File: 02gee.ht1.doc
[Headline: Hot info on battery fires]
He uses a big ceramic pot, but puts it over the pack while charging the cells. When I use a clay vessel (instead of my charging bag), I prefer placing the cells inside the pot, right side up. Which is better?
First, a disclaimer: This issue of Model Aviation might be around for a long time and available online after the paper version has turned to dust. If you’re reading an old issue, the following information might have become obsolete by recent discoveries or by people who are smarter than I.
Experts don’t agree on some aspects of LiPo handling. Several things can cause battery fires. You might see a puffed pack, with pressure inside waiting to pop out. Sometimes the entire battery pack becomes overcharged or has an electrical short, or maybe one cell has failed or is too hot. In this case, even after you extinguish the fire, the next cell can become overheated and ignite in a chain reaction.
For each fire you may see different amounts of smoke and flames, and (in addition to my screaming) you might hear a popping sound as burning material scatters. Containing this spray is why we use a pot or bag.
A fire extinguisher will fight the flames, but cooling the pack can prevent other cells from igniting. Water can cool things down, but the runoff can be a mess.
A sand bucket can be useful, but don’t bury a hot pack under sand because it can act as an insulator and make the rest of the cell overheat. Some experts say that rather than dumping the sand bucket over the burning pack, put the pack on the sand and let it safely release its energy.
There might be more than one answer for how best to use a ceramic pot for thermal protection when charging batteries.
Bill has his charging rig on a concrete floor away from everything, and the pot provides containment in the unlikely event that the pack ignites. In my opinion, he has an excellent and safe setup. I have mine upright so I can easily get water or a fire extinguisher on the problem and have the option of moving the pot (and its burning contents) if needed. Now that I think about it, moving a battery fire might not be such a hot idea after all.
Statistically, our aeromodeling LiPos are safe and reliable. Most of us will never have a battery pack ignite. We take precautions just in case. Using that clay pot or charging bag is cheap insurance!
AMA and AED
On the subject of being prepared, in a recent column I mentioned an RC club that had purchased an Automated External Defibrillator (AED) in response to a medical emergency at its field. The AMA Executive Council agreed that this was a good idea, and here is its message on the subject:
“AMA encourages AMA clubs to consider purchasing Automated External Defibrillators (AEDs) for placement at club flying sites and events, that clubs follow all applicable Federal and state AED laws, training, and certification requirements, and that they follow the AED manufacturers’ instructions for care, maintenance, service, usage, and storage. Such purchases by AMA clubs are eligible for application toward AMA Flying Site Improvement Grants. AMA encourages AMA clubs to receive certified first-aid and CPR training.”
I think that this policy could save someone’s life one day. When it happens, please contact me and I will share the story here.
Short Attention Span Modeling
Some modelers (such as I) have a tendency to lose interest in a project and put it aside for a new challenge. After we do this a few times, we end up with a bunch of half-built models stored away.
It’s not just model builders who have this weakness. I went to a terrific model and full-scale air show at the Compton, California, airport and strolled through the EAA Chapter 96 hangar. It looks like my model room, except the partially built EAA airframes are much larger. Some of the projects are moving right along, and a few others have a bit of dust on them.
I began to wonder about the safety aspect of old model airframes being finished and flown. The glue joints will not all be the same age, and exposed foam components might deteriorate. Full-scale aircraft mechanics take metal corrosion seriously, and so should we.
Have you finished an old stored model? Did you have any structural problems? Please let me know if this is an issue, and I will share the results in a future column.
Guess and Win
Howard Littman is a perfectionist who loves to tinker and tweak his model designs, trying to make each one as good as possible. His latest effort is pretty darn fine, but Howard needed all of his willpower to “freeze the design” on his new rubber-powered helicopter so I could offer the plans as a mystery airplane prize.
The SillyCopter is a new twist on a classic design. The angle of the body plates makes this little aircraft fly in a circle instead of simply hovering. Free Flight (FF) helicopters flew long before fixed-wing aircraft, and the young Wright brothers were inspired by a similar model.
Rubber-powered helis are great fun, but if you are one of those serious modelers, you can skip the funny face and draw a more stern expression on your SillyCopter.
To win these digital plans via email, send me your guess for which classic airplane is shown in the cropped photo. My email address is on the column header. You get to see the nose and the tail, which should be plenty of information.
I cut out the registration numbers because a few sharp readers were looking them up online to identify the airplane. Don’t worry, if you guess incorrectly, I’ll still email you the plans.[dingbat]
SOURCES:
Howard Littman Model Aircraft
(818) 286-2077
www.hjlmodels.com
