Morphing Trailing Edge Wings for Transport Aircraft

Abstract

Aviation was responsible for 2.5% of global energy-related CO2 emissions in 2023, and the market is projected to double over the next two decades. This growth conflicts with international targets to reach net-zero emissions by 2050. Of the available mitigation pathways, reducing in-flight energy consumption is the most immediately deployable, as it does not depend on new ground infrastructure. Aerodynamic drag is the main contributor to in-flight energy demand and is largely governed by the main wing. Since fixed wings are optimized for a single design point, they operate off-design during much of a mission. Morphing wings can adapt their shape in flight, offering a route to lower drag across a wider operating envelope.

This thesis assesses the effect of implementing chordwise two-degree-of-freedom (2-DoF) compliant camber-twist morphing trailing-edge wings on the sizing, configuration, and performance of CS-25 transport aircraft. Block fuel consumption is used as the primary performance metric, as it captures the trade-off between improved aerodynamic efficiency and the sizing penalties introduced by morphing systems.

Three methodological contributions support this assessment. First, a parameterization method was developed to describe the morphed shape of an arbitrary base airfoil using the rear spar location and two pseudo-deflection angles. Control points on the camberline are rotated and fitted with a fourth-order polynomial, after which the airfoil surfaces are reconstructed while preserving suction-side arc length to reflect compliant structure constraints. Applied at multiple spanwise stations, this method represents camber-twist morphing at wing level.

Second, the Aircraft Trimmed Performance Analysis Tool (ATPAT) was developed to evaluate trimmed cruise aerodynamic efficiency of morphing-wing aircraft. ATPAT combines a vortex lattice method with strip theory and sweep theory to resolve induced, viscous, pressure, and wave drag with runtimes of seconds to one minute per evaluation. The tool was validated against experimental and computational data on the Fokker 100 and integrated into the Initiator aircraft design toolbox with Bayesian and gradient-based optimizers.

Third, two uncertain sizing inputs were explicitly addressed: morphing system mass and achievable high-lift increment. Morphing system mass was treated as a parameter bounded by the specific mass of Fowler flaps, while RANS CFD estimated a conservative sectional lift increase of 0.63 at full deflection.

The methodology was applied to the ATR 72-600 and Fokker 100. For both aircraft, morphing designs were heavier and required larger wing areas than conventional designs due to high-lift limitations, making field performance the main constraint. Relaxing landing field length by about 20% brought sizing outcomes closer to the reference aircraft.

For the ATR 72-600, aerodynamic gains did not offset the penalties. The morphing design matched conventional block fuel only on the harmonic mission and used 6% and 4% more fuel on shorter and maximum-fuel missions. For the Fokker 100, a block-fuel reduction of up to 3.6% was achieved on the harmonic mission after a 17.5% relaxation of landing field length, with sizing nearly identical to the reference aircraft. Its transonic cruise also offers additional drag reduction potential through wave drag reduction.

The results remain subject to uncertainty. The relative contributions of sizing effects and wave drag reduction were not isolated, morphing system mass remains uncertain, and high-lift performance estimates are based on limited airfoil data. More detailed experimental validation and segmented mission analysis are recommended to refine the estimated benefits of morphing wings.