Breaking the Sound Barrier with Gravity: Tom Stanton's Supersonic Trebuchet

By Bill Smith | August 9, 2026

For years, Tom Stanton pursued a specific velocity—a number that the laws of gravity seemed designed to prevent. On a secluded field in the United Kingdom, he finally succeeded. By dropping a 40-kilogram mass, he spun a carbon-fiber arm at over 2,300 RPM, launching a tiny 4-gram projectile at a staggering 776 miles per hour.

This marks the first time a trebuchet powered exclusively by gravity has officially crossed the sound barrier.

The Physics of the Fling

Historically, medieval engineers used trebuchets to demolish castle fortifications. The fundamental mechanism involves hoisting a massive weight and allowing it to fall, transferring that potential energy through a lever and sling into a lighter projectile.

However, gravity imposes a strict speed limit. A mass in free fall accelerates at: $\text{Acceleration} (g) \approx 9.81 \, \text{m/s}^2$

If you drop a weight from a height of 2 meters, it hits the ground at roughly $6 \, \text{m/s}$. Increasing the mass doesn't increase this falling speed. Without modification, a standard trebuchet arm behaves like a car stuck in first gear: high torque initially, but insufficient top-end speed.

Energy Flow Diagram

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Engineering the Solution

To overcome the "first gear" problem, Stanton implemented a 3:1 ratio pulley system. He used a tapered drum: a large diameter at the start provides the necessary force to move the arm, while the smaller diameter at the end drastically increases the rotational velocity.

The Build Process

• Redesign drum to allow a 1.9-meter lift for maximum energy storage.
• Select material: Carbon Fiber (chosen for its high strength-to-weight ratio).
• Fabricate arm using a homemade CNC mill.
• Implement safety/cleanliness: HEPA vacuum and water spray for dust control.
• Iterative prototyping: Replace buckling 3D printed parts with reinforced carbon fiber.
• Optimize arm geometry: Remove material from the tensioned side and add bracing to the opposite side.

Component Specifications

Testing and Iteration

The release window for the projectile is incredibly tight—only a few milliseconds. Stanton spent significant time refining the pin-and-loop structure to ensure it didn't fail under extreme centrifugal force.

Trial Data

The progression of tests showed a clear correlation between weight and velocity:

1. 10 kg Weight:
   • Arm Speed: $1248 \, \text{rpm}$
   • Launch Speed: $394 \, \text{mph}$
   • Efficiency: $43.7\%$
2. 40 kg Weight (Initial):
   • Arm Speed: $2336 \, \text{rpm}$
   • Launch Speed: $716 \, \text{mph}$ (Just $51 \, \text{mph}$ shy of the barrier)
3. 50 kg Weight:
   • Result: Success $\rightarrow$ Failure: The machine snapped and the clasp shattered.

The Final Run: Breaking the Barrier

For the final attempt, Stanton returned to the 40 kg setup but made two critical adjustments: he reduced the projectile mass to $\approx 4 \, \text{grams}$ and further refined the drum taper.

The result was a triumph of engineering. The arm reached 2342 rpm. High-speed cameras captured the projectile traveling $1.94 \, \text{meters}$ in just $5.6 \, \text{milliseconds}$.

The Calculation:

distance = 1.94 # meters
time = 0.0056 # seconds
velocity = distance / time 
# Result: 346.4 m/s

This velocity converts to 776 mph, officially surpassing the speed of sound. The success was punctuated by a distinct crack and a lingering echo—the unmistakable sound of a sonic boom.

The machine survived the ordeal intact, proving that with enough ingenuity, gravity can indeed be pushed to supersonic limits.