Bizav Still Shy about Lithium-ion Batteries

 - May 11, 2016, 11:38 AM

Despite recognized benefits, safety improvements and acceptance in other segments of aviation, lithium-ion (Li-ion) battery suppliers are having a hard time persuading business aircraft manufacturers to adopt the technology. Business aircraft OEMs either never picked Li-ion for main batteries or dropped the technology after considering it. Some OEMs prevent battery providers from disclosing their name, making it hard to determine whether any business aircraft uses Li-ion.

For the purpose of this article, AIN surveyed five battery suppliers: Concorde Battery, EaglePicher Technologies, Saft, Securaplane (a Meggitt company) and True Blue Power (a division of Mid-Continent Instruments). Only two business jet makers, Dassault and Gulfstream, answered AIN’s request for information. All the operators AIN contacted declined to comment for the article.

Other aviation segments have started moving to Li-ion. The Airbus A350 XWB, a clean-sheet composite widebody in service for 16 months, is delivered with Li-ion batteries–four of them, weighing 175 pounds less than the nickel-cadmium (NiCd) batteries they replace. (Boeing’s travails with Li-ion batteries in the 787 prompted Airbus to switch to NiCds for a time.)

Last November a Bombardier Dash 8 operated by Calgary, Alberta-based R1 Airlines started revenue service with True Blue Power TB44 Li-ion main aircraft batteries. Avmax, R1’s parent firm, and True Blue Power had received an STC from Transport Canada and are seeking FAA approval.

Bell Helicopter has chosen the True Blue Power TB17 (17 amp-hour) Li-ion engine-start battery for the 505 Jet Ranger X, slated for certification this year. The TB17 uses True Blue’s nanophosphate chemistry. Weighing less than 16 pounds, the battery is 45 percent lighter than lead-acid and NiCd alternatives and requires 60 to 90 percent less maintenance, according to its promoters. It has received FAA TSO and EASA ETSO certifications.

Applying Higher Standards

The standard for Li-ion batteries is now RTCA DO-311, which was issued after the 787 had been certified.

“One of the most demanding tests, for any kind of battery, is a forced overcharge,” Brett Williams, True Blue Power’s director of engineering, told AIN. Under DO-311, one version of this test begins with all protective circuits disabled. The battery is then overcharged–going to 42V from 28V–Williams explained. High current is then sent into the battery. “We have to demonstrate there is no adverse consequence such as external overheating, leaking of hazardous material or any breach of the battery case,” Williams said. If flames result, they have to be contained.

By selecting less volatile cell chemistries and employing appropriate protections, the manufacturer can design a relatively light container, Williams said. It may be lighter, at least, than the one that mitigated the problem on the 787 (and largely contributed to the 185 pounds of weight gain).

Safety–or the perception of safety–remains a major concern for aircraft designers faced with deciding whether or not to adopt Li-ion. Yet, “technologically speaking, we are beyond that point; key chemistries can be made safe at the system level,” Mike Boost, a Li-ion battery expert with Securaplane, told AIN. The only potential problem remaining is logistics, he believes, since shipping Li-ion batteries in the cargo hold is subject to stringent rules. In fact, ICAO has banned the shipment of lithium-ion batteries as cargo on passenger aircraft.

EaglePicher’s general manager for aerospace, Ron Nowlin, expressed confidence that the industry is allaying those safety worries. “Safety for Li-ion batteries is still a concern; however, proper design and testing can alleviate those concerns,” he said.

The battery Saft has developed for the A350 is the first Li-ion battery to comply with design assurance level (DAL) A, which equates to a failure rate of one per billion hours. “This is the highest achievable DAL on an aircraft,” Jean-Marc Thévenoud, Saft’s aviation marketing manager, told AIN.

Certification standards are to be further improved. The RTCA SC-225 committee is working on a DO-311 update, said Dave Vutetakis, Concorde Battery’s v-p for advanced technology. DO-311A “will include a lot of testing protocols inspired by the NTSB 787 incident report,” he said.

Energy Density

Li-ion technology remains unrivaled when it comes to energy density. A cell can be 70 percent lighter than a lead-acid or NiCd cell, according to True Blue’s Williams, and “by the time we integrate this into an aircraft, with accompanying electronics, container and so on, we can achieve a weight saving of 50 percent or more,” he went on.

Securaplane’s Boost agreed. Should a large bizjet embark with 220 pounds of conventional batteries, switching to Li-ion could slash that number to 120 pounds, he suggested. Power density is better, too, Boost said; for a given volume, peak power will be greater.

Li-ion batteries have a battery management system (BMS) that protects against unsafe conditions, such as overvoltage, undervoltage and overcurrent, EaglePicher’s Nowlin noted. The BMS can also send real-time data to the cockpit to provide charge information and health monitoring. The charger can be built in.

A Li-ion battery does not suffer from any memory effect, and it needs much less maintenance. A conventional (lead-acid or NiCd) battery has to be taken out periodically to measure capacity, Boost said. This can be done on wing with some Li-ion battery designs.

Saft’s Thévenoud referred to “a single check every two years.” However, Li-ion cells may have to be replaced–inside the battery unit–every four years, Boost said.

The Li-ion battery is also more environmentally friendly than traditional batteries, Williams asserted. They contain no toxic heavy metal such as lead or cadmium. “Li-ion cells are safe enough to be recycled or allowed into most municipal landfills,” Williams said.

All these benefits and what arguably can be seen as a worry-free level of safety should be enough for business jet manufacturers to move to Li-ion. The need may soon become pressing. “We have found that the addition of electronic aircraft systems and electric backup actuation has driven up the amount of power needed in power-up and emergency conditions,” a Gulfstream spokesman told AIN. This has raised the number of batteries installed on Gulfstreams over the past 20 years. “We see these trends continuing in the future as emergency loads become larger,” the spokesman said.

In addition, customer demand for larger displays and more power sockets in the cabin continues unabated. Li-ion batteries could prove an attractive method to avoid a significant increase in battery weight to support those systems.

So Much for Lithium

Li-ion batteries are already on board business aircraft for back-up purposes, but they have small capacities. No airframer or battery supplier could or would name a business aircraft with Li-ion main ship batteries. In fact, in several programs the technology was selected but later dropped in favor of an older one. The Cessna Citation CJ4 initially shipped with new lithium-ion batteries. They were developed in house, met DO-311 requirements and received FAA certification. But in 2011 a ground-power charging unit caused a fire in the main battery of a CJ4, prompting an airworthiness directive that mandated replacement with NiCd or lead-acid batteries. The FAA discovered that the fire was caused by a mechanic’s intentionally bypassing the safety systems built into the battery.

Gulfstream had been planning to use Li-ion main ship Securaplane batteries in the G650, for a weight saving equivalent to one passenger. However, the OEM elected not to use those batteries after the Boeing 787’s problems. Securaplane’s Boost told AIN, “The time frame for battery certification was not compatible with the aircraft certification schedule.” Therefore, Securaplane provides conventional batteries for the G650. The larger batteries are NiCd and the emergency batteries are lead-acid.

Embraer’s Legacy 450/500 was to be equipped with Securaplane Li-ion emergency batteries. However, Securaplane said in April that none of its System Lithium products is in service on a business aircraft. Embraer did not answer AIN’s requests.

Late in 2012, EaglePicher was planning to have its first Li-ion battery certified on a very light jet in the first quarter of 2013. The hope apparently never materialized. Last March, Nowlin reported, “EaglePicher has two Li-ion main ship batteries that are currently being certified for commercial passenger aircraft.”

Manufacturers Speak Out

Although Li-ion technology and approval rules have evolved since Gulfstream elected not to install the batteries, company engineers are unlikely to change their mind in the foreseeable future. “We continue to monitor the technology but are not interested in developing and maturing these components,” a spokesman told AIN. “We have conducted significant work evaluating Li-ion and Li-ion polymer batteries. The obvious pro is the potential weight reduction; the cons are increased complexity, cost and risk during development.”

For the in-development G500 and G600, Gulfstream has kept the same battery configuration as on the G650. The larger batteries are NiCd and the emergency batteries are lead-acid. Both are “known, mature technologies that are low-cost and reliable.” With Li-ion, the complexity of the hardware and software “results in extra certification costs and could impact the reliability of the system,” Gulfstream engineers believe.

Dassault’s designers, too, believe Li-ion has not earned its way into their aircraft. Falcons use lead-acid and NiCd batteries. The suppliers are Concorde and Saft, respectively. For the two in-development types, the Falcon 8X and the Falcon 5X, the company has chosen lead-acid, François Paté, chief of the vehicle system design department, told AIN. In addition to a price that appeals to the airframer, customers have expressed satisfaction with lead-acid’s ease of maintenance and replacability.

However, Dassault has recently requested information from several Li-ion battery suppliers to assess the state of the technology and its economics. Paté believes Li-ion has now reached an acceptable level of maturity. The available chemistries are more stable, and the sophistication and stringency of the regulations have grown.

Keeping Faith

Li-ion battery suppliers are keeping faith. Securaplane is expecting “much deeper interest” from business aviation within two years. System Lithium batteries are in the process of being qualified on a military aircraft and in “other segments.” Two certifications are expected next year that should influence business aviation, he added.

True Blue Power has been working with almost every airplane and rotorcraft manufacturer and has seen “a lot of interest,” according to Williams.

Saft hopes to build on the momentum launched with the A350. “With the use of Li-ion batteries for commercial aircraft, in the coming years we will see more interest from business jet OEMs for their next-generation aircraft,” Thévenoud predicts.

Concorde is a supplier and strong promoter of lead-acid batteries. Asked about the future of Li-ion, Vutetakis first expressed wariness, saying the technology is “susceptible to undetectable failures that can cause unsafe conditions,” but then said the company has conducted extensive research and development activity in Li-ion. “Will Li-ion catch on as mainstream? If so, we will be one of the players,” Vutetakis said.

Retrofitting to Lithium?

Could Li-ion retrofits be easy? Securaplane’s Mike Boost believes so: “Our System Lithium could be a great drop-in replacement for lead-acid or NiCd batteries.” But François Paté, chief of Dassault’s vehicle system design department, does not share this view, noting that a Li-ion battery has to exchange a lot of information with the cockpit and needs much more integration than a lead-acid battery.

Nevertheless, True Blue is pursuing STCs for the Pilatus PC-12 and Cessna 208/208B Caravan, as well as the DHC-6 Twin Otter. In the rotorcraft segment, it is seeking STCs for the Robinson R44 and Airbus Helicopters AS350 AStar. The firm already holds Transport Canada STCs for the Bombardier Dash-8 and the Beech Bonanza A36.

What if a passenger’s smartphone overheats?

Cabin crewmembers are now trained to deal with thermal runaway on a passenger personal electronic device. They must not cover it with a blanket. Rather, they should drop it into the ice cube compartment of the galley, a Dassault pilot advised.

Does more-electric mean more batteries?

At the aircraft architecture level, hydraulic and pneumatic systems are increasingly being replaced with electric ones. The concept is called “the more-electric aircraft” and is expected to save fuel. François Paté, chief of Dassault’s vehicle system design department, believes going more electric will not require larger-capacity batteries. A battery works only in transient regimes, he pointed out. The rest of the time, the aircraft draws its power from generators driven by the engines, APU or ram air turbine.