Going All-Out With A Classic Balsa B-17-F – Part 15

Going All-Out With A Classic Balsa B-17-F – Part 15

This session is going to be about the first of a series of steps that have got to come before I can think about doing any “fine detailing” on the fuselage, let alone get into “finishing” (a paint job). Just as with the wing, along with all four of the integral engine nacelles, I have to add some sort of substrate, or finish base, over the unreinforced balsa structure. The functions of that finish base are to strengthen/reinforce the balsa, fill all those last traces of wood grain that will still be there no matter how carefully I did my finish sanding, and provide a stable surface on which I’ll be able to build up a meticulously sanded sealer/primer surface as the base for the color coats that are what everyone will see in the end.

On a much smaller, lighter model like the 30” span Piper J-4 I built here a while back, this step might consist of nothing more than a layer of silkspan or other tissue and a couple coats dope or whatever other sealer I might choose to use. On this B-17, though, we’re going for the real deal…fiberglass cloth and a substantial bonding agent/sealer that will polymerize. In the past I have used a polyester or epoxy product for this…now I’m going to continue with the product I demonstrated when I built the wing, Deluxe Materials EzeKote. You really need to check this stuff out!

 

B-17-15-1 Last things first…before I go ahead with the EzeKote/glass process on the fuselage I need to finish up the last left-over bit of open balsa sealing on the wing. Before I built up the bottom wing center section fairing (several sessions back), I had already glassed the wing. (This made it a lot easier to work on the fairing without digging up the adjacent wing skin). Now I have to finish glassing the surface of the fairing. Here you can see the single piece of 2 oz. Deluxe Materials glass cloth that I cut and fitted just as I did with the rest of the wing covering.

 

B-17-15-2 Off camera, I brushed EzeKote onto/through the glass in then usual way and now I’m moving on to the fuselage. At this point the fixed tail surfaces can be considered part of the fuselage and I’ll work all that stuff together. In order to save some weight I’m going to glass the tail surfaces and the rearmost part of the fuselage with 0.6 oz cloth…here I’m marking the edge of the piece that will cover the entire left side of the vertical tail and the extended dorsal fin.

 

B-17-15-3 Here’s that same piece of glass cloth (you can read the complete product description for yourself on the package label in the corner) positioned on the left face of the vertical tail as I begin brushing Deluxe Materials EzeKote over/through it to hold it in place and bond it to the balsa sheet structure. I continued brushing the EzeKote across the entire fin surface and down over/around all the edges.

 

B-17-15-4 Same game on the bottom surface of the left half of the horizontal stabilizer. I’m still using 0.6 oz. glass cloth here. Note: As soon as the glass cloth is wetted sufficiently to look “clear” along one edge like this, you can pull against it sufficiently hard to smooth out the rest of the working piece.

 

B-17-15-5 Now I’m starting on the lower surface of the fuselage from the tail gun fairing forward to the front of the tailwheel well opening. This is still 0.6 oz. glass.

 

B-17-15-6 Start brushing EzeKote onto the glass cloth at a location that will fix the entire piece in the correct position and then work “out” from there.

 

B-17-15-7 Where there is a broad overlap of this new portion of glass cloth with the covering already in place on the horizontal tail, I’m using a curved-edge scalpel blade to slice through the top layer of glass without digging into the layer beneath it. I’ll pull the “extra” material away as it is trimmed free.

 

B-17-15-8 With that done I’m smoothing/sealing down the freshly cut edge so it will blend in seamlessly.

 

B-17-15-9 I covered all the upper surfaces of the tail assembly in just the same way, then moved on to the nose. You can see the package of Deluxe Materials 2.0 oz. glass cloth I’m going to use for this part of the airplane, once I finish this last-moment sanding out of a rough spot I just discovered.

 

B-17-15-10 I sized and cut out the working pieces of 2.0 cloth just as I did with the tail…here I’m fixing the glass in place along the top fuselage centerline above the wing.

 

B-17-15-11 Working around to the fuselage sides and bottom, I chose to deal with the wing mount base surface by wrapping the glass over and around it to avoid leaving any areas of structure “bare”.

 

B-17-15-12 I finished glassing the rest of the fuselage/tail group the same way off-camera. Here’s the whole deal as seen from the rear with a single layer of Deluxe Materials glass cloth over the entire structure, bonded with a single coat of EzeKote and sanded/trimmed wherever necessary to get rid of any loose edges or raised overlaps.

 

B-17-15-13 I finished glassing the rest of the fuselage/tail group the same way off-camera. Here’s the whole deal as seen from the rear with a single layer of Deluxe Materials glass cloth over the entire surface, bonded with a single coat of EzeKote and sanded/trimmed wherever necessary to get rid of any loose edges or bumps.

 

B-17-15-14 Deluxe Materials recommends a second coat of EzeKote to fully seal the glass. To get ready for that step I’m going over the entire fully-dry, first-coated surface with 320-grit production paper to take care of any rough spots that may have gotten by me so far.

 

B-17-15-15 Putting on the second coat of EzeKote is pretty straightforward…just lay it on wet enough to cover well and brush it out just enough to eliminate any potential runs. You can see the enhanced sheen of the wet EzeKote I’ve just applied to the far side of the fuselage. I’m going to make it all look like that.

 

B-17-15-16 I also finished up that second-coat job quickly, off-camera, and after it had dried thoroughly (several hours in a warm room…EzeKote sets fast) I sanded the entire surface with 320-grit paper AGAIN. With that done I had a complete finish base on the entire airplane and it was time to start adding external structures and other details. I started with the clear molded plastic bombardier’s nose bubble that is supplied with the kit. As you see it here I have already cut away the flat base/molding flash. The outer surface of the bubble is supposed to flow smoothly into the fuselage skin surface with a flush seam (not a step or bump) and the best way to make this work is to provide a mounting flange for it to rest on. This is not provided for in the original kit design so I decided to design my own by transferring the measurement of the diameter of the inside rear edge to some 1/16” plywood…

 

B-17-15-17 …so I could cut out a new “face” to attach over the existing F-1 assembly and all the associated glued-up, sanded-off balsa sheet skin around it. Here I’m checking that the plywood face fits neatly into the rear opening of the plastic bubble. (I cut a small opening in the center of the face for ease of handling and I’m going to cut away more of it later, but you’ll have to wait to learn why).

 

B-17-15-18 There’s lots of Deluxe Materials Aliphatic Resin in that joint between the face and the old F-1. With a “closed” assembly like this a lot of solvent has to manage to escape so I want to give it plenty of time to dry. That masking tape will hold everything securely in place overnight.

 

B-17-15-19 This is the clear plastic bombardier’s bubble wrapped up in masking tape for protection while I use it as a measurement reference to see how much trimming/adjusting I might have to do on the existing nose structure.

 

B-17-15-20 As it turns out, even after “sanding back” the original frame-and-stringer structure, all that 18” balsa sheet skin I added left the fuselage at F-1 just a bit too “fat” for the bubble to fair in neatly. To fix that I’m removing some “extra” skin thickness by using my 100-grit sanding block to trim about 1/16” off the outer circumference of the nose. As you can see if you look closely, this means that I had to sand right through some of the glass cloth/EzeKote reinforcement I put on earlier.

 

B-17-15-21 I have to “make up” for this…here I’m using more Deluxe Materials EzeKote to bond a new layer of 2.0 oz. glass around the portion of the fuselage where I had to cut away material.

 

B-17-15-22 Now we can get to another of those “fun” parts. So far the fuselage has taken on the appearance of a tapered tube; without the characteristic B-17 cabin enclosure it’s just not right. Several sessions back I built I the structure for a LiPo battery tray along with some extra fuselage reinforcement, then covered it all up when I closed in the structure with all that1/8” balsa sheet skin. Now I can cut away enough of that top fuselage skin to get a working access to where the cabin enclosure is going to be…I may trim away even more of it as I go along.

 

B-17-15-23 And in fact that’s just what I did. After using the original kit plan to determine the exact mounting location of the enclosure on the fuselage I determined that more fuselage skin had to be cut away all the way forward to F-3 to provide a correctly located opening for the cockpit. With that done I decided that I would need to build in a bit of extra structure to provide a secure mounting base for the cabin. Here I’m starting on that by removing what’s left of the original upper F-4. Watch what happens next.

 

B-17-15-24 It turns out that this former location is almost exactly at the scale location of the rear cockpit bulkhead, so I’m going to retain it as one of my cabin mounting points. I kept the existing 1/8” sq. balsa cross member and added this new 1/8” balsa sheet “cabin mount” to it. You’ll see in a bit why I left it protruding so far out of the fuselage top.

 

B-17-15-25 It’s time to start working on the actual cabin enclosure. This is one of the places where I chose to make a LOT of changes to the original kit design in the interest of scale fidelity. The length of the laser-cut cabin top (the balsa sheet part in the middle) is going to work OK as designed, but I added a lamination of ¼” balsa sheet at the front to make it thicker. The big deal at this point is to modify the cockpit area structure so I will be able to add a credible shape to the area of the windshield and cockpit side windows…the side profile of the cabin top is supposed to TAPER DOWNWARD just behind the windshield and no provision was made for this. Also, the original structure here was 1/8” balsa sheet on which dummy window locations were to be represented with paint or trim film. For “real” windows I chose to splice in some 1/32” plywood from the position of the cockpit bulkhead forward…here I’m cutting off the original 1/8” balsa sheet cabin sides at that location.

 

B-17-15-26 Hang in there…all this will make sense soon. I have cut a 1/32” deep by 1/8” long recess in the original side to permit a neat overlap/splice of the new 1/32” plywood cabin side and used Deluxe Materials Aliphatic Resin to get a reliable joint. Those clothespin clamps are doing their usual job. Can you also see the second 1/8” balsa sheet cabin mount protruding beyond the fuselage surface at the rear end of the access opening?

 

B-17-15-27 This where it all starts to come together. I used the laser-cut kit cabin enclosure formers as patterns to make several extra parts which I assembled over those cabin mounts…front and back side on each of them…with a sheet of plastic wrap in between and more clamps to hold everything in place for the next step.

 

B-17-15-28 And this is how it all comes together using the original kit plan location of the cabin top as a location reference. What has happened is that I have protected the 1/8” balsa sheet cabin mounts with the plastic, assembled the cabin formers in position against them, and used more Aliphatic Resin to glue the cabin top to the cabin formers. Those few long pins you see are holding the cabin top in place while the glue dries.

 

B-17-15-29 I got busy off-camera again and removed the cabin-top/formers assembly by taking off the clamps and simply pulling the assembly straight up and letting the formers slide clear of the mounts. Again while you weren’t looking I taped a large sheet of plastic wrap across the entire fuselage top and re-assembled the cabin enclosure to the rest of the fuselage using making tape to hold it in place. The next step, which you see here, was to fit and glue those laser-cut rear cabin side pieces like this…

 

B-17-15-30      and once again use prodigious amounts of masking tape to hold it all in place while more Deluxe Materials Aliphatic Resin has time to dry.

 

B-17-15-31 The next step is pretty obvious…I cut some more 1/32” plywood pieces to fill in where the windshield is going to be and glued them in place.

 

B-17-15-32 Now it all makes sense, right? With the cabin enclosure assembly removed and turned upside down you can see how it all fits together.

 

B-17-15-33 The next step was to do some careful shaping of the outside contour of the cabin. Here I’m using a 120-grit block to round and smooth away the last traces of balsa sheet edges.

 

B-17-15-34 I used more masking tape to protect the top fuselage skin before starting another round of mistake filling and final sanding.

 

B-17-15-35 When I was sure I had the cabin enclosure right, I took it off again and gave it a final sanding in preparation for…

 

B-17-15-36 …another of those Deluxe Materials EzeKote/glass cloth lamination jobs

 

B-17-15-37 No matter how carefully you work there will nearly always be some less-than-perfect fits with resulting gaps and voids. I used more plastic wrap over the fuselage top, taped the cabin enclosure back in place as tight as I could get it, and used my favorite filler…Stits Lite Fill…to pack those voids.

 

B-17-15-38 This is why I used that plastic wrap…with the Lite Fill cured (overnight) it was easy to break the cabin enclosure loose and lift it off the fuselage…

 

B-17-15-39 …so I could go back to my sanding block to clean up all those sloppy edges…

 

B-17-15-40 …and get a perfectly fitted cabin enclosure like this.

 

B-17-15-41 Now comes the REALLY COOL part…cutting window openings into that tough, thin glass reinforced cabin structure. I used the kit plan along with my scale reference drawings to locate the EXACT positions of the windshield and side window panels and draw them in place with a pencil. Note: Can you see how that cabin top/roof tapers down to meet the upper edge of the windshield? This is the big change I was talking about a few steps back. Check your scale references again and get it right. With all that done, I drilled corner holes in the cabin roof and carefully cut out the top windows like this.

 

B-17-15-42 An emery board is the best tool I have found for tight, precise sanding jobs like this.

 

B-17-15-43 I used a 3/32” drill in my drill press to make the window corner holes in the 1/32” plywood sides…

 

B-17-15-44 …and VERY CAREFULLY cut out the window openings. While you weren’t looking I did some more careful sanding of those window frames edges and…

 

B-17-15-45 …was that worth all the effort I just put into it, or what?

 

B-17-15-46 Another glimpse of what’s to come. I still have to make various window, hatch and turret openings in the fuselage before it’ll be time to go back to the wing and finish all the details I left waiting. That starts next time.

See the entire build series: Building the Balsa B-17-F