Earlier today, I boarded an airplane via airstairs, rather than the more common jetway. Interesting experience, walking out onto the ramp and climbing the steps and being able to see the airplane itself and the sundry support equipment and personnel around it.
Also notable is seeing features on the airplane that you just don’t see from the jetway like small fins along the top of the fuselage - on today’s A319, there was one fin on the centerline over the forward doors and another one fairly close to the tail. They appeared to be about two feet tall, so I can’t imagine they’re flight control surfaces. A couple yards aft of that forward fin was a truly tiny fin at a roughly 45-degree placement (between the horizontal and vertical centers of the fuselage) and this little guy was bright yellow - just like the lifting points on the wing, but fin-shaped, rather than lifting-point-shaped and much thinner and without the hole.
So… What are all these little fins for? I know we’ve got a handful of pilots here, but do we have any airframe specialists?
On the dorsal (top) centerline are two antenna arials - the VHF communications arial located over the forward doors, and the ADF (automatic direction finder) arial located near the tail.
I could be wrong about the second one, I’m much more familiar with the A320, and there are slight differences in the avionics layout between the two.
OK, then my hunch about that little yellow one was correct - from my perspective on the airstairs, it resembled a car’s XM radio antenna, except for the part about being centered over the rear window. This airline doesn’t offer satellite radio, though.
The bigger ones - why aren’t they on the bottom? I’m assuming these are being used to connect with land-based stations?
Speaking of antennas, I also noticed a swarm of skinny rods/wires along the aft-facing edge of the wing and some on the under-wing nacelles. More antennas or static-discharge points?
Lots of activity underneath an airplane on the ground with much opportunity to break an antenna. When I worked on F-14s the UHF antenna was nicknamed the football for the frequency it was kicked and broken by people stepping over the turtledeck while doing maintenance. As for reception it doesn’t make a big difference at those frequencies if the antennas are top or bottom.
Nope, definitely too small and facing the wrong direction to be canards.
I’m quite content to believe Dorjan’s explanation of them as antennas, and Padeye’s description of how things sticking out of the belly of a plane tend to attract damage.
A typical airliner will have about 20 antennas on it. in most cases they’re installed in matched pairs with one on the belly and one on top. That ensures that during banks one or the other will always have a view of the ground in the appropriate direction.
The UHF antennas will be no bigger than your hand, whereas the VHF antennas will generally be 10-18" in length and 6-10" in span at the root.
Some of the newer longer range airplanes also carry satcom antennas, which look like a garbage can lid or pizza box laid conformally over the top of the fuelage. unlike the others, there’s never a mate on the belly.
The small rods you see trailing from wingtips and tail tips are static discharge wicks. A typical installation will have 3 or 4 on the outboard trailing edge of each wing and 2 or 3 on the trailing edge of each side of the horizontal tail & the vertical rudder. There are also often 1 or 2 more on the very tips extending away from the fuselage. Those last would be very hard to see from the cabin.
Those are probably static discharges; planes pick up large amounts of static electricity while flying through water and dust particles; this wires on the trailing edges of the wings and tailplanes (I don´t recall seeing them on nacelles though) disipate most of the charge.
In any case planes must be properly grounded after landing; as an anecdote some years ago I went to a free flight championship in Chile on an air force Fokker Friendship (the twin ship of the one that crashed in the Andes, have you seen the movie Alive?), some weeks after we came back I heard the news that the plane was lost on a fire; someone forgot to ground the plane before refueling it and a spark jumped from the filler nozzle to the airframe igniting the fuel.