Fixed-wing Mode Research Articles

A Nonlinear Robust Sliding Mode Controller with Auxiliary Dynamic System for the Hovering Flight of a Tilt Tri-Rotor UAV

The tilt tri-rotor unmanned aerial vehicle (UAV) has three flight modes: the hover mode, the transition mode, and the fixed-wing mode. Controller design in the hover mode is the premise of realizing stable flight of this kind of UAV. Due to the particular structure with odd rotors and strong nonlinearity, the modeling and control of the tilt tri-rotor UAV remain an active and ongoing research topic. To overcome these problems and achieve stable flight control, this paper proposes a sliding mode-based nonlinear control scheme for the hovering flight of a tilt tri-rotor UAV, consisting of position control, attitude control, and control allocation. First, the mathematical model of the UAV is given by using the Newton–Euler formulation. Second, a cascade flight controller consisting of the position controller and the attitude controller is developed based on sliding mode control (SMC). For the position controller, an auxiliary dynamic system composed of the hyperbolic tangent functions is introduced to the SMC approach for constraining the output magnitude of the thrust and the reference attitudes. Besides, a disturbance observer is applied to the attitude controller to alleviate the chattering and improve robustness. Furthermore, according to the structural characteristics of the tilt tri-rotor UAV, a control allocation algorithm is developed to map the virtual control quantities calculated by the cascade flight controller to the actual actuators. Simulations are conducted to verify the robustness against the external disturbances and parameter variations, and the performance comparisons with two other control schemes are also given. Finally, the experiment is also carried out to validate the performance of the proposed control scheme.

Safety of transfer, type of procedure, and factors predictive of limb salvage in a modern series of acute limb ischemia

ObjectiveThe primary objective was to evaluate the safety of transfer, type of procedure, and factors associated with limb salvage in patients with acute limb ischemia (ALI) treated at a quaternary referral center. MethodsA retrospective review of all patients with ALI secondary to thrombotic or embolic occlusion at a quaternary referral hospital from 2013 to 2016 was conducted. Patients were transferred from throughout Washington and Alaska by ambulance, helicopter, or fixed-wing modes of transportation. Demographics, transport and operative timing, Rutherford classification, level of occlusion, procedural information, and fasciotomy characteristics were reviewed. Outcomes measured included limb salvage rates, discharge disposition, and mortality. ResultsOne hundred twelve patients with ALI were identified, with 82% due to thrombosis and 18% due to arterial embolization. Fifty-seven percent of patients were transferred from a referring hospital with low mean transfer times (1.9 hours for embolic, 2.7 hours for thrombotic). Although the initial operative strategy varied according to the etiology, with 50% of thrombotic occlusions treated with endovascular therapies and 80% of embolic occlusions treated with open thrombectomy, the rates of limb salvage did not vary based on operative approach (92% endovascular first, 90% open first). Further, limb salvage rates were identical between transferred and nontransferred patients (77%). Limb salvage was successful in 91% of patients with Rutherford class 1 and 2 disease, but only 8% in patients with Rutherford class 3 disease. In-hospital and 30-day mortality rates were not different based on ischemic etiology (5%), although patients with Rutherford class 3 disease had significantly higher mortality rates (15%) compared with patients with class 1 (6%), class 2a (6%), and class 2b (2%) disease. Fasciotomy was performed in 29% of patients, with 59% of fasciotomy wounds closed primarily. Predictors of amputation include multiple attempts at limb salvage, higher Rutherford class, multilevel occlusion, more proximal levels of occlusion, and nonviable muscle seen after fasciotomy, with ischemic times trending toward higher amputation rates without statistical significance. There was no difference in discharge disposition based on ischemic etiology. ConclusionsThe modern treatment of patients with ALI is effective, with high rates of limb salvage and low mortality regardless of transfer status, etiology, or initial operation performed. In situations where compartment syndrome is unclear, fasciotomy should not be withheld because it provides valuable predictive information regarding limb salvage.

A New Closed-loop Control Allocation Method with Application to Direct Force Control

A new closed-loop control allocation method is proposed to distribute the force and moment increment commands among multiple actuators at the same time. An innovative feedback configuration for the force and moment increment produced by the actuators deflections is added into the trajectory and attitude control loop, respectively. In addition, the trajectory and attitude controllers designed by nonlinear dynamic inversion are used to derive the desired force and moment increment commands. Then, the stability of the closed-loop system is guaranteed theoretically when the actuators are healthy and fail, where there is no a fault detection method to identify the failure. Finally, the proposed method is used to achieve direct force control for decoupling the attitude and flight trajectory in the longitudinal flight. The nonlinear simulation using Canard Rotor/Wing (CRW) aircraft longitudinal model in fixed-wing mode demonstrates that this method can achieve two direct force control modes: pitch pointing and direct lift, whether the actuators are healthy or fail.

Control and flight test of a tilt-rotor unmanned aerial vehicle

Tilt-rotor unmanned aerial vehicles have attracted increasing attention due to their ability to perform vertical take-off and landing and their high-speed cruising abilities, thereby presenting broad application prospects. Considering portability and applications in tasks characterized by constrained or small scope areas, this article presents a compact tricopter configuration tilt-rotor unmanned aerial vehicle with full modes of flight from the rotor mode to the fixed-wing mode and vice versa. The unique multiple modes make the tilt-rotor unmanned aerial vehicle a multi-input multi-output, non-affine, multi-channel cross coupling, and nonlinear system. Considering these characteristics, a control allocation method is designed to make the controller adaptive to the full modes of flight. To reduce the cost, the accurate dynamic model of the tilt-rotor unmanned aerial vehicle is not obtained, so a full-mode flight strategy is designed in view of this situation. An autonomous flight test was conducted, and the results indicate the satisfactory performance of the control allocation method and flight strategy.

Arbitrary Attitude Hovering Control of Quad Tilt Rotor Helicopter

[abstFig src='/00280003/08.jpg' width=""300"" text='Arbitrary attitude hovering' ] The quad tilt rotor helicopter (QTRH), a tilt-rotor aircraft prototype, has fixed wings for long-range high-speed flight. Its rotor-tilt mechanism controls 4 rotor-tilt angles independently and controls its roll and pitch angles similarly to a multirotor helicopter. It controls yaw angle by thrust vectoring and moves forward and backward by tilting its rotors. Rotor-tilting maneuvers are the initial stage of flight-mode transition between helicopter and fixed-wing modes.

SONGBIRD – AN INNOVATIVE UAS COMBINING THE ADVANTAGES OF FIXED WING AND MULTI ROTOR UAS

Abstract. This paper describes a family of innovative fixed wing UAS with can vertical take off and land – the SONGBIRD family. With nominal payloads starting from 0.5 kg they can take off and land safely like a multi-rotor UAV, removing the need for an airstrip for the critical phases of operation. A specially designed flight controller allows stable flight at every point of the transition phase between VTOL and fixed wing mode. Because of this smooth process with a all time stable flight, very expensive payload like hyperspectral sensors or advanced optical cameras can be used. Due to their design all airplanes of the SONGBIRD family have excellent horizontal flight properties, a maximum speed of over 110 km/h, good gliding properties and long flight times of up to 1 h. Missions were flown in wind speeds up to 18 m/s. At every time of the flight it is possible to interrupt the mission and hover over a point of interest for detail investigations. The complete flight, including take-off and landing can be performed by autopilot. Designed for daily use in professional environments, SONGBIRDs are built out of glass-fibre and carbon composites for a long service life. For safe operations comprehensive security features are implemented, for example redundant flight controllers and sensors, advanced power management system and mature fail safe procedures. The aircraft can be dismantled into small parts for transportation. SONGBIRDS are available for different pay loads, from 500 g to 2 kg. The SONGBIRD family are interesting tools combining the advantages of multi-copter and fixed wing UAS.

Guidance and control of a scaled-down quad tilt prop PAV

In this paper, a flight control and guidance method for a scaled-down quad tilt prop personal air vehicle (PAV) is presented through simulations and flight tests. The developed scaled-down PAV does not fully transit into a fixed-wing flight mode, but longitudinally tiltable nacelles are used to control the longitudinal translation speed. This design concept can realize a flight maneuver with minimized attitude change because it is only necessary to tilt the nacelles of the propellers and not the attitude angle of the whole body. Although controls of a similar tilt-rotor and quad-tilt vehicles have been reported, a research on a guidance algorithm of a vertical take-off and landing (VTOL) PAV is deficient. Therefore, this paper focuses on the guidance algorithm for the quad tilt prop PAV that requires minimized fluctuation for a passenger. The dynamic behavior and responses of attitude and velocity controllers are identified with reasonable accuracy for a simulated test. Using this model, a guidance algorithm is developed for a circular path to minimize variation of a control input and system states. Through the simulated evaluation against the widely-used proportional navigation guidance algorithm, it was found that the proposed circular path guidance method has better performance in terms of total variation. In addition, through the flight test, the feasibility of the current concept for using the propeller nacelle tilt angle as a control input in forward speed control of a quad tilt prop PAV is proved.

신경회로망을 이용한 틸트로터 항공기의 적응 비행제어기 설계 및 비행성 평가

An application of adaptive flight controller is required for the non-linear and high uncertain system that configuration of tiltrotor aircraft is dramatically changed from rotary wing mode to fixed wing mode. In this paper, the applicable adaptive controller for the tiltrotor aircraft was designed using Neural Networks and DMI (Dynamic Model Inversion). The performance of the SCAS (Stability and Control Augmentation System) was simulated against manned military specification, using the fullscale model of 'Smart UAV(Unmanned Aerial Vehicle)' developed by Korea Aerospace Research Institute. And Neural Networks based adaptive controller was verified through its whole operating envelope using the established HQ (Handling Quality) criteria.

High-Speed Hover-Capable Morphing Micro Air Vehicle

The design, fabrication, and testing of a hybrid micro air vehicle capable of morphing between a high-hover-endurance rotary-wing mode and a high-cruise-speed fixed-wing mode is described. The micro air vehicle can efficiently perform a mission comprising outdoor flight to a target, followed by indoor surveillance and a return to the launch point. In addition, the micro air vehicle can function as a multirole platform, capable of flying exclusively as a fixed-wing or a rotary-wing vehicle. The key design drivers were 1) minimizing power required to hover, 2) ensuring static longitudinal stability in fixed-wing mode, and 3) minimizing the change in geometry between flight modes. Configuration trade studies were performed using blade element momentum theory for the rotary-wing mode and modified lifting-line theory for the fixed-wing mode. Design drivers for the rotary-wing mode and fixed-wing mode were often conflicting, and the selection of the final vehicle planform was primarily based on longitudinal static stability in fixed-wing mode. Two proof-of-concept prototypes with identical geometries, one for each flight mode, were constructed using off-the-shelf components and tested. Analytical predictions were validated by experimental measurements on the prototype vehicles. The final vehicle design is a flying wing with aft-swept, negatively twisted wings, having a wingspan of 394 mm and a mass of 85 g. The cruise velocity is , and the power required to hover is 11.6 W.

Closed-loop dynamic control allocation for aircraft with multiple actuators

A closed-loop control allocation method is proposed for a class of aircraft with multiple actuators. Nonlinear dynamic inversion is used to design the baseline attitude controller and derive the desired moment increment. And a feedback loop for the moment increment produced by the deflections of actuators is added to the angular rate loop, then the error between the desired and actual moment increment is the input of the dynamic control allocation. Subsequently, the stability of the closed-loop dynamic control allocation system is analyzed in detail. Especially, the closed-loop system stability is also analyzed in the presence of two types of actuator failures: loss of effectiveness and lock-in-place actuator failures, where a fault detection subsystem to identify the actuator failures is absent. Finally, the proposed method is applied to a canard rotor/wing (CRW) aircraft model in fixed-wing mode, which has multiple actuators for flight control. The nonlinear simulation demonstrates that this method can guarantee the stability and tracking performance whether the actuators are healthy or fail.

Longitudinal Flight Dynamics of a Single Tilt-wing Unmanned Aerial Vehicle

A single tilt-wing UAV has a new-concept hybrid configuration for adopting the advantages of both fixed-wing and rotary-wing aircraft. This paper presents longitudinal flight characteristics of the single tilt-wing UAV whose design is based on a tapered wing type aircraft with an actuating motor and a propeller mounted at each wing. Momentum theory is used to calculate thrust, and nonlinear modeling is performed considering lift and drag generated by slip stream effect of the propellers. Force and moment variation is considered for tilting angle change. Also, static trim on longitudinal axis is analyzed for operation airspeeds from 0 to 30m/s, and numerical simulation shows the flight dynamic characteristics of the UAV. It is verified that the single tilt-wing UAV has stable dynamic characteristics at fixed-wing mode.

National Survey of Neonatal Transport Teams in the United States

Neonatal transport in the United States is a complex process; however, little is known about the neonatal transport team (NTT) workforce. The purpose of this national study was to describe the US NTT workforce. An exploratory, descriptive design that used a Web-based survey questionnaire was used. We identified 398 NTTs, and 345 (86.7%) were enrolled. One survey was completed per team. Ten NTTs did not complete the survey (response rate: 84.2%). Of the 335 completed surveys, 229 (68.4%) were from unit-based teams and 106 (31.6%) were from dedicated teams. Twenty-six different NTT compositions were used. All except 1 (n = 334) had a registered nurse or a neonatal nurse practitioner as a team member. A registered nurse-respiratory therapist team composition was the most common for unit-based (40.2%) and dedicated (44.3%) teams. Dedicated teams used rotor and fixed-wing modes of travel more frequently, transported further distances, and had higher transport volumes than unit-based teams. The median transport volumes reported suggest that as many as 68 797 critically ill neonates are transported each year. There is wide variation in many aspects of neonatal transport, including orientation, determination of readiness for independent transport, use of protocols to guide transport care, and quality assurance activities. These results will be useful for (1) evaluating existing transport services, (2) guiding necessary changes in training or services, and (3) aiding programs that seek to develop a neonatal transport program.

Development and Conversion Flight Test of a Small Tiltrotor Unmanned Aerial Vehicle

T HE tiltrotor configuration was selected as the unmanned aerial vehicle (UAV) platform for the Smart UAV (SUAV) development program, which is one of the 21st Frontier research and development programs supported by the Korean government [1]. Some of the subsystems of the SUAV, such as the rotor system, drive system, andflight control system, were especially challenging for the Korea Aerospace Research Institute to develop, due to lack of previous development experience. To reduce the risk of failure during the development, the ironbird test of the rotor and drive system and flight simulation was conducted. Although the flight simulation mitigated the risk in the flight control system development, a downscaled model was constructed in an effort to ensure the safety in the flight test of the full-scale vehicle. The small-scale platform is shown in Fig. 1. It is expected from the flight test of the small scale model to enhance the understanding of the features of the actual tiltrotor vehicle. The size of the downscaledmodelwas determined to be 1=2:5 (2m overall length) of the full-scale SUAV (5 m overall length) so as to have large enough space for the simple flight control computer, the navigation system, and the other components such as the engine and actuators. The aerodynamic performance of the 1=2:5-scale tiltrotor was analyzed using the in-house performance code. The calculated performance data were used for scheduling the control devices, such as the collective pitch of the rotors and the flaperon deflection, in the flight control logic. In this Note, sizing and performance analysis of the downscaled tiltrotor are presented in which simple codes based on blade element and momentum theory were used. The conversion corridor of the tiltrotor was predicted and the nacelle tilt angle and air speed were compared with flight-test results. After a series of progressive flight tests, conversion flight from helicopter to fixed-wing mode was accomplished. This verified that the stability and control augmentation algorithmwork properly in the flight control software. This small tiltrotor flight test is expected to reduce risks in flight test of the 5-m-span full-scale tiltrotor UAV called Smart UAV. II. Sizing of the Tiltrotor

틸트 로터형 항공기의 플랩퍼론 연결부에 대한 크리깅 기반 피로해석

피로해석은 반복하중 하에서의 항공우주 구조물에 대한 구조적 파괴를 예방하기 위해 수행된다. 본 논문에서는 틸트로터형 무인 항공기에 대하여 피로수명에 대한 평가를 하였다. 먼저 틸트로터형 무인항공기의 기동에 맞는 하중 스펙트럼을 생성해 내었으며, F.C.L. 부품중 하나인 플랩퍼론 연결부위에 대하여 피로해석을 수행 하였다. 틸트로터형 무인항공기는 크게 두 가지 기동 형태로 나눌 수 있는데, 이 착륙시의 헬리콥터 형태와 순항시의 고정익 형태가 되겠다. 전체적인 피로하중 스펙트럼을 만들기 위해서 헬리콥터 형태에는 FELIX를, 고정익 형태에서는 TWIST를 사용하였다. 한편으로는, S-N 실험점이 해석에 사용될 때 재료수명의 전 영역에 대한 S-N 회귀식을 얻기 위하여 크리깅 메타 모델이 사용되었다. 그리고 최소 자승법을 이용한 이차 회귀식에 대한 S-N 커브 역시 생성하였다. 더욱이 이 커브들이 갖고 있는 정확도를 측정하기 위하여 결정 계수법을 사용하였다. 마지막으로는 플랩퍼론 연결 부위에 대한 피로수명 결과를 MSC. Fatigue와 비교하였다. The fatigue analysis is performed to avoid structural failure in aerospace structures under repeated loads. In this paper, the fatigue life is estimated for the design of tilt rotor UAV. First of all, the fatigue load spectrum for tilt rotor UAV is generated. Fatigue analysis is done for the flaperon joint which may have FCL(fracture critical location). Tilt rotor UAV operates at two modes: helicopter mode such as taking off and landing; fixed wing mode like cruising. To make overall fatigue load spectrum, FELIX is used for helicopter mode and TWIST is used for fixed wing mode. The other hand, the Kriging meta model is used to get S-N regression curve for whole range of material life when S-N test data are analyzed. And then, the second order of S-N curve is accomplished by the least square method. In addition, the coefficient of determination method is used to ensure how accuracy it has. Finally, the fatigue life of flaperon joint is compared with that obtained by MSC. Fatigue.

Canard Rotor Wing 항공기의 로터 성능 최적화 연구

In this study, the sizing and performance analysis program is developed for the canard rotor wing(CRW) aircraft which operates in dual modes (fixed wing mode and rotary wing mode). The developed program is verified for both fixed wing and rotary wing modes using the existing aircraft data and the design optimization formulation is made to perform the reconnaissance mission. For the canard rotor wing aircraft optimization , multi-objective function is constructed to consider both the fixed wing mode and rotary wing mode the weighting factor. For six design cases with different weighting factors and different design constraints, the optimization is performed and improved rotor design results are derived.

A Study on Transient Performance Characteristics of the Canard Rotor Wing Type Unmanned Aerial Vehicle Propulsion System During Flight Mode Transition

A propulsion system of the CRW (Canard rotor wing) type UAV (unmanned aerial vehicle) was composed of the turbojet engine, exhaust nozzles (including some tip jet nozzles and a main nozzle), and the duct system (including straight ducts, curved ducts, and master valve). The CRW-type UAV has three different flight modes, such as the rotary wing mode for takeoff and landing, the high-speed forward flight mode with the fixed wing, and the transition flight mode between the previously mentioned two flight modes. In order to evaluate transient performance characteristics of the CRW-type UAV propulsion system during flight mode transition, the propulsion system was modeled using SIMULINK®, which is a user-friendly graphical-user-interface-(GUI) type dynamic analysis tool provided by MATLAB, in this study. The transition flight mode between the rotary wing mode and the fixed wing mode was simulated by considering area variation of the master valve and the main exhaust nozzle. In order to verify acceptability of the main turbojet engine model, performance simulation results using SIMULINK were compared to results using the commercial program GSP. Through this simulation, proper operation of the master valve and the variable area main nozzle can be found for safe flight transition. Therefore, performance characteristics were investigated depending on various angle positions of the master valve.

스마트무인기 프롭로터 공력설계

본 연구에서는 틸트로터 항공기 개념을 채택하고 있는 스마트무인기의 프롭로터 공력형상 설계를 수행하였다. 틸트로터 항공기의 프롭로터는 단일 형상의 로터가 회전익과 고정익의 두 가지의 비행모드에서 운용되어야 하므로 회전익으로서의 로터와 고정익으로서의 프로펠러 요구 성능을 동시에 만족할 수 있도록 형상 설계가 이루어 져야 한다. 프롭로터의 공력형상 설계는 로터의 성능, 비행체의 공력성능, 그리고 엔진의 성능데이터를 결합하여 이루어 졌다. 모멘텀-깃요소 이론에 바탕을 둔 로터의 성능해석코드에 대한 검증은 TRAM 데이터와의 비교를 통해 이루어 졌다. 프롭로터의 공력형상 설계는 틸트로터 항공기의 고정익과 회전익 성능을 동시에 만족할 수 있는 형상을 구현하기 위하여 다양한 형태의 성능 맵이 작성되었고, 이들 선도 위에서 최적의 성능이 구현될 수 있는 성능 및 형상 파라메타가 결정되도록 하였다. The aerodynamic design of a proprotor for the Smart UAV adopting tiltrotor aircraft concept is conducted in this study. Since proprotor of tiltrotor aircraft is operated at both rotary and fixed wing mode with single configuration rotor, the proprotor has to be designed to meet performance requirements for both flight modes. The aerodynamic design of proprotor is accomplished by combining three sources of data - the proprotor performance data, the aerodynamic data of vehicle, and the performance data of engine. The performance analysis code for proprotor is based on the combined momentum and blade element theory and validated by comparison with the TRAM data. In order to design configuration for a proprotor satisfying requirements for both rotary and fixed wing mode, various kind of performance maps are constructed for many performance and configuration parameters. From the analysis the twist angle of 38 degrees and the solidity of 0.118 are decided to be the optimal geometric parameters for both operating conditions.

사이징 프로그램 개발을 통한 다중 비행 모드 Canard Rotor/Wing 항공기의 형상 최적설계

A design study was conducted for a new concept aircraft(Canard Rotor/Wing: CRW) that has the capability of dual mode flight, a rotorcraft and a fixed wing mode. The CRW can show a vertical take off/landing and a high speed/efficiency cruise performance simultaneously. It is not surprising to develop a new sizing code for this class of aircraft because conventional sizing codes developed solely for either the rotary wing or the fixed wing aircraft are not adequate to design a dual mode aircraft operated both by the rotary wing through tip jet effux and the fixed wing lift. Thus, a new design code was developed based on the conventional sizing code by adding some features including rotor performance, duct flow, and engine flow analysis, hence could eventually predict the performance of reaction driven rotor, the flight performance and the flight characteristics. The various design parameters were investigated to find their influences on the flight performance then, a small UAV(Unmanned Aircraft Vehicle) of 1500 lbs class was optimally designed to have minimum weight using the developed sizing code.

Aeroelastic deformation effects on the stopped-rotor dynamics of an X-wing aircraft

A new design concept in the development of vertical takeoff and landing aircraft with high forward flight speed capability is that of the X-wing. The X-wing is a stiff, bearingless helicopter rotor system that can be stopped in flight and the blades used as two forward-swept wings and two aft-swept wings. Because of the unusual configuration in the fixed-wing mode, there is a high potential for aeroelastic divergence or flutter and coupling of blade vibration modes with rigid-body modes. An aeroelastic stability analysis of an X-wing configuration aircraft was undertaken to determine whether these problems were likely. This paper reports on the results of dynamic stability analysis in the lateral and longitudinal directions, including the vehicle rigid-body and flexible modes. A static aeroelastic analysis using the normal vibration mode equations of motion was performed to determine the cause of a loss of longitudinal static margin with increasing airspeed. This loss of static margin was found to be due to aeroelastic wash in of the forward-swept blades and wash out of the aft-swept blades moving the aircraft aerodynamic center forward of the center of gravity. This phenomenon is likely to be generic to Xwing aircraft.