Going All-Out With A Classic Balsa B-17-F – Part 16

Going All-Out With A Classic Balsa B-17-F – Part 16

This is going to be my last session working on the B-17 fuselage for a while.  There is a lot of work on the wing left to be done to get it up to the same level of completion. You have probably already figured out that we are getting really close to the point at which I can start working on all those tricky little surface details that can make a B-17 come alive, along with the beginnings of the finish base (primer etc.) and paint job. Actually the first and most obvious of those details…the windows and various other openings cut into the fuselage…need to be done before I open any cans, and that’s where we’ll begin.

 

B-17-16-1 Let’s start work this time with what I think you’ll agree is a REALLY COOL operation…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 during the last session.. Check your scale references again and get it right. With all that done, I located and drilled corner holes in the cabin roof and carefully cut out the top windows like this.

 

B-17-16-2 An emery board is the best tool I have found for tight, precise sanding jobs like this.

 

B-17-16-3 I used a 3/32” drill in my drill press to make the window corner holes in the 1/32” plywood sides…

 

B-17-16-4 …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-17-16-5 …was that worth all the effort I just put into it, or what?

 

B-17-16-6 I still have to make the rest of the various window, hatch and turret openings in the fuselage before it will be ready for the first of many coats of sanding base primer. In addition there’s one other set of details that will need attention before I set the fuselage aside to get the wing caught up with it. That comes next.

 

B-17-16-7 All of the primary control surfaces of a B-17 (the rudder, elevator and ailerons) are designed with the hinge line axis set back from the leading edge to make static balancing of the controls easier. One characteristic of this feature is that each leading edge extends forward, or is inset, into its respective trailing edge/control surface well. The most obvious result is that the trailing edges of all the flying surface skins extend back nearly to the rounded front face of each control surface to “close the gap”…to clean up what would otherwise be aerodynamically dirty, drag-producing control surface gaps. When I added the various balsa sheet surface skins I elected to cut them off flush with the sub-trailing edge control well front faces to avoid having a lot of protruding , damage-prone 1/16” balsa sheet edges all over the airplane while finished building. Now that the exterior surface of the model is essentially complete and otherwise ready for finish base work I have to go back and add all those highly visible overhangs before I go any further. Here I’m starting with the right/upper horizontal stabilizer surface. I have chosen to use strips of 1/8” x 1/16” basswood to serve as the gap cover/skin extensions. Here I’m using Deluxe Materials Roket Hot (fast) to spot-glue the gap cover in place a few inches at a time as I as I hold it in exactly the alignment I want. Once the strip is fixed in place I’ll go back along the inside of the seam with a generous bead of adhesive to lock the strip in place.

 

B-17-16-8 Here I have moved to the vertical tail. The “top” (left side) gap cover strip is in place and I’m getting ready to measure another piece of 1/8” x 1/16” basswood to fit the opposite side.

 

B-17-16-9 I was able to get a nice, close fit between all those gap cover strips and the primary balsa sheet skins, but it wasn’t perfect so I added a layer of Deluxe Materials Wonder Fill to all of the joints and then block-sanded each area smooth after the filler had dried. Here I’m cutting the rough filler flush with the surface using 100-grit production paper.

 

B-17-16-10 Once all the little bumps and discontinuities are gone, I can use a hand-held sheet of 320-grit production paper to create a really smooth transition so none of those joints will be detectable through the final finish.

 

B-17-16-11 The navigator’s sighting dome just ahead of the pilot’s windshield mounts to the top of a convex circular base that is part of the sheet metal skin of the nose. For this to look right on the finished airplane I must get the cross section/contour of the “bump” correct right from the start. Since I’m only going to make one of these simply carving one from balsa makes more sense than making a mold and so on. I began by transferring the scale diameter of the bump from my scale reference drawing to the model and making this circular cutout. The simple block of balsa I’m holding is going to become the mounting bump.

 

B-17-16-12 The actual clear plastic dome is narrower than its mounting base, and for credible scale appearance it’s going to have to close an actual opening into the nose compartment. I used a ¾” Forstner bit to cut that hole cleanly through the middle of the block…this provides a fixed reference around which I’ll be able to shape the rest of the detail.

 

B-17-16-13 Now I can use an ordinary drawing template to mark the outer diameter of the bump. This dimension will match the opening I’ve already cut into the airplane, and…

 

B-17-16-14 I’ll use my Dremel scrollsaw to cut the working block out of the balsa matrix.

 

B-17-16-15 As I usually do in a place like this, I cut the blank just a bit oversize so I could then use this custom sanding tool to trim the hole in the nose to an exact fit…

 

B-17-16-16 …and then slip the dome mounting base blank snugly into place and use a generous bead of Super-Phatic glue, which will penetrate all the surrounding balsa and hold reliably. I’ll come back to this part later after the glue dries.

 

B-17-16-17 There are plenty of other openings in the B-17 fuselage that are going to demand some care and accurate cutting to represent properly. This is the aft end of the removable cabin top structure where the multiple window openings of the radio operator’s position have to be cut in. As before, I measured the outlines from my scale drawings and transferred them to the model with a pencil.

 

B-17-16-18 There was a lot of cutting and sanding to do before I got to this point. I’m holding the nearly-finished cabin top next to the main fuselage so you can see how these two new cutouts are going to relate to the rest of the structure.

 

B-17-16-19 Two small rectangular side windows are also features of the radio position. I located them fore-and-aft in the usual manner, marked those limits with masking tape, and re-installed the cabin top for a position reference. What’s happening here is that I’m using an awl/punch to make locating holes for the window corners to help me cut the openings accurately.

 

B-17-16-20 With those holes made I can use an ordinary No. 11 blade to cut out the correct rectangular opening.

 

B-17-16-21 The best tool I have found so far for squaring off inside edges like this is an ordinary emery board.

 

B-17-16-22 With that done and the location reference tape pulled, the openings for the radio compartment look like this.

 

B-17-16-23 Here’s some old-time wood carving practice. I’m using a sharp/new No. 11 blade to rough-cut the rounded/convex shape I need to reproduce.

 

B-17-16-24 Now I’m using a coarse (80-grit) sanding block to rough-form that balsa cylinder closer to the finished shape of the sighting dome base.

 

B-17-16-25 Now I’m back to using that emery board to get closer to the correct contour. On most contemporary airplane kits you would find a molded plastic part in the box to meet this requirement. The original kit called for a simple plastic dome to rest flush with the nose skin. When I chose to work out the structural shape more accurately I accepted the responsibility of doing some extra, delicate work to get it right.

 

B-17-16-26 The emery board left it close, still not quite right, so I’m adding a generous layer of more Wonder Fill to create a new base on which I’ll be able to do yet more fine detail sanding.

 

B-17-16-27 While that new application of filler is drying I can move on to the various side windows that are part of the nose gunner’s/bombardier’s/nav-dome compartment. As with the window’s I’ve already cut I transferred all the dimensions from the scale drawings and then used a pencil and more masking tape to mark them on the airplane for cutting. NOTE: The shape and relative location of these nose windows can vary from one B-17-F to another. Check the scale drawings that you are using to make sure you get it right.

 

B-17-16-28 As before, I used that punch to mark all the corners and then started making the window cutouts with the No. 11 blade.

 

B-17-16-29 And again as before I relied on an emery board to clean up the edges.

 

B-17-16-30 With all that done, the nose looked like this. NOTE: There’s a lot of detail work still to be done on these windows but I’m going to leave them at this stage until after I have built up the exterior base finish on all the surfaces around them.

 

B-17-16-31 We can’t forget the bottom of the airplane. Here I’m once again going beyond the original kit engineering to create a secure, “scale-credible” mounting base for the belly/ball turret. I trimmed the molded plastic ball turret that comes with the kit to shape, covered it with masking tape for protection, and set this compass to reproduce the diameter of the open end. As before I relied on my scale drawings to confirm that the location of the ball turret on the original kit plan was correct.

 

B-17-16-32 Here’s another use for one my custom sanding tools.

 

B-17-16-33 This turret mounting base ring is more 1/64” plywood. Again I’m using Super-Phatic because it penetrates into all the wood of a closed joint like this. I’ll come back later and trim/sand the excess 1 /64” plywood flush with the balsa skin.

 

B-17-16-34 Are we making progress, or what? The fuselage/tail assembly is pretty much ready for finish base priming and sanding now. From here I am going back to work on the wing to bring it up to the same stage of completion. You are going to have to wait a bit to see how that comes out…I’ll explain next time.

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