Supersonic Projectile Exceeds Engineers Dreams: The Supersonic Trebuchet

The supersonic trebuchet being modeled in software

Have you ever sat down and thought “I wonder if a trebuchet could launch a projectile at supersonic speeds?” Neither have we. That’s what separates [David Eade] from the rest of us. He didn’t just ask the question, he answered it! And he documented the entire build in a YouTube video which you can see below the break.

The trebuchet is a type of catapult that was popular for use as a siege engine before gunpowder became a thing. Trebuchets use a long arm to throw projectiles farther than traditional catapults. The focus has typically been on increasing throwing distance for the size of the projectile, or vice versa. But of course you’re here to read about the other thing that trebuchets can be used for: speed.

How fast is fast? How about a whip-cracking, sonic-booming speed in excess of 450 meters per second! How’d he do it? Mostly wood and rubber with some metal bits thrown in for safety’s sake. [David]’s video explains in full all of the engineering that went into his trebuchet, and it’s a lot less than you’d think. There’s a very satisfying montage of full power trebuchet launches that make it audibly clear that the projectile being thrown is going well past the speed of sound, with a report quite similar to that of a small rifle.

[David]’s impressive project and presentation makes it clear that all one has to do to build a supersonic trebuchet is to try. Just be careful, and watch where you shoot that thing before you put somebody’s eye out, ok?

Speaking of things that can go unexpectedly fast, check out these unpowered RC gliders that approach the speed of sound just feet off the ground. And thanks to [Keith] for the awesome Tip!

60 thoughts on “Supersonic Projectile Exceeds Engineers Dreams: The Supersonic Trebuchet

    1. Really?
      I feel that knowing a trebuchet can be built that can throw supersonic projectile is not “useless”.
      1.) It informs me that it can be done.
      2.) In that regard, why is it necessary to say what is the size (length?) of the throwing arm, or the mass (weight) of the payload.
      3.) Now, I can give up trying to be the first to do it! B^)

      1. He said 3/8 inch steel ball, and google says that a 3/8 inch chrome steel ball bearing weigh 3.5 grams. He said he gets anywhere from 400 to 490 m/s velocity based on camera frame analysis. Plug that into the good old one half em vee squared formula and you get 280 to 420 J which is getting pretty close to the kinetic energy of a 9mm pistol cartridge (between 430 and 620J according to wikipedia)

        This machine is terrifying and I flinched when he kept putting his body in the swing zone while it was armed. Really wish someone with a high speed camera would join him for some target practice. I bet this thing would do a number on a car door.

        1. That would be worth seeing. I agree on his casual approach being a bit alarming, but I am amazed at the project. Much respect to him. I am in awe of your ability with math, his ability was humbling.

      2. I think it was entirely intentional, NOT giving dimensions. He wanted to make sure that the only people building these things are the ones who can do the math, as a barrier to entry. Like maybe this will keep these from becoming a hazard to aviation and wildlife alike.

        1. I think you can give a vague description of the device in the article blurb (“a lightweight milled aluminium arm about 40cm long throwing a 6mm steel ball”) without letting any Tom, Dick or Ed build a replica.
          Also those with reading (looking?) comprehension can see the actual size of the arm in the article image.

  1. That is awesome, both the depth of the analysis and the build. People have done a lot of research on the non-intuitive varying acceleration the projectile undergoes during launch, but I’d never seen anyone do a pure speed design before.
    Now I’m curious about how small a pumpkin you can obtain, and what the design optimized for that can manage without demolishing the pumpkin.

    1. https://www.punkinchunkin.com/ has a tightly specified pumpkin for competition. It occurs to me, though, that a scaled up version of this machine would not qualify for competition as a trebuchet. Competition trebuchets are all gravity powered, and I believe that is a requirement for the category. Catapults use spring stored energy, so maybe this could qualify as a catapult. Or maybe this would fit in a new hybrid category.

  2. Hmm . . . in some respects, this looks like half of an in-swinger ballista. I wonder what kind of speed we could get on a ballista bolt by following the same kind of engineering procedure?

  3. Hm. A device that can be made of nonmetallic materials, that can throw a small object in a specific direction at supersonic speed. Should be possible to down-scale to hand-held size. Nope, can’t think of any application for such a device.

  4. Robert Heinlein, in _The Moon is a Harsh Mistress_, had revolutionary colonists (loonies? moonies? I forget) throwing rocks at Earth. I seem to recall they used a rail gun, though.

  5. Two things: As I understand, one of the signature characteristics of a trebuchet is that it is on wheels, it rolls when fired, and that is important to its operation. Second, I thought trebuchets were powered by specially shaped weights and gravity, not elasticity.

    Bottom line, it’s really impressive but I don’t think it’s a trebuchet.

      1. There’s a modern design called a floating arm trebuchet which does. No historical precedent, but the wheel is key to its efficiency. I tend to think of the sling release/lever arm combo as the defining characteristic.

    1. Can’t remember where but I’m pretty sure Mythbusters took a look at wheels vs no wheels and determined with wheels was better. The load falls more or less vertically and the carriage rolls forward and backwards. rather than with a fixed cart where the load swings and is less efficient. Something like that.

  6. This very cool, but it’s not a trebuchet. It’s sort of a springald, or perhaps a torsion catapult like a mangonel. To be a treb it needs to powered by a counterweight. Could you build a treb that threw at supersonic speeds? I’d like to see it, that or the disaster when it flies apart.

    1. Oh, man. Impressive animation – I’d seen clips from it in Scott Manley’s video about it, but the full animation tweaks it into something that is even more stunning than the reality. Looking at the normal-speed shot from the actual test footage of the projectile exiting the tube, you don’t see the projectile at all – just a puff of condensation from the sudden low pressure area after the diaphragm bursts. It’s really like watching a cannon fire – you never see the cannonball.

      By the way, a commenter on Scott’s video points out, at the moment the projectile is released, the rotating mechanism becomes severely unbalanced due to the removal of a bunch of mass from its end. No idea how they’re dealing with that.

        1. Yeah, I was thinking another mass, either on the same side, that moves outward, or on the other side, that gets pulled in. But maybe they just take the washing machine approach and mount the whole mess on springs so it can find its own center after the projectile is released. But I don’t know – the projectile probably accounts for more than half of the angular momentum in the system, so that would be difficult to recenter. And whatever is left has that much kinetic energy that needs to go SOMEwhere.

  7. David Eade, you should start your own satellite launching company. Or launching encapsulated glider drones with wings that deploy after launch, like tomahawk cruise missiles, but more delayed.

  8. Maybe this can get enough attention and a Youtube channel like The Slowmo Guys, Warped Perception, or Smarter Everyday could step in with the high speed know-how. Smarter Everyday might be the best of those options if we want to see stuff like the trying to capture images of the shockwave and precise energy breakdowns.

  9. Creator should contact Destin @ SmarterEveryday this would be right up his alley, and he would have the better high speed cameras you need to get improved video. It’s right inline with his supersonic baseball cannon.

  10. I enjoyed his presentation, and filming techniques, but he really needs to get a lapel mic or something to keep the audio more consistent.
    The engineering side of it went way over my head, but it’s good to see someone including it, and not just saying “we did some calculations”.

    The result was impressive though! Makes me wonder what the limits of the weapon are. With larger budget and size constraints could it rival a railgun for velocity and accuracy?

  11. I’m a tradesman a welder a sheet metal worker a aircraft mechanic and a non-destructive tech and I found the math so beautiful that I was taken back. I don’t understand it but it’s beautiful

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