OPULENCE OVERHEAD: FLORIDA COMPANY USES FEA TO MAKE SURE FANCY FLIGHT CABINS STAY INTACT

OPULENCE OVERHEAD: FLORIDA COMPANY USES FEA TO MAKE SURE FANCY FLIGHT CABINS STAY INTACT

It’s a world seldom seen by the average traveler. First class is one thing, but some people choose to fly in real style and they’ll spend tens of millions of dollars to create well-appointed accommodations on their private planes.

These VIP interiors are put together at businesses known as completion centers. It is in those centers that an unpainted and unfurnished airplane is transformed – at a cost ranging from $5 million to more than $100 million - from simple to spectacular. All manner of accouterments are added - from televisions to showers, from divans to bidets.

While the completion centers outfit the planes, companies such as Jormac Aerospace Inc. of Clearwater, Florida, provide engineering assistance. Jormac selected Algor Inc.’s finite element analysis software to analyze the stability of the VIP flight cabins.

Jormac co-founder Steve Jourdenais said he has seen some pretty lavish cabins in the five years he has been providing engineering services to completion centers. One particular head of state went so far as to hang natural crystals from the ceiling with fiber optics in each to light them.

"These planes are flying palaces," Jourdenais said. "They have to have a real clean fit and finish. They have to be perfect."

While the CEO or monarch might be more interested in how comfortably he or she eats, sleeps and lounges, someone’s got to make sure the televisions, walls and sofas stay put during flight.

Luxury aircraft, like the one pictured above, come with all manner of accouterments, including video screens and bidets. The planes, which come unpainted and unfurnished from the manufacturer, are outfitted at businesses called completion centers. Completion centers contract with third parties to perform engineering analysis to make sure the plane will remain safe through severe turbulence and emergency landings. Officials at Jormac Aerospace Inc. of Florida said they use Algor finite element analysis software to do that engineering because of Algor’s ease-of-use.

"Safety is critical," Jourdenais said. "When these guys go through severe turbulence and emergency landings, you have to give them the best chance for survival."

Considering that a luxury cabin might feature such things as ceiling-mounted video displays and 400-pound credenzas, Jourdenais said in-flight gusts are an area of great concern when Jormac engineers set about analysis. Wall partitions are another concern, according to Jourdenais, because their large surface area provides a target upon which room-to-room pressure differentials might act in the event of sudden cabin decompression.

Jormac engineer Jerry Koh explained what he looks for when he analyzes the partition installations.

"I want to determine that, under the ultimate cabin decompression, emergency landing and in-flight inertia load cases, the installation is properly constrained," Koh said. "That means that the interface loads of the installation will not overload the aircraft structures, and the partition assembly and attachment hardware are structurally adequate for the subjected loads."

Koh uses Algor software to perform linear static stress analysis and obtain interface loads and stress levels on the partition assembly. Jourdenais said Jormac chose Algor because of its ease-of-use and superior technical support.

"Overall, it’s the most user-friendly package. It has all the necessary tools needed to get the job done without having to spend all of your time learning and sorting through unnecessary bells and whistles," he said. "And customer service? If I have a problem or something is going wrong, I get help so that my problem is solved in a day."

Koh recently used Algor software to analyze partitions designed for a VIP flight cabin by Raytheon Systems Company of Waco, Texas, a major completion center charged with outfitting a business jet for a major aircraft company. He said the work is typical of that which goes into making VIP cabins safe.

Koh started the analysis by building a geometrical model for each partition assembly with Superdraw III, Algor’s precision finite element model-building tool. He meshed the geometrical model with the Surface Mesh Enhancement and Feature Line Adjustment features in Superdraw III.

Koh built virtually maintenance-free FEA models thanks to Superdraw III’s ability to mesh each element group separately along selected feature lines.

Koh used truss elements to represent the tie-rods attaching the partitions to the aircraft stringers. He used plate elements to model a partition wall-mounted TV monitor. He used sandwich elements to represent the partition panels.

To assign material properties to his elements, Koh referred to Federal Aviation Administration-approved data. He used 2024-T3511 aluminum extrusion for the truss elements, 2024-T3 aluminum plate for the plate elements and composite panels consisting of aluminum facesheets and high-density core laminae for the sandwich elements.

Because every ounce of weight is significant when multiplied by an inertia load factor (g), Koh paid special attention to the weight of the partition panels. He increased the density of the sandwich elements accordingly to include the weights of the non-structural details that he left out of the finite element model, such as decorative panels, panel trims, etc. Because those items are purely decorative their behavior was unimportant to Koh’s analysis.

Based on installation drawings, Koh set boundary conditions for each partition assembly. Typically, a partition is supported at the bottom by attachments to the seat track and floor panels, which are modeled as translation constraints on the partition panel. The top of the partition is attached to the aircraft frames and stringers with tie-rods, which are modeled with truss elements with translation constraints at the ends.

Following the floor plan of the aircraft, Koh combined the partition assembly models to form a single model partitioning different compartments of the cabin. Throughout the analysis process, Koh modified the applied loads and configuration of the models to cover all possible load scenarios. He altered the decompression pressures and load factors from model to model, as well as configuration changes due to functionality of items such as door open, door closed and interface loads from other installations.

For his analysis, Koh applied three types of loads to the partitions. The first load type was Cabin Decompression Pressure Differential, which was determined by a separate decompression analysis based on room volume and vent area. The second load type represented in-flight inertial loads.

The final load type was interface loads from other interior structures. When other interior structures – items such as cabinetry, galleys, ceiling grids - are attached to the partition, their interface loads must be included in the analysis.

Koh ran linear static stress analysis for the models of each load case and configuration. He found no excessive deflection of the partitions, which could cause damage to the aircraft structures and other interior structures or impede an emergency deplaning of passengers. He also found that stress levels on each laminate of the sandwich elements were within the allowable limit.

The above illustration shows a flight cabin partition assembly, made out of composite materials analyzed with Algor software to determine whether the partitions and the installation will withstand events such as sudden cabin decompression, emergency landings and in-flight inertial load cases. Engineers need to know whether a partition assembly is structurally adequate for the subjected loads, and whether it is properly constrained so that its interface loads will not overload the aircraft structures.

Through the interface loads output, however, Koh found that the loads applied to the floor panel attachment points were excessive during one particular load case with door open configuration. As a result the floor panels needed to be reinforced in that area.

Koh used Algor’s postprocessing capabilities to create images for a report he created with Algor’s Report Wizard. He also saved ASCII files of interface loads at specific nodes for his analysis.

Jormac has just recently purchased a laboratory testing machine that will help engineers like Koh validate their FEA. Jormac is now testing panel-to-panel joints used to fabricate cabinets and galleys and relating their behavior to Jormac’s FEA modeling techniques and assumptions.

Jormac has purchased Algor’s Mechanical Event Simulation package to help them accurately model large deflections and surface-to-surface contact in these structures. The goal is to avoid costly testing of these cabinets and galleys by demonstrating to the FAA that Jormac’s methods for modeling them are indeed validated against actual test results.

Koh said he saves time in the analysis of complicated installations by using Algor's finite element analysis software.

"Superdraw III's ability to show/hide group elements for analysis comes in handy when switching configuration between models (i.e. door opened/closed, direction of the decompression pressures etc.)," Koh said.

With the results Koh was able to identify the weak link of the installation, and have the completion center modify the installation to eliminate the problem before it ever arose.