aerodynamics

[silverbullet]

Like I say, it's basically a square law, so if you want it extrapolating to 156 mph, just ask.
Who is Peter Williams, should we know him and how much power is at his wheels?

Not on any forums, he is the owner/builder of the 440 Carrera bus, used to have a 996 engine then upped the ante to a 997. It's been on show a few times at VF, very nicely finished 4-seat Carat interior etc.

I hear that it used to run an LSD, but that came out as the bus was a bit of a handful on the 'Ring



The suspension is rumored to have cost a grand per corner...

[DavidPallister]

Like I say, it's basically a square law, so if you want it extrapolating to 156 mph, just ask.
Who is Peter Williams, should we know him and how much power is at his wheels?

Its not square law, its cube law: to go twice as fast, you need 8 times the power - your average family car with about 125bhp will crack 125mph, but you need a Bugatti Veyron with 1000bhp (x8) to do 250mph (x2)

[faggie]

anyone any idea what speed the norwegian monster t3 can obtain then as it must be the highest bhp van around

[silverbullet]

What one's that then? The W12 panel van is putting out 500+ and a certain 996 turbo Westy is making the better part of 600 IIRC. The latter is good for almost 160 mph (could be more than that, would have to ask around)

[Ralf85]

Like I say, it's basically a square law, so if you want it extrapolating to 156 mph, just ask.
Who is Peter Williams, should we know him and how much power is at his wheels?

Not on any forums, he is the owner/builder of the 440 Carrera bus, used to have a 996 engine then upped the ante to a 997. It's been on show a few times at VF, very nicely finished 4-seat Carat interior etc.

I hear that it used to run an LSD, but that came out as the bus was a bit of a handful on the 'Ring



The suspension is rumored to have cost a grand per corner...

Yep this is a van that cannot drive anywhere. When I saw it at a show last year there was not a speck of dust or dirt anywhere on it inside or outside. It is basically used to advertise his interior parts business at shows.

[faggie]

never seen the turbo westy any pics, the norwegian van i am on about is pushing out 1100 bhp, peter williams does use the van regurlarly i can vouch for that, he drove it to switzerland a few years ago just to drive down that fantastic road what they took the porsche aston martin and lambourghini on what was on top gear , nowadays going to a show costs a fortune in a t3 but when you have spent over £84,000 a bit of petrol to run it would seem like pocket change

[silverbullet]

Ah yes, the BB Chevy turbo mid-engined thing. Mad as a box of frogs.

It's the long winter nights that does it I reckon

[silverbullet]

I thought that I'd recycled the paper issue from late last year, then I remembered that the SAE Europe Automotive Design mag is available online!

Scroll through to page 16-18 for the Aerodynamics feature, note the comments on flat floors and wheel arch drag percentages...

http://content.yudu.com/Library/A2005j/ ... fault.aspx" onclick="window.open(this.href);return false;

For further reading on what's goin on at the sharp end http://www.automotivedesign.eu.com/maga ... fault.aspx" onclick="window.open(this.href);return false;

[HarryMann]

Good mags ok:

[faggie]

silverbullet any pics of the westy with the 996 turbo motor fitted

[silverbullet]

Er...it was at Hockenheim last summer so if you google up Hockenheim VW Bus Tuning Treffen 2012 or 2011 you should get some top track action on pootube.
Might be some pics out there somewhere, I barely glanced at it TBH as I had a fair bit of interest in the SA!

[HarryMann]

I don't know why Cd isn't an absolute measurement, which would allow for comparison. The relative figure used is only really helpful when looking at different specs of the exact same body style

Alan, have just noticed this early post about Cd....

The answer is that the whole point of Cd is that it is a coefficient for comparison purposes, irrespective of an area or a speed or air density. So you can compare large or small, of different or similar shapes.

So it does provide a good way of comparing, providing the area reference used is on the same basis; that could be frontal area, planform area, in the case of skin friction and boundary layer drag, total surface (wetted) area may be used.

Coefficients are deliberately constructed to be non-dimensional, as are many other parameters used in science and engineering e.g Mach No.

You need the area to produce an absolute comparison. Thus the mention of CdA comparisons, Cd x Area, and for a road vehicle, frontal area would be used.
For an aircraft, for total drag comparisons, planform area would usually be the reference for Cd (tot).

Hope that explains it, Cl and Cm, lift and pitching moment work in the same way.

To get the Actual drag (in say lbf) from a Cd you need not only the Area, but 'Q', the total dynamic head, caused by the airspeed and density = 1/2 x density x speed squared, effectively the kinetic energy in the wind.

[Allanw]

^WHS

Yeah - something like that!

Car makers tell us there car has a CD of .28 and we should think it is amazing... but don't tell us the area, so you can't compare it to another make and model. A much smaller car could have a CD of .34 but be so much smaller than it's total drag is actually less, so should be cheaper to run!

[HarryMann]

Yes, they may do....

But that isn't the fault of Cd, that's the fault of salesmen.

It does however tell you how much progress has been made in that area of development compared to a similar class of vehicle, which tend to have very similar sizes.

You are correct though that it would be naive to choose a car based on Cd and complain if it didn't either go faster or give better economy - it's the whole integrated package that counts.

== ==

On the tech side, there's another twist in the behaviour of airflow. Cd - despite being normalised by size (e.g. frontal area), and used as a means of comparison wouldn't be expected to be constant for the same shape at very different sizes and speeds...

That is, a wind tunnel model of car or aeroplane wouldn't give you the correct Cd that can simply be used at radically different sizes and speeds, although that is the general idea of such a comparison coefficient. Same for lift, as aeromodellers usually know.

Things fortunately tend to get more efficient as the size increases... scale effect.

[silverbullet]

Hmmm...IIRC the TWR Volvo BTCC team decided to run the estate version of the then-new 850 for so-called "long-body" aerodynamic efficiency gains, with virtually no weight penalty over the saloon model.

Never mind the publicity! I remember their first outing at Brands