Abstract:
In design and development of aircraft, standard practice uses `the icing design
envelopes' to select atmospheric conditions for modelling icing encounters.
Over the duration of these encounters, atmospheric conditions are assumed
to be constant and to exhibit no variability. In reality variability exists, to an
extent where it may adversely affect the severity of ice accretions beyond that
identified by ground-based modelling. Similarly, certain tools and systems
employed by industry may sacrifice efficiency & effectiveness in neglecting
the variability that exists.
This project considered what operational and safety bene ts might be derived
from an enhanced knowledge of ice accretion under more realistic, variable
conditions; in contrast with a reference case identified to have equivalent
constant conditions. In doing so, variable encounters were modelled experimentally
in an icing tunnel to compare against a constant-condition reference;
aerodynamic penalty was assessed numerically using CFD, allowing a comparison
to be made between variable and constant-condition profiles; and
desk-research considered variable conditions in the context of existing and
emerging technology.
Considerable differences were observed between variable profiles themselves
and with the reference profile, with aerodynamic penalty being considerably
enhanced for 25% of variable cases, and considerably reduced for a further
25%.
Desk-research suggests that in understanding variability, to reduce costs asso-
iciated with aircraft icing, more realistic ground-based modelling capabilities
could reduce the need for natural
flight-testing in the long term, though this
would require substantial enhancement to current numerical prediction capabilities.
Similarly, the power applied to ice protection systems could be
tailored more speci cally to demand, enhancing e ciency. On the basis of
current instrumentation, this would first require development of more accurate
and robust LWC measurement systems.
It was therefore recommended that specialists in meteorology, icing physics,
ice protection systems and aerodynamics; conduct more extensive research
towards understanding variability and assessing its potential to enhance
flight-safety, whilst simultaneously reducing cost.