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Those sim results, model assumptions, etc.. are a bit of a stretch. More than a bit.

Jersey Tom wrote:Those sim results, model assumptions, etc.. are a bit of a stretch. More than a bit.

just like the DWG.

Machin's model is as much of an educated guess of how it will perform as the DWG's own.

What Machin's point was, was that you could as well make something similair, probably even better with an more comforting to the eye and less radical designed car. He isnt trying to take the waiver from DWG for the 2012 24h of Le Mans

machin, thanks. That is a good quality job fleshing out the engineering issues of the deltawing. It's a modern racecar designed without rules, and it happens to have an odd front track. The front track makes it interesting but not significant.

I am skeptical DW will hit their weight target. Not because of what the claimed number is, but rather because projects like this never hit their weight target. I would love to see the car on a scale one minute before the formation lap.

And honestly, I would love to feel how it drives. Does the active diff feel awkward or good, etc.?

Thanks Wesley.

JT, which bits in particular? The physical dimensions and performance of the Deltawing are from the Deltawing website... Working out force transfer and contact patch pressures are simple maths... So which bits don't u believe?

The thin front tyres benefit from a rear biased weight distribution. Your regular F1 car already has a very light structure ahead of the cockpit and still is close to 50/50. A transverse engine could help here but anyway the DW relies on an extra long nose to provide leverage. How are the Le Mans rules regarding wheel base and overall length?

Cheers Bill,

What's annoying is that the layman will see it doing respectable lap times, read it has half the power and attribute that 'miracle' to the Delta shape, whereas that is actually a hinderance....

machin wrote:Working out force transfer and contact patch pressures are simple maths...

Are they now... do tell how you know how much inflation pressure and what kind of lateral load transfer distribution this platform is going to want, how much grip the tires will generate, etc.

Incidentally, your projected footprint pressures are wildly low for anything but a drag car.

do tell how you know how much inflation pressure and what kind of lateral load transfer distribution

OK, well let me rephrase to "its simple to get to within a close approximation of the tyre contact patch pressures and force transfers"...

Now I know you're a smart guy, so please don't assume I'm teaching you how to suck eggs, but just for completeness and anyone else reading, the maths I have employed for tyre contact patch pressures are:-

1,Knowing that force up equals force down, otherwise the tyre would either be moving up or moving down, the force on say, one of the rear tyres of the Deltawing when stationary with its Fr:Rr weight distribution of 27.5:72.5 is:- 475kg x 0.725 x 9.81 x 0.5 (i.e. lateral weight distribution is 50:50) = 1689N.
2, Knowing the rear tyre width of the Deltawing is 320mm (from their website), and estimating (by good old honest observation of similarly sized real tyres) that the distance around the circumference of the tyre in contact is about 200mm, we get an area of 0.32x0.2 = 0.064m^2.
3, Assuming even pressure over that area (a bit simplistic, but used for both cars, so I feel a pretty valid assumption for a comparison), the contact pressure is 26390N/m^2, or 26.4kN/m^2


For Force transfers the maths I used is:-

1, The over-turning moment for any car is: Cornering G-Force x Mass x CG height. Since I have stated in my comparison that G-force, mass and CG height are the same for either car it means that the total over-turning moment is the same for both cars.
2, Taking, (for the purpose of this example only) that Fr:Rr weight distribution is 50:50, and tyre size is equal front to rear it is a fairly safe-ish assumption to say that the front:rear roll stiffness is going to be about equal (to equalise tyre contact forces in steady-state cornering), and therefore the front and rear will equally share the over-turning load.
3, Taking moments about the inside tyres, the additional force at the outside tyre's contact patch (again for this example only) is then calculated by balancing the over-turning moment (for steady state cornering), i.e. half the over-turning moment must equal the additional tyre contact patch force x the track width. We know the track width, so we can calculate the additional tyre contact patch force.
4, For non-equal front:rear weight distribution and non-equal track widths you can change the numbers in the calcs and (I believe) get a good estimate for the affect of a Delta-shaped car on these forces. I wouldn't say 99% accurate, but 90%? I'd Probably go with that, if not 95%.

Even 10% inaccuracy isn't enough to change my conclusion -that a rectangular car with equal sized tyres and a conventional weight distribution and track widths is better able to distribute those forces to achieve better force distribution or tyre contact patch pressures for all situations other than the low speed straight line acceleration example.... wouldn't you agree?

As a sanity check after all of that though... 26.4 kN*m^-2 = 26.4 kPa = 0.26 bar = 3.8 psi.

I would say as a rule of thumb, footprint pressures aren't dramatically far off from inflation pressures.. and that is just way too low a number. Incidentally, if I had to take a ballpark guess at footprint pressures for a F1 car, say at the rear.. I'd put it at least or over 100 kN*m^-2, if not closer to 140.

Not that it makes much difference. I just think it's a stretch to be drawing any conclusions from such ballpark approximations. I do however agree that it would certainly be feasible (and perhaps even better) to apply 'efficient' principles to a more conventional vehicle. Of course, that all rides on the premise that we're after efficient/green racing.. and I think most people know my stance on that

Come to think of it, 320 mm wide rear tires are f'ing huge for a car so light and with so little power. Granted, I'm now used to ~1640 kg cars with 800 hp on 270 mm of tread... but 320 mm wide for ~1700 N (380 lbf!) of static load, hell even with some downforce, and that little output power is a bit of a mismatch IMO.

As a sanity check after all of that though... 26.4 kN*m^-2 = 26.4 kPa = 0.26 bar = 3.8 psi.

I would say as a rule of thumb, footprint pressures aren't dramatically far off from inflation pressures..

You've got to agree with the calculation of the vertical force on each tyre, right? And the contact patch certainly looks bigger than your pressure numbers would suggest, don't you agree?

Also, the following Avon tyre data for a front F3000 tyre agrees with my point of view; all data is at an inflation pressure of 18PSI, and yet the contact patch pressure doesn't get near that inflation pressure:-



Regardless, it doesn't matter what the actual figures are... I used the same method to calculate the pressure in each case, so even if the actual numbers are different you can still look at the % differences between the two cars... the conclusion will be the same; that a rectangular car is better than a car with a Delta Form in all but the low speed straight line acceleration case....

Jersey Tom wrote:Come to think of it, 320 mm wide rear tires are f'ing huge for a car so light and with so little power. Granted, I'm now used to ~1640 kg cars with 800 hp on 270 mm of tread... but 320 mm wide for ~1700 N (380 lbf!) of static load, hell even with some downforce, and that little output power is a bit of a mismatch IMO.

I agree; even taking the rearward weight bias into account the number's don't stack up... now you could say that the lower tyre contact pressure will help reduce tyre wear, which it should, but as I showed in my comparison, wide rear tyres plays havoc with your aero....

frontal aera is not the only point of drag, the shape, the turbulent flow, te airflow are more important then frontal aera, that's why there are no rectangular aeroplane, the contact point between wheel & ground also make lots of drag.

would you mind to share the full appearance of Machin Wingcar? and is it possible to put DW & MW model to make some CFD like soildwork?

for the tyre & brake, it is not talking about "how much grip I have" but "how much grip I can use".

on the rectangular car, there are simlar tyre size & grip between front & rear. If you brake hardly, if the rear wheel lock, it will lose friction & turn over like old type 911.

if you put lots of brake on front wheel, if will lock, lose friction & impossible to turn in the corner as the car will go stright.

the most Advantage of deltawing is, if you push hard brake, the rear wheel tend to lock up(not totally lock), at this moment, normal car will lose control, but on DW, the rear grip are still more then front wheel(as the front grip is "too" small) so it will keep stable during braking.
And when it hard braking, lots of weight transfer to front wheel, it will help for the steer as front wheel get more grip by weight transfer. however, normal car's brkae are 6:4, if you brake too hard, the front wheel will lock up when you steer. that means you can't use the maximization friction to turn in.

As DW is brake by rear wheel, the front wheel won't lock up. so it can hard brake to transfer weight to front to make the available grip maximization, but won't lock the front wheel. that's means it can get more turn in grip then the same size tyre rectangular car.

Scania wrote:the most Advantage of deltawing is, if you push hard brake, the rear wheel tend to lock up(not totally lock), at this moment, normal car will lose control, but on DW, the rear grip are still more then front wheel(as the front grip is "too" small) so it will keep stable during braking.

No.

Scania wrote:frontal aera is not the only point of drag, the shape, the turbulent flow, te airflow are more important then frontal aera,

Indeed, to quote myself:-

machin wrote:Drag
The Deltawing has a drag coefficient of 0.24 and a frontal area of approx 1.2m^2. With identical dimensions the Wingcar would have the same frontal area. Since the Wingcar’s rear tyres are in the wake of the front tyres, and (due to the narrower rear tyres) a smaller “base area” at the rear of the car the Wingcar would potentially have a lower drag coefficient.

Essentially, I believe the shape of a rectangular car with narrower tyres can be made better than the Deltawing with wide rear tyres whilst maintaining the same frontal area... just look at the rear view of my car compared to the Deltawing, -those wide rear tyres on Deltawing create a lot of blockage to the flow, don't you think?

Jersey Tom wrote:

Scania wrote:the most Advantage of deltawing is, if you push hard brake, the rear wheel tend to lock up(not totally lock), at this moment, normal car will lose control, but on DW, the rear grip are still more then front wheel(as the front grip is "too" small) so it will keep stable during braking.

No.

To expand a bit on JT's answer; No car want's to lock any wheel, particularly not a rear wheel.. once one wheel is locked the braking performance is severely reduced. Up to that point of locking a wheel the braking performance of two cars which are otherwise the same (i.e. have the same total weight, downforce, tyre contact area, etc etc) will be the one which distributes the vertical load evenly over it's tyre contact areas.... and the numbers show that the narrow front tyres on Deltawing will be overloaded (that is; higher contact area pressure compared to a similar rectangular car as described) due to the front weight transfer under braking... despite the initial rearward weight bias.

As I said originally -I don't think the Deltawing will have a problem doing 3:45's (if they can meet the performance figures on their website, like weight, drag coefficient, downforce coefficient, etc)... but I say the maths suggests a rectangular car, built to the same philosophy, would be better.