Flight dynamics and control assessment for differential thrust aircraft in engine inoperative conditions including aero-propulsive effects

Abstract

Differential thrust can be used for directional control on distributed electric propulsion aircraft. This paper presents an assessment of flight dynamics and control under engine inoperative conditions at minimum control speed for a typical distributed propulsion aircraft employing differential thrust. A methodology consisting of an aerodynamic data acquisition module and a non-linear six-degrees-of-freedom flight dynamics model is proposed. Directional control is achieved using a controller to generate a yaw command, which is distributed to the propulsors through a thrust mapping approach. A modified version of the NASA X-57 aircraft is selected for case studies, where the engine inoperative condition is considered to impact the three leftmost propulsors during climb at minimum control speed. The objective also includes the assessment of the impact of the aero-propulsive coupling for such an aircraft during a failure case. Results show that during the recovery manoeuvre, the aircraft experiences a 78% reduction in total thrust and 30% reduction in total lift caused by the aggressive yaw control effort required to control the heading of the aircraft. Consequently, the powered-stall speed is increased, and the aircraft temporarily loses altitude during the recovery manoeuvre. Differential thrust provides sufficient yaw authority during the engine inoperative condition, and is, therefore, seen to potentially replace the functionality of the rudder for the climb condition that was studied. Additionally, reduction of the vertical tail area was explored and seen to be possible if the response time of the system is low enough. For the studied configuration, this required a response within 400 ms for reduced vertical tail areas.

Switching Logic for a Direct Hybrid Electric Powertrain

“…Future work will focus on the duration of the switching times during which the power is determined by the switching procedure instead of the power demand of the power train. It is to be expected that the time required for switching can be limited to a few seconds as electric motors [41] as well as batteries have a very fast response time. A change in fuel cell power can also be achieved almost instantaneously [42], despite the fact that equilibrium conditions at the fuel cell for the new operating point might only be reached after several minutes as the dynamic behavior of fuel cells is complex [43] and gas supply, cell temperature and humidity all play a role.…”

“…After the switching conditions of The impact of the difference in thrust per wing is decreased if the number of propellers and power train units per wing is increased to two or more [40]. Such a distributed propulsion system is advantageous from a control and stability point of view [41] and enables, for example, two motors on the left wing and two motors on the right wing to compensate for each other when switching from Hybrid Mode to Fuel Cell Mode. In any case of combining powertrain units as multiples of two, the power change issue during switching can be overcome by implementing an appropriate control strategy that runs the above-mentioned sequence, enabling the switching from one mode to another.…”

Influence of Electric Wing Tip Propulsion on the Sizing of the Vertical Stabilizer and Rudder in Preliminary Aircraft Design

“…The focus of the study presented here is the investigation of the usability of the given VTP in case of engine failure-induced thrust asymmetry and the possible reduction in VTP size and its impact on the preliminary aircraft design. As investigated by Hoogreef and Soikkeli [5], as well as Vechtel and Buch [6] and proven by Schneider et al [7] in a full-scale flight test, the directional stability may also be provided by the use of differential thrust. Therefore, the influence of the directional stability on the vertical tail size is neglected in this study.…”

Application of a Semi-Empirical Method to Model Subsonic Vortex Lift over Sharp Leading-Edge Delta Wings

“…The solver ceased the process once the solution has converged to a criterion that can be defined by the user [11]. Unlike volume-based CFD solvers, FlightStream can produce flow solutions using an unstructured surface mesh, reducing significantly the time and the computational resources needed to generate solutions [12].…”