I don’t think the defensive ramifications of fantasy air power would be nearly that extensive, Gary, unless there were flying ships or citadels involved that could deposit large numbers of troops. Plus, I don’t think anyone is yet talking about massive numbers of hot air balloons or dozens of units of pegasi cavalry.
In other words, without the ability to deposit large numbers of troops quickly in any one area, fortifications don’t really need to change. The relatively tiny numbers of troops flying mounts might be able to deposit on or beyond walls would very quickly be slaughtered by any reasonable garrison. That’s also assuming that the mounts can either land safely to deposit troops (unlikely due to withering archer fire), or that those paratroopers can have access to feather fall or parachutes. Given the flavor of BR, I doubt either of the latter would or should be an option. Therefore, no paratroopers.
With no paratroopers, then you need only be worried about aerial bombardment and strafing aerial lance charges. Bombardment presents a problem because large amounts of weight can’t be carried aloft easily, particularly not without sacrificing maneuverability, speed, and altitude, the chief advantages of flying units. So only a few sacks of stones or flasks of oil would be likely, and the impact of the attack rather minimal, probably less lethal than a cloud of arrows. Archer fire from above would be a better option (requiring fewer landings to pick up more ammunition), but couldn’t amass the density of arrows that a land unit can manage because the flying units simply can’t array themselves in that kind of density, and their speed makes aiming an even less likely alternative.
That leaves aerial lance charges. These could truly be devastating, as a skilled flying unit could lower long lances and attack any non-polearm-wielding land troops with very little exposure of their own to attack. Further, a strafing charge exposes the entire land unit to attack, not just the front lines of it first, allowing the aerial unit to attack from any angle, any flank (hit the rear and the side that side that holds only a column or two of right-hand shield bearers).
I think the primary impact of aerial cavalry would be 1. Far-ranging scouting with no respect for fortifications, garrisoned troops, or borders; and 2. Massive morale impacts (not to be taken lightly!)
Fortifications need only construct wooden hoardings (typical technology for the period) and maintain archers in order to mostly nullify aerial troops. They won’t be effective against such fortifications.
I would say the typical battlefield statistics would need to include a special rule for Charging, Movement, and Morale impact, but otherwise the unit would be pretty weak. Yes, it’s kind of clumsy to have three special conditions for one unit, but aerial units are pretty different. Archers would get their normal bonus against them, and others would if they were in range.
Base: 4.5GB +2 Melee, +0 Missile, Defense 10, Move 6, Hits 2, Morale +2, Special: -2 to morale of all enemy units, +2 morale to all allied units; roll morale twice for the target of any hit inflicted by the aerial unit and take the lower result.
Typical units would probably be mustered as Scouts or Elites or both, having these stats:
Aerial Scouts (LtSc): 6GB, +2 Melee, +4 Missile, Defense 12, Move 9, Hits 1, Morale +4
Aerial Knights (EliteMed): 7GB, +6 Melee, +2 Missile, Defense 14, Move 7, Hits 3, Morale +6
Aerial Harriers (EliteMedScTgh): 9GB, +4 Melee, +4 Missile, Defense 14, Move 9, Hits 3, Morale +8
Special rules for all aerial units:
Overland movement is not limited by terrain, fortifications, or presence of units in a province (except other aerial units).
Aerial units may not be heavily armored.
Most aerial units are either considered to be either hippogriffs, pegasi, or giant eagles, or a mix of any of those. Griffons, wyverns or other units are exceedingly rare as they must be pure units mustered at an additional +4GB cost. These have base statistics of: 8.5GB, +4 Melee, +0 Missile, +12 Defense, Move 4, 3 Hits, Morale +4, same Special power.
All aerial units have 4 Attack Ranges:
- High Altitude = cannot be hit by any attacks, Unit Missile attacks can be made at -2 penalty;
- Low Altitude = can only be hit by missile attacks, Unit Missile attacks at no penalty (no melee);
- Strafing Charge = can only be hit by missile and pike attacks, Unit makes Melee attacks at +2 (for charge)
- Melee = unit lands, is vulnerable to all attacks, can use any attack form.