BIZJETS BY COMPUTER

Automation in aircraft design

Along with CATIA, PLM—Product Lifecycle Management—worked well on Dassault's 7X and now the new Falcon 5X has also been designed with this state-of-the-art computer tool.

By Mike Venables
Principal, TriLink Technologies Group


CATIA facilitates the complex process of optimizing high Mach number advanced aircraft design. This equipment is used at the Virtual Reality Center, Saint-Cloud, France.

There is a story that I believe to be true. When the legendary P-51 Mustang was being developed at North American Aviation, the machinists building the prototype made 2 of every part.

One went to the prototype aircraft being assembled and the other went to the drawing office so that drawings could be prepared. The machinists designed the aircraft in their heads! The process, from contract award to rollout, took 102 days. This was obviously an expediency required during wartime. In peacetime the process takes a little longer.

In the mid-1970s I joined Canadair to work on their new business jet, called the CL600 LearStar. Once Canadair and Bill Lear parted, the aircraft was renamed the Challenger and the company was later sold by its then owner, the Canadian government, to Bombardier, becoming the core of Bombardier Aerospace. It was very satisfying to be part of the birth of an aircraft that has spanned nearly 40 years and spawned many variants.

Canadair has a long record of aviation firsts. The CL44D (1959), based on the Bristol Britannia, was the first design that allowed large cargo access by swinging the entire rear fuselage. CL89 was the first surveillance drone to be put into service in the 1960s, long before the acronym UAV was coined. CL84 (1965) was the first VTOL aircraft that rotated the wings to achieve vertical liftoff (tiltwing), the concept used for the V22 Osprey. CL215 (1967) was the first purposed-designed water bomber.

Before CAD, aircraft design was a process of trial and error

I recall the main design office with rows and rows of engineers, each with a drafting board. The office was so large it was nicknamed "Steinberg's" after a prominent Quebec grocery store chain. The separate lofting room had drafting tables nearly as long as the aircraft so that the wing and fuselage profiles could be hand-drawn using "splines" to create the elegant and flowing curves.

People were starting to talk about "CAD," or Computer Aided Design and there was a small office with a few people experimenting with the technology, working on smaller parts such as flap tracks. But for the most part, everything was drawn manually and then many mockups were built using wood and foam parts made from these early drawings.

These mockups concentrated on different parts of the aircraft. There was one for the cockpit, another for the aft equipment bay, still another for the engine mount and nacelle, etc.

Based on the results of the fit checks, the drawings were refined and more representative parts were assembled into a full-size, skeletal mockup, or "iron bird," for systems checks. The iron bird allowed, among other things, a full test of the complete electrical, hydraulic and flight control systems.

Here we see PLM (Product Lifecycle Management) simulation of Falcon 5X manual assembly process done to ensure accessibility. Dassault Falcon 5X has been developed with strong use of PLM.

Finally several prototype aircraft were built to complete the flight test program. Of course changes were made and the tooling that was used for the prototypes had to be modified for production. This trial and error process at the hardware phase was costly and time consuming. But it was the standard of the day before computers and software modeling became possible.

As an example of the difficulties, the flight sciences group had to calculate the movement of the center of gravity as the fuel was burned off. This was a frustrating exercise because, as the fuel is burned, the CG shifts and as the CG shifts the angle of attack changes and the remaining fuel shifts in the tanks, shifting the CG, causing the angle of attack to change, which causes the fuel to shift in the tanks, and so on, ad nauseum.

This tedious task was further complicated because the Challenger, like its contemporary, the Dassault Falcon 50, was one of the first civilian aircraft to use a supercritical wing to at least improve transonic performance where regions of the wing are actually supersonic. Most wings of the day were relatively flat on the bottom and curved on the top.

Supercritical wings are the opposite. As the fuel tank bottom followed the lower curve of the wing, it was extremely difficult to accurately predict the CG with less than full tanks. In the intervening years, computers first aided the design and manufacturing tasks and now these functions are completed solely by computer. The rows of drafting boards have been replaced by pods of 3 or 4 designers, each with a high performance computer.

Dassault's CATIA software is a crucial tool for modern design and PLM process

The CATIA digital mockup supports activities far removed from just design including creating virtual mockups and images for marketing and sales purposes.

Groupe Industriel Marcel Dassault, known as the "Dassault Group," has a number of companies in its portfolio, including Dassault Aviation and Dassault Systèmes.

Dassault Systèmes is the developer of a suite of software tools called "Computer Aided 3-dimensional Interactive Application" or CATIA.

Originally designed for the aerospace and defense industry, the suite is now in use in a wide variety of industries, including architectural, consumer goods, energy, life and marine sciences—to name but a few.

Used by all major aerospace companies, CATIA is the enabling technology for a design, manufacturing and support philosophy called "Product Lifecycle Management," or PLM. PLM was first used on the Dassault 7X program but is now being used more extensively on all civilian and military programs at Dassault, including the recently announced 5X program.

First application of the PLM process on the 7X was a resounding success. It shortened the development time and reduced the technical and schedule risk on the path to certification. As a result the 5X program will fully embrace PLM. And the finished aircraft will have better performance and efficiency while being easier to maintain than would be possible with earlier, non-automated, design and manufacturing techniques.

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