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Book Experimental and Analytical Studies of a Model Helicopter Rotor in Hover

Download or read book Experimental and Analytical Studies of a Model Helicopter Rotor in Hover written by F. X. Caradonna and published by . This book was released on 1981 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present study is a benchmark test to aid the development of various rotor performance codes. The study involves simultaneous blade pressure measurements and tip vortex surveys. Measurements were made for a wide range of tip Mach numbers including the transonic flow regime. The measured tip vortex strength and geometry permit effective blade loading predictions when used as input to a prescribed wake lifting surface code. It is also shown that with proper inflow and boundary layer modeling, the supercritical flow regime can be accurately predicted. (Author).

Book An Analytical and Experimental Investigation of Helicopter Rotor Hover Performance and Wake Geometry Characteristics

Download or read book An Analytical and Experimental Investigation of Helicopter Rotor Hover Performance and Wake Geometry Characteristics written by Anton J. Landgrebe and published by . This book was released on 1971 with total page 207 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Bramwell s Helicopter Dynamics

Download or read book Bramwell s Helicopter Dynamics written by A. R. S. Bramwell and published by Elsevier. This book was released on 2001-04-06 with total page 403 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the original publication of 'Bramwell's Helicopter Dynamics' in 1976, this book has become the definitive text on helicopter dynamics and a fundamental part of the study of the behaviour of helicopters. This new edition builds on the strengths of the original and hence the approach of the first edition is retained. The authors provide a comprehensive overview of helicopter aerodynamics, stability, control, structural dynamics, vibration, aeroelastic and aeromechanical stability. As such, Bramwell's Helicopter Dynamics is essential for all those in aeronautical engineering. THE single volume comprehensive guide for anyone working with helicopters Written by leading worldwide experts in the field

Book Experimental Investigation of Transition of a Model Helicopter Rotor from Hovering to Vertical Autorotation

Download or read book Experimental Investigation of Transition of a Model Helicopter Rotor from Hovering to Vertical Autorotation written by S. E. Slaymaker and published by . This book was released on 1952 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental investigation was made of the variation of average induced flwo around a model helicopter during transition from hovering flight to steady autorotative vertical descent. Test data were obtained from simulated power failures under many different conditions. Results are summarized for variation in disk loading, blade angles, and pitch-change rate and "effective induced velocities" calculated for the varios conditions are presented. Comparisons of theoretical and experimental data indicate that conditions peculiar to vertical descent in the transition range cause variations in performance not predicted by the theoretical analysis.

Book Experimental study on the ground effect of a model helicopter rotor in hovering

Download or read book Experimental study on the ground effect of a model helicopter rotor in hovering written by Jiro Kōo and published by . This book was released on 1966 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Scientific and Technical Aerospace Reports

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Comparison of Theoretical and Experimental Model Helicopter Rotor Performance in Forward Flight

Download or read book Comparison of Theoretical and Experimental Model Helicopter Rotor Performance in Forward Flight written by JOHN P. JR. RABBOTT and published by . This book was released on 1961 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt: An analytical and experimental program was conducted to determine the degree of correlation between theoretical and experimental model rotor performance over a range of forward speeds of 100 to 161 knots and tip speeds of 580 to 850 ft./sec. The theory utilized synthesized airfoil data derived from hovering tests, and included both stall and compressibility effects. The model blades were dynamically scaled from the Sikorsky S-56 main rotor blades. Theory and experiment correlate well below the theoretically predicted stall boundary, but above stall the theory is unduly conservative in estimating rotor power required. The effects of compressibility on rotor power loading can be accurately predicted. A rotor with an NACA 0012 airfoil section incurs severe penalties in profile power when the advancing tip Mach number exceeds 0.85 to 0.90. Significant amounts of model rotor blade dynamic twisting (up to 5 degrees change in pitch at the 3/4 radius station) occur both in hovering and in forward flight. Such twisting must be taken into account to properly synthesize airfoil data from hovering tests. (Author).

Book Aerodynamic Analysis of Helicopter Rotors Using a Higher Order Free Wake Method

Download or read book Aerodynamic Analysis of Helicopter Rotors Using a Higher Order Free Wake Method written by Tenzin Choephel and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The wake has a strong influence on the aerodynamics of a helicopter rotor, andthe accurate prediction of its geometry and the resulting induced velocity fieldis extremely important for rotorcraft aerodynamic analysis. In this thesis, a newhigher-order, free-wake method for rotor aerodynamic analysis is presented. Themethod uses elements of distributed vorticity to model the lifting surfaces and theassociated wake. The use of such higher-order spanwise elements ensures higherresolution compared to traditional filament-based free-wake analysis and does notrequire explicit vortex core modeling with a user-specified core size. Since themethod uses a full-span, singularity-free, relaxed wake, it can resolve the effect ofon-blade, partial-span devices.The free-wake method is validated in both hover and forward flight againstmeasured data from well-documented experiments. In hover, the blade spanwiselift coefficients predicted by the free-wake analysis correlate well with the measureddata from the classic Caradonna-Tung model rotor experiment. The figure of merit,which is a measure of rotor efficiency, predicted by the present method is comparedto that from the experiments conducted by Knight and Hefner, and the correlationsare found to be quite good given the level of fidelity of this method, which is basedon potential flow theory. Rotor downwash, which is one of the most importantconsiderations in rotor aerodynamic analysis, is predicted very well by the free-wakemethod when compared to measured data from a full-scale rotor test performedby Boatwright. These correlation studies provide a lot of promise as to the abilityof the method in predicting the challenging aerodynamics of a helicopter rotor inhover.Validation studies are also performed to assess the accuracy of the free-wakeanalysis in predicting downwash distribution in forward flight. Comparison ofnumerical predictions with experimental data requires the rotor to be trimmed tothe conditions recorded in the experiment. To ensure this, the free-wake programis coupled with RCAS, a comprehensive helicopter analysis code developed by theiiiUS Army, in order to take advantage of its robust trim algorithm, among othercapabilities. The coupling is achieved through what is called a loose-couplingmethodology, whereby data is exchanged at the end of each coupling iteration orconverged rotor revolution. The downwash distributions predicted by the presentmethod are compared to measured data for a model rotor at various advancedratios and thrust levels taken at the U.S. Army/NASA Langley Research Center(LaRC) facility. The free-wake method not only captures the important phenomenaobserved in the experiments but the results also correlate well with the measureddata both in terms of magnitude and distribution. However, exceptions exist atthe highest advance ratio, where other methods also demonstrate poor correlations.The results from this free-wake analysis are also compared to predictions by otherexisting methods such as the University of Maryland free-wake method (UMDFW)and the vortex transport method (VTM). The present method yields resultscomparable to the ones obtained using VTM, both of which correlate better withmeasurements than does UMD-FW.Sensitivity studies show that the blade panel density and azimuthal time-stepsize do not have a significant influence on the solution fidelity. In addition, free-wakeanalyses with the azimuthal time-step size of = 3o demonstrate the robustnessof the method even with small time-steps, which is important for certain problemsincluding rotor acoustics.The thesis concludes with a discussion on the capability of the new free-wakemethod in resolving on-blade, partial-span devices. An analysis of a 2-bladed rotorwith a partial-span deflection is performed and the resulting changes in sectionalloadings, downwash distribution, wake geometry and aggregate performance parametersare highlighted to demonstrate its potential as a tool for future rotorcraftanalysis.

Book Full scale S 76 Rotor Performance and Loads at Low Speeds in the NASA Ames 80 by 120 Foot Wind Tunnel

Download or read book Full scale S 76 Rotor Performance and Loads at Low Speeds in the NASA Ames 80 by 120 Foot Wind Tunnel written by Patrick M. Shinoda and published by . This book was released on 1996 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: A full-scale helicopter rotor test was conducted in the NASA Ames 80- by 120-Foot Wind Tunnel with a four-bladed S-76 rotor system. Rotor performance and loads data were obtained over a wide range of rotor shaft angles-of-attack and thrust conditions at tunnel speeds ranging from 0 to 100 kt. The primary objectives of this test were (1) to acquire forward flight rotor performance and loads data for comparison with analytical results; (2) to acquire S-76 forward flight rotor performance data in the 80- by 120-Foot Wind Tunnel to compare with existing full-scale 40- by 80-Foot Wind Tunnel test data that were acquired in 1977; (3) to evaluate the acoustic capability of the 80- by 120- Foot Wind Tunnel for acquiring blade vortex interaction (BVI) noise in the low speed range and compare BVI noise with in-flight test data; and (4) to evaluate the capability of the 80- by 120-Foot Wind Tunnel test section as a hover facility. The secondary objectives were (1) to evaluate rotor inflow and wake effects (variations in tunnel speed, shaft angle, and thrust condition) on wind tunnel test section wall and floor pressures; (2) to establish the criteria for the definition of flow breakdown (condition where wall corrections are no longer valid) for this size rotor and wind tunnel cross-sectional area; and (3) to evaluate the wide-field shadowgraph technique for visualizing full-scale rotor wakes. This data base of rotor performance and loads can be used for analytical and experimental comparison studies for full-scale, four-bladed, fully articulated rotor systems. Rotor performance and structural loads data are presented in this report.

Book Aeromechanical Stability of a Hingeless Rotor in Hover and Forward Flight Analysis and Wind Tunnel Tests

Download or read book Aeromechanical Stability of a Hingeless Rotor in Hover and Forward Flight Analysis and Wind Tunnel Tests written by and published by . This book was released on 1983 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: A research effort of analysis and testing has been conducted in the NASA-Langley Transonic Dynamics Tunnel to investigate the ground resonance phenomenon of a soft in-plane hingeless rotor. Experimental data were obtained using a 9 ft. (2.74 m) diameter model rotor in hover and forward flight. Eight model rotor configurations were investigated. Configuration parameters included pitch-flap coupling, blade sweep and droop, and precone of the blade feathering axis. An analysis based on a comprehensive analytical model of rotorcraft aerodynamics and dynamics was used for this study. The moving-block method was used to experimentally determine the regressing lead-lag mode damping. Good agreement has been obtained between the analysis and test. Both analysis and experiment indicated ground resonance instability in hover. The paper presents an outline of the analysis, a description of the experimental model and procedures, and comparison of the analytical and experimental data. (Author).

Book Finite difference Computations of Rotor Loads

Download or read book Finite difference Computations of Rotor Loads written by F. X. Caradonna and published by . This book was released on 1985 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper demonstrates the current and future potential of finite potential of finite-difference methods for solving real rotor problems now rely largely on empiricism. The demonstration consists of a simple means of combining existing finite-difference, integral, and comprehensive loads codes to predict real transonic rotor flows. These computations are performed for hover and high-advance-ratio flight. Comparisons are made with experimental pressure data. Additional keywords: Helicopters; Equations of motion. (Author).

Book Journal of the American Helicopter Society

Download or read book Journal of the American Helicopter Society written by American Helicopter Society and published by . This book was released on 2003 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt: