Before the arrival of lithium-ion technology, hobbyists relied on a messy liquid fuel, or occasionally on an older generation of batteries that could barely get models off the ground. “Twenty years ago, somebody would laugh at you if you said ‘electric plane,’ ” Pitcock said.
Lithium-ion battery packs may revolutionize aviation as well, allowing for planes that are lighter and use less fuel.
The cause of the incidents with the Dreamliner battery packs remains under investigation by safety officials. The jets were ordered grounded in the United States and several other nations this week.
The batteries carried in the holds of cargo planes are suspected as possible factors in two fatal crashes in recent years, according to the Air Line Pilots Association International, which is lobbying to have cells classified as dangerous goods requiring special handling, adequate fire suppression and notification to pilots who carry them. Cargo planes sometimes carry tens of thousands of cells stacked together on pallets, increasing the danger, said Mark Rogers, director of the dangerous goods program for the pilots association.
“There’s no way to engineer your way out of the problem,” he said. “No matter what you do, you’re going to have incidents.”
Lithium-ion battery packs typically are made of a collection of individual cells. Coiled within each are three layers — one positively charged, one negatively charged and the third a “separator” film that keeps the charged layers apart. There also is an organic fluid that, at high temperatures, is flammable.
Fires start when electricity moves in an uncontrolled way between the positively and negatively charged layers. The cause can be manufacturing defects or damage — anything that allows the positive and negative layers to touch, causing a short-circuit and what experts call “thermal runaway.”
Manufacturers of lithium-ion batteries say their technology is safe when international standards are followed. Problems occur mainly with lower-quality, counterfeit batteries, or when cells are shipped improperly or mishandled by consumers, said George Kerchner, executive director of the Rechargeable Battery Association.
“When you damage these cells and you abuse them, you certainly are inviting problems,” he said.
For those who fly radio-controlled model airplanes, fires typically happen when batteries are overcharged, or when wiring mistakes cause short-circuits. And, then, of course, there are the crashes: The resulting damage can causes wires to touch, separator film to tear, or the positive and negative layers to come into direct contact with each other.
Damage can be subtle enough that an apparently undamaged battery can burst into flames long after an accident. Hobbyists say they sense danger when their battery packs get “puffy,” typically the result of gases that can be the first sign of thermal runaway.
The Rechargeable Battery Association’s Kerchner said he and his sons have long flown radio-controlled helicopters powered by lithium-ion batteries without encountering problems. “We love them,” he said, “but we don’t crash them into the ground to see if they explode.”