Tuesday, 16 February 2010

Priming the fuselage

As soon as the fuselage is clean corrosion will begin so it is vital that the bare fuselage is painted as soon as possible to protect it from the atmosphere. I completed the cleaning one morning which left the rest of the day, about 7 hours, to prep for, and apply, one coat of primer on the fuselage. In total, the airframe will get three coats of paint:
  1. An acid etch primer (green)
  2. A 2 pack epoxy primer (white)
  3. A top coat of white two-pack

I'm using an HVLP (High Volume Low Pressure) spraying system to apply the paints which I'm told is easier for the beginner to get good results with. The system is self contained using a turbine unit to provide air for both the spay gun and a half face mask, essential when working with harmful paints. Details of the equipment can be found at http://www.flexiblesanders.co.uk/proddetail.php?prod=COMBO4STAGE&cat=21 although I did upgrade the gun to a gravity feed type at the time of purchase.

Prior to spraying the fuselage was mounted onto a rotating jig (courtesy of Rob Lees again) which makes the painting process much easier.

I started by spraying all the inside tubes first and gradually working outwards to reduce the chance that I would smudge areas that had already been painted but because of the complexity of a fuselage I did manage to paint myself into a corner on a couple of occasions. I ended up alternating from front to back to allow painted areas to go off before returning to those tricky areas that had been previously missed.

Several tips here - get used to your gun, how to change things like the amount of paint sprayed i.e. how wet it goes on as this does vary with the type of paint your using. Practice spraying left and right handed as you're sure to need to change hands at some point. Don't let your gun run dry before recharging with more paint as the paint may dry in the gun nozzle causing problems with delivery. Always clean your gun after use.

By the end of the day I had a green fuselage and in an ideal world I would apply the next coat (white epoxy) immediately but alas I had run out of time.

The following weekend was spent checking that everything had been sprayed, all those tabs, 'u' shaped channels, weld clusters etc and where necessary those areas were cleaned ready for retouching. Now because the epoxy hadn't gone on straight away I had two choices for the next stage.
  1. lightly scuff the surface to provide a key for the epoxy.
  2. spray a light flash coat of etch prime on then apply the epoxy.

I decided on the latter which would ensure a good key over the whole frame and anyway a second light coat wouldn't add much weight at the end of the day. Two hours later I was ready to apply the epoxy using the same techniques as for the etch prime. If I had any black epoxy, it would have been worth mixing a little in so that when it came to spraying the white top coat, I would be spraying onto an off-white colour making it easier to see what I was doing - problem was I didn't have any.

The epoxy took about 5 hours to apply with a lot of time spent again on all the tricky corners, tabs, clusters etc. The two photo's show the internal tubes painted white and the final complete airframe which I'm quite happy with. The top coat could just be applied to the cockpit area which will be visible after the fuselage is complete but I may decide to cover the whole frame with top coat as it will give added protection for very little increase in weight.

In the mean time I have a lot of other bits that are ready for grit blasting and painting up....