458
B. Arizmendi et al.
case, those consequences are always unwanted and always imply a performance
penalty.
For aircraft, which will be the focus of this chapter, the consequences of a
malfunctioning go beyond economic and reliability issues. Fatal aircraft crashes
caused by in-flight icing caused life losses in the past as it is evidenced in accident
investigations [2–4]. Many aircraft are equipped with ice protection systems,
especially those which will be allowed to fly in icing conditions. However, aircraft
can be exposed to very different icing conditions and the adequate performance of
the protection systems must be ensured [5]. There are large uncertainties regarding
the icing conditions which lead to large uncertainties on the study of the ice
accretion phenomenon. The challenge intended to be addressed by the analysis and
study of ice accretion is to ensure any aircraft is protected against the most harmful
possible icing condition [6]. Deep knowledge in this field will help on the design of
more efficient icing systems.
This section presents an overview of the in-flight icing phenomena. It starts with
an introduction to the scenarios where aircraft icing occurs. Then, the icing relevant
parameters are described together with their impact on the severity of icing and
the identified uncertainties. Depending on the values of these parameters, the ice
accreted will present different characteristics that are described in the following
section. Later, possible interactions between the droplets and the aircraft surfaces
are explored. The different methods for investigating ice accretion are shown and
finally the effects that the aircraft icing has on the performance and safety of the
aircraft are described.
15.2.1 Icing Environment
Ice accretion can be caused by flying through supercooled clouds. But it can also
be caused by the impact of snow or by freezing rain, where supercooled large
droplets fall from the clouds. Furthermore, hazardous in-flight ice accretions are
caused when large droplets are encountered.
15.2.1.1 Cloud Formations
Clouds are clusters of small visible droplets. Their formation requires an uplift
air motion of humid air. The portion of raising air cools down and the moisture
condenses forming small droplets. If the temperature of the cloud decreases and
the water droplets contain no crystallization nuclei, the droplet will remain in a
liquid state below the melting temperature in a metastable phase called supercooled
[7]. Any perturbation such as impacts on the aircraft surface will alter this stability
causing the total or partial freeze of the droplets.
B. Arizmendi et al.
case, those consequences are always unwanted and always imply a performance
penalty.
For aircraft, which will be the focus of this chapter, the consequences of a
malfunctioning go beyond economic and reliability issues. Fatal aircraft crashes
caused by in-flight icing caused life losses in the past as it is evidenced in accident
investigations [2–4]. Many aircraft are equipped with ice protection systems,
especially those which will be allowed to fly in icing conditions. However, aircraft
can be exposed to very different icing conditions and the adequate performance of
the protection systems must be ensured [5]. There are large uncertainties regarding
the icing conditions which lead to large uncertainties on the study of the ice
accretion phenomenon. The challenge intended to be addressed by the analysis and
study of ice accretion is to ensure any aircraft is protected against the most harmful
possible icing condition [6]. Deep knowledge in this field will help on the design of
more efficient icing systems.
This section presents an overview of the in-flight icing phenomena. It starts with
an introduction to the scenarios where aircraft icing occurs. Then, the icing relevant
parameters are described together with their impact on the severity of icing and
the identified uncertainties. Depending on the values of these parameters, the ice
accreted will present different characteristics that are described in the following
section. Later, possible interactions between the droplets and the aircraft surfaces
are explored. The different methods for investigating ice accretion are shown and
finally the effects that the aircraft icing has on the performance and safety of the
aircraft are described.
15.2.1 Icing Environment
Ice accretion can be caused by flying through supercooled clouds. But it can also
be caused by the impact of snow or by freezing rain, where supercooled large
droplets fall from the clouds. Furthermore, hazardous in-flight ice accretions are
caused when large droplets are encountered.
15.2.1.1 Cloud Formations
Clouds are clusters of small visible droplets. Their formation requires an uplift
air motion of humid air. The portion of raising air cools down and the moisture
condenses forming small droplets. If the temperature of the cloud decreases and
the water droplets contain no crystallization nuclei, the droplet will remain in a
liquid state below the melting temperature in a metastable phase called supercooled
[7]. Any perturbation such as impacts on the aircraft surface will alter this stability
causing the total or partial freeze of the droplets.