Distributed electric propulsion in aircraft design is a concept that involves placing multiple electric motors across the aircraft’s airframe. Such a system has the potential to contribute to sustainable aviation by significantly reducing greenhouse gas emissions, minimizing noise pollution, improving fuel efficiency, and encouraging the use of cleaner energy sources. This paper investigates the impact and relationship of turbo-electric propulsion component characteristics with three performance quantities of interest: lift-to-drag ratio, operating empty weight, and fuel burn. Using the small- and medium-range “DRAGON” aircraft concept, we performed design exploration enabled through the explainable surrogate model strategy. This work uses Shapley additive explanations to illuminate the dependencies of these critical performance metrics on specific turbo-electric propulsion component characteristics, offering valuable insights to inform future advancements in electric propulsion technology. Through global sensitivity analysis, the study reveals a significant impact of electrical power unit (EPU) power density on lift-to-drag ratio, alongside notable roles played by EPU-specific power and applied voltage. For operating empty weight, EPU-specific power and voltage are highlighted as critical factors, while turboshaft power-specific fuel consumption notably influences fuel burn. The analysis concludes by exploring the implications of the insights for the future development of turbo-electric propulsion technology.

During the Vertical Take-Off and Landing (VTOL) of a rotorcraft, there is a high risk of instability and safety incidents due to the possibility of one side of the landing gear making initial contact with the ground, particularly under extreme environmental conditions and maneuvers. Furthermore, the varied performance of adaptive landing gear necessitates a landing control approach that specifically targets both sides of the adaptive landing gear. This study proposes a method that regulates the landing gear first touchdown side through an impedance controller to guarantee the stability of the rotorcraft and then tilts the landing gear toward the rear landing leg side, followed by a soft and smooth landing through the rear landing leg. This approach accomplishes steady adaptive VTOL of the rotorcraft. The fall vibration test results demonstrate that the adaptive landing gear system with impedance control has excellent adaptive landing functionality, which can handle not only landing on uneven ground at various points but also cope with different ascent rates and ground friction during stable takeoff/landing.

This paper presents an experimental study on the anti-icing performance of full-scale rotating spinners with different cone angles. The experiments were conducted in a 3 m×2 m ice wind tunnel (IWT), and the spinners were equipped with hot-air anti-icing systems. Three different cone angles (80°, 70°, and 60°) were examined. The surface temperature of the spinners was measured using an infrared (IR) camera, and ice accretion and water film flow were recorded using high-speed cameras. Numerical simulations were also performed to analyze the water collection coefficients and anti-icing heat energy. The results showed that a larger cone-angle spinner has a larger water collection coefficient but a smaller heat-transfer coefficient and total surface area, resulting in better anti-icing performance for the same conditions. Additionally, the results showed that the residual ice on the spinner exhibited small, white, discretely distributed icicles. Furthermore, the surface temperature in the icing region of the 60° spinner was found to be almost equal to the total temperature of the incoming flow, indicating rime-ice accretion even under glaze-ice conditions. This observation can be attributed to the low water collection coefficient in this region.

Coaxial, corotating (stacked) rotors have shown improved performance compared to conventional rotors, but the optimum configuration is highly sensitive to the rotor parameters. This paper reports the development of a low-order model, blade interaction prediction (BLIP), to efficiently predict the thrust and power of closely spaced rotor blades and quantify the effects of rotor geometry on total and individual stacked rotor performance. BLIP couples a vortex panel method and blade element momentum theory to combine the effects of bound circulation and rotor inflow. A cascade effect in the two-dimensional vortex panel method was implemented to incorporate the effect of airfoils rotating in a circle. Validation was performed with measurements of a 1.108-m-radius fixed-pitch stacked rotor with variable axial and azimuthal spacing, and excellent correlation was observed. It was found that small azimuthal angles and axial spacings are most effective in varying total thrust. The variation of thrust and power with azimuthal spacing was found to be a result of bound circulation, while the variation with axial spacing is due to rotor inflow interactions.

Airworthiness certification is challenging for novel aircraft concepts. To avoid the significant cost associated with the redesign for certification compliance, incorporating certification requirements into early aircraft design is desired for unconventional aircraft. However, epistemic uncertainties arising from modeling assumptions, and aleatory uncertainties stemming from uncontrollable noise factors may have impacts on the certification analysis and certification-constrained design process. This paper presents an uncertainty quantification study based on a certification-constrained design and optimization study previously conducted for NASA’s Parallel Electric–Gas Architecture with Synergistic Utilization Scheme (PEGASUS) concept. The epistemic uncertainties are modeled through a set of multiplicative factors applied to intermediate disciplinary variables. The sensitivity analysis between design metrics and multiplicative factors reveals that uncertainties in stability and control derivatives can significantly affect certification constraint predictions, and uncertainties in drag approximations have considerable impacts on the vehicle sizing process. The aleatory uncertainties added to flight dynamics simulations include wind velocities and variations of weight and center of gravity. Four representative design candidates are evaluated for their robustness against aleatory uncertainties based on the Monte Carlo simulation performed on noise factors. The results show that aleatory uncertainties can affect the aircraft dynamic responses in flight test simulations, thus compromising certification compliance.

Subscale wind tunnel data extrapolation is both a necessary and challenging undertaking. Most readily available wind tunnel facilities can achieve Reynolds numbers that are typically an order of magnitude lower than those of the full-scale flight article. Consequently, the wind tunnel data need to be scaled, with the Reynolds number disparity impacting force and moment measurements. Although computational fluid dynamics is ascending as a valuable tool for enabling scaling, the most common extrapolation methodologies are analytic and semi-empirical in nature. Consequently, a new approach is presented to scale both the minimum drag coefficient and the sectional pressure drag coefficient that uses the subscale data to define extrapolation exponents. Implementation requires a minimum of two subscale tests to enable specification of the exponents determined through coalescence of the extrapolated subscale tests. The approach is simple to implement and can be applied to both airfoils and wings. Numerous cases are presented for method validation.

A lift-offset system for a single-rotor-type compound helicopter is proposed to improve the aerodynamic performance in high-speed flight. The proposed system utilizes the differential flap deflections on the fixed wings to produce a rolling moment, which is counteracted by the single main rotor, causing the rotor to operate in a lift-offset state. The performance of the proposed system is evaluated through numerical simulations. At first, the effect of lift offset with regard to lift-share ratio on the rotor performance is investigated. Then, the impact of lift offset due to the differential flaps on the overall effective lift-to-drag ratio is studied. The results show that the lift offset significantly improves the rotor performance and the overall effective lift-to-drag ratios, especially at larger rotor lift-share ratios. The overall effective lift-to-drag ratio increases by 10% due to the differential flaps compared to the zero-flap deflections. It is concluded that the lift offset due to the differential flaps achieves more efficient cruising flight for a single-rotor-type compound helicopter.

This paper introduces the technology and performance of a new sandwich structure consisting of carbon fiber composite face sheets, a polyimide foam core, and an aluminum honeycomb panel with both heat insulation and load-bearing functions. The heat-resistant performance of the sandwich structure was evaluated. The vacuum thermal conductivity of the sandwich structure in the vertical direction ranges from 0.54 to 0.92 (W/[m⋅K]) with increasing temperature from −170 to 135°C. A multilayer finite element model of carbon fiber cloth, polyimide foam, and aluminum honeycomb was established. Finally, a comprehensive evaluation of the mechanical and thermal insulation performance of the sandwich structure was conducted through random vibration testing and thermal vacuum testing. The results showed that the sandwich structure had good stiffness and thermal insulation performance, successfully verifying the effectiveness of the collaborative design.

During the initial stages of missile design, finding an efficient method for analyzing aerodynamic characteristics is crucial. This paper proposes a novel aerodynamic modeling method based on a limited computational fluid dynamics (CFD) dataset, combining transfer learning (TL) with Dendritic Net (DD). Initially, we employ CFD-calculated aerodynamic data to establish a pretrained model using DD. Subsequently, the model is adapted to the target domain by TL, predicting aerodynamic parameters under specific conditions. The overall aerodynamic parameters are utilized to generate a relational spectrum through DD’s white-box features, from which primary features are extracted to establish an aerodynamic polynomial model. Finally, the model’s practicality is validated by ballistic flight simulations. The innovation lies in leveraging DD to generate a relational spectrum of aerodynamic parameters, leading to a high-precision polynomial model. Research shows DD outperforms traditional cell-based networks in predicting aerodynamic parameters, and TL reduces the CFD computation workload in the target domain by 3/4 while maintaining prediction accuracy. The polynomial model exhibits superior accuracy compared to the empirical fitting formulas. The method reduces the computational workload for aerodynamic data collection, and through system identification, a high-precision polynomial model is obtained, which provides a reliable basis for missile controller design.

The aerodynamics of the ship–helicopter dynamic interface play an important role in determining ship–helicopter operating limits. A review of prior studies, in conjunction with experimental work, indicates that a time-accurate rotor model and a physics-based turbulence-resolving flow solver with two-way coupling between these components are required to accurately predict rotor–airwake and rotor–rotor interactions. Here, a recently developed actuator surface model is validated against two further multirotor cases and employed for two large-scale ship–helicopter dynamic interfaces with up to three concurrent rotorcraft and five rotors. Simulations of the Sikorsky X2 rotor with significant rotor–rotor interaction match resolved unsteady rotor loading well using 1.2% of the computational effort of resolved blade calculations. Computations of the outwash from a Boeing CH-47D in hover gave results within experimental error bars for most azimuths, where discrepancies may be attributed to the estimated trim and division of rotor loading. Simulations of the dynamic interface between the Simple Frigate Shape 1 and a hovering UH-60a were presented for three wind-over-deck angles and three positions for 40 knots of wind speed. The computed thrust and root mean square thrust coefficients in the closed-loop pilot control band are presented and demonstrated to have an to have an expected dependence on immersion in the ship airwake. Finally, a large-scale dynamic interface computation was performed with two CH-47Ds and one UH-60a operating concurrently over the deck of the landing helicopter assault ship at 40 knots of wind speed and 0° and 30° angle. Results highlighted the importance of understanding rotor-wake/airwake interactions dependent on rotorcraft type and position and wind-over-deck. The computation provided unsteady thrust and torque for each of the five rotors from 60 s of data using just 11,424 central processing unit hours on a grid of 19.5×106 points. These simulations show that hybrid Navier–Stokes simulations employing actuator line or surface methods are capable of providing high-fidelity, time-accurate predictions of rotor loads at the ship–helicopter dynamic interface at substantially lower cost.