Can a gun fly?

Can you make a jetpack out of rifles? Egghead comic XKCD finds the answer. An AK’s recoil is actually greater relative to its weight than a Saturn V’s thrust. Soviet engineering, FTW. (If their rifles can do that, no wonder they’ve always had a lead in heavyweight boosters).

Well, the AK-47 can take off, but it clearly doesn’t have the thrust to spare to lift anything weighing much more than a squirrel.

The problem comes when you get to the point where the rifle goes to fire Round 31, which it does not have. From there, gravity wins. But… what if you took a lot of AKs?

Is something better than an AK? Sure, a GAU-8. Is anything better than the GAU-8… and if there is, did the Russians build it?

Read The Whole Thing™. It’s fascinating!


17 thoughts on “Can a gun fly?

  1. James F

    Also check out “What If 18” in which proposes this question:

    In Armageddon, a NASA guy comments that a plan to shoot a laser at the asteroid is like “shooting a b.b. gun at a freight train.” What would it take to stop an out-of-control freight train using only b.b. guns?

    —Charles James O’Keefe

    First of all, for the record, shooting asteroids with lasers is a great way to deflect them. Stopping a train with a BB gun might be harder.

    Randall looks at the effects of a Red Ryder spring-piston lever-action air rifle, the Tactical Edition Drozd Blackbird (a full auto BB gun) and 40,000 trained shooters firing a full clip of AK-47 ammo simultaneously.

    The last one will make any humans remaining on the train wish they had gotten off in Scranton.

  2. James

    Hmmm….,a interesting peruse,reminds me I also have too much time on me hands and need to get back to work.My big problem is I do not know were to get a GS8 much less a GSh-6-30 nor can afford enough ammo to fly even over the smaller mountains of New England.

    I also hope no squirrels were harmed during this scientific pursuit!

  3. Loren

    I suppose not even Myth Busters would have tried this one. They did try the Chines emperor going to the moon with a rocket chair one. Similar concept and had the same results as the first time it was tried.
    I’m surprised that an AK would lift off with 250 rounds but too lazy to do the math. I’m just glad my Physics 102 instructor didn’t think of it as he’d include weight reduction as the thing lifted (use 125 rounds for weight maybe?).

    1. rocketguy

      It’s not that hard to include the consumption of ammo in the lift-off calculations. That’s how conventional rocket launches work. You can even include thinning atmosphere at altitude resulting in less drag and improved performance. You get better and better performance until, suddenly, you don’t. Hopefully, you have achieved your goals by the time your fuel/ammo is expended.

      1. Hognose Post author

        Yep, both of these (declining weight due to fuel burn and better performance at altitude, to a point) are used in aviation speed and range calculations. (I kind of suspect you know this). The classic example being the Breguet Range Equation of, IIRC, the 19-teens. The reason “to a point” exists in the airplane world is that airplanes are air-breathing and, unlike rockets, get their oxidant from the atmosphere. To go stratospheric or higher requires increasingly complex compressive technologies to keep the fuel/air mixture stoichiometric in the decreasingly dense atmosphere. Above 10-15k feet you have to provide life support for the humans as well.

        A World War II airplane usually achieved stratospheric flight with a combination of mechanical and turbo supercharging. A turbojet or turbofan has an axial (or in some early models, centrifugal) compressor built in to it. The A-12 and SR-71 were powered by an exotic engine that converted from using an axial compressor to a shock-body compressor at operational altitude and speed. The engine was a turbojet in some flight regimes and a ramjet in others… pretty amazing for 1960.

        Other nations as well as the USA experimented with aircraft that had duplex jet and rocket power for extreme altitudes, but none was ever operationalized. At these high altitudes, the atmospheric density is so low that aerodynamic control surfaces which go back to the Wrights and Glenn Curtiss don’t work, and you have to provide thrusters for stability and (attitude) control.

  4. Brad

    Hah. Pretty funny! But some details not exactly right.

    For example typical multi-stage liquid propellent chemical rockets like the Saturn V have radically different acceleration depending on how much propellent is left in the burning stage. IIRC the Soyuz peaks around 4 G right before staging.

  5. Bonifacio Echeverria

    AK weight-to-ratio of 2… lol, in Soviet Russia the gun indeed shoots you…


    Hey don’t go getting any ideas about putting AKs on your airplane Hognose!

    This reminded me some how, of that story Marjor Plaster tells in his personal biography of his time in SOG, when the one dude ties a spider monkey to a parachute flare parachute and fired it out of a 81mm mortar

      1. ToastieTheCoastie

        Does it involve a pet monkey hanging on for dear life at the end of a spinning Cobra rotor?

  7. Steven Y.

    If you were to put explosive rounds in a high rate of fire autocannon….. Congratulations, you’ve just duplicated DARPA’s early proof-of-concept test flights for the ORION propulsion system.

  8. DaveP

    xkcd’s good stuff.
    Went looking for the site after seeing a pic of a sinuous redhead wearing a tight tee-shirt with one of their mottos, “Science. It works, bi***es.” Have laughed and marveled at their quirky smarts ever since.


  9. Klaus

    Can’t remember where but I can recall photos of some Saudi’s celebrating by riding there muskets like a witches broom. They looked like they were blasting off.

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