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Old 4 Apr 2008, 19:35 (Ref:2169800)   #1
Mcp138
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Expected amounts of downforce on a formula car

Hi there

This is my first post here so hopefully I can make it a good one. I’m trying to calculate the amount of downforce produced by the front and rear wings of a formula Renault. At the moment I’m returning figures of around 40Kg at the front and 50kg at the rear at the max speed. I figure this seems a reasonable figure but wanted some other peoples opinions.

Any suggestions would be appreciated.

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Old 4 Apr 2008, 22:11 (Ref:2169892)   #2
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tristancliffe should be qualifying in the top 10 on the gridtristancliffe should be qualifying in the top 10 on the grid
I would say that was a little low, but it's only a guess. Assuming running a fair amount of wing I'd have put both figures closer to the three figure mark. Without strain gauges on your wing uprights it'll be really hard to tell accurately.

One way to work it out would be to measure suspension compression at speed - this could be done with a tie wrap round the damper shaft, which will then record the most deflection. The downside is that braking or bumps will upset that record so you'd have to make sure you didn't brake and avoided bumps... Or use datalogging, if you have it on the car.
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Old 5 Apr 2008, 09:44 (Ref:2170121)   #3
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If you want just the contribution of just the wings themselves then that's not straightforward, but i think the overall figures come out somewhere around 50kg at the front and 85kg at the rear at 140mph. (CLF ~-0.21, CLR ~-0.35, with a frontal area of about 1m^2). This is obviously depending on the wing levels you're running though, and i can't say how i know those numbers, or i'll get into trouble!

Last edited by Locost47; 5 Apr 2008 at 09:47.
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Old 5 Apr 2008, 13:51 (Ref:2170332)   #4
Mcp138
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Hey, thanks for the quick replies guys. I am using the data from the car, taken from the suspension potentiometers, then reducing the frequency of the readings to try and minimize any bump/rebound effects. Firstly I am trying to concentrate on looking at the effects in a straight line and then by calculating roll angles, I would like to try and work out the cornering effects.
I’m not too savvy with aero, but trying to grasp an understanding to its effects to the balance of the car. From your figures Locost it looks like im getting respectable results at the moment.
Like i mentioned Im also trying to figure out roll angles for the maximum lateral accelerations of the car. Im getting max lateral forces of around 1.8-2g at the extremes and getting roll angles of around 10 degrees. I figure this may be too much roll. What do you guys think ?
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Old 5 Apr 2008, 15:28 (Ref:2170390)   #5
AU N EGL
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AU N EGL should be qualifying in the top 10 on the gridAU N EGL should be qualifying in the top 10 on the grid
These may help

http://www.nas.nasa.gov/About/Education/Racecar/

http://aerodyn.org/Annexes/Racing/hlifts.html


Good Luck
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Old 7 Apr 2008, 18:48 (Ref:2172541)   #6
Locost47
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10 degrees sounds like a lot of roll, especially for a single seater, but i don't have any real feel for the figures in this case. When i've tested FRenault before it's always been limited to pitch & ride height mapping at best due to budgetary contraints, so no yaw, roll or steer effects unfortunately.

One thing to watch out for when filtering the results from your potentiometers is that the aero forces are transient too, and can vary quite significantly, especially at very high or very low rear wing angles where either it or the diffuser may be near stalling, respectively. You can get quite sizeable aero fluctuations but normally they're quite high frequency (up to 30Hz ish), relative to the natural frequency of the chassis/suspension (~5Hz), so the car can't really physically respond to them in a dynamic sense and it just appears as buffeting. Sorry to add that extra layer of complication to your filtering problems.
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