Repairing a Glass Fibre Fuselage Soarer

Glider Guider · 17-12-2004

At the Nats this year I bought a Pat Teakle PIK 20 4m soarer complete with airbrakes and five servos for the princely sum of £30 from the Sunday ‘table top’ sale. Just the airbrakes and servos would fetch more than that on Ebay so there must be a catch somewhere I hear you cry especially as a similar one has just fetched £240 on Ebay. There is a catch, unfortunately it has had a heavy ‘one point landing’ which had detached the tail and caused cracking below the cockpit as well as in one wing and the tailplane, but as I paid less than nothing for it I’m not complaining.

I have just reattached the tail and thought it might be of interest to someone and hopefully generate some discussion so here goes.

As you can see below the tail was well broken off and it wasn’t a nice clean break.

Glider Guider · 17-12-2004

I decided to repair it as described at http://www.windandwavemodels.com/Repair.html by fabricating a glass fibre splint that is inserted into the two halves of the fuselage. Making the splint 6” long was convenient as I had some 6” wide wing joining glass and this gave 2” into undamaged fuselage each side of the damaged area which I thought would be sufficient to give a strong repair.

The first job was to make a plug to wrap the splint around as using the fuselage itself was not practical due to the extent of the damage. This was made from four 8” lengths of 1” square balsa glued together which was then planed down to the outside diameter of the fuselage as measured at the forward extent of the splint. By using the outside diameter there would be an overlap of the splint which would press against the fuselage both holding the splint in place and giving a better joint. The plug was then tapered over 6” of its length again to the outside diameter of the rear fuselage leaving 2” to be held in the vice as illustrated below.

Glider Guider · 17-12-2004

The splint was made from three layers of glass and epoxy resin sandwiched between acetate sheets. This sandwich (including the acetate sheets) was then compressed with a wallpaper roller to expel any trapped air and then wrapped around the plug and held in place with sticky tape. After 24 hour to allow the resin to fully cure the splint was cut from the plug by using a razor saw along its length.

I wouldn’t recommend using polyester resin, although it is cheaper and it goes off faster (20 minutes against 20 hours) the result is more brittle than epoxy resin and you also want plenty of time to get things right before it goes off.

Finally remove the acetate sheets and give the splint a rub with glass or emery paper to roughen the beautifully smooth glass like finish of the splint. Although it looks nice it is not a good surface for the epoxy to adhere to when the splint is fitted into the fuselage.

Glider Guider · 17-12-2004

The tail is quite heavy so there was no chance of just inserting the splint, binding it up and expecting the tail to be in the right position when the epoxy had cured so I built up a jig on a fuselage building board which is conveniently inscribed with squares which assist alignment. This held the fuselage still while I adjusted the tail position by using wooden wedges. Once alignment was correct the position of the wedges was marked.

Glider Guider · 17-12-2004

The splint and the inside of the fuselage were now given a liberal coating of epoxy resin and the repair was made; all being held firm by the jig. At this point I decided to bind the repair in acetate sheet and I also made a simple gauge to check the fin was at right angles to the wing-joining rod with the aid of the Mk 1 eyeball.

Glider Guider · 17-12-2004

I was concerned that the epoxy resin was very thin compared to resins I’ve used in the past and quite a lot of resin was dripping from the repair (one of the reasons I bound it) and running inside the fuselage; but nothing to be done until it had fully cured when the fuselage could be removed from the jig and the resulting strength of the repair judged.

I allowed a full 48 hours for it to cure and removed the fuselage from the jig. Although the strength of the joint seemed satisfactory I decided to reinforce it with carbon fibre tows. The joint was filled with two part filler, sanded down and a number of grooves were ground through the gelcoat until you could see the glass fibre. The tows were glued in place with cyano (superglue).

Glider Guider · 17-12-2004

This really stiffed up the joint and a final application of filler and a rub with 240 ‘wet and dry’ used wet gave the result shown below which is almost ready for spraying.

Glider Guider · 17-12-2004

I couldn't finish without a few health warnings about procedures used in this repair.

When sanding or sawing glass fibre always wear a respirator.

For a while now I have had what appears to be quite bad hayfever occasionally but this didn’t seem to relate to the current pollen levels and I wondered if it was caused by cyano glue fumes. The afternoon after gluing the carbon tows the question was answered when my nose blocked up totally and started pouring also my eyes felt sore and now 48 hours later I am still suffering but things are improving slowly. On the bottle it has an irritant warning and says not to breath the fumes but I’ve used cyano for years with no problems and it’s only recently that I’ve become allergic to it.

I’m now on the look out for a respirator that guards against fumes, Screwfix have one at £2.50 or so but the P&P on one item makes it more like £7.50, and I will wear a set of goggles as well. Other people who have had this problem have apparently used a fan to blow the fumes away before they reach the face with good effect and also the low odour cyano causes less problems - but after this bout I’m taking no chances in future, it will be respirator, goggles and a fan.

Has anyone else had this problem, if so how have you got over it?

adzam · 17-12-2004

**wonwinglo** · 17-12-2004

Very informative Dave,there is a lot of good user information contained in these postings,the warnings about these cyno fumes are very real as I have heard many people say that sometimes after years of use the user can suffer,after suffering myself from a bad skin problem on my hands these past few years now I take much greater care with these products,in this case tests showed that epoxy resin was one of the irritants but after years of usung glo-fuel,dopes and various adhesives these cannot be ruled out,herbal treatment has sorted out the skin but it is a long expensive process.
Without fear mongering it is a well known fact that the constituents of glo-fuel can cause senile dementia,so please take care and use a good barrier cream and wash your hands soon as possible,do not under estimate the dangers of some of the products we use in our model making,build and fly safely.