Must of us know what fail safe is, most of us don't care to program it. To see what happens to your plane in case of loss of connection from your radio, with the plane powered -important warning remove your propeller to be safe-, shutdown your radio and have a look at what happens to your moving surfaces and motor.

With Spektrum radios, fail safe takes the position of the controls of the radio at the moment of the bind and takes them as the values used in case of loss of connection.

I recently changed my Vagabond glider to independent channels for ailerons, using a 4 CH receptor cheaper than 6 CH, sloping over the sea as I do has a risk of total loss of glider, so the cheaper the better.

On a glider you can have separate channels for ailerons with a 4 CH receptor by assigning the motor to one of the ailerons, and using the bind connector on your receiver to power it after it is bound to your radio (requires moving connectors on your receiver after bind, it a hassle but I am cheap sometimes).

I did that, checked it was working well, and flew the glider.

After landing I powered off my radio before disconnecting the battery in the glider, and noticed that one of my ailerons went immediately to max travel. Powering radio, brought back the aileron to neutral position.

Went home, and realized afterwards (not so clever after all), that it was a consequence of the fail safe default programming (that is motor off in case of loss of connection, which is fine in case of a motor glider, not so fine in the case of reusing the motor channel to an aileron).

I bound again my receptor to the radio, taking care that the power stick was at the middle of his travel (programmed my fail safe ).

Now I can power off my radio (case of momentary loss of connection with the plane) without having an aileron shooting to it's max travel.

Experienced flyers now that no doubt, as many I knew what fail safe was, and thought that if there was a connection loss with the plane it was lost, so I didn't take the trouble of looking into it.

That explains why in some cases when you shut down your radio before your plane, your propeller suddenly spins (hence the recommendation, always disconnect your radio after powering off your plane), the motor spins because it is the value of throttle programmed for fail safe -deliberately or not-.

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