Aircraft Icing, II
The combination of flying aircraft and icing conditions can be bad news. How beautiful ice and snow may be in winter time, for aircraft 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.
The effects of ice on an aircraft can result in a wing or tail stall or even freezing up of ailerons or flaps and other important flight controls.
What happens to the aircraft
Ice forms on all exposed parts of the aircraft but apart from increasing aircraft weight (and stall speed) it also changes the aerodynamic characteristics of the wing and tail section probably resulting in a stall at a much higher airspeed than the pilot anticipates. One wing may even stall before the other introducing a roll from which recovery could prove difficult.
With ice on the wing the aircraft will stall at a lower angle of attack and higher airspeed. This will vary with the amount of ice on the wings especially if deicing works only partially and not all ice gets removed.
You may expect that ice accretion will not be the same for both wings and that each wing will stall at different speeds and angles. That will introduce a rolling action toward the stalled wing.
Aircraft with thin wing profiles are more prone to ice formation. This is also true with wings where outboard sections have a different airfoil, which helps in roll control with high angles of attack. But this may prove a problem when ice disrupts the airflow and the wing stalls begins at the aileron instead at the wing root.
If the wing stalls then the corrective action is to reduce the angle of attack, add power and increase airspeed.
Ailerons and flaps
When cold rain hits the wing it will flow to the back and freezes as clear ice (freezing rain). In heavy rain with larger droplets and higher airspeeds the possibility exist that the subzero rain flows over the top of the wing to the ailerons and flaps and freezes these solid. Leaving the pilot without roll control.
The profile for the tail sections is usually thinner than for the wing. Ice accumulation therefore is quicker and in most aircraft the pilot can not even see the tail at all. Making it more dangerous as this will go unnoticed much longer.
The tail section creates a downward force to stabilize the aircraft during flight. If the tail stalls it will introduce a nose dive and the pilot must pull back on the stick or yoke. Which is completely opposite reaction compared to a wing stall recovery.
Tail stalls are experienced when flaps are extended, pitch control forces become abnormal or erratic and a control column buffet is felt. If this happens, raise flaps and pull back on yoke or stick, reduce power if you have enough altitude and do not increase airspeed unless you need to avoid a wing stall.
When the aircraft itself is exposed to ice several things may happen: frozen windshields, blocked air vents and pitot tubes, fuel vents that become blocked may cause fuel starvation, control surfaces (flaps, rudder, elevator and ailerons) may bind or freeze solid stiff, antenna may break off.
The effects can be numerous and might lead to an accident.