Safety Comes First
John Preston
Lead/acid batteries can explode. Model restraining devices. Allow models over 55 lb. in AMA events?
Exploding batteries
I'm sure most of you are aware that when jump‑starting a dead automobile battery there is a possibility of an explosion. During the last month I received a letter from Mitch Poling enclosing a safety column he wrote for Model Builder magazine. Mitch's column illustrates that the lead/acid batteries many of us use in pursuit of our hobby may present the same hazard. Excerpts from Mitch's MB column ("Electric Power", February 1987 issue) follow.
Mitch relates a very bad charging accident discussed by John Onian in the November 1986 Model Airplane News. Mel Schmidt, well known in Free Flight, was charging his starting battery (a lead/acid battery) for gas planes. While checking the charger connection he jiggled a connector, saw some sparks fly, and the next thing he knew he was in the hospital and blind in both eyes. Since then one eye recovered, but the other was damaged beyond repair by battery fragments. The lead/acid battery had exploded so violently it sounded like a bomb; only some of the plates and part of the bottom casing remained.
A lead/acid battery generates hydrogen gas when under charge. This gas is violently explosive and sparks are a no‑no. Most of the time we get away with it, but once in awhile someone draws the unlucky number.
Jumper cable procedure (from a Shell brochure)
Several years ago I recall a brochure published by Shell Oil Co. that contained safety tips for motorists. The brochure addressed the correct procedure for connecting jumper cables between a good and a dead car battery. As best I recall, the brochure advised:
- First connect the positive terminals of the two batteries with one jumper cable.
- Attach the second cable to the negative terminal of the good battery.
- Make the final connection of the negative cable to some grounded part of the car away from the dead battery — do not make this final connection to the negative pole on the dead battery. The final connection will produce a sudden flow of current that will almost inevitably result in a spark before you achieve a secure connection.
- After starting the car with the dead battery, disconnect the jumper cables in the reverse order of their connection.
Rules for using lead/acid batteries (Mitch Poling's recommendations)
Mitch writes that he uses lead/acid batteries a lot to charge Ni‑Cd packs and that he has been lucky so far. After several close calls he adopted these rules, which he recommends to others:
- Connect the lead/acid battery charger to the battery you want to charge before you plug the charger into the AC supply. If the charger is already plugged into AC when you connect the charger output to the battery, sparks will fly. When finished charging, unplug the charger from the AC supply first. Then, and only then, unplug the charged lead/acid battery from the charger. The charging operation generates a lot of hydrogen and the charged battery will probably be bubbling. Disconnecting the battery from the charger is the most dangerous step — don't unplug the charger until the AC plug is pulled.
- Never use a lead/acid battery to charge Ni‑Cds while the lead/acid battery is on an AC charger itself. It may be producing gas, and inevitably sparks will occur when charging the Ni‑Cds. Some people use the charging battery as a leveling device (using the AC charger to run the Ni‑Cd charger) to get a high‑power charge; Mitch has discontinued this practice.
- Never connect a Ni‑Cd charger to the charge battery if the Ni‑Cd pack is already plugged in. This will cause a heavy spark if the charger is not turned off. Connect the Ni‑Cd charger to the charge battery first, then plug in the Ni‑Cd pack. When the Ni‑Cd pack is charged, make sure the charger is turned off, then unplug the Ni‑Cd pack. After that you can disconnect the Ni‑Cd charger from the charge battery.
- If you are using a charger with an inverter (one that boosts voltage so more than seven cells can be charged), be very careful. An inverter draws a very high initial current, even with no Ni‑Cd pack connected, and may cause a spark. You will be safer if you set up the charger battery with a power cable and plug the booster charger into the cable so any sparks are farther from the charge battery. Use heavy‑duty wire, 14‑gauge or heavier.
- Use sealed lead/acid batteries as much as possible. They produce very little hydrogen gas. Gel cells and Gates cells (made by GE) are of this type.
Ni‑Cd packs and fuses
While writing his Safety column Mitch described an incident that illustrates why he advocates fuses in the motor/battery circuit of electric‑powered models. One reason is the serious fire hazard a shorted Ni‑Cd pack presents. Currents can go well over 30 amps and have burned up packs that did not have a fuse.
Howard Lazerson wrote to Mitch about his plane that burned. He said it had a fuse, but the fuse was of the slow‑blow type and did not blow in time. Thanks to the efforts of people present the fire did not spread, but Howard had to pay for damage to the plane and the grass. If the fuse had been of the right type — the fast‑blow type — perhaps the pack would have been saved entirely.
Giant scale / AMA weight‑limit discussion
It has been stated that putting a cap on RC's safest area of the sport, Giant Scale, would be a tragedy. Rather than give my opinion on whether the current weight limit is stifling growth and experimentation, I'd like to seek readers' opinions. Specifically, please comment on two plans submitted to an AMA VP that may be discussed by the AMA Executive Council.
Plan #1 — Remove the existing 55‑lb weight limit and allow any size RC aircraft to be flown provided that:
- A) The aircraft is non‑man‑carrying.
- B) The aircraft meets safety requirements.
- C) The aircraft has been flown at least six (or 12) times prior to presentation.
- D) The model is to be flown for demonstration only (no other aircraft will be flown while this model is being demonstrated).
- E) The model will be flown in accordance with what its full‑scale counterpart was able to perform, and no more (for example, you would not do aerobatics with a 200‑lb C‑130).
Plan #2 — Keep the existing 55‑lb weight limit and create an Experimental category. The FAA has this category, and the EAA benefits from it. RC models of the non‑man‑carrying type would fall into the Experimental category and be subject to certain regulations similar to the restrictions above:
- A) No weight limit.
- B) Non‑man‑carrying.
- C) No engine size limitations. However, IMAA would determine recommended minimum engine sizes. Under‑powered aircraft have proven to be dangerous under certain conditions.
- D) Twelve prior, proven airworthy flights before a model could be demonstrated at an AMA/IMAA‑sanctioned event.
- E) Model must pass a safety inspection at sanctioned event(s) and meet safety standards for equipment installation. (IMAA is presently working on an updated version of its safety guidelines; a safety inspector's handbook will be available for 1987.)
If any reader would like a copy of the present (1986 and prior) IMAA safety guidelines, please drop a line to the address below and include an SASE. Note that this is a new address — I moved at the end of 1986 from Rockville, MD to Washington, DC. If by the time this column appears I have received IMAA's updated 1987 version, I will send that more recent version.
If you take the time to send me your opinion, please also send a copy to your AMA VP. He is the one who has a vote on AMA Executive Council matters.
Have a safe month.
John Preston 2812 Northampton St., N.W. Washington, DC 20015
Transcribed from original scans by AI. Minor OCR errors may remain.
