Shinobi¹ | A Home-Grown Moulded Fuselage
Part I: The Urge
Want to make your own fuselage? Or maybe make a replacement part for a broken model? Here’s how to do it at home using the KISS² method. — JH
I believe that many of you dearly beloved readers have often thought of making your own-design composite model fuselage. Looking at a model you might think: ‘well if I that was a little larger to fit my radio’ or maybe: ‘I wish it had a really strong fuse for my Fred and Barney slope’, or perhaps you just plain want to see your own work flying happily in the blue yonder — the list of reasons to embark on such a project is endless.
Well, if you do have the urge, here I will be writing a series of articles arranged as a blow-by-blow account which will tell you how I made a small fuselage plug, and then successfully manufactured the moulds with minimum tools and a very low investment. I’m not going to deal with it where processes are repeated, but I’ll describe in some detail each new part and process.
Let’s plug away!
The Sketch
I’m not going to go through the procedures that I use to design the plane here (for that, see my design series in the Resources section below), because if you are going to make your own model then you will pretty much know what you want to make. But you’ll need a drawing to work from, and ideally it should have both top and side views. I usually make a 1:1 third-angle pencil sketch of the fuselage to be made on paper — yes, I know, ‘Old Skoo’l, but then I’m an old phart so what do you expect? For those of you whiz kids that are familiar with CAD, then of course you can use that medium to make your drawing, but make sure it can be printed out 1:1.
Advice: Before you start, take time to plan your work step by step. Things like a slip-on nose cone or a removable cap type canopy will have a big effect on what you do and when you do it in the process, but if well thought out can be easy to accomplish.
Keep Calm and Laminate
The first stage in the manufacture is to find some wood that is close grained but not too hard. Goodies are jelutong, and lime wood if you can find them, bass wood is OK — but it can be a bit tough to carve — while balsa is a bit too soft — and expensive. With the wood selected, you need to laminate it into a block that is slightly larger in all dimensions than the shape you want to end up with. A good idea is to use laminations each side of the vertical plane that leave one middle joint as the centre line for reference. Use a good aliphatic wood glue like Titebond, or epoxy and clamp the laminations tightly until the glue is cured.
Advice: The glued lamination lines can be a great help in carving and sanding to final shape. Comparing one side to another or top to bottom you can easily see if the carved curves are different.
Cutting the Outline
Print out or use carbon paper to produce the fuselage side view, and then cut out and stick the cut-out shape to one side of your laminated block. When the glue is dry — I use simple paper glue or kids play glue — use a coping saw, or if you have one, a bandsaw or scroll saw to cut carefully around the fuselage shape, leaving it at least 1/8” (3mm) larger all round. Don’t worry about cutting the top view profile to shape yet — we’ll do that later, after we have made the wing stub block. At this moment it’s a good idea to leave the plug with 90º sides to make cutting the wing stub block orifice out easier.
The Wing Stub Block
This step may or may not be needed depending on your design. I tend to make two-piece wings butting up to wing stubs on the fuselage a la F3F practice, but many people prefer a one-piece wing design with a wing saddle, especially in small models.
Making the wing stub block is not hard but you need to be careful to follow the aerofoil profile as closely as you can. As with the fuselage, a slightly oversized laminated block is needed and the wing profile printed and stuck to it as a guide; or if you want to make it even better, then simultaneously cut two identical wing profiles from carbon or G10 glass fiber sheet and use those not only as cutting guides but also as the actual hard moulding faces.
Use the wing alignment pin holes to line up the two facing pieces. You will also need to cut any openings that will have to be present in the win stubs such as alignment pins, joiner and MPX connector cavity outlines etc. Also remember that now is the time to arrange any dihedral you might want on the wing stub block and do it before you glue the hard faces on.
Cutting the Wing Stub Space in the Laminated Fuselage Block
Use the accurately shaped wing stub block you have made to act as a guide to mark the cutting lines on the laminated fuselage block. Check the alignment carefully, then as with the fuselage outline, cut around the profile — only this time make the cut just inside the marked lines, so a tiny bit smaller than the wing stub. Then carefully remove the excess wood with a rasp followed by abrasive paper until the wing stub fits nicely, but don’t fix it in yet.
Now, using just small dabs of glue, as little as possible, replace the wing stub wood that you have just cut out (not the wing stub block you have made) back into the space in the plug.
Advice: Be very careful and check before you cut the wing outline to make sure that the wing stub profile is correctly aligned along the fuselage blank. Is the angle of incidence (if any) correct?
Advice: Giving the leading edge of the wing stub block a slight upwards angle will result in the model having a small nose-down flying angle — which gives an attractive predatory look when hunting up and down the slopes.
Advice: Don’t fix the wing stub block into the fuselage yet, instead, tack glue the part that you have cut out back into the fuselage. This part will be removed later and is only reinserted to help with the carving sanding of the fuselage plug shape, so just tack it back in — don’t over glue.
Shaping the Fuselage Plug
The best way to continue now is to shape the top profile — or plan view, of the fuselage plug. First stick the paper cutout of the top view onto the top of the plug. It won’t be 100% accurate as you have already shaped the side view — but it will still be a big help. Begin by using a small plane or a spokeshave to shave the plan view sides to shape. You’ll see how the laminations are very helpful as a guide to how much material has been removed on both sides. Alternate between top and bottom, and work slowly as it’s easy to get carried away with a nice sharp plane.
Check your work often during the shaping phase, adjusting your carving tool for finer and finer shavings as the plug takes shape. When you are happy that the profile is the correct shape in both side and plan views, begin to shave and round the corners. You can see now why we tack glued the cut-out wing blank back in and not the actual wing stub. It’s now much easier to shape the fuselage block when the stub block is not in the way; the cut-out will give some meat’ to allow you to shave the curves front to back and carve the shape nicely.
The last part of this stage is to slowly and carefully rough sand the fuselage positive compound curves to shape. Use a sanding block and do work slowly because a mistake here is really quite hard to correct. As my father, a boat builder used to tell me, its ‘glance of eye and touch of hand’.
Advice: Look at the lamination shapes often as you work: are they the same both sides? Top and bottom? If they are not the same then make the correction as soon as you see it. If you forget to do it you could end up with a strawberry coloured face and a banana shaped fuselage. Not recommended.
Advice: Glance often and touch often — be critical, remember what you see, is what you get.
Last Caresses
Carefully carve any other features that you need. In the case of the Shinobi I wanted a tapered tubular rear end to my ‘pod’ design so that I could mate it with a tube to act as a boom and give adjustable length. That done, using a sanding block sand, sand, sand, constantly checking the shape side to side and top to bottom and gradually arrive at the perfect profile you want. Feel it, touch it, caress it, look at it from all angles and make it yours. Use ever finer abrasive paper until the wood has a sheen at about 320 grit. That’s enough — no need to go finer than that.
Advice: ALWAYS use a sanding block and never, never use abrasive paper in your hand alone for shaping and finishing.
Advice: Sometimes a block of rubber like a large eraser can be quite useful as a sanding block in taking off high spots on compound curves as it has a bit of flexibility.
Advice: I often mark lines on the plug with a Sharpie to show that the profile is almost correct and just needs a little final sanding. This helps to eliminate the possibility of over sanding.
Next month— the wing stubs. Thank you for reading and if I can answer any questions, please post them below in the Responses section and I’ll do my best to answer as many as I can.
¹A shinobi was a covert agent or mercenary in feudal Japan whose functions included espionage, deception, assassinations and surprise attacks.Their covert methods of waging irregular warfare were deemed dishonorable and beneath the honor of the samurai. (Wikipedia)
²An acronym for “keep it simple, stupid” which is attributed to the one and only Kelly Johnson, one time chief of Lockheed’s Skunk Works.
©2021 James Hammond
Resources
- The James Hammond Sailplane Design Series Four articles covering all the design nuances of many of the popular RC glider configurations.
All images by the author. Read the next article in this issue, return to the previous article in this issue or go to the table of contents. A PDF version of this article, or the entire issue, is available upon request.
