Scratchbuilding Treehawk from Gerry Andersons Terrahawks

Scratchbuilding Treehawk from Gerry Anderson & Christopher Burr's Terrahawks

The first task was to draw up the blueprint and luckily I had a photocopy of the original working drawing to guide me. So I just had to spend a few hours comparing it to pictures of the finished studio model and altering it in a few areas to match.
To start the model I formed the basic hull shape in Balsa wood. As the hull has a simple triangular cross-sectional view and flat sides for over two thirds of its length I quickly blocked it out just using three pieces of 1/2-inch Balsa and some internal triangular supports. All I then had to do was round off the edges and flatten the top for the cockpit area.

The nose section was then carved from a collection of pre-cut Balsa sheets which were glued together to form a solid mass. This was done by first cutting out the side profile from a single sheet of wood that became the centre of the nose. The spaces on either side were then filled in with horizontal layers of Balsa cut to the shape of the top view plan. This gave me the general shape required so again I just had to round off the edges which with soft Balsa doesn't take that long. In fact the problem with Balsa is that it's often too easy to remove more wood than you need to, which is why many model makers prefer harder woods. Unfortunately the opposite effect can then manifest itself as often not enough material is removed and the models can end up looking a bit square and blocky.

With the basic shape now formed I would usually make plaster moulds and cast the model in fibreglass, however as I had no intention of ever building a duplicate I decided not to waste any time and just use this master pattern as the final model. So the soft wood was given three coats of SP113 epoxy resin and then rubbed down with wet & dry paper to create a nice tough smooth finish.

I don't really like using hardwood, but at this stage it was necessary because I needed to use it to make the two side fairings. These parts were created from one-inch dowel that I split down the middle and glued to the sides of the hull, then P38 filler was used to blend the parts into the rest of the fuselage. These hardwood fairings took a lot of effort to shape and when they did finally look correct I then had to drill out and remove the front sections as they form part of the undercarriage.

The ragged holes in the fairings were smoothed over and reformed with car filler. Then the area was carefully covered over in electrical tape, more filler was applied and the rough wood pieces that had just been removed were pushed back into place. After the filler had set the surplus bits were cut away and the wooden footpads prised away from the surface of the tape - that had acted as a barrier to prevent the filler adhering to the hull.

The undercarriage parts could now be sanded down to their correct shape whilst always checking that they still fitted perfectly into the recesses. The wooden parts were coated in resin, sanded again and finally spray-painted.

The next step was to form the top section and wing areas in mostly 2mm Plasticard with the recessed spaces having to be cut out of the wooden hull. The wings themselves were made from two layers of plastic with the fins being cut from Perspex and shaped on my beltsander.
I spent a great deal of time on the wings and the hinges as they had to move up and down with the minimum of gaps showing. The hinges themselves were custom made from Brass rods, tubes and sections of thin strip. It was only after I had finished that I realised it was all a waste of time as it would have been far easier to have detachable wings that could be set in either the open or closed position. Doh!
Detail inside the wing recesses had to be invented and was simply kit-bashed from two sets of identical parts from Tamiya tank kits and the Airfix girder bridge..

The resin coated wood hull was given several coats of spray filler and then sanded down, any minor pinholes or blemishes would show up at this stage and could be fixed. The wings were now carefully attached and the gaps around the edges, especially next to the hinges, were filled to achieve a close fit for the moving parts. The cockpit area was given some detail and outfitted with a pilot figure in line with the original design. (In later episodes the cockpit became a two-seater) The transparent window area was heat formed from 0.75mm plastic, glued in place with two-part quick setting epoxy and blended into the rest of the upper structure with car filler.
On the original model I believe the transparent moulding extended back to the start of the wing section. This is often one of the different techniques between professional and amateur model makers. Amateurs tend to come from the 'Airfix' school of thought and just build the visible window areas, trying to insert bits of transparent material into gaps in the models surface while attempting not to get glue marks on everything. Professionals often mould the whole area from transparent material and then just mask off the windows during the painting stage. If you can mould the larger parts its a much easier way of doing things..

The last major piece to be built was the large engine bell at the rear of the model. To make this part I firstly glued a smaller rough basic shape to a wood base to form the core, then cut the outline shape from a piece of 2mm Plasticard which had a pin fixed to the centre which could be inserted into a hole drilled in the top of the core. Wet plaster of Paris was then applied to the core and the plastic stencil rotated to form the desired shape. This plaster master wasn't good enough to use itself so I then heat moulded a sheet of Plasticard around it and used this to cast a duplicate in P38 car filler. This filler master could be sanded and reshaped to the correct dimensions, and when it was done a plaster mould was made and the final part produced as a thin fibreglass casting.
The only kit parts on this model are here in the open rear end, four Airfix Space Shuttle solid rocket booster nozzles and an engine bell from the Revell Lunar Lander.

The model was now sprayed with cellulose motorcar paints, Signal Orange (correct) and Silver Fox - which is a little bit wrong because it's too light and I've had to heavily weather the model to try and correct it.

Panel lines were drawn in using a standard black biro and I've lightly scored the surface to catch some of the weathering.

The Terrahawk markings were photographs, taken of the emblem printed on the back of a record sleeve, which I had retouched to correct for colour defects. As the photo paper isn't as thin as a decal I tried to minimise its extra height in the painting stage. By applying masking tapes to the model, cut to the same shape as the Terrahawk symbols, I could create slightly recessed areas in the finished hull surface that the markings could fit into.
The only other markings on the model come from the decal sheet of the Airfix 1/24th scale Harrier. .

The last problem was deciding what to do with the undercarriage, as I didn't want to fix it in either the up or down position. In the end I decided to construct the legs from an assortment of brass tubes and Perspex blocks that can be pushed together or taken apart at will. However the model looks far more interesting with the legs down, so that's its normal appearance.