Where the Cowl meets the Fuselage

[Mike Griffin]

Is there any method of finishing the edges of the cowl and the fuselage where they meet so the seam is not so noticeable?

Thanks

Mike

[Bill Little]

Hi Mike,

I sand everything to get as good a fit as I can then line both surfaces with strips of 1/64th" plywood.

Bill

[James Mills]

There were a couple of articles in Stunt News last fall or winter (I think).  I believe Bob Hunt wrote one and Matt Newman the other.

James

[Randy Powell]

I do what Bill does. If I'm still not happy with the fit, I finish the edges of the cowl (usually with glass and epoxy), sand and clean it up as well as possible then put mold wax on it. Then use SuperFil along the the fuse contact point and bolt the cowl down. If I did a good job on the cowl side and got a slick edge for the wax, the thing separates cleanly and you get a very nice fit.

But it's a lot of work and easier if you can just get the 1/64" ply to mate well.

[Randy Cuberly]

Hi Mike,
Like Bill, I use 1/64th plywood to line the edges after careful fitting to get a clean line.
However before final fitting I line the inside of the cowl with lite weight fiberglass cloth and finishing resin, for fuel proofing and stiffening.
After curing for several days this usually causes the cowl to spread ever so slightly so I install it back on the fuselage for final sanding and fitting at that time.
I cover the entire front of the airplane, including the cowl, with lite weight fiberglass cloth with nitrate dope.  Yeah... then check the cowl fit and lightly sand for final fit.
The 1/64 plywood helps maintain a clean line during all that sanding etc.

Randy Cuberly

[Mike Griffin]

Thanks guys.. i will try the 1/64th first..

Mike

[Eric Viglione]

I used to do the 1/64 ply liner trick, but since we're always looking for lighter solutions, the last few planes I just put a drop of slow CA on the mating surface and quickly wipe the CA into the surfaces with a paper towel before it sets. This hardens up the balsa so it will hold a straight edge.

As long as you're starting with a clean line to begin with, this works well. Especially if you make nice clean cuts and finish sand them with a TBar or your fuse and cowl sides came from a laser cut kit.

Then I finish per usual, and by the time you either glass the front end or silkspan or CF veil, or whatever, the surfaces should be hard enough for all but the most ham fisted of user maintenance over time.

EricV

[Ted Fancher]

Both mating surfaces have to be absolutely flat before any of the cosmetic approaches will have much value.  I make large flat sanding surfaces out of foam or shelving material, etc. that can be clamped to my perfectly flat building table.  They are large enough (1 X 4 feet, more or less) that an entire fuselage top or bottom can be flattened by moving the model surface over the flat clamped sanding surface.  Once both the fuse and cowl mating surfaces are really "flat" the rest is easy.  I've also used the 1/64 ply on the surfaces after they're flattened for wear and tear resistance and that is worth doing as well.  won't do much good, however, if the balsa mating surfaces aren't flat before you put on the ply!

Ted

[Mike Griffin]

Thanks Ted.  Just out of curiosity, what grit sandpaper do you use?

MIke

[Howard Rush]

Plenty of good advice here.  I wish I'd taken it.  I will next time.

[Curt D Contrata]

If you cut the 1/64 cross grain, it becomes extremely flexible so you can even get it to tuck into the slot you make for the tank vents. For the Needle valve, I split an arrowshaft and use those halves to line that hole. 1/64 ply is also used at the rear of the cowl at the landing gear to make those edges clean and protected as well. And finally, I use 1/64 ply as a temporary spacers when adding the cowl mounts so that the gap is the same all around.

Curt

[Allan Perret]

Ditto everything Ted said except a 1' x 4' sanding surface is rather large to cover with sandpaper.  I made the square sanding tube in the pictures about 5 years ago and used it on every fuse and lots of other parts I've built since.  Made it from one of those white melamine shelf boards, 16" wide by 48" long (about 10 bucks at HD and Lowes).  Ripped it into 4 pieces and cut rabbets in the edges to help keep everything in alignment while glueing together.  This results in about a 4" wide sanding surface which I apply sticky back PSA shop roll paper to.  There are several brands of the PSA shop roll available in a variety of grits, they are 4.5" wide by 10 yards long and typically sell for ~ $15 a roll online.  You might find the PSA shop rolls locally if you have a wood working supply place nearby.  I put 80 grit on one side and 150 grit on the opposite side.  I use this same PSA paper on the Great Planes aluminum sanding bars instead of the GP paper rolls which don't seem to stick as well.   I also use the 1/64 ply to line both faces of the fuse/cowl split line.
Mirka Gold is the latest brand that I just bought and is a different color than the shop roll shown on the square tube in pictures.

[Ted Fancher]

Thanks Ted.  Just out of curiosity, what grit sandpaper do you use?

MIke

Mike,

I put paper on both sides of the board (generally a four foot long generic shelf board from OSH or Lowes--I depended on clamping them to the flat building table to remove any bow, etc.), a medium grit for the first few passes to get the surface generally flat and then a fine grit for the obvious reasons.  Because I built reasonably carefully I didn't usually have to remove  a lot of material so the grits are probably something like 120 and 320.  I also have some shorter boards with coarser grit to take care of more "manly" operations than require rapid removal of lots of wood.

My favorite papers for bare wood were from 3M and were labled as "Fre-Cut" and "Open Coat".  They're readily identifiable by their grit colors: Light green for coarser grits, a cabernet wine color for medium grits and sort of a yellow/tan for finer cuts.

FWIW, I use(d) these boards religiously for almost any kind of "part shaping" (such as rounding off blanks for tips, stabs, rudders, etc)sanding as they allow you to move the part over the paper rather than try to hold the part in one hand and the paper in the other.  Curved surfaces are, of course, a different animal.  Sanding of fuse blocks and cowls frequently bring out the "shoeshine man" in me.  I'll rough the radius of the blocks by "counting strokes" of the razor plane symmetrically and then use a foot long (by a width appropriate) strip of sandpaper as though buffing out the gloss on the toes of your go to meetin' wingtips (shoes, that is).  The counting "plane strokes" and "buffing your shoes" approach resulted in very acceptable curve symmetry and I never bothered to use templates when shaping.

As an aside, I've got a dozen or so blue foam sanding blocks (~2" X 10" and roughly 3/4" thick) to which I use double sided tape to apply sandpaper to both sides and employ long t-bar aluminum blocks for things like evening out planking and cap strips, etc.

Don't know what got me started but...

Super glue is the greatest thing that ever happened to sanding.  I have literally dozens of wierd shaped sanding tools I've manufactured literally no time at all to do special jobs.  Paper on dowels is just the starting point. let your imagination run rampant when building and you'll find yourself doing it all the time.

Ted

Allan Perret.  Just read your post submitted while I was writing this.  I love the square  tube approach!  It pretty much self flattens itself and doesn't require multiple individual units that have to be removed, stored and replaced by the one you need at the moment.  Yes, the melanine covered shelving is exactly what I used.  I should have mentioned that I don't use 12" shelves, just the eight inch versions.

[Mike Griffin]

Ted, Allan and all, Thanks so much for the great ideas.  I appreciate them very much

Mike

[Allan Perret]

Ted
Allan Perret.  Just read your post submitted while I was writing this.  I love the square  tube approach!  It pretty much self flattens itself and doesn't require multiple individual units that have to be removed, stored and replaced by the one you need at the moment.  Yes, the melanine covered shelving is exactly what I used.  I should have mentioned that I don't use 12" shelves, just the eight inch versions.

Yes, that's exactly what led to this design.  The melamine shelving has the smooth white surface which works good with the PSA paper, but the core is particle board.  The shelf by itself would not remain flat, requiring it to be clamped to another flat surface.   But by cutting it into 4 strips and gluing in the square tube config. you make a rigid structure which will stay straight and flat.    Mine was made from a 16" wide shelf board, so it ended up 4" square.  If I was to make another one I would make it a 3.5" x 4.5" rectangle because the PSA shop rolls are 4.5" wide.  So as it is now I am having to cut 1/2" off the width of the shop roll.   

[Steve Fitton]

If you cut the 1/64 cross grain, it becomes extremely flexible so you can even get it to tuck into the slot you make for the tank vents. For the Needle valve, I split an arrowshaft and use those halves to line that hole. 1/64 ply is also used at the rear of the cowl at the landing gear to make those edges clean and protected as well. And finally, I use 1/64 ply as a temporary spacers when adding the cowl mounts so that the gap is the same all around.

Curt

Curt,

  Welcome to Sparky's forum.  Its good to see you aboard!

[Bill Little]

Hi Curt,

I second Steve's Welcome!  It's great to see you.

Bill Little

[Lauri Malila]

By the way, did you know that there is also 1/128" aircraft ply available, it has 2 layers at 0/90 degrees? I just eard of it, never seen yet. L