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Talking Trébuchets With Dayton’s Own American Chuckers

Regardless of one’s own opinion on violence, weapons of war often bring about a sense of awe just with their cunningly destructive force. One of the weapons of war that never fails to fascinate is the trébuchet, a mechanical siege engine dating back, in a less sophisticated form, to the 5^th century B.C. The trébuchet, through the aid of engineering, became fearsome engines of war, growing larger, delivering a more devastatingly larger payload with more range and accuracy, playing a pivotal role during both Crusades and then all the way into the late 1400’s. With the advent of gunpowder, the trébuchet faded away as a weapon of war, its last known use being in 1521 during a siege of an Aztec capital. The first shot, however, managed to do nothing more than to fling the payload high into the air…until gravity took over, sending the payload plummeting straight down, destroying the trébuchet itself.

This is an illustrative point about how much mechanical engineering and applied mathematics are needed to not only manufacture the siege machine, but to fine-tune the trajectory so that you don’t create a scenario that looks as if it was intended for a Warner Bros. cartoon. In recent years, trébuchets have been used more for recreational purposes, flinging anything from flaming pianos to small cars far afield for the amusement of onlookers.

The premier event for this spectator sport is the Punkin’ Chunkin’ World Championships hosted by the World Championship Punkin’ Chunkin’ Association (WCPCA) and has been held in Bridgeville, Delaware since 1986. The WPCA is a nonprofit organization which raises money for scholarships and charitable organizations through this event. They break the machines up into categories, including air cannons, centrifugals, catapults and trébuchets. I was able to speak recently with Patrick Imlay, the team captain of Dayton’s own American Chucker. The first thing I asked him was about the design of Team American Chucker’s trebuchet, which did not follow the mechanics of a historical trebuchet.

“It’s called a floating arm trebuchet, so the weight comes straight down and the arm actually rolls across a rail to make the arm go forward.” Patrick went on to describe the engineering principles and physics behind the machine. “If the weight falls in a straight line, that gives you more efficiency. If a weight swings along an arc, like a traditional trébuchet, that is less efficient. So, the higher the weight falls, the more energy you get out of the weight and the straighter the weight falls, the more energy you’ll get. With our machine, what it is doing is accelerating at about 9.8 meters per second squared and from the time it’s released, it’s accelerating downward, so the higher we can get it, the more acceleration and velocity we will get and the more energy we will have to throw with.”

Even though I flunked remedial math in high school, I was fascinated with the physics behind what most would be happy to view as a devastatingly ass kickin’ machine. Imaly stated that some of the refitting that they were doing on the trébuchet for this year’s competition dealt with increasing the weight and reinforcing the machine to be able to withstand the aforementioned weight.

“What the weight does is, the bigger the arm is, if there is more weight, it helps the arm turn the corner without slowing down. More weight creates more momentum, which means that as you try to turn a heavier, longer arm, with more weight you will turn it equally as fast. There’s a certain point where, if you have enough weight, you’ll turn that corner regardless of the size of the arm. There’s a trade off between the amount of weight you lift up and the structure that it’s going to take to lift all that weight, and the structure that you want to have in place to handle all of that weight that is falling.” As an example, Imlay then explained, “So, if you put 30,000 lbs fifty feet up in the air and drop it, your system has to be able to handle all of that force or you have to transfer all that force to the pumpkin. If you have a misfire, you have 30,000 lbs of weight coming down onto something. Most of what we do to tune the machine is to keep it light and efficient.”

All this talk gave me the urge to take my silverware and make a makeshift trébuchet to launch some chicken wings onto that table over by the door. You know, the one with the guy talking annoyingly loud on his cell phone. In fact, I have had fleeting dreams of building a trébuchet for home use. I have fantasized about being able to launch my lawn clippings several blocks over with the hopes of making a bulls-eye onto that guy’s house who lets his dog crap in my yard.

Okay, back to the competition. The Punkin’ Chunkin’ World Championships has become a big thing in the last ten to fifteen years, gaining more attention and coverage form the media outlets. The Science Channel has even dedicated a whole show to the competition, which airs on Thanksgiving. As the attention has increased, so has the level of competition.

“Right! Just in one class there were eighteen machines and there were easily sixty machines out there at that contest. The first day last year (2009), they barely got all the competitors done. It went all morning, through the day until dark.” Imlay added that, “The second and third day went pretty quick about having the next team ready and putting them on the clock. They put you on the clock and then you have to fire within that window, then they measure the throw…their pretty methodical about structure of going down the line.”

In 2009, American Chucker entered the competition for the first time and managed to walk away with second place. With each competitor allowed to have three throws, after which the distance is measured and recorded. American Chucker’s throws were relatively consistent, being 1,427.28 ft, 1,424.27 ft and 1,885.99 ft. In contrast, the first place winner, Yankee Siege’s numbers were rather erratic, which were 1,298.16 ft., 1,869.32 ft. and it’s winning throw of 2,034.21 ft. Imlay explained to me the reason for Yankee Siege’s inconsistent throws.

“It’s weight is called a hinged swinging weight, so there’s a fixed pivot point and then the weight basket is hinged so that it can drop farther, but in the end, when you watch the machine throw, it continues with this violent rocking and that is all the energy that is left in that machine while, with our machine, the load comes straight down and kind of bounces once and that is all the energy that is left.” Imlay went on to say that, “Because of the way Yankee Siege is built and how inefficient it is, they end up dropping a lot of weight…twelve tons of weight…and they end up with a lot of left over energy in the machine which means that the whole machine has to be bigger and stronger so that the weight doesn’t break it.”

Since our conversation had been almost exclusively focused on the physics of punkin’ chunkin’, I decided to ask a more personal question to end out interview: Had Imlay ever thought about duct taping a co-worker, family member or friend up and launching them form the American Chucker?

“No.” he said, then after a moment of thought added, “Maybe some of the people on the team have thought about doing that to me.”

Even though the 2010 Punkin’ Chunkin’ World Championships are already over, I will not reveal the results. This will not stop me, however, from making sucker bets with my family on Thanksgiving Day while we watch the program on the Science Channel at 8:00 pm, which will be hosted by Jamie and Adam from the Mythbusters.