Ice & Rain Protection, Module 12, Certify66

Notes

Main ideas

Rotor icing is especially serious: ice on the blades disturbs the aerofoil, adds weight, sheds asymmetrically (causing severe vibration) and raises the power required, so many helicopters are restricted from known icing unless specifically protected.
Where fitted, main- and tail-ROTOR BLADE de-icing is usually ELECTRICAL: heater elements bonded to the blade leading edges are supplied through SLIP RINGS on the rotor head and cycled by a timer to shed ice.
Engine intakes are protected against ice and foreign objects by heated/inertial-separator/particle-separator or barrier-filter arrangements; windshields and probes are electrically heated; a windshield wiper/repellent handles rain.
Ice detection warns the crew or arms the protection; pitot/static probe heating prevents air-data errors.
For the B1 technician the blade heater mats, slip rings, timers, controllers and intake protection are the key items.
⚠ Exam trap: ROTOR-blade de-icing is electrical, fed through SLIP RINGS on the rotor head and cycled by a timer to shed ice evenly; asymmetric ice shedding is what makes rotor icing so dangerous (severe vibration).

Solved examples

Why is asymmetric ice shedding from the main rotor so hazardous, and how does a rotor de-ice system address it?
If ice sheds from one blade but not another, the rotor becomes badly out of balance, producing violent 1/rev vibration that can damage the rotor head and airframe. An electrical rotor de-ice system feeds heater elements on each blade through slip rings and cycles them on a timed sequence so ice is shed in a controlled, roughly even manner across the blades, avoiding the dangerous imbalance of random shedding.

Ice & Rain Protection