An Airbus 340 dumps fuel over Nova Scotia in 2008. Credit: Bobmil42 via Wikipedia Commons
In 1978, a perilous drama played out 2,700 feet above the Hauraki Gulf on New Zealand’s north island, after the Royal Australian Air Force crew of a General Dynamics F-111C bomber got a warning of overheating in the nose wheel well. The pilots opened the landing gear doors to cool the well, and dumped fuel to prepare for an emergency landing.
However, some of the fuel streaming from the jettison nozzle behind the aircraft’s twin engine exhausts was actually flowing forward beneath the fuselage, igniting an explosive fire in the hot wheel well. The crew ejected in the F-111C’s twin-pilot escape pod and was rescued safely.
That “extraordinary” experience, says Richard de Crespigny, an RAAF pilot at the time and later an airline pilot and captain with Qantas in Sydney, was “a great example of the risks of forward airflow during jettison.”
Boeing thinks a simple technology fix could alleviate those risks and described the method in question in a patent granted in August.
Today’s fuel jettison systems tend to comprise a cylindrical tube on a wing’s trailing edge, which might not always discharge the fuel at a fast enough rate, Boeing notes in U.S. patent 12,391,398. As a result, turbulent airflow emanating from the closely spaced control surfaces on the trailing edge — flaps and ailerons — may cause some of the ejected fuel to circulate locally and stick to the wing. And, as the F-111C crew found, “having fuel adhere to aerodynamic surfaces of the aircraft creates undesirable risks,” the patent reads.
What is needed, say authors Sarah Barrett, Patrick Tang and Jonathan Lipstate — all aircraft structures engineers at Boeing’s Everett, Washington, facility — is a design that ejects fuel much faster so that it does not get the chance to stick to flight surfaces.
In their patent, the trio describe how it could be done: First, fuel is channeled to a pump that employs the “venturi” effect — accelerating flow via constriction, akin to squeezing a garden hose to spray water faster. A motor pushes the venturi pump out of the wing shroud it is stowed in to a deployed position aft of the wing. At this point, air inlets in the pump ahead of the venturi are exposed to the powerful exterior airflow of flight, and this incoming air is used to drive fuel through the pump at ultra-fast speeds.
The result? “The fuel jettison system passively causes acceleration of the fuel via the venturi effect and the discharged fuel does not adhere to flight surfaces,” the patent reads.
Boeing declined to comment when asked about its plans for the technology, but the company’s interest appears to be high, as it moved to protect disclosure of the idea until just before the patent was approved. The U.S. Patent and Trademark Office didn’t publish Boeing’s application, received Feb. 5, 2024, until Aug. 7 — 12 days before the patent was granted.
