I'd never thought about it til recently, but horse archers must have had greater range because the speed of the horse was added to the arrow's forward momentum. Did arrows fired from horseback also have a greater capacity to penetrate armor?

by serenity78

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83AbleArcher

I feel like this is more of a science question and less a history one. An arrow travels about 150-200 miles per hour, depending on a range of variables in the type and manufacture of the bow. A horse can run about 25-30mph.

All things considered, not likely under most circumstances. They'd be adding a minuscule amount of force to the arrow, likely negated by the added wind resistance.

lutgholein

Sort of related piggyback question: Did horse archers actually shoot arrows while charging forward? My impression from various media sources is that they usually shot out to the left or right instead of straight.

Skookum_J

Can’t speak to historical accounts, but I can run the numbers.
Replica horse bows, using period appropriate materials, construction techniques, and matched to appropriate weighted arrows produce an arrow velocity in the range of 170-250 fps; with lighter arrows going fastest. But, if we’re talking about a battle situation, they’d likely be using the heavier war arrows. So let’s use those in the math.
With an arrow of 600 grains mass (≈39 grams), and a velocity off the bow of 200 fps (≈ 220kph), the Kinetic energy comes out to 72.8 Joules.
Now if we re-ran the numbers, but added the sprinting speed of a horse ≈55mph (88kph); you get 142.7 joules, about double the energy. This is because kinetic energy squares with velocity. But kinetic energy isn’t everything. Momentum is also a very useful measure for how much penetrating power an arrow will have. Calculating the momentum of a shot at stand still, using the same numbers as above we get ≈2.4 kg m/s; and with adding the speed of the horse; ≈3.3 kg m/s; about 35% more momentum.
So, by the numbers, shooting from the back of a sprinting horse will add some punch to the arrows.
Of course there are other factors that come in to play when it comes to actually punching through armor; is the target standing still/running away/running towards the shooter, how thick the armor is, what kind of armor, how far the shot is, how much the arrow has slowed due to drag, the angle of impact, the flex of the arrows, etc.