Validating, Testing Landing Gear

Although it has sophisticated CAD tools, Messier-Dowty finds that the physical, full-scale mock-up is an essential tool in its product qualification. Photo courtesy of Messier-Dowty

Aircraft landing gear is an extremely complex system comprised of mechanical, electrical, and hydraulic assemblies. Retracting and extending on every flight, the range of motion for these assemblies presents unique design challenges that are complicated, additionally, by the punishment that landing gear endures.

In preparation for the test flight of the new Superjet 100 regional aircraft, Messier-Dowty Toronto validated the performance of the main landing gear with both digital and physical mock-ups. To make the 16ft-high physical mock-up, Messier-Dowty turned to RedEye for its large part prototyping service.

The Solution
Marianna Lakerdas, senior designer for systems installation, states, "We know from past experience that a full-size, physical mock-up with all the dressings is an invaluable tool. The mock-ups let us see exactly what the hoses and harnesses will do."

Mock-ups also help the engineering team confirm clearances between mechanical and electrical components.

Chris Brookfield, principal designer, explains, "Seeing actual, full-scale parts puts everything in perspective."

Lakerdas agrees, "People want to see it, feel it, and touch it. You cannot do that with a digital mock-up."

Historically, machining of Messier-Dowty's mock-ups was from wood. However, the company discovered the advantages of rapid prototyping through an earlier project with RedEye. With this past success, it decided to use RedEye for the Superjet 100, which quickly delivered precise prototypes with more detail than the machining alternative.

The 16ft tall landing gear mock-up included components measuring up to 18” x 24” x 75” (keyboard on lower left corner illustrates scale).

Brookfield contracted the rapid prototyping services from RedEye. In less than one month, Messier-Dowty received 29 landing gear components, with the largest measuring 18" x 24" x 75".

"If we would have had these machined, it would have taken two to three times longer, even though design details would have been eliminated to expedite delivery and keep costs down," Brookfield says. "RedEye actually delivered all of the landing gear components, with every design detail, faster than we could use them."

Jeff Hanson, business development manager, RedEye, notes that the four-week delivery spanned both the Christmas and New Year holidays. He explains, "Because of the size of the components, most had to be sectioned, and our model shop had to join them. In all, we processed 58 individual pieces to make the 29-component landing gear. In spite of the holidays and all of the part assembly required, we delivered a very accurate prototype of the landing gear on Messier-Dowty's tight schedule."

To start the project, Brookfield simply uploaded STL files to RedEye. "In a matter of minutes, our active involvement in the project was complete. Instead of spending time detailing CAD data and making engineering drawings, our design engineers were working on other important tasks." Brookfield says. “To be able to just hand over files and have RedEye replicate exact duplicates is phenomenal."

According to Hanson, "For the mock-up, we used polycarbonate, because of its strength and durability. This ensured that Messier-Dowty would have a functional mock-up for the duration of the design review."

Following assembly, Messier-Dowty used the mock-up for review and analysis of dynamic motion, fit, ease of assembly and servicing, and test rig design. Photo courtesy of Messier-Dowty

Delivered just four weeks after transmitting files, Messier-Dowty assembled the main gear and started its review. Prior to receipt of the dressings, the design team performed clearance, retraction, and serviceability checks.

For these applications, "Nothing beats seeing actual parts, in full scale, right in front of you,” Lakerdas comments, noting that in one instance they found a 0.20" clearance between a bracket and the belly fairing. "We were surprised by how tight the clearance was. We went back into our CAD system and confirmed that the gap, as designed, was that small. Zoomed in on the part in CAD, the clearance appears much bigger. While the gap is acceptable, seeing it on the full-scale model gave us a real sense of how tight the fit really is."

She also notes that the accuracy of the parts was 0.010". “The full scale model is very accurate. We are very happy with it," Lakerdas states.

The limitations of digital mock-ups also affect design decisions that can cause difficulties with assembly and maintenance.

“There is nothing better than getting designers in front of the mock-up to see how the design impacts assembly and servicing. It helps them grasp how difficult it will be to get a cotter pin or bolt onto the subassembly," Brookfield explains. "It is also a great tool for junior designers. The physical mock-up gives them a much better, practical sense of how to design landing gear components.”

Beyond Design
Full-scale main gears, both mock-ups and production units, are in high demand.

"Everyone is vying to get their own gears," Lakerdas says.

However, they will have to wait for production units because Messier-Dowty has other plans for its full-scale mock-up.

"We sent the mock-up to the Paris International Airshow and MAKS, the Russian airshow, to demonstrate why Messier-Dowty is the world leader in landing gear systems," Lakerdas continues. "We needed a robust mock-up, and that is why we turned to RedEye. Having a good looking mock-up that will be the showpiece is really a bonus."

Brookfield states, "The cost of a full-scale, 16ft tall mock-up is pretty expensive. But if you look long term at what it saves down the road, there is a huge benefit."

Although the cost of the mock-up was comparable to a machined, wood model, Brookfield notes that the actual expense was much less.

“With machining, we spent a lot of time creating drawings, discussing project and part details, reviewing suggested changes and fielding questions. Working with RedEye eliminates all of that. Taking all of that labor out of the project saved us money and made us more productive. Considering all of the other advantages of RedEye's large prototyping service, we will continue to use them wherever possible,” Brookfield concludes.

 

Red Eye On Demand
Eden Prairie, MN
www.redeyeondemand.com

Messier-Dowty Toronto
Toronto, Ontario, Canada
www.safranmbd.com