CH-53K control laws: Risk reduction flight testing

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Proceedings titleAnnual Forum Proceedings - AHS International
Conference67th American Helicopter Society International Annual Forum 2011, 3 May 2011 through 5 May 2011, Virginia Beach, VA
Pages12831297; # of pages: 15
SubjectAutomatic flight control systems; Basic structure; Control implementation; Control laws; Design effort; Extensive design; Extensive testing; Flight control; Flight hour; Flight test; Flight testing; Handling quality; Heavy lifts; Key elements; Level-1; Model following; Model following control; National Research Council of Canada; Open loop characteristic; Real aircraft; Risk reductions; Sikorsky; Sikorsky Aircraft; System design and development; Test program; Two-step process; Unique features; US Army; US Navy; Visual environments; Aircraft control; Computer simulation; Control theory; Design; Flight envelopes; Helicopters; Risk perception; Software testing; Systems analysis; Testing; Flight control systems
AbstractThe US Navy has contracted Sikorsky Aircraft to develop a heavy lift replacement helicopter. The CH-53K employs Model Following control laws which can provide Level 1 handling qualities in accordance with ADS-33E-PRF across the flight envelope. The core controls include a Primary Flight Control System (PFCS) and an Automatic Flight Control System (AFCS). The PFCS provides a Rate Command Attitude Hold (RCAH) system which provides the pilot with a responsive aircraft for operations in good visual environments. The AFCS implements an Attitude Command Velocity Hold system with Hover and Position hold features for operations in degraded visual environments (DVE). Radar and Barometric Altitude hold is also available, and a comprehensive set of flight director modes is also being implemented. Once the basic structure of the control laws was set, Sikorsky embarked on a very extensive design and analysis effort to ensure that the control laws were on the path to producing Level 1 handling qualities. A key element of the design effort is to carry out extensive risk reduction flight testing on one or more variable stability aircraft. This is expected to go a long way towards reducing flight controls flight test cost risk as part of the CH-53K System Design and Development program. The intent of this effort is to functionally test all PFCS, AFCS and Tactile Cueing functions on a combination of the National Research Council of Canada's (NRC) Bell 412 ASRA variable stability aircraft, and the US Army Aeroflightdynamics Directorate's JUH-60A RASCAL variable stability aircraft. This paper focuses on the approximately 60 flight hours of testing of the CH-53K PFCS and AFCS functions that was carried out between December 2009 and December 2010 on the NRC ASRA aircraft in Ottawa, Canada. A unique feature of the implementation carried out for this effort is the two step process, where first the open loop characteristics of the CH-53K aircraft were simulated on the host aircraft and then the model following loop was closed around the simulated dynamics. Once the open loop characteristics had been implemented, the complete PFCS and AFCS control laws for the pitch, roll and yaw axes were wrapped around these simulated characteristics. Extensive testing was carried out in May and June 2010 for the PFCS control laws and in November and December 2010 for the AFCS control laws. While formal handling qualities ratings were not collected, extensive evaluations were carried out using ADS-33 type MTEs by a combination of Sikorsky and US Navy pilots in order to shakedown the control implementation and find any issues ahead of implementation on a real aircraft. As a result of the risk reduction flight testing significant changes were made to the control laws and this test program is estimated to have avoided a significant number of flight test hours during the upcoming CH-53K test program with the prototype aircraft. Copyright ©2011 by the American Helicopter Society International, Inc. All rights reserved.
Publication date
AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21271643
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Record identifier45da5877-6920-41c1-b5c2-b65ace295064
Record created2014-03-24
Record modified2016-05-09
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