Design and Validation of a Control Loading System ...

International Review of Aerospace Engineering (I.RE.AS.E), Vol. 10, N. 5 ISSN 1973-7459 October 2017

Design and Validation of a Control Loading System for FAA Level 5 Flight Training Device of Cirrus SR-20 Airplanes Ashok Kuppusamy, Sug Joon Yoon

Abstract – Every aircraft simulator must undergo a series of test items to get certified by regulatory authority. For flight training devices being certified under FAA part 60 guidelines for level 5 and above, the control loading system provides a natural feel to the pilot that is a must for fulfilling the objective tests. In this paper, the test results of hardware control loader have been compared with the SIMULINK second order mathematical model representing a spring mass damper system. The parameters considered when choosing a second order transfer function are natural frequency and damping ratio. Considering the damping in the system, the values are chosen in such a way that it matches the results of hardware control loader. Hence, the spring mass damper model is named as high-fidelity control inceptor which is under-damped. The step response, frequency response analysis and pole-zero map plot are made to verify the stability of the system. The mathematical model results have been proved with actual experiments. Copyright © 2017 Praise Worthy Prize S.r.l. - All rights reserved.

Keywords: Aircraft Simulators, Control Loading System, Federal Aviation Regulations, Qualification Test Guide

Nomenclature n  c daN Ferror Fmeas Fsim k m lbs X(s)

The mechanical vibrations are nothing but the aerodynamic forces felt on the control surfaces such as elevator, aileron or rudder. As discussed earlier, the pressure distribution over the control surface like an elevator will cause a moment on the elevator hinge line which is known as an elevator hinge moment. To maintain the elevator angle position, a moment opposite to the original is provided by the pilot known as stick force. This applied stick force magnitude depends on the size of the aircraft and on thespeed for which it is designed. There are two loops in the CLS. The outer loop will control the flight control system and the inner loop will perform the force computation.For smaller aircrafts, the pilot is directly connected to anelevator and the moment is fully felt. But in the case of larger aircrafts, an elevator is bulky for the pilot to move. Hence, the CLS will provide the necessary control moment. The mechanical linkages were used often in smaller aircraft to give the natural feel for the aerodynamic forces under various sorties and this type of CLS is known as reversible control loading system [1]. A control system where movement of the control surface will not back drive the pilot's control on the flight deck is called irreversible control loading system [2]. In irreversible control loading system, the mechanical linkages are replaced by computers and electrical signals known as fly-by-wire technology. Though the technology continues to evolve each day, every pilot would like to have the natural feel how he feels in small aircrafts. This is where the artificial feel

Undamped Natural Frequency (rad/s) Damping ratio Damping Coefficient in Newton-seconds/meter (Ns/m) Dekanewton Force error Force measured Force simulated Stiffness of the spring in Newton/meter (N/m) Mass of the system in kilogram (kg) Pounds System State Variable for stick deflection

I.

Introduction

Simulators play a vital role in aircraft industry especially when they come to train the pilots. They are ground based machines. So, simulating the effects of pressure distribution over the control surface becomes one of the greatest challenges [1]-[20]. This is where the Control Loading System (CLS) comes in handy. CLS can be classified into two categories namely hydraulically driven CLS and electrically driven CLS. The CLS used for the presented experiment is an electrically driven CLS, hence the discussion would be limited to it. A CLS is a computer which controls the spring action present inside the hardware. By applying a suitable force, it is possible to obtain the mechanical vibrations and the spring action, which are controlled simultaneously.

Copyright © 2017 Praise Worthy Prize S.r.l. - All rights reserved

https://doi.org/10.15866/irease.v10i5.13233

298

Ashok Kuppusamy, Sug Joon Yoon

system made up of springs and actuators comes into picture. This controlled spring action by means of a computer is called Control Loading System. If this CLS is implemented in any simulator it is possible to avoid any crashing, stalling, over-speeding, unnecessary attitude change problem, etc. The CLS shown in this paper is integrated over a sidegrip yoke shown in Fig. 1 which simulates the perfect dynamics statically and dynamically.

The structure of this paper is the following: After the introduction of Section I, Section II illustrates the literature review. Section III presents the hardware control loading system interfacing with simulator, while Section IV describes the SIMULINK design, Section V shows the QTG generation by stateflow method. In Section VI step and frequency response analysis is presented, followed by Section VII simulation results and discussion. Finally, Section VIII will conclude the paper.

II.

Side-Grip Yoke

Literature Review

In 2001, Kenneth and Kahtan [3] proposed a generic flight control model for a reversible control loading system. The control model wasanalyzed with two types of control loader: a forward-aft control model and a control loader with inertial mass. The forward-aft model provided excellent results when compared to control loader with mass, in replicating the force and control surface values for the reversible control loading system. In 2003, Davis and Hildreth [4] worked on the problems in validating control feel in simulators. They observed that the flexibility of mechanical linkages in control loading system was more significant thanby connecting cables in an aircraft control feel system. In 2005, Gerretsen et al. [5] made a comparison among position-loop, velocity-loop and force-loop based control loading architectures. The force-loop resulted to be the best for all conditions while the velocity-loop demonstrated to be less accurate and position-loop was not suitable for any control loader because of its deficient performance. In 2006, Park et al. [6] presented a systematic control parameter tuning for an actuator in control loading system using bode plots. By tuning the proportional and integral gain of control loading system, they obtained a better performance. In 2007, Shutao et al. [7] designed a control loading system for a Boeing 737-300 simulator. They developed a triple channeled primary control loading system (PCL) by means of a rapid control prototyping technology. A mathematical model was derived for the PCL and the passive force control system was developed. The experiments demonstrated that PCL had less than 4% error between computed force and actual force following a good tracking performance. In 2007, Coiro et al. [8] presented a flight simulator for general aviation with control loading reproduction. An open source flight simulation software was used for a high-fidelity 6DOF simulation environment. Muller and Hardy [9] proposed a plan for pilot-force measurement with inertia and gravity compensation. An accelerometer was developed and installed at a specific location for each pilot control loader axis. The McFadden wheel and column pilot control loader, operated at the NASA Ames Research Center, was used to demonstrate the pilot-force measurement with compensation for inertial effects and gravity. Since this technique did not involve strain gauges near the grip handle or gloves, the pilot can hold the grip in a normal manner.

Control Loading System Unit

Fig. 1. Control Loading System with Side-Grip Yoke

The Qualification Performance Standard (QPS) test list is shown in Table I. The simulator must satisfy all the test items mentioned in such table. TABLE I QUALIFICATION PERFORMANCE STANDARD) TEST LIST No. Description Test Result PERFORMANCE CLIMB ♦ 1.c.1 Normal Climb All Engines Operating ENGINES ♦ 1.f.1 Engine Acceleration ♦ 1.f.2 Engine Deceleration HANDLING QUALITIES STATIC CONTROL CHECKS ♦ 2.a.1.b Pitch Control Position vs. Force ♦ 2.a.2.b Roll Control Position vs. Force ♦ 2.a.3.b Rudder Control Position vs. Force LONGITUDINAL ♦ 2.c.1 Power Change Force ♦ 2.c.2 Flap/Slat Change Force ♦ 2.c.4 Gear Change Force ♦ 2.c.5 Longitudinal Trim ♦ 2.c.7 Longitudinal Static Stability ♦ 2.c.8 Stall Warning ♦ 2.c.9 Phugoid Dynamics LATERAL - DIRECTIONAL ♦ 2.d.2 Roll Response ♦ 2.d.4.b Spiral Stability ♦ 2.d.6.b Rudder Response ♦ 2.d.8 Steady State Sideslip Flight Training Device (FTD) System Response Time ♦ 6.a.1 Latency ♦ 6.a.2 Transport Delay ♦ FAR Test items that meet the criteria of level 5 FTD

Copyright © 2017 Praise Worthy Prize S.r.l. - All rights reserved

International Review of Aerospace Engineering, Vol. 10, N. 5

299

Ashok Kuppusamy, Sug Joon Yoon

In 2014, Saeb and Sajad [10] designed a non-linear control loading system for a flight simulator. During an active 3DOF non-linear maneuver, a coupled stickaircraft dynamics were simulated in the vertical plane. A position control architecture was implemented by using non-linear dynamic inversion technique. The flight simulator simulated the vertical flight motion of a general aviation aircraft. The plant model included a nonlinear spring and a linear damper. Friction was compensated by means of a frictional torque observer.

It can take up to 20 seconds for the connection to get established. If an error occurs, it will be displayed in the lower part of the program. The flight simulator will be activated only if any CLS device is connected. Once the initialization is complete, the yellow lights switch to green and the system is ready to operate. The mechanism by which a computer monitors and directs the control loading system is called force feedback mechanism. The SIMULINK model is designed by means of force loop mechanism. The latency delay for the FAR qualification is 300 milliseconds [12]. Here the hardware control loader updates 32 updates/sec which will be compared with the simulator updates/sec and the difference between them will be the final delay.

III. Control Loading System Hardware and Simulator Interfacing The aircraft used in this research for QTG generation is Cirrus SR-20. To simulate the perfect feel of the aircraft, it was introduced the hardware control loader purchased from Brunner’s Elektronik Switzerland. The side-grip of the yoke was installed by the company called Model Sim South Korea which satisfies the FAR regulations. The system block schema is shown in Fig. 2. The software used to configure the hardware is called CLS2SIM and it is used to establish a simple connection between control loading systems of Brunner Elektronik AG [11] and flight simulation programs, such as: Xplane® 9/10 Microsoft flight simulator X® and Prepar3D® using TCP/IP or USB-Interface. Aircraft specific force profiles can be configured using the profile manager.

IV.

Control Loading System Design Using SIMULINK

The SIMULINK diagram shown in Fig. 3 explains the interface between the X-Plane and the SIMULINK model of a control loading system. The control loading system is designed by using a double integrator method force loop architecture with the transfer function parameters placed in the feedback path as spring and damping constant. The system is designed in such a way that the underdamped oscillations existonly when the damping ratio is set between 0< 