Delta wing car concept

[andylaurence]

you never want a rear to lock first because that results in spinning... so you bias the brakes slightly forward so that one of the fronts lock first (ideally none of them should be locked of course!).

I think that's the point though - with the majority of the grip at the rear, if the rears do lock, they're still providing greater retardation than the fronts, so the car doesn't spin. Surely a spin under braking is because the front is slowing down more quickly than the back, right?

[machin]

Surely a spin under braking is because the yudrfront is slowing down more quickly than the back, right?

I think a spin under braking is normally caused by a lack of rear end lateral grip (e.g. as occurs when a rear wheel locks) COMBINED with a lateral force... such as turning into the corner, a bump etc...

...but more than happy to hear any good examples that support your thoughts....?

[machin]

Surely a spin under braking is because the front is slowing down more quickly than the back, right?

I found this interesting paper about a model car demonstration which I'm afraid doesn't agree with your hypothesis:

http://www.physics.umd.edu/lecdem/servi ... ervlet.pdf

We are able to demonstrate the stable deceleration of the car when only front brakes are applied and also ......... the instability when only the rear brakes are applied....

Its an interesting paper and only a few pages long... worth a read....

[thisisatest]

I think that's the point though - with the majority of the grip at the rear, if the rears do lock, they're still providing greater retardation than the fronts, so the car doesn't spin. Surely a spin under braking is because the front is slowing down more quickly than the back, right?

when the front wheels lock while in a corner, the front wheels slide forward, not inward towards the turn. so theres no more turning going on, understeer.
when the rear wheels lock while in a corner, the rear wheels slide forward while the front ones keep following the turn. soon, the rear wheels pass the fronts, and then pull the fronts along, backwards.
i used to have a "key car" toy that was like a HotWheels, but with a spring loaded hole in the back, you stuck a key in it, pushed a button and it rolled along the floor. they would turn left or right depending on what they hit along the floor, except for one car that always went straight (but not all that far). the front wheels were locked.

[Jersey Tom]

you never want a rear to lock first because that results in spinning... so you bias the brakes slightly forward so that one of the fronts lock first (ideally none of them should be locked of course!).

I think that's the point though - with the majority of the grip at the rear, if the rears do lock, they're still providing greater retardation than the fronts, so the car doesn't spin. Surely a spin under braking is because the front is slowing down more quickly than the back, right?

It all comes down to where your yaw moment is coming from and what overpowers things.

In the longitudinal sense, sure, more retardation from the rears will be stabilizing - by a puny and/or insignificant amount. Let's say with a 110" wheelbase car you have 4 degrees of yaw in the thing when you start locking up. The moment arm the longitudinal forces have to act on is 7-8".

When you lock up a wheel, your lateral force goes to zero. The lateral forces in that case have a moment arm of 109-110!!"

The effect of lateral forces is 10+ TIMES that of longitudinal.

Push or spin when locking tires under brakes is much much more an effect of lateral force imbalance than longitudinal.

[Scania]

[allstaruk08]

why does the rear tyre need to be so tall?

[Pierce89]

you never want a rear to lock first because that results in spinning... so you bias the brakes slightly forward so that one of the fronts lock first (ideally none of them should be locked of course!).

I think that's the point though - with the majority of the grip at the rear, if the rears do lock, they're still providing greater retardation than the fronts, so the car doesn't spin. Surely a spin under braking is because the front is slowing down more quickly than the back, right?

It all comes down to where your yaw moment is coming from and what overpowers things.

In the longitudinal sense, sure, more retardation from the rears will be stabilizing - by a puny and/or insignificant amount. Let's say with a 110" wheelbase car you have 4 degrees of yaw in the thing when you start locking up. The moment arm the longitudinal forces have to act on is 7-8".

When you lock up a wheel, your lateral force goes to zero. The lateral forces in that case have a moment arm of 109-110!!"

The effect of lateral forces is 10+ TIMES that of longitudinal.

Push or spin when locking tires under brakes is much much more an effect of lateral force imbalance than longitudinal.

I wonder where JT came up with a 110" wheelbase? He sure does roll the numbers off easy for that particular wheelbase!

For those that don't get the joke: Nascar uses 110" wheelbase

[strad]

Total weight: 475Kg.
Horsepower: 300 BHP
Wheel base: 2.90m..(equals..114.173228 inches)
Aerodynamic drag: Cd 0.24
Front track: 0.6m
Rear track: 1.7m
O/A length 4.65m
O/A width 2.00m
Height 1.03m
Front tire: 4.0/23.0 R15
Rear tire: 12.5/24.5 R15
Weight distribution: 27.5% Front (72.5% Rear)

[Scania]

why does the rear tyre need to be so tall?

It's not rear tire, it's R18's Front Tire.....

[allstaruk08]

wow i never realised they were so big haha

[machin]

http://www.pistonheads.com/news/default ... ryId=25605

Ben Bowlby will be at an event at Nissan HQ taking questions on the Deltawing....

If anyone goes the interesting question to ask would be:-

"If using the same engine and transmission and given the same weight/aero freedoms, could you design a "Rectangular" car which is quicker around the Le Mans circuit than the Delta layout?"

Would be interesting to hear his answer to this direct question....

[EDIT] I've signed up to go... hopefully will be able to ask that question! Watch this space.

[machin]

Aerodynamic drag: Cd 0.24

The May issue of Racecar engineering has an article on Deltawing. In going from the "singleseater" version to the Le Mans version the drag coefficient has crept up a bit to 0.313, however, they're still claiming a 4.9:1 efficiency ratio (downforce to Drag) leading to a Cl of -1.54.

Back working some of the numbers quoted in the article the frontal Area works out at 1.58m^2.

These are still pretty impressive numbers... comparing to a "Le Mans Spec" Jaguar XJR-9LM (Group C ground effects car), with numbers derived from Mulsanne Corner (http://www.mulsannescorner.com/aerodata ... xjr-9.html) and working on a 2.0m^2 frontal area:-

______DeltaWing_____ XJR-9LM
A______1.58_________2.0
Cd_____0.313_______0.358
Cl_____-1.54_______-1.06

Of course, the XJR-9LM is a 25 year old design... would be interesting to see what they could do today given the same rule set....

[machin]

That post above got me thinking... how would a scaled-down version of the XJR-9 compare to Deltawing performance-wise?

I've taken the XJR-9 aero coefficients and applied them to a car with a smaller frontal area (akin to typical "Radical" dimensions), and compared its performance to Deltawing.

The cars have the same engine (300bhp @ 7500rpm), gearbox (5 Speed) and tyre compound (although tyre sizes are in accordance with their respective designs). The Deltawing is 20kg lighter.

0-60mph
Deltawing: 2.96 seconds
"Mini XJR-9": 3.14 seconds

The rearward weight bias gives the Deltawing better traction and hence better low speed straight-line acceleration.

90-120mph
Deltawing: 4.49 seconds
"Mini XJR-9": 4.89 seconds

The lower drag gives the Deltawing better high speed acceleration.

Le Mans Lap
Deltawing: 3:47.74
"Mini XJR-9": 3:51.77

The lower drag and higher downforce means the Deltawing is quicker around the high speed Le Mans circuit...

Brands Hatch Indy
Deltawing: 47.28 seconds
"Mini XJR-9": 46.68 seconds

The low speed twisty Brands Hatch Indy circuit puts a premium on pure mecahnical grip and less emphasis on low drag and downforce... for this circuit the "mini XJR-9" just has the advantage....

Interesting results I hope you all agree... to be honest, not entirely what I was expecting... it still does beg the question; what aerodynamic performance could be achieved with a modern rectangular ground effects sportscar?

[machin]

So, I went to the Pistonheads Sunday Service today and attended the talk by Ben Bowlby on the Deltawing. I recorded the whole thing and have transferred to text here; the questions were made by a combination of Tony Jardine and members of the audience, including me. They were in a slightly different order, but I've tried to order them to make them flow a bit better, there were others but these were the most interesting:-

Q: You’re working with some big names; what do they hope to gain from it?
Ben Bowlby:Its an extraordinary opportunity to challenge things and determine exactly what we can do in terms of efficiency whilst still maintaining performance.
Its a massive honour, really its a genius from the ACO to have an experimental class. I think what the Deltwaing does is quite significant; its an ultra light-weight car made from advanced materials; its the real deal; it actually can do the improvement in efficiency whilst maintaining the same performance, an electric car can’t do that at the moment. For that reason, the ACO chose us.
Q: You aren’t elligable for the win, but you will certainly have a lot of attention at Le Mans; its a very dramatic looking vehicle....
It does look like the Batmobile, but this IS a real project; its not a marketing exercise; This is the absolute most efficient vehicle to do an LMP1 lap time that we could come up, I’m sure there are cleverer people out there that would come up with a better way of doing it; but we’ve done the calcs and our simulations show this configuration is the fastest car that we were able to simulate that could do the performance we needed and burn about half the fuel of a petrol LMP1 car.
Q: Those simulations were around Le Mans, I guess, but around a circuit like Brands Hatch Indy (which is slower and twistier) do you think it would still be the best configuration, or do you think a ground effects rectangular shaped car would be better?
Urrrmmm... I think it could take on anything... its a tricky question... what’s the parameters? If you are looking at fuel consumption being the denominator of performance I think we could take on anybody no matter what format....We have greater efficiency... its going to have to be a two wheel drive car because although 4 wheel drive (there’s going to be no rules right?) 4 wheel drive is very high performance but also higher weight, so you’d go with 2WD and then you want the weight over the driven wheels. The aerodynamics, the mass, and the tyre sizes need to be in harmony with each other, once you have that you basically have a car that behaves like a normal racing car.
We did some sims with 500bhp to see what it would do... and.... it was very fast!
Q: Did you ever think about making it 3 wheels?
At one point I thought ‘yeah we’ll make it a 3 wheeler’, but a 3-wheeler isn’t a car under the the FIA definition; its a motorcycle, so what we did was put the front two wheels close together so that they act as one. We looked at racing sidecars to see what technology they’re using for steering and things like that, in fact we built a 3 wheeled radio control model to test the concept, and actually the model behaved exactly like the real thing. That was in the pre-budget; it was my own money!
Q: Its basically a mid-engined Reliant Robin isn’t it?
It is! A Reliant Robin with the mass in the right place!
Q: Does the Delta configuration make the rectangular configuration obsolete?
I don’ think so, no.... but I do think its important that the motorsport industry has a wide spread of projects; look at what Nissan are doing with the Leaf, I think its good to promote efficiency.
Q: You are in the experimental class; You are not expected to finish the race
Our expectation is that we have done enough work to finish the race, but the reality is that we probably won’t. We’re having to temper our hopes; If you were going to win Le Mans you would have probably 2 years of testing with multiple 30 hour tests, we’ve done 25 laps in succession so far without hitting a problem; Its a tough challenge; the problems haven’t been the things we thought we’d have a problem with, its the things we were certain would be OK. But each time we test we go a little faster and get a little more reliable.
Q: Under race conditions what does the engine do MPG wise?
On the dyno it does 230g/kWhr... there is virtually no petrol road car that makes horsepower at that small a fuel burn... on the race track it equates to around 12 miles per UK Gallon; it doesn’t sound that good but that is actually an impressive number; about double what the petrol LMP1 cars will get.