1859 Balloon Voyage

My wife and I went to see Big Bad Voodoo Daddy (“You and Me and the Bottle Makes Three”) Saturday at Conner Prairie, part of the Indianapolis Symphony Orchestra Symphony on the Prairie summer series. We got there a bit early and ended up sweating in the hot, hot sun waiting for the concert to start.

It’s the “largest tethered gas passenger balloon in the world” according to Wikipedia. The gondola can carry as many as 25 passengers to 350 ft. (106.68 m). The 105 ft (32 m) balloon contains 210,000 cb ft (5946.538 cu m) of helium and will lift about 4.5 tons (4082.33kg) of payload. The tether cable can take a load of 45 tons (40823.3kg).

How is helium capable of lifting so much weight? If you recall from my Ketchup Packet Cartesian Diver article, the air caught in the ketchup packet is less dense than the surrounding water which causes it to float to the top of the water bottle.

The ketchup packet contains a little over half a tablespoon (8 grams) of ketchup and if it weren’t for the air caught in the packet, the ketchup packet would sink to the bottom of the bottle. There are two forces acting on the ketchup packet: gravity and buoyancy. Gravity attracts the ketchup to the bottom of the bottle, or exerts a downward force on the ketchup. As the ketchup sinks to the bottom of the bottle, the water in the bottle is pushed out of the way, or displaced by the ketchup. The other force acting on the ketchup is buoyancy and it exerts an upward force on the ketchup packet. The buoyancy force is greater than the gravitational force—the air in the packet weighs less than the water it is pushing out of the way or displacing—and the ketchup packet floats to the top of the bottle.

The helium in the Conner Prairie balloon displaces the air around it (you can think of the air as another fluid like the water in the bottle). If the balloon was filled with ordinary air, the balloon wouldn’t rise at all since the air inside the balloon would weigh about the same as the surrounding air. The balloon would sink to the ground just like a dropped party balloon does because the balloon itself is heavier than air. Helium, on the other hand, is lighter than air. A liter of air “weighs about 1.286 grams.” A liter of helium weighs .1785 grams. Since the helium weighs less than the surrounding air, the buoyancy force is greater than the gravitational force—the helium in the balloon weighs less than the air it is pushing out of the way or displacing—and the balloon, gondola, and the passengers float gently skyward. The balloon rises higher and higher until it reaches the end of the tether cable at 350 ft.

How does the balloon get back down? The tether cable is attached to a spool which is attached to a motor. The motor turns the spool that winds the tether cable, so the motor must be powerful enough to overcome the buoyance force and reel the balloon back down to the ground. You’ll definitely want to hold on tight—it’s a pretty bumpy landing.

The Big Bad Voodoo Daddy concert was excellent, but I’m fan so I might be biased. The following video was shot from the top of the ride and I managed to catch the tail end of a marriage proposal (she said yes). Best wishes to the happy couple.