Propeller Strikes & Arming Switches

by Jim Tiller



Never, Never Stick Your Finger in the Propeller
Before I took the job as AMA Insider safety columnist, I remember lamenting to my beautiful wife that it might be hard to make the column interesting. I remember saying, “Just how many times can you tell someone not to put his finger in the propeller?” On a warm Friday afternoon in late August, I found that the answer. After 30 years of flying airplanes, I had my first encounter with a spinning propeller.

I was with a bunch of flying buddies at our preferred float-flying spot, enjoying the late summer morning. It was the first flight of the day on my .30 four-stroke powered Newbie float plane. As the flight progressed, I could see the motor was not developing full power, so I made an early landing and taxied back to do some engine adjustment.

With another flier holding the airplane, I was adjusting the high-end needle setting when my hand somehow wandered into the full-throttle propeller. In an instant, the motor stopped and the blood began to run. The cuts were quite serious and we immediately went into damage-control mode. We had a first aid kit along, but it was a small one. We applied pressure and bandaged the wound with the only high strength tape available, a roll of black electrical tape. With the blood flow temporarily stopped, I made my way to the emergency room for a two-hour stay and about 14 stitches from a very competent and friendly emergency room doctor. This little lady looked, to me, to be about 14, but she did a great job sewing up four separate propeller strikes on my right hand. She mentioned that I was her very first prop-strike victim and I replied that it was also a first for me.

Fortunately, there was no permanent damage except to my pride. I managed to hit the blade with the flat of my hand rather than the fingers. That stopped the propeller and reduced the number of strikes somewhat. It is now almost two months later and I have just the scars to remind me of my errant ways. Who do I have to blame? No one but myself—it was a preventable accident. In hindsight, I lost what the military calls “situational awareness.” I was so focused on the job at hand (no pun intended), which was tuning the engine that I totally ignored the close proximity to the spinning propeller. I know better. On that day, evidently, I did not know better and all it takes is one lapse in concentration. That is the lesson I leave with you and why I am sharing my experience.

A second observation. This little four-stroke is my smallest motor. Maybe that is why I was not as conscientious as I might have been. As you can see, small propellers do just as much damage as big ones.

A third observation; and one that my flying group has now corrected. Our first aid equipment was inadequate. We have since purchased a much better equipped first aid kit and put it in the storage locker in our retrieval boat. That kit now matches the one we have at our field. By the way, it still includes the roll of electrical tape. I can vouch for how well it worked at compressing the bandage over the wound.

A fourth observation. I have my flying buddies to thank for the help and assistance. It is important to surround yourself with fellows who are safety conscious and who can be trusted in an emergency.

And last: Never, never stick your finger in the propeller.

Arming Switches on Electric Airplanes
This past summer, I learned of a couple of instances where an electric airplane started before the pilot was ready. In one instance, the pilot turned on the transmitter but had it improperly set to another airplane program. Evidently, the programmed airplane had the throttle reversed and when the airplane battery pack was plugged in the motor engaged. Most good ESCs are supposed to prevent this by making you put the throttle to its lowest setting before arming. I’m not sure what happened here.

In the second instance, the airplane was on the bench and the transmitter had yet to be programmed. The throttle stick was in the mid-range. Once again, when the battery was plugged in, the motor engaged. An arming switch is a good way to prevent any accidental motor start on an electric airplane. They are most feasible on larger motors, but many electric gurus say they can be fitted to an airplane of almost any size.
Another good reason for the arming switch is to be able to plug in the battery and then prepare the airplane for flight. Many times there are cowlings or hatches that have to be secured or other preflight preparations to complete. Why do that with the battery and motor armed? A number of commercial arming switches are out there. They are not very expensive and are easy to use. Your local hobby shop can surely provide you with one. Q