April 2020 News Letter
No April 5 Meeting Minutes
News Letter Agenda: Safety, RC Truck/Car track design proposals, Hanger Queens, Non flying activities.
Safety 4-2020
Every so often you hear a story about somebody who had a battery that was just sitting on the shelf, completely normal and then without any warning, starts on fire. How does that happen? The truth is that healthy lithium batteries will almost never spontaneously lite on fire with no warning. They were actually giving warning signs that they were not safe to use, usually for more than a little while. It may be either the person just didn't know how to interpret the signs or just ignored them. “I say screw it. It cost me forty bucks and I'm not throwing it out. I’ll just charge it up. It'll be okay, or I hope so.”Today we are going to look at the warning signs that your batteries may not be safe to use and probably should be retired.
The first sign that your battery is not safe to use is, if when you plug it into a cell checker and any of the cells are below 3.0 volts per cell. It's time to retire it now. There's no question that discharging a lipo cell below 3.0 volts damages the cell.
You may understand that a cell can be “jump” started by flashing it with a momentary hit from a charged battery. I don't think you should do that. Number one, because any time a cell has been damaged, the risk of it then spontaneously lighting on fire does go up and you can't really justify that risk. Number two, Internal resistance also goes up and even if it does seem to hold voltage overnight and seems okay, it's not going to fly as well as it would by uncompromised standards. If the cell goes below 3.0 volts per cell, think about retiring the battery. It may partially recover, but is the liability worth the extra usage you may get? Understand that when checking cells after a flight, that a battery will recover to some degree with a little time. Because of this, it will not reflect the actual lowest voltage point experienced in flight. Cell balance is important and can tell you if any problems lay ahead. Checking the cells before and after a flight is a good way to monitor the health of your lipo battery. A well-balanced battery will be right on the money or as little as .01 volts difference. A couple of tenths of a volt will be managed buy a good charger and should bring the cells back into balance. If not, you should consider the battery suspect and may need replacing.3.8 volts per cell is a good storage value for the lipo battery. Typically, the full voltage per cell of a Lipo is 4.2 volts. The maximum discharged voltage is 3.0 volts. Lipo cells are happiest and will last the longest at their storage voltage of 3.8 volts. These lipo cells are very reactive when they are fully charger or discharged. The Lipo is likes the storage voltage of 3.8 volts per cell and will last the longest when stored at that voltage.The next question is how do I make the lipo battery safe for the landfill?The answer is simple. Completely discharge the unit. This process will require monitoring or placed out on the driveway while the discharge takes place. Do not short circuit but place a load on the battery. A 12-volt light bulb (for a 3s battery) should do just fine. There is another method that will also discharge and make safe. That is submerging the battery in salt water for at least 24 hours. At completion you will see a green haze in the water and a few clumps of reacted acid. All then is safe to enter the land fill. The water is safe to pore out on the ground. Remember lipo batteries are a high-performance battery and need certain care and handling. Store these batteries in a fire safe containment. A vented ammo can is a good choice for this. Safety is no accident. Think about what you are involved in and perform the task safely.
RC Truck/Car track design proposals
We currently have an area cleared for fee lance driving with approximately 150x 100-foot space. This will accommodate a large oval track or a multi-turn SCCA type track. Currently the track design theme is “custom”. No permanent layout, changeable to accommodate an event. Be it oval, multi-turns with jumps or drag racing, the idea is having a universal location for popular events.
Hanger Queens
Most of us have at least one favorite flying model that rarely is taken out to fly. Be it, those too nice to chance on crashing, or those that are a handful. If you would like to share, send me a jpeg and a short story.
This is one of mine. A Topflight P-51 60 size ARF, with a DLE 20 gas engine. This airplane fly’s beautifully, however the model is no longer in production. The carb needs cleaning after long term storage but it has no issues.
Non flying activities
Sitting at home until we are no longer on home confinement can present an opportunity to expand or begin our carving skills. Share if you dare your creation. The subject matter does not have to be aviation related. This is one that I am currently working on.
Helping my neighbors to cope with COVID-19. My carving talent put to use by creating a full-scale mountain lion that I plan on setting up in my front yard. This should help to take their mind off of COVID-19 as they jog past my front yard. The picture shown is a scaled down version.
