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machin wrote:That's a very good point... OK, so what we need to do is figure out how much more downforce (in terms of CdA) is required to equalise the performance of the two car types... I'll have a look at some numbers tonight...

Right... well taking the approach suggested by P.S my calculations suggest that if you take two cars, identical except one has a rectangular tyre arrangement and weighs 5% more and the other is Delta shaped (tyre sizes/layout and weight distribution), with identical CdA figures the Deltawing would need a ClA figure somewhere in the region of 15 to 20% higher than the rectangular car in order to achieve an identical lap time at Le Mans.... which I guess might be possible? Again; that's a question for CFD.... but I must say I am swayed slightly by this finding... maybe for Le Mans its not so bad an idea afterall?

Similar approach suggests for a track like Brands Hatch Indy circuit (much lower speeds and hence lower downforce levels attained) the Deltawing's ClA figure would need to be 60% higher for the same CdA to achieve the same lap time as the rectangular car.... which to my mind seems very unlikely...?

machin wrote:the Deltawing would need a ClA figure somewhere in the region of 15 to 20% higher than the rectangular car in order to achieve an identical lap time at Le Mans....

That might sound a lot, but actually at 100mph its only about 35 to 45kg of extra downforce for the same drag...... what does everyone think? Possible or not?

I have to say, I don't know if that's possible or not, but I'd kill for 45kg of downforce! Then again, maybe that's because I run a rectangular car of 450kg. The weight of this car is not impressive at all. There are 300kg single seaters with more horsepower. There's also a good few two seat cars. Look at the Force LM, which is ~350kg and ~250bhp in normally aspirated form (add ~20kg and ~130bhp in turbocharged form). I'd suggest that it has the potential to beat the Deltawing if trimmed of its wings to reduce drag.

andylaurence wrote:I have to say, I don't know if that's possible or not, but I'd kill for 45kg of downforce! Then again, maybe that's because I run a rectangular car of 450kg. The weight of this car is not impressive at all. There are 300kg single seaters with more horsepower. There's also a good few two seat cars. Look at the Force LM, which is ~350kg and ~250bhp in normally aspirated form (add ~20kg and ~130bhp in turbocharged form). I'd suggest that it has the potential to beat the Deltawing if trimmed of its wings to reduce drag.

You a hillclimber?

machin wrote:...Deltawing would need a ClA figure somewhere in the region of 15 to 20% higher than the rectangular car in order to...

I just want to say again, that I have my doubts with your numbers and simulation. In the past I was a couple of times witness at my university, when a optimisation with a simulation went wrong, because people did not know/understand the limit of the simulation/formula. Thats also happend to me more than once.

So I´m usually very carful with saying something like "I have calculated this and because I follow the rules of natural sciences, this is the truth".

There is a very good reason why the sentence "theory and practice are different matters" is so popular (in germany damn sure)!

Especially the deltawing shape is so new, and there is so little experience with it, I say again it is hopeless trying to simulate this, without verify it on the track. Deltawing them self are the only ones now to get proper experience.

And I like to repeat, that I can not verify your sough of less mechanical grip with the delta shape, on my rFactor model.

andylaurence wrote:I'd kill for 45kg of downforce!

Nice that someone with a wheel in his hands is reporting.

P.S. wrote: I just want to say again, that I have my doubts with your numbers and simulation.

And I like to repeat, that I can not verify your sough of less mechanical grip with the delta shape, on my rFactor model.

That's fair enough... I'd be skeptical too... in fact that's one reason why I started writing my own program and gathering my own data 10 years ago... so I knew what was going in to it and I'd know the limitations of its use. I must say I'm really happy with the results so far... as it replicates the performances of my car and those of my competitors very accurately, and I couldn't ask for more than that. However they are rectangular cars and as you say we don't have any real Deltawing data to draw on to produce any firm conclusions, but personally I think we know enough to apply the basics... especially now I've seen they are using 'regular' (if ever that word can be used!) tyres at the rear... both our own calculations show that the outside rear tyre on the Deltawing will see more load transfer than on a rectangular car so we can apply a typical tyre data curve and see that it would result in lower grip (all else being equal) .... does RFactor not also confirm this?

Wikipedia's take on tyre load sensitivity; en.m.wikipedia.org/wiki/Tire_load_sensitivity

Sprinter - it's like hillclimbing without the hills

I don't know whether the layout of the Deltawing would out-perform a traditional car, but I'd wager it wouldn't. Yes, there's the points that machin has made about load transfer and a marginal weight saving, but what about aero? Frontal area would be remarkably similar, but would the front wheels affect diffuser performance and is there more scope for underbody aero with a larger plan area? Would that help L/D? Frankly, I don't know!

Frontal area would be remarkably similar, but would the front wheels affect diffuser performance and is there more scope for underbody aero with a larger plan area? Would that help L/D? Frankly, I don't know!

Yeah I had the same thoughts a few pages back... its a shame someone with CFD capabilities hasn't taken up the challenge to have a go at looking at this...

The other thing I'd add to those questions is whether the Delta layout's wider rear tyres cause sufficient blockage of the flow to affect diffuser performance compared to a similar weight "rectangular" car which would have slightly narrower rear tyres? To my mind it would.... but some basic CFD would answer that..... anyone up for the challenge?!

machin wrote:

The other thing I'd add to those questions is whether the Delta layout's wider rear tyres cause sufficient blockage of the flow to affect diffuser performance compared to a similar weight "rectangular" car which would have slightly narrower rear tyres?

See previous post... the rear tires are said to be the front tires off of a Indy Lights car. Do we know the overall width of this thing?

countersteer wrote:See previous post... the rear tires are said to be the front tires off of a Indy Lights car. Do we know the overall width of this thing?

Indeed, that was my post ( )...

I think its safe to say that a car with "normal" weight distribution and equal size/weight would have narrower rear tyres than Deltawing, but obviously wider fronts by virtue of that weight distribution... don't you think?

would the front wheels affect diffuser performance?

Andy, I think this simple simulation shows the point you were making nicely; the Deltawing's central front wheels create "dirty" air in the diffuser, whereas the rectangular car's diffuser gets clean air...

That's exactly my point - dirty air into the diffuser. For reference, the Deltawing has 10" wide rear tyres. My 450kg rectangular car has 7" wide rear tyres, which means a 6" wider diffuser for the ame overall width.

machin wrote:

countersteer wrote:See previous post... the rear tires are said to be the front tires off of a Indy Lights car. Do we know the overall width of this thing?

Indeed, that was my post ( )...

I think its safe to say that a car with "normal" weight distribution and equal size/weight would have narrower rear tyres than Deltawing, but obviously wider fronts by virtue of that weight distribution... don't you think?

would the front wheels affect diffuser performance?

Andy, I think this simple simulation shows the point you were making nicely; the Deltawing's central front wheels create "dirty" air in the diffuser, whereas the rectangular car's diffuser gets clean air...

but you can get extra air supply to diffuser on DW

see the tunnle under the "second S" of "NISSAN"

thanks; that picture of the Deltawing illustrates the point nicely.... on a rectangular car you can feed the diffuser from the wide gap between the front wheels:



....you can't do that with the Deltawing because the front wheels get in the way... so you're restricted to two small tunnels either side of the chassis as opposed to one big tunnel running right down the middle of the car.....

way back on page 7 I did a drawing which actually shows those small tunnels on the Deltawing; note the relative sizes of the yellow areas in the views on the right....

machin wrote:The comparison on the right shows a section through the two cars at the centreline of the rear wheels (in dark grey), and the front tyres projected on that (in light grey). On the Deltawing the wide rear tyres create more blockage of the flow and the front tyres disturb some of the flow in the ground effect area...

On a rectangular car with narrower rear tyres the blockage is a lot less, and also I would guess the flow is cleaner as the front tyres don't get in the way...