scholarly journals Trailing edge flap control of dynamic stall on helicopter rotor blades

2006 ◽  
Author(s):  
Gregory Davis
Keyword(s):  
Rotor Blades ◽  
Dynamic Stall ◽  
Helicopter Rotor ◽  
Trailing Edge ◽  
Helicopter Rotor Blades ◽  
Trailing Edge Flap

Helicopter Rotor Blade Chord Extension Morphing Using a Centrifugally Actuated von-Mises Truss

2012 ◽  
Author(s):  
Patrick Moser ◽  
Silvestro Barbarino ◽  
Farhan Gandhi
Keyword(s):  
Leading Edge ◽  
Rotor Blades ◽  
Helicopter Rotor ◽  
Design Solution ◽  
Trailing Edge ◽  
Power Requirement ◽  
Helicopter Rotor Blades ◽  
Final Design ◽  
Von Mises ◽  
Chord Extension

Previous studies have shown that chord extension morphing over a spanwise section of helicopter rotor blades can reduce main rotor power requirement in stall-dominant flight conditions while at the same time being able to increase the maximum gross weight, altitude, and flight speed capability of the aircraft. This study examines a centrifugally driven, fully passive chord morphing mechanism for helicopter rotor blades. It is based on a von-Mises truss situated aft of the leading-edge spar, connected to a rigid extension plate which deploys through a slit in the trailing-edge. When the rotor RPM increases beyond a critical value the chordwise component of centrifugal (CF) force on the von-Mises truss and plate assembly results in the deployment of the plate beyond the slit in the trailing edge, effectively increasing chord length. On reducing the RPM, a retraction spring pulls the plate back within the confines of the blade. This study presents the design process, iterations and the final design solution for a configuration that undergoes 20% chord extension. A prototype was fabricated and tested on the bench-top as well as on a rotor test stand at rotational speeds simulating 70% full-scale CF loads. The test results demonstrate that the concept works. However, effects such as friction lead to higher force (or RPM) requirements for deployment than predicted by simulation, and are present during retraction as well. The effects are more pronounced in the high CF field in the rotor test.

Trailing-edge flap flow control for dynamic stall

2011 ◽  
Vol 115 (1170) ◽  
pp. 493-503 ◽  
Author(s):  
R. B. Green ◽  
E. A. Gillies ◽  
Y. Wang
Keyword(s):  
Lower Surface ◽  
Rotor Blades ◽  
Surface Shape ◽  
Dynamic Stall ◽  
Limiting Factors ◽  
Trailing Edge ◽  
Oscillatory Dynamic ◽  
Trailing Edge Flap ◽  
Flap Deflection ◽  
Motion Profile

Abstract Results of a series of oscillatory dynamic stall tests of a rotor aerofoil fitted with a pulsed, trailing-edge flap are presented. Flap deflection amplitude, motion profile, duration and starting phase were investigated to assess the potential of the flap for mitigating the adverse effects of dynamic stall, which is one of the limiting factors for rotor blades on the retreating side of a helicopter rotor. The tests were a continuation of the investigations by Ref. 1 who used a computational fluid dynamics method on a symmetric NACA section, and our results broadly confirm their conclusions by experimental test, using a modern rotor section. The results presented in this paper also confirm the observations from experimental work by Refs 2 and 3, which were undertaken at lower Reynolds number and with a larger flap. In the present study, the flap mitigates the high negative pitching moment and negative pitch damping seen in dynamic stall by strong suction being generated over the aerofoil lower surface, and it is the modification to the lower surface shape by the flap that creates this effect. The dynamic stall vortex acts to enhance the lower surface suction, and careful flap phasing and flap motion profile shaping can make the control more effective.

Design of Extendable Chord Sections for Morphing Helicopter Rotor Blades

2010 ◽  
Author(s):  
Silvestro Barbarino ◽  
Farhan Gandhi ◽  
Steven D. Webster
Keyword(s):  
Cellular Structure ◽  
Leading Edge ◽  
Rotor Blades ◽  
Helicopter Rotor ◽  
Trailing Edge ◽  
Element Analysis ◽  
Flexible Skin ◽  
Helicopter Rotor Blades ◽  
Global Strain ◽  
Blade Section

Chord extension in helicopter rotors allows for expansion of the flight envelope, with the helicopter capable of flying at higher gross weights, altitudes and maximum speeds. A fixed large chord, however, results in a penalty when the helicopter is well within the envelope (for example, at low to moderate gross weight, sea level, and at moderate speed cruise). Chord morphing allows the helicopter to perform optimally in these diverse conditions. In this paper, the authors present a morphing mechanism to extend the chord of a section of the helicopter rotor blade. The region aft of the leading-edge spar contains a morphing cellular structure. In the “compact” state the edge of the cellular structure aligns with the trailing-edge of the rest of the blade. When the morphing cellular structure is in the “extended” state the chord of that section of the blade is increased by close to 30% (with the trailing-edge extending beyond that of the rest of the blade). In transitioning from compact to extended states, the cellular structure slides along ribs which define the boundaries of the morphing section in the span-wise direction. The cellular section has mini-spars running along the span-wise direction to attach the flexible skin and provide stiffness against camber-like deformations due to aerodynamic loads. The paper presents a finite element analysis and a design study of the morphing cellular structure, ensuring that the local strains in the cellular structure do not exceed maximum allowables even as the section undergoes large global strain. On the other hand, the morphing cellular structure is required to be stiff enough so that the pre-stretched skin that is attached to the surfaces does not result in deformation. Another question that is considered in detail is various methods of attachment of the flexible skin to the morphing substructure, the levels of pre-strain required, and their ramifications. A model of a blade section is fabricated and shown to undergo chord morphing, as designed.

Circulation Control Span-Wise Blowing Location Optimization for a Helicopter Rotor Blade

2010 ◽  
Author(s):  
Alan M. Didion ◽  
Jonathan Kweder ◽  
Mary Ann Clarke ◽  
James E. Smith
Keyword(s):  
Stress Reduction ◽  
Rotor Blades ◽  
Helicopter Rotor ◽  
Base Line ◽  
Control Technology ◽  
Circulation Control ◽  
High Lift ◽  
Location Optimization ◽  
Helicopter Rotor Blades ◽  
Length Reduction

Circulation control technology has proven itself useful in the area of short take-off and landing (STOL) fixed wing aircraft by decreasing landing and takeoff distances, increasing maneuverability and lift at lower speeds. The application of circulation control technology to vertical take-off and landing (VTOL) rotorcraft could also prove quite beneficial. Successful adaptation to helicopter rotor blades is currently believed to yield benefits such as increased lift, increased payload capacity, increased maneuverability, reduction in rotor diameter and a reduction in noise. Above all, the addition of circulation control to rotorcraft as controlled by an on-board computer could provide the helicopter with pitch control as well as compensate for asymmetrical lift profiles from forward flight without need for a swashplate. There are an infinite number of blowing slot configurations, each with separate benefits and drawbacks. This study has identified three specific types of these configurations. The high lift configuration would be beneficial in instances where such power is needed for crew and cargo, little stress reduction is offered over the base line configuration. The stress reduction configuration on the other hand, however, offers little extra lift but much in the way of increased rotor lifespan and shorter rotor length. Finally, the middle balanced configuration offers a middle ground between the two extremes. With this configuration, the helicopter benefits in all categories of lift, stress reduction and blade length reduction.

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