Start Me Up: Smart Thinking at NAVAIR
Stop us if you’ve had a laptop and heard this refrain before: your battery draws down when not being used. If it’s recharged, it may “remember” the level it was at and can’t be brought back to full capacity. The maximum level of charge also keeps dropping. This means more frequent battery replacements if you want them to be of much use. Turns out the US Navy has heard this one too, only the NiCad batteries weren’t in laptops. They were in F-5 “aggressor” aircraft at Top Gun, powering the inertial navigation system and emergency wingtip speed brakes on EA-6B Prowler electronic warfare aircraft, running fire suppression and emergency exit lighting on H-53 helicopters, and offering last-chance backup for items like aircraft flight-control computers in case the main engine-driven generator should fail.
On the H-53 heavy lift helicopters, for example, 1 in 12 NiCad batteries failed every month because of poor design. Constant charging, maintenance to remove “memory effect,” and replacement was taking a costly toll in batteries. At 37,000 hours a year for the H-53 fleet, it was also taking a heavy toll on maintenance time. Something had to be done – and NAVAIR’s Propulsion and Power Department had an idea…
In a blast from the past, they decided to go back to the same kind of lead-acid battery found in your car – with one important modern wrinkle. Valve-Regulated, Lead-Acid (VRLA) batteries are also referred to as Absorbed Glass Mat technology. Your car battery would leak corrosive fluid if turned upside down, which a plane’s electronic innards wouldn’t appreciate. The design in your car is deliberate; it’s done so that the hydrogen gas produced by the battery doesn’t build up and explode. VRLA batteries use the same chemistry, but they’re completely sealed with no vent openings, and the acid inside them is absorbed by porous fiberglass mats between the plates. If something goes wrong with hydrogen absorption and gas does build up, a valve opens to let the gas escape.
The switch has created big savings, not least because VRLA/AGM batteries are only 1/2 – 2/3 the price of the troublesome NiCads. The new VRLA batteries must still be replaced, but it happens once every 3 years as a precautionary measure, and the batteries can be run down when if an aircraft sits for a long time with a background load that keeps important codes alive in computer memory, or if an aircraft system is left on by accident. Overall, however, the cost and time savings is dramatic.
In return for $205,000 from NAVAIR and the Defense Logistics Agency to perform engineering and testing (DLA funds), and to buy the new batteries, the US Navy saves $761,000 each year in new battery costs for the H-53 fleet, and battery-related maintenance time dropped from 37,000 hours per year to 5,000. The EA-6B Prowler replacements began in June 2007, and are estimated to save $700,000 in batteries and 24,000 hours in maintenance each year. The F-5 fleet will see the smallest savings, at only $52,000 in batteries and 67 hours in maintenance savings, but all of this still adds up to about $1.5 million per year – ROI of over 700%. NAVAIR release.