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

[Prowagen]

FFS John you have had me in stitches with a couple of your posts What a grreat addition to the lounge!

[John Maher]

John, the car is actually quite heavy, but with the excitement of a days racing ahead, I normally loose a few pounds in the morning before getting in the car!

I figured 1584lb inc driver was pretty light for a street car....  unless you're the totally wasted, strung out junkie type 
I know worshipping the weight God can be seriously addictive

[ESH]

 

[John Maher]

And the Audi A2 has a Cd of just 0.25 – how about racing one of those? Perfect for the VWDRC...

Probably more in keeping if fitted with a Subaru engine 

[John Maher]

 

Q.  What's black and yellow and full of shit?

A.  A Netto bag   

[Stephan S]

Hot Rod Magazine had some interesting articles about the subject:
http://www.hotrod.com/techarticles/body/hdrp_0609_aero_tricks_tips/index.html
... and...
http://www.hotrod.com/techarticles/body/113_0703_car_aerodynamics/index.html

[richie]

Hot Rod Magazine had some interesting articles about the subject:
http://www.hotrod.com/techarticles/body/hdrp_0609_aero_tricks_tips/index.html
... and...
http://www.hotrod.com/techarticles/body/113_0703_car_aerodynamics/index.html

Thanks stephan,at last we are getting back on track


cheers richie

[John Maher]

Hot Rod Magazine had some interesting articles about the subject:
http://www.hotrod.com/techarticles/body/hdrp_0609_aero_tricks_tips/index.html
... and...
http://www.hotrod.com/techarticles/body/113_0703_car_aerodynamics/index.html

<Serious head back on>

Great articles. Thanks for posting the links. Printing them off to add to the library.
Looks like they cover just about everything under discussion on this thread, and more.

Here's a link to the A2 wind tunnel mentioned in the feature
http://www.a2wt.com/Wind%20Tunnel%20Testing.htm

Shame we don't have such a facility in the UK: $345 per hour for the first 2 hours!

 

[beetletom]

years ago,drag beetles uses to have the metal covers over the a post gutters?
was that for aerodynamics?

[Fastbrit]

years ago,drag beetles uses to have the metal covers over the a post gutters?
was that for aerodynamics?

See post on page 3... 

[beetletom]

years ago,drag beetles uses to have the metal covers over the a post gutters?
was that for aerodynamics?

See post on page 3... 

thanks! 

[Bruce]

When doubling speed, drag increases x 4 but the amount of horsepower required to overcome extra drag goes up by cube of speed - factor of 8
Beetle takes something in the region of 25hp to travel at steady 60mph on a perfectly flat road on a calm day.
Approx 200hp at 120mph

This is correct.

Working off that theory, aiming for 150mph terminal speed when you're used to maxing out at 140mph will require a 56% increase in horsepower   
... assuming aero is the factor holding you back - not traction/handling/gearing etc

(140 to 150mph = 7% increase. 7% x 8 = 56%)

However, you haven't applied the math correctly here.
(150/140)cubed is the factor.  In this case it is 1.2299, or 23% more hp.

[John Maher]

When doubling speed, drag increases x 4 but the amount of horsepower required to overcome extra drag goes up by cube of speed - factor of 8
Beetle takes something in the region of 25hp to travel at steady 60mph on a perfectly flat road on a calm day.
Approx 200hp at 120mph

This is correct.

Working off that theory, aiming for 150mph terminal speed when you're used to maxing out at 140mph will require a 56% increase in horsepower   
... assuming aero is the factor holding you back - not traction/handling/gearing etc

(140 to 150mph = 7% increase. 7% x 8 = 56%)

However, you haven't applied the math correctly here.
(150/140)cubed is the factor.  In this case it is 1.2299, or 23% more hp.

Thanks Bruce, you're absolutely right   

Maybe best not to inform Richie.... if he increases power by 56% we may yet see a full 1/4 on two wheels 

JM

[Bruce]

Maybe best not to inform Richie.... if he increases power by 56% we may yet see a full 1/4 on two wheels 

Oops, never thought of that!  If he did increase hp by 56%, he'd be up to 162mph.

[richie]

Maybe best not to inform Richie.... if he increases power by 56% we may yet see a full 1/4 on two wheels 

Oops, never thought of that!  If he did increase hp by 56%, he'd be up to 162mph.

Mmmm,I will stick with the 56% extra just to make sure    box is geared for 164mph@8000rpm in 4th so sounds about right,and all that without any hideous wings?


cheers richie

[Martin]

Maybe best not to inform Richie.... if he increases power by 56% we may yet see a full 1/4 on two wheels 

Oops, never thought of that!  If he did increase hp by 56%, he'd be up to 162mph.

Now thats what I'm talking about! lol

[Martin]

just found this.

AERODYNAMICS
The Cx of the Beetle, measured in the wind tunnel of the Polytechnic of Stoccarda on the final prototype, measured just 0,385. This datum increased to 0,41 in the mass-production, but in any case it remained an exceptionally low value for the epoch (we were in '38!); you have to think that the aerodynamic Lancia Aprilia hardly reached the 0,47 (0,44 a Fiat127 and 0,41 the first model of the Golf). The datum was also confirmed by the particularly low value of the absorbed power to travel to 100 km/h: only 15 CV. To make a comparison you have to think that a modern Volkswagen Pole first series absorbs 17,2 CV at the same speed. Anyway, you have to notice that the aesthetic modifications introduced in the '67 (squared bumpers and vertical headlights) made the Cd of the Beetle meaningfully worse and in the last models it appeared to be equal to 0,48.

http://www.maggiolinoweb.it/technique.html#cx


Just some more ifo to throw into the pot.


Bit more info...

Found this site with a Aerodynamics database, shame the beetle isnt on it. but take a look and you can see the lift at speed created .

http://www.mulsannescorner.com/data.html

[JamieL]

Wasn't the "beetle" originally designed to have lift in order to allow a "high" top speed with a low power requirement by reducing the rolling resistance/friction - along with the whole "maximum speed is cruising speed" thing...?

[Martin]

I was at the track this weekend and only managed one high speed run the others were in the 130's more findings for you from the data logs

over the finish line 145.68 mph the suspention logs say that the car is at the same ride hight as 130, its a little higer than normal ride hight. but it felt diferant. All i can put this down to is as the tires have gotten taller the castor has reduced making the car feel a little less directed. Im going to try and increase the caster to see if this cures this little odd feeling.

going to put the suspention sensors on the front next to see what the ride hight of the car is at the top end. might try and inclanometer, but i think the G's will confuse it.

Other than thats it felt fine, but man the breaks are rubbish!! lol

[Bruce]

Wasn't the "beetle" originally designed to have lift in order to allow a "high" top speed with a low power requirement by reducing the rolling resistance/friction - along with the whole "maximum speed is cruising speed" thing...?

Doubtful.  Any change in the friction in the bearings and tires is microscopic compared to the wind resistance at 60mph.

[benssp]

over the finish line 145.68 mph

145! what times were you running?

[Martin]

over the finish line 145.68 mph

145! what times were you running?

10.10 with a 1.68 60ft, going to be working real hard on the 60 ft at night of fire

[benssp]

the axles stayed together then!

[Neil Davies]

over the finish line 145.68 mph

145! what times were you running?

10.10 with a 1.68 60ft, going to be working real hard on the 60 ft at night of fire

Has Boom Boom been teaching you how to launch?
Seriously, what sort of 60ft times are you expecting out of the car eventually? I know street tyres are a limiting factor, but 1.40's can't be far off?

[Martin Greaves]

over the finish line 145.68 mph

145! what times were you running?

10.10 with a 1.68 60ft, going to be working real hard on the 60 ft at night of fire

Has Boom Boom been teaching you how to launch?
Seriously, what sort of 60ft times are you expecting out of the car eventually? I know street tyres are a limiting factor, but 1.40's can't be far off?

See you don't need low 60ft's to go quick.

[Martin]

over the finish line 145.68 mph

145! what times were you running?

10.10 with a 1.68 60ft, going to be working real hard on the 60 ft at night of fire

Has Boom Boom been teaching you how to launch?
Seriously, what sort of 60ft times are you expecting out of the car eventually? I know street tyres are a limiting factor, but 1.40's can't be far off?

See you don't need low 60ft's to go quick.

yeah but there nice!

[Airspeed]

1.68 60 ft is still very quick by my standards 

What tires do you use Martin?

[Martin]

micky Thompson sportsman pro's, its about the only option for street eliminator as i feel the drag radials are far too heavy for my axles to cope with.
there no problem with traction

[nicolas]

OK i think along all the pages it has been said that if you fit a way it should be done with the aid off a windtunnel as there are too many things to consider. however i want to put my damn heavy car at your disposal Richie if you bring the trans and engine and see what happens. i'll let you even drive once in a while to continue your studies and observations.

But on a more serious note i do think that aerodynamics are a strange thing when you look at dragrace cars covering the 1/4mile. your car Richie does wheelies and catches a LOT off air and wind on the first gears and still manages to go fast. it isn't lowered that much so i guess it takes a lot off wind under the car as well. so i believe there are a few ways around the problem and depending on the car different solutions will be found. and indeed on most cars the wing is a teacup stand and not much else.

[Bruce]

... Richie does wheelies and catches a LOT off air and wind on the first gears and still manages to go fast.

Wind resistance is trivial at the speeds where Richie is showing off.