Chunkin’

Yes, you read correctly, Joanna and I attended our second Punkin’ Chunkin’ on Saturday. The afternoon weather prediction was not auspicious so we arrived at the third annual Howard Fire Company Fall Punkin’ Chunkin Festival by late morning. This year’s event included at least five gravity catapults (the Trebuchet type), a number of tension catapults (Ballista type), and a single torsion catapult (Onager type) … making it a field day for catapult buffs and physics geeks alike. Each machine is overseen by a team of six or eight and the object of the day’s event was to launch pumpkins out over the Bald Eagle Reservoir as far as possible. Punkin’ Chunkin’ is quite serious business and the Guinness Book lists the record for a pumpkin toss as 5,545.43 feet. This world record was established by a gigantic air gun while the catapults at our local gathering were powered by either gravity, tensioned rubber belts, or twisted nylon ropes. We watched as pumpkin after pumpkin took flight out over the water and estimated that the errant cucurbits flew well over 1000 feet and nearly as high. The torsion catapult, named Onager for the Roman siege engine, set all records for the day hurling its munitions well beyond this mark. Team Onager lists its personal best toss as 2458.45 feet which was achieved at the 2012 World Punkin’ Chunkin’ Championship. Many thanks to the members of Team Onager, and especially to Michelle, for allowing me photo access to the off limits-no spectators-danger-caution-keep back zone. Although the weather was not cooperative, this year’s festival was an enjoyable event. There was lots of good food available as were stalls of handmade items and trinkets. If you should be in this part of the world perhaps you might take in some fall color and next year’s Punkin’ Chunkin’ at Bald Eagle State Park.

Below are images of each of the three different sorts of catapult types along with something of a period schematic. The Trebuchet is perhaps the most familiar. Potential energy is stored by raising a weight against the force of gravity. When the weight is released potential energy is transformed into kinetic energy which swings the massive arm, releasing the projectile. The Ballista works by storing potential energy in semi-rigid arms connected by ropes, much like a crossbow. My favorite catapult however is the Onager or torsion catapult. Imagine stretching a rubber band between two stationary pegs. Place a pencil between the lengths of rubber toward the middle of the span and wind the pencil around a couple of times. When you release the pencil the stored energy in the bands will be released as kinetic energy and the pencil will spin … ZOOM! The single torsion rope of the machine shown below was 1″ nylon and was wrapped perhaps ten times between stationary posts. I was amazed that the projectile arm was twisted something less than 180° before it was ready for firing. Amazing. Really.

And here is a slideshow of a Trebuchet launch. It will advance on its own (at an approximate rate of 5 seconds per image)
or you may encourage the sequence forward or back with the buttons.

This slideshow requires JavaScript.

7 thoughts on “Chunkin’

  1. Pingback: Desktop Warfare Mini Ballista – 1uptreasures

  2. Very interesting! I live very near to the ‘land of Pumpkins’ in Austria (Styria – famous for pumpkin seed oil), but as far as I know there is nothing comparable here. A question: As pumpkins are irregular and thus have different weights and are subject to different frictional forces, isn’t it unfair to compare the tosses ;-)? Or is there a committee selection only ‘proper’ pumpkins?

    • The pumpkins used in this ‘demonstration’ were taken right out of the field and did indeed vary quite a bit from team to team and toss to toss. I would bet, however, that during serious competition, projectiles are selected to be more uniform in weight and size. I was commenting to Maurice that every once in a while a pumpkin will explode upon launch and I wondered why this did not happen more frequently. I also wondered what the rate of acceleration of these machines was … the torsion catapult really flies, so much so that I am surprised that each and every pumpkins doesn’t collapse under the stress of the launch. D

      • Thanks! Yes, there should be a pumpkin-shape-quality-control committee! In Europe we use to joke about our infamous standards for curvatures of cucumbers … that’s what came to my mind now when thinking about pumpkin uniformity. I wonder that the origins of such customs and rites are. I have often thought that games involving vegetables or fruit are probably due to the issue of having to getting rid of too much of them … in an era that did probably not allow for conserving all the crop? I am extrapolating from the desperate attempts of hobby gardeners who grow – too many! – cucumbers or pumpkins on their compost piles …

    • Yes indeed … you’d love it. The pumpkins land out on the water with a dramatic splash. Every so often one will self-destruct under the forces of launch … and I wonder why it doesn’t happen more often. I also wonder what the acceleration of the torsion catapult is … it’s got to be crazy fast … cause it really launches the thing for some distance down range. The maximum frame rate on my camera is 5.5 shots per second and it did a really poor job of capturing launch. D

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