Until the 1.8 update for PC Minecraft flying machines were only in mods and with command blocks. Now you can make them in vanilla thanks to slime blocks!

These designs are my own and are the fasted and most compact that I have seen yet. They have a top speed of 3.3 blocks/second which is faster than walking but a bit slower than running. Over long distances it is more effective than running as your hunger doesn't decrease, works AFK and because you are going in a straight line and not over hills it is quicker.

There is a couple of variants I am going to show you how to build. The first and easiest is the single seater, then with a small addition it can be turned into a two seater. The next is a single seater which can fire/drop tnt.

Other small additions can be added on like lights on the single and double seater can be added but that is really upto you.

These machines are single direction only. They cannot turn mid flight. To change direction you have to dismantle the machine and reassemble it facing the new direction. The machine is started by updating the piston with flint & steel (Google block update in Minecraft for more information on how this works) and is stopped by placing a Redstone block on top of one of the pistons which will lock the piston in the on state, halting movement or by running into enough blocks that the piston cannot push all of them. (A mountain or tree)

Step 1: Materials

To build the single seater you will need:

Slime blocks x10
Sticky piston x1
Normal piston x4
Redstone blocks x 2
Any movable block x1 (I use Birch wood but this could be a stone or any other movable block)
Any non-movable block x 1 (this could be obsidian, note-block, furnace,chest etc)
Boat x1
Flint & Steel

To convert the single seater to a double seater you will need:

Slime block x3
Any movable block x1 (I use Birch wood but this could be a stone or any other movable block)
Boat x1

To add lights:

Glowstone/Sea lanterns x3

To convert the single seater to fire/drop TNT:

TNT x however any you wish to drop

Step 2: Making the Single Seater

The single seater flying machine is what all the variants are based around. Watch the video or follow the step by step photos and you should be able to make a functioning machine.

Make sure you build the machine facing the way you want to fly and at the correct altitude so you are not gonna run into the first tree you see.

The non-movable block (obsidian or similar) used in construction is to stop the machine running away when you are building it. Soon as the craft is finished it can be removed and the machine will not run away on you.

The first piston placed is a sticky piston. all others are normal pistons.

Step 3: Double Seater

The double seater flying machine just has an extra support added onto the side of the machine to support a second boat.

Once you have made the working single seater the second seat just involved adding a support for a second boat on the left hand side.

Remember to add the non-movable block at the front before starting, otherwise the block update will cause your machine to take off without you.

Step 4: TNT Launching Flying Machine

All that is done from the single seater is the support for the boat where you sit is moved forward so you can place TNT on the front of the machine. If you place TNT on the front of the machine then light it, the TNT will be propelled forward and if you place it on top then light it the TNT will slide off the back and drop down and explode!

This is lots of fun for flying raids. just make sure you don't blow yourself out of the air. ;)

Step 5: Adding Lights

Because pistons can push upto 12 blocks, which means some more blocks can be added to the craft while still allowing it to function. My favorite is adding lights. This involved putting a row of Glowstone or Sea lanterns along the front slime blocks. This gives a head-light affect which I quite like. This works on both the single and double seater.

Step 6: Operation

So one you have built your machine it is time to jump in and head out on an adventure.

Make sure you have removed the non-movable block that was stopping your machine from running away and hope into the boat by right clicking on it.

Now with Flint & Steel in you hand, right click on the front facing, left hand side piston. This will cause a block update which will start your machine and your off!

A couple of things to watch while you are using the machine:

Don't get out of the boat if you are still moving or high above the ground as you will fall off the machine and die.
Be careful while shooting arrows. You may break your boat and fall out as above.
Don't use TNT on the double seater as it will stick to the TNT and blow you out of the air.
On some servers it may cause a bit of lag because of fast moving pistons and updating chunks as it travels.
If you run into something the boat may be pushed into the back block suffocating you.

Stopping the machine is done by placing a Redstone block on any of the pistons locking it on or running into a stop or other non-movable or large object.

Step 7: Have Fun!

Yay! Now you have your very own flying machines! They are lots of fun to travel on and are pretty simple to make. Now to construct an airport and you are all set!