Design and Testing of a Helicopter Rotor Blade Chord Extension System

Open Access
Hayden, Eric William
Graduate Program:
Aerospace Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 12, 2012
Committee Members:
  • Farhan Gandhi, Thesis Advisor
  • aerospace
  • helicopter
  • morphing
  • rotor
  • chord
  • extension
  • design
  • test
In high gross weight, high altitude, and high speed operations, the helicopter main rotor is susceptible to stall. The onset of stall both limits the envelope as well as significantly increases the power requirement. The ability to generate additional lift can reduce the power requirement and expand the envelope. One approach to generating higher lift is through chord extension morphing of sections of the main rotor blade. This study presents a mechanism for increasing the blade chord by extending a flat plate through a slit in the trailing edge. In order to minimize the structural impact on the blade, the device was constrained to be aft of the spar. In view of the available space constraints, the mechanism consists of a single linkage which transforms spanwise actuation output into chordwise displacement. The study has considered both electromechanical and pneumatic actuation methods. As with any morphing rotor technology, the system must be able to operate within the high-g environment present in a helicopter blade. The current prototypes have been spin tested on the Pennsylvania State University’s Adverse Environment Rotor Test Stand (AERTS). The test section for each prototype used a 16 in chord NACA 0015 airfoil with an 11.5 in span. The goal of the spin test was to show successful actuation of the design under the centrifugal acceleration present in a UH-60 helicopter blade at 73% rotor radius. The electromechanically actuated extendable chord system was able to achieve 1.3 in of chordwise extension (8.13 % chord extension) at a maximum rotational speed of 385 RPM. The corresponding centrifugal acceleration of 210 g’s is approximately 47% of the full-scale loading. The system was ultimately limited by the capabilities of the commercially available off-the-shelf electromechanical actuator. Under these conditions, the electromechanical motor required 40W of power. The pneumatically actuated system was able to provide 1.9 in of chordwise extension (11.88% chord extension). With the pressure limited to 105 psi using the AERTS facility, the system was only able to operate successfully up to 315 RPM, or at 32% of full-scale centrifugal acceleration. The experimental result showed good correlation with the numerical simulation. The analysis also showed that by balancing the chordwise and spanwise forces, actuation requirements can be dramatically reduced in subsequent designs.