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Aeromechanics Analyses of a Modern Lift-Offset Coaxial Rotor in High-Speed Forward Flight

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Abstract

This study conducts an aeromechanics analysis of a modern lift-offset coaxial rotor in high-speed flight. A lift-offset coaxial rotor of the Sikorsky X2 technology demonstrator (X2TD) is considered for the present study. For the analyses of rotor performance, blade airloads, and hub vibratory loads, a rotorcraft comprehensive analysis code, CAMRAD II, is used. For the rotor performance analysis at a flight speed of up to 250 knots, which is the maximum level flight speed of X2TD in flight test, the present prediction of rotor power is compared well with the flight test data. For the blade section airload analysis at 250 knots, the impulses of the section lift forces are observed because of the aerodynamic interactions between the upper and lower rotors. The 4/rev hub vibratory loads are predicted, and its variation trend is moderately compared with the previous analysis results. Furthermore, the rotor vibration index increases significantly in high-speed flight with an increase in the flight speed, and this is well correlated with the previous rotorcraft comprehensive analysis result. This study shows that the present modeling and analysis techniques are appropriate to analyze the aeromechanics, including the performance, blade airloads, and hub vibratory loads of a modern lift-offset rotor in high-speed flight.

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Abbreviations

c :

Blade chord length, ft

C d :

Drag coefficient of an airfoil

C l :

Lift coefficient of an airfoil

C m :

Pitching moment coefficient of an airfoil

D :

Drag force, lb

D rotor :

Rotor drag, lb

D total :

Total drag, lb

F 4P :

4/rev hub vibratory force, lb

GW:

Gross weight, lb

L :

Lift force, lb

L/D e :

Effective lift-to-drag ratio of the rotor

LOS:

Lift-offset

M :

Mach number

M 4P :

4/rev hub vibratory moment, lb ft

M Adv.Lmt :

Maximum Mach number of advancing blade tip

M roll :

Hub rolling moment of a rotor, lb ft

N b :

Number of blades for a rotor

P :

Rotor power, hp

P coaxial :

Coaxial rotor power, hp

P i :

Induced power, hp

P lower :

Power of the lower rotor, hp

P o :

Profile power, hp

P p :

Parasite power, hp

P propeller :

Propeller power, hp

P upper :

Power of the upper rotor, hp

q :

Dynamic pressure, lb/ft2

r :

Radial position of the rotor blade, ft

R :

Radius of the rotor, ft

T :

Thrust of a rotor, lb

V, V ∞ :

Flight speed, ft/sec

VI:

Vibration index

V tip :

Rotor tip speed, ft/sec

X :

Wind-axis drag force of the rotor, lb

α :

Angle of attack, deg

α 0 :

Zero-lift angle of attack, deg

η :

Propulsive efficiency

σ TW :

Total solidity of the coaxial rotor

ψ :

Azimuth angle, deg

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Acknowledgements

This work was supported by research fund of Chungnam National University.

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Authors and Affiliations

  1. Department of Aerospace Engineering, Chungnam National University, Daejeon, 34134, Korea

    Young-Min Kwon & Jae-Sang Park

  2. Aeronautics Technology Research Division, Korea Aerospace Research Institute, Daejeon, 34133, Korea

    Seong-Yong Wie & Do-Hyung Kim

  3. Optionally Piloted Personal Air Vehicle Team, Korea Aerospace Research Institute, Daejeon, 34133, Korea

    Hee Jung Kang

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  1. Young-Min Kwon
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  2. Jae-Sang Park
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Correspondence to Jae-Sang Park.

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Kwon, YM., Park, JS., Wie, SY. et al. Aeromechanics Analyses of a Modern Lift-Offset Coaxial Rotor in High-Speed Forward Flight. Int. J. Aeronaut. Space Sci. 22, 338–351 (2021). https://doi.org/10.1007/s42405-020-00300-8

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