Development of Advanced Flight Control Laws for the AH-64 Apache Helicopter: Sketches from the work of TU Delft-Boeing Project in SIMONA Simulator

A joint research project (2010-2014) between Delft University of Technology and Boeing Mesa was conducted in SIMONA Research Simulator (SRS) at Delft University with the goal to develop advanced flight control laws for handling qualities (HQs) improvements of the Apache AH-64 helicopter. The goal of the present paper is to concentrate on implementation and simulator testing of modern control laws for Apache’s AH-64D Longbow helicopter to provide improved handling qualities for hover and low speed flight in degraded visual environment. The paper will implement an “Incremental Nonlinear Dynamic Inversion (INDI)” controller into the Boeing's FlyRT AH-64 Apache baseline model for the existing partial authority stability augmentation system (SAS). The INDI will be used to provide both attitude command attitude hold and translational rate command response types based on the requirements in ADS-33E. Implementation of the INDI into Apache’s FlyRT proved to be challenging because the model was not affine in the control inputs. Actuator dynamics and rotor dynamics (most likely flapping dynamics) caused the designed INDI controller to overcontrol the helicopter. The paper proposes three adaptations of the INDI methodology that prove able to stabilize the helicopter and can be used as an alternative to a full authority, fly-bywire, control system upgrade. Handling qualities evaluations conducted in SIMONA simulator for the ADS-33 hover and pirouette maneuvers demonstrated that the INDI resulted in improving from Level 2 to Level 1 HQs, reducing the pilot workload when compared to the Apache’s legacy flight control system.