《纺织复合材料》课程参考文献（High Performance Thermoplastic Resins and Their Composites）07. Costs and Aircraft Applications of Thermoplastic Composites

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7.Costs and Aircraft Applications of Thermoplastic Composites 7.1 Costs of Thermoplastlc Composites As is the case with thermoset composites,thermoplastic composites are used in specialty,low volume applications,hence prices are high and will stay high as long as the commercial sales volume remains low.However,the majority of the high performance thermoplastic materials discussed in this report are more expensive than their thermoset counterparts,whether in the form of a neat resin,a prepreg tape or in a commingled woven fabric.Avimid K,Avimid N.Eymyd U-25.Eymyd U-35.Larc-TPI,Cypac X-7005 polyimide prepregs as well as PBI prepregs are amongst the most expensive,at least twice as expensive and in some cases 3 to 4 times more expensive than thermoset prepregs.There are however some prepregs such as reinforced PEEK,PES and PPS for which prices are comparable to some second-generation thermoset composites such as IM6/5245C (US $90-120/Ib for a quantity of about 100 Ib). Fortunately,the higher cost for the raw material can be offset by lower processing costs [221].Thermoplastic composites have indeed the potential for low processing costs.In general,they are more suitable for automated production than thermosets because most of them require only the application of heat and pressure to fabricate laminates and to form parts.No chemical reaction is required.hence no long and elaborate curing cycles are involved.They can be processed with short cycle ttes.Because they require high temperature and pressure,it is more appropriate to produce them in high volume.Automated processes such as tape laying.filament winding and pultrusion are the most cost effective processing methods for thermoset composites [1]and they are also the key to the cost effectiveness of using thermoplastic composites [221].Competition from thermoset composites and metal is important and to really pierce the market,innovative cost-effective manufacturing processes for thermoplastic composites have to be developed in spite of their good properties. Chang and Lees [2]estimated the relative cost of processes to fabricate thermoplastic and thermoset composites.Table 35 contains the relative cost of prepregging which they estimated for thermoset and thermoplastic tows.The cost of prepregging thermoplastic tow is without any doubt higher than for thermoset.Amongst the techniques to combine fibres and thermoplastic matrices,solvent and melt impregnation have the lowest potential cost and powder impregnation and commingling the highest. Table 36,taken also from Reference 2.compares the cost of part fabrication using filament winding of tows preimpregnated by each of the four prepregging methods already mentioned above.While the cost of thermnoplastic prepreg is between 1.8 and 3 times higher than that of thermoset prepreg.it is offset by lower production costs.The final thermoplastic 136

7. Costs and Aircraft Applications of Thermoplastic Composites 7.1 Costs of Thermoplastic Composites As is the case with thermoset composites, thermoplastic composites are used in specialty, low volume applications, hence prices are high and will stay high as long as the commercial sales volume remains low. However, the majority of the high performance thermoplastic materials discussed in this report are more expensive than their thermoset counterparts, whether in the form of a neat resin, a prepreg tape or in a commingled woven fabric. Avimid K, Avimid N, Eymyd U-25, Eymyd U-35, Larc-TPI. Cypac X-7005 polyimide prepregs as well as PBI prepregs are amongst the most expensive, at least twice as expensive and in some cases 3 to 4 times more expensive than thermoset prepregs. There are however some prepregs such as reinforced PEEK, PES and PPS for which prices are comparable to some second-generation thermoset composites such as IM6/5245C (US $90-12O/lb for a quantity of about 100 lb]. Fortunately, the higher cost for the raw material can be offset by lower processing costs 122 11. Thermoplastic composites have indeed the potential for low processing costs. In general, they are more suitable for automated production than thermosets because most of them require only the application of heat and pressure to fabricate laminates and to form parts. No chemical reaction is required, hence no long and elaborate curing cycles are involved. They can be processed with short cycle times. Because they require high temperature and pressure, it is more appropriate to produce them in high volume. Automated processes such as tape laying, filament winding and pultrusion are the most cost effective processing methods for thermoset composites [l] and they are also the key to the cost effectiveness of using thermoplastic composites 122 11. Competition from thermoset composites and metal is Important and to really pierce the market, innovative cost-effective manufacturing processes for thermoplastic composites have to be developed in spite of their good properties. Chang and Lees [Z] estimated the relative cost of processes to fabricate thermoplastic and thermoset composites. Table 35 contains the relative cost of prepregging which they estimated for thermoset and thermoplastic tows. The cost of prepregging thermoplastic tow is without any doubt higher than for thermoset. Amongst the techniques to combine fibres and thermoplastic matrices, solvent and melt impregnation have the lowest potential cost and powder impregnation and commingling the highest. Table 36, taken also from Reference 2, compares the cost of part fabrication using filament winding of tows preimpregnated by each of the four prepregging methods already mentioned above. While the cost of thermoplastic prepreg is between 1.8 and 3 times higher than that of thermoset prepreg, it is offset by lower production costs. The final thermoplastic 136

138 High Performance Thermoplastic Resins and Their Composites part costs are typically 40%lower than thermoset parts for the melt and solvent processes,and either 20%lower or equal to the thermoset part cost.for the powder and commingled process. respectively. Chang and Lees also compared the relative forming costs of continuous filament tape/tow for both thermoplastic and thermoset material for various parts.They are shown in Table 37 where relative costs for discontinuous drawable sheet are also included.In general, forming parts with continuous filament reinforced thermoplastic resulted in lower prices than for thermosets.The unique reprocessability feature of thermoplastic composites.that makes them reprocessable and reusable,renders them more attractive from an economic point of view.Parts with defects can be reprocessed and scrap from the fabrication of trimmed parts can be reused. 7.2 Examples of Use of Thermoplastic Composites in Aircraft Applcations Even though the questions of processing techniques.tooling.Joining and repairing have not been fully addressed by researchers and designers,applications of thermoplastic composites in aircraft structures are becoming increasingly common.Aircraft thermoplastic composite components have to be designed to the same static and dynamic loading conditions and fail-safe requirements as conventional thermoset composites [1].As suggested by the National Advisory Board of U.S.National Research Council [1],"the application of thermoplastic composite materials as aircraft structural materials can be expected to build on the data basc cstablished for thermosetting composites.Modifications to the evalualon criteria can be expected as experience develops with this family of materials."Selected applications demonstrating the feasibility of using high performance thermoplastic composites in primary and secondary aircraft structures are presented in the following paragraphs. 7.2.1 Westland 30-300 Thermoplastic Tailplane [248,249,250] Westland Helicopters is currently engaged in a project to develop and build a thermoplastic composite tailplane for the Westland 30-300 helicopter.This priary structural component was selected to evaluate and demonstrate thermoplastic composite manufacturing technology as many elements incorporated in the assembly are directly applicable to other aircraft primary structures.The tailplane also gave the opportunity to compare three technologies since it was first made of metal and then changed to epoxy composite. The materials chosen for the project were carbon reinforced PEEK and woven carbon reinforced PEI.Initially,only carbon/PEEK was selected but since it had not reached commercial maturity during the first phasc of the project,being only available in developient

138 High Performance Thermoplastic Resins and Their Composites part costs are typically 40% lower than thermoset parts for the melt and solvent processes, and either 20% lower or equal to the thermoset part cost. for the powder and commingled process, respectively. Chang and Lees also compared the relative forming costs of continuous filament tape/tow for both thermoplastic and thermoset material for various parts. They are shown in Table 37 where relative costs for discontinuous drawable sheet are also included. In general, forming parts with continuous filament reinforced thermoplastic resulted in lower prices than for thermosets. The unique reprocessability feature of thermoplastic composites, that makes them reprocessable and reusable, renders them more attractive from an economic point of view. Parts with defects can be reprocessed and scrap from the fabrication of trimmed parts can be reused. 7.2 Examples of Use of Thermoplastic Composites in Aircraft Applications Even though the questions of processing techniques, tooling, joining and repairing have not been fully addressed by researchers and designers, applications of thermoplastic composites in aircraft structures are becoming increasingly common. Aircraft thermoplastic composite components have to be designed to the same static and dynamic loading conditions and fail-safe requirements as conventional thermoset composites [ 11. As suggested by the National Advisory Board of U.S. National Research Council [l], “the application of thermoplastic composite materials as aircraft structural materials can be expected to build on the data base established for thermosetting composites. Modifications to the evaluation criteria can be expected as experience develops with this family of materials.” Selected applications demonstrating the feasibility of using high performance thermoplastic composites in primary and secondary aircraft structures are presented in the following paragraphs. 73.1 We&land 30-300 Thermoplastic Tailplane [248,249.2!50] Westland Helicopters is currently engaged in a project to develop and build a thermoplastic composite tailplane for the Westland 30-300 helicopter. This primary structural component was selected to evaluate and demonstrate thermoplastic composite manufacturing technology as many elements incorporated in the assembly are directly applicable to other aircraft primary structures. The tailplane also gave the opportunity to compare three technologies since it was first made of metal and then changed to epoxy composite. The materials chosen for the project were carbon reinforced PEEK and woven carbon reinforced PEI. Initially, only carbon/PEEK was selected but since it had not reached commercial maturity during the first phase of the project, being only available in development

Costs and Aircraft Applications of Thermoplastic Composites 139 quantities,a change in material was required.Carbon/Ultem PEI was chosen as a replacement material.Characterization of APC-2 and carbon/PEI,and investigation of the strength of bonded and mechanically fastened joints with these materials has been undertaken.Even though the environmental tolerance of carbon/PEI has been found to lie between epoxy composite and APC-2,results indicated that carbon/PEI and APC-2 materials are suitable for primary airframe structures.They exhibited acceptable properties for structural applications and improved cnvironmcntal rcsistancc compared to carbon/cpoxy composites.Damage tolerance was found to be superior to epoxy based composites.Damage was also more easily detectable. Figure 60 shows the construction details of the composite tailplane.The construction of the horizontal component of the tailplane was 4 ply (0/90/90/0)APC-2 skins,with Nomex honeycomb sandwich panels bonded to a spar and rib sub-assembly.The sub-assembly consisted ot two press formed t45 APC-2 spars,two t45 APC-2 press formed ribs and two carbon fibre reinforced PEEK injection molded attachment brackets.Leading and trailing edge reinforcements were also press formed from APC-2.The components werc asscmblcd using a combination of mechanical fasteners,welding and adhesive bonding to demonstrate a range of joining techniques. The fins were sandwich panels manufactured from woven carbon/PEI skins bonded to Nomex honeycomb.The edges were closed with vacuum formed polycarbonate capping strips and a woven aramid/PEI frangible cap cold bonded to the lower edge. The fins were bonded to the tailplane using a mortice and tenon joint.Titanfum pins that passed through the injection molded brackets and sandwich panels attached the tailplane to the helicopter.Reinforcing patches were bonded to the upper and lower surfaces at the attachment points. The different processing methods used included consolidation of flat laminates by compression molding,press forming of the pre-consolidated laminates using matched metal and rubber tooling.press-clave consolidation of prepreg material and contouring of woven fabric components.These were discussed by Griffiths et al.[248].The equipment needed,the problems encountered and the techniques used to alleviate them were presented.In addition. several types of joining techniques including mechanical fastening,adhesive bonding and welding that have been used in the manufacture of the tailplane were described.Regarding adhesive bonding,the best results were obtained when the surface was pre-treated by corona discharge while the best results for welding were achieved with ultrasonic techniques.In general,the non-destructive techniques for evaluating the quality of epoxy composites.such as X-ray analysis,ultrasonics.thermography.Fokker bond testing and visual inspection were found suitable for thermoplastic composites

Costs and Aircraft Applications of Thermoplastic Composites 139 quantities, a change in material was required. Carbon/Ultem PEI was chosen as a replacement material. Characterization of APC-2 and carbon/PEI, and investigation of the strength of bonded and mechanically fastened joints with these materials has been undertaken. Even though the environmental tolerance of carbon/PEI has been found to lie between epoxy composite and APC-2, results indicated that carbon/PEI and APC-2 materials are suitable for primary airframe structures. They exhibited acceptable properties for structural applications and improved environmental resistance compared to carbon/epoxy composites. Damage tolerance was found to be superior to epoxy based composites. Damage was also more easily detectable. Figure 60 shows the construction details of the composite tailplane. The construction of the horizontal component of the tailplane was 4 ply (O”/900/900/Oo) APC-2 skins, with Nomex honeycomb sandwich panels bonded to a spar and rib sub-assembly. The sub-assembly consisted ot two press formed +45’ APC-2 spars, two rt45” APC-2 press formed ribs and two carbon fibre reinforced PEEK injection molded attachment brackets. Leading and trailing edge reinforcements were also press formed from APC-2. The components were assembled using a combination of mechanical fasteners, welding and adhesive bonding to demonstrate a range of joining techniques. The fins were sandwich panels manufactured from woven carbon/PEI skins bonded to Nomex honeycomb. The edges were closed with vacuum formed polycarbonate capping strips and a woven aramid/PEI frangible cap cold bonded to the lotier edge. The fins were bonded to the tailplane using a mortice and tenon joint. Titanium pins that passed through the injection molded brackets and sandwich panels attached the tailplane to the helicopter. Reinforcing patches were bonded to the upper and lower surfaces at the attachment points. The different processing methods used included consolidation of flat laminates by compression molding, press forming of the pre-consolidated laminates using matched metal and rubber tooling, press-clave consolidation of prepreg material and contouring of woven fabric components. These were discussed by Griffiths et al. 12481. The equipment needed, the problems encountered and the techniques used to alleviate them were presented. In addition, several types of joining techniques including mechanical fastening, adhesive bonding and welding that have been used in the manufacture of the tailplane were described. Regarding adhesive bonding, the best results were obtained when the surface was pre-treated by corona discharge while the best results for welding were achieved with ultrasonic techniques. In general, the non-destructive techniques for evaluating the quality of epoxy composites, such as X-ray analysis, ultrasonics, thermography, Fokker bond testing and visual inspection were found suitable for thermoplastic composites

Costs and Aircraft Applications of Thermoplastic Composites 141 The estimation of the tailplane costs assuming that the material and components are being produced in volume quantity is shown in Table 38.The cost of the optimized tallplane. which uses injection molded brackets adjacent to the rear spar in place of the filled honeycomb block,is based on the assumption that laminates are tape lald prior to forming.Westland believes that the cost effectiveness of using these materials lies in automation of the processes involved.The major disadvantage in current thermoplastic manufacturing is the two stage proccss of producing consolidated preform sheets followed by a forming operation,hence an automated process that leads to a net shape component would be much preferable. 7.2.2 Advanced Tactical Fighter (ATF)and B2 Stealth Bomber [158,251-253] Advanced thermoplastic composites are widely used in developmental military aircraft such as Lockheed's and Northrop's versions of the Advanced Tactical Fighter (ATF),and Northrop's B2 Stealth Bomber[251-253].The all composite B2 bomber measuring about 5.2 m high by 21 m long with a wing span of 52.4 m consists largely of carbon/polyimide and other advanced plastic composite structure that make it virtually undetectable by radar [251].The ribs for a wing section on the B-1B bomber as well as the ribs,stiffeners,skin and leading edge on the inboard flap of the Fairchild A-10 have been made of APC-2 by the film-stacking method [252.253].Film-stacking fabrication was jointly developed under the U.S.Air Force Thermoplastic Composite Development Program. Materials for the proposed USAF ATF must retain structural performance at temperature up to 176C [74].In order to meet the service criteria defined for the aircraft,a material with a Tg of at least 200 C is required [741.Boeing Military Airplane Company has prototyped an ATF wing with 60%Amoco's Torlon polyamideimide reinforced with carbon fibres.The carbon/PAI prepreg is produced by Fiberite/ICI [253].Avimid K is being considered for the thick section,large area ATF prototype wing skins by the Lockheed/Boeing/General Dynamics team [158]. 7.2.3 Wing of the U.S.Navy/McDonnell F/A-18 Fighter Aircraft [188] MeDonnell Aircraft Co.is conducting research and development work on thermosets, thermoplastics,titanium and aluminum-lithium manufacturing technologies with direct application to future military and commercial aircraft.Presently more effort is devoted to the development of advanced thermoplastic composites than thermoset composites. To demonstrate the evolving thermoplastic composites technology and to gain manufacturing experience with these materials.an upper and lower outer wing skin for both wings of a U.S.Navy/McDonnell F/A-18 fighter aircraft have been manufactured and will be installed and service tested.The left wing panels are composed of thermoplastic composite AS4/PEEK while the right wing panels are made of epoxy composite IM-7/8551-7E.This

Costs and Aircraft Applications of Thermoplastic Composites 141 The estimation of the tailplane costs assuming that the material and components are being produced in volume quantity is shown in Table 38. The cost of the optimized tailplane, which uses injection molded brackets adjacent to the rear spar in place of the filled honeycomb block, is based on the assumption that laminates are tape laid prior to forming. Westland believes that the cost effectiveness of using these materials lies in automation of the processes involved. The major disadvantage in current thermoplastic manufacturing is the two stage process of producing consolidated preform sheets followed by a forming operation, hence an automated process that leads to a net shape component would be much preferable. 7.2.2 Advanced Tactical Fighter (ATF) and B2 Stealth Bomber [1!5S, 251- 2531 Advanced thermoplastic composites are widely used in developmental military aircraft such as Lockheed’s and Northrop’s versions of the Advanced Tactical Fighter (ATF). and Northrop’s B2 Stealth Bomber[25 1 - 2531. The all composite B2 bomber measuring about 5.2 m high by 21 m long with a wing span of 52.4 m consists largely of carbon/polyimide and other advanced plastic composite structure that make it virtually undetectable by radar [251]. The ribs for a wing section on the B-1B bomber as well as the ribs, stiffeners. skin and leading edge on the inboard flap of the Fairchild A- 10 have been made of APC-2 by the film-stacking method [252.253]. Film-stacking fabrication was jointly developed under the U.S. Air Force Thermoplastic Composite Development Program. Materials for the proposed USAF ATF must retain structural performance at temperature up to 176“ C [74]. In order to meet the service criteria defined for the aircraft, a material with a Tg of at least 200” C is required [74]. Boeing Military Airplane Company has prototyped an ATF wing with 60% Amoco’s Torlon polyamideimide reinforced with carbon fibres. The carbon/PAI prepreg is produced by Fiberite/ICI [253]. Avimid K is being considered for the thick section, large area ATF prototype wing skins by the Lockheed/Boeing/General Dynamics team [ 1581. 7.2.3 Wing of the U.S. Navy/McDonneK F/A-18 Fighter Aircraft 11881 McDonnell Aircraft Co. is conducting research and development work on thermosets, thermoplastics, titanium and aluminum-lithium manufacturing technologies with direct application to future military and commercial aircraft. Presently more effort is devoted to the development of advanced thermoplastic composites than thermoset composites. To demonstrate the evolving thermoplastic composites technology and to gain manufacturing experience with these materials, an upper and lower outer wing skin for both wings of a U.S. Navy/McDonnell F/A- 18 fighter aircraft have been manufactured and will be installed and service tested. The left wing panels are composed of thermoplastic composite AS4/PEEK while the right wing panels are made of epoxy composite IM-7/8551-7E. This

142 High Performance Thermoplastic Resins and Their Composites thermoset using a bismaleimide resin exhibits improved high temperature performance and improved toughness and resistance to delamination.Although F/A-18s will continue to be produced with carbon/epoxy outer wing panels,these experimental panels will permit comparison between thermoplastic and thermoset composites behavior under flight conditions.The reprocessability feature of thermoplastic composites has been demonstrated in this project.In the first part that was made,a disbond was present because of inadequate pressure.The part was put back into the heated press and reprocessed with correct pressure which fused the disbonded area. Development is focused at the design and construction of fully automatic manufacturing equipment capable of producing thermoplastic composite structures and will include an on-line non-destructive inspection capability. 7.2.4 Landing Gear Strut Door and Access Panel [254] The Northrop Corporation initiated and completed a project to design,fabricate and test two carbon/PEEK landing gear strut doors and access panels for the F-5F aircraft [254]. These two non-primary structures were selected because of the complexity of the design for the strut door and to acquire durability data for the access panel.This latter component is a damage prone part since it is often removed during aircraft servicing. The inner and outer skins of the landing gear door were fabricated with the thermoplastc composite materlal IM6/PEEK.Sixteen and forty-nine ply lay-ups were required for the inner skin and outer skin,respectively.The inner skin was molded using a pressure forming diaphragm process and the outer skin was formed with a vacuum bag autoclave process.The weight savings for the thermoplastic inner and outer skins compared to aluminum skins were 31%and 33%respectively.Assembly was accomplished with skin-to- skin adhesive bonding.The thermoplastic door assembly has carried the proof-test loads. The original access panel made from magnesium alloy has been fabricated with a 10 ply AS4/PEEK laminate formed in a hot platen press.Both the landing gear door and access panel have been demonstrated as flight worthy by Northrop Corporation and will be flight tested. Components for a developmental access door made of woven carbon fabric/PPS laminate sheets have been thermoformed in one-step for Boeing.Seven thermoplastic composite components were ultrasonically welded to assemble the 55.9 cm hollow access door. The thermoplastic composite door exhibited ten times the fracture toughness of carbon/epoxy 2521

142 High Performance Thermoplastic Resins and Their Composites thexmoset using a bismaleimide resin exhibits improved high temperature performance and improved toughness and resistance to delamination. Although F/A- 18s will continue to be produced with carbon/epoxy outer wing panels, these experimental panels will permit comparison between thermoplastic and thermoset composites behavior under flight conditions. The reprocessability feature of thermoplastic composites has been demonstrated in this project. In the first part that was made, a disbond was present because of inadequate pressure. The part was put back Into the heated press and reprocessed with correct pressure which fused the disbanded area. Development is focused at the design and construction of fully automatic manufacturing equipment capable of producing thermoplastic composite structures and will include an on-line non-destructive inspection capability. 7.2.4 Landing Gear Strut Door and Access Panel [254] The Northrop Corporation initiated and completed a project to design, fabricate and test two carbon/PEEK landing gear strut doors and access panels for the F-5F aircraft [254]. These two non-primary structures were selected because of the complexity of the design for the strut door and to acquire durability data for the access panel. This latter component is a damage prone part since it is often removed during aircraft sewicing. The inner and outer skins of the landing gear door weie fabricated with the thermoplastic composite material IM6/PEEK. Sixteen and forty-nine ply lay-ups were required for the inner skin and outer skin, respectively. The inner skin was molded using a pressure forming diaphragm process and the outer skin was formed with a vacuum bag autoclave process. The weight savings for the thermoplastic inner and outer skins compared to aluminum skins were 3 1% and 33% respectively. Assembly was accomplished with skin-toskin adhesive bonding. The thermoplastic door assembly has carried the proof-test loads. The original access panel made from magnesium alloy has been fabricated with a 10 ply AS4/PEEK laminate formed in a hot platen press. Both the landing gear door and access panel have been demonstrated as flight worthy by Northrop Corporation and will be flight tested. Components for a developmental access door made of woven carbon fabric/ PPS laminate sheets have been thermoformed in one-step for Boeing. Seven thermoplastic composite components were ultrasonically welded to assemble the 55.9 cm hollow access door. The thermoplastic composite door exhibited ten times the fracture toughness of carbon/epoxy [252]

Costs and Aircraft Applications of Thermoplastic Composites 143 7.2.5 Strut Fairings on the Boeing 757-200's Jet Engines[255] The four fairings used on the struts of the Boeing 757-200's jet engines (two per engine) are produced from injection-molded glass-filled PEEK.These parts approximately measure 51 cm by 30 cm in size and weigh 2.2 kg.They have to resist to hostile conditions including high levels of moisture,sonic vibrations and high air speeds.Despite daily exposure to these conditions,they must providc cfficicnt pcrformancc,givc long-tcrm durability and maintain an attractive appearance.PEEK resin was selected after evaluation of a variety of other thermoplastic materials including nylon 6/12.polyetherimide and polycarbonate.The PEEK fairings are about 30%lighter than fairings of conventional aluminum construction and they are 90%less expensive. 7.2.6 Aerosurface Components on Subsonic Missiles [256] McDonnell Douglas Astronautics Company is investigating the replacement of metallic and thermoset composite structures on subsonic missiles with thermoplastic composites.The components include metal fins and wings for the Harpoon and Tomahawk low speed missiles and the Tomahawk glass/epoxy air inlet duct and radome. Harpoon Missile Figure 61 shows the Harpoon control fin design concept.The skins are made with either continuous unidirectional tape or thermoplastic resin reinforced with woven cloth.The cloth or tape prepreg is laid-up and thermoformed.The laminate skins are placed in the mold, and the core material consisting of the same thermoplastic resin as the skin but reinforced with 30%chopped carbon fibre is injection molded forming the core. Both PPS and PEEK thermoplastic resins have been investigated for this application. Tests conducted on these materials have shown that PEEK is superior,but further cost analysis has to be performed before choosing the final material. Tomahawk Missile Figure 62a shows that the Tomahawk fin uses the same design concept as the Harpoon fin.The wings and fins,the air inlet duct,and the radome have all been redesigned with thermoplastics.The proposed wing redesign for optimum strength and stiffness is shown in Figure 62b.The two thermoformed laminate skins will be thermally welded to the core. The choice of the material to replace the hand lay-up glass/epoxy air inlet duct has not been made yet.PPS,PEEK and polycarbonate with various reinforcement combinations are candidate materials.The proposed molding process is complicated since it includes multi-shot

Costs and Aircraft Applications of Thermoplastic Composites 143 7.2.5 Strut Fakings on the Boeing 757-200’s Jet Engines [255] The four fairings used on the struts of the Boeing 757-200’s jet engines (two per engine) are produced from injection-molded glass-filled PEEK. These parts approximately measure 5 1 cm by 30 cm in size and weigh 2.2 kg. They have to resist to hostile conditions including high levels of moisture, sonic vibrations and high air speeds. Despite daily exposure to these conditions, they must provide efficient performance, give long-term durability and maintain an attractive appearance. PEEK resin was selected after evaluation of a variety of other thermoplastic materials including nylon 6112, polyetherimide and polycarbonate. The PEEK fairings are about 30% lighter than fairings of conventional aluminum construction and they are 90% less expensive. 7.2.6 Aerosurface Components on Subsonic h&Ales [256] McDonnell Douglas Astronautics Company is investigating the replacement of metallic and thermoset composite structures on subsonic missiles with thermoplastic composites. The components include metal fins and wings for the Harpoon and Tomahawk low speed missiles and the Tomahawk glass/epoxy air inlet duct and radome. Harooon Missile Figure 61 shows the Harpoon control fin design concept. The skins are made with either continuous unidirectional tape or thermoplastic resin reinforced with woven cloth. The cloth or tape prepreg is laid-up and thermoformed. The laminate skins are placed in the mold, and the core material consisting of the same thermoplastic resin as the skin but reinforced with 30% chopped carbon fibre is injection molded forming the core. Both PPS and PEEK thermoplastic resins have been investigated for this application. Tests conducted on these materials have shown that PEEK is superior, but further cost analysis has to be performed before choosing the final material. Tomahawk Missile Figure 62a shows that the Tomahawk fin uses the same design concept as the Harpoon fin. The wings and fins, the air inlet duct, and the radome have all been redesigned with thermoplastics. The proposed wing redesign for optimum strength and stiffness is shown in Figure 62b. The two thermoformed laminate skins will be thermally welded to the core. The choice of the material to replace the hand lay-up glass/epoxy air inlet duct has not been made yet. PPS, PEEK and polycarbonate with various reinforcement combinations are candidate materials. The proposed molding process is complicated since it includes multi-shot

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