Open-loop Aircraft Stability Analysis
|Definition:||The research in open-loop stability uses analytical and experimental techniques to study the aircraft's natural motion around the centre of gravity, resulting from the external forces and moments acting on the aircraft, without interference from a pilot or autopilot. In the analysis it is determined if in a certain flight condition all forces and moments are in equilibrium. Subsequently, an aircraft is considered to be open-loop stable if, after a small disturbance from an equilibrium flight condition, the aircraft has a natural tendency to return to the original condition, without interference from a pilot or autopilot.|
|Sub-domains:||1. System identification - from empirical / analytical model parameter estimation, wind tunnel tests and flight tests.|
2. Mathematical modelling - equations of motion, aerodynamics, mass properties and geometry, taking into account modelling errors and uncertainties).
3. Analytical analysis of stability and stability margins - including a sensitivity analysis to determine the most influential physical parameters.
4. Flight Tests - experimental analysis of stability and natural motion of the aircraft, including model validation, definition of suitable test manoeuvres, instrumentation.
Flight control system
|Definition:||The flight control system of an aircraft enables the pilot to control the aircraft along a desired trajectory and overcome the aerodynamic forces acting on the control surfaces. It improves the stability and flying qualities of an aircraft to a desired level. Current civil transport aircraft and military fighter aircraft are equipped with electronic fly-by-wire flight control systems providing easy, safe and economic operation of the vehicle under all operating conditions. Research on flight control systems uses analytical and experimental techniques to design a system to control the aircraft and subsequently analyse the stability of the closed-loop system, i.e. the aircraft with the pilot (or autopilot) in the loop.|
|Sub-domains:||1. System Identification (see 501).|
2. Mathematical modelling (see 501, adding sensors and FSC systems models).
3. Definition of controller requirements and desired handling criteria.
4. Controller design - control theory (architecture, algorithms, robustness).
5. Thrust vectoring and integrated flight- and propulsion control.
6. Analytical controller analysis (stability and robustness, using linear models).
7. Controller analysis using desktop simulation.
8. Controller analysis using a flight simulator (pilot-in-the-loop, handling qualities).
9. Flight test analysis (see 501, including handling qualities).
10. Development of a more efficient, integrated design and analysis process for robust controllers.
Aircraft Performance Analysis
|Definition:||In aircraft performance analysis, analytical and experimental techniques are used to determine extreme quantities of the translational motion of the centre of gravity of the aircraft, which are relevant to its operational and economic use. Typical quantities that are determined in a performance analysis are: - operational flight envelope (min/max of airspeed, altitude and load factor).- operational range and endurance - Performance in climb/descent - Cruise performance (optimum fuel consumption versus cruise speed and altitude)- performance in turns- runway performance (take-off and landing distance)|
|Sub-domains:||1. Mathematical modelling (3 DOF point mass model, equations of motion, environment, aerodynamics, engine and systems).|
2. Analytical performance calculations.
3. Performance Analysis of complex and/or dangerous manoeuvres via non-linear desktop simulation.
4. Flight Tests - experimental performance (definition of suitable test manoeuvres, instrumentation and validation of model and analytical analysis results).
Optimisation of Aircraft Performance
|Definition:||In performance optimisation research, mathematical and analytical routines are used to calculate optimal trajectories and optimal flight conditions. Usually, in the calculation simplified models of the aircraft (aerodynamics, point mass) and its environment are used. Typical examples are ?minimum-time-to-climb? or ?minimum-fuel-manoeuvre? problems.|
|Sub-domains:||1. Mathematical modelling (see 503).|
2. Selection of optimisation method and strategy.
3. Mathematical Definition of performance objectives.
4. Implementation and application of efficient optimisation routines.
5. Verification of optimisation results in simulation and flight tests.
System Failure and Damage Analysis
|Definition:||The occurrence of failures in the aircraft?s systems can lead to a degradation of stability and/ or the performance of the aircraft. Although failure cases are taken into account in the design process of the aircraft, it is useful to perform separate and detailed studies of systems failures for the analysis and prevention of aircraft accidents and incidents. Bird strike or collision with other objects is a frequently occurring example. Sufficiently accurate models of system failures and their effect on aerodynamics and system dynamics have to be generated.|
|Sub-domains:||1. Analysis of engine failure.|
2. Design of fault-tolerant/ adaptive control systems (redundancy, fault detection and reconfiguration).
3. Analysis of FCS hardware failure (sensors, hydraulic systems, control surfaces).
4. Damage to the aircraft structure, resulting in altered aerodynamic properties.
Environmental Hazard Analysis
|Definition:||Environmental hazards, which mostly occur during the critical take-off and landing phases, can lead to potentially dangerous situations. Analytical and experimental techniques (simulation and flight tests) are used to identify the effects of these hazards. For analysis and prevention of accidents and incidents, it is investigated if the aircraft remains controllable (stability) and/or has sufficient performance for a go-around or evasive manoeuvre. For each hazard, the stability, control and performance sub domain activities are undertaken as described in 501 until 504, using sufficiently accurate models of the hazards their interference with the aircraft?s dynamics.|
|Sub-domains:||1. Take-off and landing in severe crosswind.|
2. Windshear and microbursts (usually in combination with turbulence).
3. Turbulence/ gusts.
4. Terrain and airport conditions (terrain profile effects on radar altimeter, wind interference from buildings).
5. Wake vortex effects from other aircraft.
6. Icing conditions / heavy precipitation.