Variable pitch rotor blade with double flexible retention elements

Abstract

A propulsive thrust device for an engine includes a rotor blade and a hub assembly on which the rotor blade is mounted. The rotor blade comprises an airfoil and at least two support members. A propeller thrust device includes a rotor blade, a central hub at which the rotor blade centrifugal load is supported, and an outer hub supporting a control mechanism mechanically connected to the rotor blade and controllable to vary the pitch of the rotor blade on the central hub. A rotor blade for an aircraft engine or in a separate ducted fan housing driven by a powered shaft or gearbox output shaft includes an airfoil and first and second support members attached to the airfoil. An extended arm or portion of the structure at the root of the airfoil of each blade is attached to a controllable mechanism that can vary the pitch of all blades simultaneously.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application claims the benefits of U.S. Provisional Patent Application Ser. No. 60 / 651,089, filed on Feb. 7, 2005, the contents of which are incorporated herein by reference in their entirety.TECHNICAL FIELD[0002]This invention relates in general to rotor blades and, more particularly, to rotor blades for propulsive thrust devices in aircraft engines in which the rotor blades can be varied in pitch to control thrust-producing and / or power-absorbing capacities of such devices.BACKGROUND OF THE INVENTION[0003]Standard configurations of rotor blades typically used in aircraft rotary propulsion systems that allow variable pitch operation usually include a root attachment mechanism such as a ball / roller bearing and / or flex member, both of which allow pitch change of the blade with relatively low friction between components. To impart the necessary structural integrity to such mechanisms (e.g., to accommodate the substantial centrifugal for...

AI Technical Summary

Benefits of technology

"The present invention relates to a propulsive thrust device for an engine, which includes a fan or propeller for use in jet aircraft engines or other vertical / short take-off and landing aircraft engines. The device includes a rotor blade with a hub assembly for attachment to a central inner hub. The rotor blade has an airfoil with a first and second support member attached to the hub assembly. The support members can be movable relative to the hub assembly to vary the pitch of the rotor blade. The invention allows for easier control of the thrust-producing and power-absorbing capacity of the propulsive device, and can improve efficiency and responsiveness of the device. The invention also eliminates the need for counterweights and reduces the size and wear of the device. The blade attachment design is especially well-suited for thin, efficient, lightweight composite rotor blades. The invention also calculates the frangibility of the rotor blade to fail under excessive loading, reducing the risk of blade loss and extreme unbalance conditions."

Problems solved by technology

A further complication is that substantial centrifugal loads on the plate-like structures of the blades themselves also produce significant twisting or turning forces that pitch control systems must overcome.

These forces tend to turn the blade towards an undesirable flat pitch position.

In the event that a malfunction of the pitch control system occurs, the forces acting on the blades could turn the blades to the flat pitch position, reducing rotor rotational resistance, thereby resulting in rotor overspeed conditions and potential blade loss.

In other words, in an oblong airfoil having a non-circular, non-symmetrical cross section, the mass about the pitch change axis is not evenly distributed, and centrifugal forces originating from the rotor's axis of revolution and acting on elements of the airfoil cause inertial twisting forces.

However, if there is a malfunction and / or loss of control of the pitch control system (e.g., due to loss of engine power), a rotor blade will naturally turn toward lower pitch.

Because low pitch results in less rotational resistance for the engine, the situation can result in an undesirable overspeed of the rotor and engine.

In extreme conditions in variable pitch systems with no low pitch stop, the TTM can turn the blades to low pitch, and rotor thrust can suddenly switch to a high drag force that can cause possible loss of aircraft control and / or result in rotor overspeed.

In a single engine aircraft, increased drag can limit glide distance for an unplanned landing, while in a twin engine configuration, the asymmetric drag of one disabled propulsor can hinder the ability of the pilot to control the aircraft.

These weights have also been known to be substantial in mass, thereby adding unsprung weight to the rotor blades and further loading the bearings associated with the rotor hub and blade retention mechanisms.

Also, these weights often have associated retention mechanisms or other devices that may be prone to failure under normal operating conditions due to the mechanical stresses encountered.

If a failure is experienced, the high energy of the released mass may result in impact damage as well as high rotor unbalance conditions.

In at least some of these systems, if the pitch of the rotor blades is maintained in a less than optimum position for gliding (in an aircraft having a single engine configuration) or for compromised operation (in an aircraft having a twin engine configuration), increased drag forces may be generated which inhibit the ability of an operator to properly manage the system.

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