4350 replies to this topic

[jamiewillson]

I thought there were seriously diminishing returns for splitters over 10cm?  End plates would help keep the pressure on top of the splitter so would be a good idea.

 

Nope, 10cm is very much the minimum that Mike would need in order to balance out the rear wing.  We learnt a lot in the wind tunnel with regards to what you need to do to balance these cars out, front-to-back. On my Exige the splitter is now 20cm deep. I originally started with 6cm, went up to 10cm and then the 20cm it is now.

 

As far as drag is concerned, splitters are almost free, so it's worthwhile going a bit over the top if you can or need to and then if you want, you can start adding more rear end wing angle to get a higher overall total.

 

End plates are a really worthwhile addition to get the front end df where you want it. However they do create drag, as they are basically backing up the air on top of the splitter. For Mikes power output it'd be fine though.

 

[Winstar]

I thought there were seriously diminishing returns for splitters over 10cm?  End plates would help keep the pressure on top of the splitter so would be a good idea.

Nope, 10cm is very much the minimum that Mike would need in order to balance out the rear wing. We learnt a lot in the wind tunnel with regards to what you need to do to balance these cars out, front-to-back. On my Exige the splitter is now 20cm deep. I originally started with 6cm, went up to 10cm and then the 20cm it is now.

As far as drag is concerned, splitters are almost free, so it's worthwhile going a bit over the top if you can or need to and then if you want, you can start adding more rear end wing angle to get a higher overall total.

End plates are a really worthwhile addition to get the front end df where you want it. However they do create drag, as they are basically backing up the air on top of the splitter. For Mikes power output it'd be fine though.

Shape of the VX had more front down force to begin with though (yes I know it's an S2 but the same will apply)
 

So the best option, rather than putting a wing on the back it to take off the roof, and enjoy the sunshine.

Not according to those figures it isn't!

Downforce Rear closed softtop:- 186 Nm
Downforce Rear open: -142 Nm

More downforce with soft-top on

No, you've misread it.

The figures are: rear downforce closed -186Nm (that's minus 186NM, i.e. 186Nm of lift ), which is reduced to -142NM of lift with the roof off.

But, of course, the drag increases when open, thus reducing topspeed.

The figures (in weight) for the VXT closed (again from Sport Auto measured at 200kmh) are:

Front 23kg downforce
Rear 19kg lift

In comparison, for the Exige S2, they measured:

Front 18kg downforce

Rear 26kg downforce i.e. 45kg more downforce than the VXT

It not really applicable to use wind tunnel results from a car of a completly different shape

Edited by Winstar, 29 May 2013 - 11:40 AM.

[jamiewillson]

Yep I know that Mikes car is a different shape to an S2 Exige and also a different shape to mine (which we had in the wind tunnel a couple of months ago), so any results would obviously differ. However, the same principles still apply and I doubt the figures would differ by a huge amount. Both my car and Mikes share similar characteristics too, as they are of a very similar width and length, both have roof scoops, the same rear wing, coupe style engines covers, flat floor, radiator inlet/outlets in the same place, similar ride heights etc, etc....... Based on that, you can make some assumptions. In fact, the VX should be better with regards to a starting point for good aero.

Edited by jamiewillson, 29 May 2013 - 12:00 PM.

[Winstar]

Yep I know that Mikes car is a different shape to an S2 Exige and also a different shape to mine (which we had in the wind tunnel a couple of months ago), so any results would obviously differ. However, the same principles still apply and I doubt the figures would differ by a huge amount. Both my car and Mikes share similar characteristics too, as they are of a very similar width and length, both have roof scoops, the same rear wing, coupe style engines covers, flat floor, radiator inlet/outlets in the same place, similar ride heights etc, etc....... Based on that, you can make some assumptions. In fact, the VX should be better with regards to a starting point for good aero.

The front end shape is completly different on the VX and this will determin how flow will travel over, under, round, through the rest of the car. Hence why the wind tunnel test I posted above result are so different between the VXT and the S2 exige which by your assessment above should be similar.

[jamiewillson]

Oh ok, if you're leaving the backs open then I agree the drag won't be as much. However there will still be some, depending on how much of a gap there is at the back, as you're still restricting and constraining flow in a way. There are df benefits to be had from completely sealing off the back though and making them pretty big, as it shifts your df balance forwards. I have got figures for this but would have loved to have had more time in the tunnel to experiment with different sized gaps and end fences to get a clearer picture.

[jamiewillson]

 

Yep I know that Mikes car is a different shape to an S2 Exige and also a different shape to mine (which we had in the wind tunnel a couple of months ago), so any results would obviously differ. However, the same principles still apply and I doubt the figures would differ by a huge amount. Both my car and Mikes share similar characteristics too, as they are of a very similar width and length, both have roof scoops, the same rear wing, coupe style engines covers, flat floor, radiator inlet/outlets in the same place, similar ride heights etc, etc....... Based on that, you can make some assumptions. In fact, the VX should be better with regards to a starting point for good aero.

The front end shape is completly different on the VX and this will determin how flow will travel over, under, round, through the rest of the car. Hence why the wind tunnel test I posted above result are so different between the VXT and the S2 exige which by your assessment above should be similar.

 

 

As I said, there will of course be different figures for the 2 cars, but that doesn't stop you making some (probably) fairly accurate assumptions. Well, accurate enough for our level of motorsport anyway. Air flow under the car will again, broadly speaking be the same, give or take. And once the airflow has got over the front of the car, then the rest is very similar (same windscreen rake, roof etc). Sides are very different, I agree, but better on the VX anyway.

 

And by the way, I'm not trying to make out I'm some sort of aero guru, although I have done a hell of a lot of learning over the last few years in this area, as I find it really interesting and want to improve my car. What I do have on my side though, is a world respected aerodynamicist. And I have been through the VX car shape with him on a couple of occasions when sorting out Mikes rear wing. 

 

[jamiewillson]

Thanks

 

The stuff I saw on splitters was modelled on a mclaren f1.  This showed exponential drop off of DF for protrusion >10cm.  Obviously I (wrongly) extrapolated that to the plastic pig.  I'd also be interested in your thoughts on the splitter in front of the radiator apperture (mouth!).  I'd have thought it pretty useless to have much beyond an 'airdam' type protrusion here as the air escapes up through the rad.  Is this along the right lines or is my thought process way off?

 

Interesting regarding the F1. Would love to know why df dropped off after 10cm?

 

Anyway, I've asked my aero consultant the same question regarding the front middle section of the splitter before, as I was planning to only have a small protrusion there in order to give more clearance under braking, loading on trailer etc. He quickly told me that the very middle part of the splitter is doing the largest portion of downforce generating and that it was more important to have a large protrusion here than anywhere else!!!!

 

I'm assuming that the slight airdam/lip before the rad aperture allows the splitter to work as intended. Perhaps on some cars where there is no lip and where bottom part of the rad aperture is actually the top of the splitter, this would work in a different way and not be as important?

 

 

 

[techieboy]

How's your car Jamie? All systems go for Snetterton?

[jamiewillson]

Yep, all systems go. Just got to hope that Scuffers plane back from holidays isn't delayed, that's all.........

[techieboy]

Fingers crossed for an uneventful round, for once.

[Darcini]

 

Just got to hope that Scuffers plane back from holidays isn't delayed, that's all.........

  Hmm, may be a sudden demand for surface to air missiles. Group buy anyone

[Nev]

I found that a front splitter gap of 7 cm gave a huge amount of DF, but rising it up to 8.5 cm has reduced it a lot. I am pretty sure Mikes car will get it even lower than 7 cm, so it should have an epic effect considering the size of it in the last pic he posted. GL.

[rob999]

Is Scuffers flying the plane?

Edited by rob999, 29 May 2013 - 02:53 PM.

[CHILL Gone DUTCH]

Scuffers is star From 4 mins 15 secs

Edited by Chill, 29 May 2013 - 07:29 PM.

[JohnTurbo]

I didn't expect Scuffers to look like that.

....Except I did from chatting to him for 20mins at Autosport - except the "Simon" threw me at the time so I had no idea who I was talking to. But it was interesting.

 

What I mean is YOu didn't expect....

 

 

I need a cup of tea.

 

 

[smiley]

I didn't expect Scuffers to look like that.

 

 

 

Same here. You built up a weird picture after all that keyboard fun the last weeks. 

[Crabash]

That can't be him, that guy is way older than Simons avatar

 

Spotted myself in that vid too along with ciderbooze.

Edited by Crabash, 29 May 2013 - 11:30 PM.

[ciderbooze]

That can't be him, that guy is way older than Simons avatar   Spotted myself in that vid too along with ciderbooze.

A quarter second of fame @ 59 seconds in. Nearly as much time as mike got!

[Mike (Cliffie)]

See, he is almost normal when you meet him.

[ArticMonkey]

why did I think he was early 30's? I believe I could see his free bus pass in his pocket.