Many things can fly in DnD. This being DnD, there are rules! Of course, this being DnD, those rules are mostly useful for low level fighters. And we don't care about low level fighters. We care about iron men, keeping the line of battle in wooden skyships, bound together by tradition and loyalty. We care about islands of rock, towering oases of safety in the tempest-tossed skies standing bastion against the rolling clouds. We care about pilots with nerves of steel, assaulting the ships and citadels, living on reflexes and daring, swooping gloriously out of the sky.

In short, we want airships feel fantastic.

Oh! I have slipped the surly bonds of Earth

A skyfighter is usually (but not always) a small, one-man flyer. A skyfighter crew cannot take independent actions (e.g., a wizard can't ride shotgun to fling fireballs). However, every skyfighter has Flyby Attack and Run. Skyfighters add the pilot's dex bonus to AC. Skyfighters fly by aerodynamic forces. Regardless of maneuverability, they cannot hover and must move at least half their speed each round or fall (but may circle as tightly as would normally be allowed). Many skyships also have the ability to land and/or take off vertically, a complex procedure which requires a full minute.

Here's a couple ways to make a skyfighter.

Large Magical Construct
Speed: fly 100
Max turn: 45°/10ft
HP: 30, hardness 3
Cost 26000 (airframe)
Weapon Mounts: 2
Special: a destroyed steamfury explodes. Treat this as a 10d6 fireball 
centered on the pilot, which goes off at the end of the pilot's next 
action after the steamfury is reduced to 0hp.

Steamfuries shriek across the sky on trails of steam. These tiny darts zoom across the sky faster than nearly anything else. The sound of their steamjets is distinctive, terrifying, and really, really, loud.

The magic of DnD offers many new and exciting ways of making high pressure steam. The simplest is a metal sphere which fills itself with water and boils it off via Create Water and Heat Metal, but there's no wrong way to eat a Reese's. A steamfury uses this to zip across the sky like a rocket. A damaged steamfury uses it to explode in the sky like a rocket.

Large Magical Construct
Speed: fly 20
Max turn: none
HP: 20, hardness 1
Cost 16000 (airframe)
Weapon Mounts: 1
Special: none  

It is a source of continual frustration to the Gnome race that rickety deathtraps are called “Gnomish” gyrocopters. There is no indication that gnomes invented these devices, nor do they habitually use them. Nonetheless, everyone who sees one of these marvels wonders first how it avoids falling out of the sky, and second, where the gnomes who made it are. This name describes a class of skyfighters with similar characteristics, though some are more accurately helicopters (helicopters have a powered rotor; gyrocopter rotors spin freely). Gyrocopters are inferior to most other skyfighters in all but two areas: they are cheap, and their high maneuverability allows a much shorter runway.

Large Undead Construct
Speed: fly 40
Max turn: 45%/20ft
HP: 80, hardness 4
Cost 40000 (airframe)
Weapon Mounts: 2
Special: Weapon mount points can be swapped out for 2000 lbs of cargo capacity.

The simplest and cheapest way to make a skyfighter with necromancy is to take a flying critter corpse, scoop it out with a giant melon-baller, add a bit of superstructure, slap a couple of weapons on the wings, reanimate it, and you've got a Carion Glider. This necromancy isn't inherently evil, but most good cultures are unwilling to sit in the middle of a rotting corpse. As a practical matter, carrion wings' use is restricted to the evil and the desperate.

Buying a single Carion Glider is surprisingly expensive, largely because most animals don't leave cadavers suitable for building into skyfighters, and breeding the ones which do is a fairly long-term investment. However, this also means that mass-producing them is entirely feasible, and costs a fraction of what it does to buy them on the open market. Any ruler or would-be dictator who can find pilots for them and devote a couple years to the effort can raise a credible air force on the cheap.

Large Undead Construct
Speed: fly 150
Max turn: 45%/20ft
HP: 80, hardness 10
Cost 60000 (airframe)
Weapon Mounts: 4
Special: Also has swim 20.

Ghost dragons are heavy metal statues with huge wings and are generally covered with ornate stylized carvings. Most people think think the name comes from the way it's carved up, but that's not the case. Each flier is actually motivated by a haunt-shifted young dragon, which provides nearly all of the enchantment. The remainder is some fairly trivial work which allows anyone to pilot it, links in the weapons, and makes the dragon essentially immune to turning. As dragons usually frown on the use of their young as mechanical components, there are certain dangers associated with building a Ghost dragon, which tends to drive up prices. Because of intraspecies rivalries though, most dragons tolerate existing Ghost Dragons, as once created, differentiating the source materials is impossible. The exception to this rule is that gold dragons make Ghost Dragons with a fly speed of 200. However, gold dragons also strenuously object to Ghost Dragons with a fly speed over 150, and will go quite far out of their way to destroy them.

It seems like it would be easy to stick weapons on a skyfighter, but nothing could be further from the truth. Skyfighters are extremely finicky about what weapons will integrate with their controls. Any or all weapons on a skyfighter may be employed against one target with a single attack action (which allows them to be used with Flyby Attack). A skyfighter is generally designed with pre-selected weapons, which add to the cost of the airframe to determine the total cost of the skyfighter. Each weapon slot can be made modular instead, allowing for greater versatility, but greatly increasing cost. Each modular slot costs 10,000 gold extra, but allows weapons to be purchased separately, and swapped out with a 1 hour maintenance. This is a much better idea in Wish Economy games than otherwise.

There are only three types which are in common use:

Flak is small missiles which can slowly take down anything fragile enough to be affected at all. It's a great antipersonnel weapon, and is effective against lightly armored targets, such as most skyfighters. A flak weapon interfaces with a wand of magic missiles, and activates that wand with each use. A flak projector costs 2000 gold. They can also be designed to not require a wand, which adds double the base cost of the wand which otherwise would be used (e.g. to get something which shoots 4 missiles would be a CL 7 wand, so would cost 5250×2 = 10500 gold extra). This is generally not a good option in Wish Economy games.

Air-to-Air beams were originally designed as a response to the more heavily armored necromantic skyfighters. They burn through most materials, but are relatively short ranged and require a roll to hit. An Air-to-Air Beam weapon interfaces with a wand of scorching ray, and activates that wand with each use. It costs 3000 gold. They can also be designed to not require a wand, which adds double the base cost of the wand which otherwise would be used (e.g. to get something which shoots 2 rays would be a CL 7 wand of a level 2 spell, so would cost 10500×2 = 21000 gold extra). This is generally not a good option in Wish Economy games.

Bombardier tubes are fairly damaging, but are only useful for targeting something generally beneath the skyfighter (in general, bombardier tubes may only target a square which is within one square of a square which the skyfighter passes directly above. This is not a hard-and-fast rule though). Bombardier tubes interface with scrolls of Fire Seeds, and consume a scroll with each use. Damage can be divided normally. but all targets must be within five feet of each other. Bombardier tubes can be used once every three rounds, and can hold up to 25 scrolls. They cost 2000 gold each. They can also be designed to not require scrolls, which adds four times the base cost of the scroll which otherwise would be used (e.g. to get something which does 15d6 would be a CL 15 scroll of a level 6 spell, so would cost 2250×4 = 9000 gold extra). This is generally not a good option in Wish Economy games.

“Don't talk to me about naval tradition. It's nothing but rum, sodomy, and the lash.”

A skyship is usually larger, generally on a scale similar to a sailing ship. It can only take move actions, and then only when crewed by its minimum crew. Unlike a Skyfighter, a skyship which is uncrewed or does not move simply remains stationary. However, a regardless pf maneuverability, skyship may not gain or lose more than 10 feet of altitude each round. It does not fall unless destroyed. Any passengers on a skyship not acting as crew make act independently.

A man's home is his castle. Especially up here.

A skydock is a castle built from rock or metal alloyed with aetheric ore and floating on an island of the same. While no actual structure is technically required, as a practical matter every dock has one. Every skydock is a huge chunk of alloy at least 1000 feet in diameter, though most are much larger. Skydocks do not accelerate. It is possible, though immensely difficult, to tow one to another location, and some have been fitted with enormous engines, but they are unable to change direction or speed in combat, and are completely unmoved by winds less than hurricane force. Their altitude is part is set by design, and never changes without redesigning the skydock. In the unlikely event that one is forced to a different altitude, it will “fall” up or down until it reaches the correect altitude. A skydock also has no weight limit. It is not possible to build new structures on one (or rather, doing so is the same as designing a new skydock), but anything else that can be stacked on it has no effect. Skydocks have the following effects: anything directly above a skydock with a fly speed is treated as having perfect maneuverability (this explicitly allows skyfighters to hover, and skyships to fly directly up or down). Jump checks made directly above a skydock receive a +30 circumstance bonus. Falling onto a skydock happens normally, but never causes damage. Skydocks are frequently built with very tall towers and gangplanks.

Aethric ore acts as a normal metal, but has a strong and strange antigravity effect, which is proportional to the cube of distance and the squares of the masses involved. Savants are baffled as to why this would be the case. In effect, it pushes very strongly up, produces alloys that float at very specific altitudes, and makes for very unstable skyfighters and skyships.