I've wanted a good model of this craft for a long time and as a result I have constructed several over the years. Unfortunately although it looks to be a simple design it's a lot harder to build than most - and all the replicas I have seen to date simply look wrong to me. There's something about the shape that is very hard to pin down - and we aren't the only ones to have a problem because the original studio model was destroyed during production and the replacements never looked the same - or as good!
I decided that I wanted to build my replica to the same size as the original big model, the only problem being that we don't know for certain what that size is! Best guess then is somewhere around 36-38" in length.

The Build

by David Sisson.......See also Fab 58 Nov 2007

I started by drawing a blueprint - and then redrawing over and over again until I was satisfied, although in the end you just have to build the thing, see it in three dimensions and then decide if you're right or wrong.

The plans were cut out and traced onto sheets of MDF, these were then cut up and assembled using a hot-glue gun to form the overall shape of the main body.

The gaps between these sheets were then filled with blocks of balsa wood which could be cut and sanded down to give me a solid shape to work on. The one trick here is to ensure the wood grain runs in the same direction otherwise it becomes difficult to shape properly. As it is you still find that some balsa wood is softer than others and sands down at different speeds giving an uneven finish. A different technique here would be to fill the gaps with foam and skim over with a layer of car filler.

After the initial sanding stage I split the hull into its three basic pieces and worked on them individually, building some parts up using car filler and reshaping them over and over again. The three sections were often put back together again to ensure the overall shape still remained true.

There are two problems with this model, the usual one of trying to get the shape right and the added problem that the middle of the model, the pod, has to drop out.
I decided to simplify the process and forget about the pod to a degree by building the model twice! The first model to be made from these masters would be a single piece 'test' model to check the shape - then I could adjust the masters if necessary and make a second version with a detachable pod. This increased the work considerably but meant I could sell the first one to recoup all my costs on the project.
The following photographs are from both models so I hope they don't confuse you.

Work on the masters continued for quite a while as I was constantly changing the shape - which was difficult with the MDF ribs protruding although they did act as a guide to help keep the model symmetrical.
Only one side engine boom needed to be made, from layers of 1/2-inch balsa wood, as each side is identical. When I was finally happy with the shape the balsa wood masters were coated in resin and sanded smooth. Then plaster moulds were taken of each part and fibreglass castings made, six in all with two required for the pod.

I decided to mould the pod with the split line down the sides. The parts were cast quite thinly, partly to keep the weight down and also because the edges are visible on the finished model - however a series of grooves had to be cut into the finished surface so some depth was needed.
The position of the grooves was carefully drawn on to the outer surface, a tricky task as the changing shape of the pod means the distance between them varies constantly. The lines were then cut in with a knife, deepened with a hacksaw blade, widened with the edge of a metal file (to create a v-shape) and then finally softened by rubbing over with wet & dry paper.

The flat bottom of the pod did have a slight bow in it that needed fixing, here I drilled and screwed it to a flat surface then applied more fibreglass to the inside, sandwiching some horizontal steel rods in place, that straightened it out. The two halves were superglued together and a strip of fibreglass added to the inside joints to lock them together. I then found that this finished part was not symmetrical but was pulling to one side; luckily this was simply cured by pushing the end bulkheads into position. As the MDF was proving to be a good modelling material I used it again for these pieces although it has to be treated with a resin to give a good surface finish. At this stage the front piece was not permanently fixed into position as I still needed access to fit the interior detailing.

To assemble the model the front and rear sections are attached to the pod, just using tape, then the side booms are glued into position - securely to the rear piece but only just overlapping onto the front section. The connection here is only secured by building the engine intake area out of filler.
This area is a weak point in the design and broke often on the studio models during production.

Picture right; Here you can see that the bulkhead to the front section has been fitted, again made from MDF. This part of the model can only be briefly seen in a couple of episodes, such as 'Day of Disaster'.

The next step was to form the raised lip on both sides that mergers the booms to the side of the pod. This was again created using filler, built up in layers to the correct shape and sanded smooth. Clear glossy adhesive tape (Sellotape) was applied to the sides of the Pod during the process to prevent the filler from sticking to it.

With this all done the tape could be peeled away and the pod removed. Although the pod appears to have flat vertical ends it is best to angle them slightly towards the middle, (so the top of the pod is shorter than the bottom) this helps the pod to slot into place more smoothly.

The wings and tail section were again fabricated in MDF sheets, longer than required so that a good one-inch or more could be buried in the bodywork to anchor the parts in place. The pieces were quickly shaped on a beltsander, before final shaping with sandpaper and then coated in resin.

Getting the tail plane straight was a major effort and required several attempts, here using a template. The problem is that it needs to be set straight from the side angle, set horizontal from the front angle and then not appear to be leaning too far to the left or right.

The tail section also made from MDF sheets coated in resin. Here the round corners are being added in filler - apply a small amount of filler with a finger then push a length of plastic tube into it. When it sets remove the tube and you have an instant smooth corner, just trim off the surplus filler. Car filler is an excellent modelling material, depending on the amount of hardener added it can set very quickly and so doesn't hold up the building process for very long. However you can start work on it before it actually sets as it goes through a 'jelly' stage where it is very soft. At this point you can cut it roughly to shape or trim parts off with ease and it's often better to do it during this very short window period than wait for it to properly harden. One point of warning is that if you put too much stress on it then the filler might just come away from the model and you have to start again.

All the detailed inserts were fabricated in plastic sheeting with brass tubes for the small rear thrusters. The rear panels have a pattern of holes in them, so here I had to make a metal template that I could then use to drill out eight identical parts.

The rear bulkhead was now added to the inside of the model using 2mm Plasticard, this piece needed a detailed recess adding made from an assortment of kit parts.

The hollow side engine booms were also filled in using pieces of waste plastic skimmed over in filler. Then the whole model was coated in several layers of spray filler and then rubbed down with wet & dry paper to a smooth finish. I would just like to point out that this process does take some time to do - I have noticed that some people only seem to spend a short time at this stage and their finished models still look very rough with the scratch marks from the rough sandpaper still visible in the models surface.

The vertical boosters were cut from pieces of metal tubing (the hanger rail out of an old wardrobe) and embedded into the hull.

The area of the hull in the engine intakes has a concave finish. This was done by drilling out the shape and placing a piece of thin Plasticard over the hole, then filler was applied from the inside and as it began to set I simply pushed down the plastic until it bowed into the correct shape. (simple - but the filler does get a bit hot so padding is required)

The window areas were drawn and redrawn onto the model until I was happy with the shape, size and positioning. This took quite a while and I resorted to cutting the shapes of each window out of masking tape and then applying them to the hull in slightly different positions to check that they looked right. Also I held the model in front of a mirror to check that the pilots cabin windows were level - sometimes mistakes show up more clearly when the model is 'reversed' in a mirror and what at first appears to be level to the normal eye view can appear to slant in the reflection.
With the window positions decided I took some long pieces of thin transparent Plasticard and holding the ends played the middle areas gently over a heat gun until the plastic began to sag, then quickly pulled them over the marked areas of the hull until they cooled again and took on the required contours. I made another spare copy as a backup just in case I made a mistake later and damaged them.

Then the three window areas were drilled out of the hull and the interior edges painted black. It was then a case of removing the outer surface edges around the windows to allow space for the plastic to sit in position and be level with the rest of the hull. It doesn't have to be a perfect fit as the glue will take up some room, but some small slivers of plastic were glued into position to ensure the window transparency could not sink too far inwards. Two part 5 minute epoxy glue was used and when set the gaps around the parts were filled in and sanded smooth. Then the window shapes were masked off and several coats of spray filler applied and then rubbed down with wet & dry paper to finally remove any traces of the join lines between the plastic and the hull.

The interior of the pod was now blocked out with MDF and plastic sheeting. Assorted kit parts were used for detailing. The door was made from two layers of plastic, hinged with just a thin strip of folded paper (saves space over real hinges) and stays locked with the help of small magnets.

Finally the rear engine exhaust tubes were fashioned from Plasticard, EMA piping and hamster tubes from a pet shop. I inserted metal mesh into the intake areas, I'm not sure if this is accurate but it looks better than just plain plastic.

The model was sprayed with acrylic motorcar paints. The green colour looked far too bright when it was first applied and so I spent a week dirtying down with graphite pencil, which was sealed on with clear lacquer. I had some Letraset white decals for the Thunderbird markings but not for the large numbers or letters on the wing. Here I cut the shape of the numbers required out of thin plastic, which I then used as a template to carefully draw around and cut out copies from masking tape.

The masking tape numbers were placed on the model and moved around until I was happy with their position (in the series the numbers moved around from episode to episode so there is just a general area that they can go in). Then the surrounding piece of masking tape, that they had been cut from, was placed on the model and matched up to the number - that could then be removed and the area spray painted white. Then wait for the paint to dry and remove tape to reveal a perfect number - easy, but wait for it to dry and pull the tape away horizontally or the edges of the layer of paint can lift up.

Panel lines were drawn on with a biro then a sharp blade was run over them to just cut the surface of the paint. This helps to highlight the lines in the light and catch some of the weathering.

The last things to be made were the four legs. These were constructed from thin brass tubes from a model shop, cut up and superglued together. The feet were soldered from brass plates, then soldered onto the legs which were then filled with resin to make them solid and strong enough to support the model.

The tops of the metal legs are just wrapped in masking tape, increasing the diameter until they form a snug fit inside the support holes.