DOCSLIB.ORG

Assessment of Fountain Flow Effects on Two Non-Overlap Tandem Rotors Performance

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Assessment of Fountain Flow Effects on Two Non-Overlap Tandem Rotors Performance AUT Journal of Mechanical Engineering AUT J. Mech. Eng., 5(1) (2021) 173-190 DOI: 10.22060/ajme.2020.17224.5850 Assessment of Fountain Flow Effects on Two Non-Overlap Tandem Rotors Performance A. Mehrabi, A. R. Davari* Department of Aerospace Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran ABSTRACT: Very few issues are yet to be reported about the fountain flow beneath the tandem Review History: rotors configuration body in ground effect. In this paper, a series of tests have been performed using Received:15/10/2019 multipurpose test stand to study the fountain flow pattern of a sub-scale model of a generic tandem Revised: 07/02/2020 rotor helicopter in ground effect. Pressure and velocity measurements were performed by the pressure Accepted:10/03/2020 ports embedded longitudinally along a generic tandem rotor helicopter fuselage. The presence of a Available Online: 19/03/2020 second rotor in tandem rotors configuration causes a fountain flow formation in the longitudinal center region below the helicopter and a semi-quiescent flow was there. The positive effects of this flow were Keywords: detected such as increasing the sub-body pressure lifting force, the pressure distribution balance, and Pressure Distribution reinforcing the lift by the formation of the positive pressure gradient on sidewalls of the airframe. Tuft Lift force test observations confirmed the location of the fountain flow formation concluded from pressure and Non-overlapping Tandem Rotor; velocity measurements. The mentioned fountain flow aerodynamic effects must be taken into account Fountain Flow in the tandem rotor helicopter flight controls trims, stability, and control augmentation system and lift Helicopter force calculations. 1. INTRODUCTION quiescent flow region under the helicopter that is 1.1. In Ground Effect Hover likely to be similar to a fountain flow, even though no A deeper understanding of the unsteady aerodynamics measurements have already been reported to confirm of tandem rotor helicopters, which was started in past this hypothesis. In the literature, this region is known as decades, shed new light on the issue of their performance. the Fountain flow and is formed below the intersection For a helicopter flying near the ground, the direction of the two rotors where the flow is upward [4]. of flow induced by the rotor changes from vertical While a tandem rotor configuration hovers and two downwash to radial outwash due to interactions with rotors are positioned so that there is no overlap between the ground. The value of rotor disk loading determines them, there is a clear distance between them, in the upper the strength of this induced flow [1]. The outwash starts surface of the airframe the downwash and spanwise from the outboard region of the blade tip and flows flows from the blade tip vortices merge at the centerline away from the helicopter, as shown in Fig. 1. of the fuselage and will form an upward unsteady Despite the ground effect is a well-known issue fountain flow (Fig.2). This flow gets recirculated in helicopter performance, it is necessary that some into the rotors and has a significant influence on the remained dark corners of the aerodynamics behavior of aerodynamic performance of the rotors. In hover, the tandem rotors in ground effect should be discovered. upper Fountain flow causes a vertical drag force on the The ground effect is one of the primary concerns during fuselage, which is called download [5]. The experiments actual flight and also in a wind tunnel or hovering tests. made to measure the download on the wings of tilt rotors For heights less than one rotor diameter above the in helicopter mode showed that the amount of its reverse ground, the hovering performance is strongly affected effect was equal to 10-15% of the total rotor thrust and by the ground effect [3]. reduces the vehicle payload in hover Out of Ground Effect (OGE) [6-8]. 1.2. Fountain Flow When the helicopter hovers In-Ground Effect (IGE), The flow-field around the tandem rotor systems can the presence of the ground influences the wake of the be divided into five regions, based on the dominant rotors under the fuselage (Fig.2). A large part of the phenomena in each region. There can be seen a relatively wakes of the tandem rotors spanwise flows recirculate *Corresponding author’s email: [email protected] as they interact with the ground surface and meet under Copyrights for this article are retained by the author(s) with publishing rights granted to Amirkabir University Press. The content of this article is subject to the terms and conditions of the Creative Commons Attribution 4.0 International (CC-BY-NC 4.0) License. For more information, please visit https://www.creativecommons.org/licenses/by-nc/4.0/legalcode. 1 A. Mehrabi and A. R. Davari, AUT J. Mech. Eng., 5(1) (2021) 173-190, DOI: 10.22060/ajme.2020.17224.5850 the longitudinal centerline of the fuselage and form a the performance of tandem rotors [13, 14]. Ramasamy Fountain flow in a similar form to what happens on [9] studied the downwash and outwash flow behavior the upper surface of the fuselage [9]. This Fountain by conducted experiments using a sub-scale CH-47D flow will be trapped under the bottom surface of the helicopter measuring the flow-field velocities in a fuselage and causes an upward force on the helicopter vertical plane at several azimuth angles and various and reduces the download on the fuselage caused by radial distances from the rotor axis, using the particle upper surface fountain flow. Some measurements show image velocimetry technique. He reported that there is a that this positive upward force, could be as high as 9% relatively quiescent flow region under the airframe that of the rotor total thrust in tilt rotors in their helicopter is likely to be similar to a Fountain flow, but he didn’t mode [10]. So, in contrary to thrust reduction due to the perform any measurement on that region. Fountain flow in the upper surface of the fuselage, below Some studies on the upper Fountain flow of tilt- the helicopter fuselage, the Fountain flow increases the rotors in helicopter mode and side-by-side rotors were lifting capacity and payload beyond the maximum thrust conducted to identify and reduce resultant downloads of the rotors. and their unfavorable consequences. These experiments Clearly, it is very important to know the effects of were on major subjects like as effect of the tilt-rotor this flow on the performance of the tandem rotors in wing geometry on download value, the effect of the different positions to achieve better performance in rotor location on fountain flow, download force, and the the hover mode. It seems that the flow pattern of the effect of parameters such as ground effect on Fountain Fountain flow in tandem rotors varies with having flow of actual tilt rotor configurations. It is important overlap or without overlap. Investigating the effects of to note that in ground effect, contrary to the mentioned distance between tandem rotors and the ground effect configurations, the Fountain flow-field of the tandem on the pressure and velocity values of the Fountain flow rotors, even their non-overlap type is more complex. below the generic tandem model is the main topic of the Because in the side-by-side arrangement of the tilt present study. rotors, each rotor is less affected by the wake of the For a single rotor operating near the ground, the other one, but in the tandem arrangement, each rotor is direction of the downwash flow in the vicinity of the affected by vortices of other rotor’s wake. ground rapidly changes from vertical to radial along Fountain flow velocities of a full-span and a semi- the surface, extending away from the disk area. This span configuration with an image plane of a sub-scale region encompasses many turbulent vortices within the model of the XV-15 tilt rotor measured by hot-wire boundary layer with a wide range of length scales. When technique in reference [8]. It was observed that flow the rotor height above the ground decreases, it has been velocities have significant differences in the upper observed that the vortex sheet will stretch with higher Fountain-flow region in comparison with other azimuth swirl velocities, resulting in less viscous diffusion and angles. It should be noted that the Fountain flow is a an increasing number of the pairing tip vortices [11]. free jet, so the flow behavior changes by the shear layer This process preserves a much longer vortex core that forms on an image plane that was used and it is not original shape against the changes and preserves its actual. original shape [12]. It is expected that the effects of this In recent years, with the advent of digital computers physical behavior of the flow will also be observed under the and numerical algorithms, valuable information has been helicopter airframe which leads to the formation of a Fountain obtained using computational fluid dynamics [15, 16]. flow. The tip vortices and the vortex sheets along with However, accurate enough predictions at a reasonable pressure jump across the blades, impart remarkable computational time and costs are still challenging issues oscillations in the velocity which must be taken into [17]. Care must be taken in mesh generation and choice account in rotor Fountain flow measurements. of turbulence model to properly capture the details of such complicated phenomena as Fountain flow and 1.3. Research Background the rotor wake structure [18]. The comparison of the The results of studies show that the ground effect results of the numerical studies with experimental data on tandem rotor configurations cannot be modeled and actual results has shown the significant progress by linear functions of such independent variables as of these methods and their success in simulating and thrust or height of rotors from the ground.
Load more

Recommended publications
  • WHIRLYBIRDS, U.S. Marine Helicopters in Korea
    WHIRLYBIRDS U.S. Marine Helicopters in Korea by Lieutenant Colonel Ronald J. Brown U.S. Marine Corps Reserve, Retired Marines in the Korean War Commemorative Series About the Author ieutenant Colonel Ronald J. LBrown, USMCR (Ret), is a freelance writer, a high school football coach, and an educa- THIS PAMPHLET HISTORY, one in a series devoted to U.S. Marines in the tional consultant. The author of Korean War era, is published for the education and training of Marines by several official histories (A Brief the History and Museums Division, Headquarters, U.S. Marine Corps, Washington, D.C., as part of the U.S. Department of Defense observance of History of the 14th Marines, the 50th anniversary of that war. Editorial costs have been defrayed in part With Marines in Operation by contributions from members of the Marine Corps Heritage Foundation. To plan and coordinate the Korean War commemorative events and activi- Provide Comfort, and With ties of the Sea Services, the Navy, Marine Corps, and Coast Guard have Marine Forces Afloat in Desert formed the Sea Services Korean War Commemoration Committee, chaired by the Director, Navy Staff. For more information about the Sea Services’ Shield and Desert Storm), he commemorative effort, please contact the Navy-Marine Corps Korean War was also a contributing essayist for the best-selling book, Commemoration Coordinator at (202) 433-4223/3085, FAX 433-7265 (DSN288-7265), E-Mail: [email protected], Website: The Marines, and was the sole author of A Few Good www.history.usmc.mil. Men: The Fighting Fifth Marines. After almost four years KOREAN WAR COMMEMORATIVE SERIES active duty from 1968 to 1971, Brown returned to teach- DIRECTOR OF MARINE CORPS HISTORY AND MUSEUMS ing high school for the next three decades; intermittent- Colonel John W.
    [Show full text]
  • Historical Perspective September 2011 11
    Helicopter heroes It was 50 years ago that a prototype helicopter first flew and a legend was born—the CH-47 By Mike Lombardi urrently serving on the front lines The advantage of this unique design Just as earlier Chinooks proved of the global fight against terror- allows for low load-per-rotor area, elimi- themselves in wartime, the D model Cism, the CH-47 Chinook is the nates the need for a tail rotor, increases has played a key role for U.S. and epitome of the innovative tandem-rotor lift and stability, and provides a large allied troops in the deserts of Iraq helicopter designs produced through range for center of gravity. and the mountains of Afghanistan. the genius of helicopter pioneer Frank The HRP was followed by the U.S. The highly modified MH-47 series is Piasecki, founder of the company that Navy HUP/UH-25, the first helicopter to operated by the U.S. Army Special would later develop into the Boeing incorporate overlapping tandem rotors, Operations Forces. operations near Philadelphia. and the U.S. Air Force CH-21, a long- When the Chinook first flew in 1961 The CH-47, having been continuously range helicopter transport designed for Boeing Magazine wrote: “There is a modernized, has provided unmatched use in the Arctic. saying in the aviation industry that you capability for U.S. and allied troops since Piasecki stepped down in 1955 as can tell a winner by its appearance. The hard work and dedication of the Boeing its introduction 50 years ago this month.
    [Show full text]
  • A Numerical Workshop for Rotorcraft Concepts Generation and Evaluation Pierre-Marie Basset, Philippe Beaumier, Thomas Rakotomamonjy
    CREATION: a numerical workshop for rotorcraft concepts generation and evaluation Pierre-Marie Basset, Philippe Beaumier, Thomas Rakotomamonjy To cite this version: Pierre-Marie Basset, Philippe Beaumier, Thomas Rakotomamonjy. CREATION: a numerical work- shop for rotorcraft concepts generation and evaluation. Rotorcraft Virtual Engineering Conference, Nov 2016, LIVERPOOL, United Kingdom. hal-01384197 HAL Id: hal-01384197 https://hal.archives-ouvertes.fr/hal-01384197 Submitted on 19 Oct 2016 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Rotorcraft Virtual Engineering, Liverpool, 8-10 Nov. 2016 CREATION: a numerical workshop for rotorcraft concepts generation and evaluation Pierre-Marie Basset, Philippe Beaumier, Thomas Rakotomamonjy ONERA – The French Aerospace Lab, FRANCE [email protected] Abstract. C.R.E.A.T.I.O.N. for “Concepts of Rotorcraft Enhanced Assessment Through Integrated Optimization Network”, is a multidisciplinary computational workshop for the evaluation of rotorcraft concepts. The evaluation concerns both flight performance and environmental impacts (acoustics, air pollution/fuel consumption, etc.). The CREATION workshop must allow the evaluation of any rotorcraft concept whatever the level of details of the description data initially available. Therefore the tool must cope with the preliminary conception problems.
    [Show full text]
  • Xtreme, and Often Exceptionally Far Away from What a Pilot May Experience, Even in Extreme Circumstances
    Frontierswww.boeing.com/frontiers SEPTEMBER 2011 / Volume X, Issue V treme measures XTesting structures to the breaking point helps ensure Boeing products are safe PB BOEING FRONTIERS / SEPTEMBER 2011 1 BOEING FRONTIERS / SEPTEMBER 2011 On the Cover Pushing the limits Structural engineers with Boeing Test & Evaluation don’t necessarily like to go around breaking things, but often they do. Their 24 job is to make sure Boeing products such as jetliners, fighters and helicopters can be operated safely, and that means testing to the limit—and beyond. On any given day, Boeing structural labs are supporting testing requirements throughout the company. COVER IMAGE: SCOTT TEALL, LEFT, AND ANDY BAUGH OF BOEING TEST & EvaLUation prepare AN F-15 FOR fatigUE TESTING IN ST. LOUIS. BOB FERGUSON/BOEING PHOTO: CLOCKWISE FROM LEFT, PHILLIP JORDAN, MattHEW DUNCAN AND CatHERINE METTLACH ARE part OF THE TEAM CONDUCTING FULL-SCALE fatigUE TESTING ON AN F-15 IN ST. LOUIS. BOB FERGUSON/BOEING Ad watch The stories behind the ads in this issue of Frontiers. Inside cover: Page 6: Back cover: “787” is part of a series This ad recognizes Corporate citizenship of ads that reinforces the efforts of Dreamflight, refers to the work Boeing’s partnership with a U.K. charity that Boeing does, both Japan, a relationship takes seriously ill and as a company and that began more than disabled children, without through its employees, 50 years ago. The their parents but under to improve the world. campaign features the the care of a team This ad illustrates art of calligraphy, a of doctors and health Boeing’s commitment symbolic tradition of care professionals, to initiatives that Japanese culture that on a memorable nurture the visionaries communicates not only words but a deeper vacation to Orlando, Fla.
    [Show full text]
  • Aircraft Designations and Popular Names
    Chapter 1 Aircraft Designations and Popular Names Background on the Evolution of Aircraft Designations Aircraft model designation history is very complex. To fully understand the designations, it is important to know the factors that played a role in developing the different missions that aircraft have been called upon to perform. Technological changes affecting aircraft capabilities have resulted in corresponding changes in the operational capabilities and techniques employed by the aircraft. Prior to WWI, the Navy tried various schemes for designating aircraft. In the early period of naval aviation a system was developed to designate an aircraft’s mission. Different aircraft class designations evolved for the various types of missions performed by naval aircraft. This became known as the Aircraft Class Designation System. Numerous changes have been made to this system since the inception of naval aviation in 1911. While reading this section, various references will be made to the Aircraft Class Designation System, Designation of Aircraft, Model Designation of Naval Aircraft, Aircraft Designation System, and Model Designation of Military Aircraft. All of these references refer to the same system involved in designating aircraft classes. This system is then used to develop the specific designations assigned to each type of aircraft operated by the Navy. The F3F-4, TBF-1, AD-3, PBY-5A, A-4, A-6E, and F/A-18C are all examples of specific types of naval aircraft designations, which were developed from the Aircraft Class Designation System. Aircraft Class Designation System Early Period of Naval Aviation up to 1920 The uncertainties during the early period of naval aviation were reflected by the problems encountered in settling on a functional system for designating naval aircraft.
    [Show full text]
  • Using Model-Scale Tandem-Rotor Measurements in Ground Effect to Understand Full-Scale CH-47D Outwash
    JOURNAL OF THE AMERICAN HELICOPTER SOCIETY 62, 012004 (2017) Using Model-Scale Tandem-Rotor Measurements in Ground Effect to Understand Full-Scale CH-47D Outwash Manikandan Ramasamy∗ Gloria K. Yamauchi U.S. Army Aviation Development Directorate —AFDD Aeromechanics Office Aviation & Missile Research, Development & Engineering Center NASA Ames Research Center Research, Development & Engineering Command Moffett Field, CA Ames Research Center, Moffett Field, CA Downwash and outwash characteristics of a model-scale tandem-rotor system in the presence of the ground were analyzed by identifying and understanding the physical mechanisms contributing to the observed flow field behavior. A building block approach was followed in simplifying the problem, separating the effects of the fuselage, effects of one rotor on the other, etc. Flow field velocities were acquired in a vertical plane at four aircraft azimuths of a small-scale tandem rotor system using the particle image velocimetry technique for radial distances up to four times the rotor diameter. Results were compared against full-scale CH-47D measurements. Excellent correlation was found between the small- and full-scale mean flow fields (after appropriate normalization using rotor and wall jet parameters). Following the scalability analysis, the effect of rotor height on the outwash was also studied. Close to the aircraft, an increase in rotor height above ground decreased the outwash velocity at all aircraft azimuths. However, farther away, the longitudinal and lateral axes of the aircraft showed increasing and decreasing outwash velocities, respectively, with increasing rotor height. Baseline rotor measurements were made out-of-ground effect to understand the nature of inflow distribution for realistic rotor configurations and their modified characteristics in the presence of the ground.
    [Show full text]
  • AERSP 407 and AERSP 504 Aerodynamics of V/STOL Aircraft
    PENNSTATE 1 8 5 5 AERSP 407 and AERSP 504 Aerodynamics of V/STOL Aircraft Kenneth S. Brentner Department of Aerospace Engineering The Pennsylvania State University Kenneth S. Brentner, Dept. of Aerospace Engineering 1 PENNSTATE AERSP 407 and 504 1 8 5 5 Goals: To introduce and study key concepts related to aerodynamic loads, vehicle performance, basic rotor dynamics, and control of helicopters and tilt-rotor aircraft. Time: Monday, Wednesday, Friday: 1:25-2:15pm Place: 151 Willard Building Instructor: Dr. Kenneth S. Brentner 233 D Hammond Building Tel: (814) 865-6433 Email: [email protected] Office Hours: Monday and Wednesday 10:30-11:30am; by appointment; I also have an open door policy. Kenneth S. Brentner, Dept. of Aerospace Engineering 2 1 PENNSTATE Reference Materials 1 8 5 5 Textbook: Principles of Helicopter Aerodynamics, J. Gordon Leishman I will be basing lecture note primarily on this book. Other Good References: Aerodynamics of V/STOL Flight, B. W. McCormick, Jr. Helicopter Theory, W. Johnson Rotary-Wing Aerodynamics, W. Z. Stepniewski and C. N. Keys Aerodynamics of the Helicopter, A. Gessow and G. C. Meyers Kenneth S. Brentner, Dept. of Aerospace Engineering 3 PENNSTATE Outline 1 8 5 5 1. Introduction (also read Chapter 1) 2. Fundamentals of Rotor Aerodynamics (Chapter 2) 3. Blade Element Analysis (Chapter 3) 4. Blade Motion and Rotor Control (Chapter 4) 5. Basic Helicopter Performance (Chapter 5) 6. Conceptual Design of Helicopters (first part of Chapter 6) 7. Introduction to Unsteady Aerodynamics, Dynamic Stall, and Rotor Wakes – time permitting (portions of Chapters 7-10) This is my first time teaching this course, so I don’t have dates for when we will cover each of the sections.
    [Show full text]
  • Impact of Modeling and Simulation on Rotorcraft Acquisition
    Presented to: 18th Annual NDIA Systems Engineering Conference Impact of Modeling and Simulation on Rotorcraft Acquisition DISTRIBUTION A. Approved for public release: distribution unlimited. Presented by: Dr. Marty Moulton Date: 28 October 2015 Chief, Simulation and Aerodynamics Branch U.S. Army Aviation and Missile Research, Development, and Engineering Center AMRDEC Org Chart 2 Aviation Engineering Directorate Airworthiness: A Demonstrated Capability of an Aircraft, Subsystem or Component to Function Satisfactorily when used and maintained within Prescribed Limits • Required by law (49 USC 106) - Under 14 CFR, FAA does for civil aviation • Governed by Army Regulation 70-62 • Airworthiness Authority = CG AMCOM Principal Products: Airworthiness Releases, Statements Of Airworthiness Qualification, Airworthiness Impact Statements, Safety of Flight Messages What this means to the Aviation Units… •It is Safe to Operate and will Perform the Mission when Delivered •It will Continue to Safely Perform the Mission if Operated Maintained per the Manuals •Parts and Overhaul work must be per approved sources and standards to Maintain Airworthiness 3 “Demonstrated Capability” • Engineering analysis, modeling, and simulation • Formal inspection, design review, and safety assessment • Contractor development test • Component qualification test of performance under specified conditions and duration • Formal contractor demonstrations • Government testing 4 CREATE* Program * Computational Research and Engineering Acquisition Tools and Environments 5 CREATE
    [Show full text]
  • Influence of Lift Offset on Rotorcraft Performance
    Influence of Lift Offset on Rotorcraft Performance Wayne Johnson Aeromechanics Branch NASA Ames Research Center Moffett Field, California Abstract The influence of lift offset on the performance of several rotorcraft configurations is explored. A lift- offset rotor, or advancing blade concept, is a hingeless rotor that can attain good efficiency at high speed, by operating with more lift on the advancing side than on the retreating side of the rotor disk. The calculated performance capability of modern-technology coaxial rotors utilizing a lift offset is examined, including rotor performance optimized for hover and high-speed cruise. The ideal induced power loss of coaxial rotors in hover and twin rotors in forward flight is presented. The aerodynamic modeling requirements for performance calculations are evaluated, including wake and drag models for the high speed flight condition. The influence of configuration on the performance of rotorcraft with lift-offset rotors is explored, considering tandem and side-by-side rotorcraft as well as wing-rotor lift share. significant roll moment, say rotor lift offsets of 20%. INTRODUCTION. Roll moment balance of the entire aircraft requires either By operating a rotor in edgewise flight with lift offset — twin main rotors, or perhaps a wing. The coaxial more lift on the advancing side than on the retreating side helicopter configuration with lift-offset rotors is known of the rotor disk — it is possible to attain good as the Advancing Blade Concept (ABC). performance at high forward speed. A conventional rotor with an articulated hub is constrained to operate with The lift offset concept was demonstrated for the coaxial small hub moments.
    [Show full text]
  • Influence of Propeller Overlap on Large Scale Tandem UAV Performance
    Unmanned Systems, Vol. 0, No. 0 (2018) 1–19 World Scientific Publishing Company Influence of Propeller Overlap on Large Scale Tandem UAV Performance Adrian B. Weishäupla, Stephen D. Priora a Aeronautics, Astronautics and Computational Engineering, Faculty of Engineering and Physical Sciences, University of Southampton, Bolderwood Campus, Southampton, SO16 7QF, United Kingdom E-mail: [email protected] This paper investigates the interference that arises from overlapping UAV propellers during hovering flight. The tests have been conducted on 28” x 8.4” Ultralight Carbon Fibre propellers using a bespoke mount and the RCBenchmark Series 1780 dynamometer at various degrees of overlap (z/D) and vertical separation (d/D). A great deal of confusion regarding the losses that are associated with mounting propellers in a co- axial configuration are reported in the literature, with a summary of historical tandem helicopters having been conducted. The results highlight a region of beneficial overlap (0-20%), which has the potential to be advantageous to a wide range of UAVs. Keywords: Propeller, Efficiency, Tandem, Overlap, UAV, Interference Florine canted the forward and aft rotors by a 7 deg angle from Nomenclature the vertical, in opposite directions (starboard and port). His early prototypes ‘Type I’ and ‘Type II’, resulted in the flight duration c Chord (m) record of 9 minutes and 58 seconds in October 1933 [2]. d Stagger (m) k Induced Power Factor n Revolutions per Second (s-1) r Section Radius (m) s Slant Line Distance Between Rotors (m) z Propeller Plane Separation (Gap) (m) 2 AO Area Overlap (m ) CD0 Profile Drag CP Coefficient of Power CT Coefficient of Thrust D Propeller Diameter (m) P Induced Power (W) i Q Torque (Nm) Fig.
    [Show full text]
  • Aerodynamic Characteristic Analysis of Multi-Rotors Using a Modified
    Trans. Japan Soc. Aero. Space Sci. Vol. 52, No. 177, pp. 168–179, 2009 Aerodynamic Characteristic Analysis of Multi-Rotors Using a Modified Free-Wake Method By Jaewon LEE,1Þ Kwanjung YEE2Þ and Sejong OH2Þ 1ÞResearch Institute of Mechanical Technology, Pusan National University, Busan, Korea 2ÞDepartment of Aerospace Engineering, Pusan National University, Busan, Korea (Received November 23rd, 2008) Much research is in progress to develop a next-generation rotor system for various aircrafts, including unmanned aerial vehicles (UAV) with multi-rotor systems, such as coaxial and tandem rotors. Development and design of such systems requires accurate estimation of rotor performance. The most serious problem encountered during analysis is wake prediction, because wake-wake and wake-rotor interactions make the problem very complex. This study analyzes the aerodynamic characteristics based on the free-wake method, which is both efficient and effective for predicting wake. This code is modified to include the effect of complex planforms as well as thickness by using an unsteady 3D panel method. A time-marching free-wake model is implemented based on the source-doublet panel method that assigns panels to the surface and analyzes them. The numerical wake instability, the most critical problem for analysis, is resolved by adopting slow start-up and by including viscous effects. Also, the instability due to wake interference in tandem rotor analysis is resolved by configuring the initial shapes of the multi-rotor wake as that of a single rotor wake trajectory. The developed code is verified by comparing with previous experimental data for coaxial and tandem rotors. Key Words: Multi Rotor, Time-Marching Free-Wake, Unsteady Panel Method, Wake Instability Nomenclature 1.
    [Show full text]
  • Cronus a Response to the American Helicopter Society 2005 Request for Proposal Undergraduate Category
    Cronus A Response to the American Helicopter Society 2005 Request For Proposal Undergraduate Category Submitted for AERO2362 Design Project Commercial In Confidence This report describes the conceptual design of a heavy-lift VTOL rotorcraft, intended for military use. Several systems are described in detail, and basic schematic drawings are included. This report is submitted both as an AHS 2005 Design Competition entry and as the major assessment for the RMIT AERO2362 course. (in alphabetical order) Marco Attia Rodney Meadth S3024944 S3023940 Steve Chapman Vineet Naidu S3025565 S2076307F Ronish Chaudhary Dave Rocco S3006484 S3017892 Carl Corcoran Haeison Romero S2064629M S2105853V CRONUS CONCEPTUAL DESIGN JUNE 2005 ii CRONUS CONCEPTUAL DESIGN JUNE 2005 Executive Summary In response to the American Helicopter Society s 2005 Request For Proposal, an RMIT University (Melbourne, Australia) undergraduate design team has completed the conceptual design of a heavy-lift military helicopter, known as the Cronus . Trade-off studies of similar systems were conducted, and a configuration similar to that of the existing CH-47 Chinook was chosen. The tandem configuration is the most favourable for heavy-lift operations, when considering issues of stability, size constraints, and adaptability. A nine stage design process, provided by Dr Arvind Sinha, was then followed. This iterative design method provides basic information, such as weight, power required, rotor dimensions, and so on. The values obtained were more than adequate for conceptual design. These basic values were then used to carry out a more detailed performance analysis, which gave a refined engine weight, and allowed the maximum speed (governed by compressibility limits) to be determined.
    [Show full text]