ICAS 2000 CONGRESS

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Abstract

Continued pressure to achieve reductions indirect operating costs (D. O. C.) combined withever tightening environmental constraints hasleft the aircraft designer with little option but toexplore the possibilities offered by more novelconfigurations. This paper describes theprogramme of activities currently underway atthe College of Aeronautics, Cranfield, that isintended to objectively evaluate the advantagesand challenges inherent in the Blended WingBody (BWB) configuration.

The programme incorporates thedevelopment of a sub scale flying demonstratorfacility that should provide the capability toreduce risk in major advanced configurationsstudies in a highly cost-effective manner.

1 Introduction

Considerable effort continues to be invested intothe development of the ‘classical’ aeroplaneshape of passenger jets such as the Boeing 747or Airbus A-340.

Concurrent with the hard to achievedemands for reductions in Direct OperatingCosts (DOC), environmental issues have beenoffsetting much of the potential performancegains. In fact, if future projections of limitationson noise, ‘greenhouse’ emissions and radiationissues associated with vapour trails producinghigh altitude cirrus clouds are taken intoconsideration it may be that, without substantialimprovements in performance the very viabilityof air transport could be called into question.

One of the most promising ‘new’configurations is the Blended Wing-Body

(BWB). In fact if predictions can be achievedand a civil BWB transport can be realised, noconventional airliner would be able to compete.

The BWB configuration does present anumber of interesting challenges, any of whichcould prevent a feasible solution from beingachieved. A wide ranging study is underway atthe College of Aeronautics (CoA) that isintended to get to grips with the knownchallenges and to unearth the problems that maybe hidden in any detail solution.

The programme of activities will lead tothe completion of a detailed design study of afully optimised BWB configuration withintegrated propulsion system, incorporating allappropriate technologies (e.g. laminar flow)within a rigorous framework of constraints toensure that it can be successfully and profitablymanufactured and operated and to the benefit ofpassenger appeal and safety. The design willprovide a considerable degree of confidence thatall major design problems have been identifiedand addressed. To achieve this an incrementalapproach is being utilised.

2 Historical background

Of course, the BWB configuration has beenexplored from time to time over the last 90years with varying levels of success The Britishaeronautical pioneer John W. Dunne designedone of the earliest tailless wing-bodyconfigurations of note which flew in 1912.

There has been significant progress in theUSA with the Northrop series of flying wingbombers culminating in the YB 49 of 1949. TheArmstrong-Whitworth AW-52 was a

COLLEGE OF AERONAUTICS BLENDED WING BODYDEVELOPMENT PROGRAMME

H. SmithCollege of Aeronautics, Cranfield University

Cranfield, BEDS MK43 0ALUnited Kingdom

h.smith@cranfield.ac.ukKeywords: Blended Wing Body, Flying wing, Aircraft Design

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contemporary of the YB-49 but both sufferedfrom similar problems. A more successfulBritish project was the AVRO Vulcan whichserved as a strategic bomber until relativelyrecently. A civil version of the Vulcan, theAVRO Atlantic failed to get off the drawingboard, however a recent Cranfield study hasshown that a solution may exist along theselines.

2.1 The modern blended Wing body conceptAdvances in many areas of technology,particularly control systems led to the current B-2 Stealth Bomber. More recently some of thistechnology has been applied to the BoeingBWB project which was produced as the resultof a US Government-Funded national initiativeinvolving Boeing, Stanford University andNASA.

Parallel activities in the UK and other partsof Europe have also led to novel Blended-Wingprojects.

The Cranfield baseline BWB configurationis similar to the Boeing concept inconfiguration, and currently represents the onlyUK National project of its scale.

figure 1

3 Programme

3.1 Elements

3.1.1 Concepts studiesWhile considering the potential benefits of anynovel configuration, it is important that thedesigner should keep a clear idea of theintended applications. This is important as with

many novel configurations, and in particular theBWB, the concept may be heavily constrainedby operational aspects. A number of top-levelconceptual design studies have been, and arecontinuing to be, performed to evaluatepotential applications of the BWB. Thesestudies are neither detailed nor optimised as thetools and methodologies to achieve this are stillunder development. However, the resultsindicate that further work on a number ofapplications would be justified.

3.1.2 Tool developmentAircraft conceptual design tools andmethodologies have been developed in parallelwith the development of the classic aircraftconfiguration. The design of BWB aircraft is aconsiderably more complex process than that ofconventional aircraft and as a consequenceexisting design methodologies are not easilyadapted. Furthermore, any tools based onempirical data are unlikely to remain valid fornovel designs or do not have the requiredflexibility of parameters to be able to model theBWB. Studies are currently in progress toredress this deficiency.

3.1.3 Preliminary design studiesWith the benefit of experience, the viability of aconventional aircraft design can usually bedetermined with a reasonable degree ofconfidence at the conceptual design phase. Inthe case of novel configurations it is essential toproceed to at least the preliminary design phasebefore any reasonable conclusions may bedrawn. Furthermore, in the light of this lack ofexperience many potentially show stoppingdesign challenges may be hidden in the detaileddesign. These challenges cannot be furtherresearched, or designed around, until they havebeen identified.

As with the initial concept studies insection 3.1.1, the first of these preliminarydesign studies is not intended to represent anoptimum design as the tools to achieve such adesign are not yet in place. However, theintended objectives of this initial preliminarydesign study do not require the design to beoptimum. The planned phase II preliminary

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design study will be positioned considerablyfurther up the learning curve.

3.1.4 Key technology developmentAs already discussed, the BWB configurationhas been investigated in the past with limitedsuccess. The key to its success lies in theoptimal application of new technology. Someof these technologies are still at a very earlystage of development and this development isbeing continued to a point were it can beapplied. Other new technologies exist but mustbe carefully adapted to the BWB application. Ifthese technologies cannot be successfullyutilised then the BWB concept may need, oncemore, to be archived until some future date.

3.1.5 Sub scale demonstratorThere is considerable risk associated with thedevelopment of an unconventionalconfiguration and measures need to beimplemented to reduce this risk and its financialimplications. Small-scale flight vehicles haveoften been used to explore aerodynamic, flightdynamic and flight control characteristics priorto full-scale flight test.

The programme includes the design,manufacture and flight of a small-scale BWBtest vehicle.

3.2 Schedule

The programme is currently intended to runfrom early 1998 through until early 2002 bywhich time a fully optimised preliminary designstudy should have been completed and the subscale demonstrator should have completed itsinitial flight-testing.

4 Concepts studies

Throughout the duration of the programmeconceptual design studies, applying the BWBconcept to a number of practical applications,will continue. In the initial phase these havebeen intended to highlight the particularstrengths and weaknesses of the BWB to enablefurther studies to be more focused. As theprogramme continues, the more refined BWBdesign tools can be utilised as they develop.

4.1 Civil applications

The initial studies indicate that the BWB is wellsuited to two civil applications, the highcapacity civil transport and the freight aircraft.The BWB's high efficiency and flexiblepackaging potential enable it to meet thedemands of the air transport market whilstminimising the impact on the environment. Thebasic geometry of the vehicle combined with theconstraints implied by the required cabin heightfor a human payload implies better solutions forthe ultra-high capacity applications.

The air freight market is rapidly expandingand is likely to support an increasing number ofaircraft sales. The BWB configuration offersconsiderable flexibility for volume limitedpayload applications and, assuming a reasonablefraction of palate freight, could provide afeasible solution over a wide range of All UpWeight. A passenger/freight aircraft is likely tobe driven primarily by the passenger transportrole.

4.2 Military applications

4.2.1 Large vehicleWhilst the BWB's excellent payload rangecharacteristics makes it a strong contender forthe military transport application, it'sintrinsically stealthy shape brings advantagesbeyond anything offered by the conventionalconfiguration. The vehicles low ground attitudeshould prove advantageous inloading/unloading.

The BWB configuration is not ideallysuited to high density payloads, however, an airto air refuelling variant of the military transportaircraft would benefit significantly from thestealth and payload range advantages.Applications such as this could potentially makeglobal reach a practical reality.

4.2.2 Small vehicleUntil the advantages offered by low observabletechnology are eliminated by anti-stealthtechniques the BWB is likely to be the firstconfiguration considered for any moderncombat air vehicle. The BWB finds

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applications from the larger strike aircraft,through the more compact Unmanned CombatAir Vehicle (UCAV) down to the smallestunmanned aerial vehicles (UAV). Theconceptual design studies performed in this areawill become more conclusive as the design toolsbecome more refined.

5 Tool development

5.1 Mass estimation

Empirically based methods of mass estimationprovide an efficient yet accurate method fordetermining the mass of aircraft at theconceptual design stage. At a more refinedlevel low fidelity finite element based methodspresent a strategy for incorporation of moreelaborate strength and stiffness criteria.

The BWB configuration presentsdifficulties in the implementation of either ofthese approaches. The former is hindered by thelack of empirical data and the latter by the lackof experience in BWB structural layout.

As the database of mass breakdowns startsto accumulate from the preliminary designstudies, this information will be used to developempirical techniques tuned to the BWBconfiguration. Furthermore, experience will begained in how to tackle the problem of BWBstructural layout design and this will assist withthe more deterministic mass estimationapproaches.

5.2 Aerodynamic prediction

Whilst a wide range of aerodynamic predictiontools is already in existence, ranging fromsimple empirical data sheet methods to Navier-Stokes CFD techniques, the need for multi-disciplinary optimisation dictates that themethods should be computational efficient.Simultaneously, the requirement for novelconfiguration applicability demands moreflexibility than is offered by simple data sheetmethods. Current research activities arefocusing on vortex lattice methods which seemto offer a reasonable compromise. Ultimately, amulti-level approach will be required

incorporating both high and low fidelitymethods.

6 Preliminary design studies

6.1 Baseline configuration

6.1.1 Basic requirementThe primary requirements and specifications forthe BW 98 are as follows:

To design an airliner with a similar payloadand mission performance to the A3XX-200 butwith superior direct operating costs.Accommodation capacity should be 656 seats in3 class layout.

An alternative cabin layout willaccommodate a maximum of 960 passengers ina single class seating.

The design range is 7650 nm cruising atMach 0.85 with a payload of 656 passengersand their baggage. The aircraft should becompatible with existing airports and facilities.

The results of this study are too extensiveto be summarised in this paper, however, thefollowing 2 sections describe alternative centrefuselage structural designs.

6.1.2 Centre wing-body (modular)Two approaches were considered in the designof the centre wing body structure of the aircraft.One uses aluminium alloy and classicalstructure members such as frames and stringersand will be considered first. An alternativeconfiguration using composite materials isdescribed in the next section.

Flat and vaulted shell structuralconfigurations for the cabin bay wereconsidered at the beginning of the project butthe vaulted double-skin ribbed shellconfiguration was found to be superior due tothe weight savings and the load diffusion. Thusthe fuselage is built as a multi-bubble circularsection as shown in figure 2.

This fuselage configuration requires adouble-skin construction. The inner skin carriespressurisation efficiently by hoop-stress and thecabin wall is used to balance the weight of thestructure above the cabin bay and the verticalcomponent of the hoop-stress. The outer skin

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carries the major part of the bending momentand the shear force due to the aerodynamicloads acting on the aircraft. In addition, otherstructure members transfer part of theaerodynamic loads from the outer to the insideskin.

Due to the particular shape of the BW-98the number of tubes inside the fuselage varieslongitudinally. Three key cross-sections weredesigned in order to maximise the internalspace. The first is formed from a single tube, thesecond is composed of three tubes and the lastsection is formed with five tubes where thethree inner ones are used for the passengers andthe outer two are used for the baggage. Anisometric view of the inside fuselage can beseen below.

figure 2Each tube used for the passengers is double

decked.Wing bending moments and the shear

forces are carried by conventional spars. Ribs inthe longitudinal direction are used in order toattach the inner fuselage to the main structure ofthe outer fuselage.

The inner and outer fuselage are designedas a conventional fuselage which skin issupported by stringers. The stringers are used tocarry a part of the axial load due to the bendingmoment while the skin carries shear from theapplied transversal external load and torsion.Furthermore, the skin of the inner fuselage willalso carry the pressurisation loads.

As with a classical aircraft, frames are usedin order to stabilise the aircraft structure in thetransversal direction. Two frames will be useddue to the special configuration of the BW-98;

one for the inner fuselage structure and the otherfor the outer fuselage. The inner frame will beattached in the non-pressurised part of theaircraft in order to save space for the passengerbay.

Ribs in the transversal direction will alsobe used in order to attach the fuselage bubblesto the outside structure and also to help theframe to carry the shear and maintain the shapeof the of the aircraft. In order to avoid the shearbuckling of these ribs stringers will be utilised.

6.1.3 Centre wing-body (integrated)

figure 3The alternate solution considers an integratedapproach to the design of the centre wing bodysection. Here the applied, inertial and pressureloads are carried through a unified structure.

The main loading comes from the pressuredifferential applied to the large and very slightlycurved skin panels. This induces considerablebending moments in the skin panels. To limitthese, some internal walls have been arranged toconnect the upper and lower skin.

As the aim of the composite layout is tolimit the number of parts in order to reach thelowest possible weight, the outer skin takes thepressurisation loads, without the help ofadditional structure.

Thus, the pressure differential is applied onthe skin panels on top and bottom of the cabin,on the leading edge in the front and on curvedbulkheads on the sides and in the back of thecabin.

6.2 State-of-the-art configurationThe full potential of the blended Wing bodyconfiguration can only be realised through theapplication of a number of advancedtechnologies. These technologies were not

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applied to the baseline configuration for tworeasons. Firstly, the clear identification ofadvantages and disadvantages purely from theBWB configuration was required. Furthermore,the design tools were not then in place fordesigning a correctly optimised configurationand hence the integration of more advancedtechnologies would have been premature.

Later in the programme, as the design toolsdevelop, the phase II preliminary design studywill be performed. In addition to takingadvantage of these design tools, a number ofadvanced technologies will be integrated withthe design. The application of laminar flowtechnology, control configured vehicletechnology combined with a fully integratedpropulsion system is likely to result in asignificant step improvement in performance.

This preliminary design study will not onlyquantify the advantages offered by suchtechnologies but will also identify offsets interms of mass and cost due to actual engineeringsolutions.

7 Key technology development

7.1 Human factors

figure 4From early on in the study it became clear thathuman factors was the dominant issue in thedesign of BWB aircraft for civil transport. Forall ultra-high capacity aircraft (UHCA) humanfactors have already become an area of interestboth from an operational and certificationviewpoint. The situation is considerably moreacute for the BWB configuration to the pointthat it is likely to dominate the conceptualdesign. Not only must it be possible to board

the passengers within a reasonable time scale,into an environment that they find comfortable,but it must also be possible to evacuate themthrough half the exits in less than 90 seconds.The former problem stems from the largewindowless cabin volume and the latter fromthe limited scope for exit placement.

Due to their subjective nature, theincorporation of human factors issues into thedesign procedure is non-trivial. Work iscurrently in progress to establish designguidelines for layout of Ultra Wide Bodypassenger cabins to assist at the conceptualdesign stage. Numerical evacuation simulationshave been run in an attempt to establish theinfluence of cabin geometry on evacuation time.Figure 5 indicates the trend in evacuation timevs. number of exits. The wide spread of thecurve indicates the significance of exitlocations, aisle widths and other parameters.The general shape of the curve is a function ofthe shape of the cabin and in this case appears totend to a limit defined by the time taken forpassengers to progress from central regions tothe outer perimeter.

figure 5

7.2 Laminar flow technologyThe BWB configuration appears well suited tothe application of laminar flow technology. Itshould be relatively easy to accommodate thedistributed part of the system between the outerskin and the inner pressure cabin or integratedwith the outer structure. Experimentalinvestigations and preliminary design studiesindicate that the application of laminar flow

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technology to engine nacelle drag reduction isfeasible and it's introduction into service couldbe imminent. Hopefully this will spur furtherdevelopment of the technology to enable itsapplication to other parts of the airframe, inparticular, the lifting surfaces.

7.3 PropulsionA number of options are being considered forthe propulsion units on this aircraft. Theconfiguration tends to favour aft mounted over-wing engines as shown in figure 1. In this casethe Rolls-Royce RB 529 contra-rotating projectengine offers the additional benefit of lifting thecore intake clear of the boundary layer. Whilstthis is a novel concept, the BWB configurationoffers the opportunity of a far greater level ofengine airframe integration. One such novelconcept being considered is a tip turbine drivenremote fan powered by an engine coreintegrated within the airframe. This conceptalso offers the possibility of thrust vectorcontrol (TVC).

7.4 Systems integrationThe design of any classical (Boeing 707 type)configuration civil airliner can be thought of asa number of weakly linked processes such as thedesign of the fuselage, the design of the wing,the design of the empennage and the design ofthe propulsion. Whilst this simplifies the designprocess it does constrain the various systems to,essentially, operate independently of oneanother. Conversely, the highly integratednature of the BWB configuration complicatesthe design process, however, it offers a uniquepotential for the synthesis of a SystemsConfigured Vehicle (SCV). The SCV wouldexhibit an optimal balance betweenconfiguration, control system (including TVC),propulsion, laminar flow control system, highlift system, secondary power etc.

8 Certification issues

8.1 Advanced configurations issuesModern airworthiness requirements such as theJoint Airworthiness Requirements (JAR) have

been developed in parallel with the classicalaircraft configuration. Hence, when applied to anovel configuration considerable interpretationis required. Studies completed so far indicatethat there are two implications that need to beconsidered. Firstly, it is essential that any novelconfiguration is shown to be "airworthy". Nodesign will be fully convincing when it can onlybe measured against extrapolations from thegeneral requirements. Furthermore, from aconceptual design viewpoint, it is difficult tomake direct comparisons between conventionaland novel configurations if they are designed toinconsistent general requirements.

The only real precedent for this would bethe design of Concorde where a new set ofrequirements was written specifically for thisaircraft.

It is important that airworthinessphilosophies are developed in parallel with thedevelopment of the configuration itself. Thishas already spawned a number of areas ofresearch vital to this effort.

8.2 Safety

8.2.1 Human factorsHuman factors issues are likely to impose aheavy constraint on the BWB configuration inaddition to imposing a number of heavyengineering solutions locally. Hence, it is vitalthat this area be treated in a consistent manner ifan objective solution to the BWB configurationis to be found.

8.2.2 CrashworthinessThe current airworthiness requirementsessentially de-couple crashworthiness andemergency evacuation. The crashworthinessrequirements exist in the form of limits onacceleration endured by structure associatedwith passenger restraint and structure likely topenetrate the cabin volume during impact.

The requirements imply that an aircraft thatmay be evacuated within 90 seconds is saferthan one that requires 100 seconds. However, ifthe 90 second aircraft is more likely toincapacitate it's passengers in an emergencylanding/ditching then this may not be a logicalconclusion.

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The BWB configuration has a number offeatures likely to make it more crashworthy. Aplanned study utilising non linear FE analysisshould enable this claim to be substantiated.Further changes to the airworthinessrequirements will be required for theconfiguration to take advantage of this.

8.3 Advanced technology issuesIf the BWB configuration is to attain its fullpotential then the airworthiness requirementsmust allow a number of advanced technologiesto be utilised albeit within the bounds of safety.Issues relating to the application of active flightcontrol systems are already being addressed,however, they will need to be extended to bothlongitudinal and directional stability. The fullbenefits of laminar flow control can only beachieved if fuel reserves are not required toaccount for a total system failure. Theconfidence required to support suchrequirements may only be obtainable throughthe accumulation of flight hours of laminar flowequipped conventional aircraft.

9 Sub scale demonstrator

The concept of using sub-scale flyingdemonstrators to evaluate a variety of aircraftcharacteristics as a cost effective method of riskreduction is not new. Whilst quasi-static andsome dynamic aerodynamic characteristics aremore rigorously determined within thecontrolled environment of a wind tunnel testprogramme, some characteristics are morerealistically evaluated during flight test.

To achieve experimentally a satisfactoryunderstanding of the low speed characteristicsof an aircraft prior to full-scale flight-test arange of wind tunnel tests would be required. Aseries of dynamic tests would be requiredbeyond the usual static tests. The objective ofthese would be the evaluation of ground effectson take-off and landing, dynamic aerodynamicderivatives, entry into stall as a function ofattitude/flight conditions/dynamics/controlmotivator usage, departure into spin,determination of spin modes and evaluation ofspin recovery including the effects of spin

recovery devices to be utilised during flight test.Beyond this, it may be necessary to evaluateaeroelasic and aeroservoelastic characteristics.

The infrastructure required to facilitatesuch a programme would include a static tunnel,a tunnel equipped with a internal balance modelon a forced oscillation sting, a rotary balancetunnel, captive flight and free-flight tunnels andspin tunnels also using free-flight models. Evenif some of these experimental set-ups can utilisethe same tunnel, the programme will stillrequire access to at least 3 fundamentallydifferent types of tunnel. The size of thesetunnels will also dictate the maximum modelsize. Furthermore, it is not possible to evaluatecharacteristics such as susceptibility to spinentry and determination of dominant spinmodes. It is also difficult to simulate, in acontinuous manner, the development of a spinstarting from steady level flight.

Recently a NASA funded programmeenabled Stanford University to develop, buildand fly a BWB sub-scaled demonstrator (5.18mspan,54kg mass) powered by 2 35cc two-strokeengines. NASA has now announced it’sintention to flight test a jet powered BWB LowSpeed Vehicle (LSV) (10.7m span, 816kgmass). This will be powered by 3 WilliamsWJ24-8 engines at 900N each with a totalprogramme cost of some $25 million.

The Cranfield BWB testbed fits betweenthese two NASA programmes but will becompleted at a small fraction of the cost.

9.1 ObjectivesThe primary function of the vehicle is toevaluate the aerodynamic and flight dynamiccharacteristics of the BWB configuration asapplied to specific concepts and in the genericsense. Further detail can be found in SMITH [1]Additional potential studies include theinvestigation of the coupling between the flightcontrol system and the aeroelastic behaviour ofthe vehicle, enhanced control power throughpassive wing warping etc.

The vehicle is intended to be capable ofevaluating static and dynamic characteristics inaddition to stall/ pitch-up, post stall, spin andground effect situations.

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The key philosophy behind this project isflexibility. The ability to design a fullyoptimised full scale configuration is still in theprocess of development and hence the baselinegeometry is not intended to represent the ideal.As this capability develops new configurationswill need to be evaluated. Thus, the ability tomodify the vehicle geometry in a cost-effectivemanner is important.

9.2 Basic philosophyFor the flying testbed concept to work asintended and in a cost-effective manner it wasvital that the vehicle be re-configurable with aminimum of additional design hours. The scopehad to include the geometry, the massproperties, the control configuration and theflight control system. Furthermore, the vehicleneeded to be designed such that its capabilitycould be extended if, at a latter date, it becameappropriate.

Geometric reconfiguration was deemedvital within the scope of the CoA BWB researchprogramme since it was known that thesynthesis and optimisation tools would still beunder development at the time the test-bedconfiguration had to be frozen. Thus, the initialconfiguration would serve as much as a testvehicle for the test-bed facility as a prototypefor the full sized BWB. Furthermore, the test-bed would serve as a more flexible research toolif a variety of concepts could be emulated. Thefinal design is thus intended to bereconfigurable in both planform and section.To ensure that the vehicle was correctly scaledfor mass properties it would inevitably need thecapacity for ballasting to allow formanufacturing tolerances. Thus to extend this toallow for the modelling of a variety of full-scaleconcepts is simply a matter of extending theballast capacity. This also allows for thevariation of centre of gravity position both foreand aft and laterally (an important issue withBWB civil transports).

9.3 Structural conceptThe main challenges for the structural designwere, firstly, the need to keep the weight to aminimum and thus provide maximum capacityfor ballast. Secondly, to create a structuralconcept that would enable the geometry to bechanged in a cost effective manner.The concept centres around an endo-skeletalstructure that supports a light weight aero-shell.

The core of the structure consists of aframe intended to house the majority of thesystem units and provide the carry throughstructure for wing, control surface and engineattachments. The wing box mounts onto thiswith some degree of flexibility of wing sweep.This structural component is likely to be ofcomposite construction. Mounted onto the wingbox are a series of ribs which transfer loadsfrom the aero-shell to the wingbox and providemounting points for control hinges andactuators.

9.4 SystemsAt the heart of the system is the CranfieldAerospace Ltd UAV Avionics Package (usedwith permission of DERA Farnborough). Thissystem was developed for UAVs known asXRAE140 and CA3 ‘Observer’, figure 6, underthe DERA Short Range UAV programme. Thisunit has been further developed and utilised insubsequent UAVs.

Figure 6

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Basic flight data is relayed to the groundstation via radio telemetry to enable heathmonitoring and assist the operator wheremanual take-off or landing is required.

The propulsion system consists of two190N thrust turbojet engines. Fig 7.

The 2 AMT Olympus units are 130mmdiameter by 270mm long and weigh 2.4kg each.

Figure 7The basic recovery method is via a

conventional tricycle landing gear deployedusing a one-shot actuation system. Recoveryfrom an uncontrolled flight mode or in the eventof an emergency is by parachute deployment inconjunction with an airbag system. At impactthe parachute will be automatically or manuallyjettisoned. This system would typically beactivated at an altitude of 80m to minimise drift.

9.5 AirworthinessAirworthiness issues are of extreme importanceto all aircraft but, additionally, an area ofuncertainty for UAVs. The Civil AviationAuthority’s (CAA) Safety Regulation Group hasconsidered the operation of the CoA’s UAVs.Subject to approval, the aircraft will fly underan Exemption to the Air Navigation Order.Several locations are being considered for theflights including Warton, Salmesbury andBarrow-in-Furness.

10 Conclusions

In the process of completing the baselinepreliminary study many detailed problems wereencountered and solutions or compromisesfound. Some of the difficulties will be besttackled at the conceptual level and hence willfeed into the Phase II study, the BW2001.

Now that a detailed design exists, manysupporting studies such as human factors issuescan now commence using the BW98 as abaseline configuration. These studies will,again, feed into the Phase II detailed design andensure that it will represent a state of the artdesign. From this project it should be possible tomake an objective assessment of the feasibilityof the Blended Wing Body concept.

The Sub-scale demonstrator programme isprogressing rapidly with wind tunnel testing tostart shortly. There are still a number ofchallenges to be overcome but if the programmeproves successful the result will be a veryuseful, and cost effective tool for thedevelopment of novel flight vehicles offeringthe potential for risk reduction in expensive civiland military projects. The testbed facility willalso help to drive research in a wide range ofdisciplines.

11 Acknowledgements

The author would like to thank BAE Systemsfor granting access to the A-3XX-200requirement and Rolls-Royce for their RB529data used in support the baseline preliminarydesign study.

Engine image reproduced by kindpermission of AMT Netherlands.

References

[1] Smith H, Gibbons N Cranfield Blended Wing BodyFlying Testbed Facility, Unmanned Air VehicleSystems, 15th International Conference, 10th-12th

April 2000, Bristol, United Kingdom.