Once you have opened the attic dome, you can add manure to make the hovercraft work. To open the attic, release the gear lock and turn the windmill arms counter-clockwise.
The hovercraft runs on manure.
It goes to the mud swamp, which is the only place that you can use it.
In Astro Knights Island on Poptropica, the fuel for the hovercraft can be found in the fuel canisters located next to the dock where you first arrive on the island. You need to collect the fuel canister and use it to power the hovercraft to cross the toxic swamp.
There is no such power. You can fly on the hovercraft into the mud swamp, and in space aboard the Astro Zone ships. (see related questions)
You have to power it up with manure which you have to get from the farmer near the secret hatch to Mordred's Hideout
The manure is used to power the hovercraft hidden in the attic of the mill. (see related question)
In the field between the castle and the mill. You only get one bag, and it is used to power the hovercraft.
You use it to power the hover board (hovercraft) in the attic of the windmill. (see related question)
To find the hovercraft on Astro Knights Island, you need to rescue the princess and receive the Coordinates Decoder. Once you have the decoder, you can use it to uncover the hovercraft's location on one of the planets. It's located on a frozen planet called Tundara.
The farmer will give you one bag, which you use to power the hovercraft hidden in the mill attic. (see related question)
The boy at the farm near the mill will give you a bag, but only one. Use it to power the hovercraft in the Mill's attic. (see related question)
The boy on the farm just left of the Mill will give you a bag. You will use it to power the hovercraft in the attic of the Mill. (see related question)