Side view of rear wing.

When was this done?

Approximately 10 years ago.

Could you talk us through the graph and the findings please.

Cheers

Jamie

I haven't looked at the raw data yet. When I do I might be able to put some numbers on the downforce.

Without doing that the dark blue graph tells us that the standard Libra had a drag coefficient of about 0.28 which is reasonably good. Adding the GTM front splitter increased the drag slightly. Adding the rear wing added more drag - increasing as the angle of attack is increased.

(Test was at 130 km/hr and bhp absorbed by aero drag was 20.6 21.3 26.0 27.2 27.3 28.5 29.6)

The light blue curve shows some lift at the rear on a stock Libra, slightly worse with the splitter added but swapping over to downforce with the wing added.

The pink curve shows downforce on the front, improving with the splitter but reducing as rear wing is added and the centre of lift moves rearwards.

Red curve is overall downforce (front plus rear) which improved with each device added.

Thanks for that very interesting indeed, just shows how you can throw horsepower away by increasing drag, I suppose it's a balance between usable power against stability, mechanical grip with a race / track car.

Jamie

Do you have any idea what the different rear wing numbers are? Is it just a steeper angle as the numbers (1 to 5) go up?
To my untrained eye, rear wing 2 looks the best as front & rear downforce are equal. I just wondered what angle the rear spoiler was at.
Or would there be reasons why more rear downforce is better?

I posted the pictures of wool tufting which also show the flow over the car.
When I had the suspension set up the car was raked front up, even though I have fitted larger diameter tyres to the rear.
That would also severely affect the downforce.
I had too my splitter suck off to the floor at around 90
Steering went very light and twitchy.
My thought for road car is front splitter only

Very interesting data.
The Libra with the biggest wing still has a better Cd than the Spyder
A Libra effectively has a 9bhp advantage at 130kph over a Spyder for the same engine power!

Contrary to what we all think/have felt the data suggests the front has downforce even without a splitter.

Interesting that a splitter alone has marginal effect on drag but does increase front downforce to a worthwhile degree.

Interesting that the rear as standard generates lift but I guess we don't feel that because the rear end is heavy enough to not to actually go light.

Splitter has been written up as a no loss item and this proves it
Better downforce with little or no drag penalty
I wonder how the different aids changed the attitude of the car
By the book the car should have been adjusted after each change

I should have mentioned - disregard the numbers 1 - 5 for the rear wing. They are test numbers I think. The angle of attack is increasing a you go from left to right. I think what happened is the car arrived at the wind tunnel with a small AOA on the wing. They tested it like that, then reduced the AOA a couple of times (I think it still produced DF with a -ve AOA due to the cambered wing section and the downward sloping rear deck it was mounted on.) I will have a look for the numbers but IIRC the wing "angle" was measured as height of the trailing edge.

Jaimie.
Even at the largest AOA the drag hp was only 9 hp more than a standard Libra - not much.

Sanzomat.
Where do I find the Spyder numbers?

The Spyder Cd came from the information in the link Terje posted earlier in this thread. There wasn't much other than the Cd and a suggestion that rear wing could be useful. I have corner splitters on mine and I noticed an improvement in stability but I've never felt a problem with rear lift.

In the data you posted, do you know if the Hp figures were measured or calculated?

Thanks sanzomat.

The HP figures are calculated from aero drag force (measured accurately by load cells in the floor plates under the tyres) multiplied by wind velocity (also measured accurately). So the hp is aero drag hp only - does not include rolling resistance.

Summarising the results from that link: (vs Libra)
. . . . . . . . Spyder . . . . . . . . Libra
Cd . . . . . . 0.4 . . . . . . . . . . 0.27
CL frt . . - 0.071 . . . . . . . - 0.17
CL rear . . 0.214 . . . . . . . . . 0.1

The minus sign indicates downforce, positive = lift.

Comparisons not necessarily valid eg methodology - was the MIRA tunnel using a moving ground plane?, what was the test velocity? was the Spyder tested top-down or up?

All else being equal, you would expect the Spyder to absorb aero drag power of 20.6 x 0.4/0.27 = 30.5 @ 130 km/hr ie 9.9 hp more than a Libra (already stated by sanzomat). I suspect the MIRA test was top down (photo shows top-down Spyder in tunnel with smoke stream) and would undoubtedly perform better with the roof on.