Autonomous Icing Protection Solution for Small Unmanned Aircraft: An Icing Detection, Anti-Icing and De-Icing Solution

This monograph is motivated by the lack of an autonomous icing protection solution \nfor small unmanned aerial vehicles. \nThe atmospheric phenomenon commonly referred to as aircraft icing is one the \nmost dangerous weather hazards to all of aviation. When an aircraft operates in \natmospheric conditions that sustain icing, a potential of ice forming on exposed \naircraft surfaces arises. The most significant of these surfaces are the leading edge \nof aircraft wings, stabilisers, and various control surfaces. This monograph focusses \non icing as it forms on the leading edge of wings. The consequences of icing range \nfrom insignificant to dire, even fatal. For unmanned aerial vehicles, as is the case for \nconventional aircraft, the impact of icing primarily relates to controllability of the \naircraft. Once icing forms on the wings the aerodynamic shape is altered. Typically \nthis leads to changes in the aerodynamic characteristics of the wing, i.e. maximum \nlift can decrease by as much as 80% and drag can increase by more than 60%. \nFor small unmanned aerial vehicles there are no commercially available icing \nmitigating solutions, aside from grounded operations. This monograph is a presentation \nof just such a solution. The icing protection solution is based on three \nprimary elements, 1) an electro-thermal source, 2) an intelligent control unit, and \n3) a power source. In essence the solution provides according to the following; \nthe control unit is primed by an on-board atmospheric sensor package, measuring \nambient environmental conditions. Once the risk of icing is established, two ice \ndetection algorithms - working in parallel - are activated. This approach ensures \nrobustness and accuracy. If icing is detected, control algorithms trigger the power \nsupplied to the electro-thermal source, thereby achieving temperature control of \nthe thermal source. \nFor conventional aircraft, icing detection is usually performed by larger optical \nsensors or a pilots visual inspection. For UAVs icing detection is a relatively new \nresearch topic. In this monograph two markedly different approaches to icing detection \nfor UAVs are proposed. Common for both is the objective of detecting icing \nas it forms on the leading edge of aircraft wings. \nOne icing protection solution presented in this monograph is denoted the modelbased \nicing detection algorithm. It addresses the issue in a fault diagnosis framework \nby generating residuals used to detect aircraft surface faults (that is aerodynamic \nchanges), indicating that icing is forming on the leading edge of the aircraft wings. \nThe proposed algorithm relies on estimates of aerodynamic parameters - obtained \nunder nominal flight conditions - and the aerodynamic model of the aircraft. Should \nthese parameters change unexpectedly a surface fault has occurred, i.e. icing is forming on the wings of the aircraft. The proposed algorithm has been validated \nthrough numerical analyses. \nThe second icing detection algorithm proposed is denoted the electro-thermalbased \nicing detection algorithm. It also addresses the issue of icing detection in a \nfault diagnosis framework, but where the prior algorithm uses the aerodynamic \nmodel of the aircraft to accomplish this, the latter algorithm applies a model of \nthe thermodynamic system surrounding the aircraft wings and the electro-thermal \nsource. The electro-thermal-based icing detection algorithm uses temperature gradients, \nobtained from the electro-thermal source, and unexpected changes in these \nto detect changes in the thermodynamic system. A change could be an added \nelement as a layer of ice. The proposed approach has been validated through a \nsimulation study. \nTo evaluate the electro-thermal source layout and area size, several thermodynamic \nanalyses are conducted. Simulations are conducted to determine the relationship \nbetween area size and power consumption, while responses from other \nsimulations are used to investigate and evaluate the thermal distribution differences \nof electro-thermal sources applied to various UAV platforms. \nTo demonstrate the feasibility of the proposed icing detection solution wind \ntunnel experiments and flight tests have been conducted. Preliminary integration \nprocedures are developed to ensure little to no negative aerodynamic impact, while \nabiding by requirements for airworthiness and safe flight operations. \nWind icing tunnel experiments have been conducted for various required icing \nprotection program routines, i.e. icing detection, de-icing, and anti-icing. Experiments \nhave been conducted in atmospheric conditions ranging from non-icing to \nvarying severity degrees of icing. \nPreliminary flights include the worlds first flight for any UAV fitted with an autonomous \nicing protection solution, completed in a collaboration between NTNUAMOS \nand NASA Ames Research Center and conducted in Anchorage, Alaska. \nOperational flights have been conducted at Ny-Ålesund, Svalbard, where the \naforementioned icing protection program routines have been tested, verifying the \nicing protection solution.