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Author: Albert Betz
Publisher:
ISBN:
Category : Ground-cushion phenomenon
Languages : en
Pages : 544
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Book Description
In what follows an estimate will be made of the magnitude of the ground effect. For the two cases where the distance a of the propeller from the ground is very small, and very large, respectively, in comparison with the propeller radius r(sub o) the relations may be simply expressed. We consider first the effect of the ground, assuming that the thrust is held constant, as may be done by a suitable change in the propeller speed.
Author: Albert Betz
Publisher:
ISBN:
Category : Ground-cushion phenomenon
Languages : en
Pages : 544
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Book Description
In what follows an estimate will be made of the magnitude of the ground effect. For the two cases where the distance a of the propeller from the ground is very small, and very large, respectively, in comparison with the propeller radius r(sub o) the relations may be simply expressed. We consider first the effect of the ground, assuming that the thrust is held constant, as may be done by a suitable change in the propeller speed.
Author: F. A. DuWaldt
Publisher:
ISBN:
Category : Rotors (Helicopters)
Languages : en
Pages : 110
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Book Description
The report presents the development of a wake model for a lifting propeller (rotor) in ground effect and the computational procedure used to determine the spacial distribution of wake vorticity and the induced velocity field accompanying that vorticity distribution. Sample calculations for a two-bladed rotor were carried out on an IBM 7044 computer. Locations of wake vortical elements and the associated induced velocities at selected field points are presented for advance ratios of 0, 0.02, 0.05, and 0.10 for an H/R (ratio of rotor height above ground to rotor radius) of 1.0. Also, a few results for a hovering case with H/R = 0.5 are presented. A calculated root-mean-square velocity map is compared with measured hovering data (time averaged) and good agreement is obtained in the outer half of the slipstream. The implications of computed results with respect to the flow field at a horizontal stabilizer or tail rotor are noted as examples of the use of the model. The wake vortex model used for these calculations is a distorted continuous helix emanating from each blade tip. (Author).
Author: Jielong Cai
Publisher:
ISBN:
Category :
Languages : en
Pages : 77
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Book Description
With the increased usage of propeller-driven unmanned-aerial-vehicles (UAV) in closed spaces such as caves, buildings, pipelines, etc. for photography, surveillance, and inspection, understanding the influence of the ground and ceiling on a remote-controlled (R/C) propeller is of the utmost importance. The flying characteristics of drones changes when an object or a ground plane is in its close proximity due to changes in its propeller performance. The changes in performance are due to the changes in the flow field around the propeller that occur due to ground proximity, which is also known as ground effect. Ground effect on lifting rotor performance has been studied theoretically and experimentally for decades. Historically, most investigations focus on helicopter rotors, which have high aspect ratio, lower pitch and rarely have spanwise twist. This research focuses on smaller size rotors, in particular, the thin-electric propeller which is used widely on small UAVs. The research considers parameter variations not broadly available in the literature such as propeller pitch, diameter, solidity, and blockage. In particular, extreme ground effect is considered, where the ratio of ground plane stand-off distance to propeller diameter is 0.1 or less. Moreover, the propeller is reversed, to examine the ceiling effect. Typically, the ground effect investigation is done with a ground plane that is big enough to be considered an infinite plane. In this research, both infinite plane and circular plates of similar diameter (or less) of the propeller are used as ground planes. Various circular plates with different diameter to propeller diameter ratios are used in the research representing different 'blockage ratios'. The investigation gives insight into changes in propeller performance in proximity to fuselages of a given diameter in propeller-driven airplanes under pusher and puller configurations. All experiments were conducted on a thrust-stand built in-house at the University of Dayton Low-Speed Wind Tunnel (UD-LSWT) Laboratory. All propellers used in the experiment are from the "thin electric" APC series, with diameter ranging from 11 inches to 17 inches and pitch from 4.5 inches to 14 inches. The propeller peak Reynolds number varies from 90,000 to 190,000 in the experiment. Circular plates with diameter ratio from 0.5 to 1.0 are used in the blockage effect experiment. Force, torque and RPM propeller data are taken during the experiment from a propeller diameter normalized ground distance of -1.5 to 1.5. Results from the infinite ground experiment are separated into three major sections: thrust coefficient and power coefficient, power required at constant thrust, and effective thrust. A significant increment in the thrust coefficient and decrement in the power coefficient is found in ground proximity among the propellers with a pitch-to-diameter ratio less than 0.7. This results in a decrement of power required at constant thrust in ground effect. Almost identical changes in the power required at constant thrust in the ceiling effect is also found in most of the low pitch to diameter ratio propellers. For the blockage experiment, a less significant reduction in the power required in constant thrust for all propellers is found at lower blockage ratios as expected. Similar trends in the effect on? thrust for different propellers at the same blockage ratio are found. Results for the positive h/D region (the puller configuration), overlap regardless of the propeller pitch to diameter ratio or solidity. A phenomenological expression (an algebraic equation) for power required at constant thrust as a function of propeller parameter is established during the research to predict the changes in the propeller performance in ground effect which will benefit the operation of small UAVs in both open and confined areas.
Author: Gordon J. Leishman
Publisher: Cambridge University Press
ISBN: 9780521858601
Category : Science
Languages : en
Pages : 860
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Book Description
Written by an internationally recognized teacher and researcher, this book provides a thorough, modern treatment of the aerodynamic principles of helicopters and other rotating-wing vertical lift aircraft such as tilt rotors and autogiros. The text begins with a unique technical history of helicopter flight, and then covers basic methods of rotor aerodynamic analysis, and related issues associated with the performance of the helicopter and its aerodynamic design. It goes on to cover more advanced topics in helicopter aerodynamics, including airfoil flows, unsteady aerodynamics, dynamic stall, and rotor wakes, and rotor-airframe aerodynamic interactions, with final chapters on autogiros and advanced methods of helicopter aerodynamic analysis. Extensively illustrated throughout, each chapter includes a set of homework problems. Advanced undergraduate and graduate students, practising engineers, and researchers will welcome this thoroughly revised and updated text on rotating-wing aerodynamics.
Author: Daniel O. Dommasch
Publisher: Elsevier
ISBN: 1483222322
Category : Technology & Engineering
Languages : en
Pages : 480
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Book Description
Performance
Author: United States. National Advisory Committee for Aeronautics
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 616
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Book Description
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 664
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Book Description
Author: J. Gordon Leishman
Publisher: Cambridge University Press
ISBN: 9780521523967
Category : Medical
Languages : en
Pages : 544
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Book Description
Helicopters are highly capable and useful rotating-wing aircraft with roles that encompass a variety of civilian and military applications. Their usefulness lies in their unique ability to take off and land vertically, to hover stationary relative to the ground, and to fly forward, backward, or sideways. These unique flying qualities, however, come at a high cost including complex aerodynamic problems, significant vibrations, high levels of noise, and relatively large power requirements compared to fixed-wing aircraft. This book, written by an internationally recognized expert, provides a thorough, modern treatment of the aerodynamic principles of helicopters and other rotating-wing vertical lift aircraft. Every chapter is extensively illustrated and concludes with a bibliography and homework problems. Advanced undergraduate and graduate students, practising engineers, and researchers will welcome this thorough and up-to-date text on rotating-wing aerodynamics.
Author: Harry H. Heyson
Publisher:
ISBN:
Category : Ground-cushion phenomenon
Languages : en
Pages : 18
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 792
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Book Description
