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3-D Composite Design Gives Pipistrel Lift

DN Staff

June 23, 2010

5 Min Read
3-D Composite Design Gives Pipistrel Lift

Pipistrel, founded morethan 22 years ago as the first private producer of aircraft equipment inYugoslavia, made its name manufacturing ultra-light hang gliders before movinginto lightweight aircraft, including gliders, motor gliders and high-efficiencycruising planes, in reaction to market demands. While the company's models andtypes of aircraft have evolved over the years, the consistent theme forPipistrel is producing planes that are both fuel-efficient and highperformance. To do so, the manufacturer has invested in and refined a productdevelopment process that leverages composite materials and advanced 3-D designtechniques to achieve optimal aerodynamics.

"The main challenge in aviation is how to produce anairplane that has the most possible lift while producing a minimal amount ofdrag," says Tine Tomazic, research and development at Pipistrel. Given that theselection of engines for Pipistrel's chosen types of aircraft is limited, it'snot engine choice that defines a particular model, but rather the outside shapethat becomes the key differentiator. "When you start to define the shape of aplane, it becomes evident that even measurements below one tenth of amillimeter can make a difference," Tomazic explains.

Human-LikePrecision

ThePipistrel engineering team began aggressively working to address this challengeabout seven years ago. At the time, the firm used 3-D MCAD to design mechanicalsystems on the aircraft; but the system fell short of leveraging the 3-D toolsto do any type of shape or surfacing work because of what the team considered aprecision deficiency. "Aerodynamics and shapes were drawn by hand and producedin physical form by hand because the naked eye and human hand were still themost precise instrument when judging the fluidity of lines," Tomazic says.

Whilethe hands-on method was deemed more precise, it was also quite limiting interms of how the Pipistrel engineering team could evolve designs.Traditionally, the engineer or aerodynamic specialist would manually describeto the CNC milling machine operators creating the physical prototypes what kindof curve or shape they needed. Not only was the engineering team limited by thecreativity and technical skills of the person responsible for building thephysical shape, there was too much room for misinterpretation around thedesign, often leading to miscues and false starts. "The engineer or aerodynamicspecialist had to describe what they wanted to the person who was going toproduce it and there were often differences between the description and theexecuted form," Tomazic says. "We couldn't make the shapes as complex as wewould have wanted to simply because the workers didn't understand what wewanted. It was touch and go every time."

Soon afterward, the Pipistrel team began experimentingwith another 3-D MCAD tool, this one with an integrated module specifically forcomposite design - Dassault SystA"mes' CATIA PLM Express with the CompositesDesign option. Using this tool, the Pipistrel engineering team was able totransition its manual shaping and physical prototyping process for an aircraft intoa digital prototyping method that ensured consistency
while allowing the team to more fully explore a range of design options.

While composite materials deliver superior aerodynamicqualities, they introduce complexities into the design, particularly aroundblending surfaces between two adjacent parts and in accurately determining thethickness of component parts. Prior to using CATIA and the integratedComposites Design tool, the Pipistrel team struggled with blending a surfacesuch as a sharp wing structure with a round surface like that associated with afuselage. Traditionally, in an example like that, the team would produce thewings and fuselage separately and then join them together by hand. Because theprocess was so complex and nearly impossible to replicate in a drawing,designers were stuck with more of a trial-and-error process, which was timeconsuming and often didn't produce the desired results. "The fact that we candefine the outside aerodynamic shape on the computer versus describing what wewant technically to build a part has tremendous benefits," Tomazic explains."There's no more problems with fitting - if parts fit on the computer, they fitin real life."

Havingthe master shape defined in CATIA also aids in constructing the layers ofcomposite materials underneath. Take, for example, the cockpit of the aircraft.The design challenge is to create a space that is large enough to comfortablyaccommodate the people without jeopardizing the aircraft's aerodynamic shape -a task that becomes more complex given the properties of designing withcomposites. "With composite materials, it's often difficult to judge thethickness because the thickness of the walls and structure varies," he says.Since composite parts are made of plies, sometimes having too many bends orcorners makes it difficult to estimate a part's size. "CATIA integrates theability to see how thick a part or material will be regardless of whether it'smade of composites or something solid," Tomazic adds.

MCAD-EnabledPotential

Inthe two years since Pipistrel deployed the new approach, it has achieved anumber of significant milestones. Its Virus and follow on Virus SW (Short Wing)cruise aircraft both won the NASA Challenge, winning accolades for their fuelefficiency and performance. From a product development perspective, the changeshad a notable impact on improving Pipistrel's ability to get aircraft models tomarket faster. Specifically, Tomazic said the manufacturer has cut the time ittakes to get a plane from concept to market by 40 percent - an achievement heattributes to being able to explore more design iterations since both themechanical design and shape work are performed in the same package. Inaddition, because the composite models created in CATIA are so precise, thetime required for testing of parts and components is also greatly reduced - insome case as much as 25 percent. "Instead of people producing shapes, machines areproducing much more precise shapes and there are no more mistakes withtesting," he explains. Previously, every part was subjected to force andmeasurement tests, but now simple parts can be tested in the computerenvironment and the test results are accurate, Tomazic adds.

Movingforward, Pipistrel is in the midst of transferring its existing materialsdatabase from another software package into CATIA - a move Tomazic says willstreamline engineering change orders. In addition, it will create an integratedenvironment whereby all relevant parties are notified of pertinent changes andall corresponding documentation and files are updated from a single CATIAmodel.

While aircraft designs two years and older willcontinue to be produced and evolved with the company's traditional productdevelopment model, the Virus SW aircraft, a forthcoming four-seater unit, andany new designs will take advantage of the new 3-D driven composite designapproach. Says Tomazic: "Any kind of clean book design we're setting up in thenew system right from the start. Now we're able to design everything on thecomputer - not only the systems, but the shape and structure of the plane."

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