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Open rotor propellers Ice protection System

Final Report Summary - ICEPS-ORPS (Open rotor propellers Ice protection System)

Executive Summary:
Ice accretion during flight of an aircraft affects the performance and control of the plane. Aircraft icing continues to be a concern, reportedly causing numerous aviation accidents and deaths globally in the recent years. The altitude range of operation of aircraft makes them susceptible to encounter icing conditions. In addition, economic pressures dictate that aircraft must keep flying in known adverse weather conditions and these pressures will continue to increase. Moreover, there will always be risks that a flight will run into unpredictable icy forming conditions even when departing in perfect weather. On open rotor propeller aircraft, it is identified that the leading edge of the propeller blade is especially vulnerable to ice accretion in flight, as well as on the ground. When the ice built up, the increased mass due to the ice will lead to increases of drag and consequently decreases the lift. The ice accretion also caused uneven distribution of weight which prejudices the flight equilibrium and as a consequence, lowers the minimum stall angle which is hazardous. Ice also causes the control and propulsion mechanisms to be reduced in efficiency and even seize up which may endanger the aircraft. Ice can also be dangerous on propellers because these structures are finely balanced and any moderate ice accretion can seriously affect the balance, causing stress levels which could threaten the structural integrity.

There is a real need of IPS for the propellers of the advance open rotor engine as propeller aircraft are more prone to icing problems in flight than jet (turbofan) engines because:
i) They tend to fly lower in more cloudy or more moist air and it is in these conditions that most of the in-flight ice accretion occurs.
ii) They are used much more than jets for regional travel in colder parts of the world with severe winters, typically northern Europe, North America, Canada, Russia, Northern China and many other areas all over the world with high altitude terrain.

In this project, the open rotor architecture is envisaged on single aisle, short or medium range aircraft (i.e. A320 type). The project calls for a new Ice Protection System (IPS) which is suitable or adaptable to such open-rotor propeller blades. From a prior state of the art survey of IPS technologies, seven active IPS technologies have been established as having potential for being developed into a cost effective propeller IPS of high technical performance. These are (i) Hot air heating, (ii) Laser heating, (iii) Heating foils either surface mounted or embedded with either steady state or pulsed electrical heating (also known as electrical resistance heating). (iv) Electromagnetic repulsion/attraction, (v) MW (MW) heating, (vi) Low frequency forced vibration by electromechanical transducers and (vii) Ultrasonic Guided Wave (UGW).

Project Context and Objectives:
The project’s scientific and technical objectives may be summarized in the following:

i) To investigate (feasibility study) 7 active IPS techniques which includes both melting and debonding/removal of ice approaches suitable for open rotor propeller during the initial stage of the project. The implementation plan based on a pyramidal approach is used to achieve the best IPS, in term of applicability and performance, for the final trial.
ii) To investigate the viability of combining passive IPS such as ice phobic coating and antifreeze chemicals with the active IPS technique.
iii) By modelling all the 7 active IPS (subject to further state of the art study and screening within the project) a prototype, according with the specifications defined in the topic description and partner criteria for performance evaluation, robustness and cost effectiveness, will be developed.
iv) To validate the ICEP-ORPS technology to ideally different ice formation conditions for a representative blade (composite test sample).
v) To demonstrate the prototype system installed on a representative test rig and in an icing wind tunnel, tested up to Technological Readiness Level (TRL) 4.

The ICEPS-ORPS project will aim to overcome the current limitations of existing propeller blade de-icing systems by developing an innovative anti- or de-icing system suitable for the open rotor propeller architecture. By doing this, ICEPS-ORPS will provide a solution that will enable the safe and reliable operation of open rotor-propeller aircraft in adverse weather conditions. At the time of writing, these concepts are novel to the application.

Project Results:
The project was instigated with the objective to develop a new IPS (Ice protection system) for composite propeller blades suitable for an open rotor propeller system, ideally achieving to Technology Readiness Level (TRL) 4. The contents are based largely on the project Description of Works (DoW) and agreement during meetings with all partners in the Consortium.

A comprehensive investigation of the state of the art of IPSs which covers all industrial and service sector (including international patent searches) has been carried out. The following reports document the findings;
i) “Commercial de-icing systems generally covering all relevant sectors”,
ii) “Survey of commercial IPS practice in civil aviation”,
iii) “Icing protection systems still in the research stage including any patented ideas” and
iv) “Compilation of initial long list of IPS technologies”.

An introduction to the ICEPS-ORPS project is provided in terms of the problem to be addressed, the project concept, and its objectives according to the ICEPS-ORPS DoW, is provided. The End User requirement is also presented. In addition, a background of the icing climatic conditions, current practise of de-icing in the aerospace application and the physics of icing are also presented. This is carried out based on extensive literature review on all the 7 active IPS techniques (i.e. hot air heating, laser heating, electrical resistance heating, microwave heating, electromagnetic attraction and repulsion, low frequency vibration and ultrasonic guided wave). Passive IPS such as coating and antifreeze chemicals are also reviewed. Subsequently, the specification of the parameters to be used for the ICEPS-ORPS system and illustration of the different potential trial locations that are suitable for preliminary and final demonstration are documented.

An initial and final scorecard has been created The final version of the Scorecard serves as the underlying framework for the performance assessment instruments for the Ice Protection Systems (IPS) investigated. This is based on a simple and widely known approach known as the weighted sum model (WSM) for performing such multi-criteria decision analysis (MCDA). The methodology has been described in details. The final score card template has been finalised in which the contents have been subjected to full consultation with the project Topic Manager and Partners. In addition, the relative weight of importance priority has been assigned to each criterion in this final scorecard template by the Topic Manager. For the avoidance of potential doubts, each criterion is also described fully.This final scorecard is used to facilitate the selection of the two active IPS techniques.

A detailed report is presented for the computational modelling of all the 7 active IPS techniques. A commonly agreed benchmark model (fixed geometry, dimensions, material properties (mechanical and electrical), critical zone, climatic conditions, ice thickness, etc.) is used to simulate all the IPS techniques. The simulations are done with Finite Element Method (FEM) analysis software to determine their technical performance. The outcome of the modelling results is used as one of the basis for the selection of 2 potential IPS techniques for further investigation; taking the IPSs to the next stage of prototype manufacturing and testing. Additionally, this deliverable also includes the advantages, disadvantages and relative cost benefits of each IPS technique which will be taken into account for the selection criteria.

A sound outline of the different IPS technologies systems (all 7 active IPSs) to aid the design and construction of the future prototype is documented. It takes account of the available information for this system concept and architecture. The potential performance of the listed IPS solutions quantitatively by means of modelling using finite element modelling (FEM) and other for computational techniques specific to the IPS method being considered, as reported, is assessed on this report. A final result of the feasibility modelling is described and also results are compared with those on literature review. A final list of potential IPS solutions, starting from the initial list was produced, which satisfies customer specifications, additional partner criteria is demonstrated to be an implementable solution on the base of a quantitative performance analysis based on modelling is described in this deliverable. Additional criteria for performance evaluation, viability and physical requirements is described in order to facilitate the final selection of the most suitable methodologies selected for further development. When this technique is chosen for further investigation, this information presented will serve as a reference for the future IPS design.

The final weighted scorecard for the all the 7 active IPS techniques is presented taking account of the modelling results, system concept and architecture, costs etc. Common consensus has been reached by the Consortium for each score which is carried out with active discussions together in order to achieve an unbiased scoring process. Based on the final score results, microwave and ultrasonic guided wave IPS techniques are selected for further stage of investigation.

Test specifications for the performance evaluation of the selected Ice Protection Systems (IPS), namely microwave and ultrasonic guided wave (UWG) IPS were carried out. In this, the test criteria and test matrix proposal: critical design review for rig and test pieces has been outlined in which the contents have been subjected to full consultation with the project Topic Manager and Partners. Initial outlines of the propeller and test rig design provides an insight towards realisation of the functional test rig in which aims to conform to the proposed test requirements in the icing wind tunnel. This document also described the UGW and microwave IPSs to a significant degree of details. Nevertheless, this provided the outline information required for the test blade, rig, operating conditions and matrix for the final trial (i.e. icing wind tunnel) to facilitate the realization of the complete test rig and icing wind tunnel test In addition, it also covers the specifications for the initial validation (i.e. proof of concept under laboratory conditions). Preliminary laboratory tests have been performed for both IPSs on appropriate Carbon-Fibre-Reinforced Polymer (CFRP) sample. These tests indicated the applicability of de-icing on CFRP in a static condition based on the unique approach by the individual IPS (i.e. de-bonding or melting).

A more detail explanation of the hardware of the selected IPS systems (i.e. microwave and ultrasonic guide wave) that will be used in the experiments was given. The components of each IPS hardware system as well as the functionality of the system are described with significant levels of details. Further laboratory validation results showing potential to de-ice/anti-ice for both IPS techniques have also been reported. The partners have also engaged with potential vendors to seek detailed information on the components and supplementary documents supplied by the vendors were also included in this report.

The hardware (including the control software where appropriate) of the MW and UGW IPSs were finalised and a functional prototype developed. The description of the hardware and preliminary laboratory results were reported in detail.

Manufacture parts and integration of selected IPS on it follows. For this purpose, a full scale propeller blade is proposed so that it’s eliminate scaling issue and for the selected IPS to be more readily adaptable for the integration (i.e. more tolerance to the size). In order to decrease power requirement on the test rig as well as to comply with the size of the icing wind tunnel, the blade is truncated at 60 % of span in which representative of the region of interest to de-ice/anti-ice. Full analysis of the proposed blade and hub design to determine the aerodynamic parameters has been completed by the Topic Manager. Due to confidentiality issue, this task is undertaken by the Topic Manager but the results were shared to the partners. It is worth mentioning that the finalized hub-blade design will take account of the aerodynamic parameters so as to meet both operation and safety requirements (i.e. a 3.5 safety factor). Based on the operation/environmental conditions, the blade design and manufacturing process were actively discussed with the manufacturers.

Two design of the test blades have been performed for MW and ultrasonic guided wave IPSs. This is based on meeting the requirements of the final icing wind tunnel test should any of the design is selected for the final trial. A total of 4 potential manufacturers have been identified for the manufacturing of blade and hub to be used in further works. Eventually, KW Special Project was chosen (based on the manufacturing process & cost) for the manufacturing of the 8 blades (5 MW and 3 UGW blades) which were manufactured on schedule. The spinner were also design and manufactured by the same manufacturer. The mechanical test of the blades were also performed and reported.

Currently, the blade root fixation to the hub is under active discussion by the Consortium. Preliminary design of the hub – blade attachment is circulated to all partners for further discussion. It is worth mentioning that the finalized hub-blade design will take account of the aerodynamic parameters so as to meet both operation and safety requirements.

The integration and test in laboratory of the IPS systems selected in the intermediate phase of this project; Ultrasonic Guided Wave (UGW) and MWs (MW) have been reported. It presents both de-icing technologies validation in the laboratory using representative carbon-fibre-reinforced polymer (CFRP) coupons covered with ice. These tests will allow the technique leader to further estimate the impact of the technologies in terms of power consumption, weight, etc. The deliverables highlights the iterative improvements to hardware and operating software developed in the earlier work package.

The performance of both ultrasonic guided wave (UGW) and MW (MW) Ice Protection Systems on blade test pieces has been further tested in partner’s laboratories. In addition, this report also presents the performance evaluation of both IPSs carried out at GKN’s icing wind tunnel (static blade tests). The best performance among the two IPSs will be selected for the final trial at Horiba MIRA’s icing wind tunnel, in which MW IPS has been chosen.

The recommended climatic test conditions have been defined and reported. The Consortium then sought to accommodate these requirements during the trial perform at relevant icing wind tunnel. The Consortium had work closely with the icing wind tunnel operators to facilitate the test within the technical and non-technical limitations.

To-date, the Consortium has engaged 4 potential icing wind tunnel to discuss on their facilities capabilities, namely,
(i) Cranfield University, United Kingdom (visited their facilities by UBRUN and TWI)
(ii) MIRA, United Kingdom (visited their facilities by UBRUN and TWI)
(iii) CIRA, Italy (web-based teleconferencing by Consortium)
(iv) GKN Aerospace, United Kingdom (visited their facilities by UBRUN and TWI)

Before each engagement, a list of questionnaires is drafted and used to facilitate obtaining the information from these icing wind tunnel operators. The responses were circulated to the Consortium. Based on the available information and the icing wind tunnels, preliminary drawing of the conceptual design of test rig is circulated for further discussions.

The Consortium then selected the following icing wind tunnels for the test,
i) GKN Aerospace (static trial)
ii) Horiba MIRA (dynamic trial)

The test rig (for dynamic trial) is developed successfully from concept to ready to use state. This involves environment and operational condition study, concept design, detailed design using CAD techniques, design validation through FEA methods, acquisition of parts and services and last but not least the assembly and testing of the test rig. Further requirements against the test rig is to be able operate safely under -30°C, ca. 45m/s wind speed and 50+% humidity at 300 rpm in final practice safely and reliably. Thus, provides test readiness review (fulfilling the 3.5 times safety factor requirement) of the test rig system as documented. As the mechanical tests for the blade were also performed (i.e. flexural, tensile and vibration tests) in order to meet the test specifications, these results were also reported as an appendix.

The test rig and microwave IPS system were successfully integrated and delivered to the Horiba MIRA test facility. Once installed in the wind tunnel, the entire system was tested at ambient temperatures before the test chamber was chilled to -30°C for the icing trials. Ice was accreted on the blade through using a water misting nozzle attached to a compressed air line to a thickness of approximately 2mm thick. After each trial, the ice was inspected for any loss before the next test point. In all bar the final case, 2kW continuous power for 6 minutes, there was no clear evidence of deicing occurring on the test blade. The final test point showed a limited amount of deicing at the root end of the blade adjacent to the antenna insertion point, however the area was limited in size and was away from the area of interest on the leading edge.

The performance of the ultrasonic guided wave and MW IPSs were quantified in terms of its predicted effectiveness in preventing ice formation or removing formed ice during the defined climatic and operation parameters. Comparison of performance of the different IPS systems were made for both technically (i.e. power consumption as a function of per unit area) and in terms of cost benefits.

Discussions have taken place between all partners with regards to the protection of IP as the consortium is interested in protecting the investigated ice protection systems. In total, three declarations of possible patents filings have been drafted for IPS based on ultrasonic guided wave, hot air heating and laser as documented in the Final PUDF. These were drafted using the initial investigations results (i.e. modelling) except ultrasonic guided wave in which hardware and operating software has been developed for laboratory validation. Currently, an invention disclosure relating to laser IPS for open rotor architecture has been put forward by the Topic Manager. At the current stage of writing, the Topic Manager are in the process of drafting a French patent application. More details can be found in the final PUDF. Due to this, activities related to dissemination and exploitation are to be carefully handled.

Having said that, based on the outputs of the research and development work so far, there has been 2 scientific publications presented to an international conference as follows:

(i) J. Kanfoud, S. Soua, T-H. Gan, “De-icing of propeller blades: electro-thermal vs electro-mechanical techniques efficiency comparison”, the 12th International Conference on Condition Monitoring and Machinery Failure Prevention Technologies, Oxford, United Kingdom (Jun 2015).
(ii) H. Habibi, A.Y.B. Chong, J. Kanfoud, C. Selcuk, T.H. Gan, D. Mayhew, “Simulation of an electro-mechanical ice protection system for aircraft structure based on ultrasonic guided wave”, Greener Aviation 2016, Brussels, Belgium (Oct 2016).

In any case, approval has been sought by the Consortium (including Safran Aircraft Engine) for any publication to the public domain.
The website for ICEPS-ORPS is accessible on the public domain using the following URL:
It is used as a medium to disseminate knowledge and news bulletin for those interested in the technology. However, the main platform for any file exchange is done through the AirCollab file exchange server (high-level data security) which is setup for all partners by the Topic Manager. This website will be updated during the progress of the project and beyond.

The liaison with the European Commission has been carried out in an appropriate manner via the coordinator of the ICEPS-ORPS project. During the course of project, the icing wind tunnel at Horiba MIRA (UK) has been selected to be suitable to perform the dynamic test for the appropriate developed ice protection system. In addition, the test rig has been designed based on the specific MIRA icing wind tunnel requirements. Works produced were of good quality as demonstrated by the production of another publication in this second reporting period and deliverables approved by the Topic Manager.

Potential Impact:
The world’s regional turboprop aircraft passenger fleet will nearly double in the next 10 years which represents 2500 new aircrafts at a value of about $55 billion. The increased attractiveness of turboprop aircraft arises from the fact that for journeys of between 300 and 600 miles they are about a third to half of the cost of a regional jet to operate but the total journey times are only slightly longer by about 10%. A lower capital cost together with lower maintenance and operating costs makes the turboprop an attractive business proposition for a regional carrier. Also they have a much smaller ecological footprint (about 30% less CO2 emissions than a regional jet aircraft). The development of the ‘open rotor turboprop engine’ becomes even more important because of the further fuel savings (15% more fuel efficient than existing turbo-props and 30% more fuel efficient than existing regional jet turbofan engines), quieter than existing engines and will meet future noise legislation and smaller ecological footprint, when used over short haul journeys. Currently the largest market for this type of short haul aircraft is in Europe and North America but significant increases in short haul traffic will arise in the Far East and particularly China. The potential economic benefits are as follows:

i. Benefits generated for the EU aviation industry as a result more fuel efficient ‘open rotor’ engines as compared to current Regional Jet aircraft.
ii. Reduced maintenance costs (including service/repair/replace parts and man hours).
iii. Lower capital cost of ‘open rotor’ engine aircraft.

For the aviation industry to move full swing ahead with such open rotor engine, the in-service operational safety issues relating to propeller icing affecting the engine integrity will needs to be overcome. As such the development work of an effective ice protection system is essential for the safe operation of the advance open rotor engine. The project will seek to develop a high technology aircraft ice prevention or/and removal system, new advanced hardware for delivery of power to the transducer and software for operation. The aerospace industry is of vital importance for the growth and stability of the European economy since millions of workers are directly or indirectly dependent on it. It is envisage that employment prospects and level of skills in the EU will be enhanced by this development. In addition, revenue can be generated through the sales of ICEPS-ORPS Ice protection systems by licensees. In view of these, together with the other innovative technologies used to develop such open rotor engine, the IPS technologies developed will aim to make a significant contribution towards the overall impact of the advance open rotor project in relation to economic, maintenance, environmental and societal issues, subject to successful development from TRL4 to TRL 9.

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