Final Report Summary - HELI-COMFORT (Adaptable power density coating for energy efficient heating of cockpit and cabin)
Executive Summary:
The EU FP7/CleanSky Joint Undertaking project Heli-Comfort with a duration of 18 months focused on the adaptation of heatable coating technology for use in aircraft cabin and cockpit heating. The objective of the project was to demonstrate a technology readiness level (TRL) of 4 or higher for the developed prototypical heating system and to provide insight as to whether it can provide improved thermal comfort for passengers, as well as a more energy-efficient means of heating than convective systems based on the extraction of bleed air from the rotor. The core technology is based on an electrically conductive polymer that is applied as a film on selected substrates and emits radiant infrared heat when powered. The coating has already been successfully demonstrated in previous projects for applications such as motor vehicle interior heating, as well as de-icing of aircraft wings and rotors.
In order to achieve the project goals, a lightweight, damage-tolerant aircraft cabin heating system was designed and implemented in a 1:1 scale mock-up of a helicopter. The mock-up was subjected to tests in a climate and wind tunnel, and the thermal comfort of occupants was determined based on predicted mean vote (PMV) and percentage of people dissatisfied (PPD) computations, based on the actual measurement data acquired.Along with these results another crucial source of feedback were the test persons that sat inside the mock-up cabin during different test runs (0°C to -40°C, with wind speeds up to 100km/h) and rate the thermal comfort inside the cabin. The feedback obtained from these persons with different thermal sensitivities was an additional, valuable and essential feedback about the system performance. Computational fluid dynamic (CFD) simulations of different scenarios served as a comparison to the wind tunnel tests, as well as to evaluate further scenarios that were not tested in the wind tunnel. From a materials perspective, coupon samples of the heating elements were subjected to an array of accelerated environmental conditions in order to determine the performance of the system after exposure to (party extreme) conditions such as may prevail during flight but also from prolonged exposure on the ground.
The envisaged system holds potential to provide a more energy-efficient, lighter weight and more comfortable heating solution for aircraft than today’s systems, which rely on the extraction of hot engine bleed air and often provide a non-homogeneous interior heating distribution and comfort, and decrease the propulsion efficiency of the engine.
The project was able to achieve its stated goal of demonstrating a TRL of 4 for the cockpit/cabin heating system. A higher TRL was considered technically achievable, however the management, supply chain, organizational support and related issues to achieve it were outside the scope of the project. The heatable coating was also explored as an application for pipe heating for an aircraft cargo bay water drainage system. Conclusions and recommendations for achieving a higher TRL in subsequent research/development were further outcomes.
Heli-Comfort was coordinated by AIT Austrian Institute of Technology and was developed together with the partners Villinger Research & Development, CEST Kompetenzzentrum für elektrochemische Oberflächentechnologie, Rail Tec Arsenal, and H4Aerospace.
Project Context and Objectives:
Today’s cockpit & cabin heating is mainly driven by hot engine bleed air pick-up and mixing with (cold) outside air which is further processed by the air conditioning systems of the environmental control system (ECS). The air is carried into the cockpit and cabin through a complex pipe and valve system. The air exhausts are located in the cockpit and cabin at a few locations and the warm-up is achieved by air convection. Due to the high level of air leakages e.g. from a helicopter's unpressurized cockpit and cabin, the heating power losses are not negligible and the homogeneity of the heating comfort over the interior space is quite poor. In addition, without the engine running, on-ground pre-heating of the cockpit and cabin cannot be achieved. Cold spots in aircraft cockpits and the cabin in the vicinity e.g. of doors lead to considerable passenger discomfort, too. The HELI-COMFORT concept is to develop an electrical heating system that can be adapted easily to surfaces of high 3D geometry. The power density of such a heating system can be adapted all along the 3D surfaces to be equipped with the coating. The main feature of such a system is an electrically conductive polymer, able to be used as a thin coating. The semi-conductive polymer can be designed such that it has a very high infrared emission with a variable power density when a current flow is enabled.
The overall objective of the project is to advance the technology readiness level to a TRL 4 or higher, which means that an innovative, purpose made, prototypic electrical heating system integrated in a 1:1 helicopter mock-up will be investigated under large laboratory environmental conditions. This overall objective is supported by the objectives as encapsulated in the various work packages of the project. These are to:
* Design a lighter weight, highly damage- tolerant aircraft cabin heating system with improved comfort and lower energy consumption compared to a conventional system based on engine bleed air;
* Perform a thermal simulation of optimized scenarios for positioning, sizing and controls of heating elements proving efficiency of the chosen concept for cockpit and cabin heating;
* Conduct performance testing of coupons of heating elements for enabling the equipment qualification demonstration of the heating system by simulating environmental conditions;
* Prepare a mock-up of a helicopter, equipped with heating elements and made ready for testing in a climatic wind tunnel;
* Perform 1:1 scale mock-up tests for approx. 1 week inside a climatic wind tunnel to verify the thermal situation and comfort inside the cockpit and cabin in a temperature range between –40°C and +15°C.
Project Results:
Heli-Comfort makes a contribution to addressing the domain of “Management of Aircraft Energy (MAE)” within the Systems for Green Operations ITD under the CleanSky 1 program. The project pursued the overall objective to advance the technology readiness level to a TRL 4 or higher of an innovative, purpose made, prototypic electrical heating system integrated in a 1:1 helicopter mock-up and investigated under large laboratory environmental conditions. This was to be achieved by the following sub-objectives:
Objective: Design a lighter weight, highly damage- tolerant aircraft cabin heating system with improved comfort and lower energy consumption compared to a conventional system based on engine bleed air;
Results: A cabin heating system that is representative of an actual heating system installed in a real helicopter was developed, manufactured and installed in a 1:1 scale mock-up.
The heatable coating used provides an even and controlled heat-up process, due to its self-regulating characteristics. This behaviour is attributed to the material’s light positive temperature coefficient (PTC). A temperature coefficient describes the relative change of a physical property that is associated with a given change in temperature. A positive temperature coefficient refers to materials that experience an increase in electrical resistance when their temperature is raised. Therefore the heat is regulated properly and the formation of hot spots, or an uncontrolled heat build-up is prevented. As a result, a PTC coating can be designed to reach a maximum temperature for a given input voltage, since at some point any further increase in temperature would only be met with greater electrical resistance.
The majority of heating applications using this technology in the past have consisted of airplane wing de-icing systems, propeller and rotor ice protection systems, battery heating systems, and similar. Adapting the heatable coatings as an alternative heating method for helicopter cabins required major development work with respect to the formulation as well as the manufacturing capabilities. The biggest gain in expertise came from developing the exact layout for a cabin heating system. This application of the coating on more complex geometries is a delta with respect to previous applications.
Under the framework of this project, the structure and manufacturing process of the coatings were adapted such that the new coatings are characterized by a higher infrared emission than before and exhibit optimal PTC behaviour, which is required for such interior heating systems.
Contact Heat Protection
Furthermore, a flock-coating technology was developed, which is used in the top-most contact heat protection (CHP) layer. The use of a CHP layer in the system provides a more homogeneous heat transfer and improved overheat protection. It also provides good touch protection for occupants against the relatively high surface temperatures of the heating elements (60°C – 80°C and more, although the specifications for this particular project limit the temperature to 60°C) that may develop in order to deliver the necessary thermal performance.
Objective: Perform 1:1 scale mock-up tests for approx. 1 week inside a climatic wind tunnel to verify the thermal situation and comfort inside the cockpit and cabin
Results: The prepared mock-up was subjected to a set of pre-defined test scenarios in a climate and wind tunnel. The main parameters were the ambient air temperature, the wind speed, and –for occupants- the clothing factor and the metabolic rate. The thermal comfort as given by predicted mean vote (PMV) and percentage of people dissatisfied (PPV) based on measurements taken in the mock-up in the wind/climate tunnel was computed. Along with these results another crucial source of feedback were the test persons that sat inside the mock-up cabin during different test runs (0°C to -40°C, with wind speeds up to 100km/h) and rated the thermal comfort inside the cabin. The feedback obtained from these persons with different thermal sensitivities was an additional, valuable and essential feedback from actual people about the system performance.
The results of the tests show that i) in the passenger area, with a clothing factor of 1 and ambient temperature down to -10°C, an excellent (near optimal) comfort level could be attained; ii) with same clothing factor and temperatures at -30°C, an acceptable level of comfort could be reached, and with clothing factor 2, a good level could be reached at the same ambient temperature. The heating power employed to achieve thermal comfort was on the order of some 1.5kW at 0°C and 15km/h wind speed, and up to around 4.5kW at an ambient temperature of -30°C and 15km/h. As could be expected, the PMV and PPD values improved with a clothing factor of 2.
Acceptable thermal comfort could not be achieved in the tunnel for lower temperatures. This is attributed mainly to the air leakage of the insufficiently insulated mockup. The computational fluid dynamic (CFD) simulations however showed that with better elimination of air/thermal leakage, acceptable comfort could also be achieved at -40°C, the lowest temperature for which tests were conducted.
Objective: Perform a thermal simulation of optimized scenarios for positioning, sizing and controls of heating elements proving efficiency of the chosen concept for cockpit and cabin heating
Results: The idea of the new heating system is to heat up the cabin and cockpit of a helicopter by using radiative heating, instead of or in addition to conventional convective heating. Radiative heating is known as being more energy efficient than conventional heating, and in addition can lead to better passenger comfort due to higher surface temperatures of the cabin walls. In order to analyze the performance of the radiative heating system, computational fluid dynamics (CFD) Simulation was performed. The simulation aimed at giving information about cabin temperature levels and energy efficiency. Furthermore, the local temperature distribution and comfort parameters like PMV (Predicted Mean Vote) and PPD (Predicted Percentage Dissatisfied) in a variety of scenarios with different ambient and interior conditions were investigated.
In general, the temperature values for the simulation were slightly higher than the values measured during the wind tunnel test, and the required heating power was lower than in the wind tunnel test. This can be due to higher internal gains for occupants and instruments in the simulation. Furthermore, and perhaps most importantly, leakages that occur in the mock-up were not considered in the simulation model. Further differences could also be attributed to the fact that in the simulation, the heating power is the net heat flux into the cabin through the heating elements while for the wind tunnel test, the value for heating power represents the total power consumption of the heating elements, including also thermal losses to the ambient environment through cabin walls.
Notwithstanding, good agreement between the PMVs achieved in the simulation and those achieved in the wind tunenl could be established for a number of scenarios.
Objective: Conduct performance testing of coupons of heating elements for enabling the equipment qualification demonstration of the heating system by simulating environmental conditions
Results: In order to investigate the performance of the semiconducting heatable layer on two substrates (PEEK and GFRP), material coupons prepared with the heatable coating as a functional layer, and various combinations of non-functional layers (e.g. protective top coat and CHP), were subjected to environmental tests according to RTCA DO-160, corrosion tests according to DIN EN ISO9227 and to adhesion testing according to DIN EN ISO 2409. The reliability, heating uniformity and structural integrity after exposure to harsh environmental conditions as in the case of corrosion and humidity was evaluated. The electrical functionality results before and after such conditions were compared. Laboratory heating results were obtained using a self-made set-up used to calculate resistance, and an infrared camera used to monitor and record images and heat changes during the investigated time. Structural analysis of the layered coupons was also conducted by means of various microscopy techniques, and the materials used in the heating system were examined with respect to REACH regulation.
As a summary of the laboratory testing conducted on coupon substrates, some conclusions important for the further implementation can be drawn. The most important outcome after accelerated set ups is that the heating functionality of coatings is preserved after both severe corrosion and humidity tests.
The promising results achieved on lab coupon GFRP and PEEK substrates can be summarized as follows:
• Adhesive integrity of initial prototypic electrical heating system after severe environmental conditions is achieved
• Humidity impact on performance observed with acryl-based top coat
• Excellent corrosion protection of heating layer and top coat
• Resistance and thermal behavior is more uniform with an additional top coat
• Homogenous heat distribution
• The corrosion of embedded contact ribbons is reduced with an additional top coat (optical appearance).
Finally, the long term stability and heating capability, functionality and integrity of the prototypic innovative electrical heating system is slightly changed by continuous application of electrical power. From this perspective, a successful integration of the coating should therefore be possible.
For future upscaling, out of the scope of this project, suggested improvements are in:
• Better uniformity of layer thickness
• Avoidance of voids and air bubbles
• Investigation of different top coat (and/or heatable coating) formulations to provide resistance to humidity and to increase long term stability
• Corrosion protection of contact ribbons (currently non-protected section).
With regard to its electrical properties (magnetic, EMI, immunity against lightning indirect effects, voltage spike, etc.) of the heatable coating system the test results have been very promising.
There are no restrictions and only minimal risk due to magnetic affects limiting the possibilities to design and develop the helicopter interior heatable coating system into a fully qualified and certifiable helicopter system.
It can be concluded that the heatable coating system can be connected directly to helicopter/aircraft power generation and distribution system without need for a filter or voltage spike protection, since it is very tolerant with regard to voltage spikes.
Since the heating functionality is realized without any electronic switching circuits, AC/DC or DC/DC converters, the results of the tests performed are applicable for all kind of sizes or shapes of helicopter interior panels and will remain within the allowed EMI limits required for installation in helicopter or aircraft.
The electromagnetic radiated and conducted emissions are so low that even the design of exterior anti-icing systems is possible, which are usually required in close proximity to EMI sensitive antennas and sensors.
It can be concluded that the heatable coating system can be connected directly to helicopter/aircraft power generation and distribution system without need for a converter or transformer, since it is extremely tolerant with regard to lightning induced transients.
With respect to the equipment’s survival of storage in low temperatures, and operation at low and high temperatures, these appear to have no discernible effect on its functionality.
The transversal vibration/fatigue tests likewise indicated no negative impact on the functionality of the equipment.
The analysis of materials used in the substrates as well as in the functional layers of the coatings according to REACH showed no risk for human health or the environment, in the sense that none of the materials was on the list of prohibited substances.
The technology readiness level was evaluated against a set of criteria that were compared with the project results. In this respect, the project successfully demonstrated a TRL of 4 for the developed system.
Potential Impact:
Potential impact:
Within the JTI-CS-SGO (Systems for green operations), the Management of Aircraft Energy (MAE) encompasses all aspects of on-board energy provision, storage, distribution and consumption. MAE aims at two major objectives. The first one is to develop and demonstrate All-Electric Aircraft System Architectures (power by wire), involving energy users to facilitate the implementation of advanced energy management functions and architectures. The second objective is to adapt and demonstrate the control of heat exchanges (partly necessary due to the all-electric concept) and reduction in heat waste within the whole aircraft through advanced Thermal Management.
These technologies will lead either to a reduction of systems related weight or aircraft related weight, which will in turn reduce the fuel consumption. The extent of the weight reduction is to be assessed by both system suppliers and aircraft manufacturers on vehicle level, as previous studies have shown this to be a complex technical challenge. Another major benefit is the reduction of the systems related power extraction from the engine (non-propulsive thrust). Total gains up to 40% should be achievable, and will enable the engine to be further optimized as well.
Heli-Comfort supports overcoming these challenges through the reduction of heat waste within the whole aircraft through advanced thermal management. The project lays the ground work for avoiding or reducing the use of engine bleed air for cabin and cockpit heating.
Heli-Comfort demonstrated the employment of an environmentally friendly process for heating the cabin and cockpit of helicopters. With such a system, on ground pre-heating of the cockpit and cabin can be achieved without the engine running, which can lead to fuel savings. Cabin and cockpit comfort can also be improved by minimizing heated air losses through air leakages and avoiding cold spots in the vicinity of doors and windows through strategic placement of heating panels.
With further development, and depending on the level of system integration, an increased level of electrification in aircraft is supported by an IR radiant heating concept such as that of Heli-Comfort. With appropriate design, this can lead to weight and cost reductions and increased efficiency of engine and heating systems. The application is envisaged in fixed and rotary wing aircraft for new platforms with updated integrated designs, but also as an application for legacy designs.
The heating system was also investigated with regard to applicability for a pipe heating application for aircraft cargo bay water drainage.
The heating of surfaces by heatable coatings can also be applied to anti-icing or de-icing of aeroplanes outer surfaces, propellers and other critical parts, again avoiding the use of engine bleed air. A further application of electrical heatable coatings is foreseeable for the heating of windmill generator blades, again for avoiding dangerous ice accumulation. Under such icing conditions windmill generators have to be stopped and a lot of potential wind energy can then not be used for the generation of electrical energy. Such devices, once developed and widely employed, will have a great impact on the operating hours and hence the energy output of wind energy farms.
Dissemination activities:
With a relatively short duration of 18 months, the project managed to deliver very promising technical results. Many of the results became available in the second half or even close to the end of the project. At the same time, publication of scientific papers often has lead times of many months, making it difficult to reconcile with the tight timetable of the project and the timing of the availability of results. Therefore, dissemination activities are foreseen following the end of the project. These include:
• Creation of brochure/flyer providing the key information of the project, such as results, application areas of the technology, partners and contact information. It will be a consortium leaflet for public use;
• A publication by CEST on laboratory testing results for functionality of coatings applied to PEEK and GFRP substrates is envisaged in the peer-reviewed journal such as “Surface and Coatings Technology”
• From AIT side, a page on the company homepage will be dedicated to showcasing Heli-Comfort. It will be included as part of the general overhaul of the site, due to be completed by end of summer 2016. The project will also be showcased in the AIT newsletter “Tomorrow Today”
• The project can be introduced and discussed at the Aviation Forum Austria 2016
• Presentation by LKR in the form of a poster at the “Ranshofener Leichtmetalltage” in November 2016
• Further dissemination potential is given by leveraging CleanSky forums and communication channels, e.g. CleanSky final event/general forum in 2017.
• General press release.
List of Websites:
Project coordinator contact:
Boschidar Ganev
AIT Austrian Institute of Technology GmbH
Tel: +43 50550-6518
boschidar.ganev@ait.ac.at | http://www.ait.ac.at
The EU FP7/CleanSky Joint Undertaking project Heli-Comfort with a duration of 18 months focused on the adaptation of heatable coating technology for use in aircraft cabin and cockpit heating. The objective of the project was to demonstrate a technology readiness level (TRL) of 4 or higher for the developed prototypical heating system and to provide insight as to whether it can provide improved thermal comfort for passengers, as well as a more energy-efficient means of heating than convective systems based on the extraction of bleed air from the rotor. The core technology is based on an electrically conductive polymer that is applied as a film on selected substrates and emits radiant infrared heat when powered. The coating has already been successfully demonstrated in previous projects for applications such as motor vehicle interior heating, as well as de-icing of aircraft wings and rotors.
In order to achieve the project goals, a lightweight, damage-tolerant aircraft cabin heating system was designed and implemented in a 1:1 scale mock-up of a helicopter. The mock-up was subjected to tests in a climate and wind tunnel, and the thermal comfort of occupants was determined based on predicted mean vote (PMV) and percentage of people dissatisfied (PPD) computations, based on the actual measurement data acquired.Along with these results another crucial source of feedback were the test persons that sat inside the mock-up cabin during different test runs (0°C to -40°C, with wind speeds up to 100km/h) and rate the thermal comfort inside the cabin. The feedback obtained from these persons with different thermal sensitivities was an additional, valuable and essential feedback about the system performance. Computational fluid dynamic (CFD) simulations of different scenarios served as a comparison to the wind tunnel tests, as well as to evaluate further scenarios that were not tested in the wind tunnel. From a materials perspective, coupon samples of the heating elements were subjected to an array of accelerated environmental conditions in order to determine the performance of the system after exposure to (party extreme) conditions such as may prevail during flight but also from prolonged exposure on the ground.
The envisaged system holds potential to provide a more energy-efficient, lighter weight and more comfortable heating solution for aircraft than today’s systems, which rely on the extraction of hot engine bleed air and often provide a non-homogeneous interior heating distribution and comfort, and decrease the propulsion efficiency of the engine.
The project was able to achieve its stated goal of demonstrating a TRL of 4 for the cockpit/cabin heating system. A higher TRL was considered technically achievable, however the management, supply chain, organizational support and related issues to achieve it were outside the scope of the project. The heatable coating was also explored as an application for pipe heating for an aircraft cargo bay water drainage system. Conclusions and recommendations for achieving a higher TRL in subsequent research/development were further outcomes.
Heli-Comfort was coordinated by AIT Austrian Institute of Technology and was developed together with the partners Villinger Research & Development, CEST Kompetenzzentrum für elektrochemische Oberflächentechnologie, Rail Tec Arsenal, and H4Aerospace.
Project Context and Objectives:
Today’s cockpit & cabin heating is mainly driven by hot engine bleed air pick-up and mixing with (cold) outside air which is further processed by the air conditioning systems of the environmental control system (ECS). The air is carried into the cockpit and cabin through a complex pipe and valve system. The air exhausts are located in the cockpit and cabin at a few locations and the warm-up is achieved by air convection. Due to the high level of air leakages e.g. from a helicopter's unpressurized cockpit and cabin, the heating power losses are not negligible and the homogeneity of the heating comfort over the interior space is quite poor. In addition, without the engine running, on-ground pre-heating of the cockpit and cabin cannot be achieved. Cold spots in aircraft cockpits and the cabin in the vicinity e.g. of doors lead to considerable passenger discomfort, too. The HELI-COMFORT concept is to develop an electrical heating system that can be adapted easily to surfaces of high 3D geometry. The power density of such a heating system can be adapted all along the 3D surfaces to be equipped with the coating. The main feature of such a system is an electrically conductive polymer, able to be used as a thin coating. The semi-conductive polymer can be designed such that it has a very high infrared emission with a variable power density when a current flow is enabled.
The overall objective of the project is to advance the technology readiness level to a TRL 4 or higher, which means that an innovative, purpose made, prototypic electrical heating system integrated in a 1:1 helicopter mock-up will be investigated under large laboratory environmental conditions. This overall objective is supported by the objectives as encapsulated in the various work packages of the project. These are to:
* Design a lighter weight, highly damage- tolerant aircraft cabin heating system with improved comfort and lower energy consumption compared to a conventional system based on engine bleed air;
* Perform a thermal simulation of optimized scenarios for positioning, sizing and controls of heating elements proving efficiency of the chosen concept for cockpit and cabin heating;
* Conduct performance testing of coupons of heating elements for enabling the equipment qualification demonstration of the heating system by simulating environmental conditions;
* Prepare a mock-up of a helicopter, equipped with heating elements and made ready for testing in a climatic wind tunnel;
* Perform 1:1 scale mock-up tests for approx. 1 week inside a climatic wind tunnel to verify the thermal situation and comfort inside the cockpit and cabin in a temperature range between –40°C and +15°C.
Project Results:
Heli-Comfort makes a contribution to addressing the domain of “Management of Aircraft Energy (MAE)” within the Systems for Green Operations ITD under the CleanSky 1 program. The project pursued the overall objective to advance the technology readiness level to a TRL 4 or higher of an innovative, purpose made, prototypic electrical heating system integrated in a 1:1 helicopter mock-up and investigated under large laboratory environmental conditions. This was to be achieved by the following sub-objectives:
Objective: Design a lighter weight, highly damage- tolerant aircraft cabin heating system with improved comfort and lower energy consumption compared to a conventional system based on engine bleed air;
Results: A cabin heating system that is representative of an actual heating system installed in a real helicopter was developed, manufactured and installed in a 1:1 scale mock-up.
The heatable coating used provides an even and controlled heat-up process, due to its self-regulating characteristics. This behaviour is attributed to the material’s light positive temperature coefficient (PTC). A temperature coefficient describes the relative change of a physical property that is associated with a given change in temperature. A positive temperature coefficient refers to materials that experience an increase in electrical resistance when their temperature is raised. Therefore the heat is regulated properly and the formation of hot spots, or an uncontrolled heat build-up is prevented. As a result, a PTC coating can be designed to reach a maximum temperature for a given input voltage, since at some point any further increase in temperature would only be met with greater electrical resistance.
The majority of heating applications using this technology in the past have consisted of airplane wing de-icing systems, propeller and rotor ice protection systems, battery heating systems, and similar. Adapting the heatable coatings as an alternative heating method for helicopter cabins required major development work with respect to the formulation as well as the manufacturing capabilities. The biggest gain in expertise came from developing the exact layout for a cabin heating system. This application of the coating on more complex geometries is a delta with respect to previous applications.
Under the framework of this project, the structure and manufacturing process of the coatings were adapted such that the new coatings are characterized by a higher infrared emission than before and exhibit optimal PTC behaviour, which is required for such interior heating systems.
Contact Heat Protection
Furthermore, a flock-coating technology was developed, which is used in the top-most contact heat protection (CHP) layer. The use of a CHP layer in the system provides a more homogeneous heat transfer and improved overheat protection. It also provides good touch protection for occupants against the relatively high surface temperatures of the heating elements (60°C – 80°C and more, although the specifications for this particular project limit the temperature to 60°C) that may develop in order to deliver the necessary thermal performance.
Objective: Perform 1:1 scale mock-up tests for approx. 1 week inside a climatic wind tunnel to verify the thermal situation and comfort inside the cockpit and cabin
Results: The prepared mock-up was subjected to a set of pre-defined test scenarios in a climate and wind tunnel. The main parameters were the ambient air temperature, the wind speed, and –for occupants- the clothing factor and the metabolic rate. The thermal comfort as given by predicted mean vote (PMV) and percentage of people dissatisfied (PPV) based on measurements taken in the mock-up in the wind/climate tunnel was computed. Along with these results another crucial source of feedback were the test persons that sat inside the mock-up cabin during different test runs (0°C to -40°C, with wind speeds up to 100km/h) and rated the thermal comfort inside the cabin. The feedback obtained from these persons with different thermal sensitivities was an additional, valuable and essential feedback from actual people about the system performance.
The results of the tests show that i) in the passenger area, with a clothing factor of 1 and ambient temperature down to -10°C, an excellent (near optimal) comfort level could be attained; ii) with same clothing factor and temperatures at -30°C, an acceptable level of comfort could be reached, and with clothing factor 2, a good level could be reached at the same ambient temperature. The heating power employed to achieve thermal comfort was on the order of some 1.5kW at 0°C and 15km/h wind speed, and up to around 4.5kW at an ambient temperature of -30°C and 15km/h. As could be expected, the PMV and PPD values improved with a clothing factor of 2.
Acceptable thermal comfort could not be achieved in the tunnel for lower temperatures. This is attributed mainly to the air leakage of the insufficiently insulated mockup. The computational fluid dynamic (CFD) simulations however showed that with better elimination of air/thermal leakage, acceptable comfort could also be achieved at -40°C, the lowest temperature for which tests were conducted.
Objective: Perform a thermal simulation of optimized scenarios for positioning, sizing and controls of heating elements proving efficiency of the chosen concept for cockpit and cabin heating
Results: The idea of the new heating system is to heat up the cabin and cockpit of a helicopter by using radiative heating, instead of or in addition to conventional convective heating. Radiative heating is known as being more energy efficient than conventional heating, and in addition can lead to better passenger comfort due to higher surface temperatures of the cabin walls. In order to analyze the performance of the radiative heating system, computational fluid dynamics (CFD) Simulation was performed. The simulation aimed at giving information about cabin temperature levels and energy efficiency. Furthermore, the local temperature distribution and comfort parameters like PMV (Predicted Mean Vote) and PPD (Predicted Percentage Dissatisfied) in a variety of scenarios with different ambient and interior conditions were investigated.
In general, the temperature values for the simulation were slightly higher than the values measured during the wind tunnel test, and the required heating power was lower than in the wind tunnel test. This can be due to higher internal gains for occupants and instruments in the simulation. Furthermore, and perhaps most importantly, leakages that occur in the mock-up were not considered in the simulation model. Further differences could also be attributed to the fact that in the simulation, the heating power is the net heat flux into the cabin through the heating elements while for the wind tunnel test, the value for heating power represents the total power consumption of the heating elements, including also thermal losses to the ambient environment through cabin walls.
Notwithstanding, good agreement between the PMVs achieved in the simulation and those achieved in the wind tunenl could be established for a number of scenarios.
Objective: Conduct performance testing of coupons of heating elements for enabling the equipment qualification demonstration of the heating system by simulating environmental conditions
Results: In order to investigate the performance of the semiconducting heatable layer on two substrates (PEEK and GFRP), material coupons prepared with the heatable coating as a functional layer, and various combinations of non-functional layers (e.g. protective top coat and CHP), were subjected to environmental tests according to RTCA DO-160, corrosion tests according to DIN EN ISO9227 and to adhesion testing according to DIN EN ISO 2409. The reliability, heating uniformity and structural integrity after exposure to harsh environmental conditions as in the case of corrosion and humidity was evaluated. The electrical functionality results before and after such conditions were compared. Laboratory heating results were obtained using a self-made set-up used to calculate resistance, and an infrared camera used to monitor and record images and heat changes during the investigated time. Structural analysis of the layered coupons was also conducted by means of various microscopy techniques, and the materials used in the heating system were examined with respect to REACH regulation.
As a summary of the laboratory testing conducted on coupon substrates, some conclusions important for the further implementation can be drawn. The most important outcome after accelerated set ups is that the heating functionality of coatings is preserved after both severe corrosion and humidity tests.
The promising results achieved on lab coupon GFRP and PEEK substrates can be summarized as follows:
• Adhesive integrity of initial prototypic electrical heating system after severe environmental conditions is achieved
• Humidity impact on performance observed with acryl-based top coat
• Excellent corrosion protection of heating layer and top coat
• Resistance and thermal behavior is more uniform with an additional top coat
• Homogenous heat distribution
• The corrosion of embedded contact ribbons is reduced with an additional top coat (optical appearance).
Finally, the long term stability and heating capability, functionality and integrity of the prototypic innovative electrical heating system is slightly changed by continuous application of electrical power. From this perspective, a successful integration of the coating should therefore be possible.
For future upscaling, out of the scope of this project, suggested improvements are in:
• Better uniformity of layer thickness
• Avoidance of voids and air bubbles
• Investigation of different top coat (and/or heatable coating) formulations to provide resistance to humidity and to increase long term stability
• Corrosion protection of contact ribbons (currently non-protected section).
With regard to its electrical properties (magnetic, EMI, immunity against lightning indirect effects, voltage spike, etc.) of the heatable coating system the test results have been very promising.
There are no restrictions and only minimal risk due to magnetic affects limiting the possibilities to design and develop the helicopter interior heatable coating system into a fully qualified and certifiable helicopter system.
It can be concluded that the heatable coating system can be connected directly to helicopter/aircraft power generation and distribution system without need for a filter or voltage spike protection, since it is very tolerant with regard to voltage spikes.
Since the heating functionality is realized without any electronic switching circuits, AC/DC or DC/DC converters, the results of the tests performed are applicable for all kind of sizes or shapes of helicopter interior panels and will remain within the allowed EMI limits required for installation in helicopter or aircraft.
The electromagnetic radiated and conducted emissions are so low that even the design of exterior anti-icing systems is possible, which are usually required in close proximity to EMI sensitive antennas and sensors.
It can be concluded that the heatable coating system can be connected directly to helicopter/aircraft power generation and distribution system without need for a converter or transformer, since it is extremely tolerant with regard to lightning induced transients.
With respect to the equipment’s survival of storage in low temperatures, and operation at low and high temperatures, these appear to have no discernible effect on its functionality.
The transversal vibration/fatigue tests likewise indicated no negative impact on the functionality of the equipment.
The analysis of materials used in the substrates as well as in the functional layers of the coatings according to REACH showed no risk for human health or the environment, in the sense that none of the materials was on the list of prohibited substances.
The technology readiness level was evaluated against a set of criteria that were compared with the project results. In this respect, the project successfully demonstrated a TRL of 4 for the developed system.
Potential Impact:
Potential impact:
Within the JTI-CS-SGO (Systems for green operations), the Management of Aircraft Energy (MAE) encompasses all aspects of on-board energy provision, storage, distribution and consumption. MAE aims at two major objectives. The first one is to develop and demonstrate All-Electric Aircraft System Architectures (power by wire), involving energy users to facilitate the implementation of advanced energy management functions and architectures. The second objective is to adapt and demonstrate the control of heat exchanges (partly necessary due to the all-electric concept) and reduction in heat waste within the whole aircraft through advanced Thermal Management.
These technologies will lead either to a reduction of systems related weight or aircraft related weight, which will in turn reduce the fuel consumption. The extent of the weight reduction is to be assessed by both system suppliers and aircraft manufacturers on vehicle level, as previous studies have shown this to be a complex technical challenge. Another major benefit is the reduction of the systems related power extraction from the engine (non-propulsive thrust). Total gains up to 40% should be achievable, and will enable the engine to be further optimized as well.
Heli-Comfort supports overcoming these challenges through the reduction of heat waste within the whole aircraft through advanced thermal management. The project lays the ground work for avoiding or reducing the use of engine bleed air for cabin and cockpit heating.
Heli-Comfort demonstrated the employment of an environmentally friendly process for heating the cabin and cockpit of helicopters. With such a system, on ground pre-heating of the cockpit and cabin can be achieved without the engine running, which can lead to fuel savings. Cabin and cockpit comfort can also be improved by minimizing heated air losses through air leakages and avoiding cold spots in the vicinity of doors and windows through strategic placement of heating panels.
With further development, and depending on the level of system integration, an increased level of electrification in aircraft is supported by an IR radiant heating concept such as that of Heli-Comfort. With appropriate design, this can lead to weight and cost reductions and increased efficiency of engine and heating systems. The application is envisaged in fixed and rotary wing aircraft for new platforms with updated integrated designs, but also as an application for legacy designs.
The heating system was also investigated with regard to applicability for a pipe heating application for aircraft cargo bay water drainage.
The heating of surfaces by heatable coatings can also be applied to anti-icing or de-icing of aeroplanes outer surfaces, propellers and other critical parts, again avoiding the use of engine bleed air. A further application of electrical heatable coatings is foreseeable for the heating of windmill generator blades, again for avoiding dangerous ice accumulation. Under such icing conditions windmill generators have to be stopped and a lot of potential wind energy can then not be used for the generation of electrical energy. Such devices, once developed and widely employed, will have a great impact on the operating hours and hence the energy output of wind energy farms.
Dissemination activities:
With a relatively short duration of 18 months, the project managed to deliver very promising technical results. Many of the results became available in the second half or even close to the end of the project. At the same time, publication of scientific papers often has lead times of many months, making it difficult to reconcile with the tight timetable of the project and the timing of the availability of results. Therefore, dissemination activities are foreseen following the end of the project. These include:
• Creation of brochure/flyer providing the key information of the project, such as results, application areas of the technology, partners and contact information. It will be a consortium leaflet for public use;
• A publication by CEST on laboratory testing results for functionality of coatings applied to PEEK and GFRP substrates is envisaged in the peer-reviewed journal such as “Surface and Coatings Technology”
• From AIT side, a page on the company homepage will be dedicated to showcasing Heli-Comfort. It will be included as part of the general overhaul of the site, due to be completed by end of summer 2016. The project will also be showcased in the AIT newsletter “Tomorrow Today”
• The project can be introduced and discussed at the Aviation Forum Austria 2016
• Presentation by LKR in the form of a poster at the “Ranshofener Leichtmetalltage” in November 2016
• Further dissemination potential is given by leveraging CleanSky forums and communication channels, e.g. CleanSky final event/general forum in 2017.
• General press release.
List of Websites:
Project coordinator contact:
Boschidar Ganev
AIT Austrian Institute of Technology GmbH
Tel: +43 50550-6518
boschidar.ganev@ait.ac.at | http://www.ait.ac.at