Cleaning the fuselage

Christmas came and went, all the necessary welding work had been completed on the fuselage and so it was time to strip the fuselage frame of all it's paint. I had thought long and hard about how this should be done and had settled on grit blasting rather than paint stripping mainly because paint strippers are messy and toxic (in most cases). I had also decided to do the grit blasting myself rather than transport the fuselage to a professional because (a) I didn't have a means of transport and (b) because of the costs.

There were a number of prerequisites to the stripping process.

1. Create a booth that would take the whole fuselage and keep the rest of the workshop free of dust. This would also serve as the paint spray booth later on.


2. Make sure I had the appropriate blasting equipment including safety wear and consumables.


3. Get some paint stripper just in case.


4. Arrange for the AD inspection on the strut attachments at an early stage when the weld clusters had been cleaned up.

The booth was made from white tarpaulin sheet hung from the roof beams with the lights inside the booth. The dimensions were about 20 x 10 feet giving enough room to work around the fuselage. I also have a small extractor fan used to keep the dust down.

I bought a cheep hopper (http://www.northerntooluk.com/sandblasting/sandblasting-accessories/portable-shot-blasting-kit_146993E.html) which holds a 25 Kg bag of grit/bead and utilises my compressor running at about 115 psi. In practice, this would last for about 30-40 minutes before having to be topped up. I also purchased a hood with spare lenses, gauntlets and disposable overalls to wear during the blasting.

I anticipated the blasting would take three days to complete followed by a day to paint the fuselage but as ever it took longer for several reasons. After three days I had completed the initial blasting but there was a lot of paint that just wouldn't come off mainly around the cockpit area.

There was a mixture of paints, what looked like powder coating and some rubberised coating which I decided might come off better if I applied paint stripper. Another day was spent applying the stripper. The paint stripper used was SV-35/PMA formulated specifically for aviation paints (http://www.paint-stripper.co.uk/removall_paint_stripper_aviation.htm) and non-toxic. I left the stripper overnight to be cleaned off the next day. The results looked pretty good. I can recomend this product as it's easy to work with, strips the paint quickly (I was working in neart freezing conditions over winter so it should work very quickly in the summer months) and is easy to dispose of afterwards.

The approved method for removing the crud is by pressure washing with water which I don't have the equipment to do so instead it was brushed off with water, a messy and time consuming job. I then had to bead blast the whole fuselage again to clean up the remaining paint.

There were still odd spots of paint which hadn't been removed so another day was spent getting these off by using a craft knife blade followed by further bead blasting.

The finished product was cleaned with an air hose and tack cloths prior to painting.

In all the process took about 10 days spread over 4 weeks, but I did loose a week because the weather over here was so bad I couldn't get to the workshop. In hindsight I should have spent more time paint stripping and left the bead blasting just for the final finish but that's what this blog is about, helping you save time through my experiences. I think a realistic timetable for the job would have been 2 days to paint strip, 1 day to clean and 3 days to blast, still a lot of work but very satisfying once completed.

Next time, priming the fuselage.

Welding Work

During December I begun the preparation of the fuselage for it's eventual bead blasting and painting. There was no repair work necessary as the aircraft has never been crashed and there is no evidence of major corrosion but there are a number of other jobs that need to be completed.

The job list included:

1. Adding structural harness attachment points.


2. Welding on additional tabs to support the baggage sling, 'D' windows, hat shelf, floor boards and skylight.
   
3. Welding up and re drill the rear horizontal stabiliser mounting holes (to be re drilled).
   
4. Have my inspector sign of AD.2008-09-18 (Wing strut attachment bracket).

The plan was that if these jobs could be completed by Christmas, then I would grit blast and paint the fuselage in the period between Christmas and the New Year. Of course things don't always go as planned, but more of that later.

The first problem encountered was that the harness brackets that had been made (http://gbrih.blogspot.com/2009/11/harness-brackets.html) were flawed, the bolt couldn't be fitted because the fabric would interfere, so I had to make new ones to fit (see below). They were manufactured in the same way with the same spec material but now weld at an angle to give better clearance.

My friend David made four post supports from 4130 rod with an internal M6 thread. These were welded to the fuselage to provide additional support for the skylight.

The additional tabs were all welded on over a couple of evenings and I begun to plan the cleaning and painting of the fuselage frame.

The AD inspection was scheduled to be done once the fuselage had been bead blasted as this was purely a one off inspection for corrosion or cracks around the strut attachment fittings and it would mean I wouldn't have to remove paint at a later date.

I'll discuss stripping and repainting the fuselage in the next posting soon.