Semi-scale ASH25

[Jolly Roger]

Half an hour sanding got rid of all the bumps in the first layer of glass due to wrinkled parcel tape.
The next layer of glass went on much better and is now sunbathing outside. Going onto glass it takes much less epoxy than onto foam. I used exactly 1:1 epoxy:glass today.

Any views on how many layers of glass for a modestly-sized fuselage? I’m thinking 200 glass + 200 glass + 175 Diolen.

I can always add more inside if it feels squishy.

[Chris Bowles]

Hi Roger, looking good, following with interest, when I did my ASW 17 fuz, used 5 layers 160, plus 1, 80 topcoat, this was from the trailing edge area, up to the nose, behind the trailing edge,down to 4 × 160, + 1, 80, this made a firm to squeeze fuz
Chris

[Jolly Roger]

Thanks Chris, I was hoping you’d reply. So that’s a total of 880gsm in the nose of your ASW17.
I think I’ll finish with some 100gsm glass on the outside, which will take less filler to finish than the 200gsm. I’d rather have glass than filler. My total thickness with the Diolen will then be nearly 700gsm...not far off your thickness.

I must say I’m finding this glasswork really therapeutic.

[roo Hawkins]

Hi roger I use about 4 or 5 layers of 190 cloth. It may need more adding later when the foam is removed but I add this to the inside. 4 to 5 layers is ok for the back end but can be a bit thin on the front end .I do it this way because it is easy to make a lost foam fuz too heavy.

[Jolly Roger]

Thanks Roo. That's really interesting - you use a similar overall thickness to Chris - about 900gsm total. I expect I'll be adding more layers to the inside after I've removed the foam.

I've been learning loads from this website recently: http://www.lefevere.eu/modellflug/how-t ... -fuselage/

It's inspiring what wonderful standards they achieve with relatively low-tech equipment (no CNC or digital printers) and affordable materials. The emphasis is on strong, robust, light, practically-sized models designed to be flown hard off the slope or the flat.

Here's an example of their fuselage lay-up (shown in the attached drawing). Starting from the outside and working inwards...

160gsm
280 gsm(at 45 deg)
280 gsm

Although this only totals 720 gsm, they also use some bands of uni-directional glass rovings running lengthwise along the side of the front fuselage, and glass rovings around the cockpit opening.

Interestingly they avoid carbon, and give some convincing reasons for this on their website.

[Jolly Roger]

Moving on...I‘m now up to 3 layers of 200gsm cloth on the outside, rubbing down lightly after each and the surface finish has improved every time.
I then screeded the whole fus and canopy mould with microballoons. Afterwards, I thought....why did I do that? There was no trace of the grain of the cloth and I should probably just have gone to a coat of primer. Anyway, by the time I’d rubbed it back there was almost none of the microballoons left, so I’ll just consider that as my 60 mins exercise for today.

[Jolly Roger]

Then it was time to tackle the cockpit lip.
Rather than just have a, say, 10mm wide flat lip like Pat Teakle models for example, I wanted to create a square crossection ridge, rebated back from the edge by about 5mm. This was partly to make it more scale, but mostly because I believe life should be hard. I could then mould the canopy frame around that, so that it would locate really positively onto the fuselage.

First I marked where I wanted this ridge to be...

[Jolly Roger]

Then, I stuck depron (ok...it’s pizza packaging) onto the fuselage with double-sided tape. This was trimmed back flush with the fuselage edge, then a channel cut out where the ridge would be. I made a little trimming tool to keep it accurate.

[Jolly Roger]

Many metres of epoxy-soaked 12k carbon tows were looped into this channel and packed down tight. I levelled off the top with some microballoons, then layed a waxed template on top to (he said hopefully) get a flat smooth finish to the top of ridge.

I’m not sure this whole approach will work because the foam may get well impregnated with epoxy and take some removing, but my hope is that it will sand easily off to reveal the ledge I so want.

Then at last I can cut the centre of the cockpit out and start mining foam. I should be good at this...my grandad was a miner.

[Jolly Roger]

Well that worked fine...a good solid carbon ridge with a neat and accurate edge. Not perfect, but should tidy up ok.