This was one of those evenings that you skirt around for ages and in the end think … well “No one else is going to do it for you” !
So I took the big 1.8m roll of Oratex out of its protective covering and unrolled it over the prepared underside of the Top Port wing. Trimmed to length and let it hang out over the sides. You then need to set an alignment level on the leading edge .. following PHS expert advice 🙂
You need to pre glue both the wing and the material and then leave for 24 hours to go off. Use the alignment notes below to lightly mark the underside of the material so you know wher to glue up to. NOTE A biro WILL show through for ever more ! so light pencil is best
Also – try not to over glue as this will inevitably show at the overlaps.
As noted below – the leading edge p,y sheeting and trailing edge give a good sized surface to prepare BUT it’s well worth making sure you don’t leave bubbles of glue to dry .. These don’t flatten easily when ironing and, on the slightly bigger surface areas like the leading edge can show through as air bubbles … A pain to work out after the event ..
Once your 24 hours drying is up re present the covering to the wing ….use masking tape if you don’t have spare hands as I didn’t … Spare hands are MUCH better .. Cos they respond to comments like .. Can you pull that at 45 degrees !
The lower covering wraps just over the midpoint of the ply covered leading edge. As the full leading edge ply has been glued it provides a lot of surface area grab. The leading edge is then ironed into position using masking tape securing points across the full leading edge to make sure the material doesn’t slip during fixing. It’s also good practice to clamp the trailing edge where you can to get the whole covering as flat as possible before fixing the leading edge.
Once the initial line is set and ironed and cooled you can bring the heat gun into play (130 degrees not 150 as its wood which doesn’t conduct the heat away to any degree). This is where the funny little Oratex pad comes massively into play. As you heat the material and the glue starts to react, it also heats up the glue surface on the ply leading edge underneath. The Oratex felt mat lets you work relatively small areas to ensure you are bubble free and get a really solid bond as you work it back to the trailing edge of the underside leading edge.
Leave the whole lot to cool at the leading edge and trailing edge joints .. If you start to get excited and try to shrink it in the same evening it can pull away … Shrink rate of 20% makes it pretty tough
The next evening .. You can start the shrinking exercise .. And boy this is where you just fall in love with this material … Such a joy as all those saggy bits and wrinkles fall away and leave a fantastic sheen and tight finish.
Again I left it to ‘settle’ so that I could do a little more heat gun before masking up again ready for the top layer of Oratex .. Mask so that you get a good overlay AND the finished edge is well in the ‘downstream’ of the planned airflow.
NOTE – the finish you leave on your first (underside) layer shows right through the top layer .. So .. Put a wobbly first line and you will be looking at it forever ! even through the pinked 4″ doubler tape !
Bring the top sheet over the lower sheet and use masking tape again if your ‘talking hands’ aren’t available …
This means you effectively butt the top layer against the nice straight edge of the lower layer and then cover with a 4″ reenforcing strip.
One admission here ! – I had felt that the leading edge was very smooth BUT … any small pimple of glue of polyuerthane will show through the top surface so well worth a very light pre sand to ensure that is smooth as the proverbial ….