Never heard of an apple cannon but they sure look like fun particularly when being used to shoot these model airplanes out of the sky.
Sort of reminds me of the the tennis ball cannons we used in college. Those cannons fired tennis balls using lighter fluid to create the explosion. We fired them from the balcony on our dorm at the guys who were shooting at us from the balcony on their dorm. The dorms were separated by quite a distance yet a tennis ball still carried quite a wallop. Most of us survived without significant brain damage.
Punkin Chunkin cannons... They use compressed air to shoot pumpkins almost a mile. American Chunker, below to the left, set the world record at 4694 feet. Sometimes the punkins cannot withstand the force produced by the release of all that compressed air in a millisecond and the pumpkin is vaporized as it exits the barrel.
Another source indicated that the Guinness world record shot is held by a pneumatic cannon dubbed "Big 10 Inch", at 5,545.43 feet (1,690.25 m), on September 9, 2010 in Moab, Utah. Apparently this distance was not sanctioned by the governing body of the Punkin Chunkers.
Shooting down RC airplanes with an apple cannon looks like a blast. Looks like the guns are a permanent installation at that orchard. I wonder if they make more money selling apples as ammo instead of food.
I went to a punkin chunkin event a few years ago in Estancia, a nearby farming community, sponsored by the Rotary Club. It was a lot of fun indeed. And totally by coincidence, today I'm wearing the shirt that I bought at the event.