Propeller-strike injury cuts into a reader’s flying time
Dave Gee | [email protected]
I like to start each column with a “grabber,” and Tom Chytil sent in a humdinger. His electric-powered RC foam model has had an eventful history.
It was originally a high-winged version that was treed twice and badly damaged during recovery. Tom rebuilt the aircraft as a midwinger, and the airplane repaid him by slicing his arm open like a warm bagel.
Tom takes some of the blame, noting that the model has no will of its own, but I’m not so sure. He wrote:
“I was at the flying field holding the plane as shown, walking it a few steps to the takeoff area. Everything was live. The transmitter brushed against my leg and knocked the throttle up to about 30% power. The propeller thrust caused the plane to rotate in my fingers sufficient to allow the propeller to lacerate my lower arm.
“Lots of blood everywhere. Luckily, my wife was with me and drove me to a nearby emergency room where I received a dozen stitches. Interestingly, I suffered no pain during the incident, and had no idea that I’d been cut so deeply.”
Tom had several lucky breaks on this one, not the least of which was having someone with him at the field. My wife, sweet Diedra, would have cauterized the wound for me on the spot with a few choice comments. Tom’s calm spouse helped him greatly, but I’ll bet she thinks twice about going flying with him next time.
This incident is a classic, because it reminds us of several important safety points.
Lessons learned
Safety reminders
- Bring a friend. Many pilots require adult supervision; “bring a friend” is a good rule. You might end up as the helper or the helpee, but don’t fly alone.
- Treat electric systems as live. Electric systems can come to life instantly; unlike gas engines, a motor can respond to throttle-stick movement anytime the system is live.
- Use arming keys or cutoff switches. Many modelers use arming keys or switches to avoid accidents like Tom’s. There are pros and cons to having a cutoff feature, but Tom’s injury is a strong argument in its favor.
- Beware the propeller arc. Avoid inserting body parts into the direct path of the propeller. Distracted moments and inadvertent movement happen too easily.
- Minimize exposure to projected propeller pieces. When a propeller blade separates, pieces fly in a straight line along the projected propeller arc. Minimize your exposure by placing your body ahead of or behind the arc while servicing the airplane.
- Helicopter pilots: minimize exposure. Helicopter pilots have a tougher time because half the rotors are horizontal, but they should still arrange for the minimal exposure possible.
- Wear proper eye protection. Impact-resistant wraparound safety glasses can protect you from fast-moving debris. Getting an arm stitched is bad enough; losing sight is far more serious.
Additional notes on propeller hazards
- Brightly colored prop tips and other aids might help, but they are not a substitute for good habits.
- Remember that the danger zone for broken pieces is in the extended disc of the propeller; keep clear of that projected extension whenever possible.
I often recommend Zurich sunglasses because their impact-resistant wraparounds are my favorite, but there are other excellent products available. I urge you to consider making safety-rated glasses a part of your field and shop outfit.
Compressed Air (CA) power and safety
Before electric power, before even gas power, there was compressed air (CA). This quiet and challenging power system is experiencing a small resurgence among the Old-Timer crowd.
CA models must be extremely well designed to fly. Extra weight is a killer, since the setup requires a large propeller, a fairly heavy motor, and a giant onboard pressure vessel to hold the “fuel.” CA pilots are mindful of what can happen when an ultralightweight tank is filled with enough pressure to operate an aircraft motor.
Take a look at Tony Naccarato’s photo of Bud Matthews’ airplane chugging overhead. The model uses a borrowed motor and tank, both of which are antiques. Bud had to repair several leaks in the tank using old-fashioned solder on the paper-thin brass tank body.
Some airplanes carry their pressurized power in modern soda bottles. This lacks the historical appearance and romance of the old tanks, but avoids sending near-priceless artifacts into the sky on an FF model. Those pop bottles can really “pop” sometimes, so eye protection is a must when using any CA rig.
I think the new Air Hogs flying toys are partly to blame for the resurgence of CA flight. These inexpensive airplanes and helicopters are ready to fly, and boy do they fly! Their motors are small for transplanting into serious models, but some designers make good use of them.
My friend Ken Johnson has flown and had published some neat models that use commercial motors. There is not much tinkering or souping-up possible on these molded-plastic expansion motors, unlike the classic handmade systems that can be tuned and altered as the builder sees fit.
Old how-to books make it look easy to slap a CA motor together. Ha! Fitting and soldering brass takes practice and skill, especially if your project is going to safely handle a powerful supply of compressed air. Whether you try a new or old CA power plant, wear your safety glasses!
Buddy-box systems and radio safety
I read another Internet discussion about buddy-box systems that shoot down models. It's tough to get the word out to every pilot, so here’s a reminder.
There have been conflicting reports about which brands and models of radios are involved, but it is possible to rig two transmitters with a buddy cord for training or First Person View (FPV) flying and inadvertently send radio signals from the second transmitter. This apparently happens when a brand of cord other than the radio brand is used to connect the two boxes.
Recommendations:
- Use only a matching brand of connection cable.
- As a precaution, remove the crystals from the second radio during buddy-box use.
There is a wireless buddy-box system being tested that uses Bluetooth-like technology. More than one student can be online, and there are other keen features. Watch the appropriate MA columns for details.
Motor-mount feedback from readers
My recent plea for wisdom about electric-power motor mounts brought in some great e-mail. Dawson Gillaspy of Long Neck, Delaware, flies with the Lewes RC Club, but he has been building models since long before there was radio control or electric power.
He sent a photo of an unusual method of mounting a motor to the firewall. He uses sturdy plastic spacers and says that he has not had problems with side-load failures.
Dawson wrote: "The spacers stay perpendicular to the firewall by the precision molded flat ends, and the long 6-32 screws are held by blind nuts. If the battery is located near or against the firewall, it is important that the screw ends do not protrude beyond the flange of the blind nuts and allow the battery to impale itself on the screw ends in a hard landing.
"I've used this system in 5–6 different planes, large and small, and have never experienced any distortion so I'm comfortable with that method."
I was concerned about how this setup looked. It appears not to be rigid and looks vulnerable to flexing sideways under the G-forces of flight maneuvers. Dawson assured me that the spacers and screws are oversized and overengineered for strength, and that is what allows this system to deal with the stress of flight. When a guy with that much experience talks, I listen.
Send your stories and ideas
I appreciate and enjoy answering the e-mail and letters I receive. If you have a brilliant idea or a close-call story, please share it. Anonymity is available for those who are embarrassed by their occasional lapses of judgment. I should be used to it by now.
Please put "MA" in your e-mail title so my spam filter separates you from the fake-Rolex watch ads.
Sources: Dave Gee Box 7081 Van Nuys, CA 91409
Zurich Sunglasses (916) 691-6467 www.zurichsunglasses.com
Transcribed from original scans by AI. Minor OCR errors may remain.
