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Flight Dynamics of a Coaxial Compound Helicopter with Rotor-on-Rotor Interactional Aerodynamics.

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Title: Flight Dynamics of a Coaxial Compound Helicopter with Rotor-on-Rotor Interactional Aerodynamics.
Authors: Jun, Dogyu1, Cocco, Alessandro2, Saetti, Umberto3 saetti@umd.edu, Juhasz, Ondrej4
Source: Journal of the American Helicopter Society. Jan2026, Vol. 71 Issue 1, p1-18. 18p.
Subjects: Rotorcraft, Rotor dynamics, Aerodynamic stability, Helicopters, Reduced-order models, Frequency response, Linear dynamical systems
Abstract: This paper focuses on the integration of a generalized rotor-on-rotor interactional aerodynamics model in state-variable form within a flight dynamics simulation and on its subsequent linearization and linear model analysis. The aircraft chosen for this investigation is a generic lift-offset compound coaxial rotorcraft. Upon trimming the flight dynamics to hovering flight with the presence of rotor-on-rotor interactions, the linearized hover models are validated against a baseline model that do not account for rotor-on-rotor inflow interference effects. A model order reduction method is employed to guide the development of linearized models that are tractable for flight control design while still predicting the effect of rotor-on-rotor interactions on the vehicle flight dynamics. The effect of rotor-on-rotor interactional aerodynamics modeling on predictions of tip clearance between the rotors is also investigated. In hover, for the coaxial configuration considered, the model accounting for rotor-on-rotor interactions leads to a greater predicted tip clearance relative to the nominal separation, due to the thrust differential between the two main rotors. Furthermore, compared to the model without rotor-on-rotor interactions, the model with rotor-on-rotor interactions predicts smaller rolling and pitching moment derivatives with respect to lateral and longitudinal velocity, along with reduced roll and pitch stability damping derivatives. These changes in stability derivatives yield roll and pitch subsidence modes at a lower frequency and roll and pitch oscillation modes with a higher natural frequency. The resulting frequency responses show a reduction in the magnitude of the roll response to on-axis inputs (approximately 0.7 to 10 rad/s). In forward flight, the dominant effect is at low frequencies in the pitch axis. These findings are in line with previous studies focusing on model validation of the Sikorsky X2TDTM based on flight-test data. [ABSTRACT FROM AUTHOR]
Copyright of Journal of the American Helicopter Society is the property of American Helicopter Society dba Vertical Flight Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
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Header DbId: egs
DbLabel: Engineering Source
An: 191907086
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PubType: Academic Journal
PubTypeId: academicJournal
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  Data: Flight Dynamics of a Coaxial Compound Helicopter with Rotor-on-Rotor Interactional Aerodynamics.
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  Data: <searchLink fieldCode="AR" term="%22Jun%2C+Dogyu%22">Jun, Dogyu</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Cocco%2C+Alessandro%22">Cocco, Alessandro</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Saetti%2C+Umberto%22">Saetti, Umberto</searchLink><relatesTo>3</relatesTo><i> saetti@umd.edu</i><br /><searchLink fieldCode="AR" term="%22Juhasz%2C+Ondrej%22">Juhasz, Ondrej</searchLink><relatesTo>4</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+the+American+Helicopter+Society%22">Journal of the American Helicopter Society</searchLink>. Jan2026, Vol. 71 Issue 1, p1-18. 18p.
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  Data: <searchLink fieldCode="DE" term="%22Rotorcraft%22">Rotorcraft</searchLink><br /><searchLink fieldCode="DE" term="%22Rotor+dynamics%22">Rotor dynamics</searchLink><br /><searchLink fieldCode="DE" term="%22Aerodynamic+stability%22">Aerodynamic stability</searchLink><br /><searchLink fieldCode="DE" term="%22Helicopters%22">Helicopters</searchLink><br /><searchLink fieldCode="DE" term="%22Reduced-order+models%22">Reduced-order models</searchLink><br /><searchLink fieldCode="DE" term="%22Frequency+response%22">Frequency response</searchLink><br /><searchLink fieldCode="DE" term="%22Linear+dynamical+systems%22">Linear dynamical systems</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: This paper focuses on the integration of a generalized rotor-on-rotor interactional aerodynamics model in state-variable form within a flight dynamics simulation and on its subsequent linearization and linear model analysis. The aircraft chosen for this investigation is a generic lift-offset compound coaxial rotorcraft. Upon trimming the flight dynamics to hovering flight with the presence of rotor-on-rotor interactions, the linearized hover models are validated against a baseline model that do not account for rotor-on-rotor inflow interference effects. A model order reduction method is employed to guide the development of linearized models that are tractable for flight control design while still predicting the effect of rotor-on-rotor interactions on the vehicle flight dynamics. The effect of rotor-on-rotor interactional aerodynamics modeling on predictions of tip clearance between the rotors is also investigated. In hover, for the coaxial configuration considered, the model accounting for rotor-on-rotor interactions leads to a greater predicted tip clearance relative to the nominal separation, due to the thrust differential between the two main rotors. Furthermore, compared to the model without rotor-on-rotor interactions, the model with rotor-on-rotor interactions predicts smaller rolling and pitching moment derivatives with respect to lateral and longitudinal velocity, along with reduced roll and pitch stability damping derivatives. These changes in stability derivatives yield roll and pitch subsidence modes at a lower frequency and roll and pitch oscillation modes with a higher natural frequency. The resulting frequency responses show a reduction in the magnitude of the roll response to on-axis inputs (approximately 0.7 to 10 rad/s). In forward flight, the dominant effect is at low frequencies in the pitch axis. These findings are in line with previous studies focusing on model validation of the Sikorsky X2TDTM based on flight-test data. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Journal of the American Helicopter Society is the property of American Helicopter Society dba Vertical Flight Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
PLink https://search.ebscohost.com/login.aspx?direct=true&site=eds-live&db=egs&AN=191907086
RecordInfo BibRecord:
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      – Type: doi
        Value: 10.4050/JAHS.71.012008
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      – Code: eng
        Text: English
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      Pagination:
        PageCount: 18
        StartPage: 1
    Subjects:
      – SubjectFull: Rotorcraft
        Type: general
      – SubjectFull: Rotor dynamics
        Type: general
      – SubjectFull: Aerodynamic stability
        Type: general
      – SubjectFull: Helicopters
        Type: general
      – SubjectFull: Reduced-order models
        Type: general
      – SubjectFull: Frequency response
        Type: general
      – SubjectFull: Linear dynamical systems
        Type: general
    Titles:
      – TitleFull: Flight Dynamics of a Coaxial Compound Helicopter with Rotor-on-Rotor Interactional Aerodynamics.
        Type: main
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          Name:
            NameFull: Jun, Dogyu
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            NameFull: Cocco, Alessandro
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            NameFull: Saetti, Umberto
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            NameFull: Juhasz, Ondrej
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            – D: 01
              M: 01
              Text: Jan2026
              Type: published
              Y: 2026
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              Value: 71
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            – TitleFull: Journal of the American Helicopter Society
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