Making rear spoiler

esta · Post by **esta** » Wed Jul 04, 2007 10:58 am

Well, i have a college project coming up and i am considering making a rear spoiler for my GT.

How would i go about this?

I cannot find any info on how to make a spoiler from people or the internet. I know a couple of people on thsi forum have done various body parts.

I will be using firbreglass-I used this to fix up my front spoiler as their was a massive chip missing lol! I guess there is the mold i have to make, so what would i make this from? And where are the best points to mount the spoiler? I want something subtle like the hausser style, not something huge protruding from the roof lol

Cheers guys

aibast · Post by **aibast** » Wed Jul 04, 2007 11:12 am

You're planing on rear hatch spoiler?
the attachment I think is the best solved like the stock little thingis in there. They wrap aroound the glass edge on the hatch. And get thenn atached to it.hmm. I might give this one a go

I haven't got my ECu back from richard so I have some time to get started on it. Ok, next thing tomorow

I think something like this wouldbe cool

Maby do a how to manual on this one also

The difference now is. Do you wanrt to make more than one or do you like to have only one and custom. Cos if you want to make many, You'll have to do it a bit different.

esta · Post by **esta** » Wed Jul 04, 2007 12:00 pm

Yeah something like that would be perfect. The opening of the boot was the main problem i was worrying about as i didn't want to restrict it. I am planning only to make one for myself. Hopefully if all goes succesfully i will be able to make other custom parts.

aibast · Post by **aibast** » Wed Jul 04, 2007 12:08 pm

the basic steps with fiberglass are:
A. get all you need. The resin, fiberglass, plaster, paint, form material (used PU-FOAM , but it also needs more work) nice ventilated place to do it in, rubber gloves, brushes (cheap ones)
B. Make a form of what you want. But make it a bit smaler for fiberglass to be but over it.
C. Cover the mold with fiberglass and resin
D. when the resin has hardened and you are happy with the thicknes. Sand or grind it to smooth and size.
E. Ad some plaster where neede
F. basecoat, and so on - paint it

PS. It's a messy job.

that is it.

esta · Post by **esta** » Wed Jul 04, 2007 12:24 pm

so you make the mold from the pu-foam then? How do you shape it?

Yeah i realised why my friend advised to me to buy some Marigolds before fixing the front spoiler lol

aibast · Post by **aibast** » Wed Jul 04, 2007 12:54 pm

I let it dry and then with a sharp knife cut it to rough shape and after that some sandpaper, measuring and so on. Now before you ad resin and fiberglas on it you'll have to cover it with something that the resin doesn't melt (PU-FOAM melts up) I used masking tape with 1/3 cover. So there wouldn't be any leaks. For the front I left most of the foam inside the spiler and covered the backside with fiberglass also. Gives more strength to it

And for front spoiler get on a very thicl layer of fiberglass. Make it as tough as you can, cos sooner or later you'll hit something with it. On the rear I'think you don't need that much. A nice smooth shape and thin layer of fiberglass will do. Also in the rear the spoilers cross section is important. I don't know about the airflow of the 480 bodyshape so can't think of anything where and what to but. I did notice that after butting front spoiler splitters on I got 0.3L less fuel consumption for 100 km. As I see it, it diverts the air away from the cars sides and mostly wheels.

These are aircraft wing profiles. For down force you'll have to turn them upside down. But when the wing is just cosmetic I think the low drag one would be the best solution.

esta · Post by **esta** » Wed Jul 04, 2007 1:02 pm

Hey thanks so much for that!

That has been so helpful i'm feeling a lot more confident about making one now!

I'll see about getting the materials and all that now and will let you know how it goes. I should hopefully be starting it in a few weeks when i get a little bit more money behind me

Cheers again, most helpful

Ettore Bugatti · Post by **Ettore Bugatti** » Thu Jul 05, 2007 10:33 am

NASA has an online calculator which calculates the lift of an wing. Just put the profile, dimensions and of your go. I believe it's called foilSIM.

But with resonable sizes you only gets about 40kg of downforce at 200kmh. Probably a lot less.
Filling the fuel tank has more effect.

Although you can double the downforce by using a spoiler under the bumper.
If you have an increase in downforce at the rear. The next step is to put some downforce at the front, you dont want a wheelie @350kmh

(downforce is related to the power of speed; downforce=constante*speed^2)

esta · Post by **esta** » Thu Jul 05, 2007 2:46 pm

Is there a web address?

rgreenhalf · Post by **rgreenhalf** » Thu Jul 05, 2007 4:14 pm

http://www.grc.nasa.gov/WWW/K-12/FoilSim/

I believe its that. Looks like quite a cool application.

Ettore Bugatti · Post by **Ettore Bugatti** » Thu Jul 05, 2007 6:24 pm

TAda!
The online version:
http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html
Remember that you need airflow above and below the profile.

owen080808 · Post by **owen080808** » Thu Jul 05, 2007 8:51 pm

here's roughly my impression of what i imagine airflow would be like at the rear of the 480. the red lines are airflow at the speed of the car, green are slower, and blue is slower still.

i think it is likely that the most beneficial effect you could have with a spoiler would be to reduce drag by 'softening' the sharp corner at the top of the rear hatch which generates the low pressure behind the car creating recirculation zones/turbulence. this could reduce drag and might give you 0.23mph extra top speed. i dont think the back of the 480 lends itself well to anything which would generate significant downforce, but as we're FWD that doesnt really matter. and of course this sketch doesn't take any account of the turbulent mess that would no doubt be issuing from underneath the car.

anyway this is just my fairly amaturish interpretation of aerodynamics, would be interested to hear from others...

can you tell i'm bored? it's pissing with rain outside AGAIN grr

98kellrs · Post by **98kellrs** » Mon Jul 09, 2007 3:23 pm

that looks pretty similar to what I had in mind. You'd need to make the trailing edge as sharp as possible i'm reckoning? All begs the question of is rear downforce really needed? Surely lowering the center of gravity and shifting it to the right point in the car would be better, coupled with reducing the drag.

I've been trying to find a way of flattening the underside of the 480 and using vortex generators to guide underflow into some form of diffuser, but it's not too easy!

JohnTurbo · Post by **JohnTurbo** » Mon Jul 09, 2007 4:03 pm

Nice sketch owen. Looks about right to me. The wonderful world of mechanical engineering degrees. You just can't help yourself sometimes can you? (by which i mean we)

- Or am i well off the mark?

What could be interesting is using a vortex generator to reduce drag in the same way as mitsubishi did with their Lancer - and of course the golf ball's famous dimples.

Ettore Bugatti · Post by **Ettore Bugatti** » Tue Jul 10, 2007 10:34 am

BMW used little bubbles on the head and tail lights on their facelifted E36 to reduce drag and wind noise.

IMHO is worthless to design a spoiler to reduce lift or even to create downforce when you dont know what the lift/ downforce is above the wheels of the original base car.

Best bet is to create a profile with low drag, create maximum area and make the angle adjustable and set it up to taste.

Anyway it has to look good too.

owen080808 · Post by **owen080808** » Tue Jul 10, 2007 5:40 pm

you're spot on john, i just graduated, perhaps i've been lacking in my fix of suitably dull fluids courses...

i like the evo style generators, but might be a bit optomistic for the humble volvo

i think my point is that the main function of a spoiler on a 480 will have to be aesthetic.

Volvo 480 Club Europe

Making rear spoiler

Making rear spoiler

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