NASA Glenn Research Center Controls and Dynamics Technology Branch

Active Inlet Control

HSCT Airplane


For High Speed Civil Transport, the efficient and safe operation of the engine requires that the leading shock at the engine inlet be maintained within a narrow range of locations at the inlet face. If the shock moves too far out in front of the inlet, it results in a phenomenon called inlet “unstart” where there is no flow to the engine and the engine shuts down resulting in violent motions of the aircraft. The active inlet controls program is being conducted in direct support of the NASA High Speed Research (HSR) program which is developing technologies for a future commercially and environmentally viable supersonic civil transport aircraft.

The objective of the active inlet control program is to develop and validate dynamic models and advanced multivariable control systems for supersonic mixed-compression inlets. The control system will be designed to include inlet unstart prevention, automatic restart, distortion minimization and inlet/engine integrated control. The technologies are to be demonstrated through wind-tunnel tests on scaled versions of variable geometry inlet concepts developed by Boeing. Some of the challenges in implementing active inlet control are determining the best effectors for controlling the shock position and developing accurate models of inlet operation to be able to estimate shock position from pressure measurements.


  • Develop a multivariable control design methodology for HSCT inlets which includes unstart prevention, automatic restart, distortion minimization, and inlet/engine integrated control.
  • Define and validate dynamic models of candidate HSCT inlets which capture the effects of unstart, restart, buzz, variable geometry, bleed and distortion.
  • Validate inlet modeling and controls via supersonics wind tunnel tests.
  • Conduct inlet/engine operability studies to demonstrate acceptable propulsion system performance in projected HSCT flight environment.

Inlet Control Loop Diagram


  • Designed multivariable control system for 2-D Bifurcated Two-Stage Supersonic Inlet (BTSSI).
  • Successfully demonstrated control system for BTSSI in 10x10 tests
  • Developed procedure for linear model generation from nonlinear model for use in control design (Grant).
  • Generated two-duct LAPIN-code inlet model for 2-D HSR inlet and delivered to industry partners.
  • Completed initial plan for inlet control operability study for axisymmetric inlet to support HSR inlet down-select decision.

Project Contact

Kevin J. Melcher
NASA Glenn Research Center/77-1
21000 Brookpark Road, M.S. 77-1
Cleveland, Ohio 44135
phone: (216) 433-3743
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last updated: 2.29.08