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Building Tips and technical articles. => Building techniques => Topic started by: jim gilmore on March 08, 2009, 12:59:22 PM

Title: Sanding that profile fuselage.
Post by: jim gilmore on March 08, 2009, 12:59:22 PM

For those that build profile modles ai'm wondering what the consenses is on hom much sanding I should do. Do you sand the doublres to meet the fuselage with a smooth flush fit or do you just leave them as thge are and just break the edges? So far I've been sanding for about 2 hours.

Title: Re: Sanding that profile fuselage.
Post by: Glenn (Gravitywell) Reach on March 08, 2009, 01:05:58 PM

Hi there.  What I do is add a peice of 1/8th inch balsa to the end of the ply double and sand that into the fuselage.  Much easier to sand than the ply. H^^

Title: Re: Sanding that profile fuselage.
Post by: Mark Scarborough on March 08, 2009, 01:57:45 PM

Sanding the doublers on a profile fuse has more importance than cosemetic. If you leave the doubler blunt, it creates a potential stress point on the fuse that can cause problems with cracking and failure. I prefer to sand a nice long bevel on the doubler before I laminate it to the fuse blank. This creates a transition area that eliminates the edge. Think it terms of the nose with the doubler being really stiff, then in a very small area you have soft balsa, it creats a "hinge " area at the back of the doubler.when you taper it , it creates a much broader area to absorb the stress.

Be advised, I am trying to explain this as simple as possible I hope it makes some sense,,, bottom line it just isnt for pretty

Title: Re: Sanding that profile fuselage.
Post by: Ralph Wenzel (d) on March 08, 2009, 05:02:51 PM

It's ever so much easier to shape the doublers before you glue them on! I got in a hurry on my current plane (Lowry Stuka) and forgot, so I used a bunch of "Super-Fil", which looks pretty good - for now . . .

Title: Re: Sanding that profile fuselage.
Post by: Dave Rountree on March 09, 2009, 05:23:15 PM

Jim on your next profile take the doublers to your benchtop disc sander( before you epoxy).  Make sure you mark both the outsides of the doublers. Dont ask how I know. You can take the sharp edge to a nice taper. I take mine about a inch or so. Makes a nice smooth transition. Dave R

Title: Re: Sanding that profile fuselage.
Post by: Bob Reeves on March 10, 2009, 10:12:56 AM

What everyone has already said plus.... After I get everything epoxied together and the epoxy has cured I run the top and bottom edges through my router table with a round-over router bit. This makes a nice round edge that only takes a little clean up sanding. The router cuts through plywood and motor mounts should they be close enough to the outside edge like butter.

Makes for a nicely finished fuselage rather than the square top and bottom I see in so many profile photos.

Title: Re: Sanding that profile fuselage.
Post by: dave siegler on March 11, 2009, 08:40:41 PM

I use a table top belt sander, I position the edge of the plywood right at the edge (the side)  of the belt, I can make a perfect feathered edge in about 15 secs. The balsa is off the belt, so it does not dig in.