As everyone must know, goblins like to steal loot, but they also like to invent things. What better way to steal hard to reach loot then by air?
This is where the goblins decide to invent a flying machine. Imagine a very small wooden helicopter with no cockpit, just a seat with control handles.
The next thing the goblins needed to figure out is, "how are we going to destroy loot storages to get the gold?" So in comes a goblin attaching an air defense rocket to the helicopter, and viola!
Another way to look at this is like the promoted version of the goblin.
Gob-Copter (Goblin Ace):
DPS: 24
Health: 135
Targets: ground
Favorite target: resources (x2 damage)
Housing space: 5
Movement speed: 24
Cost: 3000 elixir
training time: 4 min
Range: 2 tiles in front (the rocket is fixed and therefore can only shoot downward and 2 tiles away - thus the reason they can't target air troops)
A funny spin on this was to have a goblin fly in with a giant claw helicopter and have it take one resource collector or storage and fly away with it before flying back for Another. Think of the claw machine with stuffed animals in it.