Tony Stillman, AMA’s hardworking AMA flying site assistance coordinator, forwarded me a question about why we don’t see painted propeller tips as often these days. Nearly all model aircraft propellers used to come from the factory with brightly striped tips. These days, it seems like most new propellers do not have tip markings. I think this is a move in the wrong direction.
The obvious reason for vivid paint on a propeller tip is to increase visibility of the propeller disk. A colorful stripe makes the blades show up better, and if it catches the eye it might not catch the finger. A secondary reason is that it makes your model look more scalelike and “serious” because full-scale aircraft universally have painted tips.
Having that bright, spinning flash of color doesn’t prevent all propeller strikes, but it is one more little part of the whole safety thing. Could there be more to this issue? I can see that adding paint to propeller tips would make them slightly more expensive, but it seems like an easy way for a manufacturer to reduce product-liability issues.
If there is some other reason for skipping such a useful feature, please tell me. Otherwise, I think modelers should let the suppliers know that we prefer a propeller with cool-looking painted tips, just like a full-scale airplane. And we will even pay a few cents extra to show how much we value our fingers.
Box, Bag, or Barbecue
My request for information about charging and storage containers for LiPo batteries brought a firestorm of comments. After the smoke cleared, I made a decision.
But first, a disclaimer: Thousands of flights are made with these modern batteries without a lick of trouble. Statistically, they are very safe products. The odds that a damaged or faulty pack will catch fire all by itself are slim. Most fires are apparently because of incorrect charging, such as using the wrong setting or the wrong type of charger. Thus, we see the popularity of fire-resistant containers.
Modelers have tried all sorts of boxes and materials for storing and charging their batteries. Those “fireproof” document safes sound like a good bet, until you think about it a little more. They often use plastic seals that melt to protect the contents. In our case, we are concerned with containing the fire, but releasing the smoke and heat. Let’s see, what could happen if sudden combustion occurred in a sealed chamber? Blammo! It could make a bad situation much worse.
Some pilots use metal ammunition boxes with the lid latched and drill a hole to let the cord pass through. Imagine a battery fire with all of the “products of combustion” trying to get out through the little hole. How about a rocket-powered box shooting around the workshop? Cue the cartoon music!
There are several videos online showing LiPo battery fires. Some are deliberately staged for educational purposes, and others were accidental, caught on video by chance. What they have in common is a great deal of smoke and heat being suddenly released.
Often, there will be secondary ignitions as other cells overheat and ignite after things seem to have settled down. The batteries commonly jump around when they “pop,” and will fall off of tables or bounce around the room. This is an argument against merely setting the pack on top of a charging bag or a heat-resistant surface. It needs to be contained and restrained.
The most interesting clips show these fires igniting inside fire-resistant charge bags. The bags puff out and release the smoke, but contain the flames and heat. Several companies offer these products, optimized for our use. Users confirm that they do work.
In my opinion, these special bags are the best answer to storing, transporting, and charging LiPo batteries, and I have switched to this method. The double-walled steel box I’ve been using is gone, and my new fire-resistant bag is in use. Watch some online videos and make your own decision.
My request for information about finishing old, half-built models brought some great comments. Many builders have successfully completed airplanes that sat around for long periods. The consensus is that the wood and glue joints need to be carefully inspected because poor storage conditions can have an effect. One aeromodeler said, “The hardest part was finding all the original parts that had scattered over the years, and having to replace parts that I had borrowed and put into other planes.”
There doesn’t seem to be any type of glue that holds up better than others. The storage conditions and quality of the original materials make all the difference. More than one modeler reported that multiple airplanes that had been stored together aged differently.
The good people at AMA Headquarters in Muncie, Indiana, forwarded me an actual paper letter from a reader. Better yet, it was handwritten, just like in the olden days! Earl Wheelock wrote it, and asked that I remind everyone about a critical difference between gas and electric power systems.
If a gas-powered propeller strikes something, the engine usually stalls and stops running. Electric motors are not that way. The propeller will continue to spin during and after the initial strike—all the more reason to keep our hands clear of the airscrew! Thanks for the tip, Earl.
Put a Ring on It
A related issue was raised by another reader. He saw an E-36 model with a motor reportedly turning a 7-inch-diameter propeller at 16,000 rpm. His concern was that the propeller on this model was held on by a “prop-saver” device with a single rubber O-ring, as would be found on a low-powered park flyer. Failure of the O-ring could have serious results.
I’m no expert, but I agree that the numbers seem to call for a different type of propeller-retention system—one more suited to high rpm. This situation might not be specifically covered in the rules, and it would be up to individual contest directors to make a decision.
Please contact me and say why you agree or disagree. As always, I’ll leave your name out of it, if you prefer.
Lance Gets Lanced
Lance Novak gets to wrap things up this month with a horrifying tale of laceration and pain.
“I have a special protocol with my hobby knife. I always lay it in a spot where it can’t roll, with the blade facing away. So one day I was working on MiG-15 wiring and using the hobby knife, dental tools, and hemostats, and I got sloppy and set the knife down with the blade facing me.
“Then, as I reached for another tool (while looking the other way), my forearm touched the point of the blade. The handle jammed against something firm and the blade was pushed all the way into my forearm. The blade was in so deep you couldn’t see it. Basic first aid stopped the blood flow, but it looked like I had been shot. It took several weeks to fully heal.
“The moral of the story is to never lay down a sharp tool pointing at you, and look where you’re reaching.”