The principle of Balloon Flight.
Hot air rises. The envelope (the main multi-colored compartment) traps a large bubble of hot air. If the air in the envelope is heated by a burner, the balloon will rise. If the air in the envelope is allowed to cool or if the hot air is "vented" (allowed to escape) from the top or side of the envelope, the balloon will descend. An altimeter (to measure altitude), a rate-of-climb meter, and an envelope temperature gauge are the only instruments used in the balloon. Amazingly, the pilot can control the altitude of the balloon within a matter of inches.
Balloons can go as fast as the wind blows. But if the wind is over 8 miles per hour at ground level, balloons normally are not going to be inflated because of the increased possibility of burning the fabric and because landing would likely be rough and require a large field.
How high do balloons go? Flights in hot air balloons have been recorded at over 60,000 feet, However, the sport of ballooning is most enjoyable when flying 200 to 500 feet - just above the tree tops.
Most balloons can fly for 3/4 - 2 hours depending on the outside temperature and the weight carried. On a cold day with only one person flying, a 3-4 hour flight would be possible. Balloon flights are normally scheduled for daybreak and 2 hours prior to sunset, when the air currents are most favorable for ballooning. The exception to this rule is during the summer in the south, when the afternoon temperatures are too hot causing conditions to be unstable. (i.e. thermals) Comfortable clothing is recommended, such as long pants and flat shoes.
What Weather will keep us from flying?
High wind
Wind is a balloons biggest enemy. Wind of more than about 10mph will make the balloon almost uncontrollable. To put a balloon up you must first fill it with air. This is done by laying the balloon on the ground and starting a large fan. You must hold the balloon still long enough to fill it with air before you turn on the burner to stand up the balloon. If you have any wind the balloon will begin to catch the wind like a giant sail and begin to drag itself across the field. A balloon can generate as much as 6,000lbs of pulling force in as little as a 12 mph wind. At this time we don't even want to talk about landing in windy conditions.
Poor Visibility
Balloon flying is a VFR type of aircraft. This means Visual Flight Rules. These are rules written by the Federal Aviation Administration. Not only is it illegal to operate a balloon in poor visibility but imagine driving your car with your eyes closed. You are bound to hit something and it won't be pretty. To land a balloon the pilot must slow the descent of the balloon to get it to level off right at the ground level. Hard to do when you can not see the ground.