EU research results


English EN
NTN-SNR Proposal for Propellers Blades Bearings Design and Manufacturing

NTN-SNR Proposal for Propellers Blades Bearings Design and Manufacturing

Periodic Report Summary 2 - SNRPBBEARING (NTN-SNR Proposal for Propellers Blades Bearings Design and Manufacturing)

Project Context and Objectives:
The SNRPBBearing project, led by NTN-SNR, is a SAGE 2 Integrated Technology Demonstrator from the Clean Sky programme. The goal of this project is to design, manufacture and test the propeller blade bearings for the upstream and downstream propellers of SAGE 2 Open Rotor.
The Upstream Propeller module consists of 12 propeller blades and the Downstream Propeller module consists of 10 propeller blades. The propeller blades of the two rotors are attached to polygonal rings and are orientated at various angles by the two independent Pitch Control Mechanisms.
The propeller blade bearings ensure the transfer of aerodynamic and centrifugal loads to the respective polygonal rings while allowing the pitch change of the blades.
The main functions of these bearings are to:
• allow oscillatory rotation between the polygonal ring and the propeller blade shaft;
• transmit the centrifugal and aerodynamic loads from the propeller blade to the polygonal ring;
• be resistant to the environment;
• ensure the stiffness between the propeller blade root and the polygonal ring;
• resist the load caused by the loss of a propeller blade (twice the maximum centrifugal load).
The objectives of the project were to:
• design the two bearings for each propeller;
• define the mitigation plan to reach TRL5;
• complete the mitigation plan and especially the development tests;
• successfully pass the validation test;
• manufacture the bearings for the two propellers;
• deliver 26 bearings to the Topic Manager.
At the end of the project, all the objectives have been achieved. All the tests were performed successfully and the bearings were delivered to the Topic Manager.

Project Results:
The four main bearing's specific requirements for this innovative application were:
- Criteria 1: High level of loads (especially centrifugal force) with +15% compared to the current application
- Criteria 2: Large temperature range and high level of maximum temperature (-55°C to 180°C): twice higher than current application
- Criteria 3: Smaller allocated room to design the solution than existing one
- Criteria 4: The sealing device has to be inserted in the new propeller blade bearing contrary to the current design.

To meet the specification requirements, various innovative works were conducted and different solutions were studied, namely to:
A) design a new bearing architecture addressing criteria 1, 2, 3 and partially 4
B) improve the bearing material properties using new materials which address criteria 1, 2 and 3.
C) develop a new complex tribological system in order to minimise the friction torque and avoid any raceway wear (criteria 1 and 2)
D) develop an innovative sealing system answering to criteria 4.

During the first period, NTN-SNR has worked on several points regarding technical activities: bearing architecture development, choice of the type of bearing: ball or roller bearing, Research topics concerning material, lubricant, sealing. NTN-SNR proposed four architectures of bearing and performed finite element calculation to evaluate the impact of the stiffness of Topic Manager’s parts in contact with the bearings. The best bearing architecture was selected. The research studies concerning material, sealing and tribological system were launched.
At the end of the first period, the Preliminary Design Review (PDR) was passed with success. The bearing development plan was established and thus approved by the Topic Manager.

A) Bearing architecture
During the second reporting period, NTN-SNR ended the design of the bearing. NTN-SNR performed a new global finite element with thermal study to validate the impact of the modifications of Topic Manager’s parts on the bearing. The bearing design was frozen and the Critical Design Review was successfully passed, the drawings of the bearings were done and the manufacturing process review was issued.

B) Material studies
NTN ended the studies on the bearing material properties using new materials able to address criteria 1 and 3.

C) Tribological system selection
NTN-SNR has developed a complex tribological system to allow for good bearing lubrication.
This selection was divided into three steps. Only the two last steps were studied during the second reporting period:
2) Tribological solution definition
The target of this step was to select the three best solutions regarding the global tribological behavior using the four best greases and the best surface treatment. Many series of tests of all the identified solutions for each component which composed the tribological system were performed separately. The 3 best tribological systems were selected regarding laboratory test results.

3) Validation of the selected solutions
The “False Brinelling Effect” of these 3 solutions were compared with the solution of reference used on the current application for the test at room and low temperature. However, the high temperature tests were performed to validate the good behaviour of the solutions at 180°C, where the reference is not valid.
Thanks to all these tests, NTN-SNR defined a complex tribological system which has the same performance as the propeller blade root “in service” solution in an environment respecting the requirements criteria.

D) Sealing device
Intensive work has also been done to design complex sealing devices to avoid the leakage of lubricant outside of the bearing and the penetration of pollution inside the bearing. The bearing sealing system is composed of two seals: the upper seal and the lower seal.
The detailed study of sealing was done with a NTN-SNR supplier. The Finite Element calculations were performed on the seal.
Due to the high level of risk, a sealing validation plan was performed. It consists of six additional tests:
1) material compatibility tests
2) “Raffer test”
3) adhesive test
4) dismounting test
5) starting torque measurement on seal
6) starting torque measurement on standard representative bearing.

Potential Impact:
After the completion of the four innovative works, the bearings were manufactured. After that, the prototype bearings were validated:
- for criteria 1, 2 (partially) and 3, the good behaviour of the bearing under load was validated with tests on ball bearing on a compression/torsion test machine. The two bearings successfully passed the limit and ultimate load tests. And the torque under load is two times lower than the Topic Manager’s torque requirements included in the course of the project. The two bearings will allow:
o good behaviour of the engine, allowing oscillatory rotation between the polygonal ring and the propeller blade shaft, transmitting centrifugal and aerodynamic loads from the propeller blade to the polygonal ring, ensuring the stiffness between the propeller blade root and the polygonal ring
o safe working of the engine, avoiding the loss of propeller blade.
The results of these representative tests were compared with the starting tests done on the prototype bearing. These two tests used the same level of starting torque, around 50Nm.

- For criteria 4, due to the lack of test bench availability, the relevant sealing test was not performed on the whole prototype. This criterion is only validated by the “Raffer” tests performed on the seals.
The project developed and thoroughly tested the bearing prototypes up to TRL5. As a result, 26 bearings for the two SAGE 2 demonstrator propellers with the substantiation documents have been delivered to the Topic Manager.

In conclusion, NTN-SNR has developed during this project:
- a new compact self-lubricated architecture of bearing
- a new complex tribological system to allow a good lubrication of bearing under extreme conditions (centrifugation loads and high temperatures)
- a new sealing device compliant with high fatigue safety margin.
All these innovations will be definitely validated on SAGE 2 ground test demonstrator, especially for the vibration and life duration of the bearing.

Project information

Grant agreement ID: 326023


Closed project

  • Start date

    4 February 2013

  • End date

    3 December 2015

Funded under:


  • Overall budget:

    € 1 497 817,60

  • EU contribution

    € 748 908,80

Coordinated by: