The Flared Folding Wingtip (FFWT) concept allows an aircraft’s wingspan to extend beyond airport gate limitations, while its freely moving wingtip can serve as a Gust Load Alleviation (GLA) device, potentially reducing the required structural weight of the wing.
To study the behavior of the FFWT in combination with a highly flexible wing, this project designed and manufactured a wind tunnel demonstrator, featuring ailerons on both the fixed wing section and the folding wingtip. The inboard aileron is sized to achieve a hypothetical roll rate of 15°/s, comparable to CS-25 certified aircraft, while the outboard aileron is designed to return the wingtip to its neutral position.
Sizing the wing spar of a highly flexible demonstrator while ensuring flutter occurs in the free hinge condition within the velocity range of the Open Jet Facility (OJF) at TU Delft proved to be a conflicting design requirement. This led to a predicted flutter speed of 20 m/s and a maximum wingtip deflection of 5.64%
A Ground Vibration Test (GVT) was conducted to validate the Finite Element Method (FEM) model. A comparison between the locked and free hinge conditions revealed that the locked hinge introduced unexpected flexibility into the structure, which suggests that the FEM representation should be refined to better capture the actual structural behavior.

Flared folding wing tips (FFWTs) improve aerodynamic efficiency but present aeroelastic challenges. This study develops an FFWT aeroelastic model using: (i) multibody constraint formulation for kinematics, (ii) non-linear static analysis for equilibrium under aerodynamic loading, and (iii) linearised dynamic analysis for time-dependent behaviour.

The multibody formulation defines the wing tip’s motion through hinge constraints, while the non-linear static analysis examines the effects of flare angles on equilibrium fold angles and reaction forces. The wing root bending moment (WRBM) decreases by 17% compared to a locked configuration but increases by 23.4% as the flare angle grows from 0o to 20o. For flare angles below 10o, the solver characteristics and initial equilibrium positions at lower velocities can lead to numerical issues such as zero-division errors and poorly conditioned matrices.

The linearised dynamic model, based on the static solution, is evaluated with different configurations: a locked hinge, a free hinge, and a locked-free hinge. Smaller flare angles allow higher fold angles but introduce minor anomalies in the inner wing tip’s response, while larger flare angles improve numerical stability yet cause more persistent oscillations. The locked-free case assesses hinge release during a gust encounter, where releasing the hinge at peak gust intensity leads to larger persistent oscillations. Artificial numerical diffusion and structural damping effectively reduce numerical noise in reaction moments, revealing underlying trends and improving stability.