Ground Loop

This is one of the main potential dangers of tail wheel aircraft. Tail wheel aircraft have the 2 main gear forward of the center of gravity (CG) and a small wheel located well aft of the CG. The CG will tend to try to lead the main gear. If the directional control of the aircraft is not maintained and the CG moves outside of the track of the 2 main gear, then the plane can begin to yaw and the wing that is on the outside of the rotation will dip and contact the ground. Imagine pushing a tricycle backward. It will start to turn one direction and tip over if you push it hard enough.

The problems that can occur include damage to the wing tip and the entire wing, depending on the severity of the ground loop. Also the gear box which supports the weight of the airplane can collapse as all of the weight of the airplane is loaded on a single gear box. The ground loop is the main reason that pilots need a tail wheel endorsement in their log books, to demonstrate that they know the reasons behind and avoidance of ground loops.

A ground loop is also what exists when you hear a hum in your stereo equipment. When multiple electronic devices are connected to the same electrical supply, current can leak from one device to another if there is no clear path to ground.

It can be cured by ensuring that every device in the system has a clean, solid path to a common ground. In a car, this means that every device needs a ground wire going to shiny bare metal somewhere on the car body that is at least as thick as the wire providing power. In the home, if your power amp or receiver doesn’t have a three-prong plug, the grounding lug or a screw going into the amp’s chassis should be connected to a radiator pipe, or other metal with a path to the building's foundation. Some home-improvement stores sell a blank three-prong plug with only the grounding prong made of metal, and a wire to attach to things that need to be grounded. Every device sensitive to electrical noise, like an analog tape deck or a phonograph, should be attached to the grounding point on the amp or receiver.

A ground loop often occurs in aftermarket car stereo installations, and has the potential to become a nightmare if the installer is not skilled in dealing with the situation. (It can also be exacerbated by spark plug or other engine electrical noise.) It can also occur in the home, but not as frequently since there is a common power connection standard in the wall socket. Also, equipment susceptible to ground loop noise, like a turntable, usually have an extra grounding wire to prevent such a thing from happening.