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Imagine when a jet fighter swoops in to drop a 400 pounds giant chainsaw to you just so that you can use it to grind down one problematic enemy into a pulp then discard it a foot away from you. What power source would suit such a weapon with only 1 instant use before breaking itself apart?

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    $\begingroup$ This whole concept seems unwise to me. 400lbs is crazy amount of weight to wield, which assume the chainsaw survives landing, and it lands near you. Range is way too close to have a problematic enemy for my comfort. Instead how about 100lbs or so of frag grenades or similar you can use from a safe distance. Range, damages, easy to use, and multiples can be deployed to same target easily. $\endgroup$ – cybernard Apr 9 at 15:01
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    $\begingroup$ @cybernard The whole concept is batshit insane. It's obviously intended for a fictional universe driven by the rule of cool and not by rationality. $\endgroup$ – Philipp Apr 9 at 15:11
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    $\begingroup$ @Philipp there is rule of cool and there's stuff that breaks the suspension of disbelief. I do believe that with chainsaw planes, any hope for realism goes right out the window... which doesn't necessarily make the resulting fiction bad, but it does make the need for defined inner workings quite a bit less necessary. $\endgroup$ – John Dvorak Apr 9 at 15:23
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    $\begingroup$ In a universe where coolness trumps sanity when it comes to conflict, chainsaw planes make perfect sense. As do superhero landings (They’re hell on the knees), giant floating air fortresses and flashy uniforms with the underpants on the outside. Basically this is the kind of thing any superhero film could benefit from. $\endgroup$ – Joe Bloggs Apr 9 at 16:40
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    $\begingroup$ I initially read this as the jet dropping the chainsaw directly on the enemy, which is also awesome. $\endgroup$ – ReinstateMonicaSackTheStaff Apr 9 at 23:10

20 Answers 20

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Giant coiled spring.

It would uncoil itself and drive the chain. It would provide loads of power on demand. Storing that kind of energy as a coiled spring is dangerous, but I see that as a positive thing for your scenario.

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    $\begingroup$ +1 for being rechargeable $\endgroup$ – Trevor Apr 9 at 12:25
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    $\begingroup$ I like this. It's not very realistic, but it sure as heck is cool.. $\endgroup$ – John Dvorak Apr 9 at 17:03
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    $\begingroup$ @JohnDvorak Ah yes, the quest for a realistic power source for a single use jet-delivered chainsaw. $\endgroup$ – corsiKa Apr 10 at 1:03
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    $\begingroup$ I like it as super practical. Any electric source requires an electric motor. This is the energy source and the source of rotational motion, all in one package. $\endgroup$ – cmm Apr 10 at 3:17
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    $\begingroup$ Spring tension can hold the drive train together as well. When the spring looses tension it could literally fall apart as the question suggests. If you've ever taken apart a tape measure and had a part slip out of your hands you'll get what I'm talking about. $\endgroup$ – JPhi1618 Apr 10 at 3:43
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Pyrotechnics, in the form of twin spinning rockets rotating the saw axle. You have jet fighters, missiles would look like an obvious option. And as a bonus, a faulty device would explode throwing shrapnel into the enemy.

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    $\begingroup$ I think I like this, not because it is the best answer, but because it is sooo bad that it fits perfectly with an air-dropped, single use, 400lb chainsaw. $\endgroup$ – Nosajimiki - Reinstate Monica Apr 11 at 6:17
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Capacitors. These are electric components which store an electric charge for a limited amount of time and can release it very rapidly. They are relatively cheap and easy to manufacture. They are also reusable, but that doesn't matter in this case.

Capacitors can be manufactured in many different ways depending on their desired characteristics. But in general they have a lower energy density than chemical power cells, but they can release their stored energy a lot faster.

Capacitors are usually not designed to hold a charge for longer than a couple hours, so the capacitors either need to be charged before the mission or during the mission from the fighter's internal power supply.

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    $\begingroup$ "... usually not designed to hold a charge..." ?? Depends drastically on the application. Whatever you do, never touch the flyback capacitor on a CRT without shorting it first. They hold significant voltage for years. $\endgroup$ – Carl Witthoft Apr 9 at 13:19
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    $\begingroup$ @CarlWitthoft, years is a bit of an exaggeration. The self discharge rate of capacitors (as in no bleeder resistors) is still in the range of days. Supercapacitors have a lower self discharge rate but is still not remotely in the realm of years. Though, I'm always happy to be wrong, I did some quick checking but maybe I missed some edge case where that's true. $\endgroup$ – Jarrod Christman Apr 9 at 14:54
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    $\begingroup$ Capacitor 'hold time' depends on design and materials used. While they'll slowly leak it is well within the realm of possibility to design such a capacitor that could be charged on loading of the weapon and last for a 6-12 hour mission with useful load. Also keep in mind that 'discharged' doesn't always mean 'empty' - Very large caps can still hold enough to give you a solid kick years later, even if they're well below 'useful' levels that it was intended to be used at. In short: Don't lick caps. $\endgroup$ – TheLuckless Apr 9 at 15:03
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    $\begingroup$ I updated the answer in light of the recent comments. $\endgroup$ – Philipp Apr 9 at 15:06
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    $\begingroup$ @NathanHinchey, almost all capacitors that 'hold a charge' years later have actually self-charged, just a little bit. Industrial capacitors have to be stored with the terminals shorted out or they can hurt the next person who goes to touch them. There's no useful power really, but they can get to a couple of percent of their voltage rating if you leave them alone. $\endgroup$ – Sean Boddy Apr 10 at 13:20
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Launching from a plane, that chainsaw is going to waste a lot of nice gravitational energy, which could be used for much more interesting tasks, such as providing motion to the chainsaw itself.

So, the chainsaw itself is tethered to the plane with a very long roller chain, which is connected to a pinion inside the chainsaw (think of a Beyblade launcher).
When launched from the plane, the chainsaw falls, so that the roller chain makes the pinion start rotating. The pinion will then transmit the motion to the chainsaw, so that it will rotate at full speed when touching ground!

Alternatively, a parachute could open and hold a reel with the roller chain tethered to the chainsaw, which is still falling relative to the parachute.

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    $\begingroup$ basically a flywheel, charged by gravity $\endgroup$ – ChuckCottrill Apr 10 at 18:00
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    $\begingroup$ This could cause the chainsaw to fall more slowly, as some of it's gravitational energy is being co-opted to spin it. How about letting the chainsaw fall with a slack roller chain, then when the person catches it, the roller chain, which is still attached to the jet, gets yanked away by the jet, starting the chainsaw. Like a combination of launching a beyblade and using a string attached to your dog's collar to yank a loose tooth out. $\endgroup$ – Jared K Apr 10 at 18:08
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    $\begingroup$ +1 for beating even the "pyrotechnics" answer in how ridiculously entertaining it would be to see. $\endgroup$ – mtraceur Apr 11 at 19:58
  • $\begingroup$ As the person who wrote the pyrotechnics answer, I can't but totally agree with mtraceur. This is better cool-for-buck hands down. $\endgroup$ – Dan Fernandez Jun 6 at 16:25
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I would go for a pneumatic solution. It can support easily a 40 pound high pressure container storing sufficient energy for 15 seconds.

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    $\begingroup$ Also consider the giant farting sound on, ahem, discharge. Use methane as the gas, and then light the exhaust, and use the flame jets. IDK how, but use them. $\endgroup$ – Neal Apr 9 at 20:19
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    $\begingroup$ @Neal simple: what's better than a chainsaw at maiming your enemy? The MurderCo Rocket-Propelled Chainsaw (patents pending)! Why use measly human (or whatever other species) appendages to thrust your chainsaw into your enemy when our patented diverters use the combustion exhaust to launch it at your enemy? Warning, adult supervision required, MurderCo is not responsible for loss of limbs or life, property damage, or damages caused by Acts of Stupid (which includes all actions taken using the MurderCo RPC). $\endgroup$ – Doktor J Apr 9 at 20:37
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    $\begingroup$ A flatulentic turbocharged curled discharge. Are we still talking about Taco Bell? $\endgroup$ – Juha Untinen Apr 10 at 6:26
  • $\begingroup$ The tacos in the chainsaw's taco dispenser gotta come from somewhere. I can see Taco Bell doing fine as the preferred taco contractor. $\endgroup$ – Neal Sep 3 at 14:28
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While the question does not explicitly specify this, I think it is reasonable to specify some, er, specifications.

  • Extreme energy density. The goal of this weapon seems to be to deliver as much destruction as possible in 15 seconds, in a 400lb package which is probably the weight limit for the weapon stores on the jet. It is desirable that the majority of this 400lb is gnawing teeth of mushy annihilation, and only a small part is fuel and power source.

  • Extreme reliability. If a air-dropped 400lb giant disposable chainsaw seems like the best way out of a situation, you are probably in deep, deep trouble. You don't want to be yanking a starter cord on a dodgy two-stroke while the Tentacles of Kaza'An the Soul Destroyer of Mag-Uhn squeeze the life out of your fellow unlucky party members. You shouldn't have to carefully lubricate the moving parts of your jammed chainsaw while the Teeth of Brig-Wrath the Extirpator of Zw'n-Thragg dismember your group members. You want to have instant destruction available the moment you receive the weapon. You might even want to be able to use the device on Frizhger the Mauling Shark-Fish, submerged in the Sea of Despair.

Obviously, air-breathing engines are no good, what with the underwater Mauling Shark-Fish (also, the torrential rains on Zw'n-Thragg!). Electrics are really not great either - they require careful isolation from the environment, and frankly, the energy density of batteries is quite terrible - you don't want to run out of power halfway one of Kaza'An's Tentacles.

The obvious solution is a hydrazine turbine engine. Hydrazine is an extremely reactive fuel, that does not need an external source of oxygen. It is used as a rocket fuel (where energy density is key). A turbine engine probably has the highest power-to-weight ratio of any rotating engine, and furthermore it only has a single moving part, which can be connected with a single reduction gear to the saw chain. The reaction products of running hydrazine over a catalyst such as iridium are extremely hot nitrogen and hydrogen gas, the latter of which can also combust once it does come into contact with the outside air.

The end result is a screeching whining chainsaw of death spitting blue flames from its exhaust. Chances are the extirpation days of Brig-Wrath are soon over.

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  • $\begingroup$ I like your logic, but why bother with the complexity of a turbine and reduction gearing when you could put hydrazine rockets on the chain itself $\endgroup$ – Robin Bennett Apr 10 at 14:46
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    $\begingroup$ @Robin I considered that but half of the rockets will be facing the chainsaw operators. An alternative is to have a rocket pointing directly at the chain but in these case the chain needs to be a compromise between gnawy teethiness and power transfer. All in all I liked the turbine option best. $\endgroup$ – Sanchises Apr 10 at 14:53
  • $\begingroup$ +1 for pointing out the kinds of circumstances required for this kind of weapon and delivery system to even be considered. $\endgroup$ – Perkins Apr 10 at 18:14
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    $\begingroup$ @MerseyViking No need to be so negative! The decomposition products of hydrazine are hydrogen, nitrogen and ammonia. Only the latter is mildly toxic in elevated quantities, but does not case acid rain. The only real problem is the Miak Salmon infestation - a rare fish that uses proton pumps in its gills to convert dissolved ammonia to a liquorice-like substance dubbed Sal'Miak by the local population. $\endgroup$ – Sanchises Apr 11 at 8:42
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    $\begingroup$ After reading this comment I thought to myself: surely some unwise person has tried putting Hydrazine in an ICE, right? Yep! Drag racing pioneers or suicidal nutjobs? $\endgroup$ – Avi Cherry Apr 11 at 18:26
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As an alternative to coiled spring you can have your own gyro core (or flywheel).

Make a small and dense wheel to rotate very fast on pins in your chainsaw, virtually without energy loss, and then give it all away to chain blades. After it is discharged it becomes a useless piece of metal without any electronics or stuff. It is also much safer to operate than coiled spring.

If anything it will also stabilize delivery of this chainsaw.

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    $\begingroup$ Trying to manoeuvre such a weapon would be nigh on impossible if you used it to store any appreciable energy, surely? $\endgroup$ – Joe Bloggs Apr 9 at 16:44
  • $\begingroup$ You could put your gyro core into gyro stabilizer, which will let you handle such weapon. Or maybe it's not even necessary given the question details. $\endgroup$ – alamar Apr 9 at 16:46
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    $\begingroup$ Probably storing the spun up weapons in opposite-spun pairs always would compensate some unwanted effect AND stabilize your aircraft? $\endgroup$ – rackandboneman Apr 10 at 1:39
  • $\begingroup$ Just use counter-rotating gyros. $\endgroup$ – RBarryYoung Apr 10 at 2:47
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Well if you only need it very briefly I'd recommend a power cell.

Where batteries provide a slow trickle of stored energy over time,power cells can dump all of their energy in an instant. So that chainsaw purpose built to be disposable but very deadly could literally be torn apart from the energy it exerts in its short period of activity.

Also this means that being disposable the chainsaw would be made of cheaper materials. Since the power cell never needs to be replaced as it is a one-off use it can be made non-rechargeable and self-destructing. Not in the way it blows up when used, but it burns out the internal storage from the incredible heat and shock of the energy release.

All in all, the chainsaws shall exist. And they shall be terrifying. Maybe just make the edge out of carbon nano-tubes? Nano-tubes can also be used to store energy within their mass much like batteries or power cells. So you could literally make the chainsaw one giant power cell made of an extremely energy dense but light material that at 400 lbs would have enough power to immolate an elephant entirely most likely.

Your chainsaw would have the power of a bomb, all put towards a few glorious seconds to a minute at most of incredibly destructive power as the blade super heats and the chainsaw loses cohesion as the power which simultaneously kept it together suddenly runs out.

I hope this helps.

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    $\begingroup$ Aren't batteries and power cells the same thing? A battery is a group of several cells linked together. If you cut open something like an AA battery, you will find button cells inside of it. Even car batteries are made up of several different cells. $\endgroup$ – Liam Morris - Reinstate Monica Apr 9 at 10:26
  • $\begingroup$ @LiamMorris In fact, it may even be the opposite: each power gives you some power, so you want as many as possible to have the highest possible power (but for the shortest time) $\endgroup$ – Eth Apr 9 at 10:35
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    $\begingroup$ Maybe use super capacitors. They can deliver huge amount of power in short time. $\endgroup$ – jnovacho Apr 9 at 11:41
  • $\begingroup$ @jnovacho Good idea. I will write an answer based on this. $\endgroup$ – Philipp Apr 9 at 12:04
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    $\begingroup$ That moment where tired me put power cell instead of fuel cell. -.- I am talking about fuel cells made using carbon nano-tubes. $\endgroup$ – Obelisk Apr 10 at 5:23
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Googling "battery in missiles" led me to the page of a company manufacturing and selling such solutions.

I am guessing your solution would be "thermal battery". I do not think they are selling a solution just for you but the duration and power can be tailored to application. Also, such batteries are used by military using similar "mil-tech" would probably fit the back story.

Also such batteries are single use, durable, reliable and have long shelf life.

Some of the other battery chemistries they offer might work better for you, so you might want to check them out. They might be rechargeable though.

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    $\begingroup$ Also known as "molten salt battery" $\endgroup$ – IronEagle Apr 10 at 15:26
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The parameters of the problem are:

  1. Single-use ordnance
  2. Power-to-weight is a significant constraint
  3. Brief duration of discharge
  4. Cheap-ish (we're talking about a disposable giant chainsaw here)

So you're probably looking at a chemical energy source that needs to be converted to mechanical energy. That rules out any high-explosive, and anyway, explosives expend much of their energy in brisance.

Fuels like Otto II driving a turbine are one possibility, if you'd like the system to be self-contained (i.e. not subject the user to exhaust fumes). If that is not a serious consideration (e.g. you are okay with a fire-belching disposable giant chainsaw), then the parameters of the problem closely resemble the energy requirements of a rocket.

I'm partial to a powderized-aluminum + ammonium nitrate mixture, myself.

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Well possibly the easiest power source to use would be a battery, you can accurately determine how much ‘life’ it could give to a piece of electronics by setting the max capacity and charging it until it is full.

Although, if your problem is just that you need to get the chainsaws down safely, i would recommend using parachutes or heavily padded drop boxes to ensure the contents were undamaged. At that point you could use whatever fuel you liked as it would not be damaged from the fall.

However, i don’t think you’d want to use chainsaws, especially ones that heavy, as weapons. They are not particularly effective, are slow and 400 pounds is about the weight of two humans. At that point you might as well be using a giant maul instead. Here is an answer where i explained the issues with chainsaw weapons. There is also a link to a youtube video in my answer which demonstrates my point.

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    $\begingroup$ But chainsaws are FUN . Signed, Anonymous From Texas $\endgroup$ – Carl Witthoft Apr 9 at 13:19
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Since this is the sort of weapon that Coyote would be using against Roadrunner, it must be powered by the future power supply du jour.

In the 1950s that would have meant nuclear power, nowadays everything is battery powered, though some consider that the future is in hydrogen.

It very much depends on the tone of the situation you're creating.

The clean and neat nature of modern hydrogen fuel cells and batteries may not fit the context, so you might want to find some way of making it spew smoke and fire as it's powered up, that means coal or at the least diesel powered.

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  • $\begingroup$ If you're looking for something in an 'industrial' style (spewing fire and smoke) where it doesn't have to work for very long, and is insensitive to the health of the users, you could go for boron-doped 'zip' fuels, used in aircraft and rockets, and should be roughly compatible with diesel engines (at least briefly!) As an added bonus: the flames are green! $\endgroup$ – Avi Cherry Apr 11 at 18:37
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I would go for a chemistry based solution. Think of current engines; they are all based on the concept of explosions. Now think of a giant explosion happening on release of the chainsaw. It would create enough pressure to power the chainsaw for quite some time.

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While not a chain saw, much of the effect could be delivered cheaply and reliably by a 400lb coiled spring, which has saw teeth etched into the edges. This can be deployed from the plane itself (uncoiling and lashing at the target as the plane screams overhead. Alternatively, the hero can be braced with his back to a tree or a wall and pull out the pin or cut the cord holding the coil closed, it lashes out like an Urumi from hell, striking with considerable kinetic energy and razor sharp cutting teeth.

enter image description here

As you can imagine, there is nothing close to what I am describing. Take this, increase the size to account for the 400lbs of spring steel, serrate the edges and have a cord or pin holding it closd against the spring tension

Considering a 400 lb coil of spring steel would actually be quite long, you would also have a considerable advantage of reach over most opponents, who would either think the plane is too low to drop a bomb, or the hero is too far away from then (and whatever is that drum like object he is holding?), so fail to take proper precautions.

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Expanding on Willk's answer here:

You have a "lander" and a chainsaw. The chainsaw is spring-powered. The lander has multiple rotors, say 3, that both break the fall and charge spring. It would basically look like a quadrocopter with a chainsaw at the bottom falling down.

A ratchet prevents the spring from discharging. A trigger mechanism in the chainsaw releases the ratchet and directs its power from the rotor coupling to the saw's chain - the chainsaw is running, purely from the energy from the fall.

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Dual liquid explosive, the force would trash the mechanism but its a one use weapon.

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    $\begingroup$ These are normally called binary explosives, just for reference. $\endgroup$ – ltmauve Apr 9 at 23:26
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Coffman (shotgun) starter

The Coffman starter uses a propellant fit in a shotgun shell, with the standard shotgun primer (blasting cap). It generates up to 15 seconds of pneumatic force to start large aviation and tractor engines.

Famously used on the movie Flight of the Phoenix (both versions).

Adjust size for energy need, but it's just the right energy density, weight and burn rate for the job.

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Build the chainsaw with a heavy flywheel. Add a heavy duty piston/foot that the chainsaw lands on when dropped towards you. When that piston hits ground at high collision speeds it spins up the flywheel, which directly powers the chain. You run over and grab it, go to work for your 15 seconds of glory.

No power source beyond gravity and the flywheel needed. Being all mechanical and built tough it possibly wouldn't even fall apart, later it gets picked up and reset for another drop.

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If a massive chainsaw is deployed from a jet, it should be powered by Mr. Torgue's specialty. The large weight is needed to contain and direct the C4 detonation inside to spin the chain. Maybe also the back side is stronger than the front, creating the possibility for the chain blade to launch through the enemy.

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You don't need a power source.

Humans generally have a terminal speed of 53m/s. Your chainsaw, due to weight and profile, will probably have a greater final velocity.

A 400 pounds piece of metal hitting you at 53m/s will impart you with approximately 2.54 x 108 joules, or ~ 70,555.5 wh. That's equivalent to the detonation of around 60~65 kilograms of TNT. It will turn the target to a pulp just by its kinetic delivery, as well as anyone else nearby.

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