Hydrodynamic testing

Aircraft ditching survivability testing. TRaC's test expertise incorporates a wealth of experience in hydrodynamic fixed-wing and helicopter crash testing through access to world leading test specialists and test tank facilities, assisting in fixed-wing certification for over-water flight, and assisting manufacturers or airlines in obtaining certification to travel long distances over water.

The hydrodynamic test facilities and specialists made available through TRaC are unique in their ability to provide the only commercial access in the world for testing the ditching and flotation characteristics of both fixed wing and rotary wing aircraft.

Historical Background

Interest in water borne behaviour and subsequent crew egress and survival really increased during WW2, with the need for routine long range missions to Europe. This was also a period of development and big technological advance in sea planes and flying boats.

Through the next decade the helicopter was refined and volume production commenced. This brought a whole new set of challenges for water alighting and survivability as, unlike fixed wing aircraft, the helicopter has a high C of G and has little natural stability in roll. There are some advantages if the pilot retains control, as rate of descent and forward speed can be controlled. However on touchdown, rotor braking has to be very delicately managed to avoid rapid de-stabilisation and potentially catastrophic blade impact.

Summary of Testing Process

Testing using scale models, normally in the scale range of 1:8 to 1:15, fitted with instrumentation suitable to measure the models behaviour. Bespoke miniature sealed on-board data loggers are utilised to record this information.

Hydrodynamic testing For helicopter flotation evaluation, the models capsize boundaries are established and then it is floated at various headings in random Sea States representative of open sea/ocean conditions up to a maximum achievable in the tank which is generally around SS 5-6; a significant wave height of up to 5m or so full scale. A record of performance is kept using digital video and stills.

For helicopter ditching, the model is often fitted with a dynamic working main rotor which has to provide 67% lift. The model is then suspended from a towing carriage capable of design forward speeds (up to 55knots for modern rotocrafts), accelerated to steady speed and released into the tank both in calm water and regular waves. Testing in waves is conducted on all four elements of the wave cycle as impact levels vary hugely.

For fixed-wing aircraft ditching, a large diameter tank is required to launch dynamic scaled models into the water by a gravity-powered catapult at a speed of up to 30 m/sec. Two wave generators can produce waves up to 9.1m in length along and across the basin, simulating head and beam seas as required. (Floatation testing is not required owing to the natural lateral stability and buoyancy of fixed wing aircraft.)

TRaC can offer a this full range of services for hydrodynamic testing from test planning to production of the scaled test model to production of final test reports under the control of a dedicated project manager.

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