Model the Complexity

Why wheels are important on planes

Simcenter enables Safran Landing Systems to avoid technical issues and streamline certification

By Jenn Schlegel

The Wright brothers didn’t have wheels on their first plane. So why do we? Here’s some food for thought: early aviation pioneers Wilbur and Orville Wright did not put wheels on their first plane, the 1903 Wright Flyer. The famous 12-second flight that took off on December 17th, 1903 from the beach in Kitty Hawk, North Carolina started by launching the flyer into the air using a rail system. The self-taught engineers didn’t use wheels or landing gear because, logically, they were taking off and landing in deep sand. Wheels would be problematic, to say the least.

Constructed with spruce wooden frames, unbleached muslin fabric and honestly heaps of tenacity, sheer grit and dreams, the first Wright brothers’ planes were all about getting off the ground and into “piloted” flight. Wheels were either for catapulting the early flyers into the air or for moving the Wright Flyers around on the ground. Only in around 1910 did the Wright brothers’ planes, the Military Flyer and the Model AB, feature wheels.

But back to wheels and that 1903 flyer. The 1903 Wright Flyer’s wheels were actually attached to the rail system itself. The wheels, which the brothers constructed from recuperated bicycle hubs, were part of the dolly on the launch rail track, not the airplane. The wheels ran on a rail, in reality, an 18-meter wooden track running through the sand that launched the Wright Flyers into “flight”. A later model, the 1906 Wright Flyer, had wheels as well, but they were removable and only used to roll the aircraft from one spot to the other. They were removed before taking off on the track.

Landing gear: a long way since Kitty Hawk Almost 120 years later, we have come a long way since removable landing gear and catapulting flight tracks. Think about this: At Kitty Hawk, the first Wright Flyer weighed only 275 kilograms without the pilot, who by the way, flew in a prone position. Today, a big bird like a fully loaded Airbus A380 weighs in around a whopping 575,000 kilograms. Just think of the loads the landing gear needs to handle when landing something this immense. (And just a side note: the A380 usually has four pilots on board for long flights. Two pilots are required by regulators to fly the plane. Unlike, the Wright brothers, they fly the plane seated, obviously.)

The landing gear on an A380 or similar aircraft – as you can guess – is far from recuperated bicycle hubs and home-made rail systems. A sophisticated hydraulic ecosystem in itself, modern-day landing gear systems features innovations the Wright brothers could barely imagine: decentralized hydraulic generation; integrated modular avionics braking algorithms; high-pressure hydraulics at 5,000 psi; titanium integration and integrated logistics support (ILS) – just to rattle off a bit of LG (landing gear) jargon.

With something as complex and mission-critical as landing gear at stake, entire engineering departments (and companies for that matter) are dedicated to perfecting landing gear design and development. And passionate and innovative engineers (just like the Wright brothers) have dedicated their engineering careers to designing reliable, robust, weight-efficient and environmentally responsible landing gears.

One of those engineers is Jérome Fraval, a French systems modeling and simulation method leader at Safran Landing Systems. For those of you not familiar with landing gear engineering per se, Safran is the world leader in design, development, manufacturing and support of landing gear systems.

Jérome Fraval has been a Simcenter user for years and is one of the pioneers in the field of system simulation and landing gear development. Today, he and his team help Safran provide highly sophisticated landing gear systems to a variety of aircraft programs.

Landing gear is certainly not one-size-fits-all One of the Safran team’s biggest challenges is that requirements vary among customers. And analyzing every single system performance is crucial to perfectly meet the differing expectations of each airframe manufacturer. Safran Landing Systems use two approaches to succeed, in most cases, under tight deadlines. One key to success is the use of simulation and digital twins within the engineering department to virtually anticipate system and component efficiency – long before integration into the final product. The second key to success is to implement standard engineering methodologies and streamline practices to deliver a mature product early in the development cycle.

Safran Landing Systems deploy a common methodology for simulation within internal teams as well as when interacting with customers and suppliers. Very basically, the process starts with developing the landing gear structure, then the wheels and brakes and finally system equipment, such as systems for braking, extension, retraction and steering. Safran Landing Systems designs and manufactures the majority of its key equipment and integrates other small components from hydraulics/electrics component suppliers.

System simulation in model-based systems engineering Using Simcenter combined with Safran’s in-house expertise and experience, acquired over several decades, makes it possible to perform tradeoff studies very early in the pre-design phase of complete systems.

“Today the use of model-based systems engineering is essential in our industry because incomplete knowledge of all the operational cases can lead to an incorrect analysis that originally aims at specifying the component performance, “ explains Jérome Fraval, Systems Modeling and Simulation Method Leader at Safran Landing Systems.

He adds, “Virtual integration through the digital twin makes it possible to anticipate the commissioning of our products very early on, even well before the production of the first components, which makes it possible to observe sometimes complex physical phenomena and to adjust, if needed, the product design.”

System simulation supports the certification process Virtual analyses with Simcenter enable Safran Landing Systems to support the overall aircraft qualification process and streamline the demanding documentation process. “We have to demonstrate to the authorities that the system model is valid, using the landing gear digital twin,” Fraval says. “This is demonstrated through physical correlation with the model that it is valid. The use of Simcenter allows us to support this entire demonstration procedure and complete documentation requirements." Read more about Safran Landing Systems and the Airbus A380.

Wilbur Wright landing an early prototype in 1900. Clearly, landing gear hadn’t been invented yet. Image courtesy of the Library of Congress (USA)

And from the research side of things… What is wonderful about Siemens and Simcenter is that for every innovative engineer out in the field, like Jérome Fraval at Safran Landing Systems, there is most likely someone in-house working the research side of things. Senior R&D Manager Yves Lemmens, based at Siemens in Leuven, Belgium, is one of these engineers. Yves Lemmens’ research activities focus on analysis methods of structures, mechanisms, and systems for automotive and aerospace applications. One area he works in is… landing gear.

Since the days of wooden frames and muslin wings are long gone in modern-day aviation, a key challenge for aerospace engineers, today, is complexity. Yves Lemmens and his team are working on methodology improvements to manage the complex engineering required to successfully develop future aircraft.

He writes in his blog, “Over the years, scientists and engineers have discovered many paths that can lead to better aircraft. However, highly interconnected system architectures increase the complexity and slow down the pace of innovation. Moreover, multiple dependencies and constraints between components (such as joints and limitations on available space) make the design of mechanical systems even more complex.”

Make sure to check out Yves Lemmens’ complete blog to explore cutting-edge work, which will certainly impact the aircraft development of the future.

And speaking of future aircraft, things are likely to get even more complex as we enter new frontiers like e-flight and VTOL (vertical take-off and landing) - not to mention supersonic aircraft. The world of landing gears will certainly change again in the not-so-far-away future; Siemens and Simcenter will be there to show the next generation of pioneers the path to safe, secure and super-efficient landing gear. 

Sand, grit and perseverance:

Hard work, testing and top-notch troubleshooting got the Wright brothers off the ground

Kitty Hawk is located on the Outer Banks of North Carolina, a series of barrier islands in the Atlantic Ocean. It is the 6th windiest place in the USA. A likely location for the Wright brothers and their first successful airplane flights on December 17, 1903. But what one tends to forget is that this first flight didn’t happen overnight. From their beach camp in Kitty Hawk and back home in Dayton, Ohio, the Wright brothers had been experimenting and adapting their flyers for more than four years

The two brothers, Wilbur and Orville Wright, were self-taught engineers and bicycle shop owners from Dayton, Ohio who were obsessed with the idea of “piloted” flight. They designed and built early prototype gliders that they attempted to fly in 1900 and 1901 in Kitty Hawk. Wilbur Wright eventually glided about 100 meters in 1901, but the brothers knew their early prototype was still unpredictable and some of the data they had gathered seemed to be invalid. Disappointed yet still full of faith, they returned home to Dayton and built a wind tunnel to obtain new data and update the flyer design.

In 1902, they returned to the Kitty Hawk camp and the 1902 Wright Flyer completed 600 glides. The brothers were convinced they had graduated from unpredictable glider to working airplane. The 1903 version would feature breakthrough innovation with a lightweight engine and original propeller design.

The 1903 Wright Flyer was heavier than expected, weighing in at 275 kilograms. This was five times heavier than the 1902 version and the brothers weren’t sure the engine would be powerful enough to lift the plane off the ground. This is when they came up with the idea of the launching rail system, which gave the plane enough momentum to take off. (Prior to this, helpers from the Kitty Hawk camp just ran carrying the wings of the much lighter gliders to launch them into the air.)

On December 17th, 1903, at precisely 10:35 am, Orville Wright lifted off from the launching rail at Kitty Hawk and flew for 12 seconds at an altitude of 8 feet, landing 120 feet away. The Wright Flyer hit a top speed of 6.8 mph with 34 mph winds. With both brothers piloting, they completed three more flights that day, reaching 852 feet in 59 seconds and a top altitude of 10 feet.

Further reading

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