Tiltrotor Performance Improvements through the use of Span Extensions and Winglets

Open Access
Author:
Hoover, Taylor Jacob
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Mark David Maughmer, Thesis Advisor
Keywords:
  • tiltrotor
  • aircraft design
  • aircraft performance
Abstract:
Tiltrotor aircraft have the unique ability of vertical takeoff and fixed wing cruise. This distinctive feature allows tiltrotors to operate at two different design points: hover and cruise. The conflicting requirements of hover and cruise come with consequences. Tiltrotors are plagued with an aeroelastic instability caused by structural and aerodynamic coupling of the wing and large propeller called whirl flutter. Researchers at Penn State have shown that adding span extensions and winglets to tiltrotors can improve the whirl flutter margin. These wingtip devices may improve whirl flutter margin but alter the aircraft aerodynamics and mission performance. This thesis presents a design investigation of improving tiltrotor cruise performance with the use of span extensions and winglets. The important constraint of maintaining baseline hover performance was imposed. Cruise performance is improved by optimizing span extensions and winglets for range specific transport efficiency. Range specific transport efficiency accounts for the aerodynamic and structural impacts of the wingtip devices. The aerodynamic performance is calculated using a multiple lifting line method for non-planar wing geometries. This performance tool conducts fast, accurate calculations, that when coupled with a genetic algorithm optimizer, results in a computationally inexpensive method for design optimization. The Large Civil Tiltrotor 2 and the Military Heavy Tiltrotor, were case studies for the investigation performed here. Results for the Large Civil Tiltrotor 2 show a 2.6-2.9% improvement in the lift-to-drag ratio and 2.3-5.4% increase in range specific transport efficiency, while those for the Military Heavy Tiltrotor show a improvement of 6.1-6.8% in the lift-to-drag ratio and a 7.2-8.0% increase in range specific transport efficiency.