Alternative Flight Control in Civil Aviation

This report contains a study about the possible benefits of changing the way large airliners are controlled in flight. The goal is to save fuel by decreasing the structural weight of the aircraft. Over the last decades the conventional primary control surfaces in civil aviation have not deviated from elevators, ailerons/spoilers and rudder. Eliminating one of these by compensating with others could hold revolutionary advantages. The research started out by finding alternative ways to control the aircraft around its different axes. This performance analysis was done with a Boeing 747-200 model in the RECOVER Benchmark tool with slight modifications. It was found that yaw control offered no decent alternatives besides the rudder. Pitch control can surprisingly be done with outboard ailerons, although it barely meets the requirements. This finding is attributed to the large sweep angle of the Boeing 747. Roll control offered the most alternatives due to many redundant control surfaces on the wings. Further analysis of unconventional roll control was split into four cases. The first case, flying without any ailerons, was determined to be unable to meet the legal requirements. However, the second case in which two spoiler surfaces were added to the existing six, was found to be satisfactory in all phases of flight. The efficiency of controlling the aircraft with spoilers instead of ailerons was addressed and a considerable difference was found but in the overall flight, this is not an issue. The third case was more moderate as it only removes the inboard ailerons. This case had no issues to meet requirements. The final case is entirely different: flying without spoilers. All roll requirements were met, but only after the outboard aileron was enlarged to within structural bounds. The larger issue with this case was the lack of airbraking features. The second phase of the project focused on evaluating the snowball effect in aircraft design caused by the small changes in the roll control mechanisms. First the weight of the removed components was estimated through a hydraulics model. This showed results ranging from 7% to 20% in subsystem weight decrease, depending on the case. The next step was to run these updated weights through a preliminary design phase. To facilitate the process the Aircraft Design Initiator was used. Two aircraft were reproduced and modified to assess the impact on different scales as well: the Boeing 747-200 and the Boeing 767-200, which is approximately half the size. It was found that the fuel percentage that could be saved for each case are 0.50%, 0.36%, 0.18% and 0.45% in respective order for the Boeing 747. Interestingly, these percentages are nearly identical to those of the Boeing 767. The impact on the operating empty weights does differ slightly, where the Boeing 747 loses more weight than the 767, percentage-wise. Being that the fuel saving on a standard harmonicmission profile is less than 0.50% for any of the cases of alternative roll control, the results are not revolutionary as they are now. The profitability of switching to these new control methods is debatable.