Blade pitch

About: Blade pitch is a research topic. Over the lifetime, 5321 publications have been published within this topic receiving 63134 citations.

Interference between propeller and vehicle; the ducted propeller

Abstract: This chapter analyzes the interference between propeller and vehicle. In the neighborhood of a vehicle the flow coming in toward the propeller is disturbed. In this respect the effect is different depending on whether the disturbance is caused by energy losses (regions of separated flow, viscous wakes) or whether the phenomenon being considered is velocity differences in a potential flow (displacement flow, low velocity in the neighborhood of the stagnation point, high velocity to the side of the body). It is advantageous to have the propeller placed in the region of smallest flow energy in the wake and in the region of largest velocity in the potential flow. A favorable arrangement of propeller and vehicle leads to a better efficiency than that of the same propeller in an undisturbed stream; this efficiency may be called the “propulsive efficiency,” to distinguish it from the efficiency of the propeller in an undisturbed stream. The difference can be quite considerable. The chapter also discusses about ducted propeller highlighting that the ducted propeller is better suited to variations in the flight speed.

Development of a Micro Twin-Rotor Cyclocopter Capable of Autonomous Hover

Abstract: G ROWING interest in highly portable versatile flying platforms and recent advancements in microelectronics have led to the development of a scaled-down class of unmanned aerial vehicles known asmicro air vehicles (MAVs) [1,2]. The potential applications of MAVs could range from reconnaissance, terrain mapping, and search and rescue in both military and civilian settings. For these types of missions, hover/low-speed flight capability, high endurance, maneuverability, and the ability to tolerate environmental disturbances such as wind gusts are critical requirements for MAVs. Because MAVs operate in a unique aerodynamic regime (low Reynolds numbers) with a different set of mission requirements and challenges as compared to a full-scale aircraft, it is important to explore novel out-of-the-box vehicle concepts that might have the potential for superior performance at these scales. This note describes the vehicle design and control system development of one suchMAV concept: the cyclocopter (shown in Fig. 1). The cyclocopter uses cycloidal rotors (cyclorotors), a horizontal axis propulsion concept that has many advantages such as higher aerodynamic efficiency [3], maneuverability, and high-speed forward flight capability [4,5] when compared to a conventional helicopter rotor. A cyclorotor is essentially a rotating-wing system where the span of the blades runs parallel to the axis of its rotation. The pitch angle of each blade is varied cyclically by mechanical means such that the blade experiences positive geometric angles of attack at both the top and bottom halves of the azimuth cycle (Fig. 2). Varying the amplitude and phase of the cyclic blade pitch is used to change the magnitude and direction of the net thrust vector produced by the cyclorotor. Although many breakthroughs in cyclorotor research have occurred in recent years, attempts to develop a cycloidal rotor-based aircraft date back to the early 20th century [6,7]. Numerous full-scale manned aircrafts were designed and built, but none of the attempts was successful in achieving flight. However, recently, the feasibility of this concept was demonstrated at the University of Maryland by developing two cyclocopter configurations (a hybrid twin-rotor cyclocopter [8] and quad-rotor cyclocopter [9]) capable of free hover. The only other cyclocopter capable of controlled free flight was developed at the Seoul National University [10]. The main focus of the present work is to develop an improved version of the cyclocopter built in [8] to demonstrate efficient hover capability and to develop and implement a closed-loop control strategy that can be used to autonomously stabilize and control the vehicle in hover without a human pilot.

APIAN-INF: an aerodynamic and aeroacoustic investigation of pylon-interaction effects for pusher propellers

Abstract: Advanced propellers promise significant fuel-burn savings compared to turbofans When installed on the fuselage in a pusher configuration, the propeller interacts with the wake of the supporting pylon This paper presents an experimental analysis of the aerodynamic and aeroacoustic characteristics of this pylon–propeller interaction An isolated propeller was operated in undisturbed flow and in the wake of an upstream pylon at the large low-speed facility of the German–Dutch wind tunnels (DNW-LLF) Measurements of the pylon-wake characteristics showed that the wake width and velocity deficit decreased with increasing thrust due to the suction of the propeller The installation of the pylon led to a tonal noise penalty of up to 24 dB, resulting from the periodic blade-loading fluctuations caused by the wake encounter The noise penalty peaked in the upstream direction and became increasingly prominent with decreasing propeller thrust setting, due to the associated reduction of the steady blade loads The integral propeller performance was not significantly altered by the pylon-wake encounter process However, at sideslip angles of ±6°, the effective advance ratio of the propeller was modified by the circumferential velocity components induced by the pylon tip vortex The propeller performance improved when the direction of rotation of the propeller was opposite to that of the pylon tip vortex Under this condition, a reduction was measured in the noise emissions due to a favorable superposition of the angular-inflow and pylon-wake effects

Actuation system for a gas turbine rotor blade

Abstract: An actuation system which includes apparatus for transferring control signals for varying the blade pitch from a non-rotating member to a rotating member of a gas turbine engine is described. In one embodiment, the engine includes a main disk containing a row of blades, and the disk is coupled to a main shaft which rotates about the engine axis. An actuating disk, or cone, rotates with the main disk, and the torque required to rotate the actuating cone is transmitted through ball splines attached to the main shaft. The ball splines allow transmission of torque between the disk and the cone and at the same time enable the disk and the cone to move axially relative to each other without binding. The actuating cone is supported at one end by the ball splines and at its other end by ball thrust bearings. The ball thrust bearings are pre-loaded to enable the bearings to withstand axial loads in opposite directions. The outer races of the bearings are supported by a ring, and the ring is connected to an actuator through a connecting cone. In addition to the actuating system, a blade support system is provided wherein the load of the blade is transferred from a blade "button" head to the main disk through a load transfer ring, a bearing inner race support, and a thrust bearing. A nut retains a crank of the actuating system on the blade spindle. To rotate the blade about its radial axis, the ring is moved axially by the actuator. Such axial movement of the ring imparts axial motion to the rotating actuating cone, which rotates a crank attached to the blade. The thrust bearings allow the actuating cone to rotate about the centerline of the actuator and to move axially when actuated.

Marine vessel with propeller

Abstract: A marine vessel having a propeller tunnel possessing a flow-favorable cross-sectional configuration following the flow lines of the water. Within the propeller tunnel there is mounted a propeller essentially throughout one-half of its circumference. An adjustable control plate can be extended in order to detach the flow of the water from the surface of the tunnel during rapid travel of the marine vessel. In this case, the propeller functions as a partially immersed propeller at a high rotational speed. There can be provided a control device which adjusts the control plate as a function of the rotational speed range within which the propeller operates. The propeller can be an adjustable propeller conjointly adjustable with the control plate.