J. David Powell

Engine Control Using Cylinder Pressure: Past, Present, and Future

Research into the use of cylinder pressure measurements from reciprocating internal combustion engines for real time automotive engine control has been investigated for the last 20 years. The measurement has been investigated for spark liming, fuel-air ratio control, charge temperature measurements, and misfire detection. The cost of the sensors has inhibited widespread use in production vehicles; however, it was introduced in domestic Japanese production for spark control five years ago. Its use for misfire detection is also being actively considered

OPTIMAL CLOSED-LOOP SPARK CONTROL OF AN AUTOMOTIVE ENGINE

This work concerns the application of optimization theory to develop control laws for use in closed-loop control strategies to minimize the effect of environmental changes, manufacturing tolerances, and time degradation. The paper describes the acquisition of engine mapping data for 2.3L, 4 cylinder engine, the use of the data to develop analytical functions describing the fuel consumption and emissions, and the use of the functions in an optimization procedure to arrive at control strategies and driving cycle predictions of fuel consumption and emissions. The optimum schedules were used to determine a closed-loop spark control strategy.

Observer Based Air-Fuel Ratio Control

Abstract Reduced automotive exhaust emissions strongly depend on precise control of air-fuel ratio (AFR) during both steady and transient engine operation. Furthermore, precise transient control of AFR is required for acceptable driveability of lean engines. A discrete nonlinear fuel injected SI engine model was developed and used for the design of AFR control algorithms using an observer structure. The engine model includes intake manifold air dynamics, fuel wall-wetting dynamics, and the process delays inherent in the four-stroke engine cycle. The control scheme used an electronic throttle and exhaust gas oxygen measurements. Use of a mass airflow sensor or manifold pressure sensor was not required for warmed-up operation. It has been demonstrated on a 4 cylinder automotive engine to provide 0.8% RMS accuracy in steady state with peak errors on the order of 2% during transient stoichiometric operation.

Tether damping in space

This paper analyzes the dynamics of a long tether connecting two spacecraft in earth orbit, one of the spacecraft having dominant mass. In particular, it considers the material damping of the tether. The nominal position of the tether is stabilized by the gravity gradient such that it is aligned with the local vertical. The tether is modeled as a viscoelastic flexible continuum. Modal frequencies are derived in an analytical approximation form. Damping ratios are estimated according to the linear model calibrated by ground measurements. The results show that, with properly chosen tether material and braiding structure, longitudinal vibrations of the tethered system are well damped.

Cable Angle Feedback Control Systems to Improve Handling Qualities for Helicopters with Slung Loads

The ability of a helicopter to carry externally slu ng loads makes the aircraft very versatile for many civil and military operations. H owever, the piloted handling qualities of the helicopter are degraded by the presence of the slung load. A control system is developed that uses measurements of the slung load motions as well as conventional fuselage feedback to improve the handling qualities for hover/low spe ed operations. Past research has been limited to studies focused on load damping, as oppo sed to the piloted handling qualities focus of this paper. The approach implements an explicit model following control system with cable angle feedback for the externally loaded UH-60 Black Hawk helicopter, which is optimized via multi-objective optimization software to simultaneously meet stability, performance, and handling qualities requirements. The improvements provided by this control system are demonstrated in a piloted fixed base UH-60 simulation. Pilot comments and statistics are presented to show the effectiven ess of the cable angle feedback control system as compared to a baseline control system.

Sample Rate Selection for Aircraft Digital Control

The identification and evaluation of the important considerations in selecting sample rates for aircraft digital control systems are discussed. The design method used in the evaluation is a discrete optimal synthesis technique which possesses no artificial sample rate constraints due to discretizatio n approximations. As an illustration of the sample rate selection criteria, the methods were applied to a specific longitudinal design including wind gusts and a bending mode. The dominant limitations on the sample rate were found to be the transient response characteristics and the response due to wind disturbances. Stabilization of the bending mode was not a limiting factor on the sample rate, although it was necessary to desensitize the design for acceptable performance with imperfect knowledge of the bending mode frequency. It appears that a sample rate between 10 and 20 Hz would be adequate for this example.

FLYING A TUNNEL-IN-THE-SKY DISPLAY WITHIN THE CURRENT AIRSPACE SYSTEM

Enhancing aircrew situational awareness has become recognized as a critical element in reduction of overall aircraft accident rates. Improved display concepts have been investigated for several decades as a means of enhancing awareness of position, flight path, and terrain in three dimensions. One of the most promising is the “Tunnel-in-the-Sky” primary flight display, which presents a three-dimensional depiction of the world with the desired flight path shown as a tunnel or series of hoops. A prototype system was developed to explore the real-world implications of the Tunnel-in-the-Sky display concept. This paper documents flight testing on a Beechcraft Queen Air to investigate real-world operations within the current Air Traffic Control system. A series of tunnel “overlay approaches” was designed on top of existing, published instrument procedures to demonstrate advantages for nonprecision approaches, closely spaced parallel approaches, and noise abatement. Results indicated an order of magnitude reduction in cumulative flight technical error on approach. The flight tests also showed that Tunnel-in-the-Sky displays could improve aircrew situational awareness and operational flexibility during these flight operations.

PROBABILITY OF MIDAIR COLLISION DURING ULTRA CLOSELY SPACED PARALLEL APPROACHES

This research considers the technological components required in an aircraft to safely perform simultaneous, instrument approaches into an airport with parallel runways spaced less than 2500 ft apart. Monte Carlo simulations were used in order to assess the probability of collision during an unexpected aircraft blunder, but many of the input parameters such as e ight technical error, navigation sensor error, and pilot time delay were based on recently generated experimental data. This analysis shows that with the Federal Aviation Administration’ s global positioning system-based Local Area Augmentation System operational and a reliable data link transmitting full state information between aircraft, it is technically feasible to reduce runway spacing to 1500 ft or less using the same safety criteria as that used for the recently implemented Precision Runway Monitor program.

Assessment of the possibility of a midair collision during an ultra closely spaced parallel approach

In this era of increasing delays in air travel, all means of increasing the capacity of both airports and airspace are receiving intense consideration. In anticipation of future high precision guidance, navigation, and data link systems being implemented by the FAA, procedures once deemed unsafe are again being scrutinized for feasibility. The procedure addressed in this paper is simultaneous approaches into an airport with parallel runways spaced less than 1500 ft apart. The goal of this work is to determine the necessary technological components for reducing the runway spacing to less than 1500 ft. To assess the probability of collision during any one particular approach, variables such as navigation sensor error, flight technical error, relative longitudinal spacing, relative airspeeds, and data link delay time must all be modeled as probabilistic parameters. This research used Monte Carlo simulations in order to assess the probability of collision. The analysis shows that with a GPS-based Local Area Augmentation System installed and a reliable data link transmitting full state information between aircraft, runway spacing may be safely reduced to less than 1500 ft.

Design and Flight Test of a Cable Angle Feedback Flight Control System for the RASCAL JUH-60 Helicopter

The ability of a helicopter to carry externally slung loads makes it very versatile for many civil and military operations. However, the piloted handling qualities of the helicopter are degraded by the presence of the slung load. A control system is developed that uses measurements of the slung load motions as well as conventional fuselage feedback to improve the handling qualities for hover/low speed operations. Prior research has shown a fundamental trade-off between load damping and piloted handling qualities for a feedback control system with cable angle/rate feedback. A new task tailored approach proposed and implemented herein uses a method of switching between a load damping mode and a piloted handling qualities mode. These modes provide appropriate load feedback depending on the piloting task and flight regime. This provides improved handling qualities for maneuvering flight, and for improved precision load control at hover. A new mission task element (MTE) for precision load placement is developed to test the ability of the cable feedback system to improve load placement task performance. The improvements provided by this control system are demonstrated in a piloted flight test on the JUH-60A RASCAL fly-by-wire helicopter. The average load set-down time was reduced by a factor of two for the 1000lb load on a 56ft sling.