Grounding for fan blades on an underblade spacer

A fan rotor includes a rotor body with at least one slot receiving a fan blade. The fan blade has an outer surface, at least at some areas, formed of a first material and an airfoil extending from a dovetail. The dovetail is received in the slot. A spacer is positioned radially inwardly of the dovetail biasing the fan blade against the slot. The spacer includes a grounding element, which is in contact with a portion of the dovetail formed of a second material that is more electrically conductive than the first material. The grounding element is in contact with a rotating element that rotates with the rotor. The rotating element is formed of a third material. The first material is less electrically conductive than the third material. The grounding and rotating elements form a ground path from the portion of the dovetail into the rotor.

BACKGROUND OF THE INVENTION

This application relates to a structure for electrically grounding fan blades for use in a gas turbine engine.

Gas turbine engines are known, and typically include a fan delivering air into a compressor section. In the compressor section, the air is compressed and then delivered into a combustion section. The compressed air is mixed with fuel and burned in the combustion section. Products of this combustion pass downstream to drive turbine rotors.

The fan blades are subject to a large volume of air moving across an airfoil. This can build up a large static electric charge. Conventionally, the fan blades were formed of a conductive metal that was grounded to a hub that mounts the fan blade. As such, the charge would dissipate.

More recently, fan blades have become larger. One factor allowing the larger fan blades is the use of a gear reduction between a turbine driven spool, which drives the fan blade, and the spool. The gear reduction allows a single turbine rotor to drive both a compressor section and the fan, but at different speeds.

As the size of the fan blade has increased, its weight has also increased. As such, efforts have been made to reduce the weight of fan blades. One modification is to change the material for the fan blade from titanium to aluminum. The aluminum fan blades have been covered with a polyurethane coating and fabric wear pads to protect the aluminum. These materials have insulation qualities and, thus, the blade may not be electrically grounded to a rotor.

SUMMARY OF THE INVENTION

In a featured embodiment, a fan rotor for use in a gas turbine engine has a rotor body with at least one slot receiving a fan blade. The fan blade has an outer surface, at least at some areas, formed of a first material and an airfoil extending from a dovetail. The dovetail is received in the slot. A spacer is positioned radially inwardly of a radially inner face of the dovetail, and biases the fan blade against the slot. The spacer includes a grounding element. The grounding element is in contact with a portion of the dovetail formed of a second material that is more electrically conductive than the first material. The grounding element is in contact with a rotating element that rotates with the rotor. The rotating element is formed of a third material. The first material is less electrically conductive than the third material. The grounding element and rotating element together form a ground path from the portion of the dovetail into the rotor.

In another embodiment according to the previous embodiment, the first material includes an outer coating that is relatively non-conductive compared to the second and third materials.

In another embodiment according to any of the previous embodiments, the radially inner portion of the dovetail is not provided with the outer coating and is the portion of the dovetail.

In another embodiment according to any of the previous embodiments, the second material is aluminum, and the third material includes titanium.

In another embodiment according to any of the previous embodiments, the grounding element is formed of a material that is more electrically conductive than the first material.

In another embodiment according to any of the previous embodiments, the grounding element is formed of a metal fabric.

In another embodiment according to any of the previous embodiments, the grounding element is formed of a silver-plated aluminum metal fabric.

In another embodiment according to any of the previous embodiments, the rotating element is separate from the rotor.

In another embodiment according to any of the previous embodiments, the rotating element is a lock ring which secures the fan blade within the rotor. The grounding element contacts the lock ring, which contacts the rotor to provide the grounding path.

In another embodiment according to any of the previous embodiments, the spacer is bowed such that it biases the dovetail against surfaces of the slot. The grounding element is provided on a radially outer portion of the grounding element.

In another featured embodiment, a gas turbine engine has a fan section, a compressor section, a combustor section, and at least one turbine rotor. The at least one turbine rotor drives a compressor rotor. The at least one turbine rotor also drives a fan rotor of the fan section through a gear reduction. The fan blade has an outer surface, at least at some areas, formed of a first material and has an airfoil extending from a dovetail, which is received in the slot. A spacer is positioned radially inwardly of a radially inner face of the dovetail, and biases the fan blade against the slot. The spacer includes a grounding element. The grounding element is in contact with a portion of the dovetail formed of a second material that is more electrically conductive than the first material. The grounding element is in contact with a rotating element that rotates with the rotor. The rotating element is formed of a third material. The first material is less electrically conductive than the third material. The grounding element and rotating element together form a ground path from the portion of the dovetail into the rotor.

In another embodiment according to the previous embodiment, the first material includes an outer coating that is relatively non-conductive compared to the second and third materials.

In another embodiment according to any of the previous embodiments, the radially inner portion of the dovetail is not provided with the outer coating and is the portion of the dovetail.

In another embodiment according to any of the previous embodiments, the second material is aluminum, and the third material includes titanium.

In another embodiment according to any of the previous embodiments, the grounding element is formed of a material that is more electrically conductive than the first material.

In another embodiment according to any of the previous embodiments, the grounding element is formed of a metal fabric.

In another embodiment according to any of the previous embodiments, the grounding element is formed of a silver-plated aluminum metal fabric.

In another embodiment according to any of the previous embodiments, the rotating element is separate from the rotor.

In another embodiment according to any of the previous embodiments, the rotating element is a lock ring that secures the fan blade within the rotor. The grounding element contacts the lock ring, which contacts the rotor to provide the grounding path.

In another embodiment according to any of the previous embodiments, the spacer is bowed such that it biases the dovetail against surfaces of the slot. The grounding element is provided on a radially outer portion of the grounding element.

In another featured embodiment, a grounding element is to be associated with a spacer, and to ground a blade to a rotor receiving the blade. The grounding element has a top surface to provide a contact point with a blade, and an inner area to be positioned inward of the spacer when the grounding element is received on a spacer.

In another embodiment according to the previous embodiment, the grounding element is formed of a metal fabric grounding material.

These and other features of the invention will be better understood from the following specifications and drawings, the following of which is a brief description.

DETAILED DESCRIPTION

The core airflow is compressed by the low pressure compressor44then the high pressure compressor52, mixed and burned with fuel in the combustor56, then expanded over the high pressure turbine54and low pressure turbine46. The mid-turbine frame57includes airfoils59which are in the core airflow path. The turbines46,54rotationally drive the respective low speed spool30and high speed spool32in response to the expansion.

A fan blade120is illustrated inFIG. 1Bhaving an airfoil118extending radially outwardly from a dovetail or root124. A leading edge121and a trailing edge122define the forward and rear limits of the airfoil118. Fan blade120may be used in an engine such as engine20.

As shown inFIG. 1C, a fan rotor116receives the dovetail124in a slot210to mount the fan blade120with the airfoil118extending radially outwardly. As the rotor is driven to rotate, it carries the fan blade120with it.

A lock ring100locks the blades120within the rotor116and rotates with the rotor116.

As mentioned above, the lock ring100and rotor116may be formed of titanium or a titanium alloy, while the blade120may be formed of aluminum, but coated with a non-conductive coating, such as polyurethane coating125(seeFIG. 3), or including fabric pads. As such, the fan blade120is not grounded.

As can be seen inFIG. 1C, a resilient spacer200holds the dovetail120against the groove210. A conductive element202contacts the lock ring100.

As shown inFIG. 2, the conductive element202has a forward contact face132which will contact the lock ring100.FIG. 3shows the lock ring100in contact with the forward face132. The spacer200has a curved or bowed shape, as shown inFIG. 3, along an axis of rotation of the rotor. Thus, a radially inner surface220is spaced away from a bottom300of the slot210.

When the dovetail124is moved into the slot210, it forces the spacer away from a free position, such that it is less bowed. Thus, there is a bias force from the spacer200holding the blade in contact with the walls of the slot210. The grounding element202is associated with the spacer200. The blade is provided with the coating125at locations other than a bottom surface222. Bottom surface222is generally uncoated, and thus a contact point224from the conductive element provides an electrical connection from the blade120through a top surface225the conductive element202, and into the lock ring100.

An inner area226is radially inward of the spacer200.

In embodiments, the conductive element may be formed of a metal fabric grounding material. Appropriate materials may be EMI shielded conductive elastomers, such as those available under the trademarks CHO-SEAL® or CHO-SIL® from Chomerics. Of course, other materials may be utilized. A silver-plated aluminum fabric material available as CHO-SEAL1298 is presently preferred; however, any number of other conductive materials may be utilized.

Locating the grounding element radially inward and at the platform provides a surface which is more protected from the elements then if the contact were more radially outward. As can be appreciated, the lock ring100contacts the rotor116. The lock ring100also contacts the grounding element202at forward face132, and provides an electrical connection through contact portion224. Bottom surface222of the dovetail124is the underlying aluminum substrate, and thus provides a good conductive surface such that static electricity may be drained from the fan blade120, and to the rotor116. The location of the contact is such that it is generally protected from the elements such that there is unlikely to be corrosion at the connection.

As can be appreciated, the coating material125is less electrically conducive than the aluminum at surface222, or the lock ring100.

While the disclosed embodiment provides contact between the grounding element202and the lock ring100, it is also possible to have the grounding element contact the rotor116directly.