Journal of the American Helicopter Society
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2075
(FIVE YEARS 150)

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48
(FIVE YEARS 4)

Published By American Helicopter Society

2161-6027, 2161-6027

Author(s):  
Keen Ian Chan

Corotating coaxial rotors are seeing renewed interest in distributed electric propulsion systems and electric vertical take-off and landing (eVTOL) aircraft. The recent literature reports many interesting investigations, using prescribed rotor blades, into the flow phenomena as well as aerodynamic and aeroacoustic benefits of corotating rotors. However, the subject of the design of blade geometries, optimized to a design goal, for corotating rotors is currently lacking in the literature. This paper is written from such a design perspective, by extending a previous generalized approach to the aerodynamic optimization of counterrotating rotors to corotating rotors. The previous requirement for upper and lower counterrotating rotor torques to be equal can now be lifted in the case of corotating rotors, enabling improved versatility in the optimization of corotating blade designs. The optimization is demonstrated on an application example to address the conflicting conditions that index angles (high) for aeroacoustic benefits of reduced noise are at odds with those (low) for aerodynamic efficiency. The approach demonstrated in this paper is to set the index angle for reduced noise and then recover back the aerodynamic efficiency by using the newly developed aerodynamic optimization technique.


Author(s):  
Xuan Yang ◽  
Aswathi Sudhir ◽  
Atanu Halder ◽  
Moble Benedict

Aeromechanics of highly flexible flapping wings is a complex nonlinear fluid–structure interaction problem and, therefore, cannot be analyzed using conventional linear aeroelasticity methods. This paper presents a standalone coupled aeroelastic framework for highly flexible flapping wings in hover for micro air vehicle (MAV) applications. The MAV-scale flapping wing structure is modeled using fully nonlinear beam and shell finite elements. A potential-flow-based unsteady aerodynamic model is then coupled with the structural model to generate the coupled aeroelastic framework. Both the structural and aerodynamic models are validated independently before coupling. Instantaneous lift force and wing deflection predictions from the coupled aeroelastic simulations are compared with the force and deflection measurements (using digital image correlation) obtained from in-house flapping wing experiments at both moderate (13 Hz) and high (20 Hz) flapping frequencies. Coupled trim analysis is then performed by simultaneously solving wing response equations and vehicle trim equations until trim controls, wing elastic response, inflow and circulation converge all together. The dependence of control inputs on weight and center of gravity (cg) location of the vehicle is studied for the hovering flight case.


Author(s):  
Hyeonsoo Yeo ◽  
Robert A. Ormiston

The UH-60A Airloads Workshop was a unique collaboration of aeromechanics experts from the U.S. Government, industry, and academia to address technical issues that hindered accurate rotor loads predictions. The Airloads Workshop leveraged the NASA/Army UH-60A Airloads flight test and NFAC wind tunnel test data. It functioned continuously for 17 years, from 2001 to 2018, and brought about one of the most important advancements in rotorcraft aeromechanics prediction capabilities by successfully demonstrating high-fidelity coupled computational fluid dynamics (CFD) and computational structural dynamics (CSD) analyses for both steady and maneuvering flight. The article is divided into two parts. Part I surveys the background of rotorcraft CFD/CSD development difficulties, the origins of the Airloads Workshop, and the rapid success achieved during the first phase that consisted of eight Workshops. Part II describes ongoing development during the subsequent two phases of the Airloads Workshop, the Ninth through the 13th, and the 14th through the 31st Workshops; the impact of the Airloads Workshop; and the lessons learned. Part I surveys the technical activities that led to a breakthrough for CFD/CSD coupling to successfully predict rotor blade airloads in trimmed steady-level flight conditions. This success illustrated the importance of collaboration among key experts with diverse backgrounds focused on a common objective to advance rotorcraft prediction methods.


Author(s):  
Fabio Nannoni

It is an immense honor to have been selected to hold the prestigious 41st Nikolsky Lecture and to have the opportunity to synthesize my experiences with regards to the most important principle that permeates aeronautical engineering—“the concept of safety.” Having worked in the rotary-wing field for 39 years, with growing levels of involvement and responsibilities, I have been involved in the design, development, and certification of many helicopter models at the Leonardo Helicopters Division (LHD; formerly Agusta and then AgustaWestland), such as A109, A119, EH101, A129, NH90, AW609. More recently, I had the full responsibility of design, development, certification, and entry into service of three new helicopter types within the “AW Family concept”, specifically the AW139, AW189, and AW169. I am profoundly grateful for the mentors encountered in my professional life—Bruno Lovera and Santino Pancotti, both of whom were also honored with the Nikolsky Lectureship. In working with them, not a single day passed where the word “safety” was not mentioned. They taught me that “safety” shall be the mantra of every aeronautical engineer because it is our principal duty and responsibility, towards those who travel in, work on, and work with our products and entrust their lives to our work and professionalism daily. I have tried hard never to forget this lesson, and to convey this to the young engineers that I have had the chance and pleasure to work with. If I have been able to pass on this lesson successfully, through my work with others through this lectureship, it would be the greatest achievement of my life. In this vein, this paper is organized in three parts: (i) definitions and principles, along with some “philosophical” concepts; (ii) the application of these principles at Leonardo in the design of the latest generation of helicopters, and finally (iii) a discussion of emerging “safety technologies” that promise to improve the safety of future helicopters and operations.


Author(s):  
Cory Seidel ◽  
David A. Peters

Correction to:Journal of the American Helicopter Society, Vol. 66, (1), January 2021, pp. 1–3, DOI 10.4050/JAHS.66.012001


Author(s):  
Mrinalgouda Patil ◽  
Anubhav Datta

A time-parallel algorithm is developed for large-scale three-dimensional rotor dynamic analysis. A modified harmonic balance method with a scalable skyline solver forms the kernel of this algorithm. The algorithm is equipped with a solution procedure suitable for large-scale structures that have lightly damped modes near resonance. The algorithm is integrated in X3D, implemented on a hybrid shared and distributed memory architecture, and demonstrated on a three-dimensional structural model of a UH-60A-like fully articulated rotor. Flight-test data from UH-60A Airloads Program transition flight C8513 are used for validation. The key conclusion is that the new solver converges to the time marching solution more than 50 times faster and achieves a performance greater than 1 teraFLOPS. The significance of this conclusion is that the principal barrier of computational time for trim solution using high-fidelity three-dimensional structures can be overcome with the scalable harmonic balance method demonstrated in this paper.


Author(s):  
Christina M. Ivler ◽  
Kevin Truong ◽  
Declan Kerwin ◽  
Joel Otomize ◽  
Danielle Parmer ◽  
...  

Unmanned aerial systems, commonly known as drones, present new opportunities to perform autonomous tasks. Handling qualities requirements for manned vertical lift aircraft have been well defined and documented. The need to define handling qualities requirements for vertical take-off and landing (VTOL) unmanned aerial systems (UAS) to meet mission demands is of paramount importance for all potential operators and procurement agencies. One way to relate handling qualities specifications of large-scale manned and subscale unmanned aircraft is through Froude dynamic scaling. Froude dynamic scaling based on hub-to-hub distance has shown great promise in relating the natural frequencies of scaled multicopters. There have been recent efforts to develop a VTOL-UAS handling qualities standard by scaling mission task elements and rating their performance through a Trajectory, Tracking, and Aggression (TTA) score. This paper proposes a new performance standard adapted from the TTA scoring method, along with a modified Cooper–Harper scale as a VTOL-UAS handling qualities framework that is consistent with the spirit of Aeronautical Design Standard 33 (ADS-33). These newly proposed performance standards were then validated through simulation and flight testing on a small hexacopter UAS, flown at the University of Portland. A key outcome of this work is the flight verification of a key dynamic response metric, the disturbance rejection bandwidth, and associated validation of Froude scaling for predicted handling qualities metrics.


2021 ◽  
Vol 66 (1) ◽  
pp. 1-13
Author(s):  
Wanyi Ng ◽  
Mrinalgouda Patil ◽  
Anubhav Datta

The objective of this paper is to study the impact of combining hydrogen fuel cells with lithium-ion batteries through an ideal power-sharing architecture to mitigate the poor range and endurance of battery powered electric vertical takeoff and landing (eVTOL) aircraft. The benefits of combining the two sources is first illustrated by a conceptual sizing of an electric tiltrotor for an urban air taxi mission of 75 mi cruise and 5 min hover. It is shown that an aircraft of 5000–6000 lb gross weight can carry a practical payload of 500 lb (two to three seats) with present levels of battery specific energy (150 Wh/kg) if only a battery–fuel cell hybrid power plant is used, combined in an ideal power-sharing manner, as long as high burst C-rate batteries are available (4–10 C). A power plant using batteries alone can carry less than half the payload; use of fuel cells alone cannot lift off the ground. Next, the operation of such a system is demonstrated using systematic hardware testing. The concepts of unregulated and regulated power-sharing architectures are described. A regulated architecture that can implement ideal power sharing is built up in a step-by-step manner. It is found only two switches and three DC-to-DC converters are necessary, and if placed appropriately, are sufficient to achieve the desired power flow. Finally, a simple power system model is developed, validated with test data and used to gain fundamental understanding of power sharing.


2021 ◽  
Vol 66 (1) ◽  
pp. 1-10
Author(s):  
Elena Shrestha ◽  
Brian Davis ◽  
Vikram Hrishikeshavan ◽  
Inderjit Chopra

This paper describes the design and experimental validation of an all-terrain cyclocopter micro air vehicle capable of power-efficient aerial, terrestrial, and aquatic locomotion with seamless transition between the modes. The vehicle has a mass of 1010 g and solely relies on its four cycloidal rotors (cyclorotors) to achieve all modes of locomotion. The cyclorotor rotational speeds and thrust vectors are individually modulated to sustain stable hover in aerial mode. A similar control strategy using aerodynamic forces generated by cyclorotors is also implemented for aquatic locomotion. The wheels are efficiently integrated into the carbon fiber rotor endplates since cyclorotors rotate about the horizontal axis. As a result, the cyclocopter maneuvers in terrestrial mode by directly relying on motor torque. Seamless transition is accomplished using a retractable landing gear system equipped with polystyrene foam pontoons. In aerial mode, the cyclorotors operate at 1550 rpm and consume 232 W to sustain hover. Forward translation at 2 m/s in terrestrial mode requires 28 W, which is a 88% reduction from hover. In aquatic mode, the cyclorotors operate at 348 rpm and consume 19 W, which is a 92% reduction from hover. Overall, a versatile platform capable of multimodal operation is successfully demonstrated with only a modest addition in total mass.


Author(s):  
Dheeraj Agarwal ◽  
Linghai Lu ◽  
Gareth D. Padfield ◽  
Mark D. White ◽  
Neil Cameron

High-fidelity rotorcraft flight simulation relies on the availability of a quality flight model that further demands a good level of understanding of the complexities arising from aerodynamic couplings and interference effects. One such example is the difficulty in the prediction of the characteristics of the rotorcraft lateral-directional oscillation (LDO) mode in simulation. Achieving an acceptable level of the damping of this mode is a design challenge requiring simulation models with sufficient fidelity that reveal sources of destabilizing effects. This paper is focused on using System Identification to highlight such fidelity issues using Liverpool's FLIGHTLAB Bell 412 simulation model and in-flight LDO measurements from the bare airframe National Research Council's (Canada) Advanced Systems Research Aircraft. The simulation model was renovated to improve the fidelity of the model. The results show a close match between the identified models and flight test for the LDO mode frequency and damping. Comparison of identified stability and control derivatives with those predicted by the simulation model highlight areas of good and poor fidelity.


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