bryn
Posted a lot
Posts: 3,913
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Anybody recommend any reading material on the subject of underbody aerodynamics? I want to flat tray one of my cars with venturis at the back. I can make the sheet work no problem, I also have a fair idea of shape and size... Just wanted to be sure and the more help the better I reckon... Anybody?
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Volvo, Buggy, Discovery and an old tractor.
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Interesting and probably often overlooked. I know some fast cars can take off, but cant remember if that anything to do with whats going on underneath, so lower, and i suppose thats where the long forward sticking out front spoilers come in. probably no help, sorry don't know where to suggest...
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it doesn't matter if it's a Morris Marina or a Toyota Celica - it's what you do with it that counts
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bryn
Posted a lot
Posts: 3,913
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Pictures would be good... Seeing as it's topical at the moment ;D
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Volvo, Buggy, Discovery and an old tractor.
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Mr K
Posted a lot
Posts: 2,993
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You need to get the car as low as possible if you are aiming for ground effects - forgive my poor understanding of aerodynamics; its self tought. The aim of a under tray is to achieve the same effect as that of a wing on a airplane, the distance over the top is far further than that underneath, therefore when the air hits the car it is divided, a large amount over the top, but very little can go underneath, (this is where your under tray comes in) the smooth underside of the car means the air can pass straight through as fast as it can - causing a lower pressure, however the air over the top is slowed due to having to go up and over the body, thus causing a Higher pressure which when pushing against the pressure underneath actually physically pushes the car to the ground. on a road car it is very hard to achieve and maintain ground effects due to the bumpy British roads (it stops when you bottom out - which is why the Merc Le'mans car took off at 200mph! ) You can also use ground effects on aircraft, by simply reversing it, the Russians did alot of research (back when they where a great country) into this, check out ekranoplan's. The idea behind ekranoplans is that they use ground effects to fly at a very low altitude, but can carry a very very heavy load (much more than your average aircraft (about 550tons! - whilst being a lot faster than a boat! - about400kph ), once they where airborne (just) they could also turn off most of the engines and cruise at high speed effortlessly, far better than a boat or a plan. but it never caught on. www.hydrofoils.org/Egal/egal.html look here for more info. well, i hope thats of some use, I'm sure the petrol heads will now correct my limited knowledge!! Nick
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it doesn't matter if it's a Morris Marina or a Toyota Celica - it's what you do with it that counts
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Nick
Posted a lot
Posts: 2,483
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thats all well and good and everything, but is this car a circuit car? cos surely, on the roads of the uk, haveing something relying on being sucked to the ground isnt that good when weve got bumps and potholes and the shittest road surfaces in the developed world?
not that i know what i am talking about i am just wondering..
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idea stolen from rattely eddie.
this weeks car count "5"
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the imp you have pic'd above is the one in this months retro cars, and is my mates dads. I believe he sorted his with trial and error, i can ask him where his research came from if you like?
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Ekranoplans operate on ground-in-effect, not quite ground-effects And you got the principles of lift the wrong way 'round. Airoplane's wings are more curved on the top surface than the bottom surface, causing air to travel faster over the top, more curved surface. When air speeds up, it's pressure drops. This drop in pressure on the upper surface compared to the lower surface 'sucks' the wing upwards. An 'ideal' car would have a flat top and curved undersides. F1 cars are banned from body ground effects but Indycars and CART are not (as far as I can recall). Keep the bottom flat, keep the top flat and fit sodding big wings to them. *n
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Top grammar tips! Bought = purchased. Brought = relocated Lose = misplace/opposite of win. Loose = your mum
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Mr K
Posted a lot
Posts: 2,993
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Ekranoplans operate on ground-in-effect, not quite ground-effects And you got the principles of lift the wrong way 'round. Airoplane's wings are more curved on the top surface than the bottom surface, causing air to travel faster over the top, more curved surface. When air speeds up, it's pressure drops. This drop in pressure on the upper surface compared to the lower surface 'sucks' the wing upwards. *n knew that about wings... - i assumed that by getting the car closer to the floor and getting forceing lots of air into a small gap, the air would have to travel fast underneath it you would get a low pressure? as you said, fast air = lower pressure. suppose it would also need to taper towards the back, so speed up the air. I was close....
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Last Edit: Jan 9, 2006 18:26:33 GMT by Mr K
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It does occur but it's a very fine line.
*n
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Top grammar tips! Bought = purchased. Brought = relocated Lose = misplace/opposite of win. Loose = your mum
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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under body aerodynamics slater
@slater
Club Retro Rides Member 78
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In basic words your trying to stop the air getting under the car, meaning theres less air under ther and therfore a lower air pressure
at the back you have a diffuser to let whatever air you have under there out easly, with as little turbulance as possible.
Thats the way i understand it/explain it to chavs who have rear splitters! lmao
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Last Edit: Jan 9, 2006 18:35:30 GMT by slater
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thats the first time ive ever seen an ekranoplan, looks awesome. nothing to add to the debate though.
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the imp you have pic'd above is the one in this months retro cars, and is my mates dads. I believe he sorted his with trial and error, i can ask him where his research came from if you like? Yeah it was a great article... makes me want to build a space framed car!... I think irol has that picture because he penned the feature
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mmmmmmmm zakspeed capri
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once again rocking with 1117cc and 4 gears!
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bryn
Posted a lot
Posts: 3,913
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I did indeed write the article on that Imp, you gave me the contact details Mr Keefy sir! ;D For which I thank you once again, it was a seriously gorgeous motor in the metal Talking to Kevin the owner, he had gone with the tried and tested keep it flat route and made venturis to suit at the back. All your comments are welcome, I know that on UK roads it may seem a bit pointless, but I'm going to tray my road car first, then possibly my fun car after. This way I can have a play around and see what works. The road car does about 30K pa, at least 60per cent of which is on the motorway, at appropriate speeds. It's also quite low, and I've been experiencing some road to car contact recently so whilst underneath it last week upgrading 80% of the transmission I started to look at the possibility a sump guard. I then realised how exposed the exhaust, bottom of the gearbox and even diff are, so on that note it led me to a tray... And what's a tray without some Venturis? My spare wheel well is slightly rusty and the tank could easily be relocated to the new flat boot floor... It may not be overly effective in my application but I figured it would look fantastic if nothing else, whilst rendering some form of protection if I strengthen it in the relevant areas. I guess what I'm looking for is some form of reference material in relation to venturi size and effect, also how I might seal the tray in at the sill area given that I don't have, and don't particularly want side skirts... Then there's my exhaust which exits at the rear in the centre. Side exit it? Recess it into the floor? Or isolate it and have box around it? Would then disrupt the air flow at the rear rendering the venturis useless? Oh, and yes carbon would be the law... That Polo being an example of what I mean, how does the length effect side wind handling, cornering etc. If you're firing wind out in a straight line would that make it understeer? Random I know, but there's a lot I don't know too ;D Scrapingscrap introduced me to Ekranoplans and I've wanted one of those ever since, got a vid somewhere and they're are just amazing... Phew, the more you know, the more you realise how much you don't know.
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Volvo, Buggy, Discovery and an old tractor.
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I did indeed write the article on that Imp, you gave me the contact details Mr Keefy sir! ;D For which I thank you once again, it was a seriously gorgeous motor in the metal memory like a sieve me! ;D in that case, you already have Kev's details lol.
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Mr K
Posted a lot
Posts: 2,993
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May sound crazy but....Wood.... most formula one cars have a plank of wood underneath to protect the underside - though a few sheets of marine ply isnt the lightest option!!!! (the ends of the front splitter are plywood on the bently speed 8 - i guess they take a pounding!)
Also, various F1 cars tried a small skirt around the edge, this stoped the air escapeing / entering and gave the wanted effect of a infinatly low car, but with ground clearance...... it got banned though.
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Last Edit: Jan 9, 2006 20:34:06 GMT by Mr K
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May sound crazy but....Wood.... most formula one cars have a plank of wood underneath to protect the underside - though a few sheets of marine ply isnt the lightest option!!!! (the ends of the front splitter are plywood on the bently speed 8 - i guess they take a pounding!) Also, various F1 cars tried a small skirt around the edge, this stoped the air escapeing / entering and gave the wanted effect of a infinatly low car, but with ground clearance...... it got banned though. Might be wrong because I don't take the slightest bit of interest in F1 anymore but I thought they fitted the wood underneath to check to make sure that the cars were not running to low to the ground and it was a FIA rule.
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Mr K
Posted a lot
Posts: 2,993
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May sound crazy but....Wood.... most formula one cars have a plank of wood underneath to protect the underside - though a few sheets of marine ply isnt the lightest option!!!! (the ends of the front splitter are plywood on the bently speed 8 - i guess they take a pounding!) Also, various F1 cars tried a small skirt around the edge, this stoped the air escapeing / entering and gave the wanted effect of a infinatly low car, but with ground clearance...... it got banned though. Might be wrong because I don't take the slightest bit of interest in F1 anymore but I thought they fitted the wood underneath to check to make sure that the cars were not running to low to the ground and it was a FIA rule. Ah i stand corrected.... i too don't take any notice of modern F1 due to it being... well... curse word. However, wood would (lol) still be a good option for taking a beating under your car!
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