(Yea, I posted it on PPM as well)
Well if you didn't know already, there's a technique where you can make aircraft out of vehicles by giving them a flying locomotor** and MovementZone=fly.
When a vehicle is made into an aircraft, it allows the aircraft to follow pretty much every logic that a vehicle supports -
HVA animation, troop transport, deploying, shp, harvesting (well, sort of...), and turrets, to name a few.
This method has 2 major problems:
1 - the unit can't reveal shroud - this can be more or less overcome by making the unit MoveToShroud=no, as most aircraft are anyways...
2 - the unit is invincible during flight - due to this characteristic, this method has been mostly disregarded, as it can easily cause gameplay & balance issues.
Up to this point, I've said pretty much everything we have already found out. So what's the breakthrough? get a load of this:

I told you in Jah's heli research thread I couldn't take "no" for an answer, and after doing some research of my own, I found that the flying vehicles WERE in fact vulnerable to two things:
>Firestorm defense, but more importantly:
>Railguns!
By making the railgun projectile AA=yes, they can successfully target, damage, and destroy flying vehicles!
Granted, it's not an ultimate flawless solution, as you'll need to make all your AA guns into railguns - but the important thing is that it's that it's possible, and that there IS a way to make hva anims, air transports, shp vehicles, and all that other cool stuff, without sending gameplay and balance to heck.
Dogfights? sort of.
I made these planes play a game of chicken - only one of them fired though, one time, then after that they just sat there floating. I had to order it to attack before it would fire again.

It should be also noted that they can shoot at stuff while landed (though the airplanes themselves don't need to be armed with railguns, of course

)

**I've found that the jumpjet locomotor is best - the actual
aircraft loco makes the unit get stuck on the war factory bib, unable to move, and disabling further warfactory production.

Selling/undeploying the warfactory frees the aircraft, but I would deem it too unpractical to do that for each new aircraft that you make -
it should be noted, also, that units with the the jumpjet locomotor take a decent amount of time to "get out" of the warfactory, meaning, that no other units can be produced while it's exiting the War Factory. I'd advise giving your aircraft some good speed and/or editing the [jumpjet controls] section, to achieve the most desirable result . This means, that this method would be best for things like helicopters and hot air balloons, but probably not for actual planes.
>If you found any of this useful, please be sure to let me know, it did take some testing till I achieved this info, thanks