现在客机全是常规的气动布局,为什么不用飞翼式呢,和常规气动布局比,飞翼式不被采用的原因是什么?


从飞机本身设计来说,问题是不大的,几乎所有气动,承载,仓位分配都不是足以推翻设计本身的问题,都可以解决。而飞翼式在气动效率和载客效率上的优势是巨大的,总而言之,单从飞机设计上比较,利远大于弊。

但为什么迟迟不能进入市场,其实牵扯到飞机与机场适配的更大问题。飞翼式比普通客机要宽,而且为了保持在地面上的稳定性,主轮距要比普通客机宽的多(因为重量分配较为平均,而不是像普通客机集中在机身上)。这样的主轮距在现有跑道上起降安全系数是不能达标的,唯一的解决办法就是让世界上的主要机场都拓宽跑道,这就变成了一个基建问题。另一个问题是停机设备的转化,航站楼的泊接以及候机楼的重新设计改造(比如以前能停三个的空间现在只能停两个,当然我这只是打个比方,不是真实数据,泊接桥的技术也需要改进因为飞翼式的客舱开口方向必然不会是平行于航站楼而是成角度)。还有一个问题就是很多大城市的机场已经被城市包围,改造余量非常有限,在不能新修跑道的前提下,拓宽跑道又会减少跑道之间的缓冲空间,同样又有可能造成安全隐患。这牵涉到的巨大投资,由谁来掏?航空公司?波音?还是政府?最后可能需要三方达成一个共识,但基建上的投资可能已经抵消掉了飞机本身带来的效费优势。所以飞翼式的主要问题不在他本身,而是这种跨越式发展对现有基建带来的挑战。当然解决方法是有的,比如波音可以和世界上一些新修,或者改造机场的项目进行合作,提前空出余量或者改进设计(这可能需要政府扶持并且波音自己要出血),一步一步普及自己的标准。相形之下,空客拿一个传统布局的a380狂赚一笔,等你把路铺好了他再跟著做飞翼,作为波音他自己也相当著急。这就好比你设计出来了牛b的高铁,然而不能在现有的铁路网上跑,处境非常尴尬。我也期待飞翼式能在本身和机场适配上达到一个平衡,拭目以待吧。


飞翼中间布置的座位,如何能采光,让人感觉不压抑,紧急情况怎么逃生。这都是问题。

乘客不是被运输的货物,坐飞机坐成闷罐火车可不好。


你去问一下797为什么没有推出市场问题就基本解决了


飞机在高空飞行时舱内需要增压,机身只有做成近似圆截面才能有效抵抗这种增压作用带来的机身环向拉力。B2装的是炸弹,不存在这个问题。客机即使做成飞翼,客舱还得做成圆截面的,所以重量会增加不少。其次,试航规章要求飞机发生紧急情况时候乘客可以在90秒内完成应急撤离。做成飞翼的话你告诉我乘客从哪儿跑?

飞翼相比同等翼展以及同等长度的飞机并不具备速度上的优势。最多看起来来也就是增加了一点灵活性和多出机翼部分多的一点点机位而已,而整体翼面积变大,阻力反而增加了。对于现代客机考虑到经济原因,以及首要任务是把人更快的送到目的地,飞翼完全是没有必要的,真要发展也应该是运载火箭


飞翼的好处:巡航升阻比大,容易做影身

飞翼的坏处:结构承压能力比常规布局弱,静稳定性差,低速性能差

前段时间做过飞翼、常规和双泡三种机身构型的比较,贴上来吧,虽然是英文的。

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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.

现在常规布局快发展到极限了,除非用层流技术,否则效率提高很有限了。没准不久的将来会有一种鉴于常规布局和飞翼之间的民航机。


因为世界上还没有民用机场可以停


没有必要。飞翼式载量大,但现在飞机都是点对点,完全不能满坐还有一点,这种设计要重新研究,成本绝绝对对高于应收,而且这样要摸索一段时间,成本更是无法想像。此外,可以毫不夸张地说:没有十年,这种设计经济性绝对低于传统机翼。毕竟气动设计方面,人类还没有研究出最好的外形。对,只是外形。
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