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Powell, J. D.

Publications and source records attributed to Powell, J. D..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Effects of asymmetry on the dynamic stability of aircraft

The oblique wing concept for transonic aircraft was proposed to reduce drag. The dynamic stability of the aircraft was investigated by analytically determining the stability derivatives at angles of skew ranging from 0 and 45 deg and using these stability derivatives in a linear analysis of the coupled aircraft behavior. The stability derivatives were obtained using a lifting line aerodynamic theory and found to give reasonable agreement with derivatives developed in a previous study for the same aircraft. In the dynamic analysis, no instability or large changes occurred in the root locations for skew angles varying from 0 to 45 deg with the exception of roll convergence. The damping in roll, however, decreased by an order of magnitude. Rolling was a prominent feature of all the oscillatory mode shapes at high skew angles.

Fantino, R. E.↗
NASA NTRS1975

Aircraft digital control design methods

Investigations were conducted in two main areas: the first area is control system design, and the goals were to define the limits of 'digitized S-Plane design techniques' vs. sample rate, to show the results of a 'direct digital design technique', and to compare the two methods; the second area was to evaluate the roughness of autopilot designs parametrically versus sample rate. Goals of the first area were addressed by (1) an analysis of a 2nd order example using both design methods, (2) a linear analysis of the complete 737 aircraft with an autoland obtained using the digitized S-plane technique, (3) linear analysis of a high frequency 737 approximation with the autoland from a direct digital design technique, and (4) development of a simulation for evaluation of the autopilots with disturbances and nonlinearities included. Roughness evaluation was studied by defining an experiment to be carried out on the Langley motion simulator and coordinated with analysis at Stanford.

Tashker, M. G.↗
NASA NTRS1974

Spacecraft nitrogen generation

Two spacecraft nitrogen (N2) generation systems based on the catalytic dissociation of hydrazine (N2H4) were evaluated. In the first system, liquid N2H4 is catalytically dissociated to yield an N2 and hydrogen (H2) gas mixture. Separation of the N2/H2 gas mixture to yield N2 and a supply of H2 is accomplished using a polymer-electrochemical N2/H2 separator. In the second system, the N2/H2 gas mixture is separated in a two-stage palladium/silver (Pd/Ag) N2/H2 separator. The program culminated in the successful design, fabrication, and testing of a N2H4 catalytic dissociator, a polymer-electrochemical N2/H2 separator, and a two-stage Pd/Ag N2/H2 separator. The hardware developed was sized for an N2 delivery rate of 6.81 kg/d (15lb/day). Experimental results demonstrated that both spacecraft N2 generation systems are capable of producing 6.81 kg/d (15lb/day) of 99.9% pure N2 at a pressure greater than or equal to 1035 kN/m(2) (150 psia).

Marshall, R. D.↗
NASA NTRS1974

Static feed water electrolysis module

An advanced static feed water electrolysis module (SFWEM) and associated instrumentation for generating breathable O2 was developed. The system also generates a H2 byproduct for use in an air revitalization system for O2 recovery from metabolic CO2. Special attention was given to: (1) eliminating water feed compartment degassing, (2) eliminating need for zero gravity condenser/separators, (3) increasing current density capability, and (4) providing a self contained module so that operation is independent of laboratory instrumentation and complicated startup/shutdown procedures.

Powell, J. D.↗
NASA NTRS1974

Iodine generator for disinfecting reclaimed water

System dispenses iodine into water tank automatically in quantities varying from 0.5 to 20 ppm. It stores 180-day supply of iodine crystals, sufficient to support six people consuming water at rate of 4.5 to 13.6 kg per person per day.

Wynveen, R. A.↗
NASA NTRS1974

Selection of sampling rate for digital control of aircrafts

The considerations in selecting the sample rates for digital control of aircrafts are identified and evaluated using the optimal discrete method. A high performance aircraft model which includes a bending mode and wind gusts was studied. The following factors which influence the selection of the sampling rates were identified: (1) the time and roughness response to control inputs; (2) the response to external disturbances; and (3) the sensitivity to variations of parameters. It was found that the time response to a control input and the response to external disturbances limit the selection of the sampling rate. The optimal discrete regulator, the steady state Kalman filter, and the mean response to external disturbances are calculated.

Katz, P.↗
NASA NTRS1974

Hydrogen detection study

The effectiveness was assessed of a hydrogen (H2) detection concept for regenerative environmental control life support systems (EC/LSS). The concept evaluated was that utilized for the electrochemical depolarized concentrator (EDC) design, constructed, and tested for the EC/LSS space station prototype program. The EDC contains combustible gas detectors (CGDs) which were evaluated with H2. The CGDs were evaluated for linearity, position sensitivity, reproducibility, ambient effects, repeatability, speed of response, recovery time, and interchangeability. The effectiveness of CGDs located within the EDC for sensing H2 leaks at various line replaceable units in the subsystem was determined. The effects of H2 leak rate, H2 concentration of leaking gas and air currents in the vicinity of the EDC were determined. Proposed improvements for the H2 detection concept were documented and alternative H2 detection approaches were identified and analyzed.

Shumar, J. W.↗
NASA NTRS1974

A design method for minimizing sensitivity to plant parameter variations

A method is described for minimizing the sensitivity of multivariable systems to parameter variations. The variable parameters are considered as random variables and their effect is included in a quadratic performance index. The performance index is a weighted sum of the state and control covariances that stem from both the random system disturbances and the parameter uncertainties. The numerical solution of the problem is described and application of the method to several initially sensitive tracking systems is discussed. The sensitivity factor of reduction was typically 2 or 3 over a system based on random system noise only, and yet resulted in state RMS increases of only about a factor of two.

Hadass, Z.↗
NASA NTRS1974

Life support subsystem monitoring instrumentation

The recognition of the need for instrumentation in manned spacecraft life-support subsystems has increased significantly over the past several years. Of the required control and monitoring instrumentation, this paper will focus on the monitoring instrumentation as applied to life-support subsystems. The initial approach used independent sensors, independent sensor signal conditioning circuitry, and independent logic circuitry to provide shutdown protection only. This monitoring system was replaced with a coordinated series of printed circuit cards, each of which contains all the electronics to service one sensor and provide performance trend information, fault detection and isolation information, and shutdown protection. Finally, a review of sensor and instrumentation problems is presented, and the requirement for sensors with built-in signal conditioning and provisions for in situ calibration is discussed.

Powell, J. D.↗
NASA NTRS1974

Six-man, self-contained carbon dioxide concentrator system

A six man, self contained electrochemical carbon dioxide concentrating subsystem was successfully designed and fabricated. It was a preprototype engineering model designed to nominally remove 6.0 kg (13.2 lb) CO2/day with an inlet air CO2 partial pressure of 400 N/sq m (3 mm Hg) and an overcapacity removal capability of 12.0 kg (26.4 lb) CO2/day. The design specifications were later expanded to allow operation at space station prototype CO2 collection subsystem operating conditions.

Powell, J. D.↗
NASA NTRS1973

Satellite attitude control simulations

Work was conducted to develop an extremely low drift rate gyroscope and a very precise star tracker. A proposed relativity satellite will measure very accurately the theoretically predicted 'relativistic' precession of the gyroscope relative to an inertial reference frame provided by the star tracker. Aspects of precision spinning attitude control are discussed together with questions of gyro operation, and the hopping mode for lunar transportation. For the attitude control system of the lunar hopper, a number of control laws were investigated. The studies indicated that some suboptimal controls should be adequate for the system.

Debra, D. B.↗
NASA NTRS1973

Development of an iodine generator for reclaimed water purification in manned spacecraft applications

A successful 30-day test is described of a prototype Iodine Generating and Dispensing System (IGDS). The IGDS was sized to iodinate the drinking water nominally consumed by six men, 4.5 to 13.6 kg (10 to 30 lb) water per man-day with a + or - 10 to 20% variation with iodine (I2) levels of 0.5 to 20 parts per million (ppm). The I2 treats reclaimed water to prevent or eliminate microorganism contamination. Treatment is maintained with a residual of I2 within the manned spacecraft water supply. A simplified version of the chlorogen water disinfection concept, developed by life systems for on-site generation of chlorine (Cl2), was used as a basis for IGDS development. Potable water contaminated with abundant E. Coliform Group organisms was treated by electrolytically generated I2 at levels of 5 to 10 ppm. In all instances, the E. coli were eliminated.

Wynveen, R. A.↗
NASA NTRS1972

One-man, self-contained CO2 concentrating system

A program to design, fabricate, and test a 1-man, self-contained, electrochemical CO2 concentrating system is described. The system was designed with electronic controls and instrumentation to regulate performance, to analyze and display performance trends, and to detect and isolate faults. Ground support accessories were included to provide power, fluids, and a Parametric Data Display allowing real time indication of operating status in engineering units.

Wynveen, R. A.↗
NASA NTRS1972

Improved device measures performance of batteries under load

Kordesch-Marko interrupter bridge circuit includes capability of varying frequency of interruption in steps from 60 Hz to 2000 Hz range extension, and addition of operating modes to allow instrument to serve as steady dc constant-current source or load, or source of interrupted constant current.

Powell, J. D.↗
NASA NTRS1972

Oxygen pressure control for electrolysis cells

Duty cycle of switched, constant current circuit controlled by pressure sensor provides oxygen at a constant pressure from a cell which electrolyzes water, eliminating possibility of cell damage by excessive oxygen demand.

Powell, J. D.↗