The Xuanfeng or "Whirlwind" is a basic traction catapult, and a direct descendant of the first Mohist traction catapults of the 4th - 3rd century B.C. The throwing power in a Xuanfeng comes from a team of people pulling downwards on ropes tied to the short arm of the throwing arm. The power of this catapult is limited only by the number of pullers able to fit in the space available below the lever arm. The largest versions of the Xuanfeng were recorded to have as many as 80-120 pullers!

Like all traction catapults, the Xuanfeng Pao could throw projectiles with a great variation in range simply by changing the number of pullers. The traction catapult also enjoyed a high rate of fire since the lowering of the throwing arm for reloading was a simple matter of the pullers releasing their ropes. Typical for Chinese catapults, the throw arms were made up of bundled bamboo rods. As a light catapult, the Xuanfeng would probably have been mounted with anywhere from 1 to 4 or 5 bamboo rods, with the increasing scale corresponding to an increasing ability to throw heavier projectiles.

This catapult was generally used like the sniper version of a rifle. It wasn't the power of the punch that mattered but the accuracy of the shot. The Xuanfeng, due to its lack of power, was not usually deployed to knock down walls. Instead, its main functions were to take out specific soft targets with its ability to swivel around 360 degrees. With a team of pullers pulling downwards on ropes tied to the short arm of the throwing arm, a "shooter" would guide the catapult about by pulling and aiming the catapult on the projectile side to adjust the angles before releasing for the most optimum shot. This ability resulted in incredible accuracy. This "light" catapult was used to snipe at other catapults or enemy generals with an arsenal of projectiles consisting of porcelain/clay shrapnel balls and other inventive material.

From an account in the Zi Zhi Tong Jian or "History as a Mirror", during the middle of the Tang dynasty in A.D. 759, General Li Guangbi's Imperial army confronted the rebel leader Shi Siming's army across the Huangho. In an attempt to dislodge General Li's troops from a temporary floating bridge strung across the river, Shi Siming sent hundreds of battle ships pushing burning boats at the front in the hopes of destroying the bridge. Using long poles to hold the burning boats at bay, the attack was successfully repulsed by the use of catapults against what must have been highly maneuverable rebel ships. While it is unclear what kinds of catapults General Li's troops arrayed on the northern bank of the river used, this account clearly illustrated the effectiveness of, and incredible accuracy achieved by Tang catapults.

Unlike European catapults, the Chinese anchored their catapults by sinking the legs a few feet into the ground. Many illustrations of the Xuanfeng found in classical Chinese military manuals are therefore shown with very small bases. A typical Xuanfeng stood anywhere from twice a person's height to about 3 times a person's height. Because of its small size, it was easy to transport it around by dismantling it into its various components, and to set it up again wherever it was required.

There are basically 4 general variants of the Xuanfeng Pao.

The basic Xuanfeng had 2 legs sunk into the ground for stability. The central pole was fixed to the two legs and the pivot was at the top of the pole, allowing for the entire head assembly to turn 360 degrees. It was a very light catapults for throwing small rocks, "shrapnel" balls, gunpowder explosives, human heads etc.

This catapult was the mainstay of Chinese field artillery for centuries, and was the basic form for all the other variants of catapults including those introduced into the West via the Avars and Byzantium.

The slightly heavier variant of the Xuanfeng was mounted on a more stable 4-leg base frame with horizontal crossbracing.

This heavier Xuanfeng could still maintain a 360 degree field of fire while allowing for the firing of slightly heavier projectiles. However, the pivot for this heavier Xuanfeng was at the base instead of at the top. This meant that the central pole turned along with the head assembly. This allowed for heavier projectiles to be fired since the monolithical head-column arrangement effectively lowered the fixity point of the rotational joint, making the catapult more stable.

More stable than the basic Xuanfeng, this catapult was probably not countersunk into the ground or at best at a very shallow depth. This allowed for ease of deployment without sacrificing stability and hence firing accuracy.

Xuanfeng batteries were made up of a row of light Xuanfeng catapults all mounted in a row on a single simple base. Like the basic variant, the head assemblies were made to swivel, but in addition the whole mount was also made to swivel 360 degrees, allowing for a lot more flexibility in usage.

The Xuanfeng batteries were probably used in battle to fire projectiles enmass, at the same time and in the same direction, to create fire saturation over a given enemy position. This multiple catapult was also conceivably used to create a continuous stream of covering fire during a battle to keep the enemy from returning fire.

The Xuanfeng was also sometimes mounted on a mobile wheeled platform but was still based on the basic Xuanfeng variant. The basic variant with dual fixed legs and top pivot was fairly common while the heavier variant with a 4-leg base frame and base pivot was less common.

The instance much often cited when catapults were first wheel mounted was during the Battle of Guandu when Liu Ye and Cao Cao of Wei deployed mobile catapults called the "Pili che" or (Thunderbolt cart).

These mobile catapults could be towed out to wherever they were needed, and the actual catapult throw-arm and central post were probably slotted in on-site when needed. The mounted Xuanfengs were light to medium sized catapults, overlapping in power and range at the upper end with that of the Hudun Pao. The development of mobile catapults which did away with the traditional sunken-leg base might have been a consequence of increasingly accurate enemy counter-battery fire.

The design of the Xuanfeng is such that when firing projectiles, the throwing arm impacted against the frame of the central post at the point of release. This results in a "early" release short of the vertical position, coupled with a slight whipping effect on the bundled bamboo which was the common material used to make the throw arm. Releasing projectiles short of the vertical position creates a high trajectory for the projectile, and maximises the range achievable, a requirement that is mirrored in the projectile-types typically used by this catapult. By the time of the Song dynasty in the 10th to 13th centuries A.D., the Xuanfengs were used to fire explosive grenades as well as molten cast-iron pots which could created large-area damage to troops and equipment alike, besides the usual assortment of stones, shrapnel balls, human heads and diseased meat employed by earlier dynasties.

The heyday of the Xuanfeng must arguably be said to have been during the Tang dynasty. Descriptions of the success of this catapult are recounted in various Tang dynasty siege accounts. During the Tang dynasty's founding years, in a siege of the Sui capital in A.D. 617, 300 catapults were said to have been deployed by the Engineer-General Tian Maoguang. Then again it is written that in a Tang dynasty siege of Pyongyang in A.D. 668 during the last year of the campaign against Koguryo, XuanFeng catapults were used to bring the city to its knees. Bombardment of such a massive scale would have been devastating to a beleaguered city.

The only know illustration of a trigger mechanism exists in a picture of a xuanfeng mounted on a siege boat from Wujingzongyao.

It rotates 360 degrees, but not when firing. This should be kind of obvious but it fires like a normal trebuchet with the same trajectory.

The xuanfeng is also man powered so the range would depend heavily on the number of people pulling the ropes.