How could the Kobold Cannon's munition work?

Question

"That is a weapon, NOT a teleporter" - Samuel "Whyamieventrying" Hayden

The concept is fairly simple. You have a crazy, but crazy talented kobold inventor with lots of spare time and junk. This kobold really wanted to get into a science festival. Unfortunately, the event is hosted by humans and in this world, humans don't really like kobolds, or demi-humans, or...

Anyway, the kobold decided to take revenge and get into the festival Aaand dominate it by launching himself over the audience's heads (some parts of the festival are held outdoors) and safely descending into the crowd with a parachute.

So, the invention, he intends to launch himself with, is the Kobold Cannon. The KC is a mobile portable coilgun of the kobold's own design. The cannon and the power source have to be carried separately and assembled on-site.

The primary purpose of this cannon is to safely launch fragile and even perishable cargo over long distances. It could revolutionize toilet paper delivery and bypass the defenses of Győrfi Pál (last time I checked he wasn't able to fly, I swear!) if it worked correctly.

Obviously, the kobold has to use a multi-stage coilgun, as a railgun would zap him out of existence.

1. He also has to find a lightweight, magnetizable carrier and a lightweight carrier (weight!=density) projectile,

2. come up with a way to discard the magnetic carrier once its payload exits the cannon,

3. and have the parachute open automatically when near the target.

4. Not to mention, it's important to minimalize the drag of the carrier projectile.

The power source is given, graphene supercapacitors, a diesel generator and lots of patience. What I'm having trouble with is the structure and composition of the carrier projectile. How could it work reliably and as efficiently (minimal weight and drag) as possible?

While I assume the kobold can build just about anything, simpler mechanisms are, of course, better.

When it comes to range, I didn't really have any concrete numbers only an "as far as it can travel". I think if the cannon can deliver cargo to a point, 1-2 kilometers away. That's sufficient.

As far as cargo weight comes, 50 kg should be the maximum, the cannon could safely launch.

Answer 1

This coilgun may be slightly buildable, but it will be enormously impractical, and the exact opposite of mobile.

It turns out, actually building the coilgun is not the main problem. (Although, it is a problem.) The main problem is that a gun is not a very good means of accelerating a person.

When a projectile is shot out of a gun, it is briefly (over the course of milliseconds) subject to enormous accelerations. If you tried to put a human - or presumably a kobold - through those kinds of forces, they would die. That's why Jules Verne was wrong and you can't shoot someone to the moon in a cannon; you need a rocket that accelerates people over a longer period of time. The limit for human survival for short periods is usually quoted at around 10 Gs - 10 times the acceleration of gravity, or ~98 m/s^2. In contrast, electronics built for artillery shells are rated to survive up to 16500 Gs.

A typical tank gun, say the main gun on an M1 Abrams (in the first green-shaded cell under "Technical Data") fires 120mm shells that are accurate to about 4 km. To do that, it achieves a muzzle velocity of 1,575 m/s. Your kobold probably won't fit in a bullet-shaped housing 120 mm wide; it will probably need to be more like 300 mm, which will increase drag a lot. But for now, let's assuming 1,575 m/s is the target velocity.

(Incidentally, this means your flight time is going to be a handful of seconds, at best. Slowing down at the end might be slightly problematic. You can launch yourself on a ballistic trajectory, which is safer but will require a much higher initial velocity since you're subject to drag for longer.)

If your projectile accelerates at a constant 98 m/s^2 down your coilgun barrel, it will take 16 seconds to come up to speed. However, in those 16 seconds, it will travel 12.6 km. (Assuming constant acceleration, its average velocity is half of its maximum velocity.) Since your coilgun stops imparting force once the projectile leaves the barrel, it needs to be 12.6 km long. Needless to say, that's not going to be "mobile" by any description.

All things considered, your kobold is probably better off with one of those quadcopter bathtub rigs.

Answer 2

This will be exceptionally inefficient

Given a finite but enormous power supply as specified by the OP, the critical limitations are the launching G-force and the aerodynamic characteristics of the projectile. Unfortunately, these two characteristics combine very badly in this problem due to the extremely light payload.

As pointed out in Cadence's answer, the human body can survive briefly sustained G-forces of about 10G (Assume kobolds have the same tolerance). However, forces this high are only survivable if the body is oriented correctly - basically if a person is lying on their back with their legs slightly raised. Assuming that a kobold is proportioned roughly the same as a human child massing 40ish kg, this means that the base of the carrier projectile needs to be about a metre across. Which means that the bore of the cannon must be slightly over a metre in diameter to allow for the thickness of the carrier projectile walls.

Note the massive amount of empty space in the carrier projectile. This is bad because it means that the projectile has very low density and will decelerate relatively quickly in air compared to a more dense projectile. Given that the OP has specified that there are no limits on the launch cannon's power, the brute force solution is to make the walls of the capsule heavy in order to increase the density of the carrier, although there are limits or the parachute required to allow a safe landing will be enormous. Making the capsule out of 3 mm steel sheets will add about 100 kg to the mass of the carrier, plus a bit more will probably be required as supports in the nose cone to ensure that it does not collapse, invert and impale the kobold on launch. Total mass of carrier plus payload plus parachute will be in the 150-180 kg range, so the required parachute will be slightly larger than used by an airborne soldier (assume 90 kg soldier with 30 kg of equipment). A projectile with these characteristics launched at 45 degrees with a velocity of 150-200 m/s should make it about 1 kilometre, further with a good trailing wind or by making this a base bleed projectile. This will require a cannon between 113 and 200 metres long with a bore of 1 metre.

(For those thinking that the base needs to be reinforced or it will pop out under 10G acceleration - this capsule assumes that the magnetizable carrier described in the question is a separate component behind the carrier projectile that sits behind the projectile and evenly supports the entire base while the carrier is accelerating the projectile out of the cannon.)

Alternative configuration

The above design looks at maximum survivable acceleration in order to minimise the cannon length to a mere (!) hundred metres or so. If a longer cannon is somehow feasible then the carrier projectile diameter can be reduced to around 40 cm if the kobold is sitting with their backside and feet on the base with their knees drawn up to their chest. There is a shortage of studies regarding the survivable limits of kobolds or equivalently sized midgets/children being accelerated in this pose [citation needed] but assume 6 G can be tolerated. In this case a more dense projectile with better range characteristics may be used, but the cannon length is now over 300 metres.