25-Finishing
Chapter 25 Notes: July 2010. Time has gone by and here is another rewrite. I taped the ailerons and left them in place. Since I used clickbonds, this seemed to be a great idea. Of course the clickbonds are inserted through the skin and glassed over to doubly secure them. SANDING: Look at the fourth pic to see the use of the palm sander ( I used a Bosch "Sheetloc" palm sander) and a hand held light. If you angle the light, you can see all of the contour defects. Note: My stop action for the rudder is the "little extension" of the wing, and so the point "A" plans way is not a consideration.
Finishing of strakes and fuselage
When I finished the fuel sump/fairing work, I went to the finishing work on the bottom of the fuselage. The transition pieces on the strake to wing zones makes this work easily. By easier, I mean that I don't have to put the wings on to finish them.
Click the pics for larger size.
Here are the flip the plane pics. Thanks to my hermanos.
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The wings are made with featherlite cores and so the contour is already great, and so I just need to not mess it up with the micro. I read the article that Wayne Hicks referred to on finishing a composite plane and I made the 16 and 32 inch sanding boards. I still use them, but only to check for low spots on the first fill work. you need to get a good fill on the first application, but you can always sand down and add a second layer. I have read about the "board of pain" and I made the 16 and 32 inch sanding boards and bought the self adhesive sand paper, but I only used them on the strakes. Curved surfaces are a different situation. I used Featherlite foam cores and so the contour is very even. The addition of micro and the sanding are simpler. I used 60 and then 100 grit with a Bosch "Sheetloc" hand sander and did 95% of the sanding.
Pic #1:
I bought some cheap plastic bowls that are about a one gallon size and disposed of the bowl after 2 or 3 sessions. The six inch flexible spatula is all that you need for flat surfaces. I trimmed a two inch black plastic spatula to a curved shape to mix the micro and for micro application on curved surfaces (convex and concave). The one very important detail that makes that work is to hold a light and change the angle of the light to show the contours of the micro. You have to have excellent shop light also, or you will get eye fatigue.
I used the MGS 285 epoxy for all but the inside of the fuel tanks, and so I continued with that on the fill work and used it with the same micro as all along. The weight is better than the West system and when you bond to the same type epoxy then the bond is better. I cannot speak for that stinking stuff that I used on the fuel tanks (sorry, if that's your epoxy) being used with micro for finish work.
Taping
Pic #2:
Pic #3: The winglet section below,covers more on this, but once again, the use of clickbonds makes a world of difference. There is a major difference on rudder finishing.
Pic #4: Taped elevators.
Pic #5. This shows a hinge after finishing of the outboard of the winglet and right before I touched this up with micro.
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Pic #1: The major point of good contour on the surface is to pre-fill the low spots and then sand that down evenly. This shows a pre-fill of low spots.
Pic #2:
This is right after the main fill coat (after "low fill"). This is a later session of work. At the pre-fill I had trimmed out around the bolt access panel hole (whatever it's called). I just put a plastic shopping bag on the cover and screwed it down. See the details on this type cover in chapter thirteen for the pitot access panel at the nose area. If I had it to do over, I would have made these panels with straight lines to make it easier to cut out. A kite shape on the outer skin and then expand out a little below the surface for the socket wrench to fit. You really don't get motion on the ratchet here.
Here are the details.
The micro mix is 14 squirts of epoxy/ to 22 level scoops (Mr coffee size-20 ml.) of micro.
Immediately after mixing dispense the micro onto the surface in several "globs" to keep the exothermic reaction under control. Then I applied a thin coat of micro to the skin to create adhesion and then immediately followed that with a enough micro to hide the glass color, being careful to evenly apply the micro. You can go back over the same area 3 or 4 times, since the consistency of this mix will allow that. The strake transition strip overlaps the wing, so the micro is absent there.
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Pic #1-3: I left the rudders on for the finish work. To make this work out there are some precautions.
1. I taped the hinges on the outboard side and taped under the "spur/stop" on the inboard side of the winglet.
2. I marked the lines for the re-cutout of the elevators. These sharpie lines must be preserved through the finish work. I have the lines marked on the masking tape also.
I held the rudder at the neutral position and added micro over the inboard cut line first and let that cure. This allows for a true shape of the airfoil from LE to TE.
The middle pic shows the hinge area after tape removal and before touchup. This technique worked well for the forward LG cover.