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”:-
The different aspects of the Deltawing are compared to the Wingcar below, with numbers for comparison:-
The Deltawing has a 27.5:72.5 Fr:Rr weight distribution. The Wingcar uses a ‘conventional’ 45:55 Fr:Rr distribution.
The Deltawing has a 2.9m wheelbase. The Wingcar has a 2.6m wheelbase.
The Deltawing is 4.65m long overall. The Wingcar would be 4.35m long overall.
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
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.
The Deltawing uses a 5 speed gearbox weighing just 33kg. The wingcar would use the same gearbox. No advantage to either car.
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
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.
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.
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.
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.
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.
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.
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.