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fklein(at)orcasonline.com
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 Posted: Wed Feb 11, 2009 6:08 pm Post subject: gaps for flying surfaces |
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Gentlemen,
If you can take a moment or two...think back...way back...when you
were preparing your bird for priming/painting...think back about the
gaps...for example, the one between the outboard edge of the trim tab
and the edge of the indent for it in the tailplane.
Given that, once the bird is painted, one wants to have some (but
minimal and consistent) clearance between the trim tab and the
taillplane as the trim tab rotates on its hinges...and given that one
certainly wants to avoid sanding on finished painted surfaces or edges
(say in the event that unexpected rubbing results from paint
thickness)...
What thickness does the gap want to be prior to priming/painting? I
don't see a size called out in the manual.
Would a tongue-depresser stick (0.060" thick) be adequate to establish
the gap (prior to priming/painting)?
(I have no real sense of paint thickness...)
..not that I want to get toooooo anal about this...but I'm looking for
comments/advice much appreciated,
Fred
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budyerly(at)msn.com
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| Posted: Wed Feb 11, 2009 7:44 pm Post subject: gaps for flying surfaces |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Fred,
Ready for a brain dump?
You are spot on. I start with a little more at an 1/8 inch for most aileron end gap minimums. Trim tabs to stab start about 3/32nd and it works out that by the time you fill, sand etc. your down to a 1/16 or so. Stab to fuselage gaps look good with a 1/4 to start with. This allows clearance after painting for full stab movement. Gaps along the hinge line have to be watched. I try to start with a long 1/16 so it doesn't bind. Don't make the edges really sharp as some paints fail on sharp edges or chip.
My problem is with the filler building up and a heavy handed painter at the paint shop. With you doing it yourself, you can control most of this. After all filling and sanding, and priming, then final sand, I measured my paint thickness from a chip. With Three finish coats of paint (Yes we painted it with two different whites, sanded it all down and recoated with two more coats) and two primer coats (one a filler primer, the second a sealer, of all polyurethane done properly then buffed, came in at a whopping 10-15 mils or .010-.015. I've got a lot of paint. My topcoat should only be 2.5 mils, unfortunately the primer and previous paint is probably 7 plus. Most cars have 7 mils max. But clear coats are thicker.
How much paint is needed, is a tough question. I reviewed with my painter some measurements using a paint thickness device that he had borrowed from a paint dealer. Paint thickness really depends also on UV protection and the manufacturers recommended thickness. Most urethanes recommend 2-2.5 mils minimum finish.
As for UV blocking, I use Imron. It takes a technique to apply well. Basically, a lot of pressure on the final two coats (60 then 120 psi) and a cool down during drying. All your jets use it, Peterbuilt trucks, etc. My reference for review came from my painter, but I refer folks to: http://www.auf.asn.au/scratchbuilder/coatings.html. The Aussies have real UV concerns, and they have a need for efficient glass aircraft, hence their research and advice to their builders is invaluable.
Lot's to ponder.
Be careful as these new urethanes will kill you. Get a fresh air respirator so we can see you long after your first flight.
Bud
Custom Flight Creations
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fklein(at)orcasonline.com
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| Posted: Wed Feb 11, 2009 10:59 pm Post subject: gaps for flying surfaces |
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On Feb 11, 2009, at 7:38 PM, ALAN YERLY wrote:
| Quote: | | Ready for a brain dump? |
Oh yeah, oh yeah...thanks Bud, I kinda figured you'd have this down. Truth is I have to check (and probably widen) all my gaps as I've really kept my head in the sand vis a vis the reduction of a gap by the TWO painted surfaces defining it.
Fred
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