Topic: preparing obdechi wings for glassing?

i've seen a few things about glassing but still havent done it, I've got a funfighter wing thats dangerously close to me having no more excuses and just do it.

however being obdechi the wings a little undulating and very grainy.

do you glass straight over, use lightweight filler, P-38, sanding sealer to stop the epoxy soaking in?


if i get this right, it's onto my Zipper which is a ply skinned foam wing, and i want it nice 

You will probably get many answers, we all have our own ways. I either put the cloth straight onto the obechi, having lightly sanded to get surface as smooth as poss, or , after that first sand, apply a thinned coat of resin and then sand again before using the cloth.
Good Luck

Stuart
 

i do have lightweight filler, P-38, sanding sealer ( all be it not a model specific one ) and Poly C

resin is Z-poxy.

I'm also a bit unsure of the first appliance of cloth.
do you ally it to a dry wing and then pour on the epoxy and work in.
or put a thin layer on the wing and then lay the cloth so it sticks then a bit more on top.
is there also rough guide to how much you need for a certain area?
don't want to mix up way too much, or too little.

I just use a lightweight filler over the leading/trailing edge joins and any cracks or open grain  in the veneer. Lightly sand and apply the cloth to the dry wing. I then mix a guesstimated amount of resin, prefering too little to too much. I use Z poxy which takes a while to go off so  it's no hassle to mix a little more. Pour a small amount into the centre and work it out for and aft with an old credit card so the centre of the wing is held firm. Then I work out from the centre to the root and tips to form a cross. Then fill in the gaps all the time working out to the edges of the wing. I do the under side first, when I do the top I allow the cloth to wraparound the edges.

Phil.

Have a read here..................

http://www.rcscalebuilder.com/Tutorials/glassing/default.htm

..............I've modified the process slightly since this was written for RCSB, but the basics are still there. The main change is in the rub down procedure.

1) You don't need a 'fill' anything, other than gaps, dings & dents, wood grain just needs sanding.

2) Don't 'sanding seal' the veneer............it could soak through, and the cellulose in it will dissolve the foam core.

3) Don't apply a brushed coat of resin to the wing, let it cure, then rub it down before cloth, this just adds weight.............no need, just go straight on with the cloth.

4) Follow the basic process of application as documented in my tutorial above...........IT WORKS.

5) If you can get hold of a 'Stopper Rubber' to spread the resin out, rather than an old credit card, they do do a better job. They can be obtained from specialist auto re-finishers.......(they are basically a 1/4" thick, 3" x 2" section of black rubber)

6) Mix around 20/30gms of resin at a time, maximum....this should quite easily do one complete side of a funfigher wing.

7) When mixed, pour the resin out into a shallow dish......leaving it in a mixing pot will allow heat to build up as it starts to cure, casing it to cure faster in the pot.....a shallow dish prevents excessive heat build up, giving longer pot life.

8 ) Don't try and wrap cloth (even light weight stuff) round tight edges etc.....even a LE ca be tricky. Work it 1/2 way (or just over) round a LE and leave it there. Never try and go round a TE....just let it hang over, and the excess resin will soak into the wood edge, hardening it nicely.

Any more Q's.......just yell.

Have fun.

Phil

nice one thanks.
the obdechi just worried me thats all because the grains quite deep, rubbing it out may mean going almost back to foam lol
i may sight along it and fill any of the larger troughs.

the idea of a first coat was to give a wet layer for the cloth to stick to, but i can see that would cause all sorts of wrinkle problems.
i do remember trying to do a bit myself when a mate glassed a wing for me, had a lot of trouble getting it to stick right round so leaving it sticking out and rubbing back later seemed to work well.
now just gotta decide wether to glass the strip ailerons or tissue and dope them like last time.
could just seal and then poly-c them.

i'll be giving your write up a few read throughs before screwing up doing my wing.


as a side note my sealer is household stuff with shellac ( spelling? ) as apposed to celly, tho my foam roller didn't like it much, got a bit sticky.
worked a treat on a glider i did.

Hi Cactus .you said you are using Z-poxy ? it is  the skinning or finishing resin you are using and not the adhesive epoxy .
Before you cut your glass cloth lay it out flat and spray alight coat of cheap hair laquer over it . This bonds the strands of glass and stops it loosing its neat look while you apply the resin.It also stops it fraying and makes it easier to cut . When you have spread the resin you may see some wet patches .This indicates too much resin ,which is heavy.To remove this ,lay some kitchen tissue onto the wing and this will soak up all the extra, unwanted resin and should leave the glass cloth with just the right ammount of resin to fix it to the veneer.
Hope it helps.Good luck
Phil

yep, tis finishing resin.
like the hair spray tip
you do mean before putting it over the wing and cutting to shape dont you?

started on the wing last night.
did a bottom panel first and right or wrong thought I'd cut the overlap in the middle of the wing in a diamond so it's a tapering finish on the glass rather than a straight edge and weak point.

followed Phills instructions tho mixed up too little leaving me with a nicely stuck middle line up the span, none at the front and an almost stuck rear.
next mix up did the rear and the last did the front even tho i mixed way too much and ended scraping lots off and putting it back in the pot.
fun and games getting the glass to stick even half way round the LE but i think i got there. false TE was even harder.
dont think the 3 lots helped as when i put the next lot on i didn't put it over the stuff there already but the dry cloth parts and had trouble wetting out that area, had it gone on the edge of the already wet area i could have worked it across.

didn't use hair spray because i wasn't sure about it and did end up pulling the cloth as i scraped too hard but it went back fine.
gonna go have a look at it in a mo.
i did 2 mixes of 3g and one of about 4, and used half.
think 8g should be fine next panel.


the Z-poxy bottles say to spread the expoy on the surface before the glass so it sticks down.
i followed phil and went glass the epoxy, tho putting it on first would certainly help go round the corners as there would be something there to stick too.


handy hint, if using a credit card remove the clear film either side, makes it more flexible.

So finally converted you to the art of glassing then eh?

When it comes to LE & TE, don't bother trying to glass the TE, just leave the cloth hangover then rub it back and brush some resin along the actual TE. For the LE, you can sometimes get it to glass right around by  overlapping it say 3/4 of an inch around the other side, or just leave it hang over then run back and do the overside.

A few extra tips before you start rubbing back, the most likely areas to be rubbed-thru are the LE, TE and tip so add a little extra resin in these areas.

Chris

I did it first on my P38 wing........ completely converted.

I didn't have any problems wrapping round the leading edge or wingtips though - that was using Z-poxy and 3/4oz cloth. Didn't try the trailing edge - I just left it hanging over. A few passes with a sanding block after curing and the excess comes cleanly off in one go. The trailing edge is pretty tough too (I whacked it off a door frameby accident  :-[)



Once getting past the mental block and getting a knack for spreading the resin round I think it's easiest finishing method I've ever tried.

I hate solarfilm with a passion - never got the hang of it, and think it looks horrendous even when I did it well. Dope and tissue gave me reasonable results but it's fiddly and not too tough. I also found that dope dissolves quite a few light weight model fillers 

Problem with applying resin to the wing before the cloth is that when you lay the cloth onto a 'wet' wing, if you get a wrinkle etc.....wet cloth is a PIG to level out..................apply dry cloth, then scrape resin through it will keep the cloth flat on the surface, and also uses much less resin...............

Phil

t'other side of the bottom half tonight.
i guess some people will do the whole underside of a wing as small as a funfighters in one bit, but even with a dry wing half to hold on to i still found doing the leading edge and tip a bit hard as i had to turn and twist the wing about.

wouldn't say i'm converted yet, but i'm less worried about the Zipper i want to do next and have perfect.

just a tad over 6g works out perfect for a wing pannel.
ended up using the last streaks in the bottom of the mixing pot to brush the LE over the edge.
very happy with this side.

ailerons have been done with poly-c and glass as it's quick and easy on these small bits.