Got a question for any knife throwers

[Shannon Davidson]

Hello, My name is Shannon Davidson, and I am an urban/epic fantasy writer. I'm currently working on a scene in my novel where one of my characters is trying to teach a young man how to hit a high target (15 feet) with throwing knives. The kid can do it at eye level, but doesn't seem to be able to judge the throw at an elevated height. (Yes, there's a reason).

His mentor claims that nothing is different, the rotation is the same, the distance is the same, the technique is the same, etc. But I don't think that's right. If a target were raised to 15 feet high instead of at eye level, how would you make the adjustment? If it's higher, I believe there would be a greater distance to the target. Correct? If so, how do you compensate?

(Pretty sure this is one of those geometry/algebra problems my math teacher warned me about.)

Thanks for any thoughts.

 

[Yalius]

It depends on the distance measured along ground level. If you're looking at a distance of 15' as measured along the ground, then raised 15' above ground level, you're looking at a distance to target of 15*(square root of 2) feet, or 21 feet, roughly. The longer the distance along the ground, the proportionately smaller the difference based on elevation. This part is pretty much Pythagorean theorem using a right triangle where the square of the hypotenuse (distance through the air accounting for elevation) is equal to the sum of the square of the other sides (distance along the ground+difference in elevation).

You're also working against an acceleration vector due to gravity as well, that decelerates when thrown along a non-horizontal vector. At an elevation angle of 0 degrees, there's no significant contribution to the velocity of the thrown object due to gravity, since the initial velocity is strictly orthogonal to the acceleration vector due to gravity. However, when thrown against gravity, i.e. upwards, gravity will decelerate the thrown object by a factor of sin(θ)*g/sec. So a thrown object moving at an initial velocity of, say 30 m/s at an angle of 45 degrees at a target a distance of 15 meters away needs to cover a distance of 21 meters (and these next values are pretty rough, I'm not accounting for arc of the thrown object) in a time of (again, roughly) .7 sec, which will result in a velocity of 25.2 m/s when it reaches its target.

It's actually a bit more complex than this, and the ballistic arc of a thrown object really needs to be modeled using calculus rather than strictly trigonometry, but it's probably rough enough for fiction.

Now the disclaimer, I am not a knife thrower, and have no idea regarding the usable range of a thrown knife nor the velocity. I just chose the above values for ease of calculation.

 

[Shannon Davidson]

Thank you, I understand those concepts. I shoot, and figured the issues shooters deal with as far as gravity/drop over distances would be similar.

So I guess now what I have to figure out is, how do you correct for this? What is it that this guy tells his student to do to compensate? Does he shift his stance, throw straight vs a spin? Does he adjust his release to add another turn?

Thanks for the advice!

 

[Shannon Davidson]

Thank you, I understand those concepts. I shoot, and figured the issues shooters deal with as far as gravity/drop over distances would be similar.

So I guess now what I have to figure out is, how do you correct for this? What is it that this guy tells his student to do to compensate? Does he shift his stance, throw straight vs a spin? Does he adjust his release to add another turn?

Thanks for the advice!

 

[BitingSarcasm]

Changing the height changes a lot. Knives and axes are already following a parabolic arc in order to hit a target at roughly man height. You can adjust the parabola upward to hit that 15 foot target, but now the throw is farther; picture a right triangle, and instead of throwing the 3x or 4x leg of it, you are throwing the 5x hypotenuse distance. If you are rotating the throw, distance is a critical variable. A foot isn't really a big deal if the aim and rotation are in the right ballpark, but a shot that would have gone barely point in would be bouncing. The target also won't be face on with the thrower, it will be encountering the thrown object at a point that is different from the normal throwing trajectory.

I can adjust my throw by eyeballing the distance and letting the muscles do their job. I couldn't do this when I first started, it took time to build up muscle memory and a database in my head. I could probably figure out the mechanics of it with an afternoon of practice, but it wouldn't be something I wanted to try for the first time if my life depended on it. I would need enough practice throws to see how the thrown object behaved to figure out the best way to get the pointy bits in the target.

Your mentor would need to tell his student to throw harder, account for the longer distance if he is going to rotate a throw, and practice first. A lot. Throwing with as little rotation as possible would give the best chance at getting a sticking angle. Choosing the right tool would be a good idea, too. Throwing spikes lack mass and would be tough to get to travel longer distances accurately. Knives have more mass, but still are limited by having a pointy end that has to hit first. Hawks and axes have plenty of mass to hit hard, but getting the rotation right is important unless you just want to bludgeon. Something like a Hurlbat or Japanese Shaken with numerous points would give better chances to penetrate. Or skip the whole mess and throw a Chakram--never thrown one, but they look like a lot of fun and the edge is always out.

 

[danbot]

I think the mentor would tell the student to look where you want the knife to go, throw, and then repeat until perfection.

 

[bobobama]

Not an answer to your question, but it piqued my interest. Not too long ago I bought a book entitled "The Writer's Guide To Weapons", subtitled "A Practical Reference for Using Firearms and Knives in Fiction" by Benjamin Sobieck, who has a fairly extensive resume of writing/reporting about crime and weaponry.

I found it semi-interesting, but then I'm not a writer. You may find it more useful and might want to add it to your library if you haven't already.

 

[afishhunter]

Throwing spikes lack mass and would be tough to get to travel longer distances

I dunno ... my CS "Torpedo" throwing spike at near 5 to 8 pounds has a wee bit of mass.
I'm pretty sure if I dropped it point first from waist height onto my foot, it would ventilate my leather boot, sock, and foot ...

 

[eveled]

If I was to throw at something above my shoulders I’d throw underhand.

 

[BitingSarcasm]

I dunno ... my CS "Torpedo" throwing spike at near 5 to 8 pounds has a wee bit of mass.
I'm pretty sure if I dropped it point first from waist height onto my foot, it would ventilate my leather boot, sock, and foot ...

I almost brought it up under a category of "oddball," but didn't go there. I used to throw these super large old chisels, screwdrivers, and assorted pointed metal junk with a similar idea that the end result would be spectacular even if they didn't stick. Old tire irons with a pry bar on one end are also a lot of fun, as are crowbars under 18 inches or so.