Alam, Mushfiqul

Cameron, Neil

Eberle, Brian

Fell, Th

Jump, M

Repola, C

Rogers, Jomathan

Strickland, L

University of Liverpool Repository

Summary of Progress In The Development Of A Time-to-contact Autorotation Cueing SystemM. Jump, M. Alam, N. Cameron, T.R. FellUniversity of LiverpoolJ. Rogers, B. Eberle, L. Strickland, C. Repola, Georgia Institute of TechnologyRAeS International Power Lift Conference, November 2018M Jump: mjump1@liverpool.ac.ukdrjumpjets@drmikejumpMotivation• The autorotation maneuver to land follows a partial or completeengine failure or some other catastrophic failure in a helicopter• A successful autorotation outcome requires fast pilot reactiontimes and appropriate control actions• This is particularly true for phases close to the ground• It is a complex and difficult maneuver particularly in degradedvisual environments (DVE), night time operations, or low-energyflight conditions• Even well trained, highly motivated pilots can encounter difficulties• Can additional cueing be provided to assist a pilot to carry out asuccessful autorotation maneuver?https://www.youtube.com/watch?v=BkF4b6OuXJ0Automatic Autorotation Controller • Georgia Institute of Technology (GT) have previously developedan autonomous autorotation controller1• Controller designed to interface with a standard autopilot orstability and control augmentation system (SCAS) capable ofaccepting translational rate commands (TRC)1. Sunberg, Z., Miller, N., Rogers, J., “A Real-Time Expert Control System for Helicopter Autorotation,” Journal of the American Helicopter Society, April 2015Automatic Autorotation Controller • Three main phasesi. Steady-stateii. Flareiii. Touchdown• Two additional phases to facilitate transitions between the three main phasesi. Pre-flareii. Landing• The controller progresses between each phase based ona. Altitudeb. Time-to-(ground) contact• If either criteria are satisfied → transition to the next phase• Phase transitions occur in a fuzzy manner - each phase haspartial authority during the transition.UoL interestProject Overview/Research QuestionsCould the outputs of the GT automated controller be used to cue apilot in the loop to perform a successful autorotation maneuver?Can time-to-contact be usefully used directly in the control loop?1. Develop a basic display to provide autorotation cueing to thepilot using the control law as input2. Integrate the control law into the UoL HELIFLIGHT-R simulationfacility3. Perform simulated flight tests to evaluate the performance of thepilot-in-the-loop autorotation algorithm in both GVE and DVE4. Develop a time-to-contact based controller to perform to at leastthe same standard as the ‘conventional’ GT controller?GT Controller Integration at UoL• GT provided UoL with controller (Simulink)• UoL implemented this within the FLIGHTLAB Generic Rotorcraft• Validation & verification showed the implementation to be ‘correct’:• And the proof of the pudding…Pilot-in-the-loop Testing• Test matrix consisting of:• 3 engineer pilots with real-world flight experience (2 x fixed- and 1x rotary-wing)• Minimum of 5 autorotation practice maneuvers per test point• HUD on/off• GVE/DVE• ‘Success’ criteria• Some indicative results…Parameter Condition for ‘Successful’ landingCondition for ‘Marginal’ LandingPitch Angle.  <12o <20oForward Speed, Vdes <30 knots < 60 knotsVertical Speed, z_dot < 8 ft/s <15 ft/sPitch Rate, q -30o/s < q < 20o/s -50o/s < q < 40o/sPilot-in-the-loop Testing – GVE, No HUDPilot-in-the-loop Testing – GVE, HUDGT Controller Landing Performance Results• The results for each test point are:Test Case Pilot Ground Speed [knots]TDZdot [ft/s]Pitch Angle [deg]Pitch Rate [deg/s]GVE / OFF 1 28 4 8 -242 24 1 -3 123 13 5 11 -35GVE / ON 1 13 1 -2 62 16 6 -3 -13 17 5 4 18DVE / ON 1 12 1 -1 82 15 2 -1 183 22 2 -1 19Why Tau?• Tau can handle variable, even unstable vehicle dynamics• Behaves like a model inverter without the need for any knowledge of the model• Can be ‘sensed’ actively or passivelyTau Theory• Time to contact, 𝜏, is posited to be one of the fundamental ‘optical invariants’ used by an observer to perceive motion• The term, “motion gap” refers to a perceived difference between the observer’s current and desired target state 𝜏 𝑡 =𝑥 𝑡ሶ𝑥(𝑡)motion gapgap closure rateTau Theory• Tau guidance of the observer’s motion is achieved using 𝜏coupling: that is, keeping the tau of one optically available parameter in proportion with the tau of another• Tau coupling can take two forms: extrinsic (‘x’ and ‘y’ are physically observable) or intrinsic (‘x’ is physically observable whereas ‘y’ is generated by the actor’s central nervous system, the so called motion guides)• Another coherent tau-based guidance strategy is to keep the rate of change of tau of the motion-gap constantTau Theory• Fixed-wing flare manoeuvres described by 2 different constant tau-dot-height profiles• Personal aerial vehicle approach to hover described by extrinsic coupling of taus of longitudinal distance and vertical distance to final hover positionTau Theory and the Tau GuideConstant Acceleration Tau GuideMotion 𝜏, gap distance, closure rate and acceleration when following a constant acceleration guide such that 𝜏𝑥 = 𝑘𝜏𝑔.“^”, the dressing indicates that the variables are normalized by total time, T.Flight-test Strategies• Flight test and simulated flight test autorotation manoeuvres wereanalysed• Strategies using tau derivatives ( ሶ𝜏,vertical height and longitudinaldistance) across 4 different flight phases of the autorotationmanoeuvre were identified• A new autorotation control algorithm based on the tau-guidancestrategy used by pilots was developed• PID tracking controllers implemented to track ሶ𝜏 targets in eachphaseFlight-test StrategiesPhaseName LongitudinalCyclicCollective Pitch1 Flare ሶ𝜏𝐻 (=0.6) Not used2 Reduce IAS ሶ𝜏𝑋(=0.1) ሶ𝜏𝐻(=0.1)3 Reduce Pitch Reduce pitch angle Maintain4 Land Maintain pitch angle (when Vgrnd <30ftsec, Vzi > -8ft/sec, theta <10 deg)Tau Controller Implementation (Auto)Vxf [ft/sec] Vzf [ft/sec] Theta [deg] q [deg/sec]Desired < 30 > -8 < 12 -30 <q < 20Adequate < 60     > -15     < 20 -50 <q < 40AAC 18.2 -7.7 6.2 -2.13Tau Controller Implementation• Results of the implemented controller in the tau-domain shown below• Forward speed and vertical speed at touchdown in acceptable range (~20 kts, 7 ft/s)• Max pitch angle (30 deg) observed to be excessive• ሶ𝜏 is tracked, albeit imperfectly due to coupled response between pitch, forward speed, vertical speedTau Controller Implementation• BUT, collective cue difficult (impossible) to follow• However, collective cue movement a useful cue for when to startpulling on the collective• Cyclic cue implementation a little awkward to follow whilst alsotrying to follow collective cueing if manoeuvre moved too far ‘offplan’ (think patting head and rubbing stomach)• Pilots unsure about following a display so close to the groundwhen they would prefer to be looking out of the cockpit window• Perhaps points towards haptic cueing?Concluding Remarks• Two autorotation manoeuvre controllers successfully implemented in real time simulation• Both provide an automatic autorotation manoeuvre landing capability• Rudimentary display developed to cue the pilot based upon the outputs of these controllers• Successful autorotation manoeuvres can be accomplished usingthese displays• But this solution does have issues which need to be addressedFuture Work• More systematic pilot-in-the-loop testing of tau- and conventional-based cueing (display, haptic, {audio?})• Further explore possible coherent tau motion-gap closures to be used as cue drivers• Couple this work with the GT work on ‘reachable landing points’ (also tau-based)Any Questions?The research/investigation was sponsored by the Army ResearchLaboratory and was accomplished under Cooperative AgreementNumber W911NF-16-2-0027 and the U.S. Army/Navy/NASAVertical Lift Research Center of Excellence with MahendraBhagwat serving as the Program Manager and Technical Agent,grant number W911W6-11-2-0010 and W911W6-17-2-0002. Theviews and conclusions contained in this document are those ofthe authors and should not be interpreted as representing theofficial policies, either expressed or implied, of the ArmyResearch Laboratory or the U.S. Government. The U.S.Government is authorized to reproduce and distribute reprints forGovernment purposes notwithstanding any copyright notationherein.

Summary of Progress In The Development Of A Time-to-contact Autorotation Cueing System

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Summary of Progress In The Development Of A Time-to-contact Autorotation Cueing System

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