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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Spinning mode acoustic radiation from the flight inlet

A mathematical model was developed for spinning mode acoustic radiation from a thick wall duct without flow. This model is based on a series of experiments (with and without flow). A nearly pure azimuthal spinning mode was isolated and then reflection coefficients and far field pressure (amplitude and phase) were measured. In our model the governing boundary value problem for the Helmholtz equation is first converted into an integral equation for the unknown acoustic pressure over a disk, S1, near the mouth of the duct and over the exterior surface, S2, of the duct. Assuming a pure azimuthal mode excitation, the azimuthal dependence is integrated out which yields an integral equation over the generator C1 of S1 and the generator C2 of S2. The sound pressure on C1 was approximated by a truncated modal expansion of the interior acoustic pressure. Piecewise linear spline approximation on C2 was used.

Moss, W. F.↗
NASA NTRS2011

Spin Start Line Effects on the J2X Gas Generator Chamber Acoustics

The J2X Gas Generator engine design has a spin start line connected near to the turbine inlet vanes. This line provides helium during engine startup to begin turbomachinery operation. The spin start line also acts as an acoustic side branch which alters the chamber's acoustic modes. The side branch effectively creates 'split modes' in the chamber longitudinal modes, in particular below the first longitudinal mode and within the frequency range associated with the injection-coupled response of the Gas Generator. Interaction between the spin start-modified chamber acoustics and the injection-driven response can create a higher system response than without the spin start attached to the chamber. This work reviews the acoustic effects of the spin start line as seen throughout the workhorse gas generator test program. A simple impedance model of the spin start line is reviewed. Tests were run with no initial spin start gas existing in the line, as well as being initially filled with nitrogen gas. Tests were also run with varying spin start line lengths from 0" to 40". Acoustic impedance changes due to different spin start gas constituents and line lengths are shown. Collected thermocouple and static pressure data in the spin start line was used to help estimate the fluid properties along the line length. The side branch impedance model was coupled to a chamber impedance model to show the effects on the overall chamber response. Predictions of the spin start acoustic behavior for helium operation are shown and compared against available data.

Kenny, R. Jeremy↗
NASA NTRS1973

Stall/spin studies relating to light general-aviation aircraft.

The present paper discusses the NASA Langley Research Center stall/spin research program to improve the design and the evaluation techniques relative to stall/spin characteristics of general-aviation aircraft. The program encompasses model wind-tunnel tests, spin-tunnel and radio-control model tests, and full-scale airplane spin tests. Initial spin-tunnel results on models with several tail designs representative of light airplanes and several testing techniques are discussed.

Bowman, J. S., Jr.↗
NASA NTRS1948

Supplementary Investigation in the Langley 20-Foot Free-Spinning Tunnel of the Spin and Recovery Characteristics of a 0.057-Scale Model of the Chance Vought XFU-1 Airplane, Ted No. NACA DE 311

An investigation has been conducted in the Langley 20-foot free-spinning tunnel to determine the effects of decreasing the rudder deflection, of decreasing the rudder span, and of differential rudder movements on the spin and recovery characteristics of a 0.057-scale model of the Chance Vought XF7U-1 airplane. The results indicated that decreasing the rudder span or the rudder deflections, individually or jointly, did not seriously alter the spin or recovery characteristics of the model; and recovery by normal use of controls (full rapid rudder reversal followed l/2 to 1 turn later by movement of the stick forward of neutral) remained satisfactory. Linking the original rudders so that the inboard rudder moves from full with the spin to neutral while the outboard rudder moves from neutral to full against the spin will also result in satisfactory spin and recovery characteristics. Calculations of rudder-pedal forces for recovery showed that the expected forces would probably be within the capabilities of a pilot but that it would be advisable to install some type of boost in the control system to insure easy and rapid movement of the rudders.

Berman, Theodore↗
NASA NTRS1989

Asteroid collisional history - Effects on sizes and spins

The effects of asteroid collisional history on sizes and spins of present-day objects are discussed. Collisional evolution studies indicate that collisions have altered the spin-rates of small bodies, but that the largest asteroids may have retained their primordial rotation rates. Most asteroids larger than 100 km diam have probably been shattered, but have gravitationally recaptured their fragments to form a rubble-pile structure. Large angular momentum asteroids appear to have Maclaurian spheroidal or Jacobi-ellipsoid-like shapes; some of them may have fissioned into binaries. An integrated size and spin collisional evolution model is presented, with two critical parameters: one which determines the spin rates for small fragments resulting from a shattering collision, and the other determines the fraction of impact angular momentum that is retained by the target.

Davis, Donald R.↗
NASA NTRS1950

Investigation of the Spin and Recovery Characteristics of a 0.057-Scale Model of the Modified Chance Vought XF7U-1 Airplane. TED No. NACA DE 311

An investigation has been conducted in the Langley 20-foot free-spinning tunnel to determine the spin and recovery characteristics of a 0.057-scale model of the modified Chance Vought XF7U-1 airplane. The primary change in the design from that previously tested was a revision of the twin vertical tails. Tests were also made to determine the effect of installation of external wing tanks. The results indicated that the revision in the vertical tails did not greatly alter the spin and recovery characteristics of the model and recovery by normal use of controls (fill rapid rudder reversal followed approximately one-half turn later by movement of the stick forward of neutral) was satisfactory. Adding the external wing tanks to cause the recovery characteristics to become critical and border on an unsatisfactory condition; however, it was shown that satisfactory recovery could be obtained by jettisoning the tanks, followed by normal recovery technique.

Berman, Theodore↗
NASA NTRS1980

Linear analysis of poststall gyrations

The poststall gyrations of a high-performance aircraft are investigated by approximating the equations of motion with a linear mathematical model. Equilibrium poststall spin conditions are determined, which are not limited to small angles or spin rates and are used as reference conditions about which the linear model is developed. As a result, complete coupling between lateral and longitudinal motions is retained. Three aerodynamic models are evaluated using this linear analysis. These models include pure rotary derivatives obtained from VPI&SU stability tunnel, forced-oscillation data obtained from NASA tests, and a combination of the two which separates the unsteady and pure rotary derivatives. Results indicate that this last model gives better predictions of aircraft motion during poststall gyrations at high angles of attack and large sideslip angles. Comparisons are made with full-scale flight test results.

Hreha, M. A.↗
NASA NTRS1960

Free-Spinning-Tunnel Investigation of a 1/20-Scale Model of an Unswept-Wing Jet-Propelled Trainer Airplane

A flutter analysis employing the kernel function for three- dimensional, subsonic, compressible flow is applied to a flutter-tested tail surface which has an aspect ratio of 3.5, a taper ratio of 0.15, and a leading-edge sweep of 30 deg. Theoretical and experimental results are compared at Mach numbers from 0.75 to 0.98. Good agreement between theoretical and experimental flutter dynamic pressures and frequencies is achieved at Mach numbers to 0.92. At Mach numbers from 0.92 to 0.98, however, a second solution to the flutter determinant results in a spurious theoretical flutter boundary which is at a much lower dynamic pressure and at a much higher frequency than the experimental boundary.

Bowman, James S., Jr.↗
NASA NTRS2008

Estimation of Nutation Time Constant Model Parameters for On-Axis Spinning Spacecraft

Calculating an accurate nutation time constant for a spinning spacecraft is an important step for ensuring mission success. Spacecraft nutation is caused by energy dissipation about the spin axis. Propellant slosh in the spacecraft fuel tanks is the primary source for this dissipation and can be simulated using a forced motion spin table. Mechanical analogs, such as pendulums and rotors, are typically used to simulate propellant slosh. A strong desire exists for an automated method to determine these analog parameters. The method presented accomplishes this task by using a MATLAB Simulink/SimMechanics based simulation that utilizes the Parameter Estimation Tool.

Schlee, Keith↗
NASA NTRS1990

The collisional evolution of the spin of a nonspherical body

The nonspherical shapes of asteroids are considered through a generalization of the Harris (1979) model of asteroid spin rates' collisional evolution. Since a body in spin equilibrium rotates about its axis of maximum moment of inertia, the computation of the mean-squared impact parameter through averaging over all directions of flux is not strictly valid; nevertheless, these complications have been found not to alter the conclusions reachable by means of the simpler model.

Harris, A. W.↗