A finished Shinobi inner nosecone part resting on the mould.

Shinobi | A Home-Grown Moulded Fuselage

Part VIII: In This Final Part of This Series We Make the Inner Nosecone Plug from the Outer Nosecone Plug

Readers who have not already done so may want to read the previous parts of this series before continuing with the article below. — JH

Objective

We want to make an inner nosecone for the new glider fuselage set, but obviously the hardest thing is to make sure the new part will allow your previously produced outer nosecone to fit snugly, and also to make sure there is enough ‘meat’ on the end so that it can be securely bonded to the fuselage pod. This can be a tricky job if starting from scratch, but fortunately there is no need to do that. Already shaped, the outer nosecone part of the original plug can form a perfect base for its inner part. But before we start on that:

Preparation

To make sure that the inner nosecone plug will be the correct shapes and sizes, and will fit nicely, we need trial examples of both parts to fit it to, during the carving and sanding stages. This will also give a great opportunity to try out the new moulds and get some experience.

Advice: I always make the first mouldings transparent so that the inner details and possible flaws or problems are easy to detect. Transparency in this case will also help with the inner nosecone fitting.

The Big Chop

Carefully mark the outer nosecone joining line on your plug, then check it, then take a sharp saw and cut it off! Yes — chop it off. Use a fine-toothed saw and try to be as careful as possible so that the saw kerf does not damage the nose cone or the fuselage pod parts. If you don’t have a really fine toothed saw it’s a good idea to run a strip of tape around the saw line first. Now you can wrap up your fuselage pod plug and put it away for another day — job well done!

Add the Fuselage Register

We need to add a piece on to the back of the plug that on the final moulded part will provide a register that enables the inner nosecone to be securely bonded into the rear pod. To do this, simply cut an extra piece of the same wood that you used for the main parts and glue it on to the back of the new plug on the cut line. I tend to use as much length as I can without getting ridiculous, as the more of the inner nosecone that is bonded into the fuselage then the stronger and more rigid the entire assembly becomes. Essentially this can form a kind of ring spar right on the part of the fuselage that can be prone to breakage, that is, just in front of the wing. Once the glue has set, the extra piece can be carved to the same profile as the rest of the plug.

Cut the Radio Tray

Carefully mark the radio tray area that you want to see on the final inner nosecone plug and then cut it out. As usual, take your time and carefully mark and check the lines before cutting off the unwanted wood. Try to anchor the wood temporarily to the work bench with clamps, and check while you are cutting to make sure your saw keeps to the correct line.

Here the added part glued on to the rear of the new plug can be seen. Also, the radio tray area has been removed.

Carving the Inner Nose Cone Profiles to the Correct Depth

The next part of the process is to begin to carve the new plug from the old plug. There is a trick here that my dad taught me when I was knee-high to a grasshopper that I have found really helpful in controlling the depth of wood to be removed from compound curved shapes.

Take a piece of broken metal hacksaw blade with not too low tooth count — say around 20TPI — and using fast set epoxy, glue two wood 12mm x 6mm (½” x 1/4”) strips each side. Now here’s the trick, you need to glue the strips on so that the teeth of the blade protrude about 1~1.2mm (0.40” ~0.60”) because in this way the blade cannot cut too deeply and will provide a very useful and accurate reference for carving and final sanding.

Two pieces of backing wood are glued on to a piece of fine-toothed hacksaw blade to provide a depth reference saw. Note the blue hacksaw blade protrudes 1~1.2mm past the wood backing pieces. This sets the depth for your initial wood removal and ensures that the depth is even all over.

Okay, now having made your all-singing, all-dancing depth setting saw, begin to make cuts all over the original plug to set the depth for your next job — carving and sanding the final version.

Advice: A neat trick here is to spray the plug all over (lightly) with that old rattle can that you have been meaning to throw away for ages. The paint will settle into the grooves you have made and provide a nice reference ‘grid’ for carving.

Carving off the Excess Wood

Now you should have something resembling the body of a baby crocodile; long; slim and with a lot of sawn scales. Take a razor plane or your favorite carving implement whatever it may be and you are comfortable with, set it at a really fine shaving setting and begin to carve the new curves, by shaving away the ‘scales’. Don’t go too far. Remember there has to be ‘meat’ left for sanding and finishing the new plug.

Sanding the New Plug

As usual, we need to be very careful with the sanding so as not to remove too much material and also to consider how we want to make the actual part later. Sharp corners and angles are the enemy of the glass laminator, and can also be stress raisers and so should be avoided as much as possible. Inevitably there will have to be some corners, wing stub ends, fairing ends and such like, and these can be dealt with by special layup procedures but its best to keep them to a minimum. As the radio tray area does not need to be sharp then we can easily sand in some nice radii to make the eventual part easier to produce.

Here the now extended inner nosecone plug is seen with the parts it will have to mate with. Note that the new plug now has radii at the sides of the radio tray, and has been filled, sanded and epoxy finished ready for moulding.

Use a trial moulding of the rear fuselage pod and the outer nosecone to check the fit, first at the rear where the inner nosecone part will be bonded into the rear fuselage pod. Hopefully the place where you cut the nosecone part off the rear pod will still be visible, and make a good refence for how the new plug fits inside. When that looks about right, start fitting the nosecone moulding over the new plug to check how it fits in the fuselage. It’s a good idea from time to time to fit the inner nosecone plug into the rear pod moulding, and then also try the fit of the outer nosecone with it in place. This will illuminate any problems in the final fit of both parts.

The inner nosecone plug is trail fitted in each of the mating mouldings.

Finishing

Fill any depressions that might have appeared and then fine sand to about 240~360 grit. Finish as usual with epoxy.

Making the Mould for the Inner Nosecone

Here is the Shinobi inner nosecone mould with a part as yet not removed — as can be seen it’s moulded horizontally.

Departing slightly from ‘normal’ moulding practice, the inner nosecone can sometimes be moulded with a horizontal seam and there can be advantages to this:

Remembering that the seam if joined green and overlapped will cure at least double the thickness of the common walls of the moulding. Sometimes it can be a good strength arrangement to have a seam that is not made in the same direction as the rest of the model parts. Obviously, the nose part is the most likely portion of the finished airframe that will constantly have to take a pounding from landings, so having a seam orientated at 90 degrees the other parts of the model can be a good way to distribute those stresses. Also, on occasion if the shape of the inner nosecone is more complex due to special requirements, it could be easier to mould it horizontally; and for both reasons actually I chose to mould the Shinobi inner nosecone in this manner (see key photo above the title).

Left: The parts together — wow they fit! | Right: We have been through the moulding and mould making procedure several times by now, so there is no need to do it again for the inner nosecone. Just follow all the steps for the previous parts and you will be in business.

From an idea — this is an excerpt from Part I — just to remind you how far we have come.

The Sketch

I’m not going to go through the processes that I normally use to design the plane here, 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 on paper — yes, I know, Old Skool, but then I’m an old phart so what do you expect? For those of you whizzkids 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.

The original Hamachi (now Shinobi) drawing. From an idea to the air.

Parting Shot

I do hope you have enjoyed reading this series as much as I have enjoyed putting my experience into words and pictures.

If you have any questions please don’t hesitate to post them to the Responses section below and I will do my best to answer them. Putting them here also means others will benefit from both your question and my answer.

Thanks for reading and good luck with your project!

©2022 James Hammond

All images by the authors. 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.