Saturday, December 20, 2008


While I was at Bunnings today, I had a thought about paints. My 3.7 meter wingspan glider is looking a little the worse for wear from a hasty and poorly executed repair, so I'd like to sand it back, re-glass the damaged sections, and paint it.

Sand and re-glass is easy, but the paint isn't something I've done before.

Thus, when I noticed 'epoxy gloss enamel' at Bunnings, it seems like something I should definitely try! The plane has an epoxy gel-coat, so "Epoxy Gloss" seems like it would be very compatible, right?

This afternoon I took 5 mins to sand a previously damaged nose cone and sprayed it up. It's still not quite dry yet, and it's only the first coat, but it's looking very decent indeed. When it full dry I'll cut it back to see how well the new paint is adhering.

The only issue is that my mind immediately wanders to grander plans. To wit: Rather than just re-glass, if I'm going to sand it back anyway, why not run some carbon tow under kevlar (aka aramid) sock and give it some decent strength in that area.

This is an attractive idea, but there's some practical difficulties: The fuselage is about 1200mm long, so putting it in a vacuum bag is going to be very non-trivial. And protecting the wing bolt nuts from epoxy is going to be similarly interesting. Lets not forget the tow hook underneath which is not built for large compression (750 newtons of tension yes, compression no).

So I'm still pondering what to do here. The repair certainly is ugly, and I'm concerned about the strength given the cruftiness. But the sanded back fuselage is probably not going to be up to carrying a full atmosphere of pressure in a vac bag.

Which means I need to finish off the pressure-to-I2C board I have lying around, so I can have one of the NGW100s run closed loop pressure control of the vacuum pump. But the MPX5010 pressure sensors I have only run 0 - 10 kpa, so they're only good for 1/10th of an atmosphere. So I need to get some larger range sensors. Or make a microswitch based one....

Yak Shaving again! I just start looking at repainting a plane, and now I'm off buying new solid state pressure sensors!

It's a terrible life :)

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