I primed all parts except for the forward fuse bottom skin in one large priming session. I now have a full size spray gun but am still waiting on a fitting so I had to use the mini-gun for the mid fuse skins – slow going. The paint booth was overflowing with parts but I managed to shuffle things around enough to get everything done. Now I’ve got a lot of riveting to do.
Today I scuffed, degreased, etched and primed all of the aileron parts. This should have been a straightforward job, and it was until the compressor failed when I was half way through spraying on the EAP-12. A solenoid valve on the output of motor #3 (of 4) blew up, tripping the breaker for that motor and causing a significant leak for the entire compressor. This in turn made the remaining three motors run “flat out” trying to make up for the leak. I hurried through the rest of the EAP-12 application with the compressor in this condition, in order to at least get all the parts “sealed”. Once this is done, the PPG spec says I have up to 72 hours to apply the primer. I’d already made up a pot of primer though, so if I didn’t want to waste it I had a remaining pot life of 4 hours to work out what to do.
It was very hot in the workshop mid afternoon when this happened, which could have contributed to the failure. I used a piece of rubber, some gorilla tape, and a C clamp to temporarily block up the leak (or most of it), and turned the remaining three motors back on. I waited a few hours until the ambient temperature dropped, and sprayed the primer. The three motors alone were on 100% of the time, which is not good, so I wound up the spray rate in order to complete the job quickly. This meant I didn’t achieve the usual extremely light coat on everything, so I’ve probably added a few grams of weight to the ailerons, too bad about that.
Normally an un-primed strip is left on the aileron skin trailing edges for pro-seal. I’m not using pro-seal on the trailing edge, I found on the rudder and elevators that the 3M F9460PC construction tape adhered just fine to a slightly scuffed primed surface, hence there is no un-primed strip in the attached photos.
I touched up a couple of wing parts while I was at it. Replacement solenoid valves are cheap from China, but will take a few weeks to get here, so tomorrow I’ll seal up the leak properly; running on less than four motors will be fine for normal construction and assembly work.
I primed all the internal wing parts, across four separate, boring priming sessions.
When I built the spray booth, and the frame for etching “long” parts, I sized them to fit the HS spars, since that is what I had. It turns out I should have made them slightly longer, so that the wing rear spar would fit in. Rather than build an extension on the end of the spray booth, I sprayed these parts outside – which reminded me why I built a spray booth.
I decided to prime the tail cone skins before the mountain of other parts. Get the easy part done first. The NACA vent holes, and the holes for the static ports, were treated with an Alodine pen and masked over, since the pro-seal used for these parts will achieve a better bond directly to the scuffed Alclad. The weather was a bit cold – 12 degrees C, so I mixed the primer and let the pots sit in the house family room – where there’s a wood burning stove – for the induction time. The primer went down OK, just took a bit longer to dry.
Next will be the “long” parts (stiffeners etc.) together with small parts to fill up the booth, followed by the remainder of the tail cone parts.
It was a sizzling hot day in Tassie – a good day to put on the bunny suit and prime the elevator parts. It was quite a big job to degrease, etch, spray on EAP-12 and then prime the zillion parts that make up the elevators. Just as I was shooting the primer mid afternoon, half of the motors on the compressor tripped out, so the remaining two were on 100% of the time trying to pump enough really hot air to feed the spray gun and breathing gear. I noticed the change, so after finishing I checked the compressor head temperatures with my finger tip – and promptly got burnt! I switched off the compressor for a few hours and waited until things cooled down before doing the skins.