Why do some aircraft have this?

Question

Why is it that on some aircraft there is a thin cable that runs from the vertical stabalizer to the fuselage?

http://www.dc3history.org/images/twa_dc1.jpg

Answer 1

its HF antenna

Answer 2

On the DC-3, the antenna is probably for HF communications as others have mentioned. On the Cessna, the wire is the "sense antenna" that is part of the ADF system for receiving NDB transmissions. The older ADF systems used two separate antennas, the "long wire sense antenna", and a "flat loop antenna", while a modern ADF system uses a combined "loop - sense antenna" that is very compact and fits inside an aerodynamically clean enclosure, see photo: http://www.seaerospace.com/king/ka44b.ht...

The old sense antennas were "full-wave", meaning they were a full wave-length long, or about 25 feet in length, so they typically were mounted from the top of the vertical stabilizer to a point foreward on the fuselage. In either design, the loop is used to determine direction to the NDB transmitter while the "sense antenna" is used to recieve the ground station audio signal (morse code or voice, or both). The sense antenna is also used to resolve any amibiguity in the direction determined by the loop.

Answer 3

Hey, great picture!!!!!!!!!!

Answer 4

This is an HF radio antenna or an ADF sense antenna.  It is used for picking up lower frequency radio waves. The lower the frequency, the longer the antenna needed to receive the signal.  Newer radios use higher frequencies, so they have smaller antennas, that usually look like little fins on top of aircraft.  Higher speed aircraft (jets) needed to get rid of these external wires, so you will generally only see them on older, propeller driven airplanes.

Answer 5

It reduces sway in the tail.

Answer 6

I think it's a VHF antenna for radio communication.

Answer 7

http://flyingstart.ca/FlightTraining/pre...

http://www.avweb.com/news/avionics/18323...

Answer 8

The answers that mention that it is the sense antenna for an ADF are right.  There are also HF radio installations that use a wire antenna.

The VHF comm antennas are the spikes about 14 inches long that stick up from the fuselage.

Answer 9

Two possibilities.  It is either an antenna for an HF radio, or it could be the sense antenna for the ADF.

<edit> That second picture is almost certainly an ADF sense antenna.  It's pretty unlikely that a Cessna has an HF radio installed.

Answer 10

It's an antenna for communicating with the tower or Flight Service Stations or even other aircraft.

It's just like the one sticking up in the air on your car, but it's thinner and attaches to the vertical stabilizer (something your car probably doesn't have).