{"name":"Arma 3: Advanced Helicopter Flight Model","title":"Arma 3: Advanced Helicopter Flight Model","type":"topic","url":"https://community.bistudio.com/wiki/Arma_3:_Advanced_Helicopter_Flight_Model","revid":340297,"updated":"2023-04-28T17:20:15Z","aliases":["Advanced Helicopter Flight Model in Arma3","Arma 3 Advanced Helicopter Flight Model"],"markdown":"This document relates to Helicopter_Flight_Model_Config_(XML)\n\n**Changes introduced by RTD libraries 4.1.1 in Arma 3 Helicopters DLC**\n\n1) *<Fuselage CoPX= CoPY= CoPZ=*\nchanged to **forceExertionPnt*=**\n\n2) *<Engines> maxPower=*\nchanged to **emergencyPowerHP=**\n\n*<DriveTrains> torque maximumContinuous=* and *takeoff=* have no use, were removed\n\n3) *<ControlSystem> <FCSComponent* renamed to **<CSComponent**\n\nAdded new value **rotorBrake**\n\n4) *<Rotors> <ModelConfiguration updateSubstepCount=\"360\" />*\nwere replaced by **<ModelConfiguration maxIntegrationStepSizeDeg=\"1.0\" />**\n\nnew entries\n\n```\n<Geometry>\n```\n\n**<Blades rootCutout=**\n\n```\n<AerodynamicFeatures>\n```\n\n*<InducedVelocity groundEffectFactor= >*\n**<InducedVelocityTable>**\n\n```\n<VortexRingState>\n```\n\n**<Perturbation>**\n**<RoughnessBoundaries>**\n\n```\n<Blades tipLossFactor=\n```\n\n5) *<GroundContacts>* **removed** *<GeneralConfiguration*\ngearDragCoefficient= *and* gearReferenceArea=\"0\"\n\n### Notes about VRS (Vortex Ring State):\n\nWhen the vortex ring state is entered depends on vertical velocity,\nhorizontal velocity and current thrust (roughly collective position).\nGenerally, VRS occurs at low horizontal speeds and relatively large\nvertical speeds (comparable to induced velocity at the given thrust\nsetting). Although there are different numbers mentioned in the\nInternet they are usually over-generalizations. VRS entrance\nconditions differ from helicopter to helicopter and it differs\nalso depending on the current mass of the helicopter. A loaded\nhelicopter requires more thrust, which results in larger induced\nvelocity. In this configuration, blade tip vortices are blown quickly\ndownwards and entrance to VRS is hence harder.\n\nVRS starts with vibrations. As the vertical speed increases VRS\ncondition deepens and pitch,yaw,roll and thrust oscillations can\nbe observed. Another important thing to observe is sudden loss\nof thrust; climb rate will fall quickly in VRS however it will\nstabilize after some time.\n\nOnce the VRS is fully established the thrust will not be sufficient\nto come out. Actually, if the helicopter is relatively lightly\nloaded and has powerful engines, it might eventually brake\nthe descend but usually this takes more time than simply increasing\nhorizontal speed. Getting a little bit ETL will clear the rotor\nfrom vortex rings.\n\n**RTD Implementation:**\nThere are two aspects of VRS\n\n- Average induced velocity increase\n- Changes in distribution of the induced velocity on the blades\n\nFor the first one an empirical, table look-up based model is used.\n( see <InducedVelocityTable> ). As is customariy in the literature,\nthe axes and values in this table are non-dimensionalized by dividing\nto **v_h = sqrt(Thrust/(2*airdensity*rotorArea))**\n\nMore details about this simulation approach can be found in this paper [link](http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA526709)\n\nThe second one is partly responsible for the thrust loss (increase in\naverage induced velocity also plays a major role) and also\nvibration and oscillations.\n\n- Loss of thrust: Distribution of the induced velocity at the blade elements are automatically modified in VRS.\n- Vibration: vibration is to be visually cued at the application level (e.g. vibrating console etc. ).\n- Oscillations: RTD provides a configurable means for creating thrust and moment oscillations.\n\nConfiguration of the behavior in VRS is made in <VortexRingState>\nsection of the XML. In <Perturbation> section, oscillations for thrust\nand moments can be configured with their periods and amplitudes.","sections":[{"heading":null,"level":1,"markdown":"This document relates to Helicopter_Flight_Model_Config_(XML)\n\n**Changes introduced by RTD libraries 4.1.1 in Arma 3 Helicopters DLC**\n\n1) *<Fuselage CoPX= CoPY= CoPZ=*\nchanged to **forceExertionPnt*=**\n\n2) *<Engines> maxPower=*\nchanged to **emergencyPowerHP=**\n\n*<DriveTrains> torque maximumContinuous=* and *takeoff=* have no use, were removed\n\n3) *<ControlSystem> <FCSComponent* renamed to **<CSComponent**\n\nAdded new value **rotorBrake**\n\n4) *<Rotors> <ModelConfiguration updateSubstepCount=\"360\" />*\nwere replaced by **<ModelConfiguration maxIntegrationStepSizeDeg=\"1.0\" />**\n\nnew entries\n\n```\n<Geometry>\n```\n\n**<Blades rootCutout=**\n\n```\n<AerodynamicFeatures>\n```\n\n*<InducedVelocity groundEffectFactor= >*\n**<InducedVelocityTable>**\n\n```\n<VortexRingState>\n```\n\n**<Perturbation>**\n**<RoughnessBoundaries>**\n\n```\n<Blades tipLossFactor=\n```\n\n5) *<GroundContacts>* **removed** *<GeneralConfiguration*\ngearDragCoefficient= *and* gearReferenceArea=\"0\""},{"heading":"Notes about VRS (Vortex Ring State):","level":3,"markdown":"When the vortex ring state is entered depends on vertical velocity,\nhorizontal velocity and current thrust (roughly collective position).\nGenerally, VRS occurs at low horizontal speeds and relatively large\nvertical speeds (comparable to induced velocity at the given thrust\nsetting). Although there are different numbers mentioned in the\nInternet they are usually over-generalizations. VRS entrance\nconditions differ from helicopter to helicopter and it differs\nalso depending on the current mass of the helicopter. A loaded\nhelicopter requires more thrust, which results in larger induced\nvelocity. In this configuration, blade tip vortices are blown quickly\ndownwards and entrance to VRS is hence harder.\n\nVRS starts with vibrations. As the vertical speed increases VRS\ncondition deepens and pitch,yaw,roll and thrust oscillations can\nbe observed. Another important thing to observe is sudden loss\nof thrust; climb rate will fall quickly in VRS however it will\nstabilize after some time.\n\nOnce the VRS is fully established the thrust will not be sufficient\nto come out. Actually, if the helicopter is relatively lightly\nloaded and has powerful engines, it might eventually brake\nthe descend but usually this takes more time than simply increasing\nhorizontal speed. Getting a little bit ETL will clear the rotor\nfrom vortex rings.\n\n**RTD Implementation:**\nThere are two aspects of VRS\n\n- Average induced velocity increase\n- Changes in distribution of the induced velocity on the blades\n\nFor the first one an empirical, table look-up based model is used.\n( see <InducedVelocityTable> ). As is customariy in the literature,\nthe axes and values in this table are non-dimensionalized by dividing\nto **v_h = sqrt(Thrust/(2*airdensity*rotorArea))**\n\nMore details about this simulation approach can be found in this paper [link](http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA526709)\n\nThe second one is partly responsible for the thrust loss (increase in\naverage induced velocity also plays a major role) and also\nvibration and oscillations.\n\n- Loss of thrust: Distribution of the induced velocity at the blade elements are automatically modified in VRS.\n- Vibration: vibration is to be visually cued at the application level (e.g. vibrating console etc. ).\n- Oscillations: RTD provides a configurable means for creating thrust and moment oscillations.\n\nConfiguration of the behavior in VRS is made in <VortexRingState>\nsection of the XML. In <Perturbation> section, oscillations for thrust\nand moments can be configured with their periods and amplitudes."}],"categories":["Arma 3: Editing"],"groups":["General"]}