The UK Defence and Evaluation Research Agency (DERA) has recommended a scheme allowing the Royal Air Force to enhance significantly the safety of helicopters being operated in harsh environments.
Engineers at DERA's Boscombe Down aircraft test and evaluation sector dispatched a fully instrumented Boeing Chinook HC2 to Shearwater Canadian Forces Base in the depths of the Canadian winter, with outside temperatures averaging -12 degrees C.
According to project engineer Mike Curnow, the tests allowed ice-droplet size to be plotted against temperature for a variety of conditions, allowing curves to be drawn in three bands - green, amber and red. Curnow adds that once established, the curves can give the helicopter's air-data system the extra information it needs to predict what type of ice is likely to form and where it will form, and can warn of 'wet snow', which he describes as 'the worst kind'.
The DERA recommendation is that a droplet-size detector is incorporated into the Penny & Giles Ice and Snow Detection System used on the aircraft, and that a new pilot display should be added to indicate where the aircraft is being operated in relation to the icing curves. Curnow concludes that "…it is now up to the customer (the UK's Royal Air Force) whether they want it". Instrumentation includes a "soot gun" to measure crudely the water-droplet size in the air, and a laser-backscatter Nephelometer for more accurate measurements of droplet size.
The problems encountered in such conditions range from snow causing impaired visibility or recirculating in the downwash, causing the pilot to lose ground references and visual cues; through slush ingestion causing turbine-engine flame-out; to accumulated ice breaking off and hitting another part of the aircraft. In addition, aerodynamic performance can be seriously affected, limiting the ability to hover and manoeuvre.
Source: Flight International