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20121003
20120902
中国航空发动机发展：国产高性能涡扇发动机是实现战斗机制造完全自主的最后环节
编者：2011年6月26日，美国《洞察中国》（China SignPost）网站发表了一篇题为《中国航空发动机发展：国产高性能涡扇发动机是实现战斗机制造完全自主的最后环节》，文中介绍了中国航空发动机产业的现状，对未来发展进行了展望。本刊编译并发表此文，并不表示证实或赞同其文中内容及观点，仅供关注中国航空动力产业的读者参考。
中国致力于开发国产高性能航空发动机，用于装备国产军用飞机的战略方向已经明晰，这一战略选择包含着重大的航空技术挑战，世界上仅有少数几家大公司真正掌握着这项技术。这本身并不奇怪：发动机对于飞机的重要程度，不亚于心脏对于人体。发动机的设计研发，面临着温度、压力、过载等一系列严峻问题，只有最为先进的材料，最为合适的加工方法，科学的设计，合理的使用维护，才能解决这些难题。近些年中国在材料和制造方面取得了一些进步，但在部件和系统设计、集成以及根据可靠性特征制订勤务和使用管理方案等方面仍然存在问题——这些方面是优化发动机使用效能的关键。
中国在发动机这一关键领域取得的进步仍然不够平衡，某些领域比较先进，但整体水平仍然落后。根据中国国防工业基础能力和可用资源水平判断，中国未来会取得重大进步，但目前的技术障碍以及资源集中力度的不足，将会让中国花上2到3年才能获得与当前在发动机方面投资总额相称的综合技术能力，5到10年后，中国才能稳定地批量生产第五代战斗机所需的高端涡扇发动机。一旦中国进入这个阶段，就将迈入高端发动机制造国俱乐部，又消除了一个为数不多的必须依赖俄罗斯技术输入的国防工业瓶颈，其战略意义不言而喻。
国产航空发动机战略意义何在？
对于中国，具备国产军用高性能航空发动机制造能力有两点重要的现实意义。首先，可以摆脱对外来航空发动机零部件的依赖，解决由于俄罗斯不愿输出而带来的短缺问题，同时解决俄罗斯售后服务较差带来的诸多保障问题。据估计，俄军在未来10年采购的军用发动机数量将超过苏联解体后20年的总量，这对于中国影响巨大，当年正是因为苏联解体导致军购能力大幅下滑，才促使俄罗斯将包括航空发动机在内的先进装备出售给中国。而反观现在，俄空军未来对于苏-34、苏-35和T-50等先进战机的采购，将占用俄罗斯航空发动机制造业的绝大部分产能，造成后者出口外销意愿削弱，可能限制出口数量。俄罗斯政府可能更愿意优先出售先进战斗机整机，而不是单独的发动机。即便俄罗斯继续出口航空发动机，中国也将无法获得足够的数量，用于其战斗机生产。俄罗斯航空产品的售后服务水平一贯较低，技术和备件的支持能力差，且价格昂贵，反应速度缓慢，一些重要的技术手册只有俄文版，或干脆不予提供。其次，拥有国产高性能航空发动机，中国才能在国产战斗机的销售问题上拥有充分的自主权。中国正在成为先进战斗机出口国，不希望外国发动机供应商在其军售问题上行使否决权。中国出口巴基斯坦的FC-1使用与米格-29相同的RD-33发动机，但FC-1售价低廉，在发展中国家军购市场上成为俄制飞机的有力对手，因此，俄罗斯曾一度反对中国向巴基斯坦出售FC-1。这段经历让中国认识到，只有具备国产航空发动机制造能力，才能在飞机出售问题上更加自由。中国歼10和歼11B战机也面临同样的问题，一旦中国决定出口这两型飞机，同样可能在发动机问题上遭遇掣肘。中国不希望国产最先进战斗机在动力系统方面仍要继续依靠外国技术。
中国"枭龙"战斗机使用与米格-29相同的RD-33发动机，中国在出口该机时不得不考虑发动机的供应问题。图为俄制RD-33发动机。
中国军用航空发动机产业的现状
2011年4月的一次谈话中，中国航空工业公司（简称中航工业）总经理林左鸣曾表示，尽管中国航空工业取得了快速发展，但在先进喷气发动机制造领域仍然存在较大差距。为了缩短差距，中航工业将把航空发动机研发放在优先地位，未来五年内将投资100亿人民币（15.3亿美元）用于先进航空发动机研发。
中国涡扇-10"太行"涡扇发动机及其改进型的性能指标与美国普惠F100和通用电气F110相当，这两款发动机是目前美军F-15和F-16战机的动力装置。"太行"家族据说还是歼11B的动力，可能最后取代俄制AL-31，成为歼10和歼15的动力。2010年11月有媒体报道，一款推力27 500磅（约125千牛）的涡扇10"太行"发动机已投入批生产，将用于装备歼11B。尽管如此，仍然有证据表明中航工业在扩大涡扇-10量产过程中质量稳定性控制存在问题，造成发动机可靠性不足，致使中国战机仍然严重依赖俄罗斯进口发动机。
俄罗斯国防工业认为，中国目前还不能批量生产性能可靠的高性能军用涡扇发动机。俄罗斯喷气发动机制造商土星科研生产联合体就预言，在2019年以前它仍然是中国歼10和FC-1战斗机发动机的主要供应商。有消息称，2011年中国与俄罗斯洽谈过购买190台D-30KP-2涡扇发动机事宜，这些发动机可能用于中国的俄制伊尔-76，土星的乐观可能部分地来自于此。
中国涡扇10"太行"发动机的研制成功，标志中国发动机技术取得了重大进步，但西方认为该型发动机的量产质量控制问题尚未完全解决。 李丰/绘
由于缺少足够数量高性能涡扇发动机供应，中国未来歼10、歼11、歼15乃至歼20战斗机的量产都将受到影响。歼20计划更是要求国产航空发动机在研发和生产上取得突破，因为俄罗斯显然不愿意向中国输出117S发动机，而没有这种发动机，歼20将无法实现超声速巡航，也就无法达到第五代战斗机的标准。
过去可能被中国长期忽略的一个事实是，控制软件也是航空发动机技术的重要环节。许多航空发动机性能参数都可以通过软件进行调解，发动机制造商往往会因为软件升级而向用户收取高额费用，实际上发动机控制软件的升级过程看似简单，但却能显著改变发动机性能。民用发动机和军用发动机的一项重要区别就是，前者使用一体化的软件编译模块，而军用发动机的源代码和编译模块分开存储。军用发动机软件源代码的编写耗资巨大，因为它对注释、文档、线形追溯性、整合度以及模块化有诸多要求，还要求进行稳固性测试。任何发动机出口方，都会把软件问题当作重大问题处理。以美国为例，尽管以色列等国家多次要求美国转移控制软件源代码，但美国始终没有同意。
高性能喷气发动机的制造是一项难度极大的工作，一台发动机零部件多达上万个，必须使用特殊耐用材料来制造，加工精度要达到微米级。用于军用飞机的高端发动机更是要求能在高温、高速、剧烈机动和频繁调整等极端条件下可靠工作。以喷气发动机的压缩机叶片为例，运转时要能承受高达自身重量20 000倍的离心力。至于涡轮叶片，则要能在超过大多数金属熔点的温度环境中正常工作而不发生明显形变，其对于冶金技术要求的难度，无异于用一把冰勺子搅动一锅热汤。
中国航空发动机制造能力已经显著改善，但西方当前还不能准确掌握中国的发动机设计能力。为了实现航空发动机研发和制造的重大突破，中国必须对整个发动机工业体系进行统一、改善和优化，这又要求必须使用高水平的全寿命管理工具、软件，建立从始至终的技术支持体系。以汽车动力系统为例，要制造一根曲轴相对容易，但要让整个汽车动力系统完美可靠地工作，并理解该系统各部分在各种条件下的相互作用，却绝非易事。汽车况且如此，更不用说复杂程度呈几何级数增加的军用航空发动机了。
开发高性能航空发动机需要大量的基础研究，仅就气动优化问题，就需要建立涡轮叶片周围流场变化的精确模型。高压涡轮可以通过技术手段进行强化，但如果其热力学特性发生变化，则在高温条件下膨胀方式也会发生变化，进而可能导致几何外形的非连续性变化，在运转过程中可能发生失效，甚至损坏发动机。这就需要研发部门对流场、疲劳以及可靠性问题进行细致的建模和设计工作。
先进航空发动机的设计，要求对发动机内部流场进行复杂而精细的模拟，这项工作相当艰巨，也是保证发动机设计性能的重要手段。图为美国NASA对航空发动机风扇转动状态下其叶片周围流场的计算机模拟图像。
现在用来表征航空发动机性能的一个重要指标是平均故障时间（MTBF）和平均大修间隔（MTBO），前者即发动机正常工作的期望时限，后者则是发动机工作多长时间需要进行大修。这两项指标又与发动机失效曲线和特征数据密切相关，确定这些特点同样需要大量测试和统计学分析，它们对发动机维护管理和估测发动机性能至关重要。如果这项工作没能有效完成，那么就意味着无法完全掌握发动机的失效特征，也就难以预测发动机的失效，其结果便是在使用中遭遇各种"出乎意料"的性能变化，而发动机性能的突然变化，对军事飞行危害极大。
为弥补这些技术领域的不足，保证所需的作战效能，在列装数量问题上就必须留出足够的冗余度。这就意味着，中国可能需要大约200架"侧卫"战斗机才能保证与100架F-15相当的任务效能。其他如外来异物损伤（FOD）耐受能力、低温/高温启动性能等重要指标也能反映发动机技术水平，俄罗斯发动机在外来异物损伤（FOD）耐受能力方面要逊色于西方同级产品。
简言之，确保航空发动机系统的优良品质，需要设计、制造、使用监控、全寿命管理等环节的全方位技术能力，而这种全方位技术能力在中国仍是薄弱领域，因为此前中国一直严重依赖对国外产品的拷贝和仿制，这种做法无法获得发动机研制和管理能力，其结果是中国航空发动机领域长期以来受到依赖路线的束缚，造成发动机研制生产道路日趋狭窄，水平长期徘徊在国际水准之下，综合系统能力较差，要想改变这种状况，需要投入大量资金，付出艰苦的努力。
近年中国航空发动机制造技术与工艺取得了明显改善，有消息证实，中国已经在精密切割、焊接和机械加工（如生产涡轮叶片所需的五轴精密铣削）等方面获得较大发展，特种材料叶片制造水平也有显著进步，中国最大的涡轮叶片生产设施位于西安，这里如今能够批量制造超级合金、钛合金、钴合金以及不锈钢涡轮叶片。据称涡轮叶片合格率已经超过了95%。中国已经初步具备了空心风扇叶片制造能力。空心钛合金风扇叶片要比实心同类叶片减重15%-20%，能显著降低发动机的油耗。空心叶片还能降低发动机的转动惯量，提高机动过程中发动机的加速性能。中国还正在通过过程建模提高发动机设计水平，计算机辅助过程建模分析能够让制造人员估计热应力环境中，材料、焊接以及零部件变化可能造成的问题。在开工制造之前找出潜在的隐患，能够在发动机研发过程中节约大量资金和时间，有助于制造出高性能且耐久性优良的发动机。生产过程中的自动化水平也有提高，这有助于提高制造的标准化和效率。
中国军用喷气发动机面临怎样的挑战？
中国希望批量制造普惠F100同级别的发动机，并开发歼20这类第五代战斗机使用的高推力发动机，这些雄心在技术上和过程上都面临着严峻的挑战。在技术层面，中国发动机涡轮锻造、涡轮盘粉末冶金、钛合金空心件成型等问题上仍然薄弱。这些领域在近些年都取得了不小的进展，但由于基础水平较低，问题仍然存在。
中国需要建立先进的发动机生产线，以保证国产发动机的量产质量，生产自动化水平还需要进一步提升。有消息称现在生产中加工超耐热合金材料仍然是一个难题，加工过程常常造成切割工具的频繁损耗。就质量稳定性而言，同型发动机需要在同一条生产线上生产，这样才能保证生产线的规模效益和质量稳定性。一旦设计定型投入批量生产，就应该尽量避免分线生产，这样会影响产品的一致性。在实验室制造一片涡轮叶片是一回事，而批量生产数以千计的标准化且性能可靠的涡轮叶片则完全是另一回事儿。一台喷气发动机往往需要400～500片各类叶片，稳定的量产质量是发动机制造业的必需。要做到这一点，中国必须解决冶金技术和工业流程的科学化问题。
中国国内有分析人士指出，中国发动机工业应该设法将研究和制造部门整合，创建科学的研究数据库，以便让制造更加高效，减少发动机设计、材料和制造等环节的交流障碍，培养新型的工程技术人员。他们认为在某些领域，中国航空发动机比美国落后大约30年。
批量生产的全过程质量控制对于保证量产喷气发动机的可靠性尤为重要，图为对民用燃气轮机涡轮叶片实施等离子喷涂工艺。
中国需要努力实现的，是六西格玛或全面质量管理能力，这样才能确保质量管理的有效性，确保所有质量问题得到监督，以及所有生产和质量数据的真实性。如果这一点无法实现，那么中国在发动机研发制造技术迈进过程中的代价将非常巨大。苏联国防工业的失败很大程度上就来自这一问题。
中国目前尚未采用法国达索等西方企业使用的全寿命设计工具，中国航空发动机已经在设计环节广泛应用了计算机辅助设计和制造工具，但在服役使用方面应用还很不足。只关注设计环节，会造成产品制造和维护便利性的降低。这方面中国船舶工业做得比较好，在全流程都应用了设计和仿真分析技术。
值得注意的是，中国航空发动机有自己的后发优势——他们可以从先进国家航空发动机研制的成功与失败中获取经验，这样能够显著缩短自身发动机研究–发展–制造的过程时间。美国F-22"猛禽"使用的普惠F119发动机是在上世纪八九十年代开发并改良完成的，这意味着中国不需要获取2011/2012年的最新发动机技术，就能获得非常有价值的技术参照，从而开发本国歼20所需的第五代战斗机用喷气发动机。
规模与资源问题
和美英等国军用航空发动机工业相比，中国航空发动机工业在人员规模上仍显不足，但已经超过了俄罗斯和法国的水平。黎明公司和西安航发这两家中航工业最大的军用发动机企业，人员总和接近20000人。与之相比，普惠、罗罗和通用电气航空分部每家企业人员都超过了35000人。
为了追求军用航空发动机自给化，中国航空发动机工业可能在未来会扩大规模。俄罗斯UMPO目前总人员规模为15 000人，计划在2010年生产109台AL-31和AL-41发动机。通用电气航空分部每年大约能交付200台高性能涡扇发动机和总数800台军用发动机和直升机用涡轴发动机。
经费限制在发动机采购方面应该不会构成大的问题，以每台军用航空发动机采购价格250～500万美元计算，即使中国每年生产500台军用涡扇发动机，其总费用也仅占2011年军费预算的2%左右（注：2011年中国国防预算为6 011亿元人民币，合915亿美元）。
获得特殊的材料并正确地加工，对于制造航空发动机以及保证制造成本的竞争力，都极为重要。日本石川岛播磨重工株式会社航空发动机工厂经理曾表示，航空发动机零部件成本的50%都来自材料本身。现代高性能航空发动机需要采用一些高强度、耐高温材料，包括钛、镍、铝、复合材料以及镍基和钴基超耐热合金。中国在钛、镍和钴等金属的产量十分巨大，理论上，从资源供应量来看，对航空发动机产业构不成任何制约，但仅仅是理论上而已。中国航空发动机制造商面临的材料制约并非是取得镍、钴和其他金属等原材料，最为复杂的问题是制造或购买到能够用于航空发动机的耐高温合金材料。有分析认为，中国现在超耐热合金还不能完全自给，据估计中国每年超耐热合金的生产量约为10 000吨，而需求量则为20 000吨。
一台商用航空喷气发动机通常需要700千克到两吨超耐热合金。大多数军用高性能喷气发动机自重都不超过2吨，假定每台发动机需要1吨超耐热合金，如果中国把每年超耐热合金产量的10%用于航空发动机，则可以制造1 000台军用喷气发动机。从长远看来，超耐热合金将是中国航空发动机制造业的瓶颈，未来5年可能会迅速扩大规模。
中国发动机产业的快速进步，为中国提供了更加广阔的合作前景，也让中国有更多的机会学习国际先进技术和经验。图为中国制造的航空发动机转包生产串件。
需要关注的几个性能问题
热循环损耗 大型运输机或加油机使用的发动机在大部分飞行时间都工作在比较稳定的速度范围，但战斗机用喷气发动机则完全不同，由于飞行员会在剧烈机动过程中频繁而快速地调整油门，因此发动机的转速也会频繁快速地变化。这会造成发动机温度的快速变化，这种热循环变化会产生重要的损耗。美军在装备和使用第一种真正意义上的高性能喷气发动机F100过程中，就发现热循环变化会造成难以预计的安全和维护问题。
在开发F100过程中，普惠的技术人员原本认为发动机零部件疲劳的决定因素是高温运行时间，也就是全推力或高推力运行的时间。但实际使用中人们发现，由于F100优良的性能，空军在使用中开始实践全新的战术技术和训练模式，飞行员会更加频繁地实施机动。这样一来，发动机在全推力状态下工作的时间相对较少，但其转速变化频率却超出了发动机设计人员的预期。F100设计要求规定发动机在全寿命周期内要能经受1 765次全推力过渡，但实际使用证明发动机使用寿命比预期低30%，调查发现这是因为发动机的热循环变化次数显著高于预期，到寿发动机平均全推力过渡次数接近设计数字的6倍，达到了10 360次。
在中国开发高性能军用发动机的过程中，同样的问题也会出现，需要科学合理地加以解决。鉴于中国空军飞行员训练频次和力度不及美军，因此中国是否已经为处理类似的热循环损耗问题做好充分准备，尚不得而知。取得近似作战条件下的发动机热循环损耗数据，是一项重要的工作，苏联航空兵在这方面也没有完全掌握第一手资料。
中国技术人员在改善现有发动机性能和延长其使用寿命方面已经有了明显进步，有消息报道，中国已经成功使俄制AL-31F发动机的使用寿命从900小时延长至1 500小时。据此推测，中国涡扇10以及其他新型航空发动机也会采用类似的延寿技术。
发动机的环境适应性是衡量发动机使用性能的一项重要指标，图为美国空军利用C-17"环球霸王"F117发动机进行积水吸入试验，以检测发动机在吸入积水情况下能否维持健康运行，可见平台上的积水在强大负压下呈"水龙卷"状被吸入发动机。
环境适应性 许多环境因素会给发动机带来负面影响，如高原/高温机场、含沙空气、含盐水分侵蚀以及外来异物等。传统观点认为，俄罗斯航空发动机的抗外来异物能力就低于西方同类产品。由于担心外来异物损伤发动机，2008年红旗军演中，印度空军苏-30MKI的行动受到很大限制，这并非是印度空军维护不力——根据与俄方协议，所有因外来异物损伤的发动机都必须运回俄罗斯修理。
性能稳定性 西方先进航空发动机通常具备较好的全速度/高度连续动力输出性能和抗失速性能，中国产品在这些方面仍存在不足。俄罗斯苏-27战斗机使用的AL-31F涡扇发动机据称在大迎角机动状态下推力下降较大，因为这种状态会造成气流和油流的紊乱。对于没有推力矢量技术的战斗机，其发动机的连续动力输出性能更加重要，如果大迎角状态下发动机进气紧张，那么可能导致叶片失速或气流输入的不连续，进而造成发动机氧气供应不足。通过复杂的建模技术协调这些纷繁纠葛的影响因素，改进发动机进气道设计是解决该问题的重要途径。
体制结构问题
比技术问题更难解决的，是体制问题。中国国防目前存在装备来源单一的问题。中国国产军用航空发动机完全由中航工业提供，该集团公司旗下的沈阳、西安和贵州等发动机企业在某种程度上存在竞争，但竞争的积极效应并不明显。如果存在适度竞争，那么竞争压力会促使企业生产具有创新技术且价格较低的产品，加快研制进度，提高售后服务的水平。上世纪70年代末80年代初，针对当时美国空军航空发动机领域普惠一家独大的情况，美国政府决定促进通用电气和普惠之间的合理竞争，此举使得美国战斗机在设计过程中可以拥有两家竞争企业提供的诸多动力选择方案，成果显著。中国目前的情况与美国不同，发动机领域宏观的竞争不足，而在微观问题的竞争又过多，这会造成局部利益交换和利益保护，进而造成重复工作，资源使用不当，延长研制和生产周期。中国需要决定其航空发动机行业的组织系统结构和运行方式，这样才能从上层解决其结构和体制问题。
（编者按：就先进发动机研制而言，中国的知识资源和物质资源并不充足，引入美国那样的竞争体制，现阶段未必是最好的出路。单一来源未必就一定意味着低效率，问题的关键在于现有体制运行的效率，以及对效率评估的科学性，这方面法国的经验值得学习。）
军民技术转化
军用航空发动机与民用航空发动机在性能指标上差异巨大，但在材料和制造技术上存在相似性，特别是在核心机方面。在民航飞机领域广泛应用的CFM56商用发动机，很大程度上就应用了B-1B战略轰炸机普惠F101发动机的核心机技术。
中国航空工业领域合资公司的数目正日益增多，通用电气航空分部、普惠和斯奈克玛都成了中国航空企业的合作方，但合作主要限于最终装配和维护、修理以及大修方面。通过这些合作，中国企业能够学习如何实施售后服务、完成大修，以及如何将维修数据反馈到设计和制造环节中去，以改善产品的设计和性能。而这些经验和技能，对于军用航空发动机的设计、制造和维护也有应用潜力。
CFM国际公司是世界上最大的商用喷气发动机制造商，该公司是由美国通用电气航空分部、法国赛风旗下的斯奈克玛公司组建的合资公司。该公司同时也是中国C919大型飞机项目的发动机供应商，CFM在2009年曾与中航工业探讨在上海建立发动机总装线和发动机试验设施的可能性，但据说未有任何实际结果。据来自CFM的消息，提供给中国的LEAP发动机的总装线建在哪里尚未决定。
CFM公司的LEAP-X1C已经入选成为中国C919大型客机的标准动力方案，该型发动机是否在中国制造为外界普遍关注，其中一个重要因素就是，一些人担心该其核心机技术会被中国吸收。图为中航工业在2011年巴黎航展上展出的C919缩比剖视模型。
CFM在中国采购的发动机零部件很多，用于其现行诸多发动机产品，对于LEAP-X1C发动机可能也会采取类似做法，但现在就推测哪些部件会在中国制造为时尚早——这一问题已经引起了密集关注，其中的原因不难理解，该发动机核心机应用了包括整体式叶盘——即叶片和轮盘是用一整块金属加工或铸造而成的。这样的设计能大大提高可靠性并减轻重量，最多可减重30%。通用电气F414（用于F/A-18E/F）、普惠F119（用于F-22"猛禽"）、F-135和通用电气F136（用于F-35"闪电"II）都应用了该项技术，如果能够通过商用发动机合作项目，掌握该项技术，对于中国航空发动机工业无疑是非常有利的。这对于中国涡扇15和其他先进军用涡扇发动机都有着潜在的应用价值。
结语
根据中国尚不能批量制造性能稳定的用于第四代和第五代战斗机的国产发动机这一事实判断，中国航空发动机产业与美国相比差距应该仍然超过20年。
中国航空发动机性能的进步可以从推重比和燃油消耗率两个方面透射。前者反映了设计水平和制造质量，后者则表现了发动机的燃油利用效率，这决定了战斗机的作战航程、留空时间等重要性能。至于平均故障时间和野外更换与维修等系统管理指标，中国可能采取各种办法解决薄弱问题，比如准备更多的备份发动机——在当年美国F-4"鬼怪"在越战中也采用过这种办法，那时F-4配用的通用电气J79发动机可靠性较差。
通用电气J79涡扇发动机装备F-4"鬼怪"的初期，由于可靠性不高导致多起事故，美军曾采取了增大备份发动机数量的方式来保证飞机出勤率，同时也严重增加了装备使用成本。图为现在存放在亚利桑那州图森基地的报废J79发动机。
如果研究一下美国喷气发动机和飞机发展史，可以发现新飞机和新发动机出现之间的相关性几乎可以达到1。中国正在积极研发新型战斗机，这同时也要求研制全新的发动机作为动力。对于中国正在开发的第五代战斗机，俄罗斯自然不愿意出口117S等先进航空发动机。低估中国国防工业系统的实力是不明智的。外界估计，中国将在2到3年内在批量制造高性能喷气发动机方面取得突破，但对于制造可靠的顶级航空发动机，则还需要5到10年。一旦中国迈上这一台阶，将会促成中国空军和海军航空兵的强势崛起。目前中国需要重点监控的领域是设计能力、工装设备、制造能力和系统运营与维护能力，这些问题将会影响国产发动机的性能及使用效能。
译文链接： http://hollyduke.blog.163.com/blog/static/510156420127208614228/
Jet Engine Development in China: Indigenous high-performance turbofans are a final step toward fully independent fighter production
Posted: 26. Jun, 2011 Last update: 30. Jul, 2011
Gabe Collins and Andrew Erickson, "Jet Engine Development in China: Indigenous high-performance turbofans are a final step toward fully independent fighter production," China SignPost™ (洞察中国), No. 39 (26 June 2011)
China SignPost™ 洞察中国–"Clear, high-impact China analysis."©
Deep Dive—Special In-Depth Report #2
Executive Summary:
–Engines commonly used in Chinese and other modern aircraft may be divided into several major categories: (1) low-bypass turbofans typically power military jets; (2) high-bypass turbofans typically power jet airliners; (3) turboprops typically power more fuel-efficient, usually lower-speed aircraft, including civilian commuter aircraft and military transports and surveillance and battle management aircraft; and (4) turboshafts typically power helicopters. This study will address the first category, low-bypass turbofan engines; other categories will be addressed in follow-on China SignPost™ reports.
–China's inability to domestically mass-produce modern high-performance jet engines at a consistently high-quality standard is an enduring Achilles heel of the Chinese military aerospace sector and is likely a headwind that has slowed development and production of the J-15, J-20, and other late-generation tactical aircraft.
–The Chinese aerospace industry is driven by four key strategic imperatives as it pursues the ability to manufacture large volumes of high-performance tactical aircraft[1] engines: (1) parts dependence avoidance, (2) Russian supply unwillingness, (3) aircraft sales autonomy, and (4) poor Russian after-sales service.
–To address these shortcomings, AVIC is treating engine development as a high priority and plans to invest 10 billion RMB (US$1.53 billion) into jet engine research and development over the next 5 years.
–However, evidence still suggests that AVIC's engine makers are having trouble maintaining consistent quality control as they scale up production of the WS-10, causing problems with reliability and keeping China's tactical aircraft heavily reliant on imported Russian engines.
–Key weak points of the Chinese military jet engine industry include: turbine blade production and process standardization.
–Standardization and integration may be the one area in which the costs of China's ad hoc, eclectic approach to strategic technology development truly manifest themselves. The Soviet defense industrial base failed in precisely this area: talented designers and technicians presided over balkanized design bureaus and irregularly-linked production facilities; lack of standardization and quality control rendered it "less than the sum of the parts."
–We estimate that based on current knowledge and assuming no major setbacks or loss of mission focus, China will need ~2-3 years before it achieves comprehensive capabilities commensurate with the aggregate inputs in the jet engine sector and ~5-10 years before it is able to consistently mass produce top-notch turbofan engines for a 5thgeneration-type fighter.
–If China's engine makers can attain the technical capability level that U.S. manufacturers had 20 years ago, China will be able to power its 4th generation and 5th-generation aircraft with domestically made engines (3rd and 4th-generation in Chinese nomenclature, respectively). These developments would be vital in cementing China as a formidable regional air power and deserve close attention from policymakers.
China has a clear strategic interest in developing indigenous high-performance aeroengines to power its military aircraft. This is one of the greatest aerospace engineering challenges, however, one that only a small handful of corporations worldwide have truly mastered. This should not be surprising: an engine is effectively an aircraft's cardiovascular system; it can be transplanted but not easily modified. Unlike a human system, it can be designed and developed independently, but faces temperature, pressure, and G-force challenges that only the most advanced materials, properly machined and operated as an efficient system, can handle. While China has made progress in recent years with materials and fabrication, it appears to remain limited with respect to components and systems design, integration, and management—the keys to optimizing engine performance in practice—and to making logistical and operational plans at the force level based on reliable estimates thereof.
Based on available open source evidence, Chinese progress in this critical area remains uneven and the whole remains "less than the some of the parts." Given the overall capabilities inherent in China's defense industrial base and the resources likely being applied to this problem, we expect that China will make significant strides, but barring major setbacks or loss of mission focus, it will take ~2-3 years before it achieves comprehensive capabilities commensurate with the aggregate inputs in this sector and ~5-10 years before it is able to consistently mass produce top-notch turbofan engines for a 5th generation-type fighter. When it does, however, the results will have profound strategic significance, as China will have entered an exclusive club of top producers in this area and eliminated one of the few remaining areas in which it relies on Russia technologically.
How is domestic engine production strategically relevant?
The Chinese aerospace industry is driven by four key strategic imperatives as it pursues the ability to manufacture large volumes of high-performance tactical aircraft engines: (1) parts dependence avoidance, (2) Russian supply unwillingness, (3) aircraft sales autonomy, and (4) poor Russian after-sales service. First, China likely seeks to avoid dependence on Russian suppliers for vital parts. Chinese leaders will not want the country's most modern fighter aircraft to be dependent on foreign inputs for a core system such as propulsion. Second, Russia's own armed forces are likely to buy significantly more of its jet engines in the next 10 years than they did over the 20 years since the Soviet Union dissolved. This is an important development given that the collapse in military procurement after the Soviet Union fell was the key driver of Russian jet engine sales to China.
The Russian Air Force's plans to enhance its aircraft through refurbishment and re-engineering of existing systems and acquisition of new platforms like the SU-34, SU-35, and T-50/PAK FA could stretch Russian engine makers to the point that they have little export willingness, and perhaps restrained export capacity. The Kremlin, which controls Russia's jet engine makers, will likely prioritize the export of entire aircraft such as Sukhoi Flankers that require advanced engines and the Indo/Russian 5thgeneration fighter project, which will also demand the most advanced engines Russia's defense suppliers can produce. The bottom line is that the combination of new Russian Air Force aircraft purchases, continued exports of late model Flankers, and Russia's joint 5th generation fighter project with India will stretch suppliers enough that even if the People's Liberation Army Air Force (PLAAF) can get some advanced Russian engines, it likely will not be able to obtain enough to support its desired levels of aircraft production.
Exhibit 1: Estimated Total Chinese Demand for Non-Russian Military Turbofans (2011-20)
Sources: Sukhoi, Ria Novosti, Reuters, India MoD, UMPO, Jane's, Sinodefence.com
Third, China is a growing exporter of advanced combat aircraft, as shown by its recent deals to sell FC-1 and J-10 fighters to Pakistan, and will not want foreign engine suppliers having veto power over its arms sales. A major hang-up in the FC-1 deal was that the aircraft uses the same Russian-made RD-33 engines as the MiG-29, but sells for a much lower price and is thus a threat to Russian aircraft exports in the developing world. Russia finally granted China permission to make the FC-1 sale to Pakistan, but the experience almost certainly taught Chinese aircraft makers that it will be much easier to export Chinese-made aircraft if they use Chinese engines.
This is especially true given the fact that China's J-10 and J-11B (if SAC is permitted to export it) are comparable to existing Russian tactical aircraft exports and would likely be formidable competitors in terms of price and capability. We note here that a January 2011 editorial in Nanfang Daily anticipates China becoming a major jet engine exporter within the next 10 years.[1] High aspirations by no means imply the ability to actually achieve the desired capability, but these sentiments shed light on the broad importance Chinese policymakers and thinkers place on bolstering domestic jet engine production capabilities.
Fourth, China has had painful experience with poor Russian after-sales service for components, e.g., engines. This includes engineering and spare parts support that is expensive, delayed, or simply nonexistent and manuals that are limited, in Russian only, or not available at all.
Where does China's tactical turbofan sector stand today?
In an April 2011 interview, China Aviation Industry Corporation (AVIC) head Lin Zuoming noted that despite China's rapid development as an aerospace power, the country's ability to produce modern jet engines remains a glaring weakness.[2] To address these shortcomings, AVIC is treating engine development as a high priority and plans to invest 10 billion RMB (US$1.53 billion) into jet engine research and development over the next 5 years.
China's WS-10 Taihang turbofan engine and its derivatives have performance parameters on par with the Pratt & Whitney (P&W) F100 and GE F110 engine families, which power the U.S. F-15 and F-16 fighters. The Taihang family is said to power the J-11B and is also likely slated to eventually take over from the Russian AL-31 as the main powerplant for the J-10 and J-15. Media reports from November 2010 state that a version of the WS-10 Taihang turbofan producing 27,500 lbs of thrust is now in series production and is being used to power the J-11B fighter-bomber.[3] Exhibit 2 (below) shows a timeline of China's advanced military turbofan production.
Exhibit 2: China Military Turbofan Development and Production Timeline (WS-10, WS-15)
Sources: Jane's, Global Times, China.com
However, evidence still suggests that AVIC's engine makers are having trouble maintaining consistent quality control as they scale up production of the WS-10, causing problems with reliability and keeping China's tactical aircraft heavily reliant on imported Russian engines. Russia's defense industry appears to believe that China will continue to be unable to attain reliable mass production of high-performance military turbofans. For example, NPO Saturn, a key Russian military jet engine maker, forecasts that it will continue serving as the primary engine supplier for China J-10 and FC-1 fighter programs through 2019.[4] Saturn's optimism may stem in part from the fact that is it currently in talks with China over the possible sale of 190 D-30KP-2 turbofans, which could be used on China's IL-76 aircraft.[5]
The lack of a sufficient supply of reliable domestically made jet engines could significantly impede future production of the J-10, J-11, J-15, and J-20 fighter aircraft. The J-20 program especially needs domestic engine development and production breakthroughs because the Russia appears reluctant to sell the 117S series engines that could enable the J-20 to have sufficient power to allow the aircraft to supercruise (sustain supersonic flight without using inefficient afterburners) and match the performance of 5th-generation fighters such as the Lockheed Martin F-22 and Sukhoi T-50/PAK FA.
Software is a vital aspect of aeroengines, one that China will have to master to produce its own high-performance engines; and one that it will likely consider controlling carefully should it decide to market them when they reach the requisite quality and price level. Many aeroengine performance parameters can be adjusted using software; a manufacturer may charge a customer significantly for upgrades that are easily implemented but may alter engine function significantly. There is a tremendous disparity between civilian (uncertificated) and military (certificated) source codes: the former may have explanations embedded in them, while the latter may have source codes and explanations stored separately.
Military source codes can take up to twenty times longer to produce on a per-line basis because of requirements concerning annotation, documentation, line traceability, integration, and module- and robustness-testing. How to handle the relevant engine source code is therefore a key question for any exporter of packages that include aeroengines. The U.S. is typically able to avoid divulging source codes, despite repeated requests from such customers as Israel, because its military aircraft are so desirable.
Recent developments increasingly suggest that it is unwise to underestimate China's defense-industrial complex. We believe that barring major unforeseen disruptions or shifts in focus, China's aerospace industry already has sufficient financial support and is close to attaining a critical mass of human capital that over the next ~2-3 years will help it make substantial breakthroughs in its ability to produce sufficient volumes of reasonably dependable jet engines, and reach the ability to consistently produce 5th-generation fighter performance-level aeroengines in ~5-10 years. This, in turn, will help enable robust growth of modern Chinese airpower if the country's civilian and military leaders choose to expand and upgrade China's Air Force and Navy tactical air fleets.Ongoing limitations in tooling, design capability, and systems operations and maintenance and will be key areas to monitor, however, as these may limit the performance parameters of Chinese engines and shape their development in "path dependent" ways (meaning that future options are limited by are limited by past actions, even after the circumstances that shaped those actions are no longer relevant).
Strong and Weak Points of China's Jet Engine Industry
High performance jet engines are exceedingly hard to produce, as they can contain tens of thousands of parts that must be made of durable exotic materials machined to tolerances measured in microns. In addition, jet engines used in tactical fighter and strike aircraft must be able to operate reliably under extreme conditions including high temperatures, high speeds, intensive maneuvering, and frequent throttle changes. Jet engine compressor blades, for instance, can experience centrifugal forces as high as 20,000 times the force of gravity during flight.[6] The challenge that a turbofan blade faces in performing without significant deflection despite being exposed to heat that exceeds the melting point of most metals, and consequent materials and metallurgical requirements, has been likened to stirring hot soup with a spoon made of ice.
Chinese design capabilities remain uncertain, though manufacturing capabilities are clearly improving. To reach the pinnacle of aeroengine development and performance, China must model, refine, and optimize the total system, which can only be done with top-level total lifecycle tools, software, and cradle-to-grave support. Even in a less complex machine such as an automobile, for instance, it is relatively easy to manufacture a crankshaft, but relatively difficult to make the system perform well as a unified whole and to understand the complex interaction of its components under different conditions.
To consider an aeroengine-specific example, for optimum aerodynamics, it is necessary to model the airflow implications of a turbofan blade changing slightly. A high-pressure turbine might be strengthened, but if its thermal characteristics change, then it might not expand in the same way, and the resulting discontinuity in surface geometry could lead to a failure that destroys the engine. Important areas to design for and model therefore include airflow, fatigue, and reliability.
The most important aeroengine performance metrics include mean time between failure (MTBM)—i.e., how long an engine lasts; and mean time before overhaul (MTBO)—i.e., how often an engine must be serviced fully. This, in turn, is linked to the degradation pattern/structure, which is vital to managing engine maintenance and anticipating performance. "Hitting the wall," or experiencing a sudden and marked decline in engine performance, is particularly hazardous in military aviation, where even slight deviation from optimum performance parameters can be highly problematic. Unpredictable dynamics, or lack of knowledge of existing patterns, can be make it much more difficult to make the best use of engines—even in training, but especially in combat.
Compensating for shortcomings in either of these areas might require factoring in a substantial margin of error by dedicating additional engines and airframes; were the need great enough, something like 200 Flankers might be needed to ensure the mission fulfillment capabilities of roughly 100 F-15s. Other important metrics include acceleration/deceleration patterns, foreign object damage (FOD) resistance (Russian engines have historically fallen significantly short in this regard), and cold/hot temperature starts (the former is usually more difficult than the latter, but the amount of difference varies by engine model).
In short, an aeroengine system is only as good as its design, monitoring, and lifecycle management. This may be an area of particular weakness for China, as it has traditionally relied heavily on copying and emulating foreign designs. This approach does not confer ability to design and manage aeroengines; on the contrary, it can impose path-dependent limitations that lead to dead ends or substandard, poorly integrated systems that are costly and difficult to alter and thus remain "less than the sum of their parts."
While this systemic component of Chinese turbofans remains uncertain, however, the techniques and processes to support their manufacture are clearly improving. Chinese gas turbine experts say the country's aerospace industry has improved its jet engine manufacturing abilities in key areas, including:[7]
–Precision cutting, welding, and machining, e.g., five-axis milling for production of turbine blades.
–Special materials blade production. China's largest turbine blade production facility, located at Xi'an Aero-Engine, can now undertake mass-production of turbine blades made from superalloys, titanium alloys, cobalt alloys, and stainless steel. The turbine blade quality rate is now said to exceed 95%.
–Hollow fan blade production. China is entering the nascent stages of being able to produce hollow fan blades. Hollow titanium fan blades are 15-20% lighter than their equivalents and make an engine more fuel efficient. They also reduce rotating mass and allow a tactical aircraft engine to spool up more quickly during maneuvers.[8]
–Greater automation. This improves standardization and efficiency.
–Process modeling. Computer-aided process modeling help manufacturers anticipate problems with materials, welds, and behavior of parts under heat stress. Flagging potential trouble spots before machines are started helps save time and money and also ultimately helps produce a higher quality, more durable engine.[9]
–Enhanced ability to use numerically-controlled milling machines to produce turbine disks.
–Better ability to produce high-quality, standardized spare parts. Reliable access to such parts is essential to supporting aircraft performance, particularly at the high and unpredictable operational tempo inherent in many operational scenarios. Spare parts have traditionally represented an area of weakness in China's aviation industry.
Still unclear, however, are key design, system, software, and reliability aspects of engine systems and components. Vibration testing of components is important (e.g., under high-G forces for military engines). It is difficult to determine China's stage of development for Fully Automatic Digital Engine Control (FADEC), or the capability of the engine to communicate with the cockpit; and for Engine Control Units (ECU), the "brain" of the engine, which helps it to regulate itself.
Many of the Chinese jet engine industry's recent improvements center on turbine blade production, which is logical given turbines' location at the heart of any jet engine. However, a comprehensive analysis by experts from the China Gas Turbine Establishment, which played a major role in designing the WS-10 engine, does not discuss improvements in engine reliability. Thus, better blade manufacturing and machining may still not have brought about commensurate improvements in quality control and engine reliability. The WS-10A is now said to be flying in the PLAAF's J-11B, and as engines accumulate flight hours it will be telling to see how powerful and efficient they are, how they hold up, and how frequently they require overhaul. The PLA is notably opaque about aircraft losses, but occasional reports do slip through, providing a barometer of reliability to watch as domestically-made engines spend more time in the air.
What challenges do Chinese military jet engine makers continue to face?
China's attempts to mass produce P&W F100-class jet engines and develop an engine powerful enough to give the J-20 true 5th generation performance levels face a range of technical and process challenges. On the technical side, Chinese gas turbine researchers say weaknesses remain in turbine casting, powder metallurgy for creating turbine disks, and molding hollow titanium parts.[10] Many of these areas were named as ones in which substantial progress has taken place in recent years. Nonetheless, progress may be from a very low baseline, making the claims that problems remain while progress has occurred compatible with each other.
Chinese engine makers likewise need to create advanced production lines to ensure effective logistical support for domestically-made engines and must also automate their production facilities to a greater extent. Part of the technical challenge stems from the fact that machining the tough superalloys used in jet engines requires twice the cutting force of other types of machining and that cutting tools may have to be changed up to 10 times more often than when machining softer materials like those used for making auto parts.[11]
While this necessitates highly specialized production lines, however, a given engine needs to be produced on the same line to ensure economies of scale and quality consistency. Once systems are optimized, separating production into different lines should be avoided, as a stand alone approach could disrupt or crack the system. It is one thing to make a single turbofan blade in a laboratory, and another entirely to ramp up to mass production of several thousand (a single engine contains 400-500 blades in up to two dozen stages of 2-3 dozen blades each) blades of standardized, reliable quality. This requires mastering both the metallurgy grade and mastering the industrial process to reliably produce a high-quality product.
In the very limited publicly available discussions of China's jet engine manufacturing weaknesses, local experts focus heavily on process weaknesses as major constraints on China's ability to produce high-performance turbofans of consistently good quality. Chinese analysts cite the need to better integrate the research and manufacturing segments of the industry, creating databases to save knowledge that can be used to make construction more effective, reducing the boundaries between the jet engine design, materials, and fabrication sectors, and doing a better job training new technical and engineering staff.[12] Exhibit 3 (below) depicts key technical and process weaknesses currently affecting China's tactical turbofan production.
Exhibit 3: Where China's Military Jet Engine Makers Continue to Experience Problems
Source: Defense Manufacturing Technology, USCC, China SignPost™
To put these weaknesses into context, they suggest that in some areas Chinese engine makers are roughly three decades behind their U.S. peers. Technical reports by U.S. manufacturers discussing challenges of actually making hollow fan blades that date back to 1977, implying that Chinese engine fabricators could be three decades behind the state-of-the-art curve at present.[13]
Abstracts of P&W technical papers from 1976 discuss using nickel superalloy powders to forge turbine discs for the F100 engine.[14] In contrast, as mentioned above, researchers from the China Gas Turbine Establishment cite powder metallurgy for turbine disc production as an enduring weak spot for China's jet engine industry.[15] Of course, this may represent an attempt to secure additional funding, as opposed to a true reflection of current status; when did the U.S. Air Force (USAF) ever run out of update programs for its fighters?
One cautionary point here is that Chinese jet engine makers have a latecomer advantage, which allows them to learn from other engine makers' successes and failures and potentially to shave years from their own research-development-production sequence. To put matters in perspective, the P&W F119 engine that powers the F-22Raptor was developed and refined in the 1980s and '90s, so China does not necessarily need to attain the current 2011 state-of-the-art in tactical jet engine technology to field formidable propulsion systems that could give the J-20 true 5th generation fighter performance characteristics.
What China must achieve, however, is a methodology akin to Six Sigma or Total Quality Management (TQM) to ensure quality control and sufficient organizational honesty to ensure that actual problems are reported and that figures are not doctored. Otherwise, standardization and integration may be the one in which the costs of China's ad hoc, eclectic approach to strategic technology development truly manifest themselves. The Soviet defense industrial base failed in precisely this area: talented designers and technicians presided over balkanized design bureaus and irregularly-linked production facilities; lack of standardization and quality control rendered it "less than the sum of the parts."
Mapping China's Key Jet Engine R&D and Production Assets: Size and Resources
Chinese jet engine makers may remain slightly understaffed relative to U.S./UK producers of military jet engines, but comparably staffed relative to their Russian and French peers. Liming Aero-Engine and Xi'an Aero-Engine, AVIC's flagship large military jet engine makers, have a combined staff of less than 20,000. By comparison, P&W, Rolls-Royce, and GE Aviation, the world's largest military jet engine makers, each have more than 35,000 staff (Exhibit 4).
Exhibit 4: Number of Workers at Major Global Tactical Turbofan Makers
Source: Company reports
Examining overall employment figures tends to over count personnel relevant to "Big Three" engine production and undercounts it for other manufacturers, however. The total head count at the former includes individuals involved in civilian, military, and global services programs (typically fairly-evenly-subdivided), not just dedicated R&D personnel. That at the latter does not include many R&D and metallurgy-relevant individuals employed in other organizations.
China's jet engine complex may increase staffing somewhat if it seeks to become largely or fully self-sufficient in military turbofan production. With 15,000 workers, Russian manufacturer UMPO planned to produce 109 AL-31 and AL-41 engines in 2010.[16]Larger firms like GE Aviation, by contrast, can deliver approximately 200 high performance turbofans and 800 total military jet engines and helicopter engine turboshafts per year.
Technical Challenges
High-performance tactical jet engines are difficult to produce, but the work does not stop there, as the engines often undergo demanding usage and pose key maintenance and logistical challenges. Key potential constraints China will likely face in operating the high-performance tactical turbofans it is beginning to series-produce include issues involving technical, performance, and environmental factors, the ability to obtain sufficient materials for mass production of multiple engine families, and political/economic challenges.
Thermal cycling. The engines on a large transport or tanker typically run at a fairly steady speed setting for most of a flight. Engines on tactical aircraft, by contrast, undergo extreme speed changes as pilots frequently and quickly change throttle settings during high-intensity maneuvering. As the engine undergoes rapid temperature changes, thermal cycling generates significant wear. The experiences of the USAF with the first truly high-performance U.S. afterburning turbofan, the P&W F100, exemplify the unexpected safety and maintenance challenges that thermal cycling can generate.
While developing the F100, P&W engineers believed that the key determinant of stress on engine parts would be the length of time spent at the highest temperatures (i.e. full power and/or very high speed flight).[17] In practice, however, the F100's unprecedented performance enabled new air combat techniques and training regimens that emphasized rapid and frequent maneuvering. This incurred relatively little time at full power or high Mach numbers, but entailed far more throttle changes than the engine designers had anticipated.
In fact, while the F100 design requirements called for being able to accommodate 1,765 full throttle transients during the engine's service life, actual operational use showed that engine life ended up being more than 30% lower than expected because the engine was undergoing more than five times the number of full throttle transients it had been designed for—10,360 cycles (Exhibit 5).
Exhibit 5: Key usage parameters of the F100 afterburning turbofan, November 1979
Source: The Great Engine War
As China develops indigenous high performance tactical turbofan engines, more intensive air combat training will make shortened engine life from thermal cycling an important issue to resolve. It is unclear how much experience China has in this area to date given that most Chinese pilots do not fly nearly as much as their U.S. counterparts and also may not be engaging in as intensive or realistic training. PLAAF and PLA Navy (PLAN) newspapers and other documents describe exercises in which engine use in particular is minimized wherever possible, as well as a variety of accidents that were caused by engine failures. Likewise, lower flight times in the Soviet/Russian air force, combined with different tactics, may mean that Russian engine makers are not able to draw on the same firsthand experience with combating thermal cycling wear that their American peers have.
Chinese technicians are making real progress in learning how to improve engines that are already fielded and wring the maximum life possible out of them. China's 5719 Jet Engine Repair Plant has allegedly found a way to extend the operating life of Russian-made AL-31F engines from 900 hours to 1,500 hours.[18] It is almost certain that the WS-10 and any new jet engines made in China will incorporate any life extension and other improvements that the PLAAF and PLAN Aviation have gleaned from the Russian engines that are currently the backbone of their flight operations.
Other Environmental Factors
Vibration resistance is another key determinant of engine performance. If an engine sucks in a small stone, for instance, it can nick a plate, thereby producing a small vibration, which in turn can lead to performance degradation and even failure. Environmental factors that can have negative impact include high/hot airfields (H&H), "sandy" air, salt-water corrosion, and FOD. Russian engines, for example, typically have less FOD resistance than those of Western design. Indian Air Force Su-30MKI aircraft reportedly exhibited significant limitations at the Red Flag 2008 exercises at Nellis Air Force Base because of the FOD vulnerabilities of their Russian engines. These problems were not caused by Indian maintenance procedures; agreements with Russia require that any damaged engines be shipped back to Russia for servicing.[19]
Performance Possibilities
It remains to be seen whether China can develop reliable engines with key high-performance capabilities essential for world-class military aircraft. These include thrust vectoring, the ability to control an aircraft's attitude or angular velocity by redirecting its exhaust slightly; continuous power-output at all speed and altitude settings without performance drops; and stall resistance. The last two factors could be particularly important, yet difficult, for China to master. The engine used in the Russian Su-27, the AL-31F turbofan, reportedly experiences performance power drops at certain power demands, e.g., high angle of attack (AoA) maneuvers. Under such conditions, there is a risk of disturbed air and fuel flow.
Particularly in a non-thrust vectored aircraft, if the engine becomes air-strained at a high AoA, the engine can suddenly have difficulty in using fuel, possibly leading to blade stall or discontinuous airflow, thereby starving the engine of oxygen. China's J-11 variant uses these engines, and its canards suggest that it is designed for precisely these sorts of maneuvers. The key to avoiding such problems is to design the engine inlet to optimize its cross-section geometry while avoiding a tendency toward stalling. Sophisticated modeling is needed to deconflict these countervailing factors, however; hence the importance of determining Chinese capabilities and approaches in these critical areas.
Structural Challenges
China's military jet engine sector faces a number of critical structural problems. Many of these are human and bureaucratic issues that can be much more difficult to resolve successfully than technical problems are. Two vulnerabilities stand out.
First, China's defense officials will have to deal with single source contractor risks. China's domestic military jet engine production all lies under the control of Aviation Industry Corporation of China (AVIC), a state-owned aerospace conglomerate. AVIC's jet engine production facilities at Shenyang, Xi'an, and Guizhou compete to some extent, but we suspect that the competitive and innovative pressures are not as acute as those which companies like P&W and GE Aviation face. When present in moderation, competitive pressure helps produce innovative engines, lowers costs, speeds up development, and tends to incentivize better aftermarket service. In the late 1970s and early '80s, the behavior of P&W, then a single-source supplier that the USAF felt was not being responsive to its concerns, prompted the government to foster competition between GE and P&W in the military jet engine sector. The resulting "Great Engine War" helped create architecture whereby U.S. combat aircraft can be designed around a range of powerplants produced by two competing firms. This organizational structure appears to work well. In China's case, by contrast, there may be less "competition" at the macro level but more at the micro level. This may allow for localized bargaining and patronage that leads to duplication of effort, mismanagement of resources, and an increase in time to market. Here it will be necessary to determine how the "system" of organizations involved in Chinese aeroengine development and production actually work in practice, and whether and to what degree they are "more than the sum of the parts" in practice.
Second, analyses of jet engine development and production in the U.S. credit inter-service cooperation, management stability in both the companies and government, and the use of small teams that were allowed to take risks with a minimum of red tape helped foment jet engine development and production breakthroughs.[20]
Of these two areas, China is likely to struggle most deeply with issues of inter-service cooperation, since service chiefs in China likely view themselves as competitors for slices of the pie in any given budgetary period. Resource constraints will pose less of a challenge since military jet engines typically cost between US$2.5 million and US$5 million apiece. Supporting a very aggressive tactical aircraft buildout by producing 500 tactical turbofans per year would account for only about 2% of China's total 2011 defense spending. Overall, structural issues pose major challenges, but can be dealt with incrementally once a country masters the basic technology and metallurgy of jet engine making.
Technologies and business practices to improve engine production
Quality control shortcomings have plagued Chinese indigenous jet engine production to date, particularly for high performance engines like the WS-10 series. In response to this and broader concerns, AVIC has declared 2011 to be a "year of quality" and pledges a tight focus on quality control across the aerospace production chain, which presumably will apply to aeroengine manufacturing as well.[21] AVIC's motion follows on the heels of a September 2010 State Council document that outlines steps for achieving better quality control in military hardware production in China.[22] The report does not specially mention aerospace or jet engine production, but its existence implies that the commitment to improving China's indigenous military systems production of all varieties runs straight to the top. How and to what extent these directives are realized in practice will hinge on design capability (e.g., involving materials, airflow, simulation and calculations, MTBF, systems integration, and FADEC/ECU design). It will be essential to avoid imbalances in which some parts are "better" than others, as this can introduce asymmetries and problems at the system level.
AVIC's press statement covering its desire to bolster quality control does not discuss specific details. That said, well-documented quality control programs implemented by key global jet engine makers can shed light on the likely basic mechanics of how AVIC's plans may take shape. P&W, one of the largest military jet engine makers in the world, has a system known as Achieving Competitive Excellence (ACE). ACE entails a focus on the following factors:
–Total productive maintenance
–Quality Clinic Process Chart
–Root Cause Analysis
–Mistake Proofing (this can be measured by first pass or final yield)
–Process Certification
–Setup Reduction
–Standard Work
China currently does not use total lifecycle (design) tools like the ones that Western corporations such as France's Dassault employ. The CAD-CAM (computer-aided design and computer-aided manufacturing) stand-alone tools widely employed in China are optimized for design, not operational usage. Focusing only on design at the expense of buildability and maintainability can lead to situations in which fixing parts may be problematic because of problems with fitting hydraulic tubes between electric lines, etc.
There appears to be recognition that current approaches are inadequate. A number of sources reflect the Chinese jet engine industry's interest in using process modeling and computer simulation to reduce build costs and construction time by envisioning problems before metal is cut.[23] China's shipbuilding industry already uses these technologies on an industrial scale and there is significant potential for the aerospace and jet engine sectors to learn best practices from shipbuilders, with the caveat that different tolerances become a terrible problem for aircraft under extreme environmental conditions in ways that ships never experience.
China's privately-owned shipyards are leading the way in this area. Jiangsu-based Rongsheng Heavy Industries is using concurrent design and computer simulation techniques to boost its production efficiency.[24] Concurrent design entails designing the ship hull, as well as electronics, internal components and other "guts" of the ship simultaneously using Tribon software.
Potential for Technology Transfer Between Civil and Military Industries
Military and commercial jet engines often have radically different performance parameters, but unlike other dual-use sectors like shipbuilding, the materials and construction techniques used to make key components of high-bypass turbofans for commercial airliners are in many cases quite similar to those used in making low-bypass turbofans for higher performance tactical aircraft. This is particularly true for the engine core. For example, the highly popular CFM56 commercial engine appears to share aspects of the core of the P&W F101 engine that powers the B-1B—at a minimum, there seems to be significant design overlap.
China's aerospace industry has a growing list of joint ventures (JVs) with foreign partners including GE Aviation, P&W, and SNECMA, primarily in the areas of final assembly (vice basic design and components) and maintenance, repair, and overhaul (MRO). A good example of the latter is MTU Maintenance Zhuhai, a 50-50 joint venture between MTU Aero Engines and China Southern Airlines.[25] MRO is perhaps the most important are of major aeroengine JVs for China, as it can help Chinese experts figure out how to perform after-market, in-service overhaul and how to feed repair data back into the design and MTBF loop to improve design and performance.
As such, these JVs hold real potential for transferring technology and know-how that then could trickle into military jet engine design, production, and maintenance and potentially provide tangible improvements in Chinese air combat capabilities. China's 2010 Defense White Paper states explicitly that "Defense-related enterprises and institutions are regulated and guided to make use of civilian industrial capabilities and social capital to conduct research into and production of weaponry and equipment." The concept of harvesting civilian technology for military use is already being implemented in practice, as exemplified by the recent jet engine research and development cooperation agreement signed between China Southern Airlines and the PLA's Armed Forces' Engineering Institute in May 2011.[26]
Against the backdrop of China's stated intention to use civilian industry as a source of militarily-relevant technology, presuming that jet engine-related cooperation is "commercial only" is at best naïve. JVs involving the construction and/or maintenance of jet engines deserve scrutiny based not only on the simple adherence to the letter of the law in export control regulations, but also on the potential for such jet engine technology transfer to erode U.S. competitive trade advantages and to potentially facilitate the development of a much more formidable Chinese air warfare capability, as well as contribute to greater Chinese exports of highly capable aircraft that U.S. forces might later face with respect to a third country such as Iran.
CFM International, one of the world's largest commercial jet engine makers, is a joint venture between GE Aviation, a division of General Electric of the United States; and Snecma, a division of Safran of France. Thus drawing on some of North America and Europe's most advanced aeroengine technology, it is also a designated aeroengine supplier for China's C-919 Large Aircraft Program. CFM International signed an MOU with AVIC in December 2009 to discuss the potential of establishing a final jet engine assembly line in Shanghai, as well as an engine test facility, but says nothing has been finalized yet. The company tells us that as of May 2011, it has not determined where LEAP final assembly will take place.[27]
CFM sources extensively in China for its current product line and is likely to do so for the advanced new Leap-X1C engine as well, but says it is too early to say what parts will be produced in China. The company's parts sourcing for the Leap-X1C merits close attention because the engine's core uses advanced technologies including integrally bladed rotor disks called "blisks" in which the rotor disk and fan blades are machined or cast from a single, unitary piece of metal.[28]
Blisks offer the advantage of greater reliability and significant weight savings—up to 30% over conventional blades and disks in some cases.[29] Blisks are now utilized in a range of advanced military turbofans including the GE F414 (F/A-18 Super Hornet), P&W F119 (F-22 Raptor), and P&W F-135 and GE F136 (F-35 Lightning JSF) and learning how to manufacture blisks via commercial engine cooperation would be very helpful to Chinese engine makers as they work on the WS-15 and other advanced military turbofan engines.
Engine materials
Obtaining exotic materials and having the ability to properly machine them are vital both to physically making jet engines and for keeping manufacturing costs competitive. The General Manager of IHI's Soma No. 2 Aeroengine Works in Japan says materials account for 50% of the cost of engine components made at his plant.[30]
Modern high-performance jet engines incorporate a number of high-strength, high-temperature materials. These include titanium, nickel, aluminum, composites, and superalloys based on nickel and cobalt. China is well-positioned to source many of these key materials from domestic producers. For example, flagship producer BaoTi says it can supply 95% of the Chinese aerospace industry's titanium needs. Similarly, Jinchuan Nickel uses imported ores and concentrates to produce nickel and cobalt and has the capacity to produce 130,000 tonnes per year of nickel and 10,000 tonnes of cobalt. Jinchuan produced around 4,000 tonnes of cobalt in 2010—18% of the global total—according to Norilsk Nickel. To put this number into context, a large commercial jet engine (40,000 lb thrust) typically contains between 50-60 kg of cobalt, meaning that if Jinchuan supplied only 5% of its annual cobalt output to jet engine producers, there would theoretically be enough to manufacture more than 3,000 engines per year.
"Theoretically" is the operative word because the main material constraint faced by jet engine producers is not limited to securing the raw nickel, cobalt, and other metals they need. Perhaps the most critical area is being able to purchase or produce the high-temperature superalloys needed for making a jet engine. China currently is not self-sufficient in superalloys according to Sealand Securities, which estimates that the country produces around 10,000 tonnes per year of superalloys, against consumption of 20,000 tonnes per year.
Commercial jet engines typically contain between 0.7 and 2.0 tonnes of superalloys per engine, according to the Metal Powder Industries Federation. Since most high performance tactical turbofans weigh less than 2 tonnes, we assume 1 tonne of superalloy per engine, giving China to current capability to supply superalloy for 1,000 military turbofans per year if it devotes 10% of domestic superalloy production to the jet engine sector. As such, superalloys pose a more significant potential bottleneck for jet engine production in China than base metal supplies do and are likely to see higher production facilities investment in the next 5 years.
Outlook and Strategic Implications
The history of U.S. jet engine and aircraft development shows an average correlation of nearly 1-to-1 between the creation of new aircraft and new jet engines. China is now entering a period of more rapid aircraft development, and in particular, one that increasingly involves indigenous designs or modifications of airframes that are sufficiently radical to potentially warrant the development of entirely new engines or derivatives to power them. At present, China is developing or preparing to mass produce a range of tactical aircraft including the J-15, J-16, J-20, and potentially others.
Robust aircraft development and production programs plus a desire to move into the 5th generation aircraft space where the Russians may be reluctant to supply later model engines such as the 117S create powerful motivators for achieving a greater measure of domestic jet engine production self-sufficiency. It is likely that the next 2-3 years will bring surprising breakthroughs in China's ability to produce high performance jet engines for tactical aircraft independently, with Chinese production of reliable top-notch engines perhaps 5-10 years away.
Key metrics to watch in determining Chinese progress in engine capabilities include engine thrust-to-weight ratio and specific fuel consumption. The first is an indicator of both design quality and production quality (i.e., of material tolerance). The second denotes the amount of fuel that the engine burns to reach a given level of performance, which in turn determines combat range, time over target, and the amount of strain on the engine.
Major systems management indicators include on-wing reliability (MTBF) and ease of in-field replacement and repair. China could take a variety of approaches to address these issues, including overcoming low MTBF by simply having more engines available, a process that the U.S. employed for many years when its own engines were less reliable, as was the case with the F-4 Phantom in Vietnam (in contrast to, e.g., the F-15 today).
If China's engine makers can attain the technical capability level that U.S. manufacturers had 20 years ago, China will be able to power its 4th generation and 5th-generation aircraft with domestically made engines (3rd and 4th-generation in Chinese nomenclature, respectively). These developments would be vital in cementing China as a formidable regional air power and deserve close attention from policymakers.
About Us
China Signpost™ 洞察中国–"Clear, high-impact China analysis."©
China SignPost™ aims to provide high-quality China analysis and policy recommendations in a concise, accessible form for people whose lives are being affected profoundly by China's political, economic, and security development. We believe that by presenting practical, apolitical China insights we can help citizens around the world form holistic views that are based on facts, rather than political rhetoric driven by vested interests. We aim to foster better understanding of key internal developments in China, its use of natural resources, its trade policies, and its military and security issues.
China SignPost™ 洞察中国 founders Dr. Andrew Erickson and Mr. Gabe Collins have more than a decade of combined government, academic, and private sector experience in Mandarin Chinese language-based research and analysis of China. Dr. Erickson is an associate professor at the U.S. Naval War College and fellow in the Princeton-Harvard China and the World Program. Mr. Collins is a commodity and security specialist focused on China and Russia.
The authors have published widely on maritime, energy, and security issues relevant to China. An archive of their work is available at www.chinasignpost.com.
The views and opinions contained in China SignPost™ 洞察中国 are those of the authors alone and in no way reflect the views or policies of the authors' employers.All relevant and eligible contents © Andrew S. Erickson and Gabriel B. Collins, 2010-
[1] For the purposes of this analysis, "tactical aircraft" means fighter aircraft, strike-fighters, and attack planes.
[1] "胡参谋长: 中国航空发动机超越俄罗斯不是神话" [Chief of Staff Hu: The Idea of China's Jet Engines Surpassing Russia's is Not a Myth], Nanfang Daily, 23 January 2011,http://opinion.nfdaily.cn/content/2011-01/23/content_19516764.htm.
[2] "林左鸣: 投资一百亿打一个航空发动机的翻身仗" [Lin Zuoming: 10 Billion RMB Will be Invested in Standing up China's Military Jet Engine Development], 17 April 2011,http://military.people.com.cn/GB/52934/67858/14407966.html.
[3] "军报: 国产太行量生并装备歼-11B推力12.5吨" [Military Times: China's Domestically-Made 12.5 Tonnes Thrust Taihang Engine Now Being Series Produced to Equip the J-11B], Global Times, 19 November 2010,
http://mil.huanqiu.com/china/2010-11/1270688.html.
[4] NPO Saturn, Quarterly Report, 1st Quarter 2011, http://www.npo-saturn.ru/upload/editifr/2011/38_0_greport_201101.pdf.
[5] Ibid.
[6] Global Gas Turbine News, International Gas Turbine Institute, 51:1 (February 2011): 51.
[7] "先进航空发动机关键制造技术研究" [Key Manufacturing Technology Research of Advanced Aero-Engine], China Gas Turbine Establishment, Defense Manufacturing Technology, 6 (2009): 47.
[8] G.A. Fitzpatrick and A.D. Lloyd, "Establishing Best Practice in the Design and Manufacture of Hollow Titanium Fan Blades," Paper presented at the RTO AVT Workshop on "Intelligent Processing of High Performance Materials," 13-14 May 1998, 4-1.
[9] R.C. Reed, P.D. Lee, and M. McLean, "Process Modelling of the Fabrication of Critical Rotating Components for Gas Turbine Applications," Paper presented at the RTO AVT Symposium on "Reduction of Military Vehicle Acquisition Time and Cost through Advanced Modelling and Virtual Simulation," 22-25 April 2002.
[10] "先进航空发动机关键制造技术研究" [Key Manufacturing Technology Research of Advanced Aero-Engine], China Gas Turbine Establishment, Defense Manufacturing Technology, 6 (2009): 48.
[11] Carol Hui, "High-Flying Investments," Metalworking World, No. 2 (2008): 11,http://www2.coromant.sandvik.com/coromant/downloads/articles/aerospace/MWW208_aerospace_japan.pdf.
[12] "先进航空发动机关键制造技术研究" [Key Manufacturing Technology Research of Advanced Aero-Engine], China Gas Turbine Establishment, Defense Manufacturing Technology, 6 (2009): 48.
[13] M.M. Allen, "Iso-Forging of Powder Metallurgy Superalloys For Advanced Turbine Engine Applications," P&W, April 1976, DTIC.
[14] CEK Carlson, JL Cutler, WJ Fisher, and JV Memmott, "Diffusion Bonded Boron/Aluminum Spar-Shell Fan Blade," June 1980, DTIC.
[15] "先进航空发动机关键制造技术研究" [Key Manufacturing Technology Research of Advanced Aero-Engines], China Gas Turbine Establishment, Defense Manufacturing Technology, 6 (2009): 48.
[16] «В 2010 году ОАО 'УМПО' планирует увеличить товарный выпуск на 4.7%», AviaPort, 16 February 2010,http://www.aviaport.ru/digest/2010/02/16/190463.html.
[17] Robert Drewes, The Air Force and the Great Engine War (Honolulu, HI: University Press of the Pacific, 2005), 60.
[18] "Rise with Enthusiasm: China's Jet Engine Technology is Surpassing that of Russia's AL-31F," 28 August 2010, MilChina,http://www.milchina.com/2010/0828/4519.htm.
[19] "USAF Pilot Describes IAF Su-30MKI Performance at Red Flag-08," The DEW Line, 5 November 2008, http://www.flightglobal.com/blogs/the-dewline/2008/11/usaf-pilot-describes-iaf-su30m.html.
[20] William S. Hong and Paul D. Collopy, "Technology for Jet Engines: Case Study in Science and Technology Development," Journal of Propulsion and Power, 21.5 (September-October 2005): 775-76.
[21] "中航工业全面推进航空产品质量管理工作" [AVIC Seeks to Comprehensively Improve Quality Control Management of Products it Produces], Aviation Industry of China, 28 January 2011, http://www.avic.com.cn/xwzx/jtxw/364941.shtml.
[22] "'现公布'武器装备质量管理条例" [Ordinances Pertaining to Weapon Equipment Quality Control], 30 September 2010, State Council of the People's Republic of China,http://www.gov.cn/zwgk/2010-10/08/content_1717050.htm.
[23] 陈美宁, 朴英, 王大磊 [Chen Meining, Piao Ying, and Wang Dalei], "某型航空发动机风扇串列叶栅的数值模拟" [Numerical Simulation of Tandem Cascades in an Aeroengine Fan], Journal of Aerospace Power, 5 (2010).
[24] Rongsheng Heavy Industries, http://www.rshi.cn/Design.html.
[25] "MTU Aeroengines,"http://www.mtu.de/en/company/corporate_structure/locations/zhuhai/index.html.
[26] "装甲兵工程学院与中航南方公司签约燃气轮机应用研究" [Armed Forces Engineering Institute and China Southern Airlines Sign Agreement on Research of Gas Turbine Applications], Ministry of National Defense of the People's Republic of China, 16 May 2011, http://news.mod.gov.cn/headlines/2011-05/16/content_4242087.htm.
[27] Interview with company representative, May 2011.
[28] John Croft, "CFM: Serving no LEAP before its Time," FlightGlobal, 8 March 2010,http://www.flightglobal.com/articles/2010/03/08/339093/cfm-serving-no-leap-before-its-time.html.
[29] "Repair of Blisks Made of Ti 6246," Fraunhofer-Institut für Lasertechnik ILT, Annual Report 2005, 76, http://www.ilt.fraunhofer.de/eng/ilt/pdf/eng/jb05/s76.pdf.
[30] Carol Hui, "High-Flying Investments," Metalworking World, No. 2 (2008): 14,http://www2.coromant.sandvik.com/coromant/downloads/articles/aerospace/MWW208_aerospace_japan.pdf.
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