A power arrow draws energy from a force crystal in its tail. The force crystal in turn is heated by combustible material inside the arrow's hollow shaft. Once the interior of the shaft is ignited, the force crystal converts that heat into mechanical energy, blowing a stream of air out the tail of the arrow. This in turn draws fresh air in through vents located in the arrowhead. The effect is similar to a rocket, but much more efficient. In addition, the direction of the exhaust can be adjusted easily, making the power arrow a feedback-guided projectile and thus much more accurate.
A power arrow is ignited by a match attached to a cord attached to a hook inside its nock. When the arrow is nocked, the hook is wrapped around the bowstring. When the arrow leaves the string, the cord is yanked out of the shaft, pulling on the match. The friction from the match ignites the interior of the arrow, and the heat from this activates the force crystal, thus activating the projectile and its guidance system. Once the guidance system activates, the arrow flies in a straight line until it runs out of energy. After that, it continues on a ballistic trajectory, but even then has much more range than a conventional arrow because it is moving so fast.
The main purpose of power arrows is to allow bow-equipped archers a means of returning fire against longer-ranged weapons such as ray crossbows. It also allows them to attack targets that would otherwise be able to stay out of their range, such as wingknights. Since bows provide a good rate of fire and solid punch when equipped with magic arrows, giving archers a handful of power arrows significantly increases their tactical value.
Power arrows are usually given powerful enchantments on their tips; they are usually designed to explode upon impact. However, because power arrows are so much faster than their mundane or unpowered counterparts, they can deliver a deadly punch by brute physical force alone. An arrow is, after all, much heavier than most other projectiles that would normally be going so fast. Power arrows typically go at high subsonic speeds (~600 mph); they are capable of going much faster, but are limited because arrows are not aerodynamic at supersonic speeds. Even at high subsonic speeds, a normal arrow will penetrate body armor without any real difficulty.
Wingknights usually carry power arrows as their sole ranged weapon. This is important because they usually fly too high to hit targets otherwise; using normal arrows at altitude would otherwise render the bow redundant, as a normal arrow will simply drop nearly straight down regardless of where it is aimed. A power arrow, in contrast, flies where it is aimed regardless of range. Also, power arrows are fast enough that a wingknight does not have to worry about outrunning his own shots. Occasionally, one will also find actively guided (homing) power arrows, which represent an attractive alternative to melee combat. However, such arrows are expensive, and the homing mechanisms on them are difficult to use (they require the user to guide the arrow in) and are not especially reliable.