Patent Description:
Aircrafts include, as standard equipment, a back-up power source for use in times of power outage in the main power system. This standard equipment has been in the form of a ram air-driven turbine. The back-up equipment is stowed in a storage bay within the fuselage or wing of the aircraft. If/when needed, the back-up equipment can be deployed into the airstream where the passing air relative to the speed of the aircraft causes the turbine blades to rotate.

One example of such back-up equipment is a ram air turbine (RAT). A RAT may generate hydraulic power, electric power, or both. The turbine is coupled to suitable power generating equipment, such as a hydraulic pump for hydraulic power, or an electric generator for electric power, or both in the case of a hybrid RAT.

The RAT storage bay of the aircraft, as well as an access door to the RAT storage bay, are sized to store the ram air turbine and a deployment mechanism for the ram air turbine with only enough space to closely receive the equipment, thereby minimizing wasted space. In most cases, the structural configuration of the storage bay cannot be modified without compromising the structural integrity of the aircraft.

Due to the desire to reduce weight and maximize space, the overall size and particularly the length of newer ram air turbines has been reduced. <CIT> relates to a method and device for reducing structural resonances of a ram air turbine assembly that includes a preferentially located mass that modifies or reduces the magnitude of the resonance frequency to desired levels. The example mass can be fixed in a specific location on the ram air turbine or can be extended as the ram air turbine is moved to a deployed operating position.

According to one embodiment a ram air turbine (RAT) assembly is disclosed. The assembly includes a turbine having at least one turbine blade that rotates about a turbine driveshaft, a lower gear box coupled to the driveshaft, a generator/pump housing and a strut connected between the lower gear box and the generator/pump housing. The assembly also includes a damping element connected to one of the strut and the lower gear box. The damping element includes an actuator including an extendable member and a mass element connected to the extendable member and that can be moved by linear extension by a distance d of the extendable member from a retracted position to an extended position, wherein the mass element is closer to the actuator when in the retracted position than when in the extended position.

In accordance with additional or alternative embodiments, the lower gear box has a housing and the damping element is connected to the housing of the lower gear box.

In accordance with additional or alternative embodiments, the mass element is closer to the housing of the lower gear box when in the retracted position than when in the extended position.

In accordance with additional or alternative embodiments, the damping element is connected to the strut.

In accordance with additional or alternative embodiments, the mass element is closer to the strut when in the retracted position than when in the extended position.

In accordance with additional or alternative embodiments, the assembly further includes: a blade release mechanism and the mass element is caused to be moved from the retracted position to the extended position by the blade release mechanism.

In accordance with additional or alternative embodiments, the mass element is caused to be moved from the retracted position to the extended position due to a solenoid.

In accordance with additional or alternative embodiments, the solenoid is configured to cause the movement after assembly has started to be deployed from a stowed position to a deployed position.

In accordance with additional or alternative embodiments, the mass element is caused to be moved from the retracted position to the extended position due to an electrical signal.

In accordance with additional or alternative embodiments, the electrical signal is provided after assembly has started to be deployed from a stowed position to a deployed position.

Also disclosed is a method of operating an assembly as disclosed above or otherwise herein. The method includes: extending the RAT assembly from a stowed position to a deployed position; and while or after extending the RAT assembly, causing the mass element to move from the retracted position to the extended position.

In accordance with additional or alternative embodiments, in the method the lower gear box has a housing and the damping element is connected to the housing of the lower gear box and wherein the mass element is closer to the housing of the lower gear box when in the retracted position than when in the extended position.

In accordance with additional or alternative embodiments, in the method, the damping element is connected to the strut and wherein the mass element is closer to the strut when in the retracted position than when in the extended position.

In accordance with additional or alternative embodiments, in the method, the assembly further includes a blade release mechanism and wherein the mass element is caused to be moved from the retracted position to the extended position by the blade release mechanism.

In accordance with additional or alternative embodiments, in the method, the mass element is caused to be moved from the retracted position to the extended position due to a solenoid.

It should be understood, however, the following description and drawings are intended to be illustrative and explanatory in nature and non-limiting.

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:.

As discussed above, most cases, the structural configuration of the storage bay cannot be modified without compromising the structural integrity of the aircraft. Further, Due to the desire to reduce weight and maximize space, the overall size and particularly the length of newer ram air turbines (RATs) has been reduced.

Such systems, however, may experience natural oscillation frequencies when deployed. The frequencies can be based on the rotation of the RAT as well as vibration imparted to the RAT from the aircraft.

One approach is design the RAT system such that its natural frequencies are at least <NUM>% away from the RAT turbine operating frequency/speed. One of the major factors in what the RAT system natural frequencies are, is the aircraft stiffness which historically has been difficult for air framers to predict. As a result of these uncertainties there is a significant amount of uncertainty in what the natural frequencies are on the aircraft until late in the design process when the RAT undergoes a modal survey (ping test) installed on the aircraft.

If there is a natural frequency within <NUM>% or less of the RAT operating frequency, it can lead to many negative consequences which the next slide outlines.

The dependency on aircraft stiffness for the RAT system stiffness limits the reuse of the RAT on other programs.

Further, there are currently a limited amount of changes to the design that can be made to modify the natural frequencies. Such changes could include adding material to the RAT or the airframe to damp the system but that can increase size/weight and stress the airframe.

Referring now to <FIG> an exemplary ram air turbine (RAT) assembly <NUM> is illustrated. The assembly <NUM> is included in aircraft <NUM> in use, however, embodiments herein can be directed to just the assembly before it is installed in the aircraft <NUM>. The aircraft <NUM> schematically shown in <FIG> includes an opening or a hatch <NUM> through which the RAT assembly <NUM> moves from a stowed position <NUM> to a deployed position <NUM>.

The RAT assembly <NUM> includes a turbine <NUM> having at least one turbine blade <NUM> that rotates about a turbine driveshaft <NUM>. The turbine driveshaft <NUM> is coupled to a lower gear box <NUM> adjacent a first end <NUM>. In the stowed position, illustrated using phantom lines, the RAT assembly <NUM> is disposed within the aircraft structure <NUM> and the turbine blades <NUM> are fixed in a desired orientation to prevent contact with the surrounding structure. The desired orientation of the turbine blades <NUM> provides for movement of the RAT assembly <NUM> through the opening of the aircraft structure <NUM>.

The RAT assembly <NUM> also includes a strut <NUM> connected at a first end <NUM> to the turbine <NUM> adjacent the lower gear box <NUM>, and coupled at a second, opposite end <NUM> to a generator/pump housing <NUM>. The housing <NUM>, and therefore the strut <NUM> and turbine <NUM>, is supported on the aircraft structure and is configured to rotate about a pivot <NUM> to provide for movement of the RAT assembly <NUM> between the stowed position <NUM> and the deployed position <NUM>. The housing <NUM> supports a mechanical device. In one embodiment the device is a generator (not shown) that is driven by the plurality of turbine blades <NUM>. The example generator is disposed within the housing <NUM>. The turbine blades <NUM> rotate in response to the airstream A along the outside of the aircraft structure <NUM> to drive the generator. As appreciated, although the example RAT assembly <NUM> is disclosed with a generator, the ram air turbine <NUM> could also drive any other device, such as a hydraulic pump for example.

As shown in <FIG>, The RAT assembly <NUM> includes a release lever <NUM> configured to rotate about a pivot <NUM> attached to the housing <NUM>. The RAT assembly <NUM> also includes a turbine release pin <NUM> that engages the turbine driveshaft <NUM> by way of a driveshaft aperture (not shown), such as a hole, indentation, or slot for example. A release cable <NUM> extends from the release lever <NUM> to the turbine release pin <NUM> such that a first end <NUM> of the release cable <NUM> is fastened to the release lever <NUM> and a second, opposite end <NUM> of the release cable <NUM> is coupled to the turbine release pin <NUM>. The release lever <NUM> rotates about pivot <NUM> until engaging a stop <NUM> during deployment of the RAT assembly <NUM>.

Movement of the RAT assembly <NUM> to a deployed position includes movement of the housing <NUM> about the pivot <NUM>. The movement of the housing <NUM> about pivot <NUM> causes a corresponding movement of the release lever <NUM>. During deployment of the RAT assembly <NUM>, the release lever <NUM> will rotate about pivot <NUM> until it contacts the stop. Further rotation of RAT assembly <NUM> once the release lever <NUM> engages the stop will cause the release cable <NUM> to apply a force to the turbine release pin <NUM>. The release cable <NUM> has such a length that it will pull the turbine release pin <NUM> from the driveshaft aperture once the housing <NUM> has moved past a partially deployed position, thereby unlocking the turbine driveshaft <NUM>. Removal of the turbine release pin <NUM> allows the turbine driveshaft <NUM> to rotate freely, and the turbine <NUM> to operate as intended to generate power.

As shown in both <FIG> and <FIG>, the RAT assembly <NUM> also includes a damping element <NUM>. This damping element <NUM> is provided, as more fully described below, to change the modal frequencies of the RAT assembly <NUM>. The damping element <NUM> can be positioned on the lower gear box <NUM> and, in particular, on a housing <NUM> of the lower gear box <NUM>. The damping element <NUM> could be place on other locations, however.

Alternatively, and as shown in <FIG>, the damping element <NUM> can be connected to the strut.

With additional reference now to <FIG>, the damping element <NUM> includes an actuator <NUM> that can be used to move a mass element <NUM> from a retracted position (<FIG>) to an extended position (<FIG>). The actuator <NUM> includes an extendable member <NUM>.

The extendable member <NUM> can be a shaft in one embodiment. In particular, the extendable member <NUM> can be either a rigid or telescoping shaft.

The actuator <NUM> can be any type of actuator. In one embodiment the actuator <NUM> can be a spring-loaded actuator.

Activation of the actuator <NUM> is discussed further below. It has been discovered by the inventors herein that placing a mass (e.g., mass element302) aft of the gearbox can cause the RAT natural frequencies drastically change. That is, when the extendable member <NUM>/ mass element302 are in the extended position extended, the RAT natural frequencies are different than when in the retracted position. The amount of change in RAT natural frequencies can be adjusted by the weight of the movable element <NUM> being extended away from the gear box <NUM>/housing <NUM>. Further, the distance (d) (see <FIG>) the mass element <NUM> is extended by the movable element <NUM> can also adjust the natural frequencies.

Based on the disclosure herein it shall be understood, therefore, that the mass of the mass element302 and distance (d) the mass element302 is away from the gearbox <NUM> can be easily adjusted after the aircraft ping test is performed with limited cost to the development of the RAT assembly <NUM>. Note, even if the RAT assembly <NUM> is changed this should not require returning to the high-speed wind tunnel because the purpose of the high-speed wind tunnel is not to validate the RAT structure due to loads experienced on the aircraft. Further, by employing the disclosed damping element <NUM>, a single RAT assembly design can be used on different aircraft without having to redesign the assembly <NUM>; the changes could be limited to variation in the mass of the mass element302 and distance (d) to achieve the desired minimum <NUM>% difference between the RAT operating frequency and the natural frequency of the RAT assembly <NUM> when on an aircraft.

Further, in one embodiment, the actuator <NUM> can be either automatically or manually retractable so that the size of the damping element <NUM> can be minimize so as not to exceed the required envelope of the RAT assembly <NUM> when in the stowed position.

The damping element <NUM> can be causes to extend from the retracted position to the extended position after movement of the RAT assembly <NUM> from a stowed to a deployed position has begun. Examples include having the extension begin after the housing <NUM> of RAT assembly <NUM> beings move about the pivot <NUM> or after it has cleared the doors <NUM>. In one embodiment, the damping element <NUM> is signaled to activate and deploy/extend the mass element <NUM> when the RAT has been fully deployed.

In one or more embodiments, activation of the actuator mass can be, and by way of example only, via solenoid <NUM>, or an electrical signal due to information from a sensor <NUM> or via the blade release mechanism <NUM> or a combination thereon.

As shown in <FIG>, the damping element <NUM> can alternatively be located on the strut <NUM> and operates in the same or similar as described above.

Claim 1:
A ram air turbine, RAT, assembly (<NUM>), comprising:
a turbine (<NUM>) having at least one turbine blade (<NUM>) that rotates about a turbine driveshaft (<NUM>);
a lower gear box (<NUM>) coupled to the driveshaft;
a generator/pump housing (<NUM>);
a strut (<NUM>) connected between the lower gear box and the generator/pump housing; and
a damping element (<NUM>) connected to one of the strut and the lower gear box, the damping element including:
an actuator (<NUM>) including an extendable member (<NUM>); and
a mass element (<NUM>) connected to the extendable member and that can be moved by linear extension by a distance (d) of the extendable member from a retracted position to an extended position, wherein the mass element is closer to the actuator when in the retracted position than when in the extended position.