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ByJOHN W. OCONNOR

DIRECTOR OF PRODUCT AND MARKET STRATEGYVISTAGY, INC.

38 jec composites magazine / No65 May June 2011

software

Unmanned aerial vehicles (UAVs) have experienced tremendous

growth as the value of incorporating remote sensing technologies

and weapon systems into pilotless aircraft has become more

evident. The advantages that come from long dwell times,

operational safety, and a flexible mission space make UAVs versatile

and useful complements to a variety of military, national security,

and aerial research activities. Addressing weight and cost issues iscentral to achieving the advantages that UAVs promise, but realizing

them and continuing to improve upon current designs represents a

major technological challenge.

Less is more when developingcomposite parts for UAVs

he airframe of a high-altitude UAV

represents about one-third of thegross vehicle take-off weight for theaircraft. Any savings in the weight of the

airframe translates directly into increasedsensor or weapon payload as well as longer

flight duration. So manufacturers arefocused on using industry-specificengineering processes to create new UAV

airframe designs that are less expensive todevelop and lighter than previous versions.

One solution for incorporating theseengineering processes into the

development of UAVs is VistagysFiberSIM composites engineeringsoftware. FiberSIM is fully integrated into

authoring 3D CAD systems used by UAVdesign teams including Siemens NX,

Dassault CATIA, and PTCs Pro/Engineer and provides specialized capabilities fordefining the composite structure of an

airframe. By organizing the compositeinformation in an easy-to-use, logical

system, the manufacturer is far better able

reduces development costs. FiberSIM is apowerful solution for smoothly creatingoptimal designs while fully and smartly

leveraging engineering and manufacturingsystems that are in place.

FiberSIM standardizes and automates thedevelopment process for composite

structures in UAVs, helping to achievelighter weight designs at lower cost.

T

to understand the impact of design choiceson weight and cost and can readily updatethe design when necessary.

Further, since the software has the ability

to communicate accurate and up-to-datecomposite definitions in formatscustomized for manufacturing systems, the

whole downstream manufacturing processis made more efficient, which significantly

Fig. 1: This UAV was used in Desert Rescue XI, a joint service combat search andrescue (CSAR) training exercise hosted by the United States Naval Strike and War-fare Center in Nevada. The exercise simulates downed aircrew behind enemy lines,enabling other aircrews to perform CSAR-related missions as well as experimentwith new techniques in realistic scenarios (U.S. Air Force photo by staff Sgt. Rey-naldo Ramon)

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up the possibility of creating a betterperforming UAV.

Optimizing the aircraft for cost and weight

is critical for enhancing the UAVs footprintin aviation, and composites certainly play amajor role in helping to achieve that goal.

Counting on composite designtoolsUAV programmes move at a much fasterpace than traditional aircraft programmes.

Carbon fibre is generally used for itssuperior strength-to-weight and stiffness-

to-weight properties. The suppliers doingthis work are usually experienced incomposite development. In fact, much of

the large UAV manufacturing in the pastdecade has been performed by a handful ofexperienced companies. They have lasers,

cutters, and other automation systems aspart of their operations. These

manufacturing systems need structured,purpose-developed data to run efficiently.Specialized composite design tools are

essential for this purpose.

UAVs are increasing in complexity and the

tools and techniques used in conventionalaircraft development are now appropriate

for the design and manufacture ofmedium-to-large UAVs. Composite designtools are the standard in todays

aerostructure development environmentbecause composite definitions tend to be

extremely complex and a challenge tomanage. These pressures make compositedesign tools an obvious choice for UAV

development programmes so they canincrease the performance and quality of

their designs.

Also, optimizing the design through cycles

to reduce weight and improveperformance is difficult without a

structured design data set. A structured

description of the design for analysis is alsorequired to perform this function

efficiently.

The medium and large UAV market iscoming from two directions: largeairframers are scaling down and small

manufacturers are scaling up. However, airframers face a less demanding challenge

with UAVs than traditional aircraft because

the product development cycle is muchshorter and they dont need to go through

a certification process with a regulatorybody, such as the United States FederalAviation Administration. But this is

changing, so tools and processes arebecoming increasingly important as UAVs

are scaled up in size and users seek higherperformance.

Generating reliable dataIn order to generate reliable manufacturing

data and create parts that match the as-designed definition, manufacturers need todetermine that the entered data is:

- Accurate and complete,- Easily updateable because changes are a

fact of life in design, analysis,manufacturing, in quality, and in the field,

- Exchangeable as it is rare that the samefacility or company over time will be theonly one to build a design. At some point,

manufacturing will be outsourced, and asubstitute supplier will start building the

same composite structure.

Inefficient manual tasks are reduced orcompletely eliminated, helping to increase

the overall quality of the final product. Allof this happens in accordance with the

design-to-manufacturing release cyclecommon to UAV companies and trulyaugments existing efforts. The result is a

higher quality product built with a moreefficient and robust process that produces

higher-performing UAVs at lower cost.

Optimizing airframe designAny country with a modern aerospaceindustry is interested in developing UAVs

because they are much less expensive tomanufacture and operate than mannedaircraft. However, UAVs are increasingly

becoming high-performance vehicles,featuring increased payload, speed, andduration.

Since the main purpose of a UAV is tocarry sensors or weapons, any additional

weight in the airframe reduces the amountavailable for payload or fuel. This decreasesits capabilities and/or how long it can stay

aloft. Because the airframe takes up somuch of the gross vehicle take-off weight,

minimizing the number of pounds opens

Featureaeronautics

No65 May June 2011 / jec composites magazine 3

Fig. 2: Example of a composite belly fairing designed with Vistagys FiberSIMsoftware during a CAD modelling session. Shown are the results of the producibilitysimulation for a single composite ply. This provides the designer with a window tothe manufacturing floor which enables the early detection of manufacturing pro-blems that can be addressed in design. This information is critical to productionquality

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standards similar to commercial aircraft.The industry is not there yet but it ismoving in that direction. As it does, having

a more complete and reportable set ofanalysis data will be critical to ensure that

the UAV is sufficiently robust.

For example, as part of airworthiness

certification, the different parts of theaircraft structure must be loaded to failure

and that data used to confirm that theanalysis of the structure is correct. Becauseof the complex nature of composite

materials and the challenges of getting as-manufactured fibre orientation data for

analysis, agreement between predicted andactual failure loads can be difficult toachieve.

Using composite design tools to create thedefinition of the design helps to identify

the as-manufactured fibre orientations.That data is used for manufacturing

planning, and thus assures that the fibreorientations are correct.

The ability to match a designs analysismodel with the as-manufactured definition

gives UAV developers more confidence

that their design models will accuratelyreflect performance. This makes

certification of the UAV morestraightforward and attainable.

Beyond this initial testing, the aircraft musthave a plan for maintenance as part of

continuing airworthiness requirements.This plan must include requirements forperiodic inspection and maintenance as

well as a complete overhaul of theairframe. Since a greater fraction of the

airframe structure in new UAVs is made ofcomposites, the plan must address theneeds for designing repairs of composite

structures. This requires that the initialdefinition of the composite structure be

available for the design of repairs.

Therefore, the composite structure mustbe well defined and available for use as part

of the on-going maintenance of theaircraft.

Facilitating growthUAVs are poised for remarkable growth as

they continue to develop in size anddiversity of use. One industry sourcereported that approximately $1.5 billion

was spent globally during 2008 on UAVsand that figure is expected to grow by

300% over the next decade.

Central to this growth is the incorporation

of composite technologies in the airframe.Composites give the craft its lightweight,

high strength-to-weight, and high stiffness-to-weight properties. But designing,manufacturing, and maintaining

composite structures is difficult, if notimpossible, without advanced engineering

solutions. These solutions capture thecomposite design and ensure that theUAV can carry the required loads, be

manufactured to a precise standard, andmeet certification requirements.

Vistagys FiberSIM provides just suchcapabilities, enabling manufacturers to

develop UAVs that are higher quality,lower cost, and more straightforward toproduce.n

More information:

www.vistagy.com

The way to meet the above requirements isby using a composite design system alongwith a CAD/PLM system that controls the

design. Composite design systems pluginto the native CAD platform and offer a

suite of tools that help to verify thecompleteness of the composite definitionby including design rules tailored to the

standards of the industry. VistagysFiberSIM is one such solution.

The tools within the composite designsoftware also help to determine the actual

fibre orientation of the design andcommunicate it to analysis tools in a

format appropriate for import. This avoidsmanual interactions with the data that cancause errors and helps to speed up the

design-to-analysis cycle. The way tooptimize UAVs for weight and cost is toincrease the number of analysis

optimization cycles on these airframes.

Getting certifiedEventually, UAVs will fly in civilianairspace and will require a certification for

type design similar to that of mannedaircraft. This will mean that the

development of UAVs will need to follow

40 jec composites magazine / No65 May June 2011

software

Fig. 3: Example of a wing skin designed with Vistagys FiberSIM software during aCAD modelling session. Shown are the results of the producibility simulation of aply definition across multiple zones of the design. The zone definition of the designenables direct mapping of structural requirements to the composite definition andquick updates from subsequent structural analyses