Research On Hybrid Vertical Takeoff And Landing Aircrafts

Hybrid vertical takeoff and landing(HVTOL for short)aircraft has the abilities of vertical takeoff and landing,hover like a helicopter,transition between vertical flight and level flight,and efficient wing-borne fight as fixed wing aircraft.Therefore,HVTOL aircraft has raised expectations with having advantages of helicopters and fixed wing aircraft.Not only in military application domain,such as target monitoring,military reconnaissance,unmanned border defense,battlefield information acquisition and soldier carrying combat equipment;but also in civilian field,such as oil and transmission pipeline detection,fast delivery in complex airspace,deep space exploration platform and emergency disaster relief,HVTOL aircraft has great application prospect for such special takeoff and landing manner and cruise performance.The weight of HVTOL aircraft is less than vehicle's thrust output as hovering,vertical takeoff and landing;while the weight maybe more than ten times of the thrust output as level cruise.Such propulsion system that works in wide range has brought in great challenges for energy system selection,aerodynamic configuration and conceptual design of HVTOL aircraft.These problems couldn't be easily solved by existed design methods.There are some kinds of inherent connection between design parameters,flight states and aircraft performance.Revealing the influencing laws of these parameters will help for further understanding and improving performance of HVTOL aircraft.This study aims to answer the following three questions.1.What is HVTOL aircraft.Such new concept aircraft has not been defined definitely in the field of Aeronautics and Astronautics.Base on the classification of the U.S.Federal Aviation Administration about such kind of aircraft,this paper widely collected the open literature and web information,summaried varieties of aircraft layout for example,discussed the development process,research trend,advantages and disadvantages of several typical HVTOL aircrafts.So,the initial tree genealogy of HVTOL aircrafts was established,and the reference for further design and performance analysis was provided.2.How to design HVTOL aircraft.Deferent requirement,deferent layout and size choice.This paper will take the small battery powered HVTOL aircraft for example.Because simplicity,reliability and easy to realize,the twin-rotor Tailsitter configuration was chosen for conceptual design based on weight model,energy consumption model,aerodynamical model and battery discharge model.Energy is the core of such method.Configuring the proper battery to increase energy supply,reducing the energy consumption while hover,takeoff and landing,and allocating each phase to ensure flight endurance performance were the main three design problems.According to such design ideas and processes,the conceptual design of battery powered HVTOL unmanned aircraft was carried out with the constraint of flight mission and takeoff weight.The feasible design domain determined by battery mass proportion and wing loading was analysized by numerical simulation.The influences of design parameters and flight missions on aircraft performance were discussed.The design method can provide the key parameter selection for the preliminary design of small battery powered HVTOL aircraft,and prepare for further detailed design and aircraft realization.3.How to estimate and improve the performance of HVTOL aircraft.This paper focus on the static performance of hover duration and space range,and dynamic processes between differernt flight modes.The power of hover was calculated by blade element momentum theory.Then the hover performance evaluation model was established by the linear battery voltage drop model and the optimal allocation of the electrical propulsion system.The influences of propulsion parameters on hover performance were analysized,while the results were verified by ground experiments.A non-monotonic space reachable envelope of micro battery powered HVTOL aircraft was found by the space range evaluation method based on the propeller momentum theory and the constant battery voltage discharge model.Mission profile of HVTOL aircraft was investigate and key flight transition modes were outlined for further research.In order to solve the singularity problem of the dynamic equations of the aircraft as low speed transiton,a dynamic model of the conversion process was established by using the piecewise approximation method in the plane.Transion of HVTOL aircraft from vertical takeoff to level cruise and flight height jump were studied with the goal of shortest transition time.The influences of thrust weight ratio on flight transition process were analyzed with the HVTOL aircraft weight ten kilograms.The investigation on HVTOL aircraft,including conceptual design and optimization,parameters influence analyses,hover performance eatimation and validation,and flight modes transition optimization,provide useful reference for innovative design and technical support for the engineering realization.