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  #271  
Old February 27th 2014, 02:08
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Aerodynamics of a bug

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Originally Posted by 4agedub View Post
I have been looking at the front splitter idea for some time now. Here's my progress on a splitter / bumper setup. The donor bumper came off a BMW e46 m3 circuit car. I do have a lot of data of the car without it, so will be able to see on the logger if it make any difference.



Will be interesting to see the comparisons once you get some info from the logger.

I guess the front spoiler/splitter must aid the movement of air over and around the body.However at the same time it is drawing air in at the front creating drag and probably lift.In your case it seems you have some track time so it will be really interesting to see how the car performs all round, inc cornering and at high speed.As Spannermanager points out it will bit different for a circuit racer compared to a road car due to ride height but keep us posted.

Lastly the old Kafer cup cars is where I got the inspiration for mine,I would imagine there are benefits of a splitter /spoiler or they wouldn't of used them
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  #272  
Old February 27th 2014, 02:14
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Once I do have data I will post it here. I do want to try adding some canards as well to see if they improve turn in grip.... I'm just worried with the extra grip in the front that we might have to add a wing at the back as well.

We have done some testing with a remelle cup type roof spoiler. On a back to back test we saw a 5km/h difference in top speed at the Zwartkops circuit. Going from 166km/h to 171km/h.
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  #273  
Old February 27th 2014, 05:16
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We have done some testing with a remelle cup type roof spoiler. On a back to back test we saw a 5km/h difference in top speed at the Zwartkops circuit. Going from 166km/h to 171km/h.
Thats good info! I assume the increase in speed was WITH the roof spoiler?

Effee: I haven't noticed any difference with or without the holes wrt handling.
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  #274  
Old February 27th 2014, 05:42
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Yes, the speed went up with the roof spoiler. A simple string test on the roof also showed improvement on the Gopro. I'll look if I do still have the photos.
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  #275  
Old February 27th 2014, 14:47
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The splitter produces down force, as it's name implies, it splits the airflow, sending most of it upwards And over the car, and the remainder under it, there by forcing it to increase in speed and lowering its pressure, splitters have been found to work very well at fairly high ground clearance, this makes them more benign and can incorporate a diffuser, unlike a NASCAR splitter which precludes all airflow under the car, but are far from benign for that reason, take off is not uncommon, also these don't use rear wings for reasons of racing purity, just a controlled spoiler, side skirts are not necessary on any car, modern flat bottomed skirt less cars produce huge downforce, a curtain effect is caused by simple physics, low pressure air can't bleed off into high pressure air, plus a boundary layer forming additional curtain effect that can be controlled by the lucky few with wind tunnels, most old Skool ideas have been debunked these days, side skirts and such, and new ideas prove wings can work without too much drag penalty for LOW SPEED work, say at or below about 85 mph, slaloms for example, now here's the rub, the effective wing angle can be up to 35 degs, not the 14 or 15 of the old theorists!
it was obvious last F1season that redbull ran at higher rake angles and ground clearance than most others, indicating they had downforce in hand and were using more rear ride height for other reasons, possibly rear weight transfer, side to side or to the front, or for kerb riding ability, lucky them..
As ever, the trade of is drag and weight, how much extra power do you need to pull it all to a faster lap time, non if it's well thought out and shows on the watch over a race distance, if it's faster over race distance, say 10/15 or more mins', it works.
Road cars have no datum, unless you go to a race track and time test before and after, you can't just say " that feels better", better for what? Speed? Fuel consumption? Passenger comfort? That's the problem with road cars, the right tyres and wheels and good brakes are a better bet for development with these, and good looks for the girlies of course...
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  #276  
Old March 4th 2014, 01:56
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Aerodynamics of a bug

Hi Spanners thanks for the continuing input on this as it is something I am very interested in.When my car was running for a short period before it started having engine install problems,I took it of a spin and noticed at around 80mph (on a private road )it felt completely stable. I think this is testament to how the running gear had been installed by type 2 detectives but I would imagine the splitter/spoiler must help/aid this stability ? I hear what you saying about track testing but as a road car I was able to do that speed with one finger on the steering wheel,with no steering rattle or hardly any scary shaking around you would experience in a normal bug.Obviously its a very different car now but to feel how stable and smooth it felt was a very pleasant surprise
I have not driven a modified beetle with this running gear so its hard for me to now what to expect but I gotta say it felt great.

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  #277  
Old March 6th 2014, 16:12
spannermanager spannermanager is offline
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Graham, well you've laid a good foundation by starting with the front air dam and splitter, hence the stability you have already noticed, even with a B/j car, it's the front that needs the work first, even with the much maligned ( unjustly) swing axles, the rear on both IRS and swing, is easy to get right, the reason the rear engined GT3 Porsches are so good in LMS and FIA Endurance racing with virtually no rear aero/diffuser/downforce, (flat engine layout =no room) is the already high rear loadings over the mid and front engined types with more room at the back for large diffusers, wheel loads are good to start with, tho there isn't much to choose between the three layouts, front, mid and rear engined, the advantage swings each season, maybe front engine, BMW, Corvette, Aston, were there at the season start last year, now we see Risi Ferrari holding the aces, tho it's so so close, and we know Porsche have a new car for this year...
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  #278  
Old March 7th 2014, 15:50
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I have had my 1303 to 135 on the track and was extremely stable, suspension and its settings are crucial, in my opinion the rear is a big issue at high speed on a beetle, if you are running tortion bars with old rubber bushes the toe is all over the place, unibal and coil over will fix that. I run small amount toe in on the rear and under load and tyre drag the rear is probably close to zero at high speed. The most frightening car i drove was me mates with 2.9 type 4, 230 odd hp, and when it had std rear end it was very dangerous, after unibal and coil overs and the right dial in, we did 140 no problem. Wont like a bumpy road tho!
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  #279  
Old March 7th 2014, 15:56
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Think I've mentioned elsewhere, I've had 150mph out of my cabrio, admittedly the aero is probably slightly better with the flatter roof? Only aero on mine is flush Kamei to body.. Rear suspension is torsion bar IRS but with 944 parts and aftermarket outer bushes which are probably stiffer than rubber. I also run a small amount of toe in.
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  #280  
Old March 11th 2014, 02:28
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Aerodynamics of a bug

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Originally Posted by ricola View Post
Think I've mentioned elsewhere, I've had 150mph out of my cabrio, admittedly the aero is probably slightly better with the flatter roof? Only aero on mine is flush Kamei to body.. Rear suspension is torsion bar IRS but with 944 parts and aftermarket outer bushes which are probably stiffer than rubber. I also run a small amount of toe in.
Hi Rich,how did it feel at that speed ?
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  #281  
Old March 11th 2014, 14:02
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It felt fine, bit more wind noise than I'm used to though!
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  #282  
Old March 14th 2014, 17:12
spannermanager spannermanager is offline
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It felt fine, bit more wind noise than I'm used to though!
I would think the Cab's roof line would be a big help, but imagine a Cab' with a rear wing, yuk, i think Ritchie runs one? think ive seen him drag with the top down, so thats a guide Rich',, someone needs to be brave and re profile the saloon roof to a NACA duct shape between the gutters from about the mid point back to the rear window, i cant do it for falling foul of the silhouette rules, but i have back filled the normal low pressure area behind the decklid by venting it, gaping it, and venting the rear apron, another plus for water cooled motors is they need no ducting or fan housing so are more versatile for bringing air up and over it or around them, did it work? i have to say it did, thats why sports racers run 'open deck' engine bays, its well known to reduce drag, now tho, ive gone a different rout with the engine paneled in by 'aero panels' and have made a solid GRP decklid, this will feature a spoiler when i get time next winter, Wally is on the right track with his whale tail but many poo poo these, mine will be similar but different lol, ok, not as bragging right
friendly as a wing, but we are getting good anti wing evidence coming good now, apart from a personal dislike for the B&D work mate, the spoiler is miss understood and its full function is not well documented, what they do if properly positioned is work wonders for the airflow UNDER the car, tho you need to work that area and de clutter and smooth it all to exploit it to its fullest, it smooths the turbulence behind the car and causes up flow from ground level to a height above the spoiler depending on its design and angle of attack, this then pulls yet more air out from under the car, icing on the cake if its already flowing well underneath, but most old design stock cars with busy underbodys just roll along on stagnant air, dragging the air along with it, it can then turn on a viscous effect with lift and drag thrown in for good measure, it all take work to get going, and a little understanding, the trouble starts again when flat bottomed cars get down Below the magic 40mm, which just happens to be the MSA lowest ride height rule, below 40mm, the viscous problem with drag and lift comes back to haunt you and it needs a special shaped underbody to perform, the 40mm rule is accidently the ultimate, im sure it is just an arbitrary figure to stop special needs in club racing, again, look at NASCAR for aero advantage, tho they dont cross over to well for anything else, they have skirts but they also get huge spins at 200 mph, i see those helping to stop air lifting them when side ways at huge speeds, but their spoilers work exactly as ive outlined above, the airflow so smooth and high riding it allows bumber to bumber 40 strong packs at 200 mph. what do we know?
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  #283  
Old March 16th 2014, 01:45
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Quote:
Originally Posted by spannermanager View Post
"...someone needs to be brave and re profile the saloon roof to a NACA duct shape between the gutters from about the mid point back to the rear window"
,

I had plans to build a NACA duct piece that fits down into the ragtop section, initial thoughts were intercooler intake cooling, but at this point I might stay naturally aspirated for awhile and then I don't need the volume of air a big NACA would create. What shape do you guys think might help with aero using the ragtop hole?

Jason
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  #284  
Old March 18th 2014, 14:03
spannermanager spannermanager is offline
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http://www.rjvolksperformance.com/gallery.html
Hi Jason, big question you asked! Expensive roof too! So It's probably best left alone, but here you can see Ritchie running his Cab with the roof down, this is giving aero advantage to his folded DOWN top!! Which now looks more like a well developed spoiler to me...very clever, it will be doing much of what I mentioned above, and pulling air out from under the car to help with down force, this car has run an 8 sec, pass at 150 mph, no workmate bolted on the back either, there is always a way for the clever guys to exploit ANYTHING, the good bit is those without the instinct never Suss how the quick guys do it, we are left with the starting point for efficient high speed stability being the front, mechanically sound and with a minimum of 6* castor and air flow control to kill front lift is my recommendation, oh! and it must be fun at all times! regards, Johnny.
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  #285  
Old March 19th 2014, 12:12
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IIRC Richie's car is basically a cab body draped over a tube chassis (or semi-tube chassis) and the "folded top" is basically a canvas covered wing. You can hardly call it a sleeper but it is a great looking car.

A super cabrio with a canvas cover over a folded top would probably be much more stable at speed than it's hardtop counterpart but going 100+with an open top would be a bit noisy
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