I had an experience a few weekends ago that reminded me again how important it is to remove the prop from an electric aeroplane before doing any work on it.
If you have only ever flow electric models with modern transmitters, you may think it is OK to turn off the transmitter before unplugging the battery, or that it is OK to plug in the battery without the transmitter turned on. In fact most times, nothing bad happens if you do. Spektrum even says . . .
Prevents electric motors from operating when the receiver power is on and the transmitter power is off.
Prevents the speed controller from arming until the throttle is moved to the low throttle position.
I am here to tell you that I have had two cases now, with different models, where I turned off the transmitter before disconnecting the battery and the motor started. This is why we are told to never do that, and to take the prop off when you are working on your plane.
With my first case I had the plane on a stand so the prop was on, and it started turning. Not very fast but enough to hurt if I had been in the wrong place. Speaking of “in the wrong place” props do sometimes break when you power up the motor and the blade leaves the area at a high rate of speed. Do not stand next to the model in such a way that a departing prop blade could get you. That isn’t just to the side, but also the front (in the case of a front mounted motor) because the prop blade will move out and to the front I’m told when it departs.
In my second case, I had in fact removed the prop but I had considered not doing it. But I reminded myself “safety first” and removed the prop. I then swapped out a satellite receiver connected to a flight controller that I had just updated the firmware on. I’m not sure why, but the throttle hold setting disappeared in the process and when I bumped the throttle, the motor went to a high rate of speed and tried to drill a hole in my carpet. No harm done, but if the prop had been in place there could have been an accident.
So – for the less experienced people like me, take your prop off before you work on your plane if you are going to be plugging in the battery. For the more experienced people, remember that “it is just a little change and it should be fine with the prop in place” is probably what a lot of injured people said right before they got caught by a spinning prop.