Hot Air Balloon Flight.
The Balloon Expedition Company of New Zealand take you on flights over Auckland’s north west. They pick you up at the Westgate Centre and transport you to the take off point. About half an hour is required to partially inflate the balloon with cold air then heat it up with three giant bunsen burners till the balloon has neutral buoyancy. Its time to board the basket ready for lift off.
The air in the envelope is very hot, about 95 degrees celcius so the top of your head can get cooked if you are directly under the opening. An hour later after gently floating with the breeze (there is no wind, you move with the air), Darryl a very experienced pilot puts you down gently in a field somewhere out west. The destination is a pot luck affair and is determined by wind speed, wind direction and flight duration. Landing is a stressful time for Darryl as not all property owners appreciate a 5,000 cubic metre balloon dropping into the back field as they are having breakfast. The farm owners were friendly where we landed but apparently if we had flown over the fence into the next field we would have received a frosty reception.
What the lovely people at the Balloon Expedition Company don’t tell you is that you have to pack the ballon back into its crate. Surprisingly it is no more difficult than rolling up a tent and putting it in its bag. The drive back to Westgate in the jeep is almost as exciting as the balloon flight and the champagne breakfast is first class.
Darryl’s offsider tried to tell us that champagne breakfasts were invented by early balloonists as a means of placating irate peasants when they landed in the middle of their crop fields…..hmm maybe.
Balloons are are designed so that they can reach a height of 100 meters in about a minute. Sixth form students should be able to answer questions about the rate of climb.
- what is the upwards acceleration?
- How fast is the balloon travelling after the first minute
- If you check out the combined weight of the balloon you should be able to calculate the size of the buoyant force
How big a balloon do you need to lift the combined masses of the envelope, basket, burners, gas cylinders and passengers? It turns out that the calculation is quite straightforward.
A combination of balloon volume and temperature difference between the air inside the envelope and the air outside determines the lifting force and approximately 4.073 cubic meters of hot air are needed to lift each kilogramme of mass.
This figure can be plucked quite literally out of the air using the ideal gas equation with a number of assumptions about variables. Have a look at the science, Archimedes had it all figured out 2022 years ago.
Kavanagh of Australia manufactured the balloon used in the video clip. The balloon was an E Type-20 Gore model. The envelope volume was 180,000 cubic feet or 5,100 cubic meters.(1 cubic foot=0.02832 cubic meters),
A gore is a segment of a three dimesional object fabricated from 2 dimensional material.