Refinishing gelcoat

It struck me the other day that the materials used to cover R/C models these days could be used to 'refinish' ships on which the gelcoat had deteriorated. We are already 'happy' to stick .5m wide pieces of orange tape to the surfaces of gliders and do so with impunity.

Solarfilm ( a trade name ) can be obtained in 10m long rolls up to .7m wide. I'm fairly certain that a roll would do the upper surface of a 15m ships wing. If the wing was lightly sanded first to remove any raised edges of the cracked gelcoat and to restore the profile, the material could be laminated to the wing leaving an incredibly slick finish. These materials are surprisingly srong and an entire roll weighs very little.

Even if the job was only good for a year or two it would be economically viable. A refinish on a 15m ship these days runs from £5000 to £10000 depending on who, where and how its done. I'm sure a few hours work, perhaps 10 or 20 at the most would result in a job that would fool the best of us! The materials for an upper surface recover would cost less than £100.

Continuing in the same vein, the BGA's recent investigations into collision avoidance colour markings would appear to support the idea that the so called flourescent tape applications that gained a lot of popularity over the past few years are in fact the worst at making a visibility difference. It would appear that a reflective finish may be the best at achieving this. Solarfilm makes a chrome finish covering material that is almost a flexible mirror, the stuff is very reflective. Adding a band of this to a wing and the fuselage or the fin could be very effective.

Ian, I think you are on to something.

I read several years ago about an aircraft finishing system that involved an thin film that was heat shrunk onto metal skins covering joints, rivets and all.

Bill Daniels

Solarfilm has been around for years so the available info on its propeties should be somewere on the net. I can vouch for its strength, I've seen balsa models after a crash that look like a bag of bits, the film virtualy intact.

Peter S

'I read several years ago about an aircraft finishing system that involved an thin film that was heat shrunk onto metal skins covering joints, rivets and all.'

To take Bill's point further, if the film could not be shape changed somehow then there is no way you could get span length roll of film to fit tightly to the curves of a glider wing along its full length.

John Galloway

John,

The application of heat, a little more than the average hairdryer delivers, both shrinks the film and activates a quite powerfull adhesive that is on the underside of the film. The adhesive is strong enough to remove the surface of underlying balsa structures when trying to remove the film to repair an RC model..

I'll have a word with Jim Hammerton and see if he'll let us try it out on the Ventus ( which has some surface cracking )

Ian

I like the idea of a reflective band.. wing flash as it were instead of the bright orange.. (not that we use that in the US).. information from the major manufactures would be needed on effects of wings covered with such.. many only allow a certain percentage of color other than white because of the detrimental effects of colors absorbing heat at a different rate and the effect on it's wing strength,

BT

I think that reflective is likely to absorb less energy than even white, but yes you are right someone would need to test it!

I've had some Monokote (Solarfilm equivalent) and a wing tip sitting on my bench for several months now, planning to experiment with covering up small dents in wings, bridging the depression caused by a shrinking spar, and just adding some decoration. Ian's posting motivated me to actually try sticking a few pieces on to the wing tip (left over from fitting winglets).

It's going to take some practice to get it on smoothly, I can see. Part of the problem is the temperature required to activate the adhesive (instructions say to set the iron at 275 F), which is well above the epoxy limit. Another problem is avoiding air bubbles when covering large areas. I'm sure these can be dealt with.

The biggest problem I can see is ensuring that the covering doesn't peel up in flight, perhaps rendering an aileron or elevator unusable. Determining the effects of long term exposure (longer than a year, say) will be important, as gliders typically spend far more time outdoors than model airplanes, so their experience might not be a good guide. What will sunlight, desert temperatures and wave flight chills do to the material when applied over fiberglass or carbon structures?

Even if you convince yourself it's safe and sane, regulatory and insurance issues need to be dealt with. In the US, a covering on the flying surfaces might need an FAA approval, and I'd like to be there when the first pilot goes to the insurance company and explains how he is going to cover his glider with a plastic sheet, wants to know how that might affect his coverage.

So, maybe someone with some wrecked wing parts lying around can try the idea, and set the panels outside for exposure testing. Flight testing with a full chord, 10 inch wide strip of white material near the wing root probably wouldn't be hazardous, even if the strip peeled. Ditto for pieces on the turtle deck. Or maybe on a spoiler cap - if it peels up and acts like a small spoiler, it's in the right

I think that may depend on how much the stuff will shrink.

Is this material anything like the stuff they use for those advertising wraps on busses?

The material under discussion, with brand names like Monokote and Solarfilm, can be formed around compound curves on a model airplane, which are far sharper than those on a full size glider. It's very thin, about 0.002 inches. See www.monokote.com

I din't know a lot about refinishing sailplane wings, but I do refinish many vacuum forming tools. When I encounter checking, gelcoat cracks or surface irregularitys that produce markoff, I use catalized surfacing primers for cars.

We shoot it onto the surface and wipe it into the cracks/fissures with our hands using gloves a couple coats does it. It sands well and gets you to 600 grit smooth really quickly.

Why aren't we doing this. It seems that you could DA sand the wings in a few hours, shoot 200 bucks worth of primer, sand the primer in a few hours and be ready for topcoat.

Topcoats are about 150 a gallon ready to shoot. Colorsand after paint andf you are done..........

So 600 bucks for materials and 10 hours each wing. 10 hours on the fuse/vert 4 hrs rudder, 4 hrs stab. 4 hrs each flap, 2 hrs each alerion 8 hrs diasaaembly 8 hrs reassembly.

66 hrs labor + 600 material....... 3100 for a repaint with auto paint?? 337 field approval, logbook entry and move on.

Just thinking out loud.....