Wings/aerofoils Are they really needed? and if so when?

[andy M.]

The big advantage that cabrios have is that the air passing over the top is totally disrupted and has no chance to create a low pressure area above the car, it's starting to tumble the secound it goes over the top of the wind screen rail and destroys lift. On a regular sedan this doesn't happen, low pressure builds above (in theory anyway, there are still arguements about how things actually fly) and high pressure builds below, if you could connect the two by venting the roof and floorpan together then it would prevent lift,

andy

[Prowagen]

What Martin says reminds me of when I spoke to Ron Lummus at Bug Jm or Big Bang some years ago. I asked why people put flaps in the back of the air box, I asked if it were to aid cooling or release pressure etc and he just said "Nah people think they look cool!" lol

In my mind a wing a top end would aid traction of the reat wheel and keep the rear down, but I have never been at the top end speeds like any of you guys so what do I know.

I think certain cars look hard as nails and wings suit them, Like Dave Dinning, Chris' Hembug, Jay Wottons cars all look great and I could't imagine them without thw wing, and in Jays case it add a practical place for him to put the intercooler lol

[ian c]

Golf balls! 

footballs !!

[ESH]

... footballs ...

Wouldn't work.

[ian c]

ping-pong balls ??

[Martin Greaves]

Rob James has not got his intercooler they any more it inside the car. Also i feel you don't need to much air pushing down on the back of the car. As this will make the front end to light at the top end and you don't need that.

[ian c]

yes , but it will help when you lift off over the line ?

[Martin Greaves]

yes , but it will help when you lift off over the line ?

How do you work that one out.

[richie]

yes , but it will help when you lift off over the line ?

 if your suspension unloads violently at the top end when you lift off you or your car is set up wrong

cheers richie

[richie]

wouldn't the combination of a smooth underside to the car, and a rear wing help to lift the front wheels at speed.  Hence why beetles crash at the top end of a track when there is a cross wind? 

Micheal,this is what i have been thinking,a car with a badly designed rear wing and wheelie bars is more likely to crash as the downforce acts to make the extra 2 rear wheels steer the car,I almost wonder if the front wheels have any control at all when a rear wing is used without any front end downforce additions

cheers richie

[Black Sheep]

Golf balls! 

Some surfers cottoned onto that and used it to great affect  
 let in a few dimples on the underside of their boards , the break in water flow created bubbles under the board breaking the surface tension .
http://www.racecar-engineering.com/allarticles/166403/dimpled-aerodynamic-surfaces.html
Someone has already been thinking along these lines me thinks

[ian c]

yes , but it will help when you lift off over the line ?

How do you work that one out.

allthough lifting off the accelerator will shift wieght to the front , a wing will still be creating downforce to help counter it ?

[richie]

What Martin says reminds me of when I spoke to Ron Lummus at Big Bang some years ago. I asked why people put flaps in the back of the air box, I asked if it were to aid cooling or release pressure etc and he just said "Nah people think they look cool!" lol

If you look at the quicker cars with flaps they open quite early on the run,we have experimented with this on my car but you wont see it

But to prove a point I removed the decklid catch from the rear apron and videod what happened,threw the top end the decklid was open by 3/4 inches at the bottom with the air pressure in the engine bay and a steel decklid takes some pressure to move it,a normal saloon one with out vents in it would be even worse

cheers richie

[Adele AW]

I have slowly changed my opinion on Wings over the last 6/8 months deciding where we want to go with our car. Being around the V8's alot, the amount of measurements and scientific shit that goes in to making them is unreal.

We really only wanted our because of the look, but just goes to show we dont really need one, plus i dont drink Tea   

[Martin Greaves]

yes , but it will help when you lift off over the line ?

How do you work that one out.

allthough lifting off the accelerator will shift wieght to the front , a wing will still be creating downforce to help counter it ?

So do you think lifing off the accelerator is a good thing.

[ian c]

yes , once youve done the 1/4 !!!

 

(note , no question marks on this post)

[ESH]

A smooth underside coupled with 'obstacles' on the top such as a Bugs roof or a badly placed wing to a lesser or greater degree creates lift as the air over the top has to travel further than the air along the bottom to meet back at the same spot later on. Fast cars designed with a smooth underside may be smooth on the pan but they'll be doing stuff to the air somewhere, in the case of most (designed) race cars the air doesn't have to go so far over the top in the first place anyway. If you have a surface which increases the distance the air has to travel on the bottom then you counter lift but increase drag. It's complicated by other factors too, apparently. I guess theoretically a body mounted wing higher up the car reduces the amount of distance the air has to travel down the back of the car and therefore slows the air flow a degree reducing lift, you'd probably want to kick the lower air up a bit too though.

[Martin Greaves]

Sorry i find that lifing off the accelerator at top end is a bad thing. I tend to just put it into neutral and let the car settle before braking. So having two forces working against each other is a bad thing right. That why a feel a wing is a bad thing and i do not run one.

[ian c]

pm sent

[Jonny Grigg]

I have been working on the principle that the big dining table on the back of my car is actually a spoiler, not a wing per se. I don't expect to get down force from it, I just expect it to break the flow over the car enough to reduce the uplift generated. Oh, and I like the way it looks 

I am hoping that I'll get the set up right enough in order that the rear end will not be squatting at high speed and the wheelie bars doing the steering as the front goes light 

I was considering installing a 'V' shaped lip behind the front axle line to divert some flow out from beneath car- I am told on good authority that this does aid the high speed stability. Time will tell- I just need to get my car finished and see whether it works or not.

Got it back from Wayne's today.

[BeetleBug]

yes , but it will help when you lift off over the line ?

 if your suspension unloads violently at the top end when you lift off you or your car is set up wrong

cheers richie

Amen But then again... if you skip the 28-30mm torsion bars and the drag only dampers what will then happen to your 60ft times?

[judgie]

if you can make the underside flat with a slight kick up to the rear then that would be of more benefit than a spoiler ( not a wing) you want the air under the car to have the smoothest quickest route to the rear of the car, not the side.
ever car is differant and needs slightly differant tweeks to make it work, hence mine constatly changing.
have videoed mine at speed and it seems to be making some real downforce as the ride hight is about 25cm lower at speeds above 80mph. you could not get any turn in at high speed before i fitted the front splitter.
none of the above is of any use to you guys that just run in a stright line, you all need minimum drag and the front end lift is not so much a problem, not as if you have very heavy braking and a 90* corner 50 meters after the finish line.
its a subject i have spent the last 4 years playing with on my car and am just starting to understand what is happerning and how to change it.
cheers rob

[Neil Davies]

I had a spoiler on the back of my car which was pretty much flat, just a very slight kick up to add some strength to it. As Boom Boom said, the sides are more important - keeps the air over the back end flowing straight and not spilling over the sides. Several Land Speed cars have strips running the length of the car over the roof to keep airflow straight. My car had a spoiler on the front too, don't know if it worked or not but the car always felt quite nicely balanced. True, I was only doing 100 - 110mph over the line, but it never felt squirrely at all. Dad reckoned it kept the trailer straight towing at 85mph too...

[Martin]

The big advantage that cabrios have is that the air passing over the top is totally disrupted and has no chance to create a low pressure area above the car, it's starting to tumble the secound it goes over the top of the wind screen rail and destroys lift. On a regular sedan this doesn't happen, low pressure builds above (in theory anyway, there are still arguements about how things actually fly) and high pressure builds below, if you could connect the two by venting the roof and floorpan together then it would prevent lift,

andy

There was a beetle running on the salt flats that had abig tube running from the roof to the floor to help extract the air from under the car, it didnt crash, interesting idea though.

[andy M.]

yeah, the venturi effect should equalize the pressure top to bottom, and could possibly induce negative pressure under the car to suck it down to the track, all depends on whether this would cause drag, you don't get something for nothing do you!

andy

[John Maher]

Love this subject!

From an aerodynamics viewpoint, the Beetle body shape is not good. Looking at it sideways on, the rate at which the roof line tapers down over the rear window and deck lid is far too steep for air to stay attached - it breaks away somwhere around the top of the rear window and creates a huge area of turbulence behind the car. The turbulent air creates drag and slows you down. The faster you go, the worse the problem. Drag increases as the square of speed. Say you double your speed from 60mph to 120mph. Drag just increased by a factor of four.

If your current ETs are around the 120mph mark, it'll take a lot more power to gain an extra 10mph than it will for the someone looking to go from 100mph to 110mph.

I agree with Richie that a heavier Beetle will be more stable at very high speeds than a lighter one. The extra weight is helping keep the car planted to the track (downforce). However, it would be possible for a lighter car to achieve the same level of downforce at high speed by adding the right aerodynamic aids. The advantage would be less overall weight on the startline, where extra weight is of little benefit (makes life easier on the trans), and increasing downforce directly related to vehicle speed ie exactly when you need it. Drag and downforce have to be treated separately as well as together. Reducing drag makes it easier to push a shape through the air but you also need downforce to keep it going in a straight line. Remember the pre rear spolier Audi TT high speed crashes?

A convertible Beetle with the hood down is even worse than a saloon in terms of aerodynamic drag - like andy M explained above. Because the air has no initial roofline area to attach to I believe the turbulent air is distributed and broken up over a much greater area rather than being concentrated mostly in one spot. It no doubt takes more power to push the cabrio with hood down to a given speed than it would with the hood up but it's probably less likely to lose rear wheel downforce as a result.

A low mounted front spoiler can reduce the amount of air getting underneath the car. A smooth underbody allows the air to exit quickly reducing drag and lift. To create genuine downforce you need a properly designed aerofoil section wing hung in clean, non-turbulent air. Airflow must be able to pass over the top and bottom of the wing, otherwise true downforce won't be generated. The trick is to choose a wing profile and angle of attack that generates adequate downforce with minimum drag. The rear tray style engine covers can't deliver the same effect as a wing because air only passes over one side but they can help reduce the strength of the turbulent wake at the rear of the car by breaking it up and gaining some downforce as a result.

I know of a few instances where people have had the rear lexan window pop out at high speed. It's not being blown out from the inside - it's getting sucked out by the drag created at the rear of the car. Similar thing happens with the doors on lightweight Pro Stock style cars. That's why you see helicopter latches fiited in that area. The door starts getting sucked out at the 'A' pillar when you hit a certain speed due to the air going turbulent once it hits the A post and not staying attached around the corner once it leaves the edges of the windscreen. Richie's deck lid is most likey being sucked open by drag induced at the rear of the car, as opposed to being blown open by air pressure in the engine bay.

Air is weird! We can't see it and it does strange things when you start pushing stuff through it. Really keen to hear the results of Martin's trip to MIRA. There should be some interesting lessons learned. But due to numerous variables, what works for Martin's car won't necessarily apply to others.

Airflow/drag/turbulence etc can become critical at high speeds. Hats off to Richie, Russ and the other guys running the big numbers. It takes sheer brute force to push such an aerodynamic disaster through the air at those speeds!

BTW I'm not advocating everyone start fitting huge wings and spoilers. It's a science. Getting it wrong could make things worse. And more importantly, most of them look shit  

 

[Martin]

What Martin says reminds me of when I spoke to Ron Lummus at Big Bang some years ago. I asked why people put flaps in the back of the air box, I asked if it were to aid cooling or release pressure etc and he just said "Nah people think they look cool!" lol

If you look at the quicker cars with flaps they open quite early on the run,we have experimented with this on my car but you wont see it

But to prove a point I removed the decklid catch from the rear apron and videod what happened,threw the top end the decklid was open by 3/4 inches at the bottom with the air pressure in the engine bay and a steel decklid takes some pressure to move it,a normal saloon one with out vents in it would be even worse

cheers richie

Do you not think this lid was held open due to the negitive preshure behind it? created by your car making a 140 mph hole in the air?  


as for Jonnys idea of the v's under the car, this is another thing were going to try in the tunnal.




Look at that, start to reply and old Maher jumps in! lol

[Prowagen]

Its a fascinating science! But to be honest I dont think we will truely know unless someone is willing to spend about £10million researching it! Think of how much the F1 teams invest and how cars with the same engines but different aero packages can be so far apart! Ferrari vs Torro rosso for example!

Even the Top NHRA stuff probably isn't as good as it could be but then its only a $280,000 pro stock car! So they wont invest as much as F1. So when you think you have a £40,000 beetle top end racer your aero bugget is tiny!

I think a wing/spoiler must disrupt the turbulance which should bea good thing. But I could imagine a badly designed with will have a negative effect.
I always wondered about the wing Slush puppie and Beetle Geuise ran I thought that this would make the air run off the back of the car and under it causing lift?

So what about cars running wings and a chute! Surely this is another kettle of fish!

Rob.

[Martin]

the mira package isnt that bad i thought. There top price for 4 hours in the tunnal is £3500 + vat. now some people think nothing about spending that amount on crap for there cars, (technical term) so i feel investing that amount of money in the car is cheep if it keeps the car safe, and ultimatly makes it go faster. bear in mind that less drag means less power to push it the same speed as a car with loads of drag (have you seen what happens to a car with a roof rack?)

Would you spend £3500 on making to motor more powerfull?(yes is the answer) then why not spend that on the tunnal and go faster with the old motor.


Just the way i look at it.


Martin

[Prowagen]

the mira package isnt that bad i thought. There top price for 4 hours in the tunnal is £3500 + vat. now some people think nothing about spending that amount on crap for there cars, (technical term) so i feel investing that amount of money in the car is cheep if it keeps the car safe, and ultimatly makes it go faster. bear in mind that less drag means less power to push it the same speed as a car with loads of drag (have you seen what happens to a car with a roof rack?)

Would you spend £3500 on making to motor more powerfull?(yes is the answer) then why not spend that on the tunnal and go faster with the old motor.


Just the way i look at it.


Martin

That is indeed a good price, but how many hours would it take to get it spot on, alot more than 4 I would suspect 
I think what you are doing Martin is great and it is a testament to you that you are willing to share. I think overall safety is the main thing racers should thank about, its all good and well going quick but its better to go quick and safe and to over compensate on the safety aspect!

Working at EBI this year was a real eye opener it amazes me how many prople were willing to go down the strip in a quick car with a crap show cage and looked at you like you was a kill joy when you said that they couldn't go down the strip in their shorts and t-shirt lol

Rob.