Hover performance estimation and validation of battery powered vertical takeoff and landing aircraft

Battery powered vertical takeoff and landing(VTOL) aircraft attracts more and more interests from public, while limited hover endurance hinders many prospective applications. Based on the weight models of battery, motor and electronic speed controller, the power consumption model of propeller and the constant power discharge model of battery, an efficient method to estimate the hover endurance of battery powered VTOL aircraft was presented. In order to understand the mechanism of performance improvement, the impacts of propulsion system parameters on hover endurance were analyzed by simulations, including the motor power density, the battery capacity, specific energy and Peukert coefficient. Ground experiment platform was established and validation experiments were carried out, the results of which showed a well agreement with the simulations. The estimation method and the analysis results could be used for optimization design and hover performance evaluation of battery powered VTOL aircraft.

Stable Vertical Takeoff of an Insect-Mimicking Flapping-Wing System Without Guide Implementing Inherent Pitching Stability

We briefly summarized how to design and fabricate an insect-mimicking flapping-wing system and demonstrate how to implement inherent pitching stability for stable vertical takeoff. The effect of relative locations of the Center of Gravity （CG） and the mean Aerodynamic Center （AC） on vertical flight was theoretically examined through static force balance considera- tion. We conducted a series of vertical takeoff tests in which the location of the mean AC was determined using an unsteady Blade Element Theory （BET） previously developed by the authors. Sequential images were captured during the takeoff tests using a high-speed camera. The results demonstrated that inherent pitching stability for vertical takeoff can be achieved by controlling the relative position between the CG and the mean AC of the flapping system.

Longitudinal Flight Dynamic Analysis on Vertical Takeoff of a Tailless Flapping-Wing Micro Air Vehicle

This paper first analyzed the longitudinal dynamic behavior during vertical takeoff without control of a Flapping-Wing Micro Air Vehicle （FW-MAV）. The standard linear flight dynamics based on small disturbances from trim condition was not applicable for our analysis because the initial flight condition, which was at rest on the ground, could be such a large disturbance from the trim condition that the linearization is invalid. Therefore, we derived linearized Equations of Motion （EoM） which can treat an untrimmed flight condition as a reference for disturbances. The Computational Fluid Dynamic （CFD） software ANSYS Fluent was used to compute the aerodynamic forces and pitching moments. Three flight modes were found： a fast subsidence mode, a slow subsidence mode and a divergence oscil- latory mode. Due to divergence oscillatory mode, the deviation from the reference flight grew with time; the FW-MAV tumbled without control. The simulation showed for the first 0.5 second after leaving the ground （the time that is long enough for delay of feedback control）, the FW-MAV flew up to a height of 6 cm with small horizontal and pitching motion, which is close to a vertical flight.

Retarded Harrier Maneuver as a New and Efficient Approach for Fixed-Wing Aircraft to Achieve S/VTOL

Modern day VTOL fixed-wing aircraft based on quadplane design is relatively simple and reliable due to lack of complex mechanical components compared to tilt-wings or tilt-rotors in the pre-80’s era. Radio-controlled aerobatic airplanes have thrust-to-weight ratio of greater than unity and are capable of performing a range of impressive maneuvers including the so-called harrier maneuver. We hereby present a new maneuver known as the retarded harrier that is applicable to un/manned fixed-wing aircraft for achieving VTOL flight with a better forward flight performance than a quadplane in terms of weight, speed and esthetics. An airplane with tandem roto-stabilizers is also presented as an efficient airframe to achieve VTOL via retarded harrier maneuver, and detailed analysis is given for hovering at 45° and 60° and comparison is made against the widely adopted quadplane. This work also includes experimental demonstration of retarded harrier maneuver using a small remotely pilot airplane of wingspan 650 mm.

Overall eVTOL aircraft design for urban air mobility

Electric vertical takeoff and landing(eVTOL)aircraft have emerged as a potential alternative to the existing transportation system,offering a transition from two-dimensional commuting and logistics to three-dimensional mobility.As a groundbreaking innovation in both the automotive and aviation sectors,eVTOL holds significant promise but also presents notable challenges.This paper aims to address the overall aircraft design(OAD)approach specifically tailored for eVTOL in the context of Urban Air Mobility(UAM).In contrast to traditional OAD methods,this study introduces and integrates disciplinary methodologies specifically catered to eVTOL aircraft design.A case study is conducted on a tilt-duct eVTOL aircraft with a typical UAM mission,and the disciplinary performance,including initial sizing,aerodynamics,electric propulsion systems,stability and control,weight,mission analysis and noise,is examined using the OAD methodologies.The findings demonstrate that the current approach effectively evaluates the fundamental aircraft-level performance of eVTOL,albeit further high-fidelity disciplinary analysis and optimization methods are required for future MDO-based eVTOL overall aircraft design.

Hybrid Design and Performance Tests of a Hovering Insect-inspired Flapping-wing Micro Aerial Vehicle

Hovering ability is one of the most desired features in Flapping-Wing Micro Air Vehicles （FW-MAVs）. This paper presents a hybrid design of flapping wing and fixed wing, which combines two flapping wings and two fixed wings to take advantage of the double wing clap-and-fling effect for high thrust production, and utilizes the fixed wings as the stabilizing surfaces for inherently stable hovering flight. Force measurement shows that the effect of wing clap-and-fling significantly enhances the cycle-averaged vertical thrust up to 44.82% at 12.4 Hz. The effect of ventral wing clap-and-fling due to presence of fixed wings produces about 11% increase of thrust-to-power ratio, and the insect-inspired FW-MAV can produce enough cycle-averaged vertical thrust of 14.76 g for lift-offat 10 Hz, and 24 g at maximum frequency of 12.4 Hz. Power measurement indicates that the power consumed for aerodynamic forces and wing inertia, and power loss due to gearbox friction and mechanism inertia was about 80% and 20% of the total input power, respectively. The proposed insect-inspired FW-MAV could endure three-minute flight, and demonstrate a good flight performance in terms of vertical take-off, hovering, and control with an onboard 3.7 V-70 mAh LiPo battery and control system.

Comprehensive sizing and optimization method for series-hybrid unmanned convertiplane

This paper presents a novel sizing and optimization approach for the emerging serieshybrid unmanned convertiplane,which can be used to translate the top-level design requirements into the design parameters corresponding to the optimal power supply strategy and minimum total takeoff weight.The method comprehensively considers the design constraints in the rotor,fixedwing,and transition modes,and pays special attention to the characteristic response of Series Hybrid Electric System(S-HES)in complex application scenarios,especially the coupling of battery power,energy,and state-of-charge under high-power discharge conditions,the variation of fuel economy,and the adjustment of power supply strategy.With proposed method,it's possible to rapidly explore the design space in the initial design stage and find out the optimal design results with high confidence.A case study was proposed to verify the approach.The results reveal the particularity of convertiplane in terms of power requirements,and prove the necessity to consider detailed S-HES characteristic responses during parameter determination.The optimal design parameters were obtained through the hybrid control parameter optimization,which verified the effectiveness of proposed method.Possible errors and corresponding correction methods were also presented.