Sunday, August 19th, 2012 08:24 am GMT -6 Sunday, August 19th, 2012 08:24 am GMT -6Sunday, August 19th, 2012 08:24 am GMT -6
 
Propeller Samples

Electrics have special needs when it comes to propellers.


 

 

 

Gas vs. Electric Propellers

Propellers designed for gas engines are relatively thick and strong. There are two reasons for this. First, gas engines create a lot more vibration than electric motors. You want the propeller to retain its shape and not break as it spins, so they naturally need beefier hubs and blades.

Second, as a general rule, gas engines spin their propellers faster than electrics. A faster spinning propeller means a higher Reynolds number seen by the blades. Thicker blades work better at these higher Reynolds numbers. And yes, you need thicker hubs to transmit the higher levels of power to the airplane.

Electric propellers tend to be very thin and light. They are optimized for their intended application. But that does not mean that a gas propeller won’t work on an electric motor. It will work, just not as efficiently.

Propeller Savers

All of my small electric motors use prop savers. These are propeller mounts that use an O ring to secure the propeller. If the propeller hits the ground, the O ring will give and allow the propeller to fold back. I do not think I have ever broken a prop while using one of these.

The downside of prop savers is that the O rings do not last all that long. I have gotten into the habit of inspecting them before a day of flying. That helps. Invariably, once in a while, I’m flying around and lose power. I always assume that what happened is that the battery ran down and the BEC kicked in. Then, after the airplane lands, I notice that the propeller is gone. What really happened is that the O ring gave up the ghost in mid flight. The prop is gone, never to be seen again.

Some pilots use regular propeller mounts even in their smaller models. That is your choice. I tend to use whatever the motor comes with.

Spares

Always bring at least one spare prop with you when you go flying. Even if you hardly ever break props, I guarantee you that the day that you leave the spares at home will be the day something dumb happens and you break your only prop. I guess that is one of the few dumb things that I have not done.

Use the Wattmeter, Luke

I have learned that two identical looking propellers can have dramatically different power loads on a motor. If you are flying close to the current limits of your motor or speed control, use a wattmeter to confirm you are not abusing your power system. Abused power systems bite back when you least expect them to.

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