Engineering topics

Warmbrodt, W.

Publications and source records attributed to Warmbrodt, W..

At least 19 records

NASA NTRS1987

Design Considerations for High-Speed Control Systems

Existing hardware integrated into versatile, high-speed control system. Report discusses five global design considerations to integrate array-processor, multimicroprocessor, and host-computer system architectures into versatile, high-speed controllers. Such controllers are capable of control throughputs as high as 36 MHz for 8-bit bytes and maintain constant interaction with non-real-time or user environment. Application example, architecture of high-speed, closed-loop controller used to control helicopter vibration actively discussed.

Jacklin, S. A.↗

NASA NTRS1985

The use of active controls to augment rotor/fuselage stability

The use of active blade pitch control to increase helicopter rotor/body damping is studied. Control is introduced through a conventional nonrotating swashplate. State variable feedback of rotor and body states is used. Feedback parameters include cyclic rotor flap and lead-lag states, and body pitch and roll rotations. The use of position, rate, and acceleration feedback is studied for the various state variables. In particular, the influence of the closed loop feedback gain and phase on system stability is investigated. For the rotor/body configuration analyzed, rotor cyclic inplane motion and body roll-rate and roll-acceleration feedback can considerably augment system damping levels and eliminate ground resonance instabilities. Scheduling of the feedback state, phase, and gain with rotor rotation speed can be used to maximize the damping augmentation. This increase in lead-lag damping can be accomplished without altering any of the system modal frequencies. Investigating various rotor design parameters (effective hinge offset, blade precone, blade flap stiffness) indicates that active control for augmenting rotor/body damping will be particularly powerful for hingeless and bearingless rotor hubs.

Straub, F. K.↗

NASA NTRS1985

The influence of dynamic inflow and torsional flexibility on rotor damping in forward flight from symbolically generated equations

The combined effects of blade torsion and dynamic inflow on the aeroelastic stability of an elastic rotor blade in forward flight are studied. The governing sets of equations of motion (fully nonlinear, linearized, and multiblade equations) used in this study are derived symbolically using a program written in FORTRAN. Stability results are presented for different structural models with and without dynamic inflow. A combination of symbolic and numerical programs at the proper stage in the derivation process makes the obtainment of final stability results an efficient and straightforward procedure.

Reddy, T. S. R.↗

NASA NTRS1985

The use of active controls to augment rotor/fuselage stability

Straub, F. K.↗

NASA NTRS1985

Rotorcraft research testing in the National Full-Scale Aerodynamics Complex at NASA Ames Research Center

The unique capabilities of the National Full-Scale Aerodynamics Complex (NFAC) for testing rotorcraft systems are described. The test facilities include the 40- by 80-Foot Wind Tunnel, the 80- by 120-Foot Wind Tunnel, and the Outdoor Aerodynamic Research Facility. The Ames 7- by 10-Foot Subsonic Wind Tunnel is also used in support of the rotor research programs conducted in the NFAC. Detailed descriptions of each of the facilities, with an emphasis on helicopter rotor test capability, are presented. The special purpose rotor test equipment used in conducting helicopter research is reviewed. Test rigs to operate full-scale helicopter main rotors, helicopter tail rotors, and tilting prop-rotors are available, as well as full-scale and small-scale rotor systems for use in various research programs. The test procedures used in conducting rotor experiments are discussed together with representative data obtained from previous test programs. Specific examples are given for rotor performance, loads, acoustics, system interactions, dynamic and aeroelastic stability, and advanced technology and prototype demonstration models.

Warmbrodt, W.↗

NASA NTRS1985

High-speed, automatic controller design considerations for integrating array processor, multi-microprocessor, and host computer system architectures

Modern control systems must typically perform real-time identification and control, as well as coordinate a host of other activities related to user interaction, online graphics, and file management. This paper discusses five global design considerations which are useful to integrate array processor, multimicroprocessor, and host computer system architectures into versatile, high-speed controllers. Such controllers are capable of very high control throughput, and can maintain constant interaction with the nonreal-time or user environment. As an application example, the architecture of a high-speed, closed-loop controller used to actively control helicopter vibration is briefly discussed. Although this system has been designed for use as the controller for real-time rotorcraft dynamics and control studies in a wind tunnel environment, the controller architecture can generally be applied to a wide range of automatic control applications.

Jacklin, S. A.↗

NASA NTRS1984

Hover test of a full-scale hingeless rotor

The performance and aeroelastic stability in hover of a 9.8-m diameter, hingeless helicopter rotor system was evaluated. Rotor performance and inplane damping data were obtained for rotor operation between 350 and 425 rpm for thrust coefficients (CT/sigma) between 0.0 and 0.12. At constant rotor thrust, a minimum in rotor inplane damping was measured at 400 rpm. Good agreement is shown between experimental performance data and predicted performance. The influence of different aerodynamic inflow models on predicting damping levels is also shown. The best correlation with experimental stability data was obtained when a dynamic inflow model was used instead of static or quasistatic inflow models. Comparison with other full scale, hingeless rotor data in hover is presented. The hingeless rotor data and data from a full scale, bearingless main rotor test performed on the same general purpose test apparatus were compared. Although the bearingless rotor was more highly damped at design tip speed and 1-g thrust operation, greater sensitivity to operating conditions is shown. At low thrust levels the bearingless main rotor is less damped than the hingeless rotor.

Warmbrodt, W.↗

NASA NTRS1984

Hover test of a full-scale hingeless rotor

The performance and aeroelastic stability in hover of a 9.8-m diameter, hingeless helicopter rotor system was evaluated. Rotor performance and inplane damping data were obtained for rotor operation beteen 350 and 425 rpm for thrust coefficients (CT/sigma) between 0.0 and 0.12. At constant rotor thrust, a minimum in rotor inplane damping was measured at 400 rpm. Good agreement is shown between experimental performance data and predicted performance. The influence of different aerodynamic inflow models on predicting damping levels is also shown. The best correlation with experimental stability data was obtained when a dynamic inflow model was used instead of static or quasistatic inflow models. Comparison with other full scale, hingeless rotor data in hover is presented. The hingeless rotor data and data from a full scale, bearingless main rotor test performed on the same general purpose test apparatus were compared. Although the bearingless rotor was more highly damped at design tip speed and 1-g thrust operation, greater sensitivity to operating conditions is shown. At low thrust levels the bearingless main rotor is less damped than the hingeless rotor.

Warmbrodt, W.↗

NASA NTRS1984

Hover test of a full-scale hingeless helicopter rotor: Aeroelastic stability, performance and loads data

A hover test of a full-scale, hingeless rotor system was conducted in the NASA Ames 40- by 80-foot wind tunnel. The rotor was tested on the Ames rotor test apparatus. Rotor aeroelastic stability, performance, and loads at various rotational speeds and thrust coefficients were investigated. The primary objective was to determine the inplane stability characteristics of the rotor system. Rotor inplane damping data were obtained for operation between 350 and 425 rpm (design speed), and for thurst coefficients between 0.0 and 0.12. The rotor was stable for all conditions tested. At constant rotor rotational speed, a minimum inplane dampling level was obtained at a thrust coefficient approximately = 0.02. At constant rotor lift, a minimum in rotor inplane damping was measured at 400 rpm.

Peterson, R. L.↗

NASA NTRS1984

Aeromechanical stability of a full-scale hingeless rotor in hover

The aeroelastic stability in hover of a 9.8-m-diam, hingeless helicopter rotor system is evaluated. Rotor inplane damping data were obtained for rotor operation between 350 and 425 rpm for thrust coefficients between 0.0 and 0.12. At constant rotor rotational speed, a minimum inplane damping level was obtained at a thrust coefficient of approximately 0.02. At constant rotor thrust, a minimum in rotor inplane damping was measured at 400 rpm. Correlation with a comprehensive aeroelastic stability program is found to be good. The influence of different aerodynamic inflow models on predicted damping levels is shown. Best correlation with experimental data is obtained using a dynamic inflow model rather than static or quasi-static inflow models. Comparison with other full-scale, hingeless rotor stability data in hover is presented. Also, direct comparisons are made with data from a full-scale bearingless main rotor test performed on the same general-purpose test apparatus. Although the bearingless rotor is more highly damped at design tip speed and 1-g thrust operation, greater sensitivity to operating conditions is shown.

Peterson, R. L.↗

NASA NTRS1984

The influence of dynamic inflow and torsional flexibility on rotor damping in forward flight from symbolically generated equations

The combined effects of blade torsion and dynamic inflow on the aeroelastic stability of an elastic rotor blade in forward flight are studied. The Helicopter Equations for Stability and Loads (HESL) program is extended to derive the governing equations of motion for the blade, and a Lagrangian formulation is used to obtain the equations in generalized coordinates. The program generates the steady-state and linearized perturbation equations in symbolic form and then codes them into FORTRAN subroutines. The coefficients for each equation and for each mode are identified through a numerical program; the latter can also be used to obtain the harmonic balance equations. The governing multiblade equations are derived explicitly using HESL. These equations can accommodate any number of elastic blade modes. Stability results are presented for several hingeless rotor blade structural models, and the influence of dynamic inflow in forward flight with an elastic hingeless rotor is investigated.

Reddy, T. S. R.↗

NASA NTRS1983

Fan Blade Shake Test Results for the 40- by 80-/80- by 120-Foot Wind Tunnel

This report documents the shake tests performed on the first set of hydulignum fan blades for the 40- by 80-/80- by 120-Foot Wind Tunnel. The purpose of the shake test program is described. The test equipment and test procedures are reviewed. Results from each shake test are presented and the overall findings of the shake test program are discussed.

Warmbrodt, W.↗

NASA NTRS1983

Dynamic characteristics of the 40- by 80-/80- by 120-foot wind tunnel drive fan blades

The existing 40- by 80-Foot Wind Tunnel at Ames Research Center is being modified to upgrade and expand the research capabilty of the facility. The modification project includes an enhancement of the wind-tunnel drive power capability by installing large capacity electric motors and new drive fans to attain higher airspeeds in the existing 40- by 80-ft test section. It also involves the constructin of a new tunnel leg which includes a larger 80-- by 120-ft test section. The 40-by 80-ft test section will have a maximum airspeed approaching 300 knots. It was previously limited to about 200 knots. The maximum airspeed of the 80- by 120-ft test section will be about 100 knots. Becaue of the critical nature of the drive fans in the operation of the facility, an extensive effort was undertaken to verify, for each blade-retention system, its structural integrity and its dynamic characteristics.

Warmbrodt, W.↗

NASA NTRS1983

Measured inplane stability characteristics in hover for an advanced bearingless rotor

A study was made of the inplane stability characteristics of a model of an advanced bearingless main rotor. The four-bladed rotor system was tested for aeroelastic stability in hover for both isolated and body-free conditions. Variations in several hub design parameters were tested, including blade coning and sweep angles, blade inplane structural damping, pitch-link location (delta-free effect), and fuselage structural damping. An analysis of the experimental results shows that parametric stability trends observed from isolated-rotor studies may yield incorrect conclusions regarding coupled rotor-body characteristics. For body-free conditions, the baseline rotor configuration resulted in the best stability margins at 1-g thrust as well as at the nominal design rotor speed. Blade built-in coning had little effect on the body-free damping levels at the inplane/body resonance points. Introducing blade sweep destabilized the rotor at the inplane/body pitch resonance.

Weller, W. H.↗

NASA NTRS1983

Identification of helicopter rotor dynamic models

A recursive, extended Kalman-filter approach is applied to the identifiction of rotor damping levels of representative helicopter dynamic systems. The general formulation of the approach is presented in the context of a typically posed stochastic estimation problem, and the method is analytically applied to determining the damping levels of a coupled rotor-body system. The identified damping covergence characteristics are studied for sensitivity to both constant-coefficient and periodic-coefficient measurement models, process-noise covariance levels, and specified initial estimates of the rotor-system damping. A second application of the method to identifying the plant model for a highly damped, isolated flapping blade with a constant-coefficient state model (hover) and a periodic-coefficient state model (forward flight) is also investigated. The parameter-identification capability is evaluated for the effect of periodicity on the plant model coefficients and the influence of different measurement noise levels.

Molusis, J. A.↗

NASA NTRS1982

Development of a helicopter rotor/propulsion system dynamics analysis

A time-domain analysis of coupled engine/drive train/rotor dynamics of a twin-engine, single main rotor helicopter model has been performed. The analysis incorporates an existing helicopter model with nonlinear simulations of a helicopter turboshaft engine and its fuel controller. System dynamic behavior is studied using the resulting simulation which included representations for the two engines and their fuel controllers, drive system, main rotor, tail rotor, and aircraft rigid body motions. Time histories of engine and rotor RPM response to pilot control inputs are studied for a baseline rotor and propulsion system model. Sensitivity of rotor RPM droop to fuel controller gain changes and collective input feed-forward gain changes are studied. Torque-load-sharing between the two engines is investigated by making changes in the fuel controller feedback paths. A linear engine model is derived from the nonlinear engine simulation and used in the coupled system analysis. This four-state linear engine model is then reduced to a three-state model. The effect of this simplification on coupled system behavior is shown.

Warmbrodt, W.↗

NASA NTRS1981

A full-scale wind tunnel investigation of a helicopter bearingless main rotor

A helicopter bearingless main rotor was tested. Areas of investigation included aeroelastic stability, aerodynamic performance, and rotor loads as a function of collective pitch setting, RPM, airspeed and shaft angle. The rotor/support system was tested with the wind tunnel balance dampers installed and, subsequently, removed. Modifications to the rotor hub were tested. These included a reduction in the rotor control system stiffness and increased flexbeam structural damping. The primary objective of the test was to determine aeroelastic stability of the fundamental flexbeam/blade chordwise bending mode. The rotor was stable for all conditions. Damping of the rotor chordwise bending mode increases with increased collective pitch angle at constant operating conditions. No significant decrease in rotor damping occured due to frequency coalescence between the blade chordwise fundamental bending mode and the support system.

Warmbrodt, W.↗

NASA NTRS1981

Full-scale wind-tunnel test of the aeroelastic stability of a bearingless main rotor

The rotor studied in the wind tunnel had previously been flight tested on a BO-105 helicopter. The investigation was conducted to determine the rotor's aeroelastic stability characteristics in hover and at airspeeds up to 143 knots. These characteristics are compared with those obtained from whirl-tower and flight tests and predictions from a digital computer simulation. It was found that the rotor was stable for all conditions tested. At constant tip speed, shaft angle, and airspeed, stability increases with blade collective pitch setting. No significant change in system damping occurred that was attributable to frequency coalescence between the rotor inplane regressing mode and the support modes. Stability levels determined in the wind tunnel were of the same magnitude and yielded the same trends as data obtained from whirl-tower and flight tests.

Warmbrodt, W.↗