Firing a Cone Down

[The Demented One]

Is there any place in the rulebooks that talks about a flying creature firing a spell with a cone-shaped area down on creatures below it? I'm trying to figure out the area it would hit; would it just be a spread with a radius equal to half the width of the cone at the point it hits?

[Maerok]

Seems reasonable enough. I wouldn't expect anything else to happen.

[Tempest Fennac]

I agree with Maerok: I remember a Warlock guide saying that firing Eldrich Cone down at enermies using Fell Flight is a good stratergy.

[The Demented One]

That would be a nifty way for a clever spellcaster to get around having to aim the cone around his allies. Mwahahaha....

[UglyPanda]

I always thought firing down would be a cool thing for a dragon to do. I approve and believe that that is how far the cone should spread if you're exactly above the height of the cone. The radius should be half the distance from the caster, if I remember the shape of a cone correctly.

[Arbitrarity]

Just please, don't try angle calculations for anything past vertical, and maybe 45 degrees. That would be painful.

[Rumda]

Just use what ever method you usually use for areas affected by cone shaped spells, the templates in the back of the dmg for example and just use your height above the ground as the length and then treat it as a spread with half the width as the radius, in fact looking at the templates a 30' cone directed down at a height of 20' will have a radius of 40'

[Chronos]

in fact looking at the templates a 30' cone directed down at a height of 20' will have a radius of 40'I'm not sure how you're getting that... The diameter of the cone will be 20', same as your height, so the radius would be 10'. If you fire from maximum height, the number of creatures effected actually works out to be more or less the same as if you had fired from ground level (plus or minus a bit, due to the granularity of the grid), just arranged differently.


Just please, don't try angle calculations for anything past vertical, and maybe 45 degrees. That would be painful.Why, do you have something against conic sections? A bad experience with a hyperbola, maybe?

[The Demented One]

Why, do you have something against conic sections? A bad experience with a hyperbola, maybe?
Dude, not funny. A street gang of points killed my brother. Damn degenerates...

[brian c]

Dude, not funny. A street gang of points killed my brother. Damn degenerates...

Hm... I don't think there's any way to have a cone spell take the shape of two intersecting lines. Damn.

[Fizban]

Well, technically we aren't actually using a cone, since the 2d area of the cone is actually defined as a 1/4 circle swept out from the caster, with the radius defined by the spell (eg: 15' cone=quarter circle with radius 15'). So, the maximum diameter we can affect by firing straight down will be be defined as the hypotenuse (longest side) of a triangle, where two of the sides are the radius of the quarter cirlcle/cone, r. That diameter will be (2r^2)^(1/2), the square root of (twice the (radius squared)). This maximum is achieved by firing the cone from a height of (1/2r^2)^(1/2), or the square root of (one half the (radius squared)).

I think, someone wanna double check? I just ran it through the pythagorean theorem a couple times.

Edit: in regards to the first post, that's right. The problem is figuring out how wide the cone is when it hits, since it's not even actually a cone in the rules. You probably know how to figure it out, but other people can use what I've figured, assuming it's right.

Edit2: actually rules-wise I'd probably rule it as striking only downward, like a cylinder, since IIRC cones are defined as a burst, except in a quarter circle instead of a full circle, which means that an obstacle will create a "shadow" in the effect.

I'll also take this opportunity to comment on 1: the fact that all cylinders are defined as striking downward (arbitrary much?), and 2: that fireballs as spreads annoys the crap out of me, you can't duck for cover, because it's actually napalm that flows into every crevice in the area, instead of just being an explosion. /layperson with no experience whatsoever with explosives.

[nerulean]

There's a picture in the Draconomicon that became iconic of the campaign we played with dragon PCs: it showed the effects of a dragon breathing fire straight downwards, and was captioned with the term "Blast radius". It was indeed circular.

[Prometheus]

Beat me to the geometry post.

The thing that I always think about is that no matter how fast or magical things are, they would still be affected by compression and gravity:
-A fireball in a dungeon should have the same area as open air, not the same radius (burning everyone to a crisp like a potato cannon).
-A cone of cold shot downward should stretch longer than one shot upward.

Apparently D&D describes these spell's radiating from their point of origin (often the caster's fingers) sequentially flowing across its targets from inward out, but instead it effects an arbitrary geometric area from every direction simultaneously. If that's the way magic works are all the symbols and arcane secrets just basic geometry diagrams and grade school math?

[Icewalker]

Hyperbolas are evil. Pure evil. With evil little asymptotes and a and b and foci and....

Stupid hyperbolas...

Yeah, firing a cone straight down should be relatively simple. It spreads outward with a 90 degree angle, right? That'd mean that the radius of the circle would decrease at the same rate as the height.

[Skjaldbakka]

Indeed, the radius should be equal to the height. Firing cones down can make for a good area. Especially in Arcana Evolved, where there is a spell called Deadly Spray that turns the next Line spell you cast into a cone, and a spell called Forcebeam, which is a line of force with a range of medium. Talk about a ginormous area! Of course, both spells are exotic, but it is a heinous area of really high damage. With secondary effects.