It was the promise of an expanded defence force that helped New Zealand’s Labour party win the day in the 1935 election. The government at that time was particularly committed to an improved military air service, and accepted an expansion plan for the service prepared bt RAF Wing Commander Ralph Cochrane at the end of the same year. The plan included several new airforce bases, including one near the small township of Bulls -Ohakea.
Aircraft hangars two and three at Ohakea were constructed between 1938 and 1939, and their design is replicated in similar structures at Whenuapai air base in Auckland (with modifications for lower-strength Auckland soils), and in Karachi (Pakistan) and Hyderabad (India). Designed by chief design engineer CWO Turner of the Public Works Department, the hangars each have huge two-hinged arches supporting reinforced concrete roofing – a relatively new innovation at the time.
Even the hangar doors were constructed of concrete.
Ohakea hangar in operation
The hangars at Ohakea span 67m in width and are almost 20m high. By comparison, the three-bay Brabazon Hangar at Bristol’s Filton Aerodrome was at the time of its construction (only a year later, in 1940) the largest hangar in the world. The Brabazon hangar measures an impressive 350m in length by 35m high by 80m in width.
An important consideration for the designers at Ohakea was the size and strength of the new structures. Turner worked with cardboard models as part of the design process to ensure internal space was efficiently and appropriately allocated.
Most hangars are built of metal, although wood and concrete are sometimes used. The word ‘hangar’originates from a French dialect word for cattle pens, though I’m not sure the Ohakea pilots would appreciate the inference that their aircraft are old cows! The word actually refers to the cattle pen French pilot Louis Bleriot used to store his crashed monoplane in northern France in 1909.
The ohakea hangars were designed specifically to house 30 long-range Wellington bombers (which in the end never arrived, being donated instead to the RAF on the outbreak of WWII). They also needed to be able to withstand bomb splinters in case of enemy attack. The hangars were in the end never tested by a bombing attack, although one hangar at Whenuapai proved its strength by surviving an aircraft crash during the war – with only minimal damage incurred.
The Ohakea Base at Bulls
The decision to build the Ohakea hangars to a reinforced concrete design came after in-depth consideration of a variety of alternatives, including steel and ferroconcrete designs. The final decision came down to availability, with structural steel (unlike the alternatives) able to be sourced without delay in the quantities required.
The Ohakea hangars were the first of their type to be constructed in New Zealand. Although similar monocoque, or single shell (from the French) structures had been built in NZ before the 1930s, they had typically been built of steel, rather than concrete. The concrete reinforced variants built at Ohakea were a novel innovation.
Reinforced concrete monocoque structures are strong and robust, qand provide a large clear space (no central support pillars) for storage beneath. They support the structural load through the structure’s external skin (roof) rather than by using an internal truss (fram) or posts with a non-load-bearing skin on top.
Hangar and control tower
Monocoque construction is used in areas as diverse as architecture, car and aircraft manufacture, small boat construction (such as kayaks), and for motorbike frames. Monocoque construction was first widely used in aircraft in the 1930s.
For the Ohakea hangars, each concrete pour had to take place in one operation. Formwork (into which the concrete was poured and which created the final shape required) was initially paper over wood. However, the paper stretched when wet, leaving patterns on the concrete, and so eventually plain timber formwork was used instead.
The Ohakea hangars were reroofed with steel in the 1990s, and also underwent strengthening work at that time. Despite their age, they continue to serve their purpose, as well as providing an iconic backdrop to a strategic airforce base.
© Karen Wrigglesworth and Geeky Getaways, 2011.
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