CRREL has assessed thermal deicing methods as a substitute for fluids
(Ryerson et al. 1999). These include infrared deicing and hot air deicing.
Thermal methods are very effective deicers except, without proper control, they
offer opportunities to overheat composite surfaces, especially rotor blades, and
perhaps cause delamination. Another problem is that the epoxy matrix of
composites thermally expands and contracts at a different rate than the glass or
carbon fiber matrix. Thus, given sufficient heating and cooling cycles, com-
posites could weaken internally. However, given proper control, aircraft
composites may not be damaged by thermal methods.
Infrared deicing systems have the potential of rapidly deicing helicopters,
perhaps in only 1525 minutes, if the entire aircraft is heated at once (Ryerson et
al. 1999). However, water does run into quiet areas on aircraft after snow or ice
melts, and subsequently can refreeze during taxi or in flight. Prevention of this
problem would require application of an appropriate anti-ice fluid after deicing.
In addition, portions of rotor blades, for example, typically deice and dry before
other portions. Areas that dry rapidly heat in the infrared energy, while those
areas covered with ice or snow are 0C or colder. If heating continues to melt all
of the ice and dry the blade, then portions of the blade that dry first will have a
tendency to overheat. The potential for blade overheating must be solved if
infrared deicing is to become viable for helicopters.
Hot, forced air deicing is also a potential substitute for deicing fluids. Hot air
may be taken from either an AGPU, or from an aircraft-mounted auxiliary power
unit (APU). Both power units are operated by a small gas-turbine engine, and
bleed air is used as the hot air source. Though bleed air pressure is often less than
35 psi, air flow can be 1500 cfs, and temperatures can be as high as 200C.
Though air temperature exiting the end of a 10- to 20-m hose on a cold day can
be considerably cooler, the air is still too warm for rotor blade composites. If a
deice nozzle is held close to a blade surface to heat the edge of an ice mass, dry
areas of the blade adjacent to the ice or snow can dangerously overheat. With
proper control, however, hot, forced air deicing systems could be very effective.
An entire helicopter possibly could be deiced in about 90 minutes with a single,
hand-held hot-air device.
There are a variety of options for deicing Army helicopters with non-glycol
techniques. With relatively minor additional technical development the Army
could have several effective deicing systems available for rotorcraft flight