Resolving the conflicting requirements of aircraft lightning protection and in-flight ice protection

When an aircraft flies in cold, moist air, especially at low altitudes, ice can form rapidly on the leading edges of aerofoils and other structures. Ice growth can disturb the local airflow and therefore affect the aerodynamic performance and aircraft handling characteristics, leading to the use of in-flight ice-protection systems on modern commercial aircraft. Research into future wing design, e.g. Natural Laminar Flow and morphing leading-edges serves to indicate that the icing environment will have an even greater effect on these new wing shapes than on the current state of the art. Furthermore, the increasing exploitation of composite materials and the trend towards more-electric aircraft suggest that conventional methods of preventing such ice accretion, e.g. engine bleed air or pneumatic boots, are becoming increasingly difficult to implement or are no longer viable. However, one well-established technique for continued ice protection is via electro-thermal methods. GKN Aerospace - Luton have many decades of experience in delivering reliable electro-thermal ice protection and have demonstrated the capability of reliably protecting composite and other structures whilst maintaining critical aerofoil geometry. One of the major engineering hurdles to be overcome in the design of effective electrothermal ice protection systems is that the thermal performance requirements of the materials of construction are almost directly contrary to those for adequate lightning protection. The necessarily high power densities required for ice protection drive the requirement for very low thermal resistances between heating element and the protected surface. However, the aerodynamic surface to be ice-protected, by its very nature, is frequently in a lightning strike zone [1] and the operation of in-flight ice-protection systems often coincides with the greatest probability of lightning strike [2][3]. The requirements for lightning protection demand very high insulation resistances at very high voltages (several kilovolts), requirements that inherently drive thermal resistances upwards. The current results of GKN Aerospace's on-going efforts to resolve these conflicting requirements are presented here. These efforts include material choices and their drivers, as well as methods of construction.