Problems in Validating Control Feel in Simulators

1. Problems in Validating Control Feel in Simulators By T. Scott Davis Aerospace Engineer, Member AIAA Timothy.S.Davis@saic.com Bruce Hildreth Bruce.Hildreth@saic.com

2. Overview • Introduction • Control system • Model • Control loading system • Flexure • Testing • External Instrumentation • Internal Instrumentation • Test results • Conclusions

3. Introduction • US Marine Corp KC-130T APT • Under subcontract to JF Taylor Inc / Boeing. • SAIC role • Re-host KC-130T software for modeling flight dynamics • Procure control loading system hardware • Acceptance testing of control loading system

4. Introduction (continued) • Fixed based Aircrew Procedures Trainer • Full fidelity with malfunctions • Pilot, Co-pilot, Flight Engineer, Navigator • Wide field of view visuals • Fully functional cockpit • Transportable enclosure

5. Introduction (continued) • SCT Control Loading system • 4-axes • Column • Wheel • Rudder • Tiller (Nose wheel steering) • Pilot and Co-pilot controls physically connected • Model run on a DOS based PC • Ethernet communication to the host

6. Overview • Introduction • Control system • Model • Control loading system • Flexure • Testing • External Instrumentation • Internal Instrumentation • Test results • Conclusions

7. Control System Model • Complex system of flexible linkages/cables • Position of control versus position of surface dependent on loading Column Mass and Flexibility Distributed throughout system Mechanical components, actuators, linkages and control surface Linkage or cables from cockpit to control surface Mechanical components in or under cockpit Elevator

8. Simulation Control Loading Model • Reduce system to two masses with single flexible linkage/cable All components lumped into two masses and a connecting single spring Column Forward Mass Aft Mass Flexible Cable or Linkage Elevator

9. Simulation Control Loading Trainer Layout • Actuator used to position control based on applied force Column Cockpit Floor Position Sensor Control Loader Actuator Force Sensor

10. Effect of Flexibility • Physical control loading system will flex • This may be flexibility already in model and thus be double accounted • Flex in control loading system may not be similar to forward system flex in aircraft Column Applied Force Applied Force Linkage locked

11. Overview • Introduction • Control system • Model • Control loading system • Flexure • Testing • External Instrumentation • Internal Instrumentation • Test results • Conclusions

12. Control Loader Testing • External testing (SIMES) • Force sensor at Yoke (measures applied force) • Position sensor at column (measures control position) • Effect of flexibility • External position maybe different than control loader measured position Column External Force Sensor External Position Sensor Cockpit Floor Position Sensor Control Loader Actuator Force Sensor

13. Control Loader Testing • Internal (Control loader self test) • Loader applies a fictitious force to the model • Control loader model moves control to appropriate position • Tests control loader model only, not control loaders measurement of force or position • Effect of flexibility • No flex due to no actual force applied • No ability to measure flex if it was there

14. KC-130T APT Test Results • Only the Cruise condition results for the column force versus displacement are shown • Testing method • Simulation was initialized to test condition and frozen • Control loader remained active • SIMES used to record force and position as control was slowly moved though its range of motion or to maximum measurable force • Testing also done with internal control loader software

15. KC-130 APT Results • Post processing • Force translated to reference location (pilot grip) • Position translated to angular measure from linear transducer (from calibration) • Estimation of surface position from measured control position • Initially, poor assumptions made when analyzing the data • Assumed rigid cable • Assumed rigid control loader

16. KC-130 APT Results • Needed to explain differences between SIMES results and internal results

17. KC-130 APT Results • Initially removed assumption of rigid cable

18. KC-130 APT Results • Additional testing of flex in simulator controls-Simple linear spring determined to model control flex

19. KC-130 APT Results • Force vs. deflection plot clearly illustrates relative effects RIGID SYSTEM ACTUAL FLEXIBLE SYSTEM Just Cable Stretch

20. Overview • Introduction • Control system • Model • Control loading system • Flexure • Testing • External Instrumentation • Internal Instrumentation • Test results • Conclusions

21. Conclusions • Simulator control feel liked by aircrew • Additional testing required to explain why the external test system test results were reasonable when compared to the criteria data • The above infers: • The criteria data did not include flexure of the control system in the aircraft

22. Conclusions • Expectations • Did not expect flex in simulator controls to be more significant than cable flex • Test Results • Control Loader Internal testing not able to reflect true control position to surface position • Control loader testing must measure • Control force • Control position • Surface position • Criteria should include relationship between these three parameters.

23. Conclusions • A/C Criteria data must: • Specify where the force and position sensors are for the test • Test data should be taken with an external test system at the point of pilot force application • For a two pilot a/c, both sets of controls should be measured • Specific tests should be made to measure flexure between the pilot and the control surface • Simulator control loading must: • Include aircraft control system flexure in the model • Linkages and controls • Beware of double accounting