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Flat Floor Design

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Thu Jul 30, 2015 3:01 pm PostPost subject: Flat Floor Design
AK
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Again, just bouncing ideas around and would welcome comments/suggestions.

Most of this is for a final year project (engineering degree) but I'm wanting to use some of the ideas on Fee's car in a more 'sporty' manor - i.e not just a flat floor panel, but skirts/rake/diffuser etc.

Working on a 1:18 scale Laughing

4 simple panels, skirts... simple floor between wheels rather than trying to work around them. Would aim to 'blank' the space above the floor, and between floor and arches. Vent front arch tops (louvres) and rear arches at rear of bumper area. 7-12deg diffuser with room for adjustment.














My main question just now is the addition of those small flaps/divertors at the front to get air split, and away from tyre face. You see these on production cars these days, but do you think the design in red would be better, and avoid adding turbulent air under the car. I.e i'd be forcing/channelling more air under the car than there would have been before. I think its a very minor point though Laughing





Exhaust will be a headache... and may need to sort out a side exit, or do away with some silencers to keep above floor.

Gearbox has a cooler - just need to increase, and divert air.
Rear diff - can add a cooler or larger finned cover with air flow

Some random shots of AFP Impreza



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Thu Jul 30, 2015 6:34 pm PostPost subject:
AMD
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Why not cut out the rear bumper like mark did?
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Thu Jul 30, 2015 6:47 pm PostPost subject:
AK
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Mark Robson?

Just cutting the bumper away will do very little (we did that on the GTR). It will reduce drag a bit, but you need a full flat floor and a much shallower diffuser at the end of it to make the floor really work.

On the above design a bit of the bumper would prob make way to get the full angle on the diffuser.

I also dont really like the look of all these Imprezas/EVOs with the rear bumpers chopped/halfed Smile
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Thu Jul 30, 2015 8:09 pm PostPost subject:
MrMischief
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I'm no expert but I think you want to try & create a venturi effect, reducing the cross sectional area around the centre of the car then increasing again out through the diffuser. This should accelerate the airflow & provide some ground effects.

As for your initial wide opening, I think you'd need to emulate that towards the rear to get the proper effect. Have a look at the underside of Merc SLR, it's more similar to your red sections.

Remember to aim some air to your brakes, don't forget the rears...!

This gives a good illustration of how the air flows under the R8 :
http://m.youtube.com/watch?v=7M4lzkDZWfk

Edit: Interesting comparison in this article :
http://www.autospeed.com/cms/article.html?&title=Modifying-UnderCar-Airflow-Part-2&A=2456
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Thu Jul 30, 2015 8:49 pm PostPost subject:
AK
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The rear section (of model) does widen and taper up - slowing the fast air on exit (in theory), and will draw air under the floor section faster. That and the rake (low front, higher rear) will help I think.

Will check out the SLR front.

Brakes:

Yup.... I have some plans for that... rears shouldnt need anything, but something extra to the fronts would help. Only issue is the front psgr side 'brake' duct feeds a boxed in oil cooler just now Laughing
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Fri May 27, 2016 9:12 am PostPost subject:
richmc1983
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Hi

Did you go anywhere regarding this flat floor design?
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Fri May 27, 2016 10:36 am PostPost subject:
AK
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not had time yet....

will get a lift in the garage end of this year hopefully so will be able to fully investigate in my own time/expense
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Sat May 28, 2016 12:08 am PostPost subject:
richmc1983
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AK wrote:
not had time yet....

will get a lift in the garage end of this year hopefully so will be able to fully investigate in my own time/expense


Sounds good. I plan on doing something similar myself soon then will carry out some testing.
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Sat May 28, 2016 8:18 am PostPost subject:
nefarious
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Not specifically answering the question, but a related thought.

All ground effects stuff gets much more effective as you close the gap to the road surface to as close to zero as possible. How about using garage door seals (e.g. http://www.toolstation.com/shop/p84655) to get the side strakes of the underfloor another couple of inches down.
There's probably a minor drag penalty, but it would be very cheap to try.
Kind of a pikey version of the rubber skirts they used on the Chaparral!
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Wed Jun 15, 2016 9:14 am PostPost subject:
nefarious
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In case interesting, here's a little update from my own aero modding programme on the Westie

First up, apologies for the pics - my phone camera is on the blink, so I had to use the front-facing one).

The new flat floor - nose to tail with cut outs for the sump and flywheel (gearbox mounts moved to accommodate).


The rear diffuser - with articulating pieces to allow the rear suspension to go into full droop without fouling (this have been a massive pain in the bum, allowing for fore and aft movement, rerouting brake lines etc).



New vents in the wheel arches (to relieve high-pressure spots). These are only temporary in ali, while we finish off the new carbon fibre ones.



Vents in the bonnet top (scary moments with the angle grinder!) and bonnet side (quite pleased with the mesh finish).



Finally, some of the new carbon pieces yet to go on (big front splitter, canards, prototype vent). These have been another massive time thief - everything was made first in acrylic, then aluminium, then moulds made in fibreglass, before laying up the CF. Good new skills though.


Probably going to go with the rubber garage door seals mentioned above as skirts for the underfloor tunnel - just figuring out a route that's the best compromise between aerodynamic efficiency and practicality (where to rivet it to, and leaving access for a jack etc).

We're out at Knockhill for the track evening on the 29th, and the car's all ready with new boots, pads and fluids. Hopefully the sun will shine and we'll see how much less brick-like we've made it!
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Wed Jun 15, 2016 11:34 am PostPost subject:
Fee
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Interesting progress. Keep us updated Very Happy
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Wed Jun 22, 2016 8:48 am PostPost subject:
nefarious
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Here's a rough sketch of the planned positions for the underfloor skirts:

Red bits are the splitter and diffuser, purple for the 2" rubber skirts, and the green splodges are where I *think* the downforce will be generated (aiming to focus the majority near the front)
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Wed Jun 22, 2016 9:58 am PostPost subject:
David Long
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Watching with interest Smile There are some interesting posts in the Lotus 7 archive about a guy who put his seven in full size wind tunnel. He found quite a lot to gained by adding a front spoiler but, after that, it quickly becomes a weight/drag/BHP balancing act.
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Wed Jun 22, 2016 10:07 am PostPost subject:
nefarious
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FYI - here's an old Autocar article about a Caterham at MIRA's wind tunnel

Page 1
Page 2
Page 3

I've tested the car with just the flat-floor and diffuser (but no splitter) on a run up to Oban at the weekend, and while I can't tell you anything about downforce (tricky on public roads!) drag is dramatically reduced - pull much stronger from 85+. Based on a very unscientific "keep my foot planted as lets see what she'll do" test on the motorway, I'd estimate that we've added 10-15mph to the vMax.

Underbonnet temps also stayed perfect (even though it was quite a warm day), and there were no problems with the transimssion tunnel getting too hot, or any parachuting from the rear deck (as some had warned).
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Wed Jun 22, 2016 12:16 pm PostPost subject:
David Long
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I'm interested, mainly in the diffuser, and have been following others in their quest for less drag. But bearing in mind that article is 15 years old, and only few of the features are seen on cars today, I think moving away from the essence of the seven (adding lightness) can be counterproductive.

Firstly, in a wind tunnel, the car is not moving so any gains in reduced drag need to be balance against the weight they add. Maybe a higher Vmax, but that's seldom used. Secondly the heavily coweled wheels proved to be a disaster on track as the aerodynamic loads go through the steering and suspension and that played havoc with the feel (caster) and un-sprung weight .

Front wings are seen, but only in cases where big power has added weight and understeer - seldom seen on low power cars.

But only my opinion and, as I said, I'll be interested in the difference it makes at KH, and if you're 2 secs quicker, I may follow your lead. Very Happy
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