Rotor blade icing

October 12, 2012 by Tim McAdams

Flying in conditions conducive to ice formation is problematic for virtually all helicopters. Moreover, many twin engine IFR helicopters are not certified for flight in known icing conditions. As such, helicopter pilots should understand the problems an encounter with icing can create for the rotor system.

Ice buildup on rotor blades will change the shape of the airfoil and consequentially, its ability to produce lift while increasing drag. The increased drag will slow the main rotor requiring the pilot to add power – which in some cases might not be available. Ice accumulation on the airframe can increase the helicopter’s gross weight requiring more power as well. Ice buildup is rarely, if ever, symmetrical causing an imbalance that produces vibrations in the rotor system. These vibrations can cause shedding of the ice and if all the ice comes off, vibration levels, lift and drag will return to normal. Asymmetrical shedding, however, can make the vibrations worse. Hopefully, the increased vibration will shed the remaining ice before any damage can occur. Ice accumulation is less on the outboard section of the rotor blade which is helpful because this area produces a larger amount of lift. However, an autorotation could be more difficult as the driving region is closer to the blade’s center.

Deicing refers to removing ice that has accumulated, while anti-icing is the prevention of ice formation. The few helicopters that having ice protection on the main rotor system use a de-icing system as the power required to anti-ice a main rotor system is extremely high. One of these is the Sikorsky S92 and it uses heater mats in the rotor blades to melt a thin layer of ice in contact with the blade surface causing the remaining ice to shed from the blade. According to Sikorsky, heat is applied to the mats to melt the ice in specific zones at precisely the right time for controlled shedding. Opposite main rotor blades are deiced simultaneously in order to prevent rotor imbalance and small sections of the rotor blades are deiced alternately to reducing the amount of electrical power required at any given time. The tail rotor ice protection system can be set to de-icing mode, which applies power in a scheduled manner or anti-icing mode in which heat is continuously applied to tail rotor heating mats.

  • Avi Weiss

    I would think that de-icing would inherently be problematic, as some chunk of ice could break off at wrong angle and hit tail rotor. Be interesting to see how they control that from happening

  • MIke Jasumback

    “Most”? Try hardly any! There are like 3 commercially available helos that are FIKI!

  • Terk Williams

    I flew for the USCG and despite my Kodiak tour (complete with lots of deployed shipboard time in the Bering Sea ) my worst weather flying was out of Brooklyn, NY (Floyd Bennett). On more than one “dark and stormy winter night” (most war stoies start that way….). We took off on a rescue that took us into potential iceing. We were not allowed to depart into known iceing.. but it was always up to the Aircraft Commander… More than once I encountered actual iceing. Since, by thenk, we were flying HH65 Dauphines the tail rotor was pretty well protected both from shed ice and didn’seem prone to iceing. The main rotor oblades would ice and just about the time I would be getting ready to turn back the blades would shed…usually asymetrically but with one blade shedding the rest usually followed suit. With the tough blades and rotor head I never worried about the short lived vibration (I’m also an old Viet Nam Dustoff pilot that has flown a Huey home with a few feet of one blade gone and the other damaged…). Guess the morale of this old pilots rambeling is 1). Unless you are likely to successfully save a human life DON’T screw w ice but…2). If you are willing to accept/explain some airframe damage and have a modern relatively high tech roror system .. It has been done…. by a few folks…

  • Alex Kovnat

    Has the Osprey had any problems with proprotor or wing icing, and does it have any anti- or deicing devices? Did Eurocopter design any ice protection into their experimental rotary-winger which uses side propellers for propulsion assist and torque management?

  • MJ Shipping and Transport

    This has been a really interesting Article for me. Helicopters are fascinating machines and I always enjoy trying to better understand them, especially indifferent weather conditions.

    Thank You

  • Jim Borger

    Keep in mind that the inboard section of the main rotor blades can ice up enough that you can’t maintain RPM in an auto but you will not feel any degradation in the controls until well past that point. Ice is nothing to mess with. Anti-ice and de-ice equipment, even in an aircraft certified for flight into known icing, should be used only to get out of icing conditions. An empty CH-47 flew into freezing rain in Germany and the pilot immediately started a 180 degree turn. By the time he completed the turn he had picked up so much ice he could not maintain altitude with full power and had to go all the way to the ground.

  • Alan D. Resnicke

    Some of my scariest moments flying USAF helicopters was one trip to Korea, in IFR near the DMZ in icing conditions. Our HH-53C shed the rotor icing asymetrically, which lead to some short-lived but impressive vibrations. Breaking out and warming up was a relief beyond words. As I recall, we may have nicked one tail rotor blade but had no damage otherwise. Whew! Don’t go there, folks!