There are so many variables with regard to icing on helo`s that you have to be extremely careful if you enter an icing environment. Rotor icing- depends a lot on the blade section.rotor speed ,and power setting ,but in general,ice will form from about 10-70%span,kinetic heating will stop it forming outboard;the ice formation will/may accrete back to the max. thickness area,and is 10% thicker than the blade thickness,and can project forwards by the same amount in an inverted U shape.It will also stick on blade tape.It may/may not shed .If it does it will be uneven,will increase vibn,may go down intakes/tail rotors etc.The major danger ,however, is that you will get a major Tq. increase for a constant colltve.setting.IF the tq. rises/falls periodically you may be OK,if it doesn`t and you lose an engine you now have a load of ice/lots of Drag,and you will not be able to keep RRPM.The only way of keeping RRPM is to roll into a spiral descent,and stick with it all the way down,keeping a bit of "g"on which may help to shed some ice!....Then there is the ice on the stabiliser,not de-iced,which may cause pitch oscillations.ice over cooling ducts,etc..it in no way compares with icing in a fixed wing a/c and this is only in stratiform type cloud.It also relates to Seaking/Wessex/Wasp type a/c.To say nothing about engine intake icing,and compressor damage.Never fly into rain-ice conditions with a cold a/c as the ice will form in a smooth formation on the blades with a slow Tq build-up,but you cannot shed the ice as it is forming on the rear section of the blades.Any one who flies a modern helo with deicing/anti-icing kit may disagree,but I would suggest you may be Russian and fly a big Mil.
