最近幾年，普惠（P&W）公司在新型商用噴氣式發(fā)動(dòng)機(jī)的交付方面一向表現(xiàn)不佳。不過，憑借一直堅(jiān)持的持續(xù)進(jìn)步的研發(fā)戰(zhàn)略，多款普惠新一代超高效發(fā)動(dòng)機(jī)終于即將開始服役。雖然這些發(fā)動(dòng)機(jī)采用了一些可以追溯回上世紀(jì)90年代的設(shè)計(jì)，但其中也應(yīng)用了大量新型技術(shù)，未來還可推廣至更多的噴氣式發(fā)動(dòng)機(jī)。
雖然，性能提升可能會(huì)給廠商帶來更多利潤，但這也是有高昂代價(jià)的。首先，航空發(fā)動(dòng)機(jī)的主要設(shè)計(jì)和制造問題，大多到研發(fā)后期才會(huì)真正暴露，而這時(shí)哪怕一丁點(diǎn)改動(dòng)都會(huì)產(chǎn)生巨大成本。其次，由于國際航空機(jī)組普遍進(jìn)入老齡期，全球大部分航空業(yè)客戶的購機(jī)需求急劇增加。這些航空公司越來越焦急，也越來越不耐煩，而這些壓力也將進(jìn)而轉(zhuǎn)嫁到飛機(jī)制造商和航空發(fā)動(dòng)機(jī)廠商身上。
如今，一些暢銷機(jī)型的訂單已經(jīng)排到了2020年以后。無論是訂購的新發(fā)動(dòng)機(jī)遲遲不能交貨，還是收到貨后的使用環(huán)節(jié)出現(xiàn)問題，都會(huì)讓一些航空公司付出血本，而尋求可靠的解決方案也并不像想象的那么簡(jiǎn)單。
為了應(yīng)對(duì)更大的需求，一些飛機(jī)制造商開始增加飛機(jī)的產(chǎn)量。然而，由于發(fā)動(dòng)機(jī)廠商未能按時(shí)交貨，大量已經(jīng)完成的機(jī)身只能堆在停機(jī)坪上苦苦等待。此外，如果新的發(fā)動(dòng)機(jī)在接受初始認(rèn)證或交付給航空公司后又需要進(jìn)行修改，此時(shí)飛機(jī)制造商則需要承擔(dān)二次認(rèn)證和延遲交貨的成本，已經(jīng)完工的飛機(jī)越多，需要承擔(dān)的成本就越高。因此，保證發(fā)動(dòng)機(jī)從一開始就能實(shí)現(xiàn)設(shè)計(jì)性能，并保證高可靠性一直是發(fā)動(dòng)機(jī)供應(yīng)商的重中之重。
如今，普惠的最新渦輪扇（GTF）發(fā)動(dòng)機(jī)（屬于PW1000 Pure Power靜潔發(fā)動(dòng)機(jī)系列）的到來，又引出了一些不容忽視的問題。正如《航空航天》雜志早些時(shí)候所報(bào)道的，GTF發(fā)動(dòng)機(jī)代表了一種完全不同的設(shè)計(jì)理念。這種發(fā)動(dòng)機(jī)在各個(gè)沖程均可提供最優(yōu)的推進(jìn)效率，可謂是史上最清潔環(huán)保的超靜音發(fā)動(dòng)機(jī)。
GTF發(fā)動(dòng)機(jī)在同一根軸上的渦輪扇和低壓渦輪機(jī)（LPT）之間增加了一個(gè)變速器，從而保證渦扇和渦輪機(jī)均能以各自的最佳速率運(yùn)行，即渦扇轉(zhuǎn)速更慢一點(diǎn)，而LPT更快一點(diǎn)。這款新款普惠發(fā)動(dòng)機(jī)能實(shí)習(xí)夠大幅提升能效、并帶來顯著的節(jié)油成果以及超低排放表現(xiàn)，一定會(huì)在飛機(jī)廠商中大受歡迎。事實(shí)正是如此，目前已有至少5款新機(jī)型決定采用這款發(fā)動(dòng)機(jī)，分別為空客（Airbus）A320neo、龐巴迪（Bombardier）CSeries、巴西航空工業(yè)公司（Embraer）E190-E2、俄羅斯聯(lián)合航空制造公司（UAC）MC-21及三菱(Mitsubishi)MRJ。
過去一段時(shí)間，普惠公司一直高度關(guān)注GTF發(fā)動(dòng)機(jī)的研發(fā)，未來還有可能繼續(xù)擴(kuò)大這款發(fā)動(dòng)機(jī)的應(yīng)用范圍?？傮w來說，當(dāng)選龐巴迪CSeries支線機(jī)型（130到140座）選定發(fā)動(dòng)機(jī)，是GTF的一個(gè)重要突破，代表這款發(fā)動(dòng)機(jī)開始真正有機(jī)會(huì)挑戰(zhàn)“戰(zhàn)無不勝”的CFM-56和LEAP發(fā)動(dòng)機(jī)。CSeries商用噴氣機(jī)是龐巴迪公司商用噴氣機(jī)系列中的頂級(jí)產(chǎn)品，該機(jī)型憑借自己的出色表現(xiàn)，逐步躋身于長(zhǎng)期由A320和737客機(jī)占據(jù)的全球客機(jī)市場(chǎng)。
憑借更加輕質(zhì)的高規(guī)格航空機(jī)身和超高效的低油耗發(fā)動(dòng)機(jī)，CSeries噴氣機(jī)本應(yīng)在競(jìng)爭(zhēng)激烈的商用航空領(lǐng)域占據(jù)一定優(yōu)勢(shì)。然而，先是機(jī)身研發(fā)進(jìn)度滯后，接著又是GTF發(fā)動(dòng)機(jī)在早期測(cè)試與評(píng)估環(huán)節(jié)出現(xiàn)故障，CSeries只能眼睜睜的看著自己優(yōu)勢(shì)盡失。具體來說，GTF的故障包括一起地面測(cè)試中發(fā)生的因輸油管密封泄漏導(dǎo)致PW1500G發(fā)動(dòng)機(jī)起火的問題。最終的調(diào)查結(jié)果顯示，CSeries需要在再次啟動(dòng)前充分“冷卻”，否則可能導(dǎo)致問題的出現(xiàn)。據(jù)悉，本次事故發(fā)生在CS-100認(rèn)證測(cè)試之前的緊急測(cè)試階段，已經(jīng)處于非常后期，龐巴迪公司頭疼不已，但也只能眼睜睜的看著CS-100的研發(fā)成本不斷飛漲。
普惠在發(fā)動(dòng)機(jī)故障的修復(fù)方面一直不遺余力。雖然現(xiàn)階段各家航空公司須在再次啟動(dòng)飛機(jī)前充分冷卻PW1100G發(fā)動(dòng)機(jī)，但無論如何，CSeries歷盡千辛萬苦，終于開始服役了。然而，修復(fù)后PW1100G又出現(xiàn)了其他故障，嚴(yán)重影響了A320neo客機(jī)的交付計(jì)劃。
這次PW1100G發(fā)動(dòng)機(jī)在A320neo上發(fā)生的故障與CSeries并不完全一樣，主要原因在于溫度波動(dòng)，但航空公司并不關(guān)心具體細(xì)節(jié)，因?yàn)榻Y(jié)果都是一樣的 -- 現(xiàn)在飛機(jī)不能按時(shí)飛了（與當(dāng)下A320搭載的CFM-56或V2500發(fā)動(dòng)機(jī)相比，PW1100G發(fā)動(dòng)機(jī)啟動(dòng)所需時(shí)間更長(zhǎng)。由于首批PW1100G已經(jīng)于今年早些時(shí)候交付，普惠必須盡快拿出一個(gè)緊急修復(fù)解決方案）。這個(gè)技術(shù)隱患是在認(rèn)證測(cè)試之后暴露的。如果發(fā)動(dòng)機(jī)未能在熄火后充分冷卻，再次啟動(dòng)時(shí)就會(huì)發(fā)生這個(gè)問題。具體來說，發(fā)動(dòng)機(jī)渦輪軸的溫度變化可能會(huì)導(dǎo)致特定組件失調(diào)，進(jìn)而造成發(fā)動(dòng)機(jī)振動(dòng)。此時(shí)，由于發(fā)動(dòng)機(jī)轉(zhuǎn)子葉尖間隙變化和元件之間的相互摩擦，發(fā)動(dòng)機(jī)可能因?yàn)槟p而產(chǎn)生進(jìn)一步損壞。普惠公司一方面建議客戶在再起啟動(dòng)發(fā)動(dòng)機(jī)前一定要充分冷卻，另一方面也在加緊準(zhǔn)備一個(gè)更加完善的技術(shù)解決方案。
MTU航空發(fā)動(dòng)機(jī)（MTU AeroEngines）也參與了GTF發(fā)動(dòng)機(jī)的研發(fā)，這家德國公司負(fù)責(zé)的部分主要集中在高壓壓縮機(jī)。MTU表示，公司計(jì)劃在今年晚些時(shí)候提供一個(gè)解決上述問題的軟件升級(jí)措施。
顯而易見，航空公司肯定希望在引進(jìn)新機(jī)型的初期盡量不要出現(xiàn)問題，因?yàn)榭煽啃詥栴}造成的拖延，會(huì)嚴(yán)重影響航空公司的形象，波音公司就曾因?yàn)?87的延遲推出而名譽(yù)受損。如今，盡管購買首批新機(jī)型仍有一定好處，但需要面臨的風(fēng)險(xiǎn)也正在增加。此時(shí)，飛機(jī)制造商一天不能修復(fù)問題，航空公司就一天無法放松心情。
A320neo版的GTF發(fā)動(dòng)機(jī)情況也是一樣的。當(dāng)時(shí)原定的首批客戶卡塔爾航空本來可以成為世界首家將這款機(jī)型引入客運(yùn)領(lǐng)域的運(yùn)營商，缺最終拒絕了普惠交付的產(chǎn)品。后來漢莎航空（Lufthanse）接手了這批飛機(jī)。盡管航空公司可能不得不接受現(xiàn)實(shí)在再次啟動(dòng)發(fā)動(dòng)機(jī)時(shí)等待更長(zhǎng)時(shí)間，但普惠已經(jīng)研發(fā)出一種解決方案 -- 為發(fā)動(dòng)機(jī)的轉(zhuǎn)子葉尖增加一層涂層?，F(xiàn)在，所有尚未交付的新發(fā)動(dòng)機(jī)均采用了這種方案，而已交付發(fā)動(dòng)機(jī)的修復(fù)可能最多需要2年時(shí)間。這項(xiàng)任務(wù)并不簡(jiǎn)單，工程人員必須拆開每一部需要進(jìn)行修復(fù)的發(fā)動(dòng)機(jī)進(jìn)行操作，然后重新組裝，大約每部發(fā)動(dòng)機(jī)需要6周時(shí)間。不過，好在目前僅有不到60部已經(jīng)交付的發(fā)動(dòng)機(jī)需要修復(fù)。
可以想象，GTF發(fā)動(dòng)機(jī)的問題曾引得各家航空航天和商業(yè)媒體的爭(zhēng)相報(bào)道。不過，既然現(xiàn)在原因已經(jīng)找到，普惠位于康乃狄克州和佛羅里達(dá)州的發(fā)動(dòng)機(jī)裝配線也已經(jīng)進(jìn)行了相關(guān)修復(fù)，那我們也應(yīng)當(dāng)著眼更高層面，認(rèn)可這款發(fā)動(dòng)機(jī)在銷售方面取得的巨大成功。目前，這款發(fā)動(dòng)機(jī)的年產(chǎn)量即將提升至800部，而普惠所面臨的供貨缺口超過7000部（包括所有發(fā)動(dòng)機(jī)機(jī)型）。
普惠總裁Robert Leduc表示，PW1100G的初始服役可靠性非常出色，這款發(fā)動(dòng)機(jī)在漢莎航空（Lufthansa）、靛藍(lán)航空（IndiGo）和GoAir的出勤可靠率均穩(wěn)定在99.7%以上。PW1100G還有很多其他優(yōu)勢(shì)：首先，作為這款發(fā)動(dòng)機(jī)的最大賣點(diǎn)，GTF的“超低油耗”已經(jīng)幫A320取得了超過15%的節(jié)油成果；其次，這款發(fā)動(dòng)機(jī)的噪音水平很低，預(yù)計(jì)可以為本已相當(dāng)安靜的A320進(jìn)一步降噪50%；此外，這款發(fā)動(dòng)機(jī)的CO2/NOx排放也降低了60%。
未來，其他幾款采用GTF系列發(fā)動(dòng)機(jī)的商用機(jī)型也將在未來幾年內(nèi)陸續(xù)開始服役，這也會(huì)讓GTF成為未來幾十年中應(yīng)用范圍最廣的航空發(fā)動(dòng)機(jī)設(shè)計(jì)方案。盡管進(jìn)一步的研發(fā)仍面臨延期，但CSeries系列的銷量仍然高居不下，目前還面臨大約300駕的存貨短缺，這對(duì)一款剛剛上市的機(jī)型來說是相當(dāng)不錯(cuò)的表現(xiàn)。另外，巴西航空工業(yè)公司的190-E2系列看起來信心滿滿，似乎注定將重現(xiàn)公司現(xiàn)有機(jī)型的輝煌記錄。但三菱MRJ和俄羅斯UAC MC-21的前景尚不明朗。如今的民用客機(jī)領(lǐng)域競(jìng)爭(zhēng)激烈，其他成熟廠商在銷量與設(shè)施支持方面均具有較大領(lǐng)先優(yōu)勢(shì)，這兩款機(jī)型很難打入這個(gè)市場(chǎng)。不過，目前GTF發(fā)動(dòng)機(jī)的整體市場(chǎng)規(guī)模非常龐大，這也證實(shí)了普惠的英明決定 -- 這家公司一直堅(jiān)持新產(chǎn)品的創(chuàng)新研發(fā)，愿意承擔(dān)風(fēng)險(xiǎn)，而且在出現(xiàn)初期問題時(shí)的反應(yīng)十分迅速。
今年下半年，隨著積壓的PW1100G訂單開始陸續(xù)交付，相信空客停機(jī)坪上苦苦等待發(fā)動(dòng)機(jī)的A320neo也將很快陸續(xù)交付至世界各地。對(duì)于普惠和空客而言，發(fā)動(dòng)機(jī)小故障和飛機(jī)延遲交付的確都非常讓人遺憾，不過這也同時(shí)反映了目前商用航空領(lǐng)域面臨的最大問題：如何面對(duì)史無前例地巨大市場(chǎng)需求，并同時(shí)保證超高的質(zhì)量控制標(biāo)準(zhǔn)。
Growing pains (and gains) of P&W's Pure Power engine
After many years of flat-lining in the supply of new commercial jet engines—with improved models, but with designs dating back to the late 1990s, relying on a continuous path of evolutionary development—a new generation of super-efficient powerplants is entering service, introducing many technologies that will also be applied to future engines.
But the step up in performance, with its potential for greater profitability, has come at a price, with major design and manufacturing issues emerging late in the program cycle, and the added challenge facing airplane manufacturers of having to meet the expectations of anxious and increasingly impatient customers against a backdrop of aging fleets and a surge in demand for new airplanes.
The top-selling jetliners are effectively sold-out for years ahead, stretching deliveries to well beyond 2020. Delays in the delivery of new engines, and further groundings due to in-service problems, are costing some airlines dear and achieving robust solutions is taking longer than envisaged.
As production flows are increased in assembly halls, completed airframes are starting to fill parking ramps as the delivery of engines is awaited. If new engines have to be modified after initial certification and airline delivery, then the delays and extra costs involved in rectification grow with the numbers of airplanes that have already been completed. So, getting the engines to deliver their promised performance with high reliability from the start has always been a goal that engine suppliers aim to achieve.
The highest profile problems, perhaps understandably, have come with the new engine that offers the most innovative technological design—the Pratt & Whitneygeared turbofan (GTF), which has developed into the PW1000 Pure Power series. As has been described earlier in Aerospace Engineering, this engine does offer a different design solution, with optimized propulsion efficiency delivered through the different engine stages, resulting in a quiet engine that is cleaner and greener than what has come before.
Using a gearbox to decouple the fan from the low-pressure turbine—the two seated on a common shaft—allows each element to be optimized, with the fan running at a slower rate and the LPT much faster. The promise of new levels of efficiency, significant fuel savings, and ultra-low emissions ensured that the new P&W engine would be popular with airframe manufacturers, and this is illustrated by the fact that different GTF versions have been chosen for no less than five new generation civil programs—the Airbus A320neo, Bombardier CSeries, Embraer E190-E2, UACMC-21, and Mitsubishi MRJ.
P&W has been highly focused on developing this new engine, which has great potential for scaling up later, and being selected to power the CSeries 130-140 seat regional airliner was an important breakthrough, providing a long-term opportunity to challenge the all-conquering CFM-56 and its replacement LEAP engine in the biggest aero-engine market sector. The CSeries has been a crucial program for Bombardier as it sits at the top end of its commercial jet family and nudges into the global market that has become dominated by the A320 and 737 families.
The combination of a lighter, high-specification airframe and highly efficient engines with low fuel burn should have given this program a head start in a very competitive slot within the commercial sector, but delays in airframe development and then the teething troubles that afflicted the early testing and evaluation of production GTF engines—including an uncontained PW1500G engine fire on a CS-100 during ground tests, caused by the failure of an oil feed tube seal—led to investigations that suggested a longer “cooling off” period was needed before attempting a re-start. The initial uncertainly over this incident was not helpful to Bombardier as CS development costs were soaring and this engine failure happened as Bombardier was into a catch-up testing phase prior to certification.
P&W spared no effort in working to fix the problem created for airlines by having to wait longer between hot shutdowns and restarting. But while the CSeries has finally entered service, the delay in shipping modified production engines has seriously set back the schedule for the urgently awaited PW1100G powering the A320neo model.
In this version of the engine a different problem is connected to temperature fluctuation issues but for the airlines the outcome is the same—start-up times are delayed. (The PW1100G start-up time was longer than on the standard CFM-56- or V2500-powered A320s so clearly a temporary fix became urgent earlier this year as the first PW1100Gs were delivered for service.) This technical problem arose after certification and can occur when the engine is re-started before it has sufficiently cooled after shut down. The temperature variations along the engine’s turbine shaft can lead to misalignment of particular components and this can cause vibration and possible further damage due to rotor tip clearance difficulties and the possibility of components rubbing against each other, wearing away the seal. Customers were advised to allow more time before re-start ups, while the company perfected a technical solution.
German partner on the GTF program with P&W, MTU Aero Engines, is responsible for the high-speed, LPT and four of the high-pressure compressor stages, and is planning to provide a software upgrade later this year to reduce the risk of the earlier problems returning.
Operators like to introduce new aircraft with as few teething problems as possible for obvious reasons, as delays caused by reliability issues early on can lead to reputational damage, as was experienced by Boeing after the delayed introduction of the 787. But while there are incentives allowing for the increased risk of acting as the launch customer, the longer it takes to restore the promised performance, the more nervous key customer will be.
And so it has been with the GTF version of the A320 neo. Original launch customer Qatar Airways refused to accept its delivery, which would have given the airline the lead role of introducing the aircraft into regular passenger service. That task was subsequently taken up by Lufthansa. Although the airline has had to accept and allow for the extended re-start times, P&W has developed a modification based on the application of a new coating for the tips of the rotor. This is being applied to all new engines. Retro-fitting this to existing engines will take up to two years to work through, though thankfully less than 60 early-delivery engines are involved. This task is not simple as it involves the de- and re-assembly of each affected engine, taking around six weeks each time.
The GTF problems attracted the attention of the aerospace and business media as would be expected, but with the cause now established, and modifications being incorporated in all new engines coming off P&W assembly lines in Connecticut and Florida, it is important to see the issue within the wider context of a program that is enormously successful in sales terms, with an annual production output due to rise to 800 engines, and a total backlog of over 7000 GTF engines for all models.
Initial service reliability of the PW1100G has been exceptional, according to P&W’s President Robert Leduc, claiming dispatch reliability is over 99.7% on the first few aircraft in service with Lufthansa, IndiGo, and GoAir. On the subject of low fuel burn, perhaps the biggest selling-feature of the new GTF design has lived up to its game-changing claims, with an improvement over the existing A320 of over 15%. Other benefits include ultra-low noise levels that promise to halve the noise footprint of an already quiet A320 at many airports, and a 60% reduction in CO2and NOx emissions.
The other commercial airplanes to be powered by the GTF family due to enter service over the next few years will ensure that the design becomes one of the most widely used in the decades to follow. The CSeries, despite extended development delays, has a sales backlog of little short of 300 airplanes, a respectable total at entry into service, and the Embraer 190-E2 family seems destined to repeat the success of the company’s current models. Prospects for the Mitsubishi MRJ and Russian UAC MC-21 are less clear, with both entering a highly competitive sector where rival established manufacturers have a clear lead in terms of overall sales and support infrastructure, but the combined global market for GTF engines is huge and confirms P&W’s wisdom of persisting with such an innovative new product, accepting the risks and then dealing swiftly with the resolution of early issues.
As the deliveries of PW1100Gs build throughout the rest of this year, the lines of new A320neos parked outside the Airbus assembly halls at Toulouse and Hamburg, awaiting engines to fit to their pylons, should soon start to disperse. For both P&W and Airbus, the glitch in engine and airplane deliveries has been most unfortunate, but it also reflects what has become the biggest issue in the commercial aerospace sector—coming to grips with unprecedented market demand while maintaining quality control standards.
Author: Richard Gardner
Source: SAE Aerospace Engineering Magazine
巴西航空工業(yè)公司的E-190 E2采用了一系列改進(jìn)，包括一組全新&高縱深機(jī)翼、高級(jí)電子航空系統(tǒng)、第四代線控飛行控制系統(tǒng)，以及普惠的靜潔PurePowerGTF高涵道比發(fā)動(dòng)機(jī)。具體來說，PW1700G將登陸E175-E2，而PW1900G將登陸E190-E2（如圖所示）和E195-E2。
這一新款普惠發(fā)動(dòng)機(jī)能夠提供大幅能效提升、顯著節(jié)油成果以及超低表現(xiàn)，一定會(huì)在飛機(jī)廠商中大受歡迎。事實(shí)正是如此，目前共有至少5款新款機(jī)型均決定采用這款發(fā)動(dòng)機(jī)，分別為空客（Airbus）A320neo、龐巴迪（Bombardier）CSeries、巴西航空工業(yè)公司（Embraer）E190-E2、俄羅斯聯(lián)合航空制造公司（UAC）MC-21及三菱(Mitsubishi)MRJ。
普惠公司的PW1100G GTF是空客ACJ319neo的兩款選定發(fā)動(dòng)機(jī)之一。