Delta wing car concept

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Scania
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Re: Delta wing car concept

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machin wrote:
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.
The "lock" I mean is not totally locked, but we know that the best grip tyre can applied is arround 85% rolling rate, however on the front wheel of normal car, if you steer when the front tyre is barking & get the sweet point of grip on stright, your tyre's friction wheel drop dramatically as the resistan from road increase & the rolling force from road to wheel are decrease. the braking force enough on stright are too high for turn in(so the wheel will lock up if you hrd brake & turn, but not that easy if you only hard brake but not turn. the wheel turing moment is 1 of the easiest time to lock the front wheel.)

so, if you want to let the normal car turn well, you should brake earlier, smother, and make the weight transfer to front lesser, it make the front tire can't provide its best performance.

on DW, they share the jobs of steer & brake on front & rear wheel. when driver brake hard, rear wheel on 85% rolling rate to provide its highest brake force it can give, lots of weight transfer to front, and he turn in, since the brake force is provide by rear wheel, the front wheel won't lock.

Scania
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Re: Delta wing car concept

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to explain it easier, normal share the job of speed up and brake to front & wheel, that means a axle should steer & brake @ the same time.

fow dw, it share the job of speed control & steer to front & rear. as you won't speed up & slow down @ the same time, each axle would only did 1 job @ the same time.

(p.s. FF road car are put speed up, slow down & steer on only 1 axle)

this concept a little bit like 6 wheels F1. double front axle car can use first axle to brake and second axle to steer(or maybe reverse) double rear axle car make the rear more stable during speed up, and it can keep stable even brake balance is tend to rear & provide more brake force on the rear part.

Jersey Tom
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Re: Delta wing car concept

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The front and rear tires BOTH provide cornering (turning) forces. Always. Doesn't matter what kind of weight distribution or car configuration.

In the situation you describe of biasing the majority of the braking to the rear wheel, you will reduce the rear axle cornering power and you will have a car that oversteers and wants to spin out on the brakes. You have gone from locking fronts to locking rears, which is very very bad for control.

Furthermore, since being able to outbreak your competition is generally advantageous.. you're always going to set the brake bias to distribute straight-line longitudinal utilization almost evenly front to rear. Generally the bias will be a bit front, so if anything you lock fronts rather than rears.
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Scania
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Re: Delta wing car concept

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In the situation you describe of biasing the majority of the braking to the rear wheel, you will reduce the rear axle cornering power and you will have a car that oversteers and wants to spin out on the brakes. You have gone from locking fronts to locking rears, which is very very bad for control.
I had talk that DW design make rear wheel brake is not easy to spin out. even the rear wheel tend to lock, if it is not totally locked, it's friction is still higher then front wheel, the rear wheel would spin out when it loss triction.

why you think that my concept need to set the brake bias?

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machin
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Re: Delta wing car concept

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In the ideal situation every car would have a brake bias such that both axles are just on the edge of locking up... In reality every car goes slightly forward on the bias, as JT says, to avoid the rear locking scenario (whichs causes oversteer)... If u have too much bias away from that "just forward of ideal" setting then you're simply wasting braking potential for no gain...
Last edited by machin on 23 Jul 2011, 01:18, edited 1 time in total.
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machin
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Re: Delta wing car concept

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Perhaps I was being a little unfair on the Deltawing in the braking and cornering scenarios; I compared the no downforce case.....

If the car developes sufficient downforce, in the same distribution as the static mass, then this additional force would somewhat mask the amount of longitudinal and transverse force transfer during braking and cornering.... at high speed at least, making the tyre contact area pressures higher, but more even across all the tyres.... [EDIT] HOWEVER, as shown in my subsequent post below, the car's don't make enough downforce to swamp the force transfer, so my earlier conclusion was correct; a rectangular car is better.
Last edited by machin on 23 Jul 2011, 14:17, edited 1 time in total.
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Jersey Tom
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Re: Delta wing car concept

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...and the hand waving begins.
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Scania
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Re: Delta wing car concept

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machin wrote:After running some simulations of the Deltawing I have no doubt that it should be capable of a 3:45 lap time at Le Mans, despite only 300bhp. What bother’s me about the Deltawing is that many of the benefits of the design could easily be applied to a ‘conventional’, rectangular, car and furthermore, it is suggested that the ‘delta’ shape has many disadvantages compared to a rectangular car.

To illustrate these disadvantages I have modelled a rectangular ground effects car which I humbly call the “Machin Wingcar”:-

Image

The different aspects of the Deltawing are compared to the Wingcar below, with numbers for comparison:-

Weight distribution
The Deltawing has a 27.5:72.5 Fr:Rr weight distribution. The Wingcar uses a ‘conventional’ 45:55 Fr:Rr distribution.

Wheelbase
The Deltawing has a 2.9m wheelbase. The Wingcar has a 2.6m wheelbase.

Overall Length
The Deltawing is 4.65m long overall. The Wingcar would be 4.35m long overall.

Overall Width
The Deltawing has a 2m overall width. The Wingcar would have the same overall width.

Centre of Gravity Height
Both cars would have a cg height of approximately 0.3metres. Nothing on the Deltawing would suggest a lower cg than a conventional car.
No advantage to either car

Engine
The Deltawing uses a 300bhp, turbocharged 1.6 litre engine, weighing just 77kg. The Wingcar would use the same engine. No advantage to either car.

Gearbox
The Deltawing uses a 5 speed gearbox weighing just 33kg. The wingcar would use the same gearbox. No advantage to either car.

Total Mass
The Deltawing weighs 475kg. Can a “conventional” prototype be made this light? The Radical SR3 is this light and is a spaceframe and GRP-bodied prototype. A carbon monocoque car could easily attain this weight.
No advantage to either car

Tyre Width
The Deltawing uses 320mm wide rear tyres and special 100mm wide front tyres. To obtain the same rear tyre contact area pressure the Wingcar requires 240mm wide rear tyres (due to the lower rear weight distribution). For convenience the front tyres of the Wingcar are the same size as the rear. This leads to a lower contact area pressure on the front tyres of the Wingcar than on the Deltawing, despite the higher weight on the front tyres. Lower tyre contact area pressures should reduce tyre wear.
Advantage Wingcar.

Track widths
The Deltawing has a 0.6m front track width. Its overall 2m width and 320mm wide rear tyres results in a rear track of 1.68m. The Wingcar’s overall 2m width and 240mm tyres results in a front and rear track of 1.76m.
Advantage Wingcar

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.
Advantage Wingcar

Downforce
The Deltawing reportedly will make 9300N of downforce at 200mph. Due to the wider rear tyres and small “delta” plan area the space for ground effects is small –approx 2.7m^2. The Wingcar, with narrower rear tyres and large rectangular plan area has a much larger ground effect area, approx 6m^2. This means the Wingcar’s floor loading is lower which should improve efficiency.
Advantage Wingcar
Image
Image

Braking Performance
Braking performance is highest when tyre contact area pressures are distributed evenly over a vehicle’s tyres. Assuming a 1.5G braking event and no downforce the Deltawing would have a Fr:Rr weight distribution of 43:57 resulting in approximate tyre contact pressures of 50kN/m^2 on the front and 21kN/m^2 on the rear, despite the rearward static weight distribution the narrow front tyres will be the limiting factor in braking. The Wingcar, with a conventional static weight distribution and equally sized tyres, in the same 1.5G braking event has a weight distribution of 62:38, resulting in tyre contact pressures of 30kN/m^2 (front) and 18kN/m^2 (rear). The lower tyre contact area pressures on the Wingcar should result in higher braking performance, or lower wear for the same performance.
Advantage Wingcar

Cornering Performance
As with Braking, cornering performance is highest when tyre contact pressures are distributed evenly over a vehicle’s tyres. The narrow front track of the Deltawing results in a higher load on the outside rear tyre than a conventional car as it must resist the majority of the over-turning moment. Subjected to 1.5G cornering event (again with no downforce) the pressure on the outside rear tyre of the Delta wing is estimated at 47kN/m^2. Despite the Wingcar’s narrower rear tyres, the fact that the front track width is much wider and can therefore absorb an equal amount of the over-turning moment means the rear outside tyre contact area pressure is just 40kN/m^2 in the same cornering scenario.
Advantage Wingcar

Low speed acceleration
Low speed acceleration is determined by the amount of motive force that can be transmitted to the road and this is determined by the vertical force on the driven tyres. The Deltawing’s high rear weight distribution and wide rear tyres gives the Deltawing higher low speed acceleration than a conventional car, all else being equal. At a circuit like Le Mans, with high average speeds, this is of little benefit.
Negligable benefit to Deltawing at Le Mans.

Side impact Crash protection
The Deltawing’s narrow monocoque has little room for side impact protection alongside the driver safety cell. The wingcar’s wide body work enables the fitment of long side impact crash structures within the body work.


So to conclude:- Many of the features/characteristics of the Deltawing (engine, lightweight, ground effects etc) would work equally well, if not better, on a conventional car. The ‘delta’ shape of the Deltawing has clearly been shown to be inferior to the rectangular shape of a conventional car in all but low speed straight line acceleration, which has negligable benefit at a high speed course like Le Mans.
would you like to upload the fuul looking of your car and a lap in sim?

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machin
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Re: Delta wing car concept

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I'm actually away from my computer for the weekend...

... Essentially its a fairly simple front end... I suggest the car as a whole needs to look a bit like a low aspect wing with wheels in the 'end plates'... But I'm not that precious over the design and would be open to suggestions...?
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machin
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Re: Delta wing car concept

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Jersey Tom wrote:...and the hand waving begins.

You're right.... lets put some numbers to the braking situation (since force transfer is lower in braking due to the longer wheelbase compared to track width):-

Deltawing, assuming downforce is distributed in accordance with the static mass distribution (27.5:72.5 Fr:Rr), and if we use the figure quoted by Deltawing of 950kg at 200mph and add that to the pressures I calculated previously during "no downforce" braking results in tyre contact area pressures of 114kN/m^2 (front) and 73.5kN/m^2 (rear).

"WingCar", assuming the same downforce, but distributed in 45:55 (in accordance with IT'S static mass distribution), and adding that to its "NO downforce" braking tyre contact pressures results in pressures of: 74kN/m^2 (front) and 72kNm^2 (rear).

So actually, the car's don't make enough downforce for the force transfer to be swamped by the aero loads (even at 200mph where downforce is greatest). Infact the rectangular car has a really good pressure distribution (almost identical front to rear!) and therefore my earlier conclusion was correct (that a rectangular car with equal tyre sizes IS better than the tyre sizes suggested by Deltawing, so ignore my post up the page a bit!
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machin
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Re: Delta wing car concept

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Essentially, what I'm saying, and what JT has also observed, is that the rear tyres on Deltawing appear to be too wide, and my maths also suggests the fronts' look to be relatively too narrow compared to those big rears, despite the rear weight distribution....

In the cornering scenario the fact that Delta-wing only really has one tyre to resist the over-turning moment (the outside rear), and despite that tyre's large width, means that tyre will become very highly loaded, and that's bad news for cornering performance....
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Jersey Tom
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Re: Delta wing car concept

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Indeed the difference in track widths on the DW biases an immense amount of load transfer distribution to the rear axle by default.

In any event.. would the square car be more efficient? I wouldn't doubt it.. much like I'm sure that closed wheel chassis with big floors have the opportunity to be more aero efficient than open wheelers. If that's the case and we're all horny for efficiency, why race open wheel at all? Not a very green design! Just like the DW, for all they are trying to claim, isn't all that it could be.

IMO, all points to the fact that for this type of racing the whole efficient/green thing is getting played out.
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rjsa
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Re: Delta wing car concept

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http://www.lemans.org/wpphpFichiers/1/1 ... ns-lmp.pdf

Code: Select all

a/ Wheelbase : Free but it must be identical to that
registered in the A.C.O. homologation form.
b/ Overall length : 4650 mm maximum (rear wing included)
c/ Overall width : 2000 mm maximum
d/ Height :
No part of the bodywork is permitted to be more than
1030 mm above the reference surface (See Art. 3.5.1),
except the rear rollover structure fairing that may be 10
mm maximum above the rear rollover structure.

Code: Select all

Audi R 15 TDI
Length 4,650 mm (183.1 in)
Width 2,000 mm (78.7 in)
Unless the rules are changed to allow a longer car for the DW I really can't see the DW doing anything but being extensively lapped in Le Mans. May be even giving up to start.

There is nothing to be gained from reducing front track and using rear biased brake balance on a car that should brake into corners, we have almost 100 years of Darwinism at work to show us that.

It could have been interesting running in a sepc series - which I still doubt since we never seen a working prototype.

Scania
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Re: Delta wing car concept

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machin wrote:Essentially, what I'm saying, and what JT has also observed, is that the rear tyres on Deltawing appear to be too wide, and my maths also suggests the fronts' look to be relatively too narrow compared to those big rears, despite the rear weight distribution....

In the cornering scenario the fact that Delta-wing only really has one tyre to resist the over-turning moment (the outside rear), and despite that tyre's large width, means that tyre will become very highly loaded, and that's bad news for cornering performance....
in FW08B, the front-rear wheel contact aera ratio is 1:2, in DW, it is around 1:3.
I have no caculate in a long time, but is it a big different between this 2 case?

Jersey Tom
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Re: Delta wing car concept

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And how much more power to the rear wheels does the FW08 have compared to the DW?
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