Friday, September 24, 2010

Scratch Building a 1:600 scale HAS complex (Part1)

No modern military airfield representation is complete without a HAS complex. I have not seen any commercially available 1:600 HAS models apart from some sold by PicoArmour but they look a little crude for my liking. So if I want to build my own (cheap) HAS complex then then what do I need to consider?
  1. What do they actually look like?
  2. What can I make them from?
  3. How can I mount them?
  4. How do I represent Taxiways and standings
  5. Environmental setting
HAS appearance and dimensions
I have scoured the internet for information relating to HAS (also known as TAB-VEE or PAS) and the design I wanted to represent was the US/UK 3rd generation types introduced in the early 1980's. They supplemented rather than replaced the indigenous UK first generation in the UK and Germany - I have seen an RAF Laarbruch photo of the both types next to each other. I think the change in design away from a half hexagon was more to do with the available internal space, i.e. there was room for an aircraft and the swinging cat, rather than improved protection offered. Incidentally, during tests on the American version I understand that they were demonstrated to withstand a 500lb bomb direct hit and a 1000lb near miss.

My choice of the 3rd generation type was due to their wide distribution across Europe giving a greater chance of appearing in a scenario and the easier looking construction. They have a semi-circular dimensions with externally braced, centrally split, sliding doors but with different design exhaust ports distinguishing the UK and US variants. I have failed to find any dimensional drawings and the only information I have is on length and diameter (37.5m by 23m / 120 feet long x 70.8 feet wide), I assume relating to the tubular part only. However, I have found a number of aerial photographs with aircraft parked out front so as long as the finished article looks right then that is good enough for me.  

Unibond 'No More Nails' glue tube
My first task was to find a tube that was of the right dimensions. Having looked at various bottle tops I finalised on an empty glue gun tube. I split the tube length ways and then divided it into 6 equal sections (73mm long x 50mm diameter). I used both hacksaw and Stanley knife to achieve this but I will admit that this produced some rough edges that needed sanding down but illustrated that I had chosen a robust material that held it's circular shape well.

I then offered the resultant semi circle up to some thin polystyrene (a frozen Pizza packaging base) and pushed to give an indentation. Once cut out I used my favoured 'No More Nails' glue to fix this together. As I was making a prototype I only advanced with one shelter to iron out the problems.
The Shelter 'closed'

Shelter with Lego Doors (red) and exhaust Port (blue) 
Next up I embarked upon the door and exhaust port design. Thanks must go to my son, Jacob, for allowing Dad to use his Lego in the design process. I duly constructed a solid door profile (20mm deep by 50mm wide), having long given up any hope of making the external bracing and a jet exhaust port design (45mm deep by 40mm wide).

My initial goal was then to take the Lego items to create moulds for use with either plaster of paris or Resin. Having never done this sort of thing before I was in full on experimental mode.


Exhaust Mould
 The door mould was constructed out of Milliput and the exhaust out of air drying clay. I tried both out with plaster of Paris and both took several days to dry out and the result easily crumbled when I came to try and extract the plaster cast. Does this stuff have a shelf life like building cement? (I have since use plaster from a dinosaur fossil science set of my son's and it seemed to be ready to take out of the mould within an hour).

Door Mould
 I also damaged both moulds trying to get the casts out. The Milliput one has a bit of inherent flexibility whereas the air-dryng clay is brittle. Having subsequently asked about at my gaming club the recommended approach was to use latex rubber moulds. This smacked of professionalism and as I was running out of time but only needed 6 sets of both. So necessity became the mother of invention and I went back to the drawing board. I took totally different directions on what proved to be my final solutions.

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