15 In-flight Icing: Modeling, Prediction, and Uncertainty
471
is accreted on the aircraft. Examples of these research approach were performed
by Lee [43] and Gurbacki [44].
• Icing tests—These tests are performed in icing tunnels which are equipped with
spraying water system to replicate the clouds and an acclimatization system to
reach temperatures below 0 ◦ C. They can gather data from the droplet trajectories
and their thermodynamic effects as well as the complex behavior of the runback
water. Also the approach is used to further understand the ice shapes generated
under a range of conditions and the effects of every ice shape on the aircraft
performance. Furthermore, this methodology is used to test the performance of
ice protection systems. This approach was taken by Olsen [45] and Whalen [46]
in their investigations of the ice accretion phenomenon.
• In-Flight tests—In-flight tests provide a realistic representation of the actual icing
conditions encountered. These icing scenarios can be natural or simulated and
this approach was identified as the most representative on the testing of the
performance of the ice protection systems. In-flight tests are also crucial for
certification, since the aircraft are expected to be able to adequately perform in
these conditions, and this can only be tested in-flight to some extent. However,
in-flight tests are more costly than wind tunnel tests and in addition they can
compromise the safety of the flight crew. Very little material has been published
in this matter, since the test outcome is usually protected as manufacturer
intellectual property. These tests were classified [41] in the following manner:
– Dry tests—They are analogous to the ground dry tests where the ice shapes
are replicated. In addition, these tests intend to assess the in-flight handling
qualities in iced aircraft which is generally not possible to be measured in
wind tunnels.
– Water spray tests—A tanker aircraft flights in front of the tested aircraft.
The tanker contains a water tank and sprays water to replicate the real icing
envelopes. Also, the aircraft can have water tanks and devices to spray water
near the critical regions. These tests can be used to assess the performance
of the ice protection systems and the performance of engine operation under
icing conditions.
– Flight in natural icing conditions—It consists in the controlled approach
to real icing conditions. It is the most precise testing procedure since it
fully replicates actual icing scenarios, however, it is rather costly and might
compromise the safety of the pilots (Fig. 15.5).
15.2.5.2 Uncertainties in Icing Tunnel Experiments
Icing tunnels are a type of wind tunnels where it is possible to reproduce icing
conditions to study ice accretion in different components. The airflow is cooled
down and then water droplets are sprayed to represent icing envelopes. Epistemic
uncertainties arise from the flow and the sprayed droplets attained within the tunnel.
They reflect the ability of the devices to replicate the intended icing envelopes
471
is accreted on the aircraft. Examples of these research approach were performed
by Lee [43] and Gurbacki [44].
• Icing tests—These tests are performed in icing tunnels which are equipped with
spraying water system to replicate the clouds and an acclimatization system to
reach temperatures below 0 ◦ C. They can gather data from the droplet trajectories
and their thermodynamic effects as well as the complex behavior of the runback
water. Also the approach is used to further understand the ice shapes generated
under a range of conditions and the effects of every ice shape on the aircraft
performance. Furthermore, this methodology is used to test the performance of
ice protection systems. This approach was taken by Olsen [45] and Whalen [46]
in their investigations of the ice accretion phenomenon.
• In-Flight tests—In-flight tests provide a realistic representation of the actual icing
conditions encountered. These icing scenarios can be natural or simulated and
this approach was identified as the most representative on the testing of the
performance of the ice protection systems. In-flight tests are also crucial for
certification, since the aircraft are expected to be able to adequately perform in
these conditions, and this can only be tested in-flight to some extent. However,
in-flight tests are more costly than wind tunnel tests and in addition they can
compromise the safety of the flight crew. Very little material has been published
in this matter, since the test outcome is usually protected as manufacturer
intellectual property. These tests were classified [41] in the following manner:
– Dry tests—They are analogous to the ground dry tests where the ice shapes
are replicated. In addition, these tests intend to assess the in-flight handling
qualities in iced aircraft which is generally not possible to be measured in
wind tunnels.
– Water spray tests—A tanker aircraft flights in front of the tested aircraft.
The tanker contains a water tank and sprays water to replicate the real icing
envelopes. Also, the aircraft can have water tanks and devices to spray water
near the critical regions. These tests can be used to assess the performance
of the ice protection systems and the performance of engine operation under
icing conditions.
– Flight in natural icing conditions—It consists in the controlled approach
to real icing conditions. It is the most precise testing procedure since it
fully replicates actual icing scenarios, however, it is rather costly and might
compromise the safety of the pilots (Fig. 15.5).
15.2.5.2 Uncertainties in Icing Tunnel Experiments
Icing tunnels are a type of wind tunnels where it is possible to reproduce icing
conditions to study ice accretion in different components. The airflow is cooled
down and then water droplets are sprayed to represent icing envelopes. Epistemic
uncertainties arise from the flow and the sprayed droplets attained within the tunnel.
They reflect the ability of the devices to replicate the intended icing envelopes