Realtime Hardware / Software in the Loop Simulations

Spiral Technology personnel are currently involved with many research flight projects at NASA's Dryden Flight Research Center that involve the use of real-time software and hardware in-the-loop simulations.

Real-time simulation is a mathematical model of every system that comprises the aircraft. This includes the following:

• Aerodynamic Model
• Flight Control Model
• Control Surface Actuator Models
• Control System Sensor Models
• Aircraft Engines Model

An example of a NASA/Dryden project that used simulation extensively is the F-18 High Angle-of-Attack (HARV) which completed its flight testing at Dryden. The F-18 HARV was developed to explore the post-stall regime, which to this point in aviation history had not been thoroughly exploited. Due to the uncertainties of the flight envelope (aerodynamics model) and the complexities of the aircraft quad redundant, thrust vectoring control system, the real-time simulation was used extensively throughout the program in many ways.

The simulation was used to aid in the design and development of the thrust vectoring control laws. Proposed control law changes were implemented in a software simulation by Flight Control Engineers and then evaluated using the simulation for effectiveness before making the change to the flight version. The hardware in-the-loop simulation was used to test all control law changes prior to flight. The simulation was used by research pilots to practice and develop maneuvers prior to each flight and was used by engineers to explore the flight regime without actually flying. In short the simulation was heavily relied upon by the entire project throughout the design, development, and flight testing of the aircraft.

Another example of real-time hardware/software in-the-loop simulations conducted by Spiral Technology personnel in support of a customer are the Electro-Hydraulic Actuator (EHA) simulations carried out at NASA Dryden Flight Research Center. The EHA is was flown on Dryden's F/A-18 Systems Research Aircraft (SRA), providing actuation for the left aileron. EHA uses electronic commands from the standard F/A-18 flight control system to drive an electric motor which, in turn, pumps hydraulic fluid to a piston/rod assembly for mechanical actuation of aerodynamic control surfaces. The advantage of the EHA over standard F-18 actuator assembly itself is that it utilizes a small reservoir of hydraulic fluid in a manifold on the actuator assembly itself, eliminating the weight and complexity of the standard F-18 hydraulic plumbing system, along with the associated engine-driven pumps and larger hydraulic fluid volumes.

Flight testing of the EHA was conducted, with envelope clearance philosophy being dictated by the aileron/actuator rod-end hinge moments. As aileron/actuator rod-end hinge moments are primarily a function of dynamic pressure (q), ground-based simulations were conducted using an SRA F-18 pilot training flight simulator to fly the proposed test points, thereby collecting predicated hinge moments. During these simulations, the EHA was tied into the simulation loop and responded to control stick inputs just as it would in flight. NASA research pilots/engineers and Spiral Technology personnel flew the test points in the simulator, collected hinge movement data and other critical flight parameters, and observed the response of the EHA which was later installed in the SRA.

These hardware-in-the-loop simulations allowed for a thorough pre-flight evaluation of predicted EHA system performance using the actual flight test cards/test points which are now being flown