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.

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