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Design, development and flight qualification of a supercritical composite shaft drive line for tiltrotor main drive system

Periodic Reporting for period 3 - STEADIEST (Design, development and flight qualification of a supercritical composite shaft drive line for tiltrotor main drive system)

Reporting period: 2021-08-01 to 2022-09-30

In the framework of H2020 Compound Fast Rotorcraft, we will treat technical issues on efficiency, reliability and safety
The goal is to develop supercritical and flexible composite shaft and address vibratory issues. We propose to develop a suited damping device
Manufacturing reliable innovative composite shaft requires breakthrough technologies and processes
Due to both composite material and reduction of components quantity, use of long supercritical shaft, we will reduce direct maintenance costs and weight on aircraft then improving flight’s efficiency and CO2 savings

In this context, the goal of STEADIEST (Supercritical composiTE mAin DrIvE SysTem) is to develop, demonstrate a concept of supercritical composite shaft drive line with high level of technical performances uptodate technical functionalities and costs optimization.

Besides composite shafts and flexible coupling will improve high deformation capability of the system.
Thus, key objectives of the project are development and tests:
- of supercritical composite drive shaft + flexible coupling regarding issues of innovative composite manufacturing process and metallic flexible parts
- of damping system : regarding supercritical drive line dynamic stability issue
- of monitoring device able to detect changes or damages in the drive line behavior to improve reliability, safety and maintainability

The project demonstrated the feasability of full composite transmission shaft as foreseen, however it still remains some pain points and uncertainties to remove.
WP1 Supercritical composite drive line
- Material analysis - regarding perfomances, reliability, safety procurement of whole mechanical sub-systems
- Detailed static &fatigue analysis of all parts in accordance with TM methodologies
- interfaces characterisation to consolidate vibratory behavior and manufacturing feasability
- Analytical and numerical vibratory analysis of shafts + couplings
- Global Vibratory behavior: state of the art in mechanical vibration of rotor, key parameters have been defined. Single shaft numerical model with flanges has been correlated with theoretical model to further develop a model for the whole drive line
- Design of several architectures and trade off (subcritical shaft, reference reduction…)
- Interface parts definition with aircraft and gearbox
- Space allocation validations and DMU update
- analysis of reused sub-systems coming from TM and design adaptation to be compliant with these ones
- detailed definition from DMU to drawings of items, design update according to interface or test rig limitations
- protections analysis, fixations and assembling to reduce weight balance
- Interface drawings with additional notes according to TM requirements
- detailed nomenclature with description of specification and processes
- Study of curvic definition

WP2 Damping system passive study
- State of the art, pros and cons analysis
- Architecture assessment in accordance with integration constraints
- Alternatives experimental definition for passive damper characterization
- 3D mock-up, detailed drawings
- Prototypes manufacturing

Semi-active study is achieved for damper and still ongoing for bearing implementation
- State of the art, pros and cons analysis
- Proposal for frequencies issues
- Implementation of damping bushes to modify properties of ICDS

WP3 Full drive Line Qualification Tests
- Specimens Definition, configuration and instrumentation
- Statics and fatigue tests definition, implementation, update according test rig limitation
- Implementation of thermal boxes
- Test rig update to allow higher torsional angles to assembly new shafts interface
- Vibratory test program definition

WP4 SHM system
- SHM Specification and Work Plan (SHMSWP)
- SHM architecture in accordance requirements
- Industrial analysis with offer to implement on NGCTR

WP5 Composite drive line manufacturing
- Manufacturing of simplified flanges, friction bush and composite shafts
- Manufacturing of toolings and adaptor with curvic teeths
- Assembling on representative shafts for fatigue test
- NDT analysis, definition of control methodology, criteria
- Balancing and painting of composite shafts
- Manufacturing of test rig damper including piezoelectrical sensors for characterization
- damper manufacturing and surface treatment

WP6 Project Management
monitoring project, inputs and parameters. Monthly meeting with all stakeholders
Management of recovery planning and unforseen events in accordance with remaining milestone and project ending.

WP7 Communication, dissemination, exploitation
Plan have been updated

Overview of the results:

+ AS4-8552 composite is now well known by partners
+ Items 25% lighter than metallic assembly
+ Items 25% less expensive than metallic solution
+ Frequencies positioning can be 60% higher than metallic definition
+ No proof of instability with composite shafts
+ Torsional performances at least equal to metallic technologies
- Some requirements not fully demonstrated

Exploitation and dissemination:

The project’s results will be used by the partners through innovative products, services or consultancy activities. Though, the exploitation of the project’s results is of importance. The project, allowed the identification of market opportunities and contributes to the assessment of future projects to improve the technology. The project allowed to improve expertise of the consortium in the development of transmission shaft for rotorcrafts, both in theoretical and experimental approach in several fileds.

Communication and dissemination activities allowed to increase our exposure as potential innovative partners and to identify new research project for the development of composite transmission shaft for helicopter.
This project is an opportunity to scientific contributions, unbalance excitement is supercritical shaft major criteria regarding first mode stability, theoretical and experimental analysis shall be conducted to minimise residual unbalance and control vibration coming from them

Expected results: Understand and quantify the unbalance origins on a composite shaft and define residual unbalance of our architecture proposal and finally regarding their incidence on both ICDS and aircraft to check theoretical analysis. we will have to reproduce initial/residual unbalance experimentally and carry out dynamic test. Several indicators will be monitored in both high and low residual unbalance grade:
-Unbalance impact on composite tube and coupling bending (fatigue lifetime)
-When crossing natural frequency
-During nominal rotation
-Unbalance load path from rotating shafts to bearing support fixation
-Vibratory amplitude coming from shaft unbalance on aircraft crew

Potential impacts: This study has positive impact on both development and production phase of general rotating system. Currently most of rotating shaft unbalance are defined with empiric approach and residual value are not calculated for each product depending on these operating conditions. The costs are high to verify stability of unbalance criteria by experimentation when analytical and numerical models could consolidate it. This project will generate activities and decrease by quite 5% recurrent cost of supercritical shaft and total weight of drive system that will allow weight saving on aircraft and be greener