BGW!

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Nefarious
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BGW!

Post by Nefarious »

What happens when you mix alcohol, eBay and a Ladybird book on aerodynamics

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Image

I've set it deliberately high for the moment to keep it out of the rollbars' wake while we test it (I've only modelled the wing in isolation as my CFD skills aren't up to doing the whole car), but later plan to add some faring to the back of the bar and lower the wing.

Starting testing in FWP of 18° attack overall with the second plane at 30°. If it works like the sums suggest, I'll need to get creative about adding some front downforce!

I've only driven across town with it so far so can't comment on it's effectiveness, but can confirm that schoolkids think its CAF 8-)
"If everything seems under control, you're just not going fast enough"
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Rich B
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Re: BGW!

Post by Rich B »

Full face helmet required in case anyone recognises you....
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mik
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Re: BGW!

Post by mik »

Warning - spolier. :!:
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NotoriousREV
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Re: BGW!

Post by NotoriousREV »

100mph wheelies FTW!
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Nefarious
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Re: BGW!

Post by Nefarious »

Something like this for the front:

Image
"If everything seems under control, you're just not going fast enough"
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jamcg
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Re: BGW!

Post by jamcg »

Go full countach and just screw a spoiler on top of the bonnet
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mik
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Re: BGW!

Post by mik »

jamcg wrote: Wed Jun 06, 2018 9:40 pm Go full countach and just screw a spoiler on top of the bonnet
He wants one that provides some actual downforce.
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JLv3.0
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Re: BGW!

Post by JLv3.0 »

mik wrote: Wed Jun 06, 2018 10:02 pm
jamcg wrote: Wed Jun 06, 2018 9:40 pm Go full countach and just screw a spoiler on top of the bonnet
He wants one that provides some actual downforce.
And isn't actually a bumper :lol:
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integrale_evo
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Re: BGW!

Post by integrale_evo »

Bolt one directly to the front uprights lotus 49 style 😎
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Cheers, Harry
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Nefarious
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Re: BGW!

Post by Nefarious »

integrale_evo wrote: Wed Jun 06, 2018 11:10 pm Bolt one directly to the front uprights lotus 49 style 😎
Remind me how that worked out for Graham Hill and Jochen Rindt at Barcelona 69? ;)
"If everything seems under control, you're just not going fast enough"
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JonMad
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Re: BGW!

Post by JonMad »

:D that's a serious bit of diffuser going on at the back as well.
Left over crest; tightens.
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Nefarious
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Re: BGW!

Post by Nefarious »

There has been some high speed testing.

Subsequent to my original post, I did some more sums and realised that the configuration in the above photos was going to be catastrophically wrong - far too small a gap, and way too much overlap between the two planes. It would have effectively acted as one plane with way too much attack, causing air to stall and the whole thing to basically be an understeer-inducing parachute.

So I adjusted before even bothering to take it for its first proper run - gap between the two planes increased from 1mm to 6mm (approx 3.3% of the chord), the overlap reduced from 25mm to 11mm (5.9% of chord). This is tricky stuff because a) tiny differences in the position of the mounting holes make a massive difference to the geometry b) every time you change something, everything else changes too! I've managed to keep the overall angle of attack in the right ballpark (15%, instead of the 16-18% range I was hoping for) but the angle of the second plane is way off (<20% instead of 30-35%). I also decided to drop the whole arrangement by 100mm, on the basis that it would still largely be out of the rollbar's wake, and more height would just mean a grater pivot effect from whatever drag was created.

Anyway, after a couple of hours of measuring, calculating and drilling yet more holes, I got bored and decided to just run it up the motorway and see what happened. The findings are as follows:
- It doesn't wheelie! At 120 it doesn't feel noticeably lighter at the front and sharp lane changes are no problem. It also handled a wide-radius 270 degree motorway junction at 100+ with no understeer issues at all. Not really a proper evaluation, but at least I'm happy there are no dangerous front-end effects.
- It feels like there is noticeable downforce. The whole car feels more planted and stable. At speed, it literally feels like the difference between having a passenger and not, in terms of how much the car hops around and responds to road imperfections. Straight line acceleration is less scrabbley (especially between 60 and 80 ish) and the whole thing fell very planted through the high speed constant-radius test.
- There is drag. Best estimate is 10mph off the VMax (traffic limited proper testing), and acceleration from 110+ is noticeably blunted. Unfortunately, this will only get worse with my next round of planned angle adjustments to the wing, although may improve a bit with the addition of rollbar faring.
- The car maybe feels more vulnerable to cross winds. I guess its a natural side effect for downforce - you get used to the feel of what is effectively a fat bloke sitting on the back, then get a cross wind or pass a high-sided lorry and all of a sudden he disappears for a moment. It's a tricky one to test back-to-back, as no two incidents are the same and the lightness of the car does mean that it was always susceptible to some extent. One to keep an eye on.

Overall, I'm pretty happy. It's not a complete failure (i.e. totally ineffective, massively unbalanced, unstable etc) and deserving of some further fettling.

Next step is to add the rollbar faring, so this afternoon I shall mostly be sitting with a long length of 112mm PVC gutting and a paint-stripper gun trying to bent it into a lens shape (sharp edged elipse) and attach into position by the power of cable-ties and double-sided tape.
"If everything seems under control, you're just not going fast enough"
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Nefarious
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Re: BGW!

Post by Nefarious »

There has been more testing of my silly wing, this time on track.

TBH, I wasn't expecting much success, as the wing itself is only a part of the "phase 2" package (the various other bits weren't ready in time), and as such hasn't been optimised (apart from anything else, it's still sitting about 8" higher than it should be!). So that means no front wing to balance, no faring on the rollbars, and none of the extra little bits that will reduce overall drag and help guide the air to where it wants to be.
As is so often the case, circumstances meant that proper quantitative back-to-back testing was impossible - mixture of wet/damp/dry conditions, different tyre pressures (due to a set-up error last time out!), and the fact that the data logger was playing up, so qualitative evaluation is the best I can offer at this stage. But there was still very useful learning.
The first few sessions were largely dry, and the testing yielding a bit of a mixed bag of results. The bad news is that the drag penalty is huge - 8mph off terminal speed at the end of the main straight, and you can really feel the poor little engine struggling against the bloody great parachute slung out back. The good news is that the balance isn't anything like as bad as I thought it would be - no additional understeer, and just like in the earlier on-road test, the car just feels very solid and planted, especially on corner exit. I didn't get enough laps to really explore the outer limits of apex speeds at the faster corners like Duffus and Clarkes, but my overall impression was that there was definitely more to come (although perhaps not enough to outweigh the straightline penalty).
Then it rained. It really, really rained. So much that the officials were forced to close the track for a while. Even when it re-opened, few drivers were brave enough to venture back out immediately. But time was ticking on, so I donned the waterproof suit and headed back out (this time with Ross Howe in the passenger seat). Oh and I'm so glad I did. The car was absolutely magic. The wing's drag/downforce trade-off all of a sudden made sense. I made no suspension adjustments for the wet, and normally I'd expect it to be two handfuls on such a water-logged track, but absolutely not - it was rock-solid and seemed to generate other-worldly levels of grip (note the lack of mashing and sawing in the video!). OK, things were probably helped by newish R888Rs on the back and actually getting the tyre pressures right, but without really pushing we were literally running rings round everything else on track (i.e. lapping the same cars 3-4 times in a 15 minute session). Duffus, Leslies and Clarkes, where I'd expect to see the biggest gains were awesome, but surprisingly there were also stability improvements through slower corners like McIntires and the chicane (perhaps helped by the psychological effect of greater stability elsewhere).
So, overall, very happy with the result of the test (and quite a lot of fun had into the bargain!). Next steps will be to get the drag reduction pieces fitted (which in turn will allow the rear wing to move into its lower position) to see if I can get the drag penalty down to a more acceptable level. The front wing will follow, but I think I need to do a bit more head scratching over that, because I suspect we might not want to go as aggressive as I'd initially planned, given the current balance without it.
Anyway, here's a little vid - note the rate at which it reels in everything else on track (including the green Caterham R500). Oh, and be very glad of your roofs and windscreens, I was a bit damp after that session!
https://youtu.be/BUAT7jP7reU
"If everything seems under control, you're just not going fast enough"
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ZedLeg
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Re: BGW!

Post by ZedLeg »

Nefarious wrote: Wed Jun 06, 2018 8:57 pm Something like this for the front:

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Is that Andy Forrest's one?

I saw a video of his at Knockhill over the weekend, looked pretty spritely and made me think of what you're doing with your one.
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Nefarious
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Re: BGW!

Post by Nefarious »

Yeah, that's Andy Forest's. Serious piece of kit that - turbo-charged Vtec putting out 350-400bhp and a gearbox that's worth nearly twice my whole car! Last time I saw him at KH, he had about £10k's worth of logging gear strapped to it - so it's being fairly thoroughly developed. No surprises then that he's at least a couple of seconds up the road from me!
"If everything seems under control, you're just not going fast enough"
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Foz
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Re: BGW!

Post by Foz »

What sites/books etc is there out there to use for actual aero development- want to look into the loltus... albeit the under the car stuff, the splitter and spoiler stuff is sorted- although the latter could do with being moved back into cleaner air.
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Nefarious
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Re: BGW!

Post by Nefarious »

Couple of good books:

Aerodynamics for racing and performance cars Good, simple introduction (and seemingly very very cheap!)

Competition car aerodynamics - might be particularly useful for you, as there's a case study with a Motorsport Elise in it.

Race Car Aerodynamics - next level beyond the above. Prepare for some proper maths. Free PDF download from the same author to give you an idea

If you're in hardcore-maths mood, there are some good sections in Milliken and Milliken too - there's a free PDF version floating about somewhere (which I previously posted on the old forum), but I can't now immediately find it online.

Oh, and if you need to make a wing, there's a free online database of profile shapes and associated data here: http://airfoiltools.com/plotter/index

All that said, if you're just worried about the floor (without venturis etc), just make it as flat as possible, and do what you can to seal the edges (I used industrial garage door seals from Toolstation!). Not much maths required!
"If everything seems under control, you're just not going fast enough"
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Foz
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Re: BGW!

Post by Foz »

:) thanks!
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