
Inderjit ChopraUniversity of Maryland, College Park | UMD, UMCP, University of Maryland College Park · A. James Clark School of Engineering
Inderjit Chopra
BSc Aero, ME, ScD
About
563
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Introduction
Inderjit Chopra currently works at the A. James Clark School of Engineering, University of Maryland, College Park. Inderjit does research in Aeronautical Engineering, Aerospace Engineering and Mechanical Engineering. His current projects are 'Quadrotor Biplane, Package delivery drone," "Rotor/Body/Engine coupled Vibraton Analsysis," "Rotor/Body/Wings/Propeller Model Testing in Wind Tunnel for Compound Rotorcraft Studies," "Rotor Design using Comprehensive Analysis," and "Mast Bumping Studies for a Teetering Rotor."
Publications
Publications (563)
A thrust compounded helicopter—a main rotor with a trailing propeller was tested in the Glenn L. Martin Wind Tunnel to evaluate its performance under different flight conditions. The main rotor rig consists of a hingeless hub with four fully instrumented NACA 0012 blades and a modified Robin fuselage. The propeller rig consists of a rigid Sensenich...
Slowing down the rotor RPM is a viable method to alleviate the compressibility effect at the advancing side of a rotor in forward flight, which is proved effective in raising the cruise speed limitation of a compound helicopter. A series of wind tunnel tests were conducted in the Glenn L. Martin Wind Tunnel, and some basic understandings were gaine...
A blade-tip-propeller driven rotor consists of small electric motors and propellers attached to the rotor blade tip to spin the main rotor. This study address a propeller driven shortcoming that was identified in previous research: a high required power to spin the main rotor. To investigate this, a series of wind tunnel and hover stand test campai...
In this paper, we develop and validate a 3D feature-based algorithm for tracking stochastic ship-deck motion at high sea states, specifically Sea-State 6 using data from the Navy SCONE dataset. The new vision algorithm was developed from the structure-from-motion technique, which recovers the 3D structure of an object from a series of 2D images, an...
The aeroelastic stability of rotor blades in the flap, lag, and torsion degrees of freedom is analyzed in preparation for high-advance ratio wind tunnel testing of Mach-scaled rotors. A wide range of advance ratios (0 ≤ μ ≤ 3) are evaluated for articulated and hingeless rotor configurations. Linearized equations of motion in the rotating frame are...
An aeromechanics analysis of a Mach-scaled rotor with lift compounding was conducted to understand the impact of various wing configurations on performance and loads. An assessment of the single retreating side wing and dual wing configurations was conducted for advance ratios up to μ = 0.7, two wing incidence angles (4° and 8°), and three rotor sh...
The objective of this work is to refine and experimentally characterize a two-dimensional, feature-based vision algorithm for tracking a stochastically moving ship-deck under degraded visual conditions. A 2.75-kg quadrotor UAV (unmanned aerial vehicle), with only the accessories essential for vision-based navigation, is specifically designed to est...
This paper describes the gust rejection study of a twin-cyclocopter micro air vehicle with two cyclorotors and an anti-torque nose rotor. A gust rejection controller relying on velocity feedback and onboard flow sensing was implemented in a closed-loop feedback system. Tethered experiments were conducted with the vehicle mounted on a 6-DOF stand in...
The objective of this paper is to experimentally validate our 2D, feature-based vision algorithm for tracking stochastic ship deck motion. Two main advancements are described in this work. First, the feature-based algorithm is computationally intensive and therefore requires a larger, more powerful flight computer to run in real-time. To accommodat...
A thrust compounded helicopter - a main rotor with a trailing propeller was tested in the Glenn L. Martin Wind Tunnel (GLMWT) to evaluate its performance under different flight conditions. The main rotor rig consists of a hingeless hub with four fully instrumented NACA 0012 blades and a modified Robin fuselage. The propeller rig consists of a rigid...
The aeroelastic stability of rotor blades in the flap and lag degrees of freedom is analyzed in preparation for high advance ratio wind tunnel testing of Mach-scaled rotors. A wide range of advance ratios (0 ≤ μ ≤ 3) and Lock numbers (0 ≤ g ≤ 18) are evaluated for articulated and hingeless rotor configurations. Linearized equations of motion are de...
This paper describes isolated rotor and fuselage testing in the Glenn L. Martin Wind Tunnel at the University of Maryland, College Park. The multi-part test included both steady and transient rotor testing and fuselage aerodynamics testing. A T-Motor 28x9.2 rotor was tested under steady conditions from hover to 35 m/sec wind speeds over a 180-degre...
A blade-tip-propeller driven rotor utilizes small electric motors and propellers attached at the blade tip to spin the main rotor. Potential applications of this technology are for high performance, mechanically simple, vertical takeoff and landing unmanned aerial vehicles. This paper presents a method of systematically characterizing the performan...
Compound rotorcraft can be a viable option to achieve moderately high speeds of 240 knots. However, there is no systematic wind tunnel test data in the public domain to understand the complex interactional aeromechanics involved. This work is part of a test campaign to conduct multiple high-speed wind tunnel tests of various compound configurations...
This work is a continuation of the ship-deck landing research presented at VFS Forum 2021, which established a vision-based method to track ship-deck motion before landing when conditions are favorable. This paper makes advancements on two fronts: 1) Demonstrating the effect of velocity feedback on tracking stochastic deck motion, and 2) Developing...
This paper details the propeller analysis in forward flight to finalize the wind tunnel test matrix of the thrust compounding rotorcraft model. First, the University of Maryland Advanced Rotorcraft Code (UMARC) is validated with main rotor hover test data at the tip Mach number of 0.2 and 0.5. It is further validated with slowed rotor (tip Mach num...
Electric variable RPM rotors are increasingly being used for propulsion and control of unmanned air vehicles. As these vehicles scale to carry heavier payloads of 50 to 400 lbs (20 to 180 kgs) in the group 2 and 3 UAS category, there are concerns about their aerodynamic performance and handling quality degradation. First, a universal electric power...
Compound rotorcraft can be a viable option to achieve moderately high speeds of 240 knots. However, there is no systematic wind tunnel test data in the public domain to understand the complex interactional aeromechanics involved. This work is part of a test campaign to conduct multiple high-speed wind tunnel tests of various compound configurations...
Instantaneous force and structural deformation experiments were performed on a flexible, structurally characterized, low-aspect-ratio representative flapping wing. A six-component force balance was used to measure aerodynamic-force time history over a flap cycle. A VICON motion capture setup tracked the wing deformations while flapping. Measured ae...
This Paper explores the development of a novel hybrid air vehicle for package delivery called the quadrotor biplane tail-sitter. This vehicle uses differential thrust to effect body attitude changes like a traditional quadrotor, ensuring full transitional control between hover and forward flight modes. This method of control also allows the vehicle...
This paper describes the development of avionics and control systems, followed by flight demonstration for vision-based landing of a multirotor UAS on a moving platform replicating a ship-deck. The UAS is a quadrotor designed and fabricated in-house with an integrated avionics package developed for autonomous vision-based navigation. A monocular ca...
The analysis of multiple compound configurations is performed systematically to enhance the cruise speed and efficiency of a rotorcraft. Comprehensive analysis is performed using modified UMARC including a refined time marching freewake to capture the interactions between rotor, wing, and propeller wake. Maximum cruise speeds of 193 knots and 240 k...
A high-fidelity coupled computational fluid dynamics and comprehensive analysis solver is developed for helicopter flight on Mars. The objectives are accurate prediction of flight loads and fundamental understanding of Martian aeromechanics. Performance, structural loads, pitch link loads, rotor wake, and interrotor blade separation are studied for...
In this work, the aerodynamic performance and optimization of a vertical-axis wind turbine with a high tip-speed ratio are theoretically studied on the basis of the two-dimensional airfoil theory. By dividing the rotating plane of the airfoil into the upwind and downwind areas, the relationship among the angle of attack, azimuth, pitch angle, and t...
A computational study is conducted on thin flat plates to simulate flows of Reynolds numbers at 104 to provide understanding and guidance for micro air vehicles and other low-Reynolds-number airfoil designs. A synergistic effort between experiments and validated and computational fluid dynamics (CFD) tools were used as part of this
study. The CFD t...
Hybrid vehicles that can hover and cruise efficiently offer potential advantages such as extended range/endurance and higher top speed. This paper discusses the design, performance, and testing of a 230 gram Quadrotor Biplane Tail-sitter (QBiT) UAV, a mechanically simple VTOL platform. A standard quadrotor and six quadrotor-wing configurations were...
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 locomotio...
A single main rotor helicopter's maximum forward speed is limited due to the compressibility effects on the advancing side and reverse flow and dynamic stall on the retreating side. Compound helicopters can address these issues with a slowed rotor and lift compounding. There is a scarcity of test data on compound helicopters, and the present resear...
During the past two decades, there has been major growth of small-unmanned aerial vehicles (sUAV) for hobbyists and rapidly expanding commercial and military applications. The impetus for this dramatic expansion has been due to the explosion of mobile technology in terms of microelectronics, data processing and transmission capability, high-energy-...
The predictions of an upgraded UMARC comprehensive analysis are compared to experimental lift offset rotor results. The experiments cover a range of collective pitch angles (θ°) from 2° to 10°, advance ratios (μ) from 0.21 to 0.53, and lift offset from 0% to 20%. The experimental model rotors are from a system of coaxial hingeless rotors, with two...
This paper presents an investigation of the effects of tip sweep on highly twisted composite rotor blades by acquiring strain data in vacuum. Three parametric test cases were designed for strain measurements, and predictions from a special three-dimensional (3-D) finite element method were used for assessment of data. A set of rotating aluminum bea...
A high-fidelity coupled computational fluid dynamics (CFD) and comprehensive analysis (CA) solver is developed and demonstrated for helicopter flight on Mars. The objectives are accurate prediction of flight loads, and fundamental understanding of Martian aeromechanics. Performance, airloads, structural loads, pitch link loads, rotor wake, and inte...
In forward flight, slowing down a rotor alleviates compressibility effects on the advancing side blade tip, extending the cruise speed limit, and inducing high-advance-ratio flight regime. Previous wind tunnel tests have shown that an articulated rotor trimmed to zero hub moment generates limited thrust at high advance ratios, because the advancing...
It is a well known fact that the forward speed of a single main rotor helicopter is limited because of the compressibility effects on the advancing side and reverse flow and dynamic stall on the retreating side. Compound helicopters are a viable option which could increase the forward speed while minimizing hover penalty. Much analysis has been car...
Quadrotor based micro air vehicles with the capability to perform both in hover and forward flight have emerged as the potential vehicle for multiple missions. This paper explores the aerodynamic characteristics of three distinct non-planar wing configurations with the goal of expanding the operational envelope of this type of vehicle. The three co...
To expand the cruise speed of a compound helicopter, alleviating the compressibility effects on the advancing side with reduced rotor RPM is proved to be an effective design feature, which results in high advance ratio flight regime. To investigate the aerodynamic phenomena at high advance ratios and provide data for the validation of analytical to...
The rotor blade double-swept-tip geometry can effectively improve the aerodynamic and aeroacoustic behaviors of a rotor. However, the aeroelastic or aeromechanical behaviors of a double-swept rotor helicopter are a challenge to helicopter flight safety and need to be investigated. In this paper, the aeromechanical stability of a bearingless rotor h...
Multi-mode air vehicles with hover and high cruise speed capabilities can meet a wide range of mission requirements but are typically subject to design compromises that come from accommodating a wide range of flight speeds. This paper evaluates the mission capabilities of a quadrotor biplane tail-sitter vehicle augmented with a folding winglet syst...
Rotorcraft flight speed is limited by compressibility effects on the advancing blade side and decreasing lift potential on the retreating blade side. It may thus be beneficial to employ a hingeless rotor to generate additional lift with the advancing blade and compensate the resulting rolling moment with a fixed wing on the retreating blade side. T...
This paper presents a methodology to analyze the coupled structural dynamic response of an elastic airframe and engines of a helicopter in response to main rotor hub loads. Transfer functions of individual components (airframe, engine, mount struts, and torque tube) are coupled together using a substructuring approach to obtain consistent coupled s...
The results of hover and wind tunnel tests of a reduced-scale, closely spaced, rigid, coaxial counterrotating rotor system are presented, along with results from a comprehensive analysis. The system features two-bladed upper and lower rotors, 2.03 m in diameter, with uniform section, untwisted rotor blades. Measurements include upper and lower roto...
Hybrid air vehicles with VTOL capability and fixed wing efficiency continue to find application in the expanding aerospace landscape. One such concept, the quadrotor biplane tail-sitter, has a baseline configuration that is mechanically simple and utilizes a conventional quadcopter control scheme. The subject of this paper is the expansion of the b...
This paper presents an investigation of the effects of swept tip on highly twisted composite rotor blades. The focus is on detailed three dimensional (3-D) strain measurement. Both vacuum chamber tests and 3-D finite element method (FEM) analysis were carried out in the investigation. Strain distribution on three sets of in-house fabricated composi...
Slowing down the rotor in forward flight is a viable means of extending the cruise speed of a rotorcraft by alleviating compressibility effects at the advancing side blade tip. It was shown by previous wind tunnel tests that an articulated rotor trimmed to zero hub moment generates limited thrust at high advance ratios, because the advancing side o...
A high-fidelity coupled computational fluid dynamics (CFD) and comprehensive analysis (CA) solver is developed for application on the Mars helicopter. Accurate aeromechanical understanding of a coaxial rotor on Mars is necessary in order to make proper design decisions for future aircraft with longer range and greater payload. The objectives are to...
Multi-mode micro air vehicles with hover and high cruise speed capabilities can serve a wide range of mission requirements but are limited in their performance in either mode due to the design compromises that come from operating across a wide speed range. This paper describes a morphing winglet for a Quadrotor Biplane Tail-sitter (QBiT) that is pr...
As unmanned aerial systems(UAS) begin to operate in more dynamic and stochastic environments as presented by urban setting, new problems for tracking and control are introduced that must be addressed. Reinforcement-Learning(RL) techniques for control combined with deep-learning are promising methods for aiding UAS in such environments. This paper i...
This paper presents a methodology for preliminary sizing of unconventional rotorcraft using a physics-based approach to estimate the weight of primary load-carrying members and rotor efficiencies. The methodology is demonstrated for a quadrotor biplane tailsitter, a tilt-body configuration that can operate in both helicopter and airplane mode. A be...
A swashplateless rotor trim using brushless DC motor actuated trailing edge flaps was achieved in the Glenn L. Martin wind tunnel. A 6-ft-diameter, four-bladed articulated rotor with motor–flap system integrated into the NACA 0012 airfoil section was fabricated. A Maxon EC-10 brushless DC motor as an on-blade actuator and a lightweight mechanism we...
Owing to its ability to alleviate the compressibility effect on the advancing side, the slowed rotor operating at high advance ratios is a key feature in high-speed compound rotorcraft. A series of wind tunnel tests were conducted in the Glenn L. Martin Wind Tunnel with a four-bladed Mach-scaled articulated rotor. The objective of the tests was to...
One challenge that plagues the high-speed operation of rotorcraft is the inherent increase in size of the reverse flow region on the retreating side of the rotor disk. The present work experimentally investigated a portion of the reverse flow region on a 1.7- m-diameter sub-scale slowed rotor at advance ratios up to \(\mu =0.9\) and three shaft til...
This paper presents the first use of integrated three-dimensional (3D) aeromechanics modeling, defined as a coupling of 3D solid finite element analysis structural dynamics with 3D computational fluid dynamics (CFD), to study a real rotor, the NASA Tilt Rotor Aeroacoustic Model (TRAM) proprotor. The goal is to demonstrate the development of this ne...
This paper describes the effects of a composite coupled blade spar on the performance of a slowed-rotation-frequency helicopter rotor in high-speed edgewise flight. Antisymmetric composite coupling in the spar of a UH-60A-like rotor can provide a significant efficiency increase when rotation frequency is reduced. Comprehensive analysis was performe...
This paper presents a methodology for preliminary sizing of unconventional rotorcraft using a physics-based approach to size and estimate the weight of primary load-carrying members. The methodology is demonstrated for a Quad-rotor Bi-plane Tailsitter (QBiT), a tilt-body configuration that can operate in both helicopter and airplane mode. A beam la...
To meet the performance demands of modern UAV operations, hybrid air vehicles that incorporate the speed and efficiency of fixed wing vehicles and the VTOL capabilities of rotorcraft have come to the forefront. This paper presents work being done to expand the performance of one such hybrid air vehicle, the quadrotor biplane. This vehicle takes fli...
A detailed aeromechanical understanding of a coaxial rotor flying on Mars is presented using a combination of vacuum chamber tests and free-wake based comprehensive analysis. The objectives are to understand the limits of performance, structural loads, control loads (pitch link), wake interaction, and blade strike for hingeless and articulated coax...
Visual-inertial odometry has demonstrated the ability to turn a traditional micro-aerial vehicle (MAV) into an advanced platform for aerial robotics. Traditional MAV platforms suffer from strict weight limitations and in some cases flight controllability issues. Qualcomm's Snapdragon Flight™ is utilized to solve both of these problems. It is chosen...
Comprehensive vibration analysis of a rotor-airframe-engine-drivetrain system using a time-domain modal coupling approach was conducted. Pair-wise couplings of components (airframe and drivetrain/engine) were performed to isolate the contribution of each component to the complete coupled system, and the effect of each component on blade loads and h...
34th Annual AHS International Student Design Competition 2017 - 24 Hour Hovering Machine Conceptual Design, Graduate Entry
This paper presents modeling and simulation, and validation of a teetering rotor helicopter using rotorcraft comprehensive analysis. This model is partially validated with test data for two level flight speed sweeps for different CG locations within the fuselage. Finally, the effect of weight/CG location, steady pilot cyclic controls and time-varyi...
A computational study is conducted on thin airfoils to simulate flows of Reynolds numbers between 10^4-10^5 to provide understanding and guidance for micro air vehicles and other low Reynolds number designs. The computational fluid dynamics tool utilized in this study was a Reynolds-Averaged Navier--Stokes solver with a Spalart-Allmaras turbulence...
A computational study has been conducted on various airfoils to simulate flows at Reynolds numbers (Re) primarily between 104 and 105 to provide understanding and guidance for MAV and other low-Reynolds-number designs. The computational fluid dynamics tool used in this study is a Reynolds-averaged Navier–Stokes solver with a Spalart–Allmaras turbul...
The increasing usage of low-Reynolds-number (10,000–100,000 tip Reynolds number) scale quadrotors for civilian and military applications provides the impetus for the development of reliable design methodologies. At present, there is limited understanding of how to accurately size quadrotor components for a specific mission. These components include...
A 1.7 m-diameter Mach-scaled slowed rotor was tested at advance ratios up to µ = 0.9 and three shaft tilt angles of −4, 0 , and 4 deg. Two-component time-resolved particle image velocimetry was used to characterize the flow field around a blade element in the reverse flow region, nominally positioned at ψ = 270 deg and y/R = 0.4. Four dominant flow...
This paper discusses the design, hardware and software methodology, and testing of an ultralight inertial navigation system (Embedded Lightweight Kinematic Autopilot-Revised (ELKA-R)) that can be used as a controller in a wide range of micro air vehicle systems. ELKA-R was designed using the 32-bit low-power ARM Cortex-M4 microprocessor as the micr...
This paper describes the design, controls system development, and hover testing of a 60 -g meso-scale cycloidal-rotor based (cyclocopter) micro air vehicle. The cycloidal rotor (cyclorotor) is a revolutionary vertical take-off and landing concept with a horizontal axis of rotation. The twin-cyclocopter utilizes two optimized cyclorotors and a horiz...
This paper presents a methodology to analyze the coupled structural dynamic response of an elastic airframe and engines of a helicopter in response to main rotor and tail rotor hub loads. Transfer functions of individual components (airframe, engine, mount struts and torque tube) are coupled together using a sub-structuring approach to obtain consi...
Multi-mode mobility is prevalent in biological systems where organisms efficiently switch between different modes of locomotion to conserve energy, traverse long distances, and maneuver through confined spaces. This paper describes the design and experimental validation of an all-terrain cyclocopter MAV capable of efficient aerial, terrestrial, and...