mmadsen said:
How high do you think "that high" is? A longbow can only launch an arrow a few hundred yards (horizontally); I doubt it could shoot straight up more than 200 yards. The aerial cavalry doesn't have to fly high enough to avoid WWII-era ack-ack; it only has to fly a few hundred yards up -- and that height adds to the energy of any missiles shot down.
You need to be able to concentrate arrow fire to win a decisive battle. You can be militarily effective without winning a big, set-piece battle.
Hoooh, boy...
That's the point. They can hit any non-hardened target at will, and they can attack with little threat from below. If they have a flying base, then they don't have to fear a ground-based attack at all.
First off, like I said earlier, if the leaders on the ground are halfway competent, they will likely have at least some limited air defenses already prepared. According to the original poster, the sky kingdom has already dealt with the ground folks and was on a friendly basis with them until a greedy new king came along. Now, the ground folks are probably a bit in awe of the sky kingdom, but any competent military leader will say, "well, they are nice to us now, but what about tomorrow?" and at least covertly prepare defenses against a possible aerial attack.
Firing an arrow from horseback takes a lot of practice and is still generally a lot harder than firing an arrow from on foot. In a strictly missile battle, 100 archers on foot will usually win out against 100 horse mounted archers, as long as the bows and arrows are equal and the 100 foot guys are not novices fighting against veterans of the Russian steppes. Firing arrows from a flying mount adds a whole extra level to the difficulty - firing straight down - as somebody mentioned above - involves leaning out over the horses wing or leaning back over the horses wing. Or, it involves the pegasus or eagle being flying straight up or straight down. Not exactly an easy shot.
The mass phalanx of pikes that Alexander the Great used (I did not see the movie...) was partly designed to deflect incoming arrows with the way they held their pikes. Now, if they know a possible air attack is coming, they maybe wear armor that protects their heads and shoulders and allow that their pikes will prevent the pegasi from physically engaging them.
Back to the original post - I don't believe he said anything about archers on pegasi. They specifically said knights in shining armor mounted on pegasi charging land based troops. If the pegasi were merely a part of the sky kingdoms army, then they can be used to great effect, assuming the sky kingdom can get their foot soldiers down onto the ground.