Problems in Validating Control Feel in Simulators By T. Scott Davis Aerospace Engineer, Member AIAA Bruce Hildreth

Overview Introduction Control system –Model –Control loading system –Flexure Testing –External Instrumentation –Internal Instrumentation –Test results Conclusions

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

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

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

Overview Introduction Control system –Model –Control loading system –Flexure Testing –External Instrumentation –Internal Instrumentation –Test results Conclusions

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

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

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

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 Linkage locked Column Applied Force

Overview Introduction Control system –Model –Control loading system –Flexure Testing –External Instrumentation –Internal Instrumentation –Test results Conclusions

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 Control Loader Actuator Position Sensor Force Sensor External Force Sensor External Position Sensor Cockpit Floor

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

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

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

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

KC-130 APT Results Initially removed assumption of rigid cable

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

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

Overview Introduction Control system –Model –Control loading system –Flexure Testing –External Instrumentation –Internal Instrumentation –Test results 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

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.

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