLD]

Interesting read that thread, thanks.  Very different from the aero data I've seen for the VX which had lift front and rear.  I'd be interested to see how the step at the rear screen generates lift as I'd thought it is more likely to be airflow over the haunches.  I'll have to go back and re-look at the lotus data.

Edited by FLD, 07 April 2014 - 09:34 AM.

[siztenboots]

I took the wing off at Spa and it was evil.

[jameso]

Interesting read that thread, thanks.  Very different from the aero data I've seen for the VX which had lift front and rear.  I'd be interested to see how the step at the rear screen generates lift as I'd thought it is more likely to be airflow over the haunches.  I'll have to go back and re-look at the lotus data.

 

Winstar will be the man to ask but - I *think* it's because:

 

• The air doesn't re-attach to the body so you have an area of dead air between the fast moving air above the car and the car body itself
• This then gets sucked in to the fast moving air above the car (I suppose this effect also helps pull air out of the engine bay thru the top vents)
• This creates an area of very low pressure air above the boot - which in turn creates lift

I guess the faster you go the more void of air (and lower pressure) this area becomes?

 

This is why a coupe back is better for aero (and why the exige is coupe backed i think?) - it removes the void.

 

That make sense?

 

NOTE: all of the above could be rubbish and a figment of my own imagination

Edited by jameso, 07 April 2014 - 09:57 AM.

[Winstar]

 

Interesting read that thread, thanks.  Very different from the aero data I've seen for the VX which had lift front and rear.  I'd be interested to see how the step at the rear screen generates lift as I'd thought it is more likely to be airflow over the haunches.  I'll have to go back and re-look at the lotus data.

 

Winstar will be the man to ask but - I *think* it's because:

 

• The air doesn't re-attach to the body so you have an area of dead air between the fast moving air above the car and the car body itself
• This then gets sucked in to the fast moving air above the car (I suppose this effect also helps pull air out of the engine bay thru the top vents)
• This creates an area of very low pressure air above the boot - which in turn creates lift

I guess the faster you go the more void of air (and lower pressure) this area becomes?

 

This is why a coupe back is better for aero (and why the exige is coupe backed i think?) - it removes the void.

 

That make sense?

 

NOTE: all of the above could be rubbish and a figment of my own imagination

 

 

Nope this is about the only post in this whole thread that conveys anything that is correct about the airflow and the rest is internet experts who've read a book on car aero are why I've given up posting for sake of going scuffer's on a thread. If it was simple as reading a book there wouldn't be so much spent on CFD and testing.

 

The only effect your missing is that the low pressure in the region above the boot is used to drive the cooling flow through the engine bay which is why I've said in the past if you fit a coupe boot you need to completely rework the cooling flow.

 

As for splitter it pretty simple how they work the front of the car causes an air dam to create a high pressure region (P~1/2*density*vel^2) and then is acts on the top area of the splitter like someone standing on it, very effective but very inefficient.

 

[jameso]

Dunno why the rest of us even bother posting on aero threads when we have winstar

 

And I think I did mention the cooling effect of the lower pressure region sucking air thru the engine bay - just not as eloquently as you

 

J.

[siztenboots]

foilsim is very good , https://www.grc.nasa...lane/foil3.html

 

size : 0.2m chord, 2m span = Area 0.4sqm , A/R 10.0

flight : speed 160km/h ( 100mph )

 

and just play with the Joukowski airfoil , watching the Lift and Drag , with different angle of attack

 

[mbes2]

Im too busy hanging on to feel any difference with my aero mods.

 

One thing I did notice after fitting the (Robin) splitter was a drop in eng temps, which I guess was more air being pushed up from the splitter. 

Edited by mbes2, 07 April 2014 - 10:47 AM.