Propeller Safety

We all know that propellers are dangerous, but it may be less obvious that propellers on electric-powered aircraft carry some additional risks. Here are two important risk factors to be aware of, and how to deal with them.

The first is the problem of accidentally bumping the throttle stick. Speaking from experience, it is very easy to move the throttle stick with your body or clothing, especially if you keep the radio around your neck when leaning over a model. On a gas or glow plane, this will just move the throttle servo, but there's no danger that the engine will start. By comparison, an electric motor will come alive instantly, with serious consequences.

Here are three easy steps to prevent this:

1. Put the transmitter down flat on the ground when working on your plane. Don't stand it up vertically - it could easily fall forward.
2. Buy a speed controller with an arming function. Good ESCs require you to move the throttle stick all the way to the top, then all the way to the bottom before the motor will start.
3. Program your radio to have a throttle kill switch. This is a toggle switch which will prevent the propeller from turning no matter where the throttle stick is. Helicopter pilots know this as Throttle Hold, but some radios only offer this feature in helicopter mode.

Here's how I programmed my Futaba 7C for a kill switch (thanks to Futaba Support for this technique):

1. Choose an available P-Mix, in this case P-Mix 1, and make it active.
2. Set the master and slave both to channel 3.
3. Set the top rate to -100% and the bottom rate to 0%.
4. Cursor down to OFS (offset), set the throttle stick to the bottom, and press and hold the click wheel.
5. Set the switch to an available toggle switch. I chose B with a down arrow, which means the throttle kill is active when the switch is up.

I use this on all my planes, and always have the throttle kill active when plugging in the battery. Throwing this switch is the last thing I do before takeoff, and the first thing I do after landing.

The second problem to be aware of is interference. I have seen motors suddenly start for an instant in both my planes and helicopters for no apparent reason. This is scary, but there are a few things you can do to minimize it:

1. Always turn on your transmitter before turning on the receiver, and turn off the receiver before turning off the transmitter.
2. If you use an FM radio (PPM or PCM), in addition to making sure no one else is using your frequency, never point the transmitter directly at the model at short range. This can overload the receiver and cause glitches.
3. And finally, consider switching to spread spectrum technology the next time you upgrade your radio equipment. We recently mentioned the new Futaba 7C 2.4 GHz radio, and the Spektrum offerings are also very popular.

Hopefully this article has given you some good tips on how to stay safe. Remember to have a healthy respect for propellers, and go fly!