Build your first flying scale model - Chapter 3 - Fuselage assembly

Having successfully completed the first fuselage half, we now have to make an identical second one if we want to ensure a square and true fuselage. So, pull out all the pins, carefully remove the clingfilm without disturbing the plan. Now place the completed fuselage half over the plan, and cover it with the clingfilm. You should be able to pick up the original pin holes in the plan around the outside when you pin it down, through the clingfilm.

The K1 pieces and longerons are placed exactly over the those in the first fuselage half. Again, angled pins on the inside of the frame can be used to hold the strips down. Add all the spacers and diagonals, plus the nose sheeting. Be especially careful at the nose and tail to get the uprights exactly matched to the other half.

When it is dry, you can remove the pins and take off both halves.

As an aside, one advantage of stripping your own wood is that you can be fairly certain that if the strips were cut from the same part of the same sheet, they will be of the same stiffness and strength, and this will give you the best chance of getting a straight and symmetrical fuselage.

It is worth spending a bit of time trimming and cleaning the frames up, removing excess glue with a sharp knife blade, and giving them a bit of a sand to smooth away any steps or rough areas.

One thing I like to do (and you may well think this overkill) is to gently sand down the frames on a sheet of well used 360 grit wet and dry paper which has been glued to a Perspex offcut. This is what I used to use to sand my plastic vac-form kits on, but it works just as well with balsa parts (as long as you do not try to use it wet). The advantage over the emery boards is that there is no danger of digging a corner in, or accidentally sanding one area too much. I use a gentle circular motion, and apply a bit more pressure to problem areas (e.g. hard lumps of glue). Do keep checking to make sure you have not gone too far though. I confess to being very, very fussy about the smoothness of my airframes, as this gives you the best chance of a neat and wrinkle-free covering job. This sanding method is very helpful for removing any steps that may be present, for instance an upright standing slightly proud of a longeron. I guess you really only need to sand the outside faces, but as I said, this is perhaps an area where I am a tad obsessive!

To begin assembly of the fuselage, you will need to cut out parts F.7 and F.8. Test fit them to the fuselage halves, and adjust the slots if necessary to get the bottom of the formers flush with the bottom of the fuselage frames.

There are a couple of ways of initially joining the fuselage halves together. One method would be to glue F.7 and F.8 to one half, set at 90 degrees, then add the other half. Make sure the frames are parallel when viewed from above, and that the top longerons of both halves are parallel when viewed from the side.

I think a more foolproof way is to join the frames at the tailpost, lining up the top longerons so they exactly match, then gluing in former F.8. Check from the top that the triangle you have formed looks symmetrical when viewed from above.

When dry, put some glue on former 7, and squeeze the fuselage halves together at the front until the longerons and keels are snugly located in the former cut-outs. Hold until dry.

I confess this was the point where I had my first breakage. Because the grain in formers 7 and 8 runs vertically, they are prone to splitting if you squeeze them from the sides too much. Needless to say, that is exactly what I did. The lighter the wood you are using, the more of an issue this will be.

This photo shows the fix, which I did after repairing the former. All you need to do is glue a strip of 1/16” square balsa strip across the bottom at right angles to the grain. I also did this retrospectively to former F.8. Remember the former could split after you have finished the model if you hold it a bit too tightly when launching, for instance, and it will be much more difficult to repair then.

The next former to be added is F.4 at the nose. I used balsa cement, and held it in place until the glue set. The photo shows that I have cut as large an opening as I dare, to make it easier to get the rubber back into the plane after stretch winding. The small thrust button hole shown on the original part would be hopeless. The slot at the top centre has been reduced to just 1/16” deep, so the corresponding keel K.4 will have to be adjusted to suit.

Completing the fuselage is now just a matter of filling in the spaces with more formers at the top and matching cross pieces below. After cutting out the remaining formers from the sheet, I reinforced them with 1/16” strips as shown to stop me accidentally splitting them during assembly. If you cut the matching 1/16” cross pieces to exactly match the formers, you will ensure your fuselage sides remain square (you can see these laid out under their corresponding formers).

Here we see the fuselage with all the formers and cross pieces in place. The front upper keel F.4 has been also added, plus the centre top 1/16” square stringer behind the cockpit. These stabilise the structure nicely, before the rest of the stringers are added. To get the rear upper stringer dead straight, I found I needed to cut the slot in formers F.10 and F.11 a bit deeper.

The kit plan seems to show the rear stringers just sort of vaguely ending in free air somewhere in front of the tailplane, so to tidy up this area, I added a piece of 1/16" x 3/16" soft balsa just in front of the 1/16" square cross piece, as shown here. It was notched to fit between the longerons, and sticks up 1/8" above them. A 1/16" deep notch was cut at the centre to receive the top stringer.

As mentioned before, the front of F.4 needs to be cut away inside to clear the enlarged nose opening.

The upper 1/16" square stringers can now be added. If you add them in pairs, alternating between the left and right sides, this will give the least risk of introducing distortion in the fuselage. The wood used for the stringers can be lighter stock than you used for the longerons, as they do not have such a structural role.

The stringers underneath the nose were left off at this stage, until the undercarriage had been attached.

A dry run trying out the stringers in the former slots will show if you get a nice smooth run front to rear. If the wood seems to be being forced out of line anywhere, open up the slot at that former in the appropriate direction until everything lines up nicely. Don’t worry about leaving a gap at one side of the slot, as we will be sanding many of the formers away between stringers later anyway. Note that I have not worried at all at this stage about trimming the stringers to an exact length - the excess can be trimmed and sanded flush later.

This photo shows how I ended the stringers in front of the tailplane location. The outermost ones have been chamfered and glued to the top longron, and the ones inboard of these have been let into the balsa strip added earlier. It will all be sanded smooth later.

This photo shows the most extreme example of slot enlargement I had to do (on former F.5). Although not absolutely necessary, I filled the gaps in this case with scrap strip. The small pieces were trimmed behind the former later (longer lengths are easier to handle).

You might also spot that I (deliberately) broke the top two stringers at the position of the wing leading edge, so I would get a completely flat run under where the wing sits. If you just let the stringer run smoothly over this former, it would bulge up and interfere with the bottom of the wing (or am I being just too darned fussy again?)

In case you were wondering about the backwards lettering on the formers, this is due to the method of transfering the patterns to the wood. As the paper is placed face down on the wood, you get a mirror image produced of any lettering.

In the next chapter we will tackle the undercarriage.

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