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Aviation History
1984
1984 - 0762.PDF
Chinook's trial by ice All-weather capability is one of the ZA most important assets that any •"• aircraft can have, but it has never been achieved. There is no aircraft in the world that cannot be grounded by some meteorological condition, but the lower this possibility, the better. Some aircraft are termed "all-weather", but what is really meant is "most-weather". Poor visibility, windshear, turbulence, etc, all limit aircraft operation, but perhaps the most restricting condition for helicopters is icing. Regulations governing the flight of helicopters in icing vary among countries and among civil and military operators. No British military helicopter is cleared to fly in icing below —10*6, and few are allowed to remain in icing for long. Wg Cdr W. A. "Dick" Rich ardson, the RAF's Chinook liaison officer, says "we have a great need to expand our flight envelope. Our [helicopter] clear ances always quote a minimum cloudbase, so if severe icing is encountered our aircraft descend into clear air. Without rotor de-icing we believe we're limited in the wintertime support we can provide". To correct this the RAF is spending $12-6 million on a programme run jointly with Boeing Vertol and the UK Ministry of Defence, to develop a Chinook de-icing system which should lead to a clearance for continuous operation in severe icing down to -20°C outside air temperature. US Army Chinooks have been cleared for operation in light icing since the mid- 1960s. Trials with CH-47s were made in 1978, 1979, and 1980, using natural icing and a helicopter-mounted icing spray rig. 1160 FLIGHT International, 28 April 1984 An RAF Chinook has been equipped as a flying icing laboratory to develop a de-icing system. Ian Parker reports from Nova Scotia. Icing poses a problem for helicopters because few de-ice and anti-ice systems have been developed. There is no intrinsic disability in rotary-wing aircraft- helicopters shed ice better than aero planes because of the centripetal effect of blade rotation and higher vibration levels. But if an anti-ice or de-ice system is required on a helicopter there are prob lems in connecting the rotating components to the stationary parts. In fixed-wing aircraft four systems are in common use—fluid, pneumatic boot, electrical (usually propellers only), and hot bleed air (turbines only). But the mechanics of connecting a fluid, pneu matic, or hot-air system to a helicopter rotor blade are complex. Electrical slip- rings are commonly used, and electricity is the easiest way of providing energy to clear ice from a helicopter rotor blade. Controlling the pattern and the rate at which ice is removed is important. Simply leaving the heater mats on would cause Top RAF Chinook number 20 (ZA708) has been equipped for the trials. Right The best icing is often found in the bottom left area where damp air comes off the Bay of Fundy and is lifted over high ground. Local air traffic control has been very helpful, allowing the Chinook to fly unrestricted within a chosen area
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