The Physics of the Stick: Deconstructing the Traditional Longbow

In an age of compound bows with 85% let-off, laser rangefinders, and drop-away rests, the traditional longbow remains a defiant anomaly. It is a piece of wood and string that demands everything from the archer and gives nothing for free. Yet, its popularity is surging. This renaissance is not driven by nostalgia alone, but by a rediscovery of the raw, tactile physics of the shot.

The Sanlida Royal X8, a 68-inch reflex-deflex longbow, serves as a perfect modern specimen to examine these ancient mechanics. When an archer draws this bow, they are not just pulling a string; they are engaging with a complex system of potential energy, hysteresis, and ballistic dynamics. A closer look at the data reveals that this simple “stick” is actually a finely tuned energy converter, governed by physical laws that dictate everything from the speed of the arrow to the thump in the hand.

To truly understand the longbow is to look past the romance of Robin Hood and peer into the equations of Newton. This analysis deconstructs the Royal X8 not as a sporting good, but as a machine, exploring the trade-offs between speed, momentum, and the inevitable price of “hand shock.”

The Energy Storage System: Limb Geometry and Laminates

A bow is a spring. Its job is to store work done by the human body. The Royal X8 utilizes a Reflex-Deflex design. Unlike a straight “stick” bow (like the English Longbow), the limbs of the X8 curve forward (reflex) and then back (deflex) when unstrung.
When strung, this shape puts the limbs under “pre-load.” This geometry is a critical innovation in traditional archery history. It allows the bow to store more energy per inch of draw than a straight bow, while avoiding the instability of a full recurve.

The Composite Advantage

The X8 is constructed from a maple wood core sandwiched between layers of high-strength fiberglass. * The Wood (Core): Acts as a lightweight spacer. It keeps the fiberglass layers apart. In engineering terms, increasing the distance between the tension and compression faces increases the “Second Moment of Area,” making the limb stiffer and more powerful without adding significant mass. * The Fiberglass (Skins): The glass on the back (target side) stretches; the glass on the belly (archer side) compresses. Fiberglass has a much higher modulus of elasticity than wood, meaning it can store vastly more energy before failing.

This composite construction allows the X8 to be thin and whip-like, reducing the physical mass of the limbs. Light limbs accelerate faster. This is the first rule of bow efficiency: energy spent moving the heavy limbs is energy not moving the arrow.

The Efficiency Paradox: Heavy vs. Light Arrows

One of the most revealing data points for the Royal X8 comes from a user’s chronograph test. * 404 grain arrow: 162 fps -> 31.9 Joules KE. * 563 grain arrow: 144 fps -> 35.1 Joules KE.

Why does the slower arrow carry more energy? This phenomenon is explained by Hysteresis and Virtual Mass.
When a bow fires, not all the stored potential energy goes into the arrow. Some is lost to:
1. Limb Hysteresis: Internal friction within the limb materials as they return to shape.
2. String Mass: Accelerating the string itself.
3. Limb Mass: Moving the tips of the bow.
4. Aerodynamic Drag: The limbs moving through air.

A lighter arrow accelerates very quickly. It leaves the string so fast that the limbs don’t have time to “unload” all their energy completely into the projectile before it separates. The remaining energy is trapped in the bow (we’ll discuss where it goes later).
A heavier arrow accelerates more slowly. It stays on the string for a few milliseconds longer. This allows the limbs to push against it for a greater portion of their travel, transferring a higher percentage of the stored potential energy.
The Lesson: For the Royal X8, efficiency increases with arrow weight. If you want to extract the maximum power from the bow (for hunting, for example), you pay for it with a slower trajectory. It is a zero-sum game of physics.

The Momentum Debate: Penetration Physics

While Kinetic Energy (KE) is often marketed, Momentum ($p=mv$) is the better predictor of penetration. * Light Arrow Momentum: 1.29 kg·m/s * Heavy Arrow Momentum: 1.60 kg·m/s

The heavy arrow has 24% more momentum. Momentum is a vector quantity that describes how hard it is to stop an object. When an arrow hits a target (or a deer), resistance applies a force to stop it. An object with high momentum requires a larger impulse (Force x Time) to stop.
This explains why traditional archers favor heavy arrows (often 10-12 grains per pound of draw weight). The Royal X8, with its wooden riser and fiberglass limbs, is optimized to drive these heavy shafts. Shooting a super-light carbon arrow out of it might yield a fast chronograph reading, but it robs the system of its true hitting power.

The Ghost in the Machine: Hand Shock

“Hand shock” is the nemesis of the longbow shooter. It is the jarring vibration felt in the grip upon release. Physically, hand shock is Waste Energy.
Remember the energy that didn’t go into the light arrow? The 3.2 Joules difference between the light and heavy arrow shots? That energy didn’t disappear. It remained in the bow.
This residual energy manifests as high-frequency vibration in the limbs and riser. * D97 String: The Royal X8 comes with a Flemish D97 string. D97 is a modern, low-stretch material (Dyneema). While it makes the bow faster (less energy lost to string stretch), it also acts as a harsh transmission. It stops the limbs abruptly at brace height, sending a shockwave through the riser. * The Cure: This is why the heavy arrow feels “smoother.” It absorbs more energy, leaving less behind to rattle the archer’s teeth. Using string silencers (like the rabbit fur included) also helps. They act as air brakes and mass dampers on the string, absorbing the high-frequency oscillation before it reaches the riser.

The Draw Cycle: “Stacking” and the Wall

Reviews mention the bow “stacking” past 28 inches. Stacking is a geometric limitation.
As a bow is drawn, the angle of the string relative to the limb tips changes. Ideally, you want good leverage. “Stacking” occurs when this angle becomes inefficient—you are pulling against the limb tips rather than bending them.
In a 68” bow like the Royal X8, the draw should be smooth up to about 29-30 inches. Beyond that, the force required to pull an inch increases disproportionately (e.g., jumping from 2lbs/inch to 4lbs/inch).
For archers with long draw lengths (30”+), this bow might feel like hitting a “wall.” This is simple geometry. The fix is a longer bow, but 68” is already quite long for a hunting style bow. For the average archer (28” draw), the Royal X8 sits in the “sweet spot” of the Force-Draw curve, offering maximum energy storage without the mechanical disadvantage of stacking.

Conclusion: The Honest Machine

The Sanlida Royal X8 is an honest machine. It doesn’t use cams or pulleys to cheat the laws of physics. It is a direct converter of human effort into projectile motion.
By analyzing the ballistic data, we see that this bow “wants” to shoot heavy arrows. It rewards the archer who understands momentum with a quiet, smooth, and hard-hitting shot. It punishes the speed-chaser with noise and vibration.
Owning a traditional bow is a partnership with these physical realities. It is about tuning the arrow to the bow, and the archer to the system, until the energy flows efficiently from muscle to target, leaving nothing behind but the hum of the string.