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Flight mechanics of short take-off and landing aircraft with active high-lift system and propeller engines exhibit excellent low airspeed flight performance on the one hand but also flight mechanical challenges on the other. These are results of previous work of the 60s as well as of the Collaborative Research Centre CRC 880. In the CRC 880 project, new knowledge about unsatisfactory handling qualities was gained by flight dynamics modeling and simulations based on a high-fidelity computational fluid dynamics database of the CRC reference aircraft. This paper summarizes the results of the flight dynamics that confirm excellent flight performance, minor challenges in the longitudinal motion and major challenges in the lateral-directional motion. Passive and active countermeasures are discussed to improve the handling qualities. Moreover, it is shown that only partial failures of the active high-lift system can be compensated. Finally, the paper gives an outlook on future work.

Active high-lift aircraft need exceptional aerodynamic control performance to operate at low airspeed. In this study a new concept for the improvement of controllability is investigated, incorporating the special capabilities of a blown Coanda flap system. The blowing system along the flaps is divided into twelve independently controllable segments. This provides the opportunity to influence the lift distribution along the wingspan by individual blowing performance settings for each segment without changing the flap deflection. This offers the chance to control the airplane in the final approach phase with fully deflected flaps by using only the blowing system and to dedicate specific control tasks to particular segments. A model for the blowing system influence on the local wing aerodynamics is implemented in an existing nonlinear full aircraft flight mechanics model. The system capabilities in terms of roll control and the climb performance are investigated by criteria evaluation and dynamic simulation assessment. The ability to fly turn/altitude change maneuvers by utilizing the active high-lift system is proven and a corresponding control concept is presented. It also includes the compensation of different blowing failure cases, which leads to acceptable but still improvable aircraft reactions.

In this paper an adaptive control system for a passenger aircraft with active high-lift system is presented. Failures in the high-lift system parts of such aircraft are critical and consequently need to be handled automatically. An adaptive controller is proposed which consists of incremental nonlinear dynamic inversion (INDI) with a reference model and linear controller. As the INDI is adaptive against uncertainties or system failures, no additional adaptive element like a neural network is needed. The implementation of the INDI requires a nonlinear system model which is permanently linearized during the runtime in order to obtain the current input matrix which here basically consists of the control surfaces effectiveness. It also requires feedback of the translational and rotational acceleration measurements which usually suffer from noise. In order to test the adaptivity of the INDI, a partial failure of the high-lift system during the landing approach is regarded. It shows that the INDI is capable of compensating the error by only using the conventional control surfaces.

In this study, the aerodynamics of wings using an active high-lift system are investigated. The target is the flight mechanical description of the spanwise forces and resulting moments and the influence of the active high-lift system to their distribution. The high-lift system is a blown flap system divided into six segments per wing. Each segment is assumed to be individually controlled, so the system shall be used for aircraft control and system failure management. This work presents a flight mechanical sub-model for the simulation of flight dynamics, which has been derived from high-fidelity CFD results. An assessment of single-segment blowing system failures will be presented including recommendations for compensation of either lift or rolling moment loss. For this investigation, the compensation is required to act at the same wing side on which the failure appears. Thus, the potential for an increase of system reliability shall be proven. The results show that less performance investment in terms of pressurized air is necessary to compensate the rolling moment of a failing segment instead of its lift. However, large blowing performance increases for the remaining wing segments that occur for some of the failure cases.

Simulation results of the longitudinal motion of a civil twin-engine aircraft with an active high-lift system are presented. The investigated system uses the lift-increasing effect of blowing over Coanda flaps along the wing. The core elements of the nonlinear model describing the dynamic behavior of an aircraft with this specific type of active high-lift system are explained. The main focus lies on the analysis of the aircraft’s reaction to an instant symmetric total failure of such a system. Initial investigations analyze the outcome of such failures, if throttle is set to maximum and elevator is controlled, without using stabilizer or flaps. Subsequently, an investigation has been performed estimating the effect of flap reconfigurations and stabilizer adjustments. The paper also considers a temporary failure of the system due to an engine failure combined with a too low power setting of the remaining engine which has to be increased first before the restart of the blowing system. The investigated situations vary from inconvenient to unrecoverable. Recommendations for backup systems and procedure changes are made to prevent such situations. A procedural approach is analyzed and respective simulations prove the efficiency of this solution.

The paper deals with the propagation of uncertainty in input parameters through the aircraft model in clean cruise configuration triggered by the elevator pulse. Assuming aerodynamic coefficients as random variables and processes, the evolution of uncertainties in the aircraft state is estimated with the help of efficient nonintrusive procedures—stochastic collocation and the nonintrusive Galerkin approaches, here contrasted to the slow convergent Monte Carlo integration. These numerical methods are implemented by using the flight simulator in a black-box manner. In this way, the set of samples of aircraft states is simply obtained by solving the corresponding systems of deterministic ordinary differential equations. Additionally, the paper provides the variance-based sensitivity analysis of a flight model carried out with the help of the polynomial-chaos approach.

This paper outlines recent flight dynamic analysis results of a civil aircraft with active high-lift system using blown Coanda flaps. The main focus lies in the trim analysis of the aircraft. Therefore, the basic structure and core elements of the nonlinear model, describing the dynamic behavior of an aircraft with this specific type of active high-lift system are presented. The center of gravity range allowing controllability and static stability of the aircraft is determined, and the resulting characteristics of the aerodynamic model and their impact on the trim results of the aircraft are analyzed. The results show specific flight dynamic difficulties related to the active high-lift system, namely in the flying characteristics necessary for safe take-off and approach procedures. The flight physics is explained and discussed. The necessity of the application of a wing leading edge device is outlined by preliminary studies and further remedial means are proposed.