Flight Dynamic Characteristics Research Articles

Aero-propulsive coupling modeling and dynamic stability analysis of distributed electric propulsion tandem-wing UAV with rapid ascent capability

The distributed electric propulsion tandem-wing unmanned aerial vehicle (UAV) offers higher aerodynamic efficiency than conventional electric vertical takeoff and landing UAV and superior rapid ascent takeoff and landing capabilities compared to regular fixed-wing aircraft. However, for this configuration, the aero-propulsive coupling effects between the propellers and wings are significant. To study the mutual interaction between distributed electric propulsion and aerodynamics on the flight dynamics characteristics and rapid ascent flight capability of UAV, an aero-propulsive coupling model incorporating the effects of propellers slipstream is established. Ground-based blown wing experiment is conducted to validate the modeling accuracy. Subsequently, a theoretical modeling framework based on standard stability derivatives is developed, incorporating the influence of thrust on the dynamics within stability derivatives. The dynamic characteristics of distributed electric propulsion tandem-wing configuration are then studied and aero-propulsive coupling effects on natural modes of motion and flight qualities are analyzed. Finally, flight simulations and actual flight tests are conducted to validate the rapid ascent flight capability of UAV in real-world. The experimental results indicate that UAV can achieve rapid ascent flight with significant pitch angles and high climb rates, showing promising results with more than a 91.9% improvement in takeoff performance compared to conventional rolling takeoff.

Flight control design for a hypersonic waverider configuration: A non-linear model following control approach

AbstractDLR is currently investigating the potential of hypersonic flight systems in the context of different mission scenarios. One configuration type of higher interest for civil and military purposes is the hypersonic glide vehicle (HGV). Such HGVs operate over broad flight envelopes and pose complex flight dynamic characteristics. This article presents DLR’s generic hypersonic glide vehicle 2 (GHVG-2) and proposes an integrated non-linear flight control architecture that is based on the idea of the non-linear dynamic inversion and non-linear model following control methodologies. The proposed control scheme is designed to sufficiently and robustly handle the system dynamics of the over-actuated flight vehicle. The approach is first discussed, and the performance of the suggested control laws is later investigated via simulations of a high-fidelity non-linear flight dynamic model in the nominal case and under the presence of parametric uncertainties. The presented results demonstrate that the proposed NMFC approach provides benefits for the robust control of the regarded hypersonic system.

Flight Dynamic Characteristics of Wide-Body Aircraft with Wind Gust and Turbulence

In this research, a wide-body aircraft was analyzed with critical monitoring of its states, a function of several control inputs (wind gust, turbulence, and microburst). The aerodynamic and stability coefficients of a Boeing 747-200 were obtained from previously published works and 6- DOF equations were formulated. Simulations were conducted for various control inputs to determine the aircraft’s free response, as well as the forced response. In order to understand the nature of the atmosphere, three different models were incorporated, including (i) the Dryden Model, (ii) wind gust, and (iii) microburst. The aircraft was found to be stable in the longitudinal and lateral flight modes, with trim conditions agreeing with published data. For a vertical wind gust of −10 ft/s, the AoA and pitch rate were observed to oscillate sinusoidally and became stable with new trim conditions. These states were found to regain trim conditions once the gust was removed. In the case of 3D gust, it was found that the longitudinal modes achieved a new trim condition through Phugoid oscillations, whereas the lateral modes underwent short-period oscillations. For the case of turbulence, random fluctuations were observed for trim conditions with no unstable behavior. When considering the microburst case, it was found that the aircraft initially gained altitude in the region of the headwind; this was followed by a sharp descent under the influence of a vertical velocity component.

High-Speed Virtual Flight Testing Platform for Performance Evaluation of Pitch Maneuvers

To research serious nonlinear coupling problems among aerodynamics, flight mechanics, and flight control during high maneuvers, a virtual flight testing platform has been developed for a large-scale, high-speed wind tunnel, based on the real physical environment, and it can significantly mitigate risks and reduce the costs of subsequent flight tests. The platform of virtual flight testing is composed of three-degrees-of-freedom model support, measuring devices for aerodynamic and motion parameters, a virtual flight control system, and a test model. It provides the ability to realistically simulate real maneuvers, investigate the coupling characteristics of unsteady aerodynamics and nonlinear flight dynamics, evaluate flight performance, and verify the flight control law. The typical test results of a pitch maneuver with open-loop and closed-loop control are presented, including a one-degree-of-freedom pitch motion and a two-degrees-of-freedom pitch and roll motion. The serious pitch and roll-coupled motion during a pitch maneuver at a high angle of attack is revealed, and the flight control law for decoupled control is successfully verified. The comparison of the test results and the flight data of a real pitch maneuver proves the reliability and capability of virtual flight testing.

Flight dynamics modeling and analysis for a Mars helicopter

Flight dynamics modeling for the Mars helicopter faces great challenges. Aerodynamic modeling of coaxial rotor with high confidence and high computational efficiency is a major difficulty for the field. This paper builds an aerodynamic model of coaxial rotor in the extremely thin Martian atmosphere using the viscous vortex particle method. The aerodynamic forces and flow characteristics of rigid coaxial rotor are computed and analyzed. Meanwhile, a high fidelity aerodynamic surrogate model is built to improve the computational efficiency of the flight dynamics model. Results in this paper reveal that rigid coaxial rotor can bring the Mars helicopter sufficient controllability but result in obvious instability and control couplings in forward flight. This highlights the great differences in flight dynamics characteristics compared with conventional helicopters on Earth.

Simulation and analysis of drag for inflatable aerodynamic decelerator

Inflatable aerodynamic decelerator, as a novel deceleration and recovery technology, has received attention due to its lightweight and freedom from the launch vehicle fairing size constraints for the space mission. Aimed at the aerodynamic characteristics of the inflatable aerodynamic decelerator, this work studied the effect of the cone angle on its drag and discussed the drag varied with the angle of attack under the different cone angles. The simulation showed that the drag was affected by the cone angle and increased locally with the angle of attack. Furthermore, the larger cone angle was beneficial to the stability of the flow field on its leeward in the case of a high Mach number. The math model of drag with the Mach number and the angle of attack was obtained by fitting the data, which provided favorable support for the prospective discussion of the flight dynamics characteristics.

The optimization method of wing ice shape regulation based on flight dynamics characteristics

Ice on aircraft wing changes the aircraft aerodynamic shape, and has negative effects on flight dynamic characteristics, seriously threatening flight safety. Plasma ice shape regulation is a new de-icing method. Plasma actuator produces an apparent thermal effect, which is designed to dissolve the continuous ice into intermittent ice pieces. How to achieve the optimal regulation ice shape to improve the flight dynamics characteristics under icing conditions is a technical problem restricting the application of this method. A simulation ice shape based on previous ice tunnel experiments and a scale model of swept wing were established. The aerodynamic parameters of no ice, full ice, and two regulation ice schemes were obtained based on wind tunnel. Six degrees of freedom flight dynamics model was established, and flight simulation had been carried out. As the analysis of trim characteristics, dynamic stability, and maneuverability, flight dynamics characteristics were better improved when the ratio of ice width to the mean aerodynamic chord was 0.15. The evaluation method of plasma ice shape regulation schemes was proposed. The proposed method, which can compare and optimize the arrangement of plasma actuators, realized the optimal regulation ice shape on the premise of balancing flight safety and energy consumption.

Faster-than-realtime inverse simulation method for tiltrotor handling qualities investigation

The tiltrotor aircraft has unique flight dynamics characteristics because of the extensive aerodynamic interference and the unique control strategy. Inverse simulation offers an opportunity to study a vehicle's performance during manoeuvring flights. In this paper, an improved inverse simulation method is developed with an Automatic Differentiation (AD) approach embedded in the code based on the verified flight dynamics model of the tiltrotor aircraft. The AD algorithm would accelerate the computational rate of the inverse simulation process and make it achieve faster-than-realtime capability. Then, the XV-15 tiltrotor's control inputs and flight states encountered during a pop-up manoeuvre are investigated using this AD-augmented inverse simulation method, and the real-time capability of this method is also evaluated. The results indicate that the proposed method guarantees both accuracy and faster-than-realtime calculation performance. Lastly, the tiltrotor's manoeuvrability is assessed by executing this manoeuvre in different flight states and manoeuvre settings. Lastly, an envelope involving the velocity and nacelle incidence angle is calculated to indicate the safety region to achieve this pop-up manoeuvre.

Flight dynamics analysis of a small tandem helicopter considering aerodynamic interference

The interference calculation is essential to the flight dynamic analysis especially for multi-rotors configurations. To analyze the flight dynamic characteristics of a small tandem helicopter precisely, a vortex method is utilized to obtain the aerodynamic interaction between the tandem rotors and the fuselage. Specially, the unsteady air loads and the wake of the rotors are developed using a lifting surface method and the viscous vortex particle theory, respectively, and the fuselage is modeled by the panel method to simulate the blocking effect on the rotors. Then the aerodynamic interference of the small tandem helicopter is analyzed under the conditions of different vertical or horizontal distance between the rear and front rotors. Subsequently, to save calculation time during flight dynamic analysis, a hybrid optimization trimming method combining the equilibrium optimizer and the improved delta method is proposed. At last, the flight dynamic analysis for the small tandem helicopter with different configurations are carried out and the results indicate that configuration in which the rear rotor is located higher than the front rotor and the one with larger longitudinal distance between tandem rotors are beneficial to increase the stability in lateral and longitudinal directions, respectively.

Flight Stability of Rigid Wing Airborne Wind Energy Systems

The flight mechanics of rigid wing Airborne Wind Energy Systems (AWESs) is fundamentally different from the one of conventional aircrafts. The presence of the tether largely impacts the system dynamics, making the flying craft to experience forces which can be an order of magnitude larger than those experienced by conventional aircrafts. Moreover, an AWES needs to deal with a sustained yet unpredictable wind, and the ensuing requirements for flight maneuvers in order to achieve prescribed control and power production goals. A way to maximize energy capture while facing disturbances without requiring an excessive contribution from active control is that of suitably designing the AWES craft to feature good flight dynamics characteristics. In this study, a baseline circular flight path is considered, and a steady state condition is defined by modeling all fluctuating dynamic terms over the flight loop as disturbances. In-flight stability is studied by linearizing the equations of motion on this baseline trajectory. In populating a linearized dynamic model, analytical derivatives of external forces are computed by applying well-known aerodynamic theories, allowing for a fast formulation of the linearized problem and for a quantitative understanding of how design parameters influence stability. A complete eigenanalysis of an example tethered system is carried out, showing that a stable-by-design AWES can be obtained and how. With the help of the example, it is shown how conventional aircraft eigenmodes are modified for an AWES and new eigenmodes, typical of AWESs, are introduced and explained. The modeling approach presented in the paper sets the basis for a holistic design of AWES that will follow this work.

Conceptual design and preliminary experiment of icing risk management and protection system

Icing is one of the main external environmental factors that causes aircraft to lose control. The flight safety assurance system under icing condition is particularly important. However, most of the systems do not consider the coupling characteristics of aerodynamics and flight dynamics of icing aircraft. This will affect the accuracy of the calculation results. Besides, the icing risk management system helps the pilot to realize the possible dangers in advance and perform correct maneuvers, based on quantitative assessment and visualization methods of flight risk. The envelope protection system realizes flight safety guarantee based on the real-time boundary protection method of key flight parameters. Finally, based on distributed simulation technology, a flight simulator was used as a platform to integrate the icing risk management system and envelope protection system to realize man-in-the-loop simulation. Two fictional but historically motivated icing scenarios are designed to test the system, and the results demonstrate that the icing risk management and protection system would be useful for aviation safety and can also be used for pilot training and reproducing flight accidents to find the causes.

Nonlinear Helicopter Rigid-Elastic Coupled Modeling with Its Applications on Aeroservoelasticity Analysis

This paper represents a new mathematical model for helicopters with flexible fuselages. The theory connects the two commonly separated research areas of flight, dynamics and structural dynamics, by considering all necessary effects of a flexible fuselage on helicopter flight dynamic characteristics. They are rigid-elastic couplings of the flexible fuselage between six rigid-body degrees of freedom and elastic deformations, along with inertial and kinematic couplings between subcomponents and the fuselage. This is achieved by using the floating frame theory and deriving the acceleration coupling matrices of subcomponents analytically. In addition, the obtained formulation is explicitly decoupled such that all unknown absolute accelerations could be obtained in a single step without iterations, which could improve computational efficiency greatly. This model is suited for aeroservoelastic analysis, and is particularly suited for heavy lift helicopters (HLH) because they usually have slower turning rotors and more flexible fuselages due to their larger scale, leading to closer frequency ranges between rigid body motions and high-frequency rotor and structural modes. The model is validated before being applied to a numerical example of a sample HLH with a feedback loop for stability augmentation. The results show that the feedback loop connects actuators, fuselage deformation, and rigid body motion and induces divergent oscillation, which is the aeroservoelastic instability that cannot be predicted without the additional sensor measurements feedback caused by dynamic deformation. Since the 10-second step response could be calculated in three seconds, the presented helicopter mathematical model is expected to be used in real-time simulations or even further in pilot-in-the-loop simulations, ultimately helping with the design of modern helicopters with nonnegligible fuselage flexibility.

Envelope radiation characteristics of stratospheric airship

To investigate the envelope radiation characteristic of stratospheric airship, three kinds of airship models with different dimensions (fineness ratio of 3, 4, 5) are selected. After establishing the thermal equilibrium equations of the selected models, the influence of the envelope radiation characteristic on the envelope and airship gas is first addressed to determine the optimal fineness ratio by considering the flight dynamics characteristics. Furthermore, the effects of envelope emissivity, envelope absorptivity, solar cells radiation characteristics, and typical envelope materials on the envelope radiation characteristics of airship are discussed in depth. The results show that: (1) With the assumption of same absorptivity and emissivity, the larger the fineness ratio of the airship, the smaller the diurnal temperature difference of the main helium gasbag, and the better the thermal characteristics of airship as well. When the envelope radiation characteristics vary, the temperature difference of main helium gasbag with a fineness ratio of 4 in one day is always less than 1 K, compared with the fineness ratio of 5. However, the temperature difference of main helium gasbag with a fineness ratio of 3 exceeds that with the fineness ratio of 5, and reaches its maximum of 6 K. Therefore, the fineness ratio of 4 is regarded as optimal by considering the floating constraints of low drag and high buoyancy. (2) In the case of higher long-wave emissivity and lower short-wave absorptivity of the envelope material and solar cells, the diurnal helium temperature difference is the smallest, and the thermal performance of the aerostat is better. (3) Among the five typical envelope materials, i.e., white Tedlar film, white PU film, silver-plated Teflon film, aluminized PET film, and white PVF film, the aluminized PET film is more conducive to controlling the helium temperature difference and reducing the volume change of gasbags. The aforementioned results can provide a theoretical basis for improving the thermal performance of stratospheric airships.

Nonlinear Flight Dynamics and Control of a Fixed-Wing Micro Air Vehicle: Numerical, System Identification and Experimental Investigations

The flight dynamics of Micro Air Vehicles (MAVs) exhibit significant nonlinear characteristics, which cannot be ignored in simulation or analysis. In this study, a full nonlinear simulation of the flight dynamics characteristics of a fixed-wing MAV is performed. To strengthen the developed nonlinear mathematical modeling, the MAV’s mass properties and propulsion characteristics are experimentally investigated. Moreover, the aerodynamic characteristics of the designed fixed-wing MAV are experimentally measured in a wind tunnel. The experimental aerodynamics investigation includes the propeller wash effect and the same flight conditions of the MAV. These measured data are fed to the nonlinear flight dynamics model to improve its accuracy and ensure the nonlinear aerodynamics effect on the flight dynamics. The enhanced model is then validated against response experimental measurements of the MAV in the wind tunnel that is free to pitch at different control inputs and initial conditions. Furthermore, it is compared to the response of the system identification model. The nonlinear simulation and dynamic testing investigations indicate many nonlinear phenomena, such as the appearance of the limit cycle in the longitudinal flight. This paper shows that the aerodynamic center of MAV with a low aspect ratio in the low Reynolds number regime of flow can move as a response to flap deflection. The validated nonlinear mathematical model was used to evaluate the MAV’s dynamics, design and evaluate a PID controller in flight conditions similar to the MAV’s actual flying mission. Moreover, the presented model can be used for flapping-wing MAVs using time-dependent experimental measurements.

Validation of flight dynamic stability optimization constraints with flight tests

Numerical optimization in aerospace sciences and industry is now used on a daily basis. Since, aircrafts are very complicated objects, analyzing multiple disciplines and using Multidisciplinary Design Optimization became a regular practice. Coupling both aerodynamic and structural analyses in the optimization framework is classical example. On the other hand, flight dynamic stability analyses are very rarely incorporated into the optimization process, or if so, in very limited way. Yet, having appropriate flight dynamic stability characteristics is crucial for the aircraft handling qualities, which are regulated by the airworthiness regulations. Methodology for the design and optimization coupled with dynamic stability constraints has been previously established by the authors of this article. This paper presents validation of this design methodology by comparing data acquired from the design and optimization process with the test flight data of UAV aircraft, which was designed basing solely on the developed methodology of the multidisciplinary optimization framework.

UAV's Precise Trajectory Tracking Control Based on Nonlinear Dynamic Inverse and Quaternions

The precise tracking 3D trajectory that changes dramatically within the boundary of flight performance is the essential capability of the UAV applied to air combat, which requires that flight control law design be adapted to nonlinear characteristics of flight dynamics and solve the singularities problem during the flight. Continuous trajectory control on the basis of nonlinear dynamic inversion (NDI) is studied. The singularities problem is caused by continuous trajectory expressed by flight velocity and flight-path angles. A sudden change of flight-path axis system happens when aircraft flies along a continuous trajectory which results in singularities. A method for amending flight-path axis system is presented to solve the sudden change problem of flight-path axis system. Finally, the combination of the maneuver generator based on quaternions and amending flight-path axis system realize the precise trajectory tracking control without singularities and obtain excellent tracking characteristics.

Propeller design to improve flight dynamics features and performance for coaxial compound helicopters

The coaxial compound configuration has been proposed as a concept for future high-performance rotorcraft. The co-axial rotor system requires no anti-torque device, while the longitudinal thrust is provided by a propeller. A well-designed propeller can ensure both the performance and the cruise efficiency. The propeller design also influences the flight dynamics of such configuration. To design the propeller parameters of the coaxial compound helicopter, the propeller modelling and design method devised by Adkins and Liebeck is firstly introduced. A flight dynamics model of the coaxial compound helicopter is developed. Trim characteristics, power consumption results, and handling qualities features are calculated with variable propeller parameters at optimum (corresponding to the maximum flight range) and maximum speeds. The results indicate that the propeller parameters alter its efficiency and improve the performance characteristics of this helicopter. In addition, the propeller design also influences the flight dynamics characteristics and handling qualities of the coaxial compound helicopter, and consequently affect the power consumption indirectly. In this light, a design method for the propeller has been developed by formulating the design procedure into the nonlinearly constrained optimisation problem based on the flight dynamics characteristics. The method is demonstrated by evaluating propeller parameters to improve the performance in both optimum and high-speed range, which could also guarantee the handling qualities of the rotorcraft for related requirements.

Parameter Adaptive Terminal Sliding Mode Control of Flexible Coupling Air-Breathing Hypersonic Vehicle

The highly nonlinear and coupling characteristics of a flexible air-breathing hypersonic vehicle create great challenges to its flight control design. A unique parameter adaptive nonsingular terminal sliding mode method is proposed for longitudinal control law design of a flexible coupling air-breathing hypersonic vehicle. This method uses adaptive reaching law gain instead of the additional adaptive compensation term to handle the uncertainty to improve robustness. The stability of the close loop system is proved via a Lyapunov way. The longitudinal tracking control law for velocity and angle of attack is designed based on a rigid dynamic model of a flexible air-breathing hypersonic vehicle. A strong coupling model of the same vehicle, considering aerodynamic-scramjet engine-flight dynamic-elastic couplings, is established as the verification platform of the designed control law. The remarkable differences of flight dynamic characteristics between this strong coupling model and the rigid body model can be seen, which mean the controller needs to endure very great uncertainty, unmodeled dynamics, and other types of internal disturbance. Simulation results based on the coupling model demonstrate that the designed control law has good performance and acceptable robustness.

Stability Characteristics of Wing Span and Sweep Morphing for Small Unmanned Air Vehicle: A Mathematical Analysis

Morphing aircraft are the flight vehicles that can reconfigure their shape during the flight in order to achieve superior flight performance. However, this promising technology poses cross-disciplinary challenges that encourage widespread design possibilities. This research aims to investigate the flight dynamic characteristics of various morphed wing configurations that can be incorporated in small-scale UAVs. The objective of this study was to analyze the effects of in-flight wing sweep and wingspan morphing on aerodynamic and flight stability characteristics. Longitudinal, lateral, and directional characteristics were evaluated using linearized equations of motion. An open-source code based on Vortex Lattice Method (VLM) assuming quasi-steady flow was used for this purpose. Trim points were identified for a range of angles of attack in prestall regime. The aerodynamic coefficients and flight stability derivatives were compared for the aforementioned morphing schemes with a fixed-wing counterpart. The results indicated that wingspan morphing is better than wing sweep morphing to harness better aerodynamic advantages with favorable flight stability characteristics. However, extension in wingspan beyond certain limits jeopardizes the advantages. Dynamically, wingspan and sweep morphing schemes behave in an exactly opposite way for longitudinal modes, whereas lateral-directional dynamics act in the same fashion for both morphing schemes. The current study provided a baseline to explore the advanced flight dynamic aspects of employed wing morphing schemes.

Performance Analysis of Medium Altitude Low-Cost Autonomous Quadcopter

In modern engineering, the rapid growth in the development of unmanned aerial vehicles which deserves the major space in the area of intelligence and surveillance operations. Unlike the conventional aircraft, the number of rotors mounted in an autonomous body that determines the propulsive efficiency as well as the maneuvering capabilities of unmanned aerial vehicles. The main objective of this research reveals that the low cost and an autonomous aerial vehicle with four rotors configuration design to achieve the long endurance flight limit. The developed Quadcopter flying model integrated with Arduino autopilot module which effectively controls the various maneuvering actions during the flight. This paper also reveals the entire hardware structure of the designed Quadcopter and its flight dynamic response characteristics. The remotely operated Quadcopter model was subjected to the flight test and the performance parameters have recorded. The flight test was conducted in an open environment in which stability parameters has been observed during onboard. Pitch angle, the Rotational speed of four rotors and the various attitudes of Quadcopter were changed accordingly to maintain the steady level flight. Findings are plotted with respect to the flight endurance.