When a strong wind blows across an airfield tarmac, a small block of wood or plastic is the only barrier preventing a multimillion dollar aircraft parked outside from rolling away. Unless the block fails.

To greatly reduce the risk of potential damage to aircraft from wheel chock failure, the Air Force has begun using a new polyurethane chock designed and developed by the University of Dayton Research Institute to secure the tires of all fighter aircraft between flights. 

"We developed four different sizes of chocks, two for fighter aircraft and two larger sizes for cargo and transport aircraft, and the two fighter chocks have been added to the Department of Defense Logistics Agency supply system," said Eric Troidl, a senior product support mechanical engineer. "That's exciting because all new orders for fighter wheel chocks from now on will be for the chocks we designed, so as old chocks are replaced with new over time, ultimately every U.S. Air Force fighter aircraft will be touching UDRI wheel chocks," Troidl said, adding that there is a high likelihood that foreign military partners will adopt the chocks as well.

The two larger chocks for cargo and transport aircraft are in the approval process, Troidl said. 

Wheel chocks work by being snugged up against tires to prevent them — and the aircraft — from moving. Legacy chocks made of wood sometimes fail for a variety of reasons, Troidl said. "Wood by nature can vary in weight and density, so some may float away in a strong rain; others may get waterlogged and become very heavy or get stuck under a tire. Wood can easily warp or splinter off pieces that could be sucked into the aircraft engine on start up."

Plastic chocks, which have been used with some Air Force aircraft for about two decades, can also be problematic, Troidl said. "Plastic chocks sometimes crush under the weight of the aircraft and they have little traction, so they can slide easily on most surfaces or float away in a heavy rain.

"If a chock securing an aircraft shifts and allows a tire to start rolling, it can roll over the chock and then the aircraft is loose to keep rolling."

The new wheel chocks designed by UDRI have a unique honeycomb design on the bottom, which allows the chocks to be a lighter weight while also being more rugged and crush-resistant, maintaining strength and durability over time. The design restricts slippage on low-friction surfaces and prevents the chocks from floating away in a hard rain, Troidl said.

"Our extensive testing shows these chocks will have a lifespan of at least 10 years, which means an estimated savings to the Air Force of $6.8 million in that time period vs. having to replace wood or plastic chocks every six months to two years."

Troidl said the program team looked at a number of existing domestic and foreign commercial and military chocks, then designed, created and tested several iterations designed to provide a much improved part. "We put a lot of thought and creative engineering into this critical safety component to ensure it would keep the aircraft in place. Because the last thing anyone wants to worry about is chock failure and a loose aircraft when a big storm comes through."

The wheel chock program was performed by UDRI's Aerospace Product Support Engineering group under contract to the Air Force Life Cycle Management Center's Support Equipment and Vehicles division. Troidl said researchers with expertise in various disciplines from six additional groups across the Institute provided critical support to the program in the form of Impact, slippage and  fluid-contamination testing, temperature cycling, UV testing and more.

"This program is a great example of the power of collaboration across our Institute leading to an outstanding outcome for our customers."

For more information or interviews, contact Pamela Gregg,University of Dayton Research Institute senior communications manager, at 937-229-3268 or Pamela.Gregg@udri.udayton.edu.