An idea out of the woodwork

Engineers use hobbies to design new type of aircraft window joint

Kevin Chapla woodworking banner

Kevin Chapla, a Raytheon Intelligence & Space principal mechanical engineer, with more than a decade of experience in woodworking, works on building furniture. Chapla used his hobby to help solve an engineering problem for a customer.

Engineers at Raytheon Intelligence & Space solve customers’ problems all the time. But they don’t often do it by dipping into their knowledge of woodworking and cycling.

The problem: Critical sensors on a next-generation aircraft were being blocked, and the culprits were the bulky window mullion joints in between the panes of glass. The sensors’ performance was suffering.

“We had to go back and look at other ways to mount the aircraft windows differently,” said Catherine Trent, an engineering fellow at RI&S’ Advanced Concepts & Technology, an arm of the business that researches and investigates next-generation warfare technologies.

So Trent, a veteran triathlete, teamed with co-worker Kevin Chapla, a mechanical engineer and woodworker, to brainstorm. The engineering duo had two goals: improve sensor performance and ensure the windows are easy to maintain.

“I knew of joinery techniques that are common in the fine woodworking world and thought it could be a creative means of tackling this problem,” said Chapla. “We wanted to essentially minimize the distance between two panes and maintain the strength of the interface. We couldn’t allow for structure to interfere with the sensor’s performance capabilities, and yet the design needed to both be producible and maintainable at the same time.”

On the aircraft, the sensor sits behind panes of glass that are typically assembled to multifaceted frameworks. Those frameworks often have relatively large separations in order to balance the sensor performance behind the windows and the structural integrity. Then engineers bond the complex assembly of window panes with aerospace-grade adhesives between thick mullions, which ultimately reduced sensor performance.

The engineers discovered a thinner, flexible mullion that interlocked two window panes without compromising the mullion stiffness needed to provide structural support. In addition, the innovation allows for the windows to be easily replaced or swapped out, dramatically easing window maintenance.

Windows for next-generation aircraft are costly and extremely heavy, but also brittle. They can shatter under small amounts of stress or movement.

“So we had to keep the windows under manageable amounts of stress or strain while allowing for movement between the individual windows,” said Trent. “So that’s where the real innovation came from — how do you hold the two windows — allowing the flexure of the individual windows while still meeting the needs of the sensor.”

The delicate balancing act drew experience from their hobbies.

Catherine Trent trains for a triathlon.
Catherine Trent, an RI&S engineering fellow, trains for a triathlon. Trent and a coworker, who has experience as a woodworker, used their hobbies to help solve an engineering problem for a customer.

Trent thought about the articulation of the front wheel bicycle fork within the frame. It serves two purposes: enables the bicycle to turn left or right and prevents road vibrations from flowing into the bicycle frame.

“Think about the ability of a bicycle to allow two aspects of the bicycle to articulate in different directions with different loads and stresses on each part,” said Trent. “The two parts perform different functions while working together as an assembly.”

“With the limited space we had to join two flat window frames to one another,” said Chapla. “It’s not all that different from the way one would attach two sides of a drawer for a cabinet.”

The flexible mullion solution that they engineered ensures stress on one window does not affect the opposite window.

“In addition, there are many applications for the flexible mullion,” explained Chapla. “We developed it with open systems architecture standards in mind so that the customer can plug and play a variety of sensors on other planes.”

Published On: 02/16/2021