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Meeting	ACGS Committee Meeting 99 - Boulder - March 2007
Agenda Location	5 SUBCOMMITTEE E – FLIGHT, PROPULSION, AND AUTONOMOUS VEHICLE CONTROL SYSTEMS 5.3 Control retrofit architecture to maintain throttle to thrust response as the engine ages
Title	Control retrofit architecture to maintain throttle to thrust response as the engine ages
Presenter	Sanjay Garg
Affiliation	NASA Glenn
Available Downloads*	presentation
	Downloads are available to members who are logged in and either Active* or attended this meeting.
Abstract	As an aircraft engine deteriorates with usage, there is noticeable change from the throttle setting to the thrust response. In a workshop sponsored by NASA to identify technology development needs for reducing pilot workload and increasing autonomy with respect to operation of aircraft engines, various pilots stated that the asymmetric thrust, caused by this deteriorated engine response, causes additional workload for them in having to make adjustments to individual throttles in a multi-engine aircraft. The pilots' preference will be to move the multiple throttles together and have symmetric thrust response so that individual throttle adjustments are not required during any part of the flight operation. Since thrust is not measurable, typical engine control consists of tracking a fan speed command based on a throttle setting. The fan speed command setting is determined based on the fan speed to thrust relationship for a "nominal" engine model. For different engines of the same type, due to manufacturing tolerances and due to difference in usage, the fan speed to thrust relationship differs from the "nominal" and changes over time due to deterioration of engine components with usage. For a multi-engine aircraft, this difference in fan speed to thrust relationship results in variations in throttle to thrust response for different engines. One approach to addressing this issue and providing consistent throttle to thrust response for multiple-engines that is currently being investigated is to change the overall control architecture to a model-based control. However, such a change is expected to take a long time to reach a high enough level of technical maturity to be able to meet the stringent certification requirements for safe operation of aircraft engines. Typical engine control is implemented on a FADEC (Full Authority Digital Engine Control) which has both throughput and processing limits to make full model-based control implementation very challenging. Additionally, to guarantee safe operation of the engine over a wide operating envelope and under varying atmospheric conditions, and to enable an economically viable on-wing life, various limits are placed on the operation of the engine which are accounted for through the control logic in the FADEC. For these reasons, it is imperative to find a solution to the consistent throttle to thrust requirement which can be implemented within existing FADEC capabilities and will require minimal changes in the existing control implementations for operational safety. The engine performance deterioration mitigation control (EPDMC) currently being developed at NASA GRC presents such a retrofit approach. The main elements of EPDMC Outer Loop control are: i) A thrust estimator which provides an accurate estimate of the engine thrust based on available sensor measurements and actuator commands; ii) Thrust demand logic which estimates the thrust that a "nominal" engine will generate for a given throttle setting; and iii) a PI (Proportional plus Integral) control which provides an incremental fan speed command to the FADEC to compensate for the difference between estimated thrust and thrust demand. This presentation describes the development of various elements of the architecture and implementation on a engine simulation representative of a modern high by-pass commercial turbofan engine. Results are presented from both steady state and transient evaluations and also some preliminary fixed base piloted simulations.