Solvay developmentS for the hB-SIa prototype aIrplane, 2 0 ... · PDF fileapplications of our materials, ... anode in lithium ion cells. ... 1-2 Solef® pvdf: high-performance binder

Solvay developmentS for the hB-SIa prototype aIrplane, 2 0 0 4 - 2 0 0 9 .

AROUND THE WORLD IN A SOLAR AIRPLANE

4 SOLvAy / SOLAR ImPULSE PARTNERSHIP

5SOLvAy / SOLAR ImPULSE PARTNERSHIP

Solvay became Solar Impulse’s first main Partner by signing a partnership contract on October 28, 2004.In addition to the cash contribution, Solar Impulse and Solvay agreed that Solvay would also be a Technology Partner, contributing to the project with technical support, making available to Solar Impulse its recognized competence in material development and applications.

During the design and construction phase of the HB-SIA prototype airplane, from November 2004 to November 2009:� 27 subprojects defined as ‘work packages’ were successful,

(Table 1);� 9 subprojects are still in progress and could lead to a

positive conclusion for the HB-SIB airplane which will attempt the round-the-world flight (Table 2);

� 29 subprojects were unsuccessful (Table 2).



This document describes in more detail the successful applications of our materials, solutions or competencies, grouped into the following key development platforms:oEnergy chainoStructureoLightweight / metal replacementomiscellaneous applicationsoSimulations

In summary, 11 Solvay products from the Chemicals and Plastics Sectors are on board the first solar airplane HB-SIA, contributing 25 different applications and more than 6000 parts, mainly in the 3 main platforms of energy chain, structure and weight reduction.



1. EnErgy chain1-1 f1eC: high performance electrolyte additive for lithium

batteries

monofluorethylene carbonate, commonly called ‘F1EC’ or ‘FEC’, is a new additive for the battery electrolyte in rechargeable lithium ion batteries. Depending on the specific application it can represent up to 20% of the electrolyte blend. FEC is currently commercialized by Solvay Fluor.

Compared to the widely used vinylene carbonate (vC), the main advantages of the new F1EC are� a more flexible film (solid-electrolyte interphase, SEI) on the

anode in lithium ion cells. � better overall performance, higher capacity and improved

calendar life of secondary lithium batteries, and improved safety.


1-2 Solef® pvdf: high-performance binder for lithium batteries

An important contribution to the energy management is the use of Solef® PvDF. The electrical energy harvested by the solar cells is stored in lithium batteries, where the product is used as a binder for both electrodes.

Additionally, the electrochemical stability of the cells is improved, allowing repeated charging and discharging cycles, also at high rate, without deterioration of battery performance.

The original design of the plane (2004) was made with Li batteries having an electric density of 180 Wh/Kg. The actual 4x 100 Kg batteries of HB-SIA have an electric density of 220 Wh / Kg.

A recently developed new grade offering very high adhesion to the electrodes is under testing and could also contribute to the weight reduction of batteries for HB-SIB.


1-3. Solar cells encapsulation: halar® eCtfe

The film that protects the photovoltaic (Pv) cells from the harsh environment that will be encountered by the plane on the ground and in air is made from Halar® ECTFE. Solar Impulse started the development of the plane with small Pv cells produced by RWE*(see page15). These cells have a regular textured surface to increase light trapping. This feature gave us the idea of a new product and process for the protection of the Pv modules for the Solar Impulse plane. A new Hyflon® mFA polymer was designed and produced to satisfy the high technical requirements for the HB-SIA. The films made from this new polymer had very high transparency and a lower melting point than commercial products. The film was directly applied to the top active surface of the Pv cells using a new thermal process; the physical adhesion given by the textured surface of the Pv cells proved to be sufficient for the application. Both the polymer and the process have been patented. This technique eliminated the use of adhesives, leading to a reduction in overall weight of the solar panels.

Solar Impulse then found new, larger Pv cells with higher efficiency and the above method was not suitable for these new cells. Solvay Solexis developed another transparent film based on Halar® ECTFE.



The fluorinated films have to be surface treated. Both plasma and corona treatments have been studied in order to increase their adhesiveness to the epoxy layer, the encapsulation material used by Solar Impulse. The polymer Halar® was chosen over Hyflon® mFA because the surface treatment process was easier and its effect lasted longer, at least 6 months, similar to that of the competition product. The thickness of the film was reduced to 17 microns compared to the 26 microns of the competing film, resulting in about 35% weight savings with the same electrical performance. Thus the solution offered by Solexis was not just a replacement of the product in use, but an improvement. This film was produced by Ajedium in the USA, a recent acquisition of Solvay Solexis.

Solvay Solexis will continue to work with Solar Impulse to further improve the performance of the protective films for the PV cells to increase electrical efficiency and also to save weight (a solution with a single product replacing both the epoxy /GF layer and the top film is under study).



1-4. Solar cells encapsulation: Solef® pvdf-based adhesive tape

The solar cells are not adjacent to each other and there is a need to close the gaps between them. This is done with an adhesive tape which must be Uv transparent and Uv resistant. Such a tape, based on Solef® PvDF, has been successfully developed.

The original design of the plane was made with mono crystalline Silicon photovoltaic cells, having a thickness of 180 microns and an energy efficiency of 18%. The actual PV system is made of 11628 mono crystalline Silicon cells which thickness is below 150 microns for an energy efficiency of 22% after encapsulation.

*Initially, Solar Impulse used cells from RWE Solutions that later became AZUR SPACE Solar Power GmbH. These were small cells with both front and back electrical contacts.

Then SI decided to use large cells (125 mm x 125 mm) from Sun Power (California) that are now on the Prototype. These have back contacts, higher efficiency, and need less electrical connections due to their larger size.



2. StructurE2-1 Glue for paper assembly in honeycomb structures:

torlon®aI10

The wing and stabilizers spars are made of a sandwich structure which is a honeycomb structure entrapped between 2 carbon fibre foils.

Typically the honeycomb structure is a paper structure impregnated with a Torlon®AI10 polymer by a dipping process.

This complex composite structure combines excellent mechanical properties (strength, torsion, flexion, vibration) with an incredibly light weight. As an example each 20 metre element of the wing spar can be easily handled just by a few men.

A new structure with higher compression strength is under evaluation. It will be used eventually in the HB-SIB or other application.



2.2 Solkane® 365 mfc blowing agent for high insulation polyurethane foams

The cockpit of the SI airplane must vitally be lightweight, but stable and still providing optimal insulating values against the freezing outside temperatures high up in the air. Lightweight but still stable construction can be provided by using polyurethane foams, which are produced basically from a polyol, an isocyanate and a foam expansion agent, also called blowing agent (‘BA’)

Solvay Fluor’s 3rd generation blowing agent Solkane® 365 offers the best gas phase lambda (thermal conductivity) value in its class. Combined with its very low diffusion factors, this results in excellent polyurethane foams with challenging properties:� best foam insulation values � best foam dimensional stability� best foam compressive strength� best moisture resistance.


All of those factors together influence the foam properties and provide the excellent performance characteristics of the lightweight but high insulation polyurethane foam which forms the basis for the SI cockpit, the 4 motor gondolas as well as the wing tips. A special original ‘Solvay solution’ was developed for producing these important pieces: foaming big blocks of foam and thereafter machining the ‘eggshell’ parts or wing tips out of them.

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2-3. Wingtips: Solkane® 365 mfc blowing agent for high performance polyurethane structural foams

The wingtips have been machined out of the foam blocks produced originally for the cockpit and for the motor gondolas.


2-4. laminate for the back covering of wings, stabilizers (intrados) and moving wing parts (flaps, airbrakes): Solef® pvdf

Solef® PvDF-based laminate is used to cover the ailerons, elevators, rudder, airbrakes and spoilers. Thanks to its mechanical strength at low thickness (15 microns), this laminate (PvDF / acrylic adhesive/ polyamide net) offers a weight reduction that is critical for the success of this mission. This laminate is an entirely new product specifically developed for this mission. It will be used on the HB-SIA for small parts (1.5 metres width). The PvDF brings its excellent mechanical stability and environmental resistance in the wide range of temperatures in which the plane will fly.

It will be used for the entire HB-SIB airplane wings if we can provide it in 3 metres width. This product is being developed together with Parkinson (USA) for the film extrusion and with Jehier (Hutchinson France) for the lamination.


The 60 m wing spar made of honeycomb-carbon fibres supports the 120 ribs which profile the shape of the wing with the encapsulated PV system on top and a high resistance laminated film for the underside.

This complex system is more rigid than expected as the deflection (difference between ground and flight positions) at the wing tips is less than 0.5 metres.



3. Light wEight / mEtaL rEpLacEmEnt3-1 Instrument panel housings: radel®

The computer and throttle box housings are produced using a rapid prototyping technology called FDm (fused deposit modelling). This technology allows prototypes or small numbers of parts to be produced in choice of different materials. To get the lowest weight, we have used the Radel® R PPSU base product, which presents the highest rigidity within the FDm product range.

Typically, with FDm technology, parts are manufactured layer by layer. Each layer is built by an extrusion head that deposits a fine thread of molten material. Choice of material is based on the requirements of the parts. In such applications, the

conductivity of the metal provides natural EmI shielding of the part. The Radel® PPSU base material, however, is not conductive, meaning that we have, in collaboration with Emitech, developed a solution to apply a special conductive layer using painting technology. On those parts, the weight saving from metal replacement is 750gr.



3-2 Circuit board spacer and assembly: primoSpire® Srp

Circuit boards are usually assembled using metal screws and spacers embedded in elastomers. The major requirement for this metal replacement is to maintain fixation (no movements) between the boards within the temperature range imposed by the applications (-50°C to +60°C). Due to its high compression modulus for a density of 1.2 gr/cm3, Primospire SRP has been selected for this assembly that includes 2 washers, 1 screw, 1 bolt and 1 spacer for each connection. On the throttle box alone, 8 of those assemblies are used and save 61 gr.



3-3 throttle box internal parts: primoSpire® Srp, KetaSpire® peeK, torlon® paI, amodel® ppa and radel® ppSU

Initially the throttle box part was composed entirely of metallic parts. Aluminium housings were made out of Radel® PPSU with EmI shielding painting. Circuit board assemblies were manufactured in PrimoSpire® SRP. All metal fixations (screws) were reviewed in order to check if replacement with PrimoSpire® SRP m3 screw was possible. It was not possible to replace the aluminium lever because rigidity with small thickness is the key attribute of this part of the application. The tilting mechanism at the bottom of the lever has been produced with KetaSpire® PEEK (KetaSpire® KT 820 CF 30) and with Torlon® PAI (Torlon® 4301). Those materials were selected for their friction properties as well as for the inherent mechanical properties associated with their low density.

On this full throttle box part, the weight saving due to metal replacement amounts to around 650 gr over 60 parts.


3-4 Bushing for propeller damping system: torlon® paI

A damping system for each propeller is provided in the direction perpendicular to propeller rotating plane. This damping system requires a material with excellent friction and wear properties at low speed and high load. Torlon® PAI 4301 has been selected for this metal replacement application. Total weight saving for the 8 parts (2/propeller) is 21 gr.


3-5 landing gear mechanism: Ixef® para, primoSpire® Srp and radel® ppSU

A centering cylinder (internal and external part) for the landing system, initially designed in aluminium, has been partially (only the internal part) replaced by Ixef® 1022. Starting from an extruded rod of Ixef® 1022, the internal part has been machined to its final dimension. The external part has been maintained in aluminium due to impact requirements. The shaft assembling of both parts has been produced out of PrimoSpire® SRP due to it intrinsic modulus and its machinability. Finally, due to its high deformation capability, Radel® has been selected for the rear attachment legs in the landing system assembly.

Many other parts, more than 6000 all together, such as bolts, screws, nuts, washers of all shapes and all sizes, presenting the best performance to weight ratio, have been produced for Solar Impulse and are already on board the HB-SIA prototype.



4. OthEr miScELLanEOuS appLicatiOnS4-1. elements of the electric bench test (not on board): Ixef® 1022

Ixef® 1022 was used for the electric bench test developed for testing the electric chain batteries / engines which will be installed on the plane:

� for the the insulation plate, thanks to its elec-tric insulation and high compressive strength properties.

� for the coupling axis between the electric engine and the brakes, due to its torsion resis-tance and excellent machinability.



4-2. Glue for strain gauges: torlon®aI10

The Torlon®AI10 polymer is used as a glue component.

4-3. leds for energy savings: amodel® a 1133 / 4122

Two grades of Amodel® were selected to produce by injec-tion the cups of the LEDs which will be installed on the plane. Amodel® 4122 grades are widely used as an LED grade because of their high reflectivity, their reflectivity properties after ageing and their processing properties.



4.4 lubrication with fomblin®

The advanced PFPE-based Fomblin® lubricants that were used in the mars Sojourner lubricate the bearings of the HB-SIA’s electrical motors that turn the propellers. Fomblin® lubricants have excellent performances in extreme conditions, like low and high temperatures, and low pressures (vacuum) throughout the life of the components. These lubricants reduce the mechanical losses significantly and hence the energy consumed, especially at the sub-zero temperatures encountered during flight.



For the design and development phases of Solar Impulse, Solvay undertook finite element analysis (FEA), using the ABAQUS commercial code, of the thermo-mechanical behaviour of the several modules under different load and boundary conditions. Solvay has specific expertise in the field of non-linear numerical simulation which is the only type able to accurately predict the behaviour of flexible structures.

These simulations were performed in 2 key domains:

� materials behaviour� solar cells encapsulation� epoxy bonding� structure� solar panels� wing ribs� wing leading edges.

All together Solvay contributed more than 2000 hours of simulation, which in many situations was decisive for the progress of the project.

5. SimuLatiOnS




approved applications -> Solvay inside hB-SIa

1 Cockpit egg-shell and motor gondolas Solkane® 365 mfc

2 Wing tips Solkane® 365 mfc

3 Li-ion battery Fluorinated electrolyte additive(F1EC)

4 High-tech lubricant for moving parts PFPE Fomblin®

5 Battery binder PvDF Solef® homo-polymer

6 Laminates for Intrados PvDF Solef® film laminated on PET net

7 Pv cells encapsulation ECTFE Halar® thin film

8 Pv cells gaps closing PvDF Solef® based adhesive tape

9 Honeycomb (flat panel sandwich) PAI Torlon® AI10

10 Strain gauges PAI Torlon® AI10

11 Other housings / boxes Radel®

12 Throttle box - parts: - levers - different axis + knobs - friction control stator + spacer

PPA Amodel® A1630PEEK KetaSpire® KT820 CF30PAI Torlon® 4301 or 4435

13 Throttle box - base plate SRP PrimoSpire®

14 Top view LEDs PPA Amodel®

table 1. Solvay products / Solutions approved (november 2009)


15 Bolts, screws and washers SRP PrimoSpire®

16 Control surfaces hinges (axis) PAmXD6 Ixef®-3008

17 Sliding parts PAI Torlon® 4203

18 Landing gear centring spring housing PAmXD6 Ixef®-1022

19 main landing gear: - bearing bushing for lock - threaded rod m6x250

PAI Torlon® 4301SRP PrimoSpire®

20 Outrigger parts PAI Torlon® 4301

21 Air data boom attachment (sleeves, lugs, bolts)

PAI Torlon® 4301PPSU Radel®SRP PrimoSpire®

22 Bushings control system belcranks PAI Torlon® 4435 / KetaSpire®

23 Bushings propeller PAI Torlon® 4301

24 Limiters (PCB fixation to the housing / spacers

SRP PrimoSpire®

25 Simulation: materials behaviour and structural design

ABAQUS software

Approved applications -> materials used other than on board the airplane

26 Insulation plate for electric test bench Ixef® Para 1022/0008

27 Coupling axis for motor fixation on test bench

Ixef® Para 1022/0008


table 2. Solvay products / solutions still under development or not selected (november 2009)

Work in progress -> might become Solvay inside hB-SIB

1 Transport crates Nidacell®

2 Battery binder PvDFSolef ® copolymer

3 Battery insulation Foamed PvDFSolef ®

4 Wing cover (3m width) PvDFSolef ® film

5 Encapsulation resins to replace current epoxy resin (+ film)

PFPE / PU

6 Wire coating for T resistance PvDFSolef ®

7 Seat inflatable cushions Foamed PvDFSolef ®

8 Transportable hangar PvC Ferrari sheet,

9 TBD (insulation, pilot suit) Aeronag (Silica aerogel)


products / solutions not selected

1 Battery & electronic devices insulation Rigid PUR

2 Battery & electronic devices XPS

3 Wing sandwich structure XPS

4 motor parts PAI Torlon®

5 Canopy PSU Udel® polysulfone with PvT treatment

6 Helmet n/a

7 Power LEDs PPA Amodel®

8 Film for insulating material backing (TABS) n/a

9 Foam/core for the ribs in wing structure SRP PrimoSpire® /PPSU Radel®

10 Inserts for fixation screws PPSU Radel® / veradel®

11 Honeycomb (flat panel sandwich) PAITorlon® AI10(in new Cormaster N636 developed for SI)

12 Elastic foil to bond solar modules n/a

13 modules bonding to skin n/a

14 Wing cover n/a

15 Resins TBD

16 Battery cushioning Foam material

17 Turbo-compressor parts TBD


18 Wiring fixation elements on structure n/a

19 Solar panel clips TBD

20 Bushings landing system PAI Torlon® 4301

21 Wing main hardpoints (replacements for steel spherical bearings)

PAI Torlon® 4435,SRP PrimoSpire®, PEEK KetaSpire®

22 Sensors Piezo-electric fluoro copolymer

23 Encapsulation films Hyflon® (mFA)

24 Pilot suit, others Piezo-electric fibres

25 Stopper for propeller teetering FKm Tecnoflon®

26 Wing panel gap covering FKm Tecnoflon®

27 Conductive material for wing cover Fluorolink® T as surface teatment

28 Conductive material for wing cover Fluorolink® T as additive to resin

29 Battery separator PvDF co-polymers

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authOrS and cOntactS

Technical development Solvay Advanced Polymers:

michel [email protected]

Technical development Solvay Solexis:

padmanabhan [email protected]

Technical development Solvay Fluor:

Johannes [email protected]

Design and Simulations:

Jean-marie [email protected]

Management of the Solvay Solar Impulse partnership:

Claude [email protected]

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Solvay developmentS for the hB-SIa prototype aIrplane, 2 0 ... · PDF fileapplications of our materials, ... anode in lithium ion cells. ... 1-2 Solef® pvdf: high-performance binder

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