XJet

At last we've got a fine weekend here (it rained for the entire month of Febnuary which is supposed to be *summer* here in NZ).

In my eagerness to get in the air, I've cut a set of foam cores for a delta and inlayed a carbon-fiber spar.

What I want to know is -- what's the quickest, cheapest, easiest way to finish these cores?

I was thinking of self-adhesive plastic film -- like the stuff you line cupboards with -- but it doesn't seem sticky enough.

Balsa is too expensive and requires additional finishing so I was thinking of just using tissue applied with some watered-down PVA glue. That should create a skin that is reasonably strong under tension and so will stiffen the cores enough to make them airworthy.

Have others tried this technique -- or is there a better way?

I'll put my tired old Black Widow on the nose to start with but if that won't haul it around I'll stick the Norvel 061 on and see how that goes.

Got to get into the air -- got to get into the air :-)

combatpigg

My Feedback: (3)

HI XJET! I have used BLACK BARON film and a real low temp directly on foam. Another way to go that is very light and cheap is to use craft store colored cellophane and 3M77 adhesive, again with a low temp.I don't think there is a lighter method, but the seams need to be sealed with polyurethane for a lasting job.The paper and glue techniques are too heavy for 1/2A IMHO. The best way to go might be this stuff called SOLITE, but I haven't tried it yet.

ZAGNUT

My Feedback: (1)

never tried tissue and PVA but can comment on a similar technique. i've been using brown wrapping paper or newspaper (lighter) and thinned elmer's wood glue over foam for years on most of my wings. brush the thinned glue on to the foam and then lay the wet paper in place and use a playing card as a squeegee. the wet paper will shrink back to size and make a very tight skin that adds much more stiffness than that self sticking shelf paper. i normally don't use any kind of spar or leading edge. you also have to do both sides at the same time to avoid nasty warps.

hope this helps

dave

ajcoholic

My Feedback: (10)

most modern wood glues are PVA based. White or yellow, doesnt matter.

I have also tried the brown kraft paper/wrapping paper with 50% thinned out glue, works well. It should also work with a lighter weight paper such as tissue but it will be harder to stretch out the wrinkleswithout tearing.

Give it a go on some scrap foam!

AJC

Jeff Leavitt

XJet,

Hey! how about silkspan? Silkspan is light, strong, and pretty inexpensive. On the subject of glue, I have used one called "Weldbond" with really good results. I also know that we have a master of this method right here in 1/2a wonderland. Larry Driskill uses Silkspan over foam in strategic locations on his World famous 1/2a Combat LiteHawk kit. This is very cool. Maybe we could impose on Larry to give us some "Dual" on his tequnique.... EARTH TO LARRY.... EARTH TO LARRY...... Got yer ears on good buddy? Rgds, Jeff

Larry Driskill

The LiteHawk uses silkpan attached with 50/50 white glue (Elmer's or other common variety) and water on the swoopy tips to keep them stiff. It uses .5 oz fiberglass cloth attached with the 50/50 around the fuse boom and motor mount to help keep the foam panels and other bits together. Then the whole wing is covered with 1.3 mil laminating film to make everything fuel proof, smoother, and add a bit of stiffness and strength.

Here is a tip ready for the 50/50 treatment.

Larry Driskill

OK, trying again... here is the tip.

Larry Driskill

The fiberglass around the nose covers roughly the same area as the painted triangle by the engine mount. A similiar triangle of fiberglass cloth is at the rear over the fuse boom. Both areas are top and bottom.

I brush the 50/50 over the area to be glassed or spanned. Then the fibreglass cloth (.5 oz)( cut it with a single edge razor blade, a metal straight edge and a board) is applied dry and more glue is brushed over the glass. I mist the silkspan with water before laying it over the glue and then again brush glue over the span.

'Usually takes overnight for the glue to dry. After it has been on 30 minutes or so I go back and brush out any big dastardly runs that have showed up.

After it is all dry, a touch-up with 220 grit smooths things nice enough for a Combat plane.

The laminating film is very inexpensive. I buy it on 200 and 500 foot rolls. I doubt a 36 inch LiteHawk cost more than 50 cents to cover. Maybe not that much.

Sometimes I mix a very thin white glue / water solution, maybe about the same thickness as 2% milk, and brush the entire wing before adding the laminating film. When sanded this makes for a little nicer surface than bare foam and helps the low temp film covering stick better.

Some, every few..., of these techniques were my ideas. Most of them have been used by CL Combat foam flyers for years.

Andrew

I've been doing a little experimenting with off the shelf products on foam. I've never been very satisfied covering foam with film, probably due more to my ineptness than the product, but I do not get a very good finish.

I have had some success using DAP Ultralight spackling -- mix it with water to a slurry and paint it directly on a foam wing using a foam brush. It tends to fill in the voids on extruded wings and any deformaties on cut cores -- sand lightly.

I have also used water based polyurethane to stick down .5 oz cloth -- you have to apply sparingly to keep the weight down, but it significantly stiffens the core -- and the water based is not yellow and is foam safe. Careful sanding with fine paper will yield a fairly smooth surface without sheeting -- use lightweight spackle for filler if you want. For small models, the weight penalty may be too much, but for the larger planes, it is an alternative to the films and inexpensive.

Here is a source that I have been using for laminating film -- some companies will only sell rolls in pairs for laminating machines -- but you can buy one roll with free shipping. It is 24.99 for a 25" x 500' roll. The adhesive side is frosted, but becomes clear with heat.

http://www.schooloutfitters.com/cata...ucts_id/PRO130

the "other" Andrew

BMatthews

Some of the electric parkflyer guys have recently been using 1/2 oz glass cloth with water based polyurethane (Flecto Diamond Kote for example) or Minwax Polycrylic. I found the Polycrylic is NOT fuel proof at all while the Diamond Kote is quite durable as long as exposure to high nitro raw fuel is limited.

I think this would also work well with Silkspan or similar light pourous products. You won't get the same skin hardness as if epoxy was used but it would be much better than open foam and lighter than some other options. Either way skinning the foam will provide a good stressed skin effect. Art store tissues may also be a good source of material.... May I suggest a nice pink and lavender floral print? (oooo... I'm gonna get it for that one... )

A few years back I did some foam control line combat models using newspaper and thinned white glue. These days I'd use the Poly Urethane for the same effect and less weight. In my case I used multiple layers of staggered sizes under the final top layer to form paper mache spars and engine mount reinforcements rather than other methods. This worked GREAT. The 15 powered models survived many crashes and only secumbed to the dreaded mid air. I tested the remains by banging the engine mount on a concrete floor. Several one foot to three foot simple drops failed to even loosen the engine mounts. Forced hammer like impacts of up to 2 feet banged HARD into the floor did no worse. It took a full powered overhand swing to finally loosed but not destroy the engine mounts. A few more full powered overhands finally popped the mount loose.

I've been quite impressed with foam and paper ever since.

Japanman

Has anyone tryed a verylightweight silk and thinned p.v.a/polyurethane? I used some for re-inforcing some wing areas on my Dehav. Vampire, and it seemed REALLY strong.
I am thinking of covering my next 'scaleish' plane this way- i was a bit disapointed with paper ang p.v.a as it is very stiff and `crunchy` so minor contacts with debris on landings soon damaged the leading edge.
Silk on the other hand seems much tougher (and stronger!)... seems good especially if i can find some really thin stuff.
How about (coloured?) packing tape? cheap, fast and oh so durable!

J.M

combatpigg

My Feedback: (3)

HI JM! I made some of the same inquiries about covering technique when it came time to cover 10 planes I built for AMA RC combat. I didn't want to make the same mistake times 10. There are some pretty detailed threads in the combat forum about using silk, or rip stop nylon and glue. The more I read about it the more I was convinced that it wasn't a very exact science to get good results. I ended up buying some rolls of 2" wide clear packing tape, and that worked very well, and was a very cheap way to go. There was even a link to getting the tape in different colors.

Japanman

Man, When a friend and i discovered packing tape covering, was it a revelation!!
The coloured stuff looks good enough too me, and it is light and strong. My first norvel .061 plane was a tapey, four hs80`s a 4cell 270mah nicad pack and a windser6/3.. unlimited vertical! And it was fast to make.
Its just such good stuff.
p.s i found some here in japan!! Very cool stuff with the colour in the plastic film(I think) and the adhesive is white, so should give a good, consistant red rather that the pink that can sometimes result. Dunno how it is for fuel/oilproofness yet though!

J.M

Larry Driskill

There is a construction article where tape is used as the covering on an RC Combat wing at http://www.texascombat.com/

From the list on the left choose Workshop, then build an SSC Smack Wing.

The taping stars on the third construction page.

XJet

Well I went ahead and used box-tissue (didn't have any modelspan) and PVA on the cores and they came up quite a bit stiffer than they were before.

Of course it looks butt-ugly because it's impossible to get the wrinkles out of box-tissue -- it goes really weak and falls apart if you try and shift it once it's wet.

However, this has bought about a revelation in aircraft design -- I figure that if I make this little plane ugly enough, the ground will repel it and thus it's bound to fly: :-)

If I get time I'll post pictures tomorrow -- avert your eyes! :-)