Things From Movies That Cannot Exist Number 1: The Grapple Gun

The grapple gun is a staple of the action movie genre: simply point the hook skywards, fire and have the gun lift you onto the roof of your local Abandoned Warehouse™ or Deserted Chemical Plant™. The Batman is particularly fond of the Grapple Gun, making it a staple of his famous Utility Belt.

So let’s look at the physics:

Assuming The Batman is a well-built adult male and that he’s wearing a substantial amount of body armour and equipment, a mass of 150kg is probably reasonable. Raising a 150kg weight to the top of a ten storey (30m) building requires about 45,000 joules of energy (45 kJ). If The Batman takes thirty seconds to do the journey then that is equivalent to a power of 1500 W. A motor capable of lifting The Batman’s 150 kg weight is probably about 75% efficient, meaning the motor has to develop about 2000 W.

If we assume that the grapple gun’s motor is no more than 5 kg in mass (for ease of wielding) that gives a power-to-weight ratio* of 400 W/kg. This is within the capabilities of modern electric motors, but only just. Finding a battery that can provide 45 kJ is not difficult; lithium ion batteries can provide about 600 kJ per kilogram. However, they can’t supply that electricity quickly enough, managing only about 300 W/kg which means that the Grapple Gun’s 5 kg motor is going to come with a substantial 5kg battery to match. Then there’s the weight of the gun itself and the super-strong cable to consider …

Whilst devices for firing grappling hooks do exist (I’m told the Battelle Tactical Air Initiated Launch system is good) and powerful electric motors are fairly common, merging the two to create a useful handheld device is beyond the capabilities of physics at the moment. A real grapple gun would be far too bulky, heavy and unwieldy to be of any practical use.

* Of course this should really be power-to-mass ratio, but I’m going to stick with the more commonly used term.

6 thoughts on “Things From Movies That Cannot Exist Number 1: The Grapple Gun

  1. lol silly author. Yes, the power thing is a problem but we’re talking about a fictional universe with advanced technology. Their batteries are better, and you can also consider that it may have a combination between both batteries and some sort of spring-loaded mechanism that takes some of the load off the battery. I definitely think it could exist.

    However, I wish people would stop saying that bulky piece of **** that the Army designed is equal to Batman’s grapple gun. It’s not remotely as cool. Also, in some depictions that grapple guns just launch the line so he can swing, with no reeling mechanism. That could DEFINITELY work. He doesn’t swing enough in the films. Instead, he always goes up and down. More swinging because it’s cool to see.

    Arrow proved that the swinging effects can be done, realistically and beautifully.

    Anyway, author, stop just assuming things. For all your fancy equations, you never once stopped to think about comic book technology being ahead of ours, a mechanical aid to the motor and other such things.

  2. Yeah, silly author….*laugh*

    Actually, Mr Reid, your reaction was much like mine. Now I can agree with the poster about “it’s a fictional universe” but even in it, the laws of physics aren’t going to change. So we should just enjoy it as a fun story but at the same time, realize it won’t work in reality.

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