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Interactional Aerodynamic Assessment of a Quad-Rotor Tail Sitter using CFD

Richard Healy, Rensselaer Polytechnic Institute
Matthew Floros, Phuriwat Anusonti-Inthra, US Army CCDC - ARL

https://doi.org/10.4050/F-0079-2023-17964

Abstract:
Efforts towards enhanced Unamnned Aerial System (UAS) efficiency has lead to the development of the Quadrotor Biplane Tailsitter (QBiT) configuration that employs variable blade pitch to control the aircraft. To reduce the overall system complexity, an alternative control system using fixed-pitch/variable-RPM trim is explored, with the rotors' relative positions/tilt to the wing varied to provide improved rotor efficiency in cruise. Medium-fidelity aerodynamic models of the baseline and modified QBiT reveal that the power required for high-speed level flight (40 - 70 kts) with fixed-pitch rotors tilted 60° nose-up is comparable to that for the baseline variable-pitch rotor configuration. The modified Quad Rotor Tail Sitter (modified QRTS) configurations are also simulated using a high-fidelity CFD software, revealing that wing-rotor aerodynamic interactions are responsible for up to 34.5% thrust deficit on the aft rotors due to wing-induced downwash. This thrust deficit contributes to a 5.4-6.3% lower overall system efficiency measured by L/De (compared to a system without aerodynamic interaction). When trimmed using CFD-CSD loose coupling, this reduced efficiency in part makes the modified QRTS power only 26.9% lower than a fixed blade pitch QBiT (compared to the 60.2% reduction predicted by comprehensive analysis). Interactional aerodynamic penalties can be mitigated somewhat by adjusting the mounting position of the rotors with wing lift increasing when aft rotors are positioned behind the wing. At a high flight speed (50 kts), interactional aerodynamic penalties are extended, with greater aft rotor thrust deficit and wing lift penalty causing a 7.2 - 7.9% drop in L/De (compared to isolated rotors and wings). Overall, the modified QRTS (with fixed-pitch/RPM control and optimal rotor tilt/position) shows an increased aerodynamic efficiency over the baseline QBiT (with variable-pitch control) due to a reduction in axial rotor flow despite interactional aerodynamic penalties.


Interactional Aerodynamic Assessment of a Quad-Rotor Tail Sitter using CFD

  • Presented at Forum 79
  • 25 pages
  • SKU # : F-0079-2023-17964
  • Advanced Vertical Flight

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Interactional Aerodynamic Assessment of a Quad-Rotor Tail Sitter using CFD

Authors / Details:
Richard Healy, Rensselaer Polytechnic Institute
Matthew Floros, Phuriwat Anusonti-Inthra, US Army CCDC - ARL