CFD analysis and design of a low-twist, hovering rotor equipped with trailing-edge flaps

This thesis reports the analysis and design of a hovering rotor equipped with both slotted and blended trailing-edge flaps. This was accomplished by combining a simple blade element method with 3D inviscid and RANS CFD that allowed for a robust sequence of design specification, analysis, and verification. Most modern helicopters have high levels of blade twist and various tip shape designs to help improve hover performance. However, such blade designs face problems due to compressibility effects on the advancing blade in forward flight. The twisted blade gives rise to negative incidence at the blade tip, which accelerates shock formation on the lower surface. The current work looks to evaluate the implementation of a low twist rotor for improved forward flight performance and recovering any potential losses in hover performance by deflecting fixed, trailing-edge flaps

comprehensive aeroelastic analysis of helicopter rotor with trailing-edge flap for primary control and vibration control

A comprehensive aeroelastic analytical model of helicopter rotors with trailingedge flaps for primary and vibration controls has been developed. The derivation of system equations is based on Hamilton principles, and implemented with finite element method in space and time. The blade element consists of fifteen degrees of freedom representing blade flap, lag, torsional, and axial deformations. Three aerodynamic models of flapped airfoils were implemented in the present analysis, the unsteady Hariharan- Leishman model for trailing-edge flaps without aerodynamic balance, a quasi-steady Theodorsen theory for an aerodynamic balanced trailing-edge flap, and table lookup based on wind tunnel test data. The trailing-edge flap deflections may be modeled as a degree of freedom so that the actuator dynamics can be captured properly. The coupled trim procedures for swashplateless rotor are solved in either wind tunnel trim or free flight condition. A multicyclic controller is also implemented to calculate the flap control inputs for minimization of vibratory rotor hub loads. The coupled blade equations of motion are linearized by using small perturbations about a steady trimmed solution. The aeroelastic stability characteristics of trailing-edge flap rotors is then determined from an eigenanalysis of the homogeneous equations using Floquet method. The correlation studies of a typical bearingless rotor and an ultralight teetering rotor are respectively based on wind tunnel test data and simulations of another comprehensive analysis (CAMRAD II). Overall, good correlations are obtained. Parametric study identifies that the effect of actuator dynamics cannot be neglected, especially for a torsionally soft smart actuator system. Aeroelastic stability characteristics of a trailing-edge flap rotor system are shown to be sensitive to flap aerodynamic and mass balances. Key parameters of trailing-edge flap system for primary rotor control are identified as blade pitch index angle, torsional frequency, flap location, flap length, and overhang length. The swashplateless rotor is shown to achieve better rotor performance and overall more stable than the conventional configuration. Simulations of flaps performing both primary control and active vibration control are carried out, with the conclusion that trailing-edge flaps are capable of trimming the rotor and simultaneously minimizing vibratory rotor hub loads

Aeronautical engineering: A continuing bibliography with indexes (supplement 242)

This bibliography lists 466 reports, articles, and other documents introduced into the NASA scientific and technical information system in July, 1989. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Assessment of the AH-64D Longbow Apache’s Handling Qualities for Instrument Meteorological Conditions/Instrument Flight Rules Flight

An assessment of the handling of the AH-64D for flight in IMC and under IFR was conducted. Testing was performed in the configurations listed in table 1 and under the conditions presented in tables 3 and 4. All test objectives were met. IMC mission maneuvers with all systems working resulted in satisfactory handling qualities with no excessive compensation required from the pilot (altitude and attitude holds ON). However, as the aircraft systems were progressively degraded the workload for the evaluating pilot increased significantly. The high workload coupled with the absence of a vertical speed indicator (VSI) and torque indication during an AC failure and the observed errors in the standby altimeter and airspeed indicators would most likely prevent flying a successful unusual attitude recovery, an airport surveillance radar (ASR) approach, or a precision approach radar (PAR) approach. The inadequacy of the standby instruments is a deficiency. The aircraft’s longitudinal gust response with FMC OFF required extensive pilot compensation to maintain altitude and airspeed within adequate parameters, further increasing the overall pilot workload, and is a deficiency. Additionally, the aircraft’s battery life does not meet the 30- min requirement for IMC/IFR flight that would be required in the unlikely event of an aircraft AC power failure and results in a deficiency. Engineering maneuvers conducted to quantify the handling qualities of the AH-64D with FMC OFF confirmed the high pilot workload and extensive compensation required. These maneuvers revealed an oscillatory divergent long-term mode, an oscillatory divergent lateral-directional oscillation (LDO), negative spiral stability when banked to the right, and significant coupling between pitch and roll. While conducting these maneuvers, excessive instrumentation lag was observed in the standby altimeter during climbs and descents. This resulted in errors of up to 300 ft between boom data and the standby altimeter. The excessive observed instrument lag and inaccuracy of the standby altimeter is a shortcoming. Other findings included the absence of any information on IMC/IFR procedures in the operator’s manual was also found to be a shortcoming. Consequently a clearance for aircraft operation in IMC is not recommended. Plots of representative engineering data collected in the heavy weapons (configuration 3) and two-tank configurations (configuration 5) are in Appendix D

Retreating blade stall control on a NACA 0015 aerofoil by means of a trailing edge flap

Trailing edge flaps may provide a mechanism for alleviating retreating blade stall. In the present investigation numerical simulations were conducted involving a NACA 0015 aerofoil section fitted with a plain trailing edge (TE) flap. All simulations were conducted using DIVEX, a tool being developed at the University of Glasgow, Department of Aerospace Engineering. In summary, the code uses a surface shedding discrete vortex method (DVM) for the simulation of 2-D incompressible flows around pitching aerofoils. The aero-foil is oscillating in pitch about its quarter chord axis and the clap undergoes negative pitch inputs, i.e. upward. An interesting feature appears to be that the cause of the severe nose down pitching movement introduced during dynamic stall is due to the cortical pair of the DSV and TEV where it is shown that the former feeds the latte in the case of the clean aerofoil for the range of reduced frequencies varying between k = 0.128 and k = 0.180. This fact suggests that manipulation of the vorticity in the vicinity of the trailing edge may be a mechanism for modification of the dynamic stall vortex (DSV) trajectory. This was found to relieve the aerofoil from severe pitching moment undershoot occurring during dynamic stall under appropriately phased flap actuations. Results obtained so far encourage the employment of a flap with fairly small size, 15% of the aerofoil chord. A parametric study is described which identifies the proper aerodynamic and actuation parameters for the current problem. In addition a simple open loop control scheme is developed based purely on rotor and flap related quantities

Aeronautical engineering: A cumulative index to a continuing bibliography (supplement 248)

This publication is a cumulative index to the abstracts contained in Supplements 236 through 247 of Aeronautical Engineering: A Continuing Bibliography. The bibliographic series is compiled through the cooperative efforts of the American Institute of Aeronautics and Astronautics (AIAA) and the National Aeronautics and Space Administration (NASA). Seven indexes are included -- subject, personal author, corporate source, foreign technology, contract number, report number and accession number

Aeronautical Engineering: A continuing bibliography with indexes

This bibliography lists 382 reports, articles and other documents introduced into the NASA scientific and technical information system in June 1982

Aeronautical engineering, a continuing bibliography with indexes

This bibliography lists 567 reports, articles and other documents introduced into the NASA scientific and technical information system in January 1984

Bibliography of NASA published reports on general aviation, 1975 to 1981

This bibliography lists 478 documents which relate to all heavier-than-air fixed wing aircraft exclusive of military types and those used for commercial air transport. An exception is the inclusion of commuter transport aircraft types within the general aviation category. NASA publications included in this bibliography are: conference publications (CP), reference publications (RP), technical memorandums (TM, TMX), technical notes (TN), technical papers (TP), and contractor reports (CR). In addition, papers and articles on NASA general aviation programs published by technical societies (AIAA, SAE, etc.) are included, as well as those listed in NASA's Scientific and Technical Aerospace Reports (STAR) Journal. Author and subject indexes are also provided to facilitate use of the bibliography

Aeronautical engineering: A continuing bibliography with indexes (supplement 279)

This bibliography lists 759 reports, articles, and other documents introduced into the NASA scientific and technical information system in May 1992. Subject coverage includes: design, construction, and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics