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Open Rotor Engines Advanced Technologies II

Final Report Summary - OREAT II (Open Rotor Engines Advanced Technologies II)

Executive Summary:
Environmental considerations defined by Clean Sky objectives such as reduced aviation carbon footprint, reduction of nitrogen emissions and noise, demand significant fuel burn reduction over current state of the art aviation propulsion systems. An Open Rotor propulsion system has higher propulsive efficiency than the current technology by virtue of its much higher By-Pass Ratio (BPR), a major contributor in achieving significant fuel burn savings. In order to maintain each propeller in a contra-rotating propeller at its correct and efficient operating point, its blade pitch must be controlled to absorb the supplied power and achieve the required rotational speed. The most effective systems in use today have independent hydraulically actuated pitch-change mechanisms (PCM) driven by a single turbo-propeller engine through a differential epicyclical gearbox. A Counter Rotating Open Rotor (CROR) in a Pusher configuration, such as the SAGE2, adds additional elements of technical difficulty i.e. blades that are situated at large diameters, severe thermal conditions and extreme loads. A novel pitch control mechanism is required for actuation and control of the blade pitch of an Open Rotor engine. Furthermore, robust and accurate PCM control system is crucial for exact control of the blade pitch and thus for frictionless operation of CROR engine. This project was aimed to address PCM technology maturation and development challenges required for reliable Pitch Change Mechanism operation in SAGE2 Counter Rotating Open Rotor engine.
Two main deliverables were foreseen as part of this program:
1. A preliminary design of the forward and aft pitch change mechanisms for the SAGE2 Open Rotor
2. A pitch change mechanism architecture with a Technology Readiness Level of 5
Both of these objectives were successfully met within this program. The first was through the delivery of both 3D models and successful completion of Preliminary Design Reviews for both FWD and AFT PCMs with the Topic Leader. The novel designs were able to meet all of the difficult integrational and functional requirements.
The second, and much more involved subject, was to ensure that the main PCM architecture was verified in a laboratory environment. In support of this point, a new test facility was developed to perform full scale system integration testing of a PCM. The testing was successfully carried out with the Topic Leader in the first quarter of 2016. The testing was broken down into two main areas; verification of PCM characteristics and endurance testing. Several key conclusions were made regarding the PCM as part of this testing:
• on the whole modelling of PCM characteristics was validated
• the PCM architecture did not undergo any unforeseen failure or wear as a result of the test campaign
• several novel solutions (lubrication and kinematics) worked successfully
The overall conclusion is that the PCM architecture that was tested as part of the OREAT II project could be used for the SAGE2 GTD testing.

Project Context and Objectives:
3.2 Summary description of project context and objectives
The OREAT II (Open Rotor Engines Advanced Technologies) program, a follow-up to OREAT I, whose main goal was to mature Open Rotor PCM concepts, defined in the latter. The OREAT Consortium was made up of three different partners; General Electric Company Polska (GECP), General Electric Aviation Systems (GEAS) and the Institute of Aviation in Warsaw (WIA). The project started in December 2011 and lasted 52 months, finishing in March of 2016.

3.2.1 Background

Open Rotor blade pitch change mechanisms add a great deal of unavoidable dynamic mechanical complexity to aircraft propulsion systems, particularly with pusher-configuration engines. It will be one of the greatest challenges to the eventual introduction of the undoubted open rotor efficiency benefits into commercial aviation to overcome the unreliability burden that comes with this complexity, particularly in the especially difficult environment of the pusher configuration.
During the OREAT I Program, several Key Technologies were identified for comprehensive testing to assess and improve their reliability and durability in the PCM and Open Rotor environment.

3.2.2 Objectives

The program of design, testing and dynamic modelling was to have a strong positive impact on the verification of component reliability, durability and system interaction which would then lead to a reduced risk for the SAGE2 program as a whole. Specifically the full scale testing of the main PCM architecture was to provide a very good insight into high risk areas such as:
• Assembly
• Balancing of a rotating structure with translating features
• Large diameter actuation and sealing capability
• Complex PCM kinematics
• Hydro-mechanical system interaction
• Durability of components in an Open Rotor environment
Project Results:
3.3 Description of main S&T results/foregrounds
Based on the first objective of providing preliminary FWD and AFT PCM designs, two unique approaches were taken for the SAGE2 GTD. The FWD PCM design was based on the principles of minimizing complexity by having a minimum part count and relying on mature standard components. The design was prepared so that it would not vary greatly from that which was already conceived as part the System Integration testing being planned (Modular Test Bench) in Warsaw.
The main PCM architecture that was created for the GTD was based on the following concept (US Patent 20140294585; EP2763893A1):
• Single static annular actuator
• Load Transfer Bearing
• Multiple Crank Rods

Figure 1: Forward Pitch Change Mechanism
For the AFT PCM, two key factors drove the design that was developed within OREAT II; specific technical requirements and a need to test to differentiate the PCM architectures. As such, the AFT PCM resulted in a design that varied greatly from that of the FWD design. Ultimately, to reduce overall SAGE2 risk a decision was made by the Topic Leader to unify the design of the two PCMs and base both on the design of the FWD PCM.
The second objective necessitated the design and construction of a new test facility located at the Institute of Aviation in Warsaw. The test facility, built from the ground, included the following:
• a hydraulics system with separate low and high pressure and temperature configurations
• a test cell room with a modular test plate
• an electric drive system
• a control and data acquisition system
• full instrumentation of the facility and test article
The test vehicle itself, known as the Modular Test Bench, is a full-scale rotating test bench capable of testing PCMs under CTM (Centrifugal Twisting Moment) loads. The test facility allowed for the validation of the integration of the PCM control system (Topic Leader) with the PCM (OREAT) itself.

Figure 2: Modular Test Bench used for System Integration Testing in Warsaw

Key findings, for the PCM, from the testing were as follows:
• the PCM architecture did not undergo any unforeseen failure or wear as a result of the test campaign – see Figure 3.
• several novel solutions (lubrication and kinematics) worked successfully
• on the whole analytical modelling of the PCM was validated

Figure 3: Piston surface following test campaign

Potential Impact:
3.4 Potential impact and main dissemination activities and exploitation results
3.4.1 Potential Impact

With the undeniable performance gain of a variable pitch blade (whether it be a fan blade or propeller), pitch change mechanisms will be part of engine architectures in the near future. Thus it is of utmost importance to begin the task of realizing a PCM configuration that will be robust enough to survive the harsh environment of the Open Rotor. A substantial amount of work was done in the 1980s to this point but with the change in oil prices all momentum was lost. The new Clean Sky initiative has once again allowed aerospace companies to explore this challenging design space.
With this in mind, a new PCM configuration has been proposed and validated to TRL 5 within this program. This should allow the Topic Leader to lead a successful SAGE2 GTD testing campaign in 2016.

3.4.2 Main dissemination activities and exploitation results
The project developed the following type of results:
• Knowledge and capabilities in the form of large actuator design, lubrication design and kinematic and dynamic modelling
• Data from test campaign
The data from this project will not be disseminated outside of the project group and thus has a dissemination level of Confidential (CO).

List of Websites:
The public program website address is not applicable.