Going All-Out With A Classic Balsa B-17-F – Part 20

Going All-Out With A Classic Balsa B-17-F – Part 20
It’s time for more detail work…all the “little stuff” that brings out the “scale” in scale aeromodelling. Like other small/fine details that represent actual structure (as opposed to markings which exist only on the surface) all these things need to be completed before I can move on to the final stages of putting a finish on the airplane. But, you ask, home come there is already a lot of that finish, in the form of primer, already on the model? Here comes another of those judgment calls I’ve talked about. The stuff I’m working on now is a lot easier to get right (that means “accurate”) if I am working on a clearly defined, smooth solid surface rather than on raw balsa. Take a good look at the first image and you’ll see what I’m talking about.

 

B-17-20-1 Representing those little rectangular openings along the top surface of a B-17 wing more or less behind the nacelles won’t make this model B-17 fly any better, but making them right sure will make it look better. To be consistent with the other detail work I have already done, they have to be real holes/openings and not just black-painted shapes. What are they for? They are not exhausts, but rather simple vents to give the hot air flow generated around the intercoolers a place to go. That, by the way, will be important to remember when it’s time to airbrush in exhaust stains behind the nacelles. I chose not to rely on markings on the original kit plan, but instead measured and transferred dimensions from those same scale reference drawings. With the exact location of all the necessary cut lines drawn in with a sharp pencil you can see how having a solid finish base to work on is going to help here.

 

B-17-20-2 For those short, straight cuts through the 1/16” balsa wing skin and the EzeKote/fiberglass reinforcement over it, my No. 11 knife blade is easier to control than a razor blade. Note…if you have any doubt at all about your ability to keep those cuts STRAIGHT, use a metal straightedge for control.

 

B-17-20-3 Once you get the dimensions correctly marked on the wing, following the lines to make the actual cuts is easy.

 

B-17-20-4 Now I have to think ahead a bit. Because the inset face of each vent lies at an angle to the surface, I am making corresponding beveled cuts at the rear edges. Watch to see how this works out.

 

B-17-20-5 An emery board becomes the ideal tool to clean up and define those beveled cuts.

 

B-17-20-6 Those holes I just cut into the wing still look too much like holes I cut into the wing. The inside of each full scale air exit is defined by a sloping “ramp” of sheet metal, so I need to do something to make my model look the same. More of that .007” aluminum sheet I’ve used already in other places is the answer. Here I have used a strip of tape to mark off a piece just “deep” enough to match the width of the exit holes, and I’m scoring it so it will break free neatly.

 

B-17-20-7 When I cut off individual pieces to length, they look like this. I used Deluxe Materials Roket Rapid (thick) to stick them in place.

 

B-17-20-8 For now I’ll give each bank of openings a generous brush coat of Stits Poly Spray as a primer that will highlight any big errors.

 

B-17-20-9 Let’s move on to the engine exhaust/supercharger assemblies that are provided in the kit as moldings of lightweight white plastic. Knowing that they weren’t likely to stand up well to the cutting and modifying I planned, I chose to use them as molds in which I can cast four much stouter supercharger assemblies with Stits Lite Fill epoxy (the blue stuff).

 

B-17-20-10 Here’s a shot of one of my reference photos of the full scale assemblies I want my new epoxy moldings to look like.

 

B-17-20-11 See how well that process reproduced the correct shape in a part that won’t split or collapse when I cut and sand on it.

 

B-17-20-12 More of that red auto body putty makes it easy to fill in the few bubbles/voids I allowed to creep into the molding job. It turns out that the exposed portion of the outboard pair of superchargers is longer than the inboards, which are abbreviated to clear the landing gear and will require that I add “extra” exhaust housings on the sides of the No. 2 and 3 nacelles. (I’ll get to that later). However, according to my references the actual exhaust outlets look very different from what is represented by the plastic kit parts. Study the reference images and see how I managed to do a fairly simple job of representing them with some aluminum tubing attached to the cut-off moldings.

 

B-17-20-13 The original kit design calls out for you to stick the supercharger moldings to the undersides of the respective nacelles. A quick check of the reference photo shows that this approach is not going to look right. Here’s how I decided to fix that. I traced a pattern just enough larger than each molding to represent the edges of the openings in the skin they’ll fit into onto some scrap 1/64” plywood…

 

B-17-20-14 …and used my scrollsaw to cut out four copies, like this.

 

B-17-20-15 See what happened next. I taped each cutout in place and traced its outline onto the correct nacelle in turn. This happens to be the No. 4 (outboard) nacelle. Remember that the outboard superchargers are going to appear larger.

 

B-17-20-16 That’s what I’m working on here. I’ll put the 1/64” plywood pattern aside for a moment, then you’ll see why I made more than just the simple paper pattern.

 

B-17-20-17 Let’s make a hole! An ordinary No. 11 hobby blade is the best way to follow those curves.

 

B-17-20-18 Now I lift out the piece of surface skin that’s been cut away and discard it.

 

B-17-20-19 This is why I made those patterns the way I did…each one fits into a recessed cutout in its respective nacelle to serve as a “floor” for the supercharger molding.

 

B-17-20-20 Getting those plywood floors set deep enough inside each nacelle to look right leaves gaps. With some extra work I could clean them up to look “exact scale”, but I have compromised the integrity of each nacelle by cutting a big hole in it and I want to restore some of that strength.

 

B-17-20-21 That happens like this. I used more of that 1/64” plywood cut into strips across the grain so they would bend easily and fitted them into each cutout in turn like this, using various grades of Roket CYA to hold everything in place.

 

B-17-20-22 That last image was an outboard (long) cutout. Here’s what the shorter inboard cutout looks like before I add the 1/64” plywood liner.

 

B-17-20-23 Let’s back up a bit. Here’s a clearer look at how I assembled the liner in the other (long) outboard nacelle cutout…

 

B-17-20-24 …and then the same job on one of the inboards. Can you see the main landing gear ort of hiding nearly out of sight on the left?

 

B-17-20-25 All assembled up to this stage of the job, the underside of the right inboard and outboard supercharger cutouts look like this. As you can see I have some trimming left to do.

 

B-17-20-26 These short, curved-blade snippers are the safest way I’ve found to trim that long, thin overhanging edge of plywood without risking splitting it.

 

B-17-20-27 With the plywood trimmed down close to the nacelle, now I can safely block sand the edges completely flush and smooth.

 

B-17-20-28 That job came close, but it wasn’t perfect. I used more Stits Lite Fill epoxy to fill in the last few stubborn crevices.

 

B-17-20-29 As I have managed to do in the past, I finished sanding that epoxy filler job off-camera where you didn’t get to see it, and then I used thick Roket CYA to fix all of the four supercharger assemblies in place and gave the whole deal a generous spray coat of Stits Poly Spray primer. Here’s the No. 2 (left inboard) assembly all ready for some of the fine detail work that comes later…

 

B-17-20-30 …and, the left outboard supercharger looks like this at the same stage of completion. We will get some more fun stuff done next time.

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