ICING¡¦¡¦¡¦yikes ! Blade icing is the bad one
Unfortunately , the helicopter I fly ( a well established medium twin), does not have a BLADE de-icing or anti icing system¡¦.oh , I wish
I have experienced airframe icing but at the same time no blade icing. Conversely there have been times (not often) when I have picked up blade icing but hardly any airframe ice. On one occasion , years ago in a 61 , we picked up ice on the windscreen and its appearance was almost explosive. One minute it was clear, the next , completely white.
Referring back to my regular medium twin , its particular blade shape , I am told , is susceptible to icing. Another well known medium blade shape , not so.
I believe that it is extremely hard to predict icing conditions but particularly BLADE icing conditions.
I am led to believe that the friction of the rotating blade against the air causes an 8¢ª C rise in the blade temperature so that BLADE icing conditions will only be met when it is lower than minus 8¢ª at your altitude and you are flying in visible moisture. ie cloud.
So , in my area , we are forever being handed forecasts (in winter) that indicate enroute moisture and temps below minus 8. Note that this is FORECAST icing. Bear with me while we go to the dictionary. Forecast means ¡°estimate in advance , especially to predict¡¦..predict as in prophesize¡±
The Flight Manual of our medium twin referred above ¡°prohibits flight in KNOWN icing conditions¡±¡¦..and this is my point. We do not know , until we get out there and in it.. If we did not launch every time we were handed a FORECAST indicating icing conditions , then we would have to shut down over winter. Further more , I have flown regularly in these conditions and have not experienced blade icing ( or any other icing for that matter) when I was half expecting it. It is a real quandary.
In this particular medium twin , we set 62% cruise torque and watch it intently. If it starts to rise , we have flown into KNOWN icing conditions and we usually have two options. 1. Turn around and go back home or 2. Climb out of the cloud (moisture) and into the sunshine where the ice will burn off. Descending is not an option when sea level OAT was below minus 8 (and as low as minus 20). The decision to get out , must be made right NOW or you end up at 100% torque with IAS dropping and eventually the aircraft heading in the direction of down.
I have heard some real horror stories but what it boils down to is that manufacturers MUST fit those three buttons mentioned previously , if they are to sell their helicopters to cold weather operators.