problems and decisions of wings

8/9/2019 Problems and Decisions of Wings

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Aircraft Design 4 (2001) 193219

Invited paper

Flying wingFproblems and decisions

A.L. Bolsunovsky, N.P. Buzoverya, B.I. Gurevich, V.E. Denisov, A.I. Dunaevsky,L.M. Shkadov*, O.V. Sonin, A.J. Udzhuhu, J.P. Zhurihin

Central Aerohydrodynamic Institute (TsAGI), 1 Zhukovsky str., Zhukovsky, Moscow Region 140160, Russia

Abstract

Traditionally, one of the priority directions in TsAGIs research activity is searching for new concepts in

the field of aviation technologies. In the context of these studies basic problems related to the development

of advanced large-capacity aircraft of a flying-wing (FW) configuration have been studied at TsAGI since

the late-1980s (Byushgens, Aviation in XXI century, Symposium on Aeronautical Technology in XXI

Century, Moscow, September1989; Denisov et al., Conceptual design for passenger airplane of very large

capacity in flying wing layout, ICAS 96-4.6.1, 1996). In the present paper primary emphasis is placed on

the rationale of selecting FW main design solutions, aerodynamic configuration, structural concept as well

as on development and analysis of alternative configurations. Consideration is also given to the problem,

which is in the opinion of experts the most critical for this airplane type, namely, meeting FAR-25standards with respect to airplane operation in emergency situations. At present the work on this concept is

being conducted under the International Scientific and Technical Center grant No. 548. The project

collaborators are AIRBUS INDUSTRIE and Boeing. r 2001 Published by Elsevier Science Ltd.

1. Introduction

One of the approaches to improving the efficiency of future airplanes is to increase their

passenger capacity. This will make it possible to reduce direct operating costs per passenger

(Fig. 1) and to relieve large airports by decreasing the number of flights. However, forconventional airplanes with Cayley concept of separating component functions an increase in

dimensions can lead to degradation of weight efficiency. The stated feature as well as the

requirements of the airplane size dictated by the infrastructure of available airports can

significantly limit maximum passenger capacity of a conventional airplane configuration. At

the same time, increase of the airplane dimensions enables an entire payload or its portion to be

accommodated in the wing and, thus, a flying-wing (FW) concept will become possible, where the

*Corresponding author. Tel.: +7-95-556-4412; fax: +7-95-556-4481.

E-mail address: [email protected] (L.M. Shkadov).

1369-8869/01/$ - see front matterr 2001 Published by Elsevier Science Ltd.

PII: S 1 3 6 9 - 8 8 6 9 ( 0 1 ) 0 0 0 0 5 - 2


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component functions are integrated. The length of such an airplane is substantially less than that

of a conventional airplane and the span of outboard wings can be reduced in operating on the

ground by deflecting their tips upward. An increased structure depth of the center section makes it

possible to increase the wing span with less weight penalties as compared with conventional

airplanes and, thus, to increase the FW lift-to-drag (L=D) ratio.An additional increment of the L=D ratio is provided due to the following factors inherent inthe FW configuration:

* higher Reynolds numbers on the wing with chords twice as large as those of the conventional

configuration;* absence of a horizontal tail with corresponding friction and induced drag penalty;* reduced static margin in the longitudinal channel and even small instability at cruise.

It was assumed that the total increase in L=D ratio of the FW configuration could be about20% as against a conventional layout with load ratio close to the latter. So, there were serious

reasons for carrying out comprehensive studies on a large-capacity airplane of flying wing or closeto its configurations. The investigations carried out at TsAGI can be arbitrarily divided into three

stages:

* The baseline FW configuration was developed at the first stage. It formed the basis for

computational and experimental studies and definition of the requirements of the project.* The second stage was dedicated to the development of three candidate concepts covering a

variety of possible configurations from updated conventional through intermediate to complete

FW configurations. In addition, for the purposes of comparison, a traditional airplane

configuration was developed for the same requirements.

Fig. 1. Comparative DOC.

A.L. Bolsunovsky et al. / Aircraft Design 4 (2001) 193219194


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* Detailed computational and experimental investigations are to be made at the third stage for

the most promising layout.

2. Preliminary studies

Using preliminary parametric studies as well as limited experimental investigations and some

considerations given below, the baseline configuration for a large-capacity airplane of an FW type

was developed (Fig. 2) [1]. It formed the basis for further computational and experimental

investigations.

The configuration corresponded to the preliminary concept with engines located over the rear

center section and fins arranged on wing tips. The configuration defined is a certain compromise

and involves such components of conventional designs as reduced nose and possibly rear fuselage

sections. The airplane was intended to carry 940 passengers in economy class for 10,000 km rangeat a cruise Mach number of 0.8.

2.1. Wing configuration

2.1.1. Wing center section

The FW concept presupposes considerable dimensions of the wing center section where the

passenger cabin is housed. The wing with such a center section may have large front and rear

chord extensions. The center-section planform, leading-edge sweep, relative size of the front and

rear chord extensions greatly influence the behavior of moment characteristics at high angles of

Fig. 2. FW baseline configuration.

A.L. Bolsunovsky et al. / Aircraft Design 4 (2001) 193219 195


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attack. For tailless configurations these characteristics define to a large extent the feasibility of the

airplane.

Definition of a rational wing configuration was one of the main tasks in the experimental

investigations carried out at the first stage of the project. For this purpose three aerodynamic

models with wing span of about 1.6 m and center section of various shapes were tested in the

TsAGIs low-speed wind tunnel. The results of those tests are presented in Fig. 3. Based on the

results obtained, the wing configurations with a large front chord extension were excluded from

consideration in favor of the wings with an enlarged rear extension, which, in addition to

satisfactory moment characteristics, provides sufficient inner volumes in the wing center section.A number of contradictory factors affect the center-section span. Decrease of the center-section

span is beneficial from the standpoints of:

* decreasing wave drag;* increasing the high-lift devices span;* alleviating lateral and vertical g-loads acting upon passengers in airplane X-rotation;* decreasing passenger path in emergency escape.

On the other hand, decrease of the center-section span results in:

* reduction of the wing portion with large structural depth and increase of wing weight;* large difference in chords of neighboring sections, leading to a certain increase in induced drag;* elongation of the passenger cabin and, as a consequence, widening of the center-of-gravity

(CG) range and increase in trim losses.

When analyzing the above contradictory factors, the basic value of the relative center-section

span was taken as %Z 0:22:

2.1.2. Outboard-wing parameters

The parameters of the main wing trapezoid were selected on the basis of aerodynamic and

weight calculations. The absolute wing span was not limited by the 80 m value, because it was

Fig. 3. The investigated wing configurations.



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assumed that the wing tips would be deflected at rest and in taxing. The outboard wing span

should be sufficient to accommodate the control units. The wing panel taper ratio must be greater

than that of a conventional airplane to improve the stall characteristics. At first, fins were

mounted on the wing tips to achieve the winglets effect. Later on, it became clear that because ofsuch arrangement the critical flutter speed was reduced by more than 200 km/h and the fin was

located on the fuselage. For the FW configuration an optimal aspect ratio of the main wing

trapezoid is somewhat higher than for the conventional configuration owing to the large

structural depth of the center-wing section with lower cost to weight. At the first stage of studies

the following main trapezoid parameters were assumed: aspect ratio 10, taper ratio 0.4, leading

edge sweep 361.

As a whole, it was assumed that the functions and arrangement of the control units on the wing

would be identical to those for the FW XB-35 and YB-49 designed by Northrop in the 1940s.

Simple hinged flaps are installed close to the center-of-gravity position to minimize pitch-down

moment, which can be compensated by upward deflection of the trimming elevons at the wing tips(Fig. 4). Besides, these tip elevon segments can be constructed as split rudders to provide extra

yaw control in the low-speed engine-out condition. A special aerodynamic half-model was tested

in wind tunnel to define the effectiveness of the split flaps more precisely. Mid-spanwise segments

are used as elevators and high-speed ailerons. Additional elevators are installed on the center-

section trailing edge.

Slats along the outboard wing occupy the wing leading edge.

Fig. 4. Control units.



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2.2. Static stability margin

Investigations into the problems relating to the reliability of a fly by-wire control system and

flight safety have indicated that the airplane in takeoff and landing regimes is able to have thedegree of static stability close to zero (CCLm p0), while in cruise flight the instability should be

limited by CCLm p0:03: This restriction requires that the configuration considered previously shouldbe revised. Since, unlike the conventional configuration, it is impossible to achieve a specified

stability margin for the FW by selecting a wing position relative to the fuselage, the main way is to

select the location of engines on the airplane.

The configuration with engines arranged over the wing tailing edge considered early at TsAGI

[3] as well as the layout described by Liebeck in Ref. [4] have a high static instability not meeting

the requirement CCLm p0:03:Therefore, in the present investigations we considered the configuration shown above (Fig. 4)

with engines arranged on pylons under the wing that is typical for conventional configurationairplanes.

2.3. The type and arrangement of the powerplant

Various options of engine arrangement and types of powerplants were analyzed, and along with

turbofans, propfans were also considered. In this case a cruise Mach number was limited by the

value 0.780.80. With the aim of increasing efficiency, the engines were located within stagnant

flow over the trailing edge of the center-wing section on the pylons. Such an arrangement was

considered preferable from the standpoint of reducing noise in the passenger cabin and increasing

the passenger safety in failure of rotating elements. It was supposed that the utilization ofpropfans might appear an important feature and an advantage just of the FW configuration,

because it is difficult to locate propfan engines in such a manner on a conventional configuration.

To define the efficiency of the propfan powerplant mounted over the rear wing section,

computational and experimental investigations were carried out. The experimental facility, which

comprised a propeller device and wing section, was specially designed for testing in a large

subsonic wind tunnel. The test results proved the availability of favorable interference between the

wing and the propeller, which further contributes to the low fuel consumption of the propfans.

However on closer examination of the problem it was decided to abandon the

propfan powerplant and the engine arrangement over the rear wing in general for a number of

reasons:

* to increase the FW competitiveness, a decision was made to increase the cruise Mach number

up to M 0:85 (propfans are inefficient at this speed);* for over-the-wing engine arrangement it is problematic to compensate nose-down moment due

to engine thrust without severe losses of lift in takeoff regimes;* for rear engine arrangement the airplane has an unacceptably high instability in the lateral

channel or, in any case, excessively wide scatter of CG positions at different variants of airplane

loading;* for engine arrangement in a row, failure of one of them can cause a successive failure of all

others.



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2.4. Structure concept

Main features of the FW passenger airplane are associated with the placement of the passenger

cabin in the center-wing section and the way of taking up excessive pressure acting upon the cabinwalls. Calculations carried out have revealed that rather massive upper and lower panels of the

center-wing section are able to carry both pressure and bending loads. Flat highly loaded panels,

separating undercarriage bays from the pressure cabin, also take up the undercarriage loads and

pressure loads simultaneously without a significant addition of structural materials (Figs 5 and 6).

Fig. 5. Center-wing section layout.

Fig. 6. Center section, rear part.



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For the nose and rear parts of the center-wing section, where aerodynamic loads are small

enough, the main factor defining the thickness of flat three layer panels and their weight are

aerodynamic constraints on the value of allowable wing surface deformation. A concept of

separately taking up the loads with flat panels absorbing external loads and cylindrical shells

absorbing cabin pressure may appear rational for these zones (Figs 5 and 6).

2.5. Rational airplane size

When defining a rational airplane size (passenger capacity), fuel efficiency and DOC were used

as a figure of merit. It has been revealed that a rational number of passengers can be 750 seats in a

three-class layout (950 seats in all-economy layout). With 650700 passengers, the conventional

airplane operating costs were obtained close to minimal (Fig. 7). The length of a conventional

airplane is about 80 mFa limiting value from the airport standpoints. Based on preliminary

estimates it was assumed that the FW airplane of such a passenger capacity could meet FAR-25

with respect to safety and is compatible with existing airport infrastructure.

2.6. Experimental investigations of the baseline configuration

On the basis of the preliminary studies an aerodynamic model of an airplane intended for a

cruise Mach number of 0.8 was designed and tested in TsAGIs large transonic wind tunnel.

The test results validated the possibility of achieving a very high cruise L=D ratio for realisticFW configurations, 2025% higher than that of conventional counterparts. At the same time,

favorable lift and moment characteristics at high-angles-of-attack regimes have been demon-

strated.

Fig. 7. DOC comparison.



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3. Current investigations

3.1. Definition of requirements

Taking into account the results obtained at the preliminary stage together with collaborators

from AIRBUS INDUSTRIE new project specifications and the level of basic technologies were

defined.

Main specifications:

Nominal range 13,700 km (7400 n.m.)

Passenger capacity in 3-class layout 750 seats

Cruise Mach number 0.85

Takeoff field length, ISA, sea level +151C 3350 m

Condition:ACN 65

Standards FAR-25

3.1.1. Technology level

Although it is unlikely that the airplane will be put into operation until 20152020, that is, the

time when the problem of creating a high-capacity aircraft generation following the A3XX may

become urgent, it was decided to employ current advanced technologies used for aircraft being

designed at present.

This approach corresponds to the following technical solutions:

* basic structural materialsFaluminum alloys;* limited application of composite materials;* low degree of static instability (B3%) at cruise, neutral or stable airplane at takeoff and

landing;* engines which are now under development;* current infrastructure of airports.

Also defined were critical technologies making the greatest impact on the feasibility of an FW

concept:

* aerodynamic configuration;* airframe/engine interference;* systems providing stability, controllability and flight safety;* center-wing section structure;* aeroelasticity and flutter;* passenger cabin arrangement meeting FAR-25 with respect to emergency passenger

escape;* compatibility with airport infrastructures.



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3.2. Development of alternative configurations

At the preliminary stage the emphasis was placed on searching for main design approaches,

defining critical technologies as well as on the test verification of aerodynamic performance of theaccepted layouts. At the same time the developed baseline configuration was, in some sense, of a

conceptual nature because design problems associated with meeting the airport requirements and

the FAR-25 standards relating to the airplane operation had not been examined in detail. At this

stage, great attention was paid to the following aspects:

* number, location and structure of emergency exits;* waterline position in ditching;* possible charts of embarkment and deployment in standard and emergency situation;* level of comfort in passenger cabins;* arrangement of service compartments (galleys, coat rooms, crew berths, etc.);* cabin floor inclination at cruise;* arrangement and service of cargo bays;* landing gear wheel base and track;* airplane turn on taxiways;* airfield pavement loads from undercarriage;* engine arrangement;* operational CG range at different modes of airplane loading, positioning and capacity of fuel

tanks, fuel usage sequence;* stretched versions possibility;* possibility of cargo and combi versions.

To investigate the design problem more thoroughly, a decision was made to consider a wide

range of possible configurations, from updated conventional through some hybrid layouts to a

pure FW. Besides, for comparison purposes a conventional configuration for 750 seats was also

developed. Four developed configurations are as follows:

Configuration 1. Conventional configuration: It is a classical configuration with a traditional tail

(Figs. 8 and 9). The passengers are accommodated in the fuselage at two levels.

Configuration 2. Hybrid layout (IWB): This configuration has been evolved out of the baseline

layout (Fig. 2). It is an integral configuration combining a shortened fuselage and a wing with

enlarged center section. We call such hybrid scheme the integrated wingbody (IWB) scheme [3].

About 40% of the total passengers are accommodated in the center-wing section. The rest of the

passengers are placed on two decks in the fuselage. The general view of the IWB configuration isshown in Figs. 10 and 11. The arrangement is presented in Fig. 12. The main features are as

follows:

* integration of the wing/fuselage structure;* least relative center-wing thickness with large absolute structural depth;* availability of windows in the first-class and business-class cabins;* distribution of emergency exits over two levels (upper and main passenger cabins), which

simplifies their arrangement;* stretched versions possibility.



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Configuration 3. Lifting-body configuration: The configuration has a center-wing-fuselage oflarge width, where the passengers are accommodated at one level, while the lower deck houses the

service and cargo compartments (Figs 1315). The main features are as follows:

* absence of the upper passenger cabin deck, which significantly simplifies the airplane

maintenance;* large volumes of containers in a cargo version;* shift of the galleys to the lower deck which makes it possible to serve them and make passenger

embarkment and deployment simultaneously;* short undercarriage legs yet enabling takeoff without angle-of-attack limitations;*

large control surface on the trailing edge of the shaped center-wing-fuselage, the effectiveness ofwhich does not depend significantly on structure elasticity.

Configuration 4. Pure flying wing: This configuration corresponds most closely to the

definition flying wing. Here all the passengers are accommodated in an enlarged wide center

section at one level (Figs 1618). The main features are as follows:

* absence of the upper passenger cabin deck, which significantly simplifies the airplane

maintenance;* smooth concatenation of wing consoles and center section.

Fig. 8. Conventional configuration general view.



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Fig. 9. Conventional configuration layout.



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Fig. 10. Hybrid configuration general view.

Fig. 11. Hybrid configuration perspective view.



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3.3. Comparison of alternative variants of airplane

The studies carried out previously made it possible to reveal the FW peculiarities, to elaborate

the requirements of an advanced airplane of high passenger capacity and to develop a number of

alternative layouts. For further detailed analysis it is reasonable to choose the most advanced

configuration with the best characteristics among the layouts under consideration. The layouts

were compared on the basis of the following technical and operating data:

* aerodynamic efficiency;* weight efficiency;

Fig. 12. Hybrid configuration layout.



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Fig. 13. Lifting fuselage configuration general view.

Fig. 14. Lifting fuselage configuration perspective view.



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Fig.

15.

Lifting

fuselageconfiguration

layout.



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Fig. 16. Flying-wing configuration general view.

Fig. 17. Flying-wing configuration perspective view.



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* fuel efficiency;* operational characteristics:* cabin floor slope at cruise;* maximum distance to emergency exits;

Fig. 18. Flying-wing configuration layout.



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* availability of windows in passenger cabins;* number of cargo containers;* operating CG range;* stretching capability.

Some geometric parameters of alternative configurations are presented in Table 1.

As it is seen in Fig. 19, the configurations No. 2, 3, 4 (IWB layout, lifting body configuration

and pure FW) have actually equal aerodynamic efficiency at M 0:8: However, due to smallrelative center-wing section thickness, the IWB layout has less wave drag and, as a consequence,

higher L=D-ratio at cruise M 0:85:

Table 1

Some geometric parameters of alternative configurations

Conventional IWB Lifting body FW

Wing span (m) 84 100 100 100

Airplane length (m) 78 61.7 51 50

Airplane height (m) 26.5 22.6 14.5 15.7

Aria of basic trapeze (m2) 833 1089 1083 1020

Wing planform area (m2) 867 1588 1670 1651

Wing trapezoid aspect ratio 8.5 9.2 9.23 9.8

Wing aspect ratio 8.17 6.3 6.0 6.06

Airplane wetted area (m2) 4100 4080 4040 3860

Fig. 19. Aerodynamic efficiency.



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3.3.1. Weight efficiency

Minimum takeoff weight of the airplane (Fig. 20) and operating empty weight per onepassenger (Fig. 21) may be used as the criteria of airplane weight efficiency and price. It follows

from Figs 20 and 21 that the IWB and FW configurations are superior in these criteria.

Due to high aerodynamic and weight efficiency the IWB configuration is superior to other

configurations in fuel consumption per one passenger-kilometer (Fig. 22).

3.3.2. Operating and other characteristics

Generalizing the results of the investigations carried out, it may be concluded that all but one of

the configurations considered could meet the requirements of FAR-25. The FW configuration (see

Figs 1618) with two engines out of four mounted on the rear of the center-wing section is

Fig. 20. Gross takeoff weight comparison.

Fig. 21. Empty operated weight per one passenger comparison.



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unacceptable due to impermissibly high instability in takeoff and landing regimes. Besides, the

emergency exits of this configuration are located lower down the waterline (Table 2).For further investigations, in accordance with the criteria adopted, the IWB configuration

(Figs 1012) was selected, which:

* includes all the peculiarities related to a configuration of an FW type;* is the most thoroughly developed as a logical successor of the baseline layout (Fig. 2), enabling

the use of experimental results of the preliminary studies;* has many common features with a conventional aircraft in operation and production and

satisfactorily solves the emergency evacuation problem;* is superior in technical and economic criteria.

Fig. 22. Fuel consumption per one passenger comparison.

Table 2

Comparison of operating and other characteristics

Conventional IWB Lifting body FW

Cabin floor slope (degree) 1 4 4.5 4.5

Maximum distance to emergency exit (m) 11 11 13.2 11.5

All exits work 16.6 22 25 28

50% exits work

Windows availability in passenger cabinsFirst class + + +

Business class + +

Tourist class + 7 7

Number of LD-3 cargo containers 42 40 43 32

Center of gravity range (%) 32 37 30

Possibility of the modifications creation + 7



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4. IWB scheme characteristics

4.1. Basic data of the scheme

Basic data of the scheme are presented in Table 3. The relative dimensions of the normal and

IWB schemes are shown in Fig. 23.

4.2. Center-of-gravity range

On the basis of studying possible variants of the control system it was decided to assume static

instability ofo3% MAC in the longitudinal channel at cruise. The corresponding L=D-ratiodecrease will be no more than 0.5 as compared to the absolute value, which is realized at a very high

instability level of about 1214%. In takeoff and landing regimes the airplane must be neutral or

statically stable. The allowable CG range for the configuration chosen and the control unitcharacteristics adopted should not exceed 66.5% of MAC in takeoff and landing regimes. It should

be noted that the MAC is related to the total wing area with the center-wing section and exceeds

more than twice the MAC of a conventional airplane, so the pointed cg range corresponds to the

CG range of 1215% for conventional configuration. But even if the stated notion is taken into

account, the allowable CG range will be lower for FW than for current conventional airplanes.

The CG range was computed for all stages of flight for the following variants of the airplane loading:

* maximum number of passengers in three classes+luggage;* maximum number of passengers in three classes+maximum cargo;* maximum loading of aircraft (one-class layout of cabin with increased passenger density+

maximum cargo);* 25% of passengers in the first half of compartments of each class;* 25% of passengers in the rear half of compartments of each class;* ferry version.

Table 3

Basic data of IWB scheme

Wing span in flight and on runway (m) 100

Wing span at rest and in taxiing (m) 79

Airplane length (m) 62

Height (m) 22.6

Capacity, 3-class, pax. 750Max. capacity (economy class), pax. 975

Maximum takeoff weight (t) 572

Maximum landing weight (t) 437

Operating empty weight (t) 301

Maximum payload (t) 114

Fuel capacity (t) 280

Typical fuel per flight (including fuel reserve) (t) 199

Range (n.m.) 7650

Cruise Mach number 0.85

Takeoff field length (SL, ISA+10) (m) 3350



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The computations carried out have revealed that with fuel transfer taken into consideration

the resulting CG positions are within the allowable range at all stages of flight. The important

factor enabling CG requirements to be met is the lesser length of the FW cabin and cargo bay as

compared with conventional configurations.

In selecting design solutions providing a required CG range, the effect of aeroelasticity on the

position of aerodynamic center must be thoroughly considered (Fig. 24).

The CG control is fulfilled mainly by assigning the order of fuel utilization and (or) fuel

transfer. A sufficiently large volume of outer wing box and the availability of the small fuel tanks

in the center-wing section make it possible to solve this problem properly.

4.3. Cabin floor slope at cruise

The floor of the passenger cabin of a conventional airplane at cruise is close to a horizontal

position. Such a floor inclination is provided by wing settings relative to fuselage of 341. For FW

concept with positive pitch-moment deficit a large incidence of the layout is favorable from the

standpoint of high L=D-ratio.Wing-fuselage inclination results in an inadmissible reduction of the passenger cabin, and

cannot be actually more than 11. Thus, the cabin floor inclination will be high enoughB33.51 at

cruise. During flight this circumstance may present some problems in moving food trolleys whose

Fig. 23. External dimensions of IWB and conventional configuration comparison.



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weight is up to 100 kg. In the considered variant of the airplane the food trolleys are arranged in

the front part of the passenger cabin in order to push the loaded trolleys down.

4.4. Emergency evacuation

In Figs 2527 the emergency exits for passenger evacuation on ground and water are shown.

According to FAR-25-800, the emergency evacuation during the airplane landing on ground

requires that no more than 50% of exits should be used. In this case it is customary to use the exits

arranged along one side of the airplane. The FW airplane passenger cabin is significantly wider

than that of a conventional airplane and this may increase the distance to the exit. Thus, the

maximum distance from the farthest row of seats to the exit does not exceed 16.5 m (see Fig. 25)

Fig. 24. Variation of the center of gravity.



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Fig. 25. Emergency exits in IWB configuration.



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Fig. 26. Emergency evacuations on land (IWB configuration).

Fig. 27. Emergency evacuations on water (IWB configuration).



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for conventional airplanes, while for the FW under consideration this distance amounts to 22 m.

In order to not allow the increase of time for emergency escape, the following design solutions are

used. The number of three-seat blocks making the exit difficult is brought down to a minimum.

The seat-block pitch is increased and as a main solution the aisle width is increased almost oneand a half times (from 0.506 to 0.72 m). Such an increased width corresponds to a new standard

for advanced airplanes being in consideration at present.

5. Conclusion

A number of investigations on defining the configuration and possible characteristics of an FW

type airplane with super high passenger capacity were conducted. The level of technologies used in

the project corresponded to the near-term perspective. The outcomes confirmed preliminary

suppositions on the possibility of achieving higher technical and economical characteristics of FW

configuration airplane as compared with conventional airplanes. In the authors opinion, the

hybrid layout (or integrated wingbody scheme) which represents an intermediate link between a

pure FW and a conventional airplane is the best competitive concept. The IWB scheme retains

a primary advantage of FWFhigh L=D-ratio (L=DB24.5 at M 0:85) and at the same timecould meet all main paragraphs of FAR-25.

References

[1] Byushgens GS. Aviation in XXI century. Symposium on Aeronautical Technology in XXI Century, Moscow,

September 1989.

[3] Denisov VE, Bolsunovsky AL, Buzoverya NP, Gurevich BI. Recent investigations of the very large passenger

Blended-WingBody aircraft. ICAS 98-4.10.3, 1998.


problems and decisions of wings

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