N&R Engineering has developed aircraft engine control technologies for the Vehicle System Safety Technologies (VSST) project under NASA’s Aviation Safety Program.
During emergency scenarios such as when an aircraft’s normal flight control surfaces are inoperative or damaged, modulating engine power may be the only resort for the crew to safely land the plane. The problem is that because the engines are not designed for this purpose, they do not exert as much authority over how the aircraft moves nor do they respond as quickly as the normal flight controls.
Working with NASA’s research engineers, we developed risk-based control algorithms that are able to increase engine performance beyond the maximum levels that were originally designed. Specifically, these control modes, when active, enhance both the maximum power of the engine and its dynamic responsiveness. The trade-off is the unavoidable increase in the risk of engine failure. This heightened risk may or may not be acceptable depending on the severity of the emergency. To assist in this decision, the control modes were designed with this risk in mind. Namely, the amount of extra performance the control modes extract from the engine is directly related to a maximum acceptable rate of failure that is predefined. This maximum risk level is converted into limits on sensed parameters, such as rotational speeds and gas temperatures within the engine. The control mode then directs the engine to those limits, thus enhancing performance without violating the maximum allowable risk level.
Figure 1 illustrates this point. During normal engine operation, the failure rate may vary a great deal depending on a multitude of conditions (altitude, speed, engine age, etc.). However, when the control modes are activated, performance is increased until the risk of failure converges to a predefined acceptable maximum limit regardless of these conditions. After evaluations using a flight simulator at NASA Glenn Research Center, we found that this technology made it easier to fly an aircraft using engines only and less likely to lose control (Figure 2).
- Control System and Design Analysis
Liu, Y., Litt, J.S., Sowers, T.S., Owen, A.K., and Guo, T., “Application and Evaluation of Control Modes for Risk-Based Engine Performance Enhancements,” 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Cleveland, Ohio, 28-30 July 2014.
Liu, Y, Litt, J.S., and Guo, T., “Design and Demonstration of Emergency Control Modes for Enhanced Engine Performance,” 49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, San Jose, California, 14-17 July 2013