現在客機全是常規的氣動佈局,為什麼不用飛翼式呢,和常規氣動佈局比,飛翼式不被採用的原因是什麼?


從飛機本身設計來說,問題是不大的,幾乎所有氣動,承載,倉位分配都不是足以推翻設計本身的問題,都可以解決。而飛翼式在氣動效率和載客效率上的優勢是巨大的,總而言之,單從飛機設計上比較,利遠大於弊。

但為什麼遲遲不能進入市場,其實牽扯到飛機與機場適配的更大問題。飛翼式比普通客機要寬,而且為了保持在地面上的穩定性,主輪距要比普通客機寬的多(因為重量分配較為平均,而不是像普通客機集中在機身上)。這樣的主輪距在現有跑道上起降安全係數是不能達標的,唯一的解決辦法就是讓世界上的主要機場都拓寬跑道,這就變成了一個基建問題。另一個問題是停機設備的轉化,航站樓的泊接以及候機樓的重新設計改造(比如以前能停三個的空間現在只能停兩個,當然我這只是打個比方,不是真實數據,泊接橋的技術也需要改進因為飛翼式的客艙開口方向必然不會是平行於航站樓而是成角度)。還有一個問題就是很多大城市的機場已經被城市包圍,改造餘量非常有限,在不能新修跑道的前提下,拓寬跑道又會減少跑道之間的緩衝空間,同樣又有可能造成安全隱患。這牽涉到的巨大投資,由誰來掏?航空公司?波音?還是政府?最後可能需要三方達成一個共識,但基建上的投資可能已經抵消掉了飛機本身帶來的效費優勢。所以飛翼式的主要問題不在他本身,而是這種跨越式發展對現有基建帶來的挑戰。當然解決方法是有的,比如波音可以和世界上一些新修,或者改造機場的項目進行合作,提前空出餘量或者改進設計(這可能需要政府扶持並且波音自己要出血),一步一步普及自己的標準。相形之下,空客拿一個傳統佈局的a380狂賺一筆,等你把路鋪好了他再跟著做飛翼,作為波音他自己也相當著急。這就好比你設計出來了牛b的高鐵,然而不能在現有的鐵路網上跑,處境非常尷尬。我也期待飛翼式能在本身和機場適配上達到一個平衡,拭目以待吧。


飛翼中間佈置的座位,如何能採光,讓人感覺不壓抑,緊急情況怎麼逃生。這都是問題。

乘客不是被運輸的貨物,坐飛機坐成悶罐火車可不好。


你去問一下797為什麼沒有推出市場問題就基本解決了


飛機在高空飛行時艙內需要增壓,機身只有做成近似圓截面纔能有效抵抗這種增壓作用帶來的機身環向拉力。B2裝的是炸彈,不存在這個問題。客機即使做成飛翼,客艙還得做成圓截面的,所以重量會增加不少。其次,試航規章要求飛機發生緊急情況時候乘客可以在90秒內完成應急撤離。做成飛翼的話你告訴我乘客從哪兒跑?

飛翼相比同等翼展以及同等長度的飛機並不具備速度上的優勢。最多看起來來也就是增加了一點靈活性和多出機翼部分多的一點點機位而已,而整體翼面積變大,阻力反而增加了。對於現代客機考慮到經濟原因,以及首要任務是把人更快的送到目的地,飛翼完全是沒有必要的,真要發展也應該是運載火箭


飛翼的好處:巡航升阻比大,容易做影身

飛翼的壞處:結構承壓能力比常規佈局弱,靜穩定性差,低速性能差

前段時間做過飛翼、常規和雙泡三種機身構型的比較,貼上來吧,雖然是英文的。

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The conventional

multi-arc design has been used in most commercial airplanes such as C919,Boeing 747 and A380. The design has many advantages such as an appropriatevolume, easy to sustain a high pressure inside, a low drag, a mature technology.Multi-arc design has an advantage over precisely circular design or multi-aisletransporters because it can be wider at the cabin.

The design is

very efficient to sustain inner pressure, which can be illustrated in Fig.1. However,when it comes to a bigger aircraft, such as the double-aisle vehicle, theaircraft may be too tall. In order to solve this problem, some new design suchas blended wing body design, double bubble design has been considered to use inthe design of commercial planes.

Figure.1 High bending stress associated with a non-cylindrical

pressure vessel (cite from [1] )

The blended wing

body design has long been used in military planes, such as B-2, F-117, X-47Band so on. The main advantage of the design is that the whole body can be usedas a lifting body, which provides an extremely large lift compared withtraditional design. In addition, the blended wing-body can obtain low wettedsurface area to volume ratio and reduced interference drag [7].

For the aspect

of wave drag, according to Equ.(1), wave drag varies proportionally to thesecond derivative of the cross-sectional area. This thus suggests that a smooth,linear variation of the cross-sectional area provides the least wave drag [8,9].

Consequently, since the BWB geometry is smoothly defined with uniform area distribution

across either sides of the centre -body, the BWB configuration is well suitedfor high subsonic and transonic flight.

(1)

For the unique

characteristic of high L/D, this kind of design has also aroused the interestof commercial plane designers.

The performance promotion

compared to the tradition design can be quantified by [2]:

Fuel Burn 27%

lower;

Takeoff Weight

15% lower;

Operating

Empty Weight 12% lower;

Total Thrust

27% lower;

Lift/Drag 20%

higher.

Figure.2 A case of blended wing body design(cite from https://www.nasa.gov/centers/langley/news/factsheets/FS-2003-11-81-LaRC.html)

Figure.3 Isometric view of the Blended-Wing-Body

design (cite from [2])

However, the

blended wing body design also has some disadvantages. Firstly, its stability

characteristic is not good. Although this problem can be solved by the highly

developed control system of the modern airplane, it still adds insecurity tothe flight. The second disadvantage is that fewer passengers are able to enjoythe sightseeing along the flight. Thirdly, the structural characteristic isworse than the tradition method, which would add to its total mass. Fourthly, thelow speed characteristic of the BWB design is not good due to its lower maximumlift coefficient, which may require larger airport and stronger engine. The strongerengine is in some way a waste in cruising, which then lower the efficiency ofthe aircraft.

For these

reasons, I think that this concept maybe a good design for transport plane

rather than commercial plane.

The double

bubble design, which has been used in D8 Series future aircraft design concept,comes from the research team led by the Massachusetts Institute of Technology. Themain feature of this kind of design is that the fuselage is designedconsidering both providing lift and enough containing volume.

The D8 series

aircraft would be used for domestic flights and is designed to fly at Mach 0.74carrying 180 passengers 3,000 nautical miles in a coach cabin roomier than thatof a Boeing 737-800. The fuselage is composed of two bubbles rather than one, whichcan contain more passengers and provide lift. The lift generated by this componentallows both wing and horizontal-tail areas to be reduced, yielding weight and aerodynamicefficiency benefits. It also provides a well-shielded mounting location for theultra-high-BPR engines, whose close integration minimizes nacelle penalties. Likethe Boeing designs, advanced structural technologies are incorporated, and the cruisingspeed is reduced (to Mach 0.74) in order to take advantage of the benefits of anunswept wing. In this case, these include sufficient lift-generating capabilityto eliminate the need for a leading-edge high-lift device. The other air frame noisetreatment is landing-gear fairing; the trailing-edge flaps are conventional [5].

The main

advantages of the double bubble design over the tradition design are asfollows:

– increased optimum carryover lift and effective span, via fuselage

shape

– built-in

nose-up trimming moment, via fuselage lift on nose region

– partial span

loading via 216」 wide fuselage (vs 154」)

– reduced

floor-beam weight via center floor support

– improved

propulsive efficiency via fuselage BL Ingestion, enabled by lower cruise Machto eliminate inlet diffusion and secondary flows into the fan (SimultaneousOptimization of the Airframe, Powerplant, and Operation of Transport Aircraft)

Figure.4 D8.X airdraft(cite

from https://www.nasa.gov/content/the-double-bubble-d8-0)

Figure.5 B737 and D8.x comparison of spanwise lift

distribution. For D8.x, the fuselage carryover portion is significantly larger(which shrinks the wing), and also distributed to produce a nose-up moment(which shrinks the tail). (cite from [6])

The

multi-bubble fuselage configuration concept was developed for balancinginternal cabin pressure load efficiently, through membrane stress ininner-stiffened shell and inter-cabin walls. An outer-ribbed shell was designedto prevent buckling due to external resultant compressive loads. The structureanalysis is illustrated in Fig.6 and Fig.7. In this aspect, the design may benot so perfect as the traditional design, but the loss is affordable.

Figure.6 Double-bubble concept: Nodal Von- Mises stress in due to

127530 Pascal (18.6 psi) internal pressure. (cite from [1])

Figure7. Triple bubble force balanced three floor fuselage

configurations: Nodal Von-Mises stress due to 127530 Pascal (18.6 psi) internalpressure (cite from [1])

Overall, I would suggest the

double-aisle transport to use the double-bubble design, because it can enhanceL/D by providing lift using its fuselage. Also, its cabin is big ,and itsstructural characteristic is good.

Reference

[1]Mukhopadhyay V. Blended Wing Body

(BWB) Fuselage Structural Design for Weight Reduction[C]// Aiaa/asme/asce/ahs/ascStructures, Structural Dynamics and Materials Conference. 2005.

[2]AIAA. Blended-wing-body subsonic

commercial transport[J]. 2000.

[3]Drela M. Development of the D8

Transport Configuration[J]. 2011.

[4]AIAA. Multi-Disciplinary Design

of Aircraft Fuselage Structures[C]// Aiaa Aerospace Sciences Meeting andExhibit. 2007.

[5]Graham W R, Hall C A, Morales M

V. The potential of future aircraft technology for noise and pollutantemissions reduction[J]. Transport Policy, 2014, 34:36-51.

[6]M Drela Simultaneous Optimization

of the Airframe, Powerplant, and Operation of Transport Aircraft

[7]Okonkwo P, Smith H. Review of

evolving trends in blended wing body aircraft design[J]. Progress in AerospaceSciences, 2016, 82:1-23.

[8]R.Liebeck,Blendedwingbodydesignchallenges,AIAA(AIAA2003-2659),

2003,pp.1–12. [9]D.Roman, R.Gilmore, S.Wakayama, Aerodynamics of High Subsonic Blended-Wing-Body Configurations, AIAA(AIAA2003-554),2003,pp.1–9.

現在常規佈局快發展到極限了,除非用層流技術,否則效率提高很有限了。沒準不久的將來會有一種鑒於常規佈局和飛翼之間的民航機。


因為世界上還沒有民用機場可以停


沒有必要。飛翼式載量大,但現在飛機都是點對點,完全不能滿坐還有一點,這種設計要重新研究,成本絕絕對對高於應收,而且這樣要摸索一段時間,成本更是無法想像。此外,可以毫不誇張地說:沒有十年,這種設計經濟性絕對低於傳統機翼。畢竟氣動設計方面,人類還沒有研究出最好的外形。對,只是外形。
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