Investigation of a Light Boxplane Model Using Tuft Flow Visualization and CFD

In this paper, we addressed the flow patterns over a light boxplane scale model to explain the previously discovered disagreement between its predicted and experimental aerodynamic characteristics. By tuft flow and CFD visualization, we explored the causes yielding a large zero lift pitching moment coefficient, lateral divergence, difference in fore and aft elevator lift, and poor high lift performance of the aircraft. The investigation revealed that the discrepancy in the pitching moment coefficient and lateral stability derivatives can be attributed to insufficient accuracy of the used predictive methods. The difference in fore and aft elevator lift and poor high lift performance of the aircraft may occur due to the low local Reynolds number, which causes the early flow separation over the elevators and flaperons when deflected downward at angles exceeding 10°. Additionally, some airframe changes are suggested to alleviate the lateral divergence of the model.

Estimation and Separation of Longitudinal Dynamic Stability Derivatives with Forced Oscillation Method Using Computational Fluid Dynamics

This paper focuses on estimating dynamic stability derivatives using a computational fluid dynamics (CFD)-based force oscillation method, and on separating the coupled dynamic derivatives terms obtained from the method. A transient RANS solver is used to calculate the time history of aerodynamic moments for a test model oscillating about the center of gravity, from which the coupled dynamic derivatives are estimated. The separation of the coupled derivatives term is carried out by simulating simple harmonic oscillation motions such as plunging motion and flapping motion which can isolate the pitching moment due to AOA rate (Cmα˙) and the pitching moment due to pitch rate (Cmq), respectively. The periodic motions are implemented using a CFD dynamic mesh technique with user-defined function (UDF). For the validation test, steady and unsteady simulations are performed on the Army-Navy Finner Missile model. The static aerodynamic moments and pressure distribution, as well as the coupled dynamic derivative results from the pitching oscillation mode, show good agreement with the previously published wind tunnel tests and CFD analysis data. In order to separate the coupled derivative terms, two additional harmonic oscillation modes of plunging and flapping motions are tested with the angle of attack variations from 0 to 85 degrees at a supersonic speed to provide real insight on the missile maneuverability. The cross-validation study between the three oscillation modes indicates the summation of the individual plunging and flapping results becoming nearly identical to the coupled derivative results from the pitching motion, which implies the entire set of coupled and separated dynamic derivative terms can be effectively estimated with only two out of three modes. The advantages and disadvantages of each method are discussed to determine the efficient approach of estimating the dynamic stability derivatives using the forced oscillation method.

Climbing parrots achieve pitch stability using forces and free moments produced by axial-appendicular couples

During vertical climbing, the gravitational moment tends to pitch the animal's head away from the climbing surface and this may be countered by 1) applying a correcting torque at a discrete contact point, or 2) applying opposing horizontal forces at separate contact points to produce a free moment. We tested these potential strategies in small parrots with an experimental climbing apparatus imitating the fine branches and vines of their natural habitat. The birds climbed on a vertical ladder with four instrumented rungs that measured three-dimensional force and torque, representing the first measurements of multiple contacts from a climbing bird. The parrots ascend primarily by pulling themselves upward using the beak and feet. They resist the gravitational pitching moment with a free moment produced by horizontal force couples between the beak and feet during the first third of the stride and the tail and feet during the last third of the stride. The reaction torque from individual rungs did not counter, but exacerbated the gravitational pitching moment, which was countered entirely by the free moment. Possible climbing limitations were explored using two different rung radii, each with low and high friction surfaces. Rung torque was limited in the large-radius, low-friction condition, however, rung condition did not significantly influence free moments produced. These findings have implications for our understanding of avian locomotor modules (i.e., coordinated actions of the head-neck, hindlimbs, and tail), the use of force couples in vertical locomotion, and the evolution of associated structures.

Aerodynamic Shape Multi-Objective Optimization for SAE Aero Design Competition Aircraft

The SAE Regular Class Aero Design Competition requires students to design a radio-controlled aircraft with limits to the aircraft power consumption, take-off distance, and wingspan, while maximizing the amount of payload it can carry. As a result, the aircraft should be designed subject to these simultaneous and contradicting objectives: 1) minimize the aerodynamic drag force, 2) minimize the aerodynamic pitching moment, and 3) maximize the aerodynamic lift force. In this study, we optimized the geometric design variables of a biplane configuration using 3D aerodynamic analysis using the ANSYS Fluent. Coefficients of lift, drag, and pitching moment were determined from the completed 3D CFD simulations. Extracted coefficients were used in modeFRONTIER multi-objective optimization software to find a set of non-dominated (Pareto-optimal or best trade-off) optimized 3D aircraft shapes from which the winner was selected based to the desired plane performance.

Design Concept and Structural Configuration of Magnetic Levitation Stage with Z-Assist System

Magnetic levitation technology is expected to provide a solution for achieving nanometer-scale positioning accuracy. However, magnetic leakage limits the application of the magnetic levitation stage. To reduce magnetic density, motors should be installed at an appropriate distance from the table. This increases the axis interference between the horizontal thrust and the pitching, making it difficult to achieve stable levitation. In this study, a magnetic levitation stage system that has a unique motor structure fusing a gravity compensation function and pitching moment compensation is proposed. This compensation mechanism operates automatically using the passive magnetic circuit structure, ensuring that noises from the coil current and the timing gaps do not affect the driving characteristics and that neither wiring nor sensors are required. The basic characteristics were evaluated through the driving experiments, and the efficiency of the proposed gravity and pitching moment compensation system was demonstrated.

Effect of Aerodynamic Moment on High-Speed Maglev Train Under Complicated Conditions

As the next generation of high-speed rail transportation, the high-speed maglev train has a design speed of 600km/h, whose Mach number is about 0.49. The severe aerodynamic effect caused by this high speed has a substantial impact on the train’s stability and safety. In this paper, the aerodynamic moments of two three-carriage maglev trains passing by each other in open air are investigated by numerical simulation. To get transient moments acting on the train, this study adopted the sliding mesh method and the k-ε turbulent model, and a user-defined function was compiled to define the motion of maglev. The results show that the pitching moment is the most important factor for the steady of maglev trains running in the open air. The oscillation of the total aerodynamic moment mainly comes from the moment acting on the lower part. The coupling of the pitching moment acting on the upper and lower part of carriages make the peak of the total pitching moment behind the total yawing moment.

Gull-inspired joint-driven wing morphing allows adaptive longitudinal flight control

Birds dynamically adapt to disparate flight behaviours and unpredictable environments by actively manipulating their skeletal joints to change their wing shape. This in-flight adaptability has inspired many unmanned aerial vehicle (UAV) wings, which predominately morph within a single geometric plane. By contrast, avian joint-driven wing morphing produces a diverse set of non-planar wing shapes. Here, we investigated if joint-driven wing morphing is desirable for UAVs by quantifying the longitudinal aerodynamic characteristics of gull-inspired wing-body configurations. We used a numerical lifting-line algorithm (MachUpX) to determine the aerodynamic loads across the range of motion of the elbow and wrist, which was validated with wind tunnel tests using three-dimensional printed wing-body models. We found that joint-driven wing morphing effectively controls lift, pitching moment and static margin, but other mechanisms are required to trim. Within the range of wing extension capability, specific paths of joint motion (trajectories) permit distinct longitudinal flight control strategies. We identified two unique trajectories that decoupled stability from lift and pitching moment generation. Further, extension along the trajectory inherent to the musculoskeletal linkage system produced the largest changes to the investigated aerodynamic properties. Collectively, our results show that gull-inspired joint-driven wing morphing allows adaptive longitudinal flight control and could promote multifunctional UAV designs.

Trim Solutions of Multirotor Vehicles using a Fast Performance Prediction Method

A fast multirotor performance prediction method is presented. The method uses an algorithm to determine the flight performance and trim solutions of multirotor vehicles in steady, level flight. The method considers parasitic drag, force trim, fuselage interference, rotor interference, moment trim, and power prediction. In order to validate the method, vehicle lift, drag, and pitching moment predictions are compared to experimental data from NASA Ames for the 3DR Solo, a commercially available vehicle. The performance comparison with wind tunnel data show similar lift, drag and pitching moment trends when using estimated rotor and vehicle geometries. In addition, the predicted rotor speeds, vehicle power, and vehicle pitch are compared to flight test data of the Aeryon SkyRanger. The lead and rear rotor speed results show that the application of moment trim into the performance model provides rotor speed estimates that reflect the differential rotor speeds the flight test. An orientation study is conducted to explore the effects of rotor and fuselage interference velocities on rotor performance and the performance differences of a four-rotor vehicle flying in diamond and square configurations. Finally, a mass offset study is presented to predict the changes in rotor speed distribution of a SkyRanger vehicle when a 100 g mass is added to the support arm, which simulates asymmetry in centre of gravity location. The predicted performance results show overlapping results with flight testing with and without the mass offset at airspeeds below 5 m/s. At higher airspeeds, the rotor speed predictions that are established by moment trim requirements reflect the rotor speed trends shown from flight test data.

Trim Solutions of Multirotor Vehicles using a Fast Performance Prediction Method

A fast multirotor performance prediction method is presented. The method uses an algorithm to determine the flight performance and trim solutions of multirotor vehicles in steady, level flight. The method considers parasitic drag, force trim, fuselage interference, rotor interference, moment trim, and power prediction. In order to validate the method, vehicle lift, drag, and pitching moment predictions are compared to experimental data from NASA Ames for the 3DR Solo, a commercially available vehicle. The performance comparison with wind tunnel data show similar lift, drag and pitching moment trends when using estimated rotor and vehicle geometries. In addition, the predicted rotor speeds, vehicle power, and vehicle pitch are compared to flight test data of the Aeryon SkyRanger. The lead and rear rotor speed results show that the application of moment trim into the performance model provides rotor speed estimates that reflect the differential rotor speeds the flight test. An orientation study is conducted to explore the effects of rotor and fuselage interference velocities on rotor performance and the performance differences of a four-rotor vehicle flying in diamond and square configurations. Finally, a mass offset study is presented to predict the changes in rotor speed distribution of a SkyRanger vehicle when a 100 g mass is added to the support arm, which simulates asymmetry in centre of gravity location. The predicted performance results show overlapping results with flight testing with and without the mass offset at airspeeds below 5 m/s. At higher airspeeds, the rotor speed predictions that are established by moment trim requirements reflect the rotor speed trends shown from flight test data.

Investigation on the aerodynamic interaction between a rotor and ship with opened hangar door

Unsteady aerodynamic interference between a rotorcraft and a ship occurs during shipboard launch and recovery operations and has a negative impact on the safety. An experiment of a reduced-scale model rotor and a CFD analysis in hover was carried out to investigate the performance and flow field of a rotor approaching a ship. In this paper, the thrust and pitching moment of the rotor hovering above the ground, deck were tested, and the influence of hangar door on the thrust, pitching moment, and flow field was also measured. A CFD method based on RANS and overset technology was used to investigate the flow field of the rotor operating on the model-scale ship. As the rotor approaches the deck, its thrust first decreases induced by a recirculation near the deck, and then increases induced by the effect of deck, and finally obviously decreases caused by the recirculation near hangar door. The deck and hangar door also affects the flow field to yield an intensive nose-down pitching moment. The status of the hangar door has a significant influence on the rotor thrust and pitching moment. The recirculation is weakened with an opened hangar door resulting in recovery of the rotor thrust and decrease of the nosed down pitching moment.