這幾個月來，波音公司一直在進行ecoDemonstrator 757 的飛行，服務于2015年一批新技術的第一輪評估工作。這些新技術旨在降低自然層流的環(huán)境影響，希望在提高空氣動力效率的同時，降低噪音與二氧化碳排放水平。
波音對ecoDemonstratror 757 機型的左翼進行了改造，專門用于對波音的未來機翼設計專利技術進行測試，其中包括與自然層流有關的一些先進技術。本文著重介紹其中的一種可變弧度的克魯格襟翼，波音將在測試中評估其防止昆蟲在機翼前緣積聚的能力。
克魯格襟翼是一種覆蓋在機翼前緣的下行襟翼，其功能是為飛機提供更多的升力。在測試過程中，技術人員使用一臺安裝于機身頂部的紅外攝像機監(jiān)控流過機翼的氣流。飛機將在多種環(huán)境與條件下飛行，以確定它們對機翼氣流可能造成的影響。
此外，波音還與NASA簽訂了協(xié)議，參與NASA的環(huán)境保護型航空項目（ERA）。在協(xié)議中波音同意將ecoDemonstrator 757 用于兩種新技術的測試。在洛杉磯什里夫波特附近舉行的一系列飛行測試中，NASA將在該機型的右翼上測試幾種防昆蟲附著的涂料，以減少昆蟲撞上機翼前緣后留下的殘渣。這樣做的最終目的是為了在機翼上方的其余部分產生更多可減輕拖拽的層流。有研究顯示，保持機翼上方氣流順暢最多可減少6%的燃油消耗。
NASA為飛機右翼提供了應用納米表面涂層技術的前緣板。該測試將確定這些涂層是否能有效抵御昆蟲污染，從而降低相關的阻力和燃耗，測試結果將用于未來機翼設計。盡管昆蟲殘骸并非大問題，但任何阻斷機翼上方平滑氣流的因素都會提高阻力。
“更高的阻力意味著更高的油耗，從而導致更多污染物將排向大氣。我們項目的目標是研究未來30年內能夠降低飛機對環(huán)境影響的設計理念與技術，”NASA空氣動力研究任務理事會ERA項目經理Fay Collier表示。
NASA蘭利研究中心的工程師開發(fā)了一系列防粘涂層，并在一個小型風洞和一架NASA蘭利噴氣機的機翼上進行了測試。他們從中選擇了最好的一些涂層產品，用于在ecoDemonstrator 右翼上的測試。
在15次測試飛行中，研究人員將在ecoDemonstrator 757 的機翼前緣上使用幾種不同的涂層。首先他們將使用無涂層表面進行測試，建立昆蟲積累速率的基準數(shù)據(jù)。接著他們將移除無涂層板，并安裝5種不同的涂層板樣本。工程師所關注的測試重點之一是涂層的耐久性，因為涂層板只有在扛得住嚴苛飛行環(huán)境的條件下，才能發(fā)揮減少阻力的作用。
“降低1%-2%的燃耗聽起來不是很多，”Collier表示，“但在飛機上，降低幾個百分點的燃耗就意味著節(jié)省下數(shù)百萬美元的成本，此外還能保護環(huán)境免受有害物質的污染。”
在垂直尾翼上，NASA和波音將對主動氣流控制系統(tǒng)（AFC）進行測試，該系統(tǒng)可改進方向舵上方的氣流，并實現(xiàn)空氣動力效率最大化。研究團隊安裝了31個名為“橫掃噴氣制動器（sweeping jet actuators）”的小型噴氣機，這些裝置可以按照實際情況的需要，對流過ecoDemonstrator 757垂直尾翼和方向舵上方的空氣進行操縱。飛機的垂直尾翼主要用于在起飛降落時提高穩(wěn)定性，并增加垂直方向上的控制，這在發(fā)動機失靈的情況下尤為重要。但當飛機在高空中巡航時，沉重的垂直尾翼就不是那么必要了。
一支由NASA、波音公司、亞利桑那大學和 Caltechresearchers 研究中心的專家組成的團隊曾在NASA的埃姆斯研究中心對一臺全尺寸757飛機的垂直尾翼進行地面研究，風洞測試的結果顯示，AFC噴氣機可提升20-30%的側向力。研究人員希望飛行測試也可以證明這一結果。如果側向力提升20%，設計師可以將垂直尾翼縮小17%左右，并最多減少0.5%的燃耗。
工程師認為，從理論上來說，借助“橫掃噴氣機”不僅可以減少垂直尾翼的體積，還能在起飛降落時產生與大型尾翼相當?shù)膫认蛄?。因此，這一裝置不僅能夠降低飛機的重量與阻力，還能同時降低燃耗。
“我們的研究人員正在努力開發(fā)降低飛機燃耗、噪音和排放的技術。如果能在飛行測試中證明這些理念，那么它們將來在商用機隊中應用的可能性就大大提高了，” Collier表示。
在9次飛行測試中，ecoDemonstrator 757 飛機中搭載的儀器將測量AFC增強版垂直尾翼的表現(xiàn)。飛機將嘗試各種飛行條件，讓研究人員對噴氣機在垂直尾翼與方向舵周圍增加的側向力進行評估。這些飛行條件中包括發(fā)動機失靈模擬、噴氣機的配置更改與氣流速度的變化。
除此之外，ecoDemonstrator 項目的工程師還在考慮在六月或者七月進行其他一些測試。屆時波音公司將會宣布在以測試為目的租賃出去的ecoDemonstrator 757 上將會進行何種測試。當這些飛行測試結束后，波音將協(xié)同機隊回收協(xié)會（Aircraft Fleet Recycling Association），以及負責出租業(yè)務的Stifel公司的飛機財務部，一起以環(huán)保的方式完成757飛機的回收。
自2011年ecoDemonstrator項目啟動以來，已經為40多個新技術提供了測試平臺，除757外，參與測試機型還包括下一代737與787型夢幻客機（Dreamliner）。在該項目中進行測試的技術，都考慮了短期到中期的各種應用，這些技術所處的成熟階段均不相同。
2012年在ecoDemonstrator 737 飛機上測試的技術，有幾個已進入下一個研發(fā)階段，或已根據(jù)測試結果進行了調整。在該項目中總共測試了15種技術，其中包括旨在將新737 MAX機型的燃油效率提高1.8%的“先進小翼技術（Advanced Technology Winglet）”中的一些方面。
787機型上測試的一些技術仍在進行未來應用評估。在該項目中進行了使用15%環(huán)保型柴油與傳統(tǒng)噴氣機汽油組成的混合燃料進行的首飛測試，其結果將用于支持在商用飛機上推行環(huán)保型柴油的舉措。
除了波音公司的專利技術之外，NASA在ecoDemonstrator 合作項目中獲得的知識都將向全行業(yè)公開。
Boeing’s ecoDemonstrator 757 used to get the bugs out
Boeing is in the midst of several months of flights with its ecoDemonstrator 757 in a first-round effort to evaluate new technologies in 2015 that are expected to reduce environmental effects on natural laminar flow as a way to improve aerodynamic efficiency while reducing noise and carbon emissions.
On the ecoDemonstratror 757, the left wing has been modified to test Boeing-proprietary technologies in support of future wing designs, including advances related to natural laminar flow. Specifically, a variable-camber Krueger shield is being tested to see how well it can block insects from accumulating on the wing leading edge.
A Krueger shield is a flap that comes down over the leading edge of the wing to provide added lift for the plane. During the testing, an IR camera attached to the top of the fuselage will monitor the air flow over the wing. Boeing will be flying through different environmental conditions to study the potential effects that the conditions have on the wing flow.
Boeing is also under contract with NASA's Environmentally Responsible Aviation (ERA) Project to test two technologies on the ecoDemonstrator 757. On the right wing, in a series of flight tests near Shreveport, LA, NASA will test bug-phobic coatings to reduce the residue left by bug strikes on the leading edges of aircraft wings; the goal is to enable more drag-reducing laminar flow over the remainder of the wing. Studies have shown that keeping the flow smooth over a wing can reduce fuel consumption as much as 6%.
NASA supplied leading edge panels for the right wing that incorporate nanotechnology surface coatings. The testing will determine whether the coatings are effective in resisting insect contamination that can result in more drag and greater fuel use for future wing design. While the issue of bug residue might seem small, any disruption in the smooth flow of air over the surface of a wing increases drag.
"Increased drag means increased fuel consumption, which results in more pollutants in the atmosphere. The goal of our project is to develop aircraft concepts and technologies to reduce the impact of aviation on the environment over the next 30 years," said Fay Collier, Manager for the NASA Aeronautics Research Mission Directorate's ERA Project.
Engineers at NASA's Langley Research Center developed and tested a number of non-stick coatings in a small wind tunnel and on the wing of a NASA Langley jet. They selected the best candidates to test on the right wing of the ecoDemonstrator.
During 15 planned flights researchers will install sections of coatings onto the leading edge slats of the ecoDemonstrator 757. First they will establish a baseline using uncoated surfaces, to capture insect accumulation rates. Then they will remove those sections and install samples of the five treated panels. One of the things engineers want to test is how durable the coatings are. Treated surfaces will only be effective as drag reducers if they can withstand the harsh flying environment.
"Solutions to reduce fuel use by one or two percent may not sound like much," said Collier. "But shaving aircraft fuel consumption even a few percentage points can save millions of dollars and help protect the environment from harmful emissions."
On the vertical tail, NASA and Boeing are testing active flow control (AFC) to improve airflow over the rudder and maximize its aerodynamic efficiency. The team installed 31 tiny jets called sweeping jet actuators that can manipulate, on demand, the air that flows over the ecoDemonstrator 757's vertical tail and rudder surfaces. An aircraft’s vertical tail is primarily used to add stability and directional control during takeoff and landing, especially in the event of an engine failure. But when the aircraft is cruising at altitude the same large, a heavy tail is not necessary.
Ground studies by a team of NASA, Boeing, University of Arizona, and Caltechresearchers on a full-scale 757 vertical tail in a wind tunnel at NASA's Ames Research Center showed the AFC jets could increase side force by 20 to 30%. Researchers expect the flight tests to confirm those results. A 20% increase in side force could allow designers to scale-down the vertical tail by about 17% and reduce fuel usage by as much as 0.5%.
Engineers theorized they could reduce the size of the vertical tail by using the sweeping jets to generate the same side force during takeoff and landing that a larger tail does. That would reduce the weight and drag of the airplane and decrease its fuel consumption.
"Our researchers have been working hard to develop technologies to reduce airplane fuel consumption, noise, and emissions. Being able to prove those concepts in flight tests gives them a better shot of getting into the commercial fleet," said Collier.
Instruments onboard the ecoDemonstrator 757 flight test airplane will measure the performance of the AFC enhanced vertical tail in nine flights. During those tests, the plane will fly various maneuvers to evaluate the increase in vertical tail and rudder side force caused by the jets. The maneuvers will include simulated engine failures and variations in jet arrangements and flow rates.
ecoDemonstrator program engineers are reviewing some options for additional tests. This particular set of tests will go well into June, possibly July, and Boeing will announce any additional tests with the ecoDemonstrator 757, which was leased for testing purposes, before then. After the flights are complete, Boeing will work with the Aircraft Fleet Recycling Association and the lessor, Stifel's aircraft finance division, to recycle the 757 using environmental best practices.
Since it was launched in 2011, the ecoDemonstrator Program has tested more than 40 technologies with a Next-Generation 737 and a 787 Dreamliner. The program strives to test technologies over a spectrum from near- to long-term application. All the technologies are at different stages of readiness.
Several technologies tested on the ecoDemonstrator 737 in 2012 have moved to the next phase of development or have been adjusted based on the testing. That program tested 15 technologies including aspects of the Advanced Technology Winglet that is expected to improve fuel efficiency by 1.8% on the new 737 MAX.
Technologies tested on the 787 are still being evaluated for future use. That program included the first flight tests using green diesel in a 15% blend with conventional petroleum jet fuel. The tests will be used to support industry efforts to approve the use of green diesel in commercial aviation.
With the exception of Boeing proprietary technology, NASA knowledge gained in collaboration with Boeing from ecoDemonstrator research will be publicly available to benefit industry.
使用在波音757飛機尾翼上的技術，用以測試主動氣流控制。（波音/NASA）
圖中所示波音ecoDemonstrator 757正在飛越華盛頓州的奧林匹克島。幾個月以來，該飛機一直服務于新技術的測試，這些技術有可能提高商用飛機的效率、降低噪音和碳排放。
NASA蘭利研究中心的研究人員正在準備即將使用在試飛機翼上的防粘涂層，該飛機將在夏末季節(jié)飛越昆蟲繁多弗吉尼亞州。