What is the equivalent glass skin for balsa over foam?

[Bosk]

Hi folks,

Here's a bit of background...

I've got an old Graupner Albatross which is a 2m electric that has 2m wings in three parts: 1m straight center section, .5m tips attached with dihedral at the joins.

Now it goes OK, but I got it second hand and it's bent, won't turn left very well, needs left rudder to stop the right hand turn tightening up the centre section of the wing is 1080g on it's own and the whole thing weighs a little over 2kg all up. So I was thinking of making new (lighter) wings and tail for it as it's also very tail heavy.

The thought of cutting ribs along with the cost is prohibitive, but I have made a couple of balsa sheeted white foam wings for my Ricochet in the past so I thought I'd give that a go. I'm starting to make a start on foam core cutting and thanks to another member of the forums, I am now the proud owner of a working fridge compressor. Given I have a vacuum pump now, it seems worthwhile to glass the wings instead of balsa sheeting them and having to cover those with film (as you can guess I'm looking for cheaper & faster & lighter)

Now the question ...

But what layup do you use?

The balsa (1.5mm or 1/16th) straight over the foam cores of the Ricochet without any spars seemed enough for both the flexing and torsional loads, even up to 3m in span on the Unlimited version, but I'm not sure of what to use on this wing.

Can I just use plain glass over the white foam core in the same way or does it need to have carbon, spars, Kevlar etc.

I'm looking for something that will build:

1. Quickly and easily (hence trying to avoid spars etc),
2. Cheaply (hence trying to avoid carbon and kevlar)
3. Light enough for it to thermal but strong enough to handle a little bit of wind on a gentle slope (just cruising and slermaling)

I'm limited to using white EPS at the moment, so is there a glass layup that would provide the sparlessness of a 1.5mm balsa skin and be lighter than what I've already got?

Any help would be appreciated.

Regards,

Bosk

[eissmann]

I've bagged a lot of wings and repaired a lot of bagged wings for myself and others.

In my opinion what you're describing will be a disaster waiting to happen. (unless you use about 2 layers of 3 oz glass, then there goes your lightness)

Everything in the structure of an aircraft is a compromise. If you can compromise on ease of building, weight, and cost to just a small degree, you can make it work.

First, eps foam sucks as a core for fiberglass. It's OK if you sheet with balsa or plywood, but it compresses too easily for fiberglass. It will pick up hangar rash easily and any little stress riser will result in compression failure.

Medium to high density extruded foam is much better.

If you don't mind your wing being dimpled up like a golf ball just because you picked it up with one hand, you can get around the structural problems, but the build becomes more difficult and slightly more costly.

It will have to have a spar. Since you're not talking about a lot of speed or winch load, 1/8 by 3/8 spruce or 1/8 by 3/4 balsa. Make sure the grain is straight. You can make a sanding tool to cut the spar groove or hot wire it.

Use 2 oz glass on a 45 degree bias for the skin, and put a 2 oz glass dart over the spar, (3" wide at center, 1" wide at end of main panel).

If you don't have mylars already, and can't borrow any, you might as well spring for 1/16" balsa skins to start with. That will be cheaper than buying the mylar.

You can bag the balsa skins on without mylars and it makes a strong unit that is a lot less prone to hangar rash. Polyurethane varnish to prep and you can paint it.

If it was me - extruded foam,carbon darts, 1.4oz glass.

[Bosk]

Thanks for the advice, I feared that this was the response that I would get, but hoped that I could be wrong. :o

...Medium to high density extruded foam is much better.
...
If it was me - extruded foam,carbon darts, 1.4oz glass.
Unfortunately, blue foam is very expensive over here and you need to buy a lot of it at once usually > $150 at a time. It means that the cores for a wing like this can cost as much as $60 for the foam alone. So apart from one set of blue foam cores I've been given, I'm stuck with EPS for the moment.

So, if I use a spar (say spruce like I would in the built up version) I could get by with the glass alone as long as I expect it to "dimple" when compressed?

But if you were using extruded foam, you'd be happy with just the carbon darts and one layer of 1.4oz glass straight over the core or would you use more than one layer of glass?

BTW how do you cut the cloth on the bias to cover a 1m span? Can you/Do you need to do it in more than one piece and overlap them at some point? If so how much overlap do you need and does that show up as a ridge on the finished product?

Bosk

[AndrewBurns]

Bosk, I'm in Sydney and I found a place that sold blue foam that let me rummage through their scrap bin. Full 2.5m x 0.6m x 0.05m sheet of extruded blue foam cost me $30 because it had some damage. If you call up melbourne suppliers they might let you do something similar.

[jirvin_4505]

Thanks for the advice, I feared that this was the response that I would get, but hoped that I could be wrong. :o


Unfortunately, blue foam is very expensive over here and you need to buy a lot of it at once usually > $150 at a time. ......

Bosk

Hi Bosk welcome to the world of composites....

If a quick simple low cost replacement wing is your goal than i think the balsa on foam wing is the go. Skip the expensive money coat and use 3/4oz glass, laminating film or book covering as a finish. If 'economic downturn' is the driver here then brown paper over foam with a hardwood spar will do the job;)


You are probably in the Oz state with the most composite suppliers, builders and resources.

Any chance of you linking up with the Handlaunch guys or Slope (jart) builders in Vic. I'm sure they could help you up the learning curve.

Explore the excellent build logs by Samotage in the slope section to see what is happening in victoria.

Up here (qld) we would build thermal models (winch launch) using high density EPS - they had imbedded spars with balsa sheer webs (very doable). Usual skin was close weave 100gm glass commonly 2 layers - very durable.

I'm sure Blue foam is available in Vic at a reasonable price - its 1/2 that price here in QLD and I believe we get it shipped in from Vic?

cheers Jeff

[Bosk]

Bosk, I'm in Sydney and I found a place that sold blue foam that let me rummage through their scrap bin. Full 2.5m x 0.6m x 0.05m sheet of extruded blue foam cost me $30 because it had some damage. If you call up melbourne suppliers they might let you do something similar.
I'll have to do that again, and see what happens. There is one company here who suggested that I trawl through their 'cut-offs" bin which means panels that are probably 1.2m by 100mm by ?? (ends off the 2.4mx1.2m full sheets) but they wouldn't give me a price and their full sheets were something like $180+ Not an outlay I really want to put out in the current GFC. I've got a friend who works in the cool-room manufacturing business so they use EPS and have heaps of offcuts for free which is currently a better price.

He gave me 6 500mmx50mmx1.2m sheets of SL to start with. Is there any advantage in going with the denser EPS? I know it will be heavier, but would that make for better stiffness?

[Bosk]

Hi Bosk welcome to the world of composites....

If a quick simple low cost replacement wing is your goal than i think the balsa on foam wing is the go. Skip the expensive money coat and use 3/4oz glass, laminating film or book covering as a finish. If 'economic downturn' is the driver here then brown paper over foam with a hardwood spar will do the job;)


You are probably in the Oz state with the most composite suppliers, builders and resources.

Any chance of you linking up with the Handlaunch guys or Slope (jart) builders in Vic. I'm sure they could help you up the learning curve.

Explore the excellent build logs by Samotage in the slope section to see what is happening in victoria.

Up here (qld) we would build thermal models (winch launch) using high density EPS - they had imbedded spars with balsa sheer webs (very doable). Usual skin was close weave 100gm glass commonly 2 layers - very durable.

I'm sure Blue foam is available in Vic at a reasonable price - its 1/2 that price here in QLD and I believe we get it shipped in from Vic?

cheers Jeff

I've actually wondered about using heavy card like we used for pasting pages for projects on at school ~300-500gsm and using that instead of balsa.

I'm not sure that 3/4oz glass is cheaper than iron on film though as its around $25/m down here. The heavier stuff is cheaper which is why I wondered if that would be sufficient. Interesting to hear that brown paper would be stiffer than fibreglass though!

[Bosk]

...
Up here (qld) we would build thermal models (winch launch) using high density EPS - they had imbedded spars with balsa sheer webs (very doable). Usual skin was close weave 100gm glass commonly 2 layers - very durable.
...
Hi Jeff, just re-read your post about using High density EPS. That's something I can get for free (or next to nothing I think) from my cool-room mate (I think). That sounds like it would be possible. You wouldn't expect it to be a problem with this size wing using the higher density EPS then? (BTW what grade were you using?)

Did those layups come out heavier than built up wings? My calculations have the 1m centre section with a 45cm chord (straight no taper) would use 0.9 to 1sqm of cloth for top and bottom and using 2x100gsm layers would only weigh 200gm plus the epoxy and about 150gm for the foam and spars (~350gm + epoxy) The current built up version is over 1000gms, the epoxy isn't likely to weigh 650gm so I should be well ahead on the weight comparison then.

If the HD foam is available then I guess that would be a good place to start. Do you think it would be OK for this machine if I put in the spars and possibly the shear web?

Just thinking though that 100gsm cloth is only 1/3oz! Even 230gsm cloth is only 3/4oz and eismann was talking about using 1.4oz (425gsm) over bluefoam or 2oz (610gsm) over EPS foam. Have I got my conversions wrong or is 100gsm cloth correct? Also such light cloth always seems to be way more expensive than the higher weight stuff so would it be OK to go with the single layer of the heavier cloth instead of two layers of the lighter more expensive cloth?

Also what type of weave do you use or doesn't it matter and how do you get it biased over the span when the width of the roll isn't long enough to accomodate the panel length on the bias?


Bosk

[jirvin_4505]

Hi Jeff, just re-read your post about using High density EPS. That's something I can get for free (or next to nothing I think) from my cool-room mate (I think). That sounds like it would be possible. You wouldn't expect it to be a problem with this size wing using the higher density EPS then? (BTW what grade were you using?)

IIRC 2.2lb small bead - however times have moved on and it will work but the equivalent weight blue foam is a better material.

Did those layups come out heavier than built up wings?
Will probably never build a built up wing as a comparison:D I don't have anything for comparison - will weigh the wings later. BTW I flew the wings for 10 years never thought Oh gee wish they were lighter - not such a believer in lighter is better as i can't seem to build lighter...:o
My calculations have the 1m centre section with a 45cm chord (straight no taper) would use 0.9 to 1sqm of cloth for top and bottom and using 2x100gsm layers would only weigh 200gm plus the epoxy and about 150gm for the foam and spars (~350gm + epoxy) The current built up version is over 1000gms, the epoxy isn't likely to weigh 650gm so I should be well ahead on the weight comparison then.

100gsm = 3oz squ yard..

If the HD foam is available then I guess that would be a good place to start. Do you think it would be OK for this machine if I put in the spars and possibly the shear web?

I'm not an engineer - you could probably replicate the spar in your current model into a foam wing. When in doubt I study Mark drela's designs on the Charles river site for inspiration and ball park figures..

100gsm - 3 oz plain weave tight weave - commonly available from most suppliers

Also what type of weave do you use or doesn't it matter and how do you get it biased over the span when the width of the roll isn't long enough to accomodate the panel length on the bias?

Bias is on the 45 degree cut so a 1m wide cloth gives you a longer cut on the diagonal (something to do with pythagoras:p) However a overlap is fine - doesn't really print through much.

cheers Jeff


Bosk

cheers Jeff

[jirvin_4505]

Hi folks,

Here's a bit of background...

I've got an old Graupner Albatross which is a 2m electric that has 2m wings in three parts: 1m straight center section, .5m tips attached with dihedral at the joins.

Now it goes OK, but I got it second hand and it's bent, won't turn left very well, needs left rudder to stop the right hand turn tightening up the centre section of the wing is 1080g on it's own and the whole thing weighs a little over 2kg all up. So I was thinking of making new (lighter) wings and tail for it as it's also very tail heavy.

..snip....

Bosk

Hey Bosk .... mostly anything built with care will be lighter than these wings:eek:

Cheapest/simplest wing i can think of is white foam eps covered with veneer.

If you are really hooked on light than as a reference i recently built a 2m wing out at 320gm (one piece) It was blue foam and 1.7kevlar plus carbon d box as per phil barnes video. This is probably too light/expensive for your application but it is a reference point.

Whats you budget and experience with composite work .. this may guide the suggestions?

Were you looking to get into composites (are you ready for the learning curve?)

cheers jeff

[Bosk]

Hey Bosk .... mostly anything built with care will be lighter than these wings:eek:

Cheapest/simplest wing i can think of is white foam eps covered with veneer.
...
Whats you budget and experience with composite work .. this may guide the suggestions?

Were you looking to get into composites (are you ready for the learning curve?)

cheers jeff
Jeff, i've been out of the modelling game for a while but now have the time to take it up again, however I no longer have the money that I once did, so I'm back to doing things cheaply. In the past I've made three sets of wings for my Southern Sailplane's Ricochet, but that was using the old latex contact cement and weights to hold down the skins method. I covered the Unlimited one with 3/4oz cloth and epoxy as a finish, but that really just made it heavy as I didn't have a vacuum system and it was just brushed/rolled on and left to settle then rubbed back.

The reason I want to use EPS is that the price is right (read free) at least for the moment. Now I would normally use balsa skins on EPS, but that puts the price up to around $30-40 in balsa to skin the wing plus then the cost of covering the wing as well.

Just a couple of weeks ago someone kindly gave me a fridge compressor which works well as a vac pump so I thought that if I could cover wings in one layer of glass instead of balsa and covering, I could be ahead on price, finish and maybe even weight. Given that I'd still need to use epoxy to bond the balsa skins and probably wouldn't use much more when glass skinning from what I've read. Epoxy seems to be around the $27 for 1.2l from FGI so it seemed it may have been cheaper, quicker because once out of the bag it'd be pre finished and ready to go and therefore easier.

So I'm kind of stuck as I can't really justify buying blue foam when I can get EPS for free. I'd still need to buy the epoxy in any case, so I'm hoping that the glass cloth is cheaper than balsa plus covering. I'm also hoping that it would be as strong but I think that's just not going to happen even with high density EPS. The problem now is that from what I'm gathering 100gsm cloth will run into the $30/m which means I'm looking at $60 per wing (2 layers) so I'm thinking that it's just not going to cut it as a cheaper alternative. the cheaper cloth which would make it competitive price wise is around the 800gsm and that's way too heavy but maybe I'll just have to compromise on that because I have a saying:

You can biuld it: Light, Strong or Cheap. Pick any two!

(And I have to pick cheap as one of my options at the moment.)

[jirvin_4505]

Hi Bosk I'm getting an idea of how cheap you need to be :)

By the time you get mylars, glass etc. you will be over budget!:eek:

Cheap.... Heaviest small bead EPS you can find - some tassie oak from Bunny's for a spar then....
Following links provided on you other threads... Pva and brown paper- give it a go (You will be under 1kg for a center panel) You won't waste much of Kevin's economic stimulus cheque building wings like this :)

Bunch of the pensioners up here build training 2m gliders using this system. They are able to take a high start launch.

Still hooked on vac bagging.... Use epoxy and bag the brown paper on:D

Cheers Jeff
ps I've done even cheaper .... EPS foam, spruce spar and packing tape finish. Just like the slope wings

[jirvin_4505]

I'm starting to doubt your composite supplier....

>100gsm cloth will run into the $30/m

ether that or I haven't bought cloth for a while? I think I paid $12/m last time.

At that price you could get close to 1.7oz kevlar at $50/m from Dick at Ironbark

cheers Jeff

[flyonline]

Not sure where you got those prices from.

I got my 600mm x 50mm x 2.4m blue foam for $66 pick up, though they know it as isoboard (I did ask for blue foam but??). 50mm foam is thick enough to do a L and R set of wings in the same blank (just flip over) for most wings unless you're going super thick/wide.

My invoice from ironbark composites shows 23gsm glass (960mm wide) is $5.90/m2 (or for me 3 linear M = $17), even the 200gsm CF Uni 24k (more expensive, the 12k is 1/2 the price from memory. K = the number of tows, more = stronger = more expensive) is $20/m2 (my 5LM = $30 @ 300mm width), the 162gsm glass is $7.40/m2 (1.25m wide roll). To put it into perspective, I got enough carbon, 162gsm glass and 3/4oz glass to make 2x1.25m wings (200mm root chord) + enough left over for a fuse and a few more other wings and bits and pieces for $100 delivered to my door.

Send an email to dick at ironbark (or call him) to check the prices, I'm guessing a couple of m2 of some 23gsm and 100gsm cloth would do the trick and still cost less than $30-40 (add $20 or so delivery). Even FGI had a 5m x 1m roll of 200gsm for $33 (I think) when I was there last in their offcut bin.

If you want to add a spar, golf shafts work excellently, though you do have to pick and choose to get two that match in size and the slots are easily cut with another template.

Steve

[Bosk]

Thanks for the replies folks, it seems that I've mis-calculated my conversions from oz to gsm. I got some quotes for 3/4oz cloth and was told by the supplier that it was 230gsm and cost $27/m + GST so I figured that 100gsm would have to be more expensive! Since my last post I discovered my mistake, so I asked FGI about 130gsm (4oz) and they said it was a little over $5 + GST which is much more reasonable.

I'll have to check out ironbark as those prices are much, much better and makes everything much better value.

Now that I'm confused as to what would be recommended could you please confirm that we're talking about a layup of:

1 x 100gsm-130gsm cloth
1 x 23gsm cloth

over EPS with a full vertical grain balsa shear spar?

Would that be for SL EPS, the high density EPS or only on bluefoam?
Is the 23gsm just for surface finish and would both layers need to be cut on the bias or only one of them?

[Bosk]

Another question, does using heavier cloth make much difference to strength or does it just mean that it soaks up and holds more resin ie just gets heavier? For instance would it be better to do a 23gsm layer over a 100 gsm layer or just one layer of say 130gsm, 154gsm or 185gsm?

If so would you get a better finish by using the 154gsm twill instead of a plain weave or HS (whatever that is)?

[flyonline]

See here (http://www.solarcomposites.com/fabricchoice.html) and here (http://www.favonius.com/soaring/materials/material.htm) for some fabric definitions.

Another question, does using heavier cloth make much difference to strength or does it just mean that it soaks up and holds more resin ie just gets heavier? For instance would it be better to do a 23gsm layer over a 100 gsm layer or just one layer of say 130gsm, 154gsm or 185gsm?
yes and yes. From memory (and someone can correct me here) but I think the weight of the resin is about 40-60% of the layup weight. More layers are generally betters than one THICK layer, but again its a case of finding the right balance i.e. 9x23gsm isn't better than 1x200gsm.

As for the spar, if you want to go with the vert grain balsa you'll need a spar cap of some sort (usually CF) for strength. Pre made CF spar caps are cheap to buy and much better than anything you could probably make for now. I think I saw some 1mm x 12mm x 1m for about $5 in dandenong. You probably only need the spar on the inner panel anyway.

I'm no expert but 3/4oz will give you a better finish on the wing than the thicker gear, but like everything its a compromise.
1) Thicker layup/less or no spar/stronger skin/heavier
2) thinner lighter layup/spar/thinner skin/lighter

My suggestion would be to search around here for similar planes to yours, check out the Aegea (http://charlesriverrc.org/articles/aegea2m/markdrela_aegea2m.htm) site (these get winched up so they should be strong enough for what you want - use glass instead of Kevlar) and make up some tail groups and smash 'em around a bit to get an idea on strength ;)

Steve

[Bosk]

... make up some tail groups and smash 'em around a bit to get an idea on strength ;)

Steve
I like the way you think Steve :)

Thanks for the info about the weaves, as to the spar, do you use just the one on the upper surface or still build the I beam with a spar on top and bottom of the shear web?

I'm itching to get that pump doing something! I've got it set up and working with an old vacuum advance and when I tested it by holding my thumb over the end of the air hose with tank you gave me (I soldered a 1/4" brass tube into the relieve valve that was in it to connect the hose) it holds vacuum for longer than I could be bothered holding the hose closed >3 mins. In a really basic bag (ziplock bag with hose just stuck in the corner and held closed it would hold vacuum for around 70 seconds then cycle on for <1 sec.

My next problem at the moment will be to improve the bag connector I've made as you can hear the air being sucked into the bag around it at the moment. Once I get that sorted I reckon it'll be good to go for bagging.

Laci

[jirvin_4505]

Some ideas for vac bag connectors..
http://www.rcgroups.com/forums/showthread.php?t=658528

[flyonline]

Having just recently made a full shear web spar with carbon caps, I'd suggest you give the balsa a miss and just rout out a spot for the carbon to sit in. See here (http://www.favonius.com/soaring/bagging/bagging.htm) for a run down on adding a carbon cap (though I bag it all in one, rather twice as he does and he uses tows rather than a pre made CF cap) and adding root ribs. Cutting the wing in half to add the shear web does give a risk of a mis-shaped wing when you glue it all back together again.

I know some guys have just used a corner cut off the bag, poked the hose in and used some silicon to seal it all up (I've used blu-tak before too).

Steve

[Bosk]

Yeah, I tried doing it with the barbed hose coupling with rubber washers sandwiched between steel washers and tightened with a nut, but the air gets in between the outside steel washer and the thread of the hose connector. I'm going to try sealing it with epoxy, or maybe find a brass washer that I can solder and seal that way.

Failing that I think the nylon bolt with the hole drilled through it may work.

[Bosk]

Steve do you put the CF cap on both top and bottom surface? Also do you do the "ply/balsa wing ribs to hold the joiner tube" thing? From memory my Ricochet just had the tubes glued into pre-cut tunnels in the core without any reinforcement (though it was balsa skinned).

Do you need to do this for an all flying tailplane as well (again Ricochet just had the tubes straight into the foam)?

[flyonline]

Yes, yes and yes, although I just do a smaller sub-rib at the end of the joiner like this (http://www.slopeflyer.com/artman/publish/twf-joiners_1of4.shtml) rather than the full rib he does. It will make it much stronger than just poking the tube into the foam as the foam can collapse under stress. For a FF stab, you could easily use a shaped balsa one instead of a foam one, that way all you have to do is cut a slot for the tube and fill with epoxy and shape (no real need for any ribs either).

Steve

[jirvin_4505]

.....

Failing that I think the nylon bolt with the hole drilled through it may work.

Piece of plastic tube stuck through the bag sealed with blue-tac works for me... Check out the above link:o

Jeff....always doing slow but rough:D

[Bosk]

... Pre made CF spar caps are cheap to buy and much better than anything you could probably make for now. I think I saw some 1mm x 12mm x 1m for about $5 in dandenong. You probably only need the spar on the inner panel anyway.
Steve
Steve, not being familiar with this new fangled CF :) , I'm surprised that a sparcap that is 1x12mm is strong enough and is that installed horizontally or vertically in the foam? My first thought was vertically and that should be more rigid for bending, but I'm not sure.

[Bosk]

For a FF stab, you could easily use a shaped balsa one instead of a foam one, that way all you have to do is cut a slot for the tube and fill with epoxy and shape (no real need for any ribs either).
Steve
Steve, by this do you mean a solid piece of balsa the full size of the stab sanded to profile then covered in glass, or a solid piece of balsa at the root the depth of the joiner tube glued to the end of the foam core?

One of the aims of the exercise was to cut down weight, so would a solid balsa sheet sanded to profile still be light? would it only need a really light glass layer, say 1x 23 gsm?

[Bosk]

I finally got a chance to try the glass skinning on a test tailplane. It was an interesting experience! I had some 200micron polythene which I tried to make a bag from but it seems to leak a lot, it has the pump running 25s with a 50s break. I don't have a vacuum gauge yet and that makes it difficult.

I used one layer of 86gsm plain weave over the SL Grade EPS core I cut. I was really surprised how little resin is needed to wet out the glass! I mixed 18g of it (15g resin & 3g hardener) and it seemed like that would have been enough for both tails. I used the poythene as the mylar substitute (because I was eager to get something done) and it may or may not have been thick enough.

It cured ok after about 10-12 hours given how cold it is. However it was rather dimpled when it came out (again no vac gauge, don't know what vacuum it was under) and as alluded to earlier it dimpled easily and creased at one point about 2/3 to the tip. I suspect that the dimpling was due to excess vacuum for the EPS. It is only about 5mm thick at the root so it's not very thick at all, but it was interesting.

The TE wasn't very stiff though so I'm not sure if it needed thicker glass and if that would make a difference, but the glass and resin added 13g to its weight. The core was about 1g and finished it came out at 14g. The original built up and covered one was 16g so it doesn't seem to be much of a saving, but it was a saving.

I'm trying to get hold of a vac gauge so that I don't go over the 8" for white foam and see if that makes a difference. I've also just got some heavier stuff now from Ironbark today so I will give that a go hopefully over the weekend and see how it turns out with strength and weight in comparison. BTW Dick is quite inexpensive when you get your weights right and compare apples with apples. Thanks for the tip to talk to him.

Thanks again folks for your help with this.

Bosk

[T.D.]

Bosk, will you be winch launching this glider?

Will the wing be one piece or three piece?


T.D.

[blewis01]

The TE wasn't very stiff though so I'm not sure if it needed thicker glass and if that would make a difference, but the glass and resin added 13g to its weight.
Bosk

I always add some extra resin to the TE and it solves the stiffness problem. I use a squeegee to place a bead of resin along the TE, along the line where the foam core ends. Extra resin will be squeezed out under vacuum, so I am fairly generous with the expoxy.

Bruce

[Bosk]

Bosk, will you be winch launching this glider?
Will the wing be one piece or three piece?
T.D.This will be for a eMotor glider and it's used mainly on the slope for slermalling, so for this one no winching. However I'm also hoping that I'll be able to take my learnings here and apply them to new wings for:

a. SR7 (with modified wing section)
b. Ricochet slope wings (I discovered that 20 years ago I put a crease in one wing when I pranged it.
c. Ricochet UL wings (replace the wings with balsa skin and heavy glass epoxy coating that are really heavy)
c. Ridge Rat, Sagitta 600.... and others that have need of new wings.

[Bosk]

Thanks Bruce, I'll give that a go. When I trimmed the TE it was about 0.5mm thick so I'll leave some more epoxy there.

Some things that i noticed when I had a closer look this morning 3 days after I took it out of the bag.

1. It seems much stronger/stiffer now and doesn't bend as easily even over the crease.
2. One of the skins slid off the root and out to the tip by 10mm or so leaving part of the root uncovered with glass but only with resin.
3. The TE excess and surface generally seems to have small pin pricks in them. it looks like the fibre and resin were squashed flat but not enough to cover the gap between the warp and weft. They have tiny SQUARE holes in them when it seems like the epoxy was squashed flat and the fibres were widened but not enough to bridge the gap between the fibres.

Is it usual for it it harden up some more over time?
Any tricks for stopping the skin from sliding out over the tip?
Have I not used enough resin?

Regards,

Bosk

[flyonline]

Some things that i noticed when I had a closer look this morning 3 days after I took it out of the bag.

1. It seems much stronger/stiffer now and doesn't bend as easily even over the crease.
2. One of the skins slid off the root and out to the tip by 10mm or so leaving part of the root uncovered with glass but only with resin.
3. The TE excess and surface generally seems to have small pin pricks in them. it looks like the fibre and resin were squashed flat but not enough to cover the gap between the warp and weft. They have tiny SQUARE holes in them when it seems like the epoxy was squashed flat and the fibres were widened but not enough to bridge the gap between the fibres.

Is it usual for it it harden up some more over time?
Any tricks for stopping the skin from sliding out over the tip?
Have I not used enough resin?

Regards,

Bosk
Yes, they usually harden up over time. I try and put them somewhere warm lying flat in the beds to cure for a week or so if possible (sometimes I can't wait that long :p ). You could make up a small hotbox to add some hardness if you wanted to go that far (search for info on hotboxes). You can also add a strip or two of CF tow along the TE to stiffen it up some. I can't remember if you said earlier, but did you lay the glass on a bias??

To stop the mylars moving around, I usually tape them together at the TE, lay the core down (all post wet out), fold over the top and tape together at the LE. Use electrical tape as it sticks to anything and will pull free without leaving any sticky residue or breaking as most tapes do on hardened epoxy. You can also tape mylars together at the roots and/or to your root rib.

I bought a small 4" lino print roller from an art shop which works great for really smooshing the layup down. I don't use it to add resin, just to smoosh it all together once generally wet out, and it also works well if you use it to roll some paper towel on the layup to remove excess resin - it's easier if less efficient if putting the layup/towel into the vac bag for a few minutes.

I've also found the small dimples when using the polythene as the mylar. Since switching to the proper stuff they've gone away completely. Mylar is very stiff in one direction, but floppy in the other so it will follow the curve of the wing but bridge the top of any small dints etc. Mylars might sound an expensive proposition, but don't forget that you can use them many times if you are making the same wings more than once, or you can recycle the bigger ones into smaller ones. They also handle MUCH better than the polythene and won't flop about with your layup falling off (don't ask how I know :rolleyes: ). I've also gone the cheapass route and cut them the same size so that I can use them for a L and R wing, just flip them over and clean well.

Steve

[Bosk]

I did cut the cloth on the bias (almost on the bias for the TE on one side...) and taped them with masking tape at the TE. Then I poured on some resin and spread it around with a spreader that seemed to wet it all through so it was translucent. I used some paper towelling to soak up some excess resin and rolled it with an Aquadhere tube as that was all I had to hand. When I looked it all seemed to be wet (ie translucent) but I could easily see the weave of the cloth. I did notice that the cloth stretched slightly lengthwise though.

I didn't tape the LE together, just the TE and I can see the depression where the TE tape was. I gather this really means that the polythene carrier (200micron) wasn't thick enough as it allowed the extra thickness of the tape to make a dint in the cloth.

I'll look into the lino print roller as I've been thinking about that. I did see some rollers that seemed to be made of washers separated slightly at FGI, I wonder if they would help smoosh the glass layers together if using more than one or if the lino roller would be enough.

i'll investigate the mylar route, or see if I can get some thick laminating film from the local snap printers...

[flyonline]

Sorry missed your questions on the last page.

You can either go with a simple I spar with a pre made CF ribbon, or a T spar with 2, obviously the T will be stronger but more hassle so as always trade-offs.....

If you've got any PU, I'd suggest you have a go at using it instead of the epoxy. Check out here (http://www.rcgroups.com/forums/showthread.php?t=1065446) for a thread on how to use PU in a vac bag instead of epoxy. I've done a tail with PU and 3/4oz glass with CF tow for torsional stiffness and it's quite strong and cosmetically good (smooth that is). I just shaped up some solid 6mm balsa in a symmetrical shape. If you're desperate to save weight, you could cut out some holes and add some covering to make it airtight. For comparison, my stab of 100mm x 80mm x 540mm is ~40g but it is WAY over strong for what you want (this has a target top end speed of 150mph+) - but lacks any tubes/rods/pins.

I think that you're probably over emphasizing the weight issue. Unless your wanting a HLG type weight/performance I suspect that a few extra gm's/oz's aren't really going to hurt your performance as much as a floppy tail/wing. If they turn out a bit heavy but strong then they can be consigned to slope duty and you can work on getting the next set lighter for the flat field.

BTW Dick is quite inexpensive when you get your weights right and compare apples with apples. Thanks for the tip to talk to him.
No worries, I hope you found him as helpful as I did.

Found a vac gauge (http://www.crazysales.com.au/index.php?productID=375) here for $26AU if that's in your price range. Would be worth watching Ebay vac gauges (http://shop.ebay.com.au/?_from=R40&_trksid=m38&_nkw=vacuum+gauge&_sacat=See-All-Categories) as well if you want to go really cheap.

Steve

[flyonline]

I'll look into the lino print roller as I've been thinking about that. I did see some rollers that seemed to be made of washers separated slightly at FGI, I wonder if they would help smoosh the glass layers together if using more than one or if the lino roller would be enough.

i'll investigate the mylar route, or see if I can get some thick laminating film from the local snap printers...
My experience with 2 different ones of this type is that they don't work well for our application. I kept picking up threads and pulling the fabric up, though I believe they do work well for seaming with moulds and/or shell halves of fuses. When doing my big 1.25m wings, I did notice that if you run the roller with epoxy along the fabric fibres it wets out best, and if you mush at 45 deg to the fibres it mooshes together best (or maybe the other way around). Either way, there seems to be a better way of running the roller.

If you have trouble with the fabric stretching, try a light mist of hairspray (not spray adhesive) this fixes the fibres in place so they can't move too much. Just make sure you get the scentless or your partner will start asking questions...... :o

If I'm down your way soon I'll give you some mylar to do a stab or fin and have a play if you like. Or if you send me SAE big enough I'll cut a couple of pieces and send 'em back.

Re: bias, see this post (http://www.rcgroups.com/forums/showpost.php?p=8516411&postcount=169) for best bias orientation.

Apologies if I've posted any links/tips multiple times.

Steve

[T.D.]

.....

[Bosk]

If I'm down your way soon I'll give you some mylar to do a stab or fin and have a play if you like. Or if you send me SAE big enough I'll cut a couple of pieces and send 'em back.That'd be great Steve, I'll PM you to arrange something.