Wing flexibility is well established as providing gust rejection and delayed onset of stall for micro air vehicles. As such, many designs adopt wings of a flexible material mounted onto a skeleton comprised of a stiff leading-edge spar and stiff chordwise strips, called battens. These battens are shown to provide additional strength at localised regions of the wing and thus improve the gust rejection and delay stall; however, their effect on the flight dynamics is less studied. Using a numerical modeling approach, this paper explores a design space of vehicles with a varied number of wing battens mounted onto a baseline vehicle with a flexible wing. The battens are modelled as stepwise changes in torsional stiffness along the wing span. The resulting trim characteristics, static stability metrics and flight dynamics are evaluated. The battens are shown to improve gust rejection but otherwise have a complicated effect across the design space. A reduction in the number of battens improves the longitudinal static stability derivative slightly but lowers the lateral and directional static stability. The damping is decreased for the short period mode and increased for the phugoid and dutch roll modes as the number of battens is reduced.

A novel formulation of the flight dynamic equations is presented that permits a rapid solution for the design of trajectory following autopilots for nonlinear aircraft dynamic models. A robust autopilot control structure is developed based on the combination of the good features of the nonlinear dynamic inversion (NDI) method, integrator backstepping method, time scale separation and control allocation methods. The aircraft equations of motion are formulated in suitable variables so that the matrices involved in the block backstepping control design method are diagonally dominant. This allows us to use a linear controller structure for a trajectory following autopilot for the nonlinear aircraft model using the well known loop by loop controller design approach. The resulting autopilot for the fixed-wing rigid-body aircraft with a cascaded structure is referred to as the diagonally dominant backstepping (DDBS) controller. The method is illustrated here for an aircraft auto-landing problem under unknown actuator failures and severe winds. The requirement of state and control surface limiting is also addressed in the context of the design of the DDBS controller.

The effect of the wake of a leading aircraft on a following aircraft is demonstrated by calculating the rolling motion consisting of three terms: (i) the free rolling motion due to initial bank angle and roll rate; (ii) the forced wake response due the rolling moment induced by the wake encounter; (iii) the forced control response due to aileron deflection to counter the wake vortex effects. It is shown that in the absence of control action, the roll rate of the following aircraft goes through a peak, and then decays, leading to a constant asymptotic bank angle; the latter is a measure of the magnitude of the wake effect, e.g. is larger for weaker damping. The exact analytical solution of the roll equation appears as a power series of a damping factor, whose coefficients are exponential integrals of time; it is shown that the first two terms give an accuracy better than 2%. The theory is used to simulate 15 combinations of wake vortex encounters between leading and following aircraft in the five ICAO/FAA weight categories: light, medium, heavy, special (B757) and very large (A380).

The development of adaptive morphing wings has been individuated as one of the crucial topics in the greening of the next generation air transport. Research programs are currently running worldwide to exploit the potentiality of morphing concepts in the optimisation of aircraft efficiency and in the consequent reduction of fuel burn. Among these, SARISTU represents the largest European funded research project which ambitiously addresses the challenges posed by the physical integration of smart concepts in real aircraft structures; for the first time ever, SARISTU will experimentally demonstrate the structural feasibility of individual morphing concepts concerning the leading edge, the trailing edge and the winglet on a full-size outer wing belonging to a CS-25 category aircraft. In such framework, the authors intensively worked on the definition of aeroelastically stable configurations for a morphing wing trailing edge driven by conventional electromechanical actuators. Trade off aeroelastic analyses were performed in compliance with CS-25 airworthiness requirements (paragraph 25.629, parts (a) and (b)-(1)) in order to define safety ranges for trailing-edge inertial and stiffness distributions as well as for its control harmonics. Rational approaches were implemented in order to simulate the effects induced by variations of trailing-edge actuators’ stiffness on the aeroelastic behaviour of the wing also in correspondence of different dynamic properties of the trailing-edge component. Reliable aeroelastic models and advanced computational strategies were properly implemented to enable fast flutter analyses covering several configuration cases in terms of structural system parameters. Already available finite elements models were processed in MSC-NASTRAN® environment to evaluate stiffness and inertial distributions suitable for the stick-equivalent idealisation of the reference structure. A parametric stick-equivalent model of the reference structure was then generated in SANDY3.0, an in-house developed code, that was used for the definition of the coupled aero-structural model as well as for the solution of aeroelastic stability equations by means of theoretical modes association in frequency domain.

Obtained results were finally arranged in stability carpet plots efficiently conceived to provide guidelines for the preliminary design of the morphing trailing-edge structure and therein embedded actuators.

Dynamic stability data on axially symmetric pointed and blunt cones, parabolic profiles and other ogive and blunt cylindrical shapes is readily available in literature; the dynamic stability on elliptic blunt paraboloids has not been studied at any great lengths in the past. Both numerical and experimental results are scarce. The present paper uses the shock expansion method to obtain the unsteady pressure distribution on blunt elliptic conical bodies at small angles-of-attack. The resulting unsteady pressure distribution is suitably integrated over the surface of the elliptic body to obtain appropriate analytic expressions for static and dynamic stability. Owing to scarcity of meaningful numerical or measured data for elliptic bodies, the results are compared in qualitative terms against published dynamic stability data on pointed elliptical cones or other axisymmetric blunt cones.

Generally, pylon-mounted external stores significantly affect the aerodynamic characteristics of the aircraft due to their flexibility. Therefore, many investigations upon the dynamic and aeroelastic characteristics of an aircraft wing with external stores have been done over the last few decades Recently, a study was carried out regarding the aeroelastic effects on wings by the engine placement For severe operation conditions, classical linear theory with a small amount of amplitude vibration may not be an appropriate analysis. Nonlinear vibration analysis will be required, especially when the amplitude of the vibration is larger than the wing thickness. Chia performed static, dynamic, and post-buckling analyses of various isotropic and composite plates for that purpose. Dumir and Bhaskar derived finite element formulations to analyse the nonlinear vibration of beams and plates. Moreover, the variational-asymptotic plate formulation and the accompanying equations for the global analysis for the plates have been studied. That approach accounted every possible geometrical non-linearity associated with large displacement and small strain.