In some commercial aircrafts one wire or rope is connected through vertical tail to upper surface of fuselage.

Question

what is this and what is its function..

Answer 1

I don't know for sure, but I'm thinking it could possibly be a grounding wire to diffuse static electricity caused by wind friction. Or a sort of "lightning rod" to absorb electrical charges in bad weather. It could also be the "Pitot Static". (yes, pitot, not pilot) which is neither wire nor rope, but a hollow tube through which air passes while travelling, and sends a signal to the cockpit which registers air speed.

Answer 2

ADF sensing antenna. Not used anymore but still seen on older aircraft.

Answer 3

it is half of the antenna for the ADF.

there is another half below the plane.

there is an integrated version too, only one belly antenna.

Answer 4

I'm with Gary, it would be an HF or VLF antenna. Definitely not VHF..But most likely HF/ADF

Answer 5

could also be an HF antenna for communicating long distances (trans-oceanic)

ADF antennas can be pretty small and still pick up a signal.  HF antennas need to be longer because they need to actually transmit the signal.

Answer 6

It is an antenna wire usually for the VHF radio. These are installed on mostly older aircraft and have largely been replaced by smaller, sleeker antennas that look like the ones you see on the back of some newer cars.

Wire antennas are also used for ADF and UHF radios. it depends on the kind of airplane you're talking about.