An alternative to Fibreglass......perhaps!

[Deskpilot]

Whilst wasting time on my 'Smart' TV, I came across a motoring series on YouTube. A couple of guys building a 4 wheel drive, Celica powered Mini rally car. To cover their wide wheels, they had to modify some plastic arches. Watch this video (fast forward to 9.00 if you're not into the subject matter) and see what they use.

 

Then post you comments.

 

 

[Marty_d]

I like it.

 

Next cyclist I see, it's out with the resin....

 

Now I've never done fibreglassing, but am I correct in thinking that stretching a length of lycra over a male mould and whacking on a couple of coats of resin would be easier than laying up fibreglass? Wonder what the strength difference is?

 

 

[facthunter]

You'd have to get Tony to stay still till it sets. Nev

 

 

[Litespeed]

Strength wise the glass should be stronger than lycra, especially if you user a quality woven glass cloth. It was used simply for ease and ability to stretch a compound curve.

 

I would have done them in formula R - extruded polystyrene foam which sands beautifully smooth and shapes so easy. first coat is peel ply and then glass. When done, finish outside to a smart finish with fairing compound then remove the foam.

 

I do love Binky as a project. Mini - my introduction to car building at age 8 and my oldest brothers stove hot cooper S, with a de-seamed body and full custom interior. Full wood and leather dash full of Smiths gauges, proper sports seats. The de-seaming was a huge job but done beautifully and really changed the look and aero.

 

And all done by a 18 year old. In 1978 this was probably Australia's best mini road car.

 

So naturally at 14 I bought a mini..................

 

 

[spacesailor]

You could also turn over the "Lycra mold" & glass the under-side for extra strength.

 

spacesailor

 

 

[Deskpilot]

I'm about to do some test pieces to see how how the resin penetrates the Lycra. Also want to find out just how much to stretch it before lay-up. Can resin be thinned at all, if so what with? Thinking two coats, one thin, one as it comes.

 

 

[spacesailor]

Hi Deskpilot

 

You could have a bit of trouble if making the first coat thin as it will run through the lycra,

 

also put a separation layer under the lycra so it is removable,(clingwrap).

 

spacesailor

 

 

[Jaba-who]

I'd be reluctant to use it for anything that needed any structural strength without getting some idea of how it compares to glass.

 

 

[bexrbetter]

I have 'glassed a considerable amount of stretchy material, i don't know what it is but it's silky on one side and a little furry on the other. it stretched one direction but not so much in the other.

 

I stretched it over tube to make all the shapes seen here ..

 

 

Early attempts I just brushed resin on but wetter in some spots than others, and when it dried it shrunk in some spots more than others, a complete failure.

 

Later I learned to use a spray pot with a lot of patience, sprayed layers of fine mist over the fabric, let dry a bit in between, and repeat a few times until strong enough to brush on.

 

The mist looked like it just sat on top in very fine balls, like water mist on waterproof fabric, but slowly built up. As I said, patience is the key.

 

 

[turboplanner]

To make structures using the honeycomb principle, I've used cardboard tubes cut to length, cardboard sheet pressed into a 90 degree ripple, cut to length and then placed nose to nose to form hundreds of little square tubes. These cores were placed on a wet FRP layup of polyester and fibreglass chopped strand matt, then another pre-cured layup was covered in polyester resin and layed on to of the in-situ core.

 

This was good for very strong fillets and other structural uses,

 

Exciting material to design with.

 

 

[Deskpilot]

Hi DeskpilotYou could have a bit of trouble if making the first coat thin as it will run through the lycra, also put a separation layer under the lycra so it is removable,(clingwrap).

spacesailor

OK, so here's how I did it. First, found an old photograph frame, cut some Lycra that I estimated would need about a 75% stretch to fit over the frame. Machined both sides to make a bag and then slipped that over the frame. Now, I realised that there might be problems with the thinned coat so I just covered the photo back card with clingfilm so that, if necessary, I had something to press on when working the resin in. Next I pulled the bag down to cover the bottom half of the frame and pinned it into place. Here are photos of the before and after applying the resin.

 

You can see the clingfilm crinkled under the wet resin. I'm leaving it to dry and harden until tomorrow then I'l cut it off the frame for some bend tests.

 

Now to get on with my engine which is a sorry picture.

 

Note missing seals on all but one bearing. I think the remains of them are in the black sludge of the lower crank case. Any one ever refitted them, cause I need help.

 

 

 

 

 

 

[aro]

I think the lack of stretch in glass is what gives fibreglass it's strength, so I wouldn't expect good results from a stretchy material.

 

 

[Oscar]

OK, this is a subject that anyone who has a 'glass ( mainly, Jabirus) / other composite structure aircraft ( mainly Carbon fibre Euro 'fantastics') perhaps needs to understand.

 

Caveat: I have followed Project Binky for several years, and as someone who has built several racing cars and done serious modifications for road and rallye cars, I am in total AWE of what they are doing. As a fellow Pratchett (Binky is Death's horse in Pratchett books, and acknowledged by the guys as the inspiration for the name), and also Wallace and Grommit ( watch the series and you'll see their attachment there), they are kindred spirits. So this is NOT any kind of negative rant against what they are doing!

 

A composite structure is a combination of fibres (of glass, Carbon fibre, kevlar and some other weird and wonderful materials, particularly aramids), and a resin that holds those fibres together so they can take out loads. By comparison with the fibre matrix, the resin is relatively 'plastic' - but it grips to the fibres well and doesn't deflect much, so the loads being taken out by the matrix are shared well by the entire fibre mass.

 

The resin also provides 'toughness' - resilience to local shock loads. That comes at a cost of weight to strength: for pure strength, the resin/fibre ratio by weight is around 55%. It can get lower, with techniques such as Vacuum infusion.

 

For high-strength, low-weight composite structures, the designers take into account the fibre mass directions: you can find bi-xaxial, tri-axial and quadraxial fibre cloth, where the strength in one axis may be far higher than the strength in a secondary or tertiary axis. The fibre orientation of the matrix may be a critical part of the design equation.

 

We are all familiar with the 'reo' that is laid into house slabs: it is there for a reason - it adds strength to the concrete (which we might like to think of as the 'resin', though that is not the best explanation.)

 

When high strength and low weight is required, carbon fibre is fairly much the preferred option. That is because the carbon fibres are very, very 'stiff' and strong. But that comes at a price: the structure is increasingly brittle, and non-damage tolerant. The OTHER price, is increased production cost: not just the cost of the C/F cloth but the entire production cost, often requiring autoclaving ( high temp., vacuum conditions) requires very large investment in moulds and processing equipment.

 

Your average, polyester-resin and chopped-strand mat laid up yacht, bounces off wharves. Pure C/F Maxi-racers and America's Cup yachts break.. because the composite matrix - the resin AND the reinforcement - become overstressed.

 

The guard extensions for Project Binky were done to produce quickly an acceptable shape ( and you can note that the Lycra did not really conform to the compound curve, but required a lot of bog-filling..) The only 'structural' requirement for those guard extension, is the ability to not be damaged by stones thrown up by the tyres - and the Lycra is fine in the use for a very 'tough' against impact, but almost zero 'strength' requirement.

 

 

[Jaba-who]

Oscar, that was my concern as well. I have seen some stress studies on fibreglass wings and fuselage components and the science of stress lines and dissipation of forces by the direction of the glass fibres was quite astonishing.

 

I would never trust something like Lycra for a strength requiring component until I had seen some similar stress and force dissipation studies.

 

 

[Deskpilot]

I'm considering using Lycra/resin in lieu of Dacron for my Thruster. In this application, it would not be a 'structural' element. I think that it will be stiff enough not to distort under pressure changes but should retain a nice smooth surface to provide the lift needed to fly. I'm not sure about UV effects but with a very light coat of paint (colour matching only) it should be better than Dacron (IMO)

 

My sample dried over night and is quite firm but not rigid. I pushed the resin too hard in application so the finished surface shows the Lycra weave and is fairly rough. I will apply a second coat today hoping to achieve a smooth surface and a bit more rigidity.

 

 

[turboplanner]

How is the weight per area compared to plain dacron; the weight goes up exponentially on a large flat surface, so can be very significant.

 

An example of this is using 5 mm chequerplate on a trailer floor vs 3 mm.

 

 

[Old Koreelah]

A great resource for building up a complex shape for fibreglassing is Klegecell. This PVC foam is strong, light (75g/litre) and mates well with resins. If heated to 60C, sheets of it can be bent into compound forms and then easily shaped with sanding tools. I particularly enjoy using it as a sandwith between layers of thin ply; you get a very rigid, easily-shaped result, but not as impact resistant as fibreglass.

 

 

[turboplanner]

A great resource for building up a complex shape for fibreglassing is Klegecell. This PVC foam is strong, light (75g/litre) and mates well with resins. If heated to 60C, sheets of it can be bent into compound forms and then easily shaped with sanding tools. I particularly enjoy using it as a sandwith between layers of thin ply; you get a very rigid, easily-shaped result, but not as impact resistant as fibreglass.

Could be good for making moulds.

 

 

[Deskpilot]

Just letting you know that I will be off line for the next week. Thanks for your replies so far.

 

 

[Old Koreelah]

Could be good for making moulds.

...and whole aeroplanes, boats...

I'm totally over the work and expense of making a female mould, just to make one decent item.

 

Klegecell should be superior to polystyrene as a base for the Rutan building method, as it doesn't seem to "crumb" after years of flying loads.

 

 

[eightyknots]

Just letting you know that I will be off line for the next week. Thanks for your replies so far.

Enjoy your holiday DP!

 

 

[bexrbetter]

That is because the carbon fibres are very, very 'stiff' and strong. But that comes at a price: the structure is increasingly brittle, and non-damage tolerant.

This is a nonsensical myth around the internet about CF, it completely depends on what layup and resin schedule you use. here's me bending CF, and I can also show you brittle steel, aluminium, wood, plastics that don't bend at all ...

 

 

No, they break because they are designed to the absolute knife edge of strength and weight just as the wooden and fiberglass ones break for the same reasons.

 

 

[Deskpilot]

Enjoy your holiday DP!

Not a holiday by a long shot 80knts. Just had enough of overseas call centers so decided to change ip address. This in turn required a new phone number and email address. I think I've finally got it all working right so time will tell.

Now, during the time I've been away, I tested the piece of Lycra/resin to breaking point. I found that the second coat of resin was not homogeneous with the first and on bending it 180degrees, it started to separate. Not good.

 

Test piece 2 was initially coated with a thinned down resin, very lightly brushed on. Thinning resin isn't normally recommended.

 

I let it cure for 3 hours and then brushed on another coat. My application wasn't very good but as you can see in the photograph, it appears to be a good bond. Although not recommended, spraying on the top coat would be the go over a large area.

 

The finished piece is very strong (for a skin only, nothing structural) and should be impervious to UV rays, unlike Dacron which I'm about to replace.

 

underside with no drip through resin. Had use flash as my workshop lighting isn't all that great.

 

topside, showing poor brushmanship

 

will wrap around just about all L/E shapes, I think. I can pull both side to touch (full circle)

 

All comments recommended as usual.

 

 

[spacesailor]

I have found frp is heavier than aluminum for sheet work, but big problem with compound curves. I tried making an alloy "nose cone" shape but gave up on it.

 

spacesailor

 

 

[onetrack]

I tried making an alloy "nose cone" shape but gave up on it.

It's obvious you never had an English wheel, then. Once you gain proficiency in the use of an English wheel, it's amazing the shapes you can produce with it.