Warbirds in my Workshop

David Glen BSc (Hons) MSc, Model Maker, Journalist and Author

Formerly Spitfire in my Workshop

Nose and fuselage balsa blocking

Saturday, 12th October, 2013

By about mid-summer of this year (2013) and by way of diversion from preliminary work inside the incipient cockpit, I returned to the model’s nose and rear fuselage sections to complete, or substantively advance, the balsa ‘blocking out’. The sooner this was done, the sooner I could be reasonably sure of avoiding temperature- or humidity-induced warping of the largely unsupported plywood ‘skeleton’.

From the start I had intended to use a harder variety of balsawood for this model in the hope of ameliorating any slight tendency for shrinkage or scalloping between the ply sections (I had observed this in previous models). Yet, as so often is the case, I fell victim to my own impatience, simply because the soft variety was available in abundance at my local model shop. Only time will tell if there is a further price to pay.

As described previously, I made the nose section as two sub-assemblies so as to more easily cope with the opposing curvatures along the line established by the base of the top cowling. However, before adding any balsa, I reinforced the ply substructure along both mating faces with hardwood batons drilled through to take four steel fixing studs. This way I would be able to remove and replace the top cowling repeatedly during the build, and particularly during the skinning operations. It is also worth mentioning that before blocking out started and at several intervals during the process, I took pause to test fit the major sub assemblies, including the wing centre section, to ensure that there was no induced distortion.

Blocking out hardly requires description, so I will let my pictures speak for themselves, except to say that I tried the relatively new Aliphatic wood glue. This is said to sand well when used with balsawood, and I have found no immediate fault with it. For the most part, once the glue was dry I cut and carved away the surplus balsa as I progressed, coarse sanding the rear fuselage almost but not quite to the ply formers. I would have plenty of opportunity to fine-tune later. As I write in early October, the fuselage is still not fully blocked, and there are gaps left deliberately to allow for future installations, for example around the tail wheel strut. However, I decided to fully finish the nose and cowling sections, partly by way of experiment in my search for the optimum filler. In general I have found that the ‘fluffy’ lightweight fillers used by aero modellers too soft for my needs. So far the results fall in favour of the softer automotive fillers.

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The top engine cowling section is screwed to the building board during the preliminary stages of 'balsa blocking'. Note the sheet of paper to prevent glue from sticking to the board.
The job is now ready for carving and sanding back to the ply edges.
A start is made on the lower part of the nose section.
By now the entire assembly has been filled with balsa and carved and sanded to shape.
Steel studs through integral hardwood members hold the two nose-section sub-assemblies together, and the temporary apertures through which to tighten the nuts are just visible. The trial use of two different sorts of filler is very obvious in this picture.
Meanwhile the rear fuselage has been receiving similar treatment. At this stage the fuselage frames are in position only temporarily.
Time for an inspector to sign off progress to date.
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Mustang in my Workshop

A book to inspire, encourage and empower the enthusiastic model maker to scratch build a masterpiece.