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

Reporting period: 2020-05-01 to 2021-07-31

In the overall innovative project H2020 Compound Fast Rotorcraft, we aim to answer to technical issues on efficiency, reliability and safety
The goal is to develop supercritical and flexible composite shaft that lead to vibratory issues. We propose to solve by developing a suited damping device (passive, semi-active or active concept)
Manufacturing reliable innovative composite shaft requires breakthrough technologies and processes

Due to both composite material and reduction of components quantity, thanks to 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 (low weight, improved dynamic behavior), uptodate technical functionalities (monitoring device, damping system) and costs optimization (reduction of references and design to cost approach). These are key factors to be competitive, safe and reliable
Additionally, using composite shafts with flexible coupling will improve the capability of drive line system to support high deformation of fuselage
Thus, the specific and concrete objectives of the project will be the following
- design, development and tests of supercritical composite drive shaft and flexible coupling: regarding issues of innovative composite manufacturing process and manufacturing of metallic flexible parts
- design, development and tests of damping system : regarding dynamic stability issue of supercritical drive line
- design, development and tests of monitoring device able to detect changes or damages in the drive line’s behavior : regarding improvement of reliability and safety drive line and friendly maintainability
WP 1 Supercritical composite drive line
- Material analysis - technical/operational regarding perfomances, reliability, safety procurement of whole mechanical sub-systems in accordance with PDR justification
- Detailed static & fatigue analysis of composite shaft, and all parts in accordance with PDR justification and TM methodologies
-> Composite shafts mock-up to characterize interfaces, to consolidate vibratory behavior and manufacturing feasability
- Analytical and detailed numerical vibratory analysis of shafts with or without couplings in accordance with PDR design
-> Detailed global Vibratory behavior : After state of the art in mechanical vibration of rotor, theoretical behavior and key parameters have been defined. Numerical model of single shaft with flanges has been created and correlated with theoretical model in order to further develop a model for the whole drive line to define the global vibratory behavior
- Design of several drive line architectures and trade off opportunities (subcritical shaft, reference reduction…)
- Definition of interface parts with aircraft and gearbox technical opportunity with Titanium welded adaptor on coupling
- Space allocation validations loop ,which lead to ICDS DMU update
- Detailed analysis of reused sub-systems coming from TM and design adaptation to be compliant with these ones
- Detailed definition, from digital mock-up to drawings, of ICDS items to manufacture
- Detailed analysis of protections, fixations and assembling to reduce weight balance

WP 2 Definition of damping system
Passive study
- State of the art
- Pros and cons analysis regarding current technologies
- Architecture assessment in accordance with integration constraints
- Alternatives experimental definition for passive damper characterization
- 3D mock-up
- 2D interfaces drawings
- Prototypes manufacturing review

Semi-active study is achieved for damper and still going for bearing implementation
- State of the art
- Pros and cons analysis regarding current technologies
- Proposal for both frequencies settings and instability issues

WP3 Full drive Line Qualification Tests
- Definition of experimental specimens, configuration and instrumentation (static, vibratory, fatigue test)
- Definition of statics and fatigue tests conditions and implementation
- Preliminary definition of vibratory tests

WP 4 Structural Health Monitoring system
- Definition of SHM System Specification and Work Plan (SHMSWP) as global guideline
- Definition of SHM architecture. Sensors compatibilities are in accordance with TM and regulations requirements

WP 5 Supercritical composite drive line manufacturing
- Procurement of raw material for demonstrative, qualification and partially parts of flight clearance delivery
- Manufacturing of flanges, friction bush and composite shafts for demonstrative, qualification and flight clearance prototypes
- Assembling with demonstrative and consolidate process on representative shafts for fatigue experimentation
- NDT process analysis : definition of control methodology, mean of measurement, criteria and results to demonstrate
- Manufacturing of passive and semi-active damper, including alternatives parts and piezoelectrical sensors for experimental characterization

WP 6 Project Management and deliverables follow-up
Implementation of an efficient monitoring - through a general dashboard which includes all project inputs and parameters. Monthly meeting have been held involving all stakeholders

WP 7 Communication, dissemination and exploitation
Dissemination and communication Plan have been updated regarding current recovery plan and technical objectives from experimental tests
The opportunities provided by this project is of interest for the DGAC and will be eligible to complementary R&D project on mechanical drive line for helicopter
This project is an opportunity to scientific contributions as far as 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 until the end of the project : First result will be to theoretically understand and quantify the unbalance origins on a composite shaft then to define residual unbalance of our architecture proposal and finally regarding their incidence on both ICDS and aircraft to verify: theoretical analysis, we will have to reproduce initial/residual unbalance experimentally and to 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’s load path from rotating shafts to bearing support’s fixation
-Vibratory amplitude coming from shaft unbalance on aircraft’s 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. Design office spend lots of money to verify stability of unbalance criteria by experimentation when analytical and numerical models could consolidate it. This project will also generate activities and decrease by almost 5% recurrent cost of supercritical shaft and total weight of drive system that will allow weight saving on aircraft and improving green efficiency and CO2 savings