Tom Stanton’s supersonic trebuchet breaks sound barrier with gravity alone

汤姆·斯坦顿（Tom Stanton）的超音速投石机仅靠重力突破音障

Tom Stanton has spent years chasing a number that gravity itself seemed to forbid. On a quiet field somewhere in the UK, a 40-kilogram mass dropped a short distance, spun a carbon-fiber arm past 2,300 revolutions per minute, and sent a 4-gram projectile into the air at 776 miles per hour. That is nine miles per hour past the speed of sound. For the first time, a purely gravity-powered trebuchet crossed the barrier.

汤姆·斯坦顿多年来一直在追求一个重力似乎本身就禁止的数字。在英国某处的一片宁静田野上，一个 40 公斤重的物体短距离坠落，带动碳纤维臂以超过每分钟 2300 转的速度旋转，并将一颗 4 克的弹丸以每小时 776 英里的速度射向空中。这比音速快了每小时 9 英里。这是纯重力驱动的投石机首次跨越这一障碍。

Medieval engineers created these machines to fling huge stones at castle walls. The basic idea is to hoist a large heavy weight, let it fall down, and then use the lever and sling to redirect that energy into a much lighter projectile. Unfortunately, physics gets in the way. A weight in free fall accelerates at a maximum of 9.81 meters per second squared; drop one from 2 meters and it smacks into the ground at around 6 meters per second. No matter how heavy you make the weight, the speed remains constant, and a typical arm is like a car with a bike chain stuck in first gear, with lots of torque at first but just enough to get it moving by the end.

中世纪的工程师们发明这些机器是为了向城堡城墙投掷巨石。其基本原理是吊起一个沉重的配重，让其坠落，然后利用杠杆和投石索将能量传递给轻得多的弹丸。不幸的是，物理定律成了阻碍。自由落体物体的最大加速度为每秒平方 9.81 米；从 2 米高处落下，撞击地面的速度约为每秒 6 米。无论配重有多重，速度始终保持不变，典型的投石臂就像一辆自行车链条卡在一档的汽车，起步时扭矩很大，但到最后只能勉强移动。

Stanton devised a creative engineering solution to the speed problem. The counterweight is suspended from a pulley system with a 3:1 ratio, as a large diameter at the beginning propels the arm with plenty of force, and as it winds down, the smaller diameter end provides a significant jump in rotational speed. In the end, the drum was redesigned so that weight could be lifted up to 1.9 meters, storing more power in the system than previous iterations.

斯坦顿为速度问题设计了一个创造性的工程解决方案。配重悬挂在一个 3:1 比例的滑轮系统上，起初的大直径能以巨大的力量推动投石臂，而随着转动，较小直径的一端则提供了旋转速度的显著提升。最终，卷筒经过重新设计，使配重可以提升至 1.9 米，从而比之前的版本在系统中储存了更多的能量。

The arm has to be both incredibly light and super rigid. Carbon fiber was really the only option because it isn’t heavy enough to weigh down the entire system while yet being able to withstand punishment. Stanton used his homemade CNC mill to carve the piece, keeping the dust under control with a HEPA vacuum and a good spray of water. It weighs only 116 grams. Stress tests and numerous defective 3D printed prototypes revealed that it would buckle under the sling’s pressure, so he modified the design to compensate, removed material from the tensioned side, toughened up the opposite side, and added some extra bracing for good measure.

投石臂必须既轻盈又极其坚固。碳纤维确实是唯一的选择，因为它既不会因太重而拖累整个系统，又能承受巨大的压力。斯坦顿使用自制的 CNC 铣床雕刻该部件，并用 HEPA 真空吸尘器和喷水来控制粉尘。它仅重 116 克。压力测试和多次失败的 3D 打印原型表明，它会在投石索的压力下弯曲，因此他修改了设计以进行补偿，去除了受拉侧的材料，加固了另一侧，并额外增加了一些支撑以确保稳固。

Aluminum hubs connect the arm to a short counter-arm, keeping the spinning bit as balanced as possible. The projectile now starts near the axle, wrapped firmly in a sling that unwraps at just the right moment. The entire system is mechanically released, using a spring-loaded catch that opens after a certain number of rope rotations. The release window is only a few milliseconds long, which is plenty of time to complete the task. Early iterations failed under stress, but the final pin-and-loop structure held up.

铝制轮毂将投石臂与短配重臂连接起来，使旋转部分尽可能保持平衡。弹丸现在从靠近轴心的位置出发，紧紧包裹在投石索中，并在恰当的时机解开。整个系统通过机械方式释放，使用一个在绳索旋转一定圈数后打开的弹簧锁扣。释放窗口仅有几毫秒，这足以完成任务。早期的版本在压力下失效，但最终的销钉和环结构经受住了考验。

Testing was carefully increased, and he began with a 10 kg weight. The modified aerodynamic arm reached a respectable 1248 rpm and launched at 394 mph with an incredible 43.7% efficiency. Twenty and thirty kilograms passed thru without a hitch. 40 kg, on the other hand, sped the arm to 2336 rpm and the missile to a blistering 716 mph, falling only 51 mph short of the magic barrier. The machine eventually snapped, and the clasp shattered beneath the weight of 50 kg.

测试过程小心翼翼地推进，他首先使用了 10 公斤的配重。改进后的空气动力学投石臂达到了可观的 1248 转/分，并以 43.7% 的惊人效率实现了 394 英里/小时的发射速度。20 公斤和 30 公斤的测试顺利通过。而 40 公斤的配重将投石臂加速至 2336 转/分，弹丸速度达到惊人的 716 英里/小时，距离那个神奇的音障仅差 51 英里/小时。最终，机器在 50 公斤的重压下断裂，锁扣粉碎。

Stanton reduced the projectile weight to approximately 4 grams, changed the drum taper once more, and returned to the test area with the 40 kilogram setup. The final test is obviously the most important, since the arm spun up to 2342 rpm. Tip speed reached a staggering 274 mph. The high-speed footage was truly eye-opening, as the missile traveled 1.94 meters in 5.6 milliseconds. Crunching those statistics yields 346.4 meters per second, or a more than respectable 776 mph. To top it all off, there was a loud crack followed by a pleasant echo, confirming the sonic boom to everyone within earshot. Not one aspect of the machine came close to failing, or so we’d like to think.

斯坦顿将弹丸重量减至约 4 克，再次改变了卷筒的锥度，并带着 40 公斤的配置回到了测试场地。最后的测试显然最为关键，投石臂旋转至 2342 转/分。末端速度达到了惊人的 274 英里/小时。高速摄像机拍摄的画面令人大开眼界，弹丸在 5.6 毫秒内飞行了 1.94 米。计算这些数据得出速度为每秒 346.4 米，即相当可观的 776 英里/小时。最重要的是，现场传来一声巨响，随后是悦耳的回声，向所有在场的人证实了音爆的产生。机器的任何部分都没有出现故障的迹象，至少我们愿意这样认为。