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

Reporting period: 2019-02-01 to 2020-04-30

What is the problem/issue being addressed ?
In the overall innovative project of H2020 Compound Fast Rotorcraft, we will aim to answer to technical issues on efficiency, reliability and safety.
In fact, the goal to develop supercritical and flexible composite shaft will lead to vibratory issues which we will propose to study and to solve by developing an appropriate damping device (passive, semi-active and/or active concept). Also manufacturing reliable and innovative composite shaft requires study and analysis of breakthrough technologies and processes that we propose to carry out during this project.

Why is it important for society ?
Indeed, due to both composite material and reduction of components quantity, thanks to long supercritical shaft, we will reduce direct maintenance costs and total weight of drive system. It will allow lightening the weight of aircraft and consequently improving flight’s efficiency and CO2 savings.

What are the overall objectives ?
In this context, the main objectives of STEADIEST project (Supercritical composiTE mAin DrIvE SysTem) will be to study, develop and to demonstrate by testing a concept of supercritical composite shaft drive line with high level of technical performances (low weight, friendly supports, improved dynamic behavior reducing vibration), modern technical functionalities (monitoring device, damping system) and optimization of costs (architecture and interfaces between parts, reduction of references and design to cost approach). These are key factors in order to be competitive, safe and reliable for next years.
Additionally, using composite shafts associated to specific flexible coupling will improve the capability of drive live 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 somposite drive line (Definition of drive line main architecture)
- Material analysis - with technical/operational comprises regarding perfomances, reliability and safety procurement - of whole mechanical sub-systems
- Static analysis, fatigue analysis of composite shaft, coupling, splined and bearing
--> Development of composite shafts mock-up to characterize material, size flange link, consolidate vibratory behavior and ensure manufacturing process have been done
- Analytical and numerical vibratory analysis of composite shafts with or without couplings
--> Global Vibratory behavior : first of all a state of the art in mechanical vibration of rotor has been carried out to define theoretical behavior and key parameters. Afterthat a 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 whole drive line with several architectures definitions and associated opportunities (subcritical shaft, reference reduction…).
- Definition of interface parts with aircraft and especially gearbox technical opportunity with Titanium welded adaptor on coupling
- Space allocation validations loop ,which lead to ICDS DMU update DMU

WP 2 / Definition of damping system
* Passive study
- Bibliography
- State of the art
- Pros and cons analysis regarding existing technological solutions
- 3D digital mock-up for ICDS implementation
- 2D interfaces drawings
- Alternatives manufacturing proposal for passive damper characterization
* Semi-active study
- Bibliography
- State of the art
- Pros and cons analysis regarding existing technological solutions
- Solution proposal for both frequencies settings and insatbility issues

WP 4 / Structural Health Monitoring system
- Structural Health Monitoring System Specification and Work Plan (SHMSWP) has been defined as global guideline document which aims to describe major aspects of the future monitoring development that will be carried out and provide informations related to product, study and definition process which will be applied in the next period of the project.

WP 5 / Supercritical composite drive line manufacturing
- raw material procurement
- Flanges, friction bush and composite tube manufacturing.
- Assembly process demonstration

WP 6 / Project Management and deliverables follow-up
To have efficient monitoring, weekly meeting have been held involving management and engineering team. During this first period, the management of the project and the follow-up of the deliverables progress will be a large part of monitoring and coordination activities. We prepared all the plans planned like Management Plan, Dissemination and communication Plan or Structural Health Monitoring.
Progress beyond the state of art: STEADIEST project is an opportunity to scientific contributions.
Indeed, 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 to conclude 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 (updated fatigue lifetime)
o When crossing natural frequency
o During nominal rotation
- Unbalance’s load path from rotating shafts to bearing support’s fixation (sizing of bearing, screw…?)
- Vibratory amplitude coming from shaft unbalance on aircraft’s crew

Potential impacts (including the socio-economic impact and the wider societal implication of the project so far): This study has positive impact on both development and production phase of general rotating system. Indeed, 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 trying to verify stability of unbalance criteria directly by experimentation when analytical and numerical models could consolidate it. Secondly, this project will generate activities and decrease by almost 5% recurrent cost of supercritical shaft and total weight of drive system that will allow lightening the weight of aircraft and consequently improving flight’s green efficiency and CO2 savings.