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

[benssp]

how does Jim Smiths car behave at the top end, bearing in mind the bottom of his car is realtively smooth?

[JamieL]

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.

This will probably have everyone cringing, but when Jonny and I were at University together.... we used to talk about this a great deal with my Engineering tutor who was also our halls warden. Of interest here is perhaps the fact that he was a fluid dynamicist and alongside academic commitments worked on/for the aerodynamics for Ferrari F1 and high speed trains, like the japanese bullet train... Anyway, he always expressed concern about the shape or profile of our Bugs, stating that they must be really unstable due to the lift that is created...

For me, its not so much about creating downforce, but more a question of reducing lift - i.e. using spoilers to break-up airflow over the top of the car and "splitters" or whatver you want to call them to restrict airflow under the car. For example - with Richie's car, undoubtedly the cabrio shape, especially when running without the roof or roof down, will have significantly less lift than a regular hard top sedan as the airflow over the top is disturbed. With Russ Fellows' car, lift is also reduced by restricting airflow under the car at the front. As someone else has already said of downforce, for lift to occur you need airflow over both sides of an "airfoil" section in order to create the pressure differential...

Secondly, regards the issue of weight - this is simple physics according  i.e.  the Force that is "pushing" the car onto the ground (which we all know and feel as gravity) can be quantified by F= MA
For a car; A = gravity and M = the mass of the car.

For argument's sake, let's consider two virtually identical Bugs travelling in a straight line at "high" speed.

Both cars are experiencing an equal "force" upward upon them, caused by aerodynamic "lift" induced by the shape of the car.

However, one car is significantly heavier than the other and is experiencing a different opposing "force" downwards on it according to F=MA. i.e. the heavy car is being pushed down more than the lightweight one.

From this, it is clear to me that a lightweight car is therefore more susceptible to "lift", which we might also call high speed instability, or even (unfortuantely) crashing at the top end. "Lifting-off" merely transfers weight and alters the stability of a car and, as above, will be more of a problem for lightweight cars than heavy ones.

As an illustration of this "lift", with my old Karmann Ghia the all steel and v. heavy decklid would soemtimes lift open and flap about at the top end of a run when I would be doing 110ish mph. Ok it did this because the latch wasn't fitted because the valance wasn't fitted - but it was caused by the pressure differential above and below the car - i.e. LIFT caused by airflow over the top of the car travelling at a greater speed than air below... (oh - after this was observed by startline crew, I cabled tied it shut...)

Martin - good luck with your testing - I think there are many of us fascinated to learn the results...

[richie]

Morning John,thought you might put your head above the wall for this one  

Interesting thoughts,after i wrote about my decklid I thought about it somemore and did come to the conclusion it might be affected by both suction from the rear and the forwrd momentum,you really need to see inside the old package tray area of my carn ow to get an idea of where the pressure is coming from,after removing the package tray to fit the header,turbo intercooler etc the air seems to come along the bottom of the pan into this void and have no escape except out of the engine bay,when I made these changes i lost 5/7mph and have spent the last year and 1/2 trying to find it back again.[there were other changes hat could affect it as well]
Strangley enough the roof up or down doesnt seem to affect mph and my best ever mph was on one of those were it actually opened itself from flex after a hard wheelie/landing

The problem with a double acting true wing is
1 they look so shit
2 the rules seem to deem them illegal

It would be interesting to put my car in a wind tunnel but I feel that as i continuously change stuff which alters what the air will do/does it would be somewhat pointless as the needed changes may no longer have any effect,while Martin doing his may benifit alot more people as they have similar body style/shape.

So anymore thoughts?anyone,this has been mostly usefull so far  

cheers richie

[JamieL]

The problem with a double acting true wing is
1 they look so shit
2 the rules seem to deem them illegal

Indeed...

[richie]

how does Jim Smiths car behave at the top end, bearing in mind the bottom of his car is realtively smooth?

No idea ben,it been that long since he got a good pass   But I am not convinced his car is any better than a pan,he still has all the voids we have
Interestingly it did go 5/7mph faster than it ever has before or after when he damaged a rear fender/wing and had to remove them to be able to carry on running which shows the drag and pressure build up in there

[benssp]

thought you'd say that about jims passes

Great thread

[Berger]

I think it might be interesting to this subject to find out what really happend to Håkans car last weekend. He told Tekken by e-mail that he lost traction (don`t know front or rear) at the end of the strip.
The car has the wing and the wheelebars, and is from what I saw at SCC maybe a little to stiff in the rear suspension.

I also think it would be interesting to see how at beetle without a wing, but with a totaly sealed underbody would behave

[John Maher]

Nice post JamieL... looking to reduce lift is a great approach.

Again,looking at the Beetle in profile, you could say it resembles a crudely drawn airplane wing ie curved on top and mostly flat on the bottom. If a wing generates lift by forcing air to travel more quickly over the increased surface area on the top side vs the shorter distance on the bottom we can see how a Beetle generates lift. By limiting flow over the underside, lift will be reduced. Spoilers are correctly named - they 'spoil' the airflow rather than treat it aerodynamically. A front spoiler should attempt to direct flow around the sides of the car rather than dam it up in front like a snow plough. Those old Kamei front spoilers actually did something! Time for a revival? 

Reducing ride height also does good things - it reduces the area available for air to flow under tha car and lowers the centre of gravity for better handling/stability. Many years ago Jon Webster built a front spoiler for Paul Sutton's 10sec Beetle (I've probably got a pic somewhere). It worked on the same principle as the one he'd already
made and fitted to Danny Cockerill's Ford Pop. It was flat bottomed and sat approx 3-4" off the ground. It was spaced away from the front body work by a similar distance. It was probably around 6-8" tall IIRC. It leaned back at the top at the same angle as the front valence. It performed two roles. It limited the amount of airflow going under the car simply by closing the gap, same as any other front spoiler. The interesting bit was the gap between itself and the body was supposed to suck up some of the air that made it underneath the spoiler. This worked on the basis there was more airflow going over the top of the car than below, so this would create negative pressure in the gap between body and spoiler. No idea if that's what was actually going on but it looked like a good idea to me at the time. After it was fitted Paul said his car was more stable going through the top end. Ultimately Paul's car crashed but I don't believe that was due in any way to the spoiler - he had other handling issues at the time. Not sure if that design has been repeated on other cars? This is why it's so difficult to evaluate the various aero mods carried out to VW racecars - everyone has a different combination.

Re underside: smoothing it reduces turbulence. Think of all the ugly shaped pieces and void areas under there just wanting to catch the air. Some high end road cars and plenty of single seat race cars have carefully engineered contours on the underside, acting like a venturi, with the closest point to the ground being engineered to apply the most downforce in an area that best benefits handling.

On to the back of the car. The Beetle roof profile could never be reworked to keep airflow attached. You have to make the best of a bad job. Flat rear wings must help as they extend into the area of turbulent air, disrupting/spoiling it and possibly adding a little downforce. The other approach is hanging an aerofoil shaped wing high up, away from the turbulence - it won't work if it's in turbulent airflow. In clean air the wing profile will be upside down compared to the Beetle body profile ie the largest surface area is on the bottom of the wing and the smallest on top, therefore the airflow over the wing generates downforce.

The structure for downforce generating wings needs to be substantial. Many cars have crashed due to broken wing supports. It's hard to believe how much effective weight is being applied to an aerodynamic wing at high speed. For a Beetle it could be equivalent to a couple of people standing on it! If you reckon your wing couldn't support that kind of weight, don't rely on it to stay in place down track.

Martin will get the opportunity to put figures to all this stuff on his MIRA trip. If that doesn't fit within your budget there's a poor man's wind tunnel option racers have
been doing for years: wool tuft testing. You can't measure downforce and you won't get figures but it can show the areas on your bodywork where flow goes turbulent. Check the pic - sorry about the car  .   Could also be used to check the effectiveness of aerodynamic wings as it will show if air is correctly attached to both top and underside.



Tape wool tufts in the areas you want to investigate and have someone drive alongside with a camera. You can clearly see turbulence around the rear end of the car where some of the wool tufts are inverted and/or flapping in the breeze.

[Prowagen]

Cool trick with the wool!

Also I have always wondered what about having holes in the front and rear wings/fenders to release air, as surely the air under the curved almost parachute shaped wings causes alot of lift?
Alot of the HiPo cars like R8's and Veyrons have vented wheel arches and rear spiltters.

Rob.

[Neil Davies]

how does Jim Smiths car behave at the top end, bearing in mind the bottom of his car is realtively smooth?

No idea ben,it been that long since he got a good pass   But I am not convinced his car is any better than a pan,he still has all the voids we have
Interestingly it did go 5/7mph faster than it ever has before or after when he damaged a rear fender/wing and had to remove them to be able to carry on running which shows the drag and pressure build up in there

I did give Jim a couple of fibreglass '56-'61 tail-light pods, the idea being to fit them to the rear wings and cut out the wing behind them, also leaving the lenses out as a way of relieving the pressure under the wings after his incident. Don't know if he ever thought about using them or not though.

[Black Sheep]

 Look cool , don't think they work too well , the shape's all wrong but maybe if you change the angle

Some how don't think anyone thought you would see a bug going over 130 mph
and worrying what would happen when you came off the gas when these were made 

[richie]

Well so far I dont see any evidence that what is comercially available actually improves safety or ET in any way that can be proven,hopefully we can get more input from people actually running wings/aerofoils etc

cheers richie

[Martin]

Im with you on that Richie, im sure the wing that i had on before would have created downforce as it was in the 'clean air' above the car, we will never know as i sold it to andy raw and its currently on his funny car.


I'll see if i can capture the screen shot from my data log.




Martin.

[Martin]

did it!

right let me explaine.  the top two graphs are the rear suspention travel, and the bottom is engine speed so you can follow it down the track.

if you look at the far left of the suspention travel lines that is me driving after the burnout so you can take this as level. now as the graph goes up the more the car is squatting and if the line goes bellow then the rear of the car is lifting.

now follow the rpm (i bogged real bad in 1st gear) now you can see the car moving about, now look as im in 3rd and 4th you can see that the car is starting lift a little. on this run i was doing 138 mph over the finish line.





hope you can see it!

this log was just at the start of me tuning the dampers, the graph now is a load smoother. but there still is lift at the high speed.

the next thing to do is log the front end and follow that movement (i only has enough $ for the rear sensors so far)




Martin.

[flatfire]

Okay I will put my hand up  I have a wing When I first got Betelgeuse it had this wing



I took it off and being a fairly light weight car it changed its stabilty at the top end even though it was just going through the traps at 120mph.

I replaced the wing with a big wig and IMHO suits the car and does give top end stabilty. I no longer use the wheelie bars as I think they are partly responsible for damaging gearbox's in this particular car. The downside for me was fitting this wing the engine runs hotter. To be modified

[richie]

the next thing to do is log the front end and follow that movement (i only has enough $ for the rear sensors so far)




Martin.

No need to spend any money there,I can tell you exactly what you need to know!!


The front dampers should extend fully on launch then stay extended till just after the finish line when you get of the gas pedal

cheers richie

PS I am sure the graph helps but it might as well be in Greek to me

[richie]

Okay I will put my hand up  I have a wing When I first got Betelgeuse it had this wing



I took it off and being a fairly light weight car it changed its stabilty at the top end even though it was just going through the traps at 120mph.

I replaced the wing with a big wig and IMHO suits the car and does give top end stabilty. I no longer use the wheelie bars as I think they are partly responsible for damaging gearbox's in this particular car. The downside for me was fitting this wing the engine runs hotter. To be modified

Thankfully the links didnt work so I am not blinded by the monstroserty

Did you gain or lose MPH when you removed the first wing?

cheers richie

[dave.d]

talking of lifting the front wheels i have a disc here for you

[Prowagen]

Flatfire is that the same car?
Looks great in the second pic with the big wig wing.

[flatfire]

Thankfully the links didnt work so I am not blinded by the monstroserty


Did you gain or lose MPH when you removed the first wing?

cheers richie
[/quote]

What you didn't like the wing 

I improved my mph with it removed but probably didn't better Stretchs best MPH.
My aim is to better the cars reliability and its performance.

Jim Bowen created a great car I just need to do it justice

Yes Prowagen its the same car I wish I could change my image as easily.
Thanks for the kind words

[John Maher]

Well so far I dont see any evidence that what is comercially available actually improves safety or ET in any way that can be proven,hopefully we can get more input from people actually running wings/aerofoils etc

cheers richie

Just like you can't step into a shop and buy a replica of your engine, you won't find any "guaranteed to improve the aerodynamics and downforce of your Beetle Cabrio" products on the shelves of your local 'Made in China' VW parts supplier.

The people who've taken the trouble to make or buy and fit rear wings need to convince themselves they work. If they work, how do they know? Seat of the pants testing works for most. The alternative is to admit they wasted their time and money.  Some cars fitted with wings aren't reaching high enough speeds for the wing to make a contribution but the car goes straight therefore it must work.... 

The fast cars without wings (eg yours) are spoiling it for all the guys who are trying to justify their aerodynamic strap-ons 

Seriously though, the right aero mods will work. It's not so simple physics. Clean up the aero on your car and it will take less force to push it through the air. Add downforce as necessary to keep it stable at speed.

If you want to find something that'll improve the stability/downforce/drag coefficient of your car, you'll probably have to take a route similar to the one taken with your engine i.e. experiment and refine lots of different combinations. Engines can be tested on the dyno or at the track. Aero mods can be tested in a wind tunnel or at the track. If the engine mods go wrong, worst case scenario is you need a new motor. If the aero stuff goes wrong, you could wreck the car and take a ride in an ambulance.

If you come up with a list of mods you think might work and have the funds to take a trip to MIRA, you'll find out what works and learn a lot. But they can only test what you've brung - so there's still no guarantee you'll come away with a positive result. At worst you'll have discovered what doesn't work. MIRA's not an option for most but at the kind of speeds you're running, you'd probably benefit more than most.

If you decide to take the trip, expect to see engine lids bearing the slogan:
"No Nitrous, No Turbo, No EFI, No Wind Tunnel"    

[Martin]

for got to say, we found on the rollers that the tires im using (sportsman pros) grow by over 2 inches past 120 mph. so thats also altering the angle of the car.


Martin

"No Nitrous, No Turbo, No EFI, No Wind Tunnel"...........why go slower lol



(best thread ever)

[richie]

 If you decide to take the trip, expect to see engine lids bearing the slogan:
"No Nitrous, No Turbo, No EFI, No Wind Tunnel"    

So does this mean you are coming back out to play? as thats mostly your old slogan

And I have a slightly different approach to find out what will work,no surprise there then i there
along the lines of the newbie you posted a pic off and a very long piece of desert   Its cheaper to take it there than Mira,but is kind of spelled the same

cheers richie

[richie]

for got to say, we found on the rollers that the tires im using (sportsman pros) grow by over 2 inches past 120 mph. so thats also altering the angle of the car.


Martin

(best thread ever)

Never took that into consideration,obviously you see the fuel car tyres growing but didnt think of it on our scale of things,how much does that affect your 4th gear ratio,is that 2inches taller exactly? or just an estimate? as I assume it would be difficult to measure unless you use known rpm/mph and calc the difference from static?

cheers richie

[Neil Davies]

Just throwing something in here about Cabriolets and centre of gravity - just think of how much weight there is lower down with the sill strengtheners, A-post re-inforcers, the rear seat area, rear windown winder mechanisms and inner quarter panel skins... is that a reason why Richie's cab is so stable?

[ian c]

dont forget richies car changes shape at speed !!! 

[John Maher]

So does this mean you are coming back out to play? as thats mostly your old slogan

If I ever make it, at least one of those statements will have to be scratched out 

And I have a slightly different approach to find out what will work,no surprise there then i there
along the lines of the newbie you posted a pic off and a very long piece of desert   Its cheaper to take it there than Mira,but is kind of spelled the same

cheers richie

I just knew the ball of wool and masking tape option would appeal - you're probably unravelling your cardigan as we speak 

JM

[Martin]

for got to say, we found on the rollers that the tires im using (sportsman pros) grow by over 2 inches past 120 mph. so thats also altering the angle of the car.


Martin

(best thread ever)

Never took that into consideration,obviously you see the fuel car tyres growing but didnt think of it on our scale of things,how much does that affect your 4th gear ratio,is that 2inches taller exactly? or just an estimate? as I assume it would be difficult to measure unless you use known rpm/mph and calc the difference from static?

cheers richie

The rollers i use have a speed sensor and you can see as the tire grows the ratio between between engine rpm and road speed increases quite dramaticaly, we plotted it when the car was on a cool down and it was about 10 mph (by just following the graph. its was only a tea break!)

next time i'll film the tire, as the speed goes up the tire gets taller and narrower, that was at 25 psi, chuff know what it does at 11psi!

as for the 2" exactly we were jsut using a tape meashure and sighting it up.

[Fastbrit]

Interesting stuff. I've always had a thing about aerodynamics, but I guess if the truth be told, most of my ideas came from looking at what others did and second-guessing what might or might not work. My elder step-son Mark is a Formula 1 aerodynamicist (worked alongside Ross Brawn at Arrows, then on to Ligier, Lola, Jaguar F1 and the Jaguar Group C team. Now with Honda) and we had many discussions about the subject while I was racing No Mercy (is it really 15 years ago?).

Now No Mercy was very heavy for a tube-chassis car. It weighed 1700lbs with me in it (weighed by Jon Webster) and was powered by a relatively small 2165cc turbo motor. The best time was 9.87 @ 139.8mph. I would like to think some of the aerodynamic bits I tried helped, but of course that may be wishful thinking. Here's what I ended up with...

1 ) Flat floor – aluminium skin under the chassis from front to rear bulkheads
2 ) Roof chop – may or may not have helped
3 ) Flush-mounted windows
4 ) Aluminium plates fitted to windscreen pillars to smooth airflow over gutters (drip-rails) – VW did this on the Mk1 GTI
5 ) 'Adam Wik' front end with deep airdam
6 ) Lips round the front edges of each wheelarch opening to deflect air away from rotating wheel (Mark says that a rotating wheel is one of the biggest sources of drag on any car) – this is commonly done on Funny Cars
7 ) Abbreviated rear fenders to allow air to escape from under back of car
8 ) Hinged 'lid' at bottom of engine cover to allow air to escape, also
9 ) Large spill plates on each side of rear 'spoiler'
10) Adjustable rear edge to spoiler (approx 3in – 75mm – deep)
11) Gurney flap added to rear edge of spoiler (disturbs airflow without increasing drag)
12) Limiting straps on front end

OK, other things that were tried early on included a strut-mounted true airfoil 'wing' from a F5000 Lola mounted up in the clean air above rear of car. This was interesting. The ETs fell by, on average, 0.15secs but the TS also fell by an average of 2mph! I put the former down to increased traction at the top end (there was some evidence of tyre slip at speed) while the latter was down to the increased drag, I guess. The wing was probably too 'severe' for this car – a smaller design might have worked better.

Anyone who remembers seeing the car run will recall how arrow-straight it ran, time after time. It was the easiest car I have ever driven – part of that must be down to the sophisticated four-bar rear end and IRS, but part must ls be don to the aerodynamics. Or is that just wishful thinking? Whatever, if I built a chassis car again, I'd not hesitate to follow a similar route.

No nitrous, No turbos, No fun...

[John Maher]

Anyone who remembers seeing the car run will recall how arrow-straight it ran, time after time. It was the easiest car I have ever driven – part of that must be down to the sophisticated four-bar rear end and IRS, but part must ls be don to the aerodynamics. Or is that just wishful thinking? Whatever, if I built a chassis car again, I'd not hesitate to follow a similar route.

No nitrous, No turbos, No fun...

Hi KS,

I must have seen your car go down the track at least a hundred times and agree totally - it always went straight. Only once did I see you have an issue. IIRC that was after you'd fitted a quick acting steering rack. Think it got removed for the next meet 

I believe some of your aero mods had to help - but like you say, how do you prove it? However a car with a ton of consistent passes under its belt is a good basis for evaluating stuff.