The longer the arrow, the less spine matters. I use long arrows with a shortbow for this reason. Just my two cents about physics.

That's fair, but you still need some amount of flexibility just to deal with the string producing an off-center force -- the arrow is going slightly to the left of the bow but the string is going directly towards it, and the only way to deal with that conflict is an arrow that bends a bit.

But the feathers? Apparently you can shoot arrows w/o, but not as well and not on a moving target

@OwenReynolds I said I'd apply disadvantage...

@Molot If you get a long enough arrow, you can actually do away with the bow! But at that point you've invented a sword.

@Fifth_H0r5eman A sharp bit on the end of a stick is a spear.

@Fifth_H0r5eman An arrow about 150% as long as it needs to be is long enough to pretty much ignore the spine value most of the time. Far from being a sword or spear.

Comments are for suggesting possible improvements. You could, if you wanted to, add to the "won't bend like wood" part how the arrow also won't have feathers or a groove to nock it.

@OwenReynolds Why wouldn't it have a nock or fletching? If you can shape an arrow, you can shape it with all the details, right? The faux-fletching might not survive into flight, but if you're getting into that kinda detail, the arrow would almost certainly shatter on release anyway.

What about a crossbow bolt? Those are usually short and don't bend as much, right?

@Cullub That's a good point! Crossbow bolts don't flex, and while they still need fletching and would likely still explode from the launch forces, if we're going with fantastical/rule-of-cool (ha!) then you could probably get away with an icicle crossbow bolt. Realistically, it probably wouldn't come up very often in play, but it could work.

-1, the improvised weapon rules explicitly state that in general you should treat an improvised weapon as the weapon it is most similar to. Disadvantage is incredibly punitive - if you like clever, as a GM, making it so the archer hits about half as much means he should likely switch to almost any other option, or simply 'buy a backpack full of arrows' (most games don't even track ammunition, making ice arrows probably a roleplaying choice on his part). Disadvantage = -5. Negates high rolls nearly always. Immense debuff. Not trivial.

@user2754 You talk like I'm not aware of how disadvantage works. Punitive is the intent! Making an arrow from ice should be a thing you might do in an emergency situation, not your everyday source of weaponry. Arrow-making (fletching) is a skilled craft, and a weird side-use of a cantrip shouldn't be able to simply replace it.

@user2754 Anyway, the improv weapon rules are weird. An improv weapon is no worse than the real thing. I don't really have a problem with using a random length of wood as a club or a sledgehammer for a warhammer since they're basically identical. But disadvantage is the correct way for a DM to handle a weaponlike object that's kinda the right shape, but not at all designed for fighting with. Many farm implements are "a stick with a sharp bit on the end", yet we as a species still went out of our way to create made-for-purpose polearms. Why? Because they work better.

The conventional wisdom is that D&D is not a physics simulator, and we have a lot of questions and answers that rely on that: rpg.stackexchange.com/search?q=physics+simulator

@DarthPseudonym Lol fair. that's on me for skimming after paragraph 2. I'll delete my first comment... BUT if you want to head off skimmers like me, I'd recommend adding a second heading for your second half to emphasize your discussion about fantasy :)

If you want to punitively punish something, why is your answer saying you like it and talking about it like it's a minor thing to apply disadvantage. That is just confusing for any reader who does not already know the math behind disadvantage.

If you already know how the improvised weapon rules work, why are you stating that there are no rules for improvised ranged weapons? You've literally said that they can only be thrown. This answer as it stands is factually incorrect and misleading - please fix these issues.

Is this more clear?

Frankly that's my problem with improv weapons that "count as" another weapon. We can say an ice arrow is an 'improvised arrow' but what does that even mean? If it's mechanically identical to an arrow, it isn't meaningfully improvised at all, it's just an arrow. Disadvantage is one of very few levers the DM can pull to make a clear distinction.