Ideas, CF roof skin

General Composites Discussions Composites Talk
#1

Hi! Im new here. Im playin round with a bit of carbon fibre and kevlar and have started making a few parts for our race cars (guards, boot lids, air ducts etc). Im normally sifting around racingcomposites.net and now ive found another fantastic site here!

We are looking to cut the roof out of our circuit car (Nissan Skyline GTR) and replace it with a carbon fibre skin. Our reason for this is to try and lower the centre of gravity of the car ever so slightly, and getting rid of weight in the roof is the best way.

We plan to wax the top of the roof, then do a carbon fibre overlay. Then release the overlay and cut it to shape.

Then we’ll either;

-use some type of foam or something (?) and resin it on the underside of the carbon fibre skin, followed by another layer on the underside, effectively leaving us with carbon/foam/carbon product

or

-lay another layer of carbon on the underside of the carbon skin to stregnthin it

pros and cons of each?

Then attach it as in the pic below, with both foam and locktite… (Its ART!! :):))

good ideas/bad ideas?

Let us know people!!!

thanks,
Adam

#2

Have you strengthen that part of the frame significantly? Once you remove a huge section of the roof, you will lose a lot of torsional rigidity.

Have you consulted the racing organization regarding the use of a composite roof panel? Most that do allow use of composite body panels have regulations regarding minimum thicknesses of body panels. You should start looking there first.

If you just make an overlay, now you have a flimsy piece. Another layer of CF + foam isn’t going to make it stiff enough either. Plus it’ll distort and not be the same shape when you put it back on the car. A flapping body panel is not good for aerodynamics either.

If it was me, I would make a mold of the roof and add a step where it would be mounted to the sheetmetal. Lay up with enough layers of CF with either a foam or honeycomb sandwich. Then epoxy and rivet the panel to the car, using countersunk solid rivets.

But before I would even consider doing something like that, you will have to look at the weight savings and how it would affect the CG. You don’t want to spend all your time and effort to change a lightweight part to have neligible change in CG when there are other things that are easily relocated with significant change in CG. Moving the moveable ballast, aka driver, lower and closer to the roll center will make a bigger change in CG than replacing the roof. Just something to think about.

#3

The car does have a 9 point cage so that takes care of the torsional rigidity.

The problem we may possibly may have is if the car rolls, the driver will be showered in carbon fibre splinters, ouch! :eek:

We have a very similar parts car on its way from Japan, so were gana chop the roof off and see how it weighs in, compared to an estimate of a carbon fibre skin. If the benefits aren’t all that much then we’re not gana bother.

But yea as you say, taking a mould of the roof would be a far far better way of doing it, after looking into it a bit more that makes a lot of sence.

#4

One word, Kevlar. It’s is a pain in the butt to cutt without good shears. It’s a pain in the butt to trim/sand post cured. It starts trying to delaminate when you work with it after it cures. But, it doesn’t fracture when you exceed the tensile strength like with carbon fiber, it just delaminates.

#5

Ahh yes yes good thinking. The same application method with a mould as carbon fibre? I have played with kevlar a bit, and yea hard to cut, but is it about as light as carbon fibre for the same stregnth yea?

#6

by the time you add the weight of teh bolts you will exceed the weight of the steel panel, If you bond it on you may save a few ounces. lowering the engine and driver an inch will lower the CG much more. IF you are looking to take out wieght and have a cage start by removing inner structure, It doesnt show and carrys lots of wieght. we used to run GT3 pintos and always got below minimum weight with an all steel body by gutting the interior structure. we always sat the driver on the floor and lowered the engine/trans as much as possible to lower CG.

#7

Yea we lowered the seat as much as possible, and were suprised with the results from that, so it might be a much better idea to look into lowering the engine and gearbox. The owner wanted me to look into it, and now i have looked into it i think itd probably going to be a waste of time/effort making a carbon roof skin.

Thanks!:smiley:

#8

If you want a good example of how to lower the CG on a car, take a look at the last 3 years Ford Focus WRC. They went on a huge diet and weight redistribution to lower the car CG. Everything got moved as low as possible and to the center of the vehicle. The co-driver’s sight line is now staring at the dash. The driver isn’t much higher. Any switches, displays, guages that aren’t necessary got moved to the floor.

#9

Yea thats what we’l be concentrating on more so in the off season, we’l be looking at weight distribution of the wrc cars and working on aerodynamics of the underside and front of the car. will forget about roof for a while!

cheers!
adam

#10

You might want to consider what we Nascar 4 cylinder racers do, make a Fiberglass skin of the body panels and cut all the steel away! Try checking out www.LAracers.com then Irwindale Speedway, then any Mini Stock race date. I’m in the #54 Mercury Capri 2 (only one of that make & model and they never know what I changed as nothing to compare it to…).