On the Handling Qualities of Two Flying Wing Aircraft Configurations

The coupling of the longitudinal and lateral stability modes of an aeroplane is considered in two cases: (i) weak coupling, when the changes in the frequency and damping of the phugoid, short period, dutch roll, and helical modes are small, i.e., the square of the deviation is negligible compared to the square of the uncoupled value; (ii) strong coupling, when the coupled values may differ significantly from the uncoupled values. This allows a comparison of three values for the frequency and damping of each mode: (i) exact, i.e., fully coupled; (ii) with the approximation of weak coupling; (iii) with the assumption of decoupling. The comparison of these three values allows an assessment of the importance of coupling effects. The method is applied to two flying wing designs, concerning all modes in a total of eighteen flight conditions. It turns out that lateral-longitudinal coupling is small in all cases, and thus classical handling qualities criteria can be applied. The handling qualities are considered for all modes, namely the phugoid, short period, dutch roll, spiral, and roll modes. Additional focus is given to the pitch axis, considering the control anticipation parameter (CAP). The latter relates to the two kinds of manouever points, where damping vanishes, that are calculated for minimum speed, take-off, and initial and final cruise conditions. The conclusion compares two flying wings designs (the “long narrow” and “short wide” fuselage concepts) not only from the point of view of flight stability, but also from other viewpoints.

Relook at Aileron to Rudder Interconnect

The implementation of interconnect gain from aileron to rudder surface on the majority of the aircraftis to decrease sideslip which is generated because of adverse yaw with the movement of control stick in lateral axis and also enhances the turning rate performance.The Aileron to Rudder Interconnect (ARI)involves significant part to decouple the Dutch roll oscillations from roll rate response to aileron command. ARI is feed-forward gain whichis susceptible to aircraft system uncertainty. Incorrect ARI gain can lead to side slip buildup which can cause aircraft to depart in case of fault scenarios. Four systematic ARI design methods are proposed. One of the proposed methods which use the norm of ARI transfer function at roll damping frequency is suitable for online reconfiguration of control law. The reconfiguration of ARI gain is illustratedwith the simulation responses of fault scenario case of aileron surface damage.

Effects of propeller flow on the longitudinal and lateral dynamics and model couplings of a fixed-wing micro air vehicle

This paper analyzes the effects of propeller flow on the linear coupled longitudinal and lateral dynamics of a 150 mm wingspan fixed wing micro air vehicle (MAV). The effects propeller flow on the lift, drag, pitching moment and side force is obtained through wind tunnel tests. The aerodynamic forces and moments are modeled as a function of angle of attack, sideslip angle, control surface deflection and propeller rotation per minute. The nonlinear six degrees of freedom model is linearized about straight and constant altitude flight conditions for different trim airspeed to obtain linear coupled longitudinal and lateral state space model. The eigenvalues and eigenvectors of linear coupled longitudinal and lateral state space model are compared with and without propeller flow effects. The variation in the natural frequencies and damping ratios of short period mode, phugoid mode and Dutch roll mode are analyzed for various trim airspeed. An increase in the natural frequency is observed for phugoid mode and Dutch roll mode with propeller effects. The stability of the spiral mode is enhanced by the propeller flow and also the response of the roll subsidence mode is faster with propeller effects. Detailed analysis of eigenvalues and eigenvectors shows the importance of incorporating propeller flow in analyzing the dynamics of the MAV.

SIMULATED PILOT-IN-THE-LOOP TESTING OF HANDLING QUALITIES OF THE FLEXIBLE WING AIRCRAFT

This article aims to indicate the differences between rigid and flexible wing aircraft flying (FQ) and handling (HQ) qualities. The Simulation Framework for Flexible Aircraft was used to provide a generic cockpit environment and a piloted mathematical model of a bare airframe generic high aspect ratio wing aircraft (GA) model. Three highly qualified test pilots participated in the piloted simulation trials campaign and flew the GA model with both rigid and flexible wing configurations. The results showed a negligible difference for the longitudinal HQs between rigid and flexible wing aircraft. However, significant changes were indicated for the lateral/directional HQs of the flexible wing aircraft. A wing ratcheting phenomenon manifested itself during the roll mode tests, the spiral mode exhibited neutral stability and the Dutch roll mode shape changed from a horizontal to a vertical ellipse. The slalom task flight tests, performed to assess the FQs of the aircraft, revealed the degradation of both the longitudinal and lateral/directional FQs.

Experimental Study of Aircraft Achieving Dutch Roll Mode Stability without Weathercock Stability

Weathercock stability is usually considered essential to achieve normal flight, while the Dutch roll mode stability can still be achieved without weathercock stability which has been algebraically proved. This paper proposed a flight experiment to investigate the characteristics of an airplane with Dutch roll mode stability but no weathercock stability. Firstly, the algebraic analysis based on a standard lateral-directional mode approximation was made to demonstrate the effect of yawing stability derivative Cnβ on the Dutch roll mode characteristics. The flight experiment was organized after that using a model glider which was modified to have zero Cnβ but with marginal change on Cyβ. The convergence of Dutch roll mode in flight meets the algebraic and numerical analysis as expected. However, the difference of handling characteristics between the original and modified configurations indicates some other roles the weathercock stability plays in flight as well as some limitations of utilizing mode criterion in flight quality analysis.

Effect of Aerodynamic Configuration Parameters on Lateral-Directional Stability of Double-Swept Flying Wing Aircraft

Poor lateral-directional stability due to the absence of vertical stabilizer is a great risk to the aircraft with flying wing layout. In this paper, an unmanned aerial vehicle with this kind of configuration is chosen as the research object. A three-dimensional model of the unmanned aerial vehicle is established, and then the sensitivity analysis is performed to obtain the effects of main aerodynamic shape parameters on lateral-directional flying quality. The results show that the roll mode and spiral mode of the aircraft meet the requirements of Level 1 flying quality in MIL-F-8785C. But the Dutch roll mode is generally divergent, which means that the flying quality of the aircraft is unacceptable. Thus it can be seen that the Dutch roll mode is the key to the dynamic stability of the aircraft. Further studies show that increasing the value of wing aspect ratio or decreasing the values of dihedral angle and torsion angle are useful for improving the Dutch roll mode. It is valuable to reveal the influence mechanism of aerodynamic shape parameters on lateral-directional flying quality for the design of flying wing aircraft.

Influences of airfoil profile on lateral-directional stability of aircraft with flying wing layout

Purpose The purpose of this study is to analyze influence of airfoil profile on lateral-directional flying quality of flying wing aircraft. The lateral-directional stability is always insufficient for aircraft with the layout due to the absence of vertical stabilizer. A flying wing aircraft with double-swept wing is used as research object in the paper. Design/methodology/approach The 3D model is established for the aircraft with flying wing layout, and parametric modeling is carried out for airfoil mean camber line of the aircraft to analyze lateral-directional stability of the aircraft with different camber line parameters. To increase computational efficiency, vortex lattice method is adopted to calculate aerodynamic coefficients and aerodynamic derivatives of the aircraft. Findings It is found from the research results that roll mode and spiral mode have a little effect on lateral-directional stability of the aircraft but Dutch roll mode is the critical factor affecting flying quality level of such aircraft. Even though changes of airfoil mean line parameters can greatly change assessment parameters of aircraft lateral-directional flying quality, that is kind of change cannot have a fundamental impact on level of flying quality of the aircraft. In case flat shape parameters are determined, the airfoil profile has a limited impact on Dutch roll mode. Originality/value Influences of airfoil profile on lateral-directional flying quality of aircraft with double-swept flying wing layout are revealed in the thesis and some important rules and characteristics are also summarized to lay a theoretical basis for design of airfoil and flight control system of aircraft with the layout.