Aircraft Icing, III
The combination of flying aircraft and icing conditions can be bad news. How beautiful ice and snow may be in winter time, for airplanes it can spell havoc. Aircraft depend on the airflow over their wings and any amount of ice disrupts that, increasing weight and more importantly: lift is affected.
For general aviation and homebuilt aircraft pilots its important to remove any trace of snow and ice from the aircraft if it has been parked outside during freezing winter nights or after a snow shower. Recognizing where icing conditions can develop is very important for all pilots.
Some are certified for known icing conditions. They have either deicing or anti-ice equipment on the aircraft, protecting them against the effects of ice.
Certified for Ice
There can be only two types here: either certified for known ice conditions or not certified at all. To get certified aircraft must be vigorously tested for that situation. Other aircraft only have enough equipment to get them out of the area into clearer skies or warmer air.
Light general aviation and some homebuilt kit aircraft normally carry only a heated pitot tube. That's not nearly enough to combat any form of ice. If the pitot tube becomes blocked then the airspeed indicator will function as an altimeter. For these aircraft the advice is to stay well away from icing conditions.
Ice protection systems
Ice protection systems come in two forms: anti or de-icing. Anti icing systems are able to keep the aircraft clear by a protective layer of a viscous fluid flowing over the wing (weeping wing) or sprayed onto the propeller. These systems have a limited capability as the fluid needs to be carried by the aircraft and is limited by volume/contents.
De-icing systems are operated when the aircraft has accumulated a small layer of ice.
These ice protection systems are usually pneumatic boots, heated strips, de-icing fluids, propeller and windscreen de-icing and for the helicopters rotor blade de-icing equipment. On aircraft the leading edges of wings and the tail section are protected.
Larger airliners are de-iced on the airport during winter time just before the flight commences, from that point on the de-icing equipment can keep the exposed surfaces clean. Until the ice accretion is higher than the system can handle.
These rubber like tubes are attached to the leading edge of the wings, horizontal stabilizer and vertical fin. These boots are to be inflated and thus break the ice. For pneumatic boots to work the aircraft needs to build up a small layer of ice which then breaks away. Wait too long and the boot won't work and if you operate the boot too early it pushes the ice away without breaking and it freezes again rendering the boot totally ineffective.
In turbine class airplanes compressed air from the turbine can be used to heat parts prone to ice. Although it costs some engine power and as such it may not be an option to use this during take-off.
Anti icing fluids
During flight glycol based fluids are used to de-ice the leading edge of the wing, propeller and other parts on the aircraft. It oozes out of very small perforations in leading edge panels, which must be kept clean to keep the system working properly. Glycol has cleaning properties by design and will not harm the paint.
Operation is simple: just turn it on and when icing condition are left behind, turn it off again. Some systems will provide ice protection from one to three hours.
Usually done by routing incoming cold air over the exhaust of the engine. Although you will encounter de-icing systems based on electrical heating of the windshield.
Only a small section of the blades are heated or treated with fluid. Ice forms on the inner sections of the blades as the angular speed at that point is lower than at the tips, where ice can not attached easily.
In some small twin piston engined aircraft a special combustion heater (Janitrol) is used for cabin / cockpit heat and it runs on avgas from the aircraft tanks. Most other light aircraft use either heat coming from an airflow over the exhaust or through a coolant or oil radiator to heat the cabin.