Principles Of Balloon Flight
Balloons work on the very simple principle that hot air rises, as it is less dense than cold air.
A balloon has a set of burners to heat the air, which fills the fabric of the envelope and causes ‘lift’. As the air is heated, the lifting force eventually overcomes the force of gravity and causes the balloon to rise.
The balloon will not rise forever though since the air in the envelope will eventually cool causing the balloon to descend.
As the balloon rises the air pressure also decreases. This means that there is less cool air to support the balloon and it will begin to drop again.
By varying the temperature of the air in the envelope the balloon’s altitude can be controlled.
A hot air balloon burner system
mounted on the balloon’s basket.
The arrows are used to indicate wind direction at differing altitudes.
Once the top of the balloon enters a ‘layer’ where the direction differs, the direction of the balloon’s flight will change accordingly.
Since a balloon always flies ‘with’ the wind, there is no discernable sense of motion for the passengers in the basket.
Setting Up The Balloon
To set up a balloon is fairly simple. First the basket is positioned upwind of the balloon’s envelope. This is so that while inflating, the envelope will not blow into the basket and get either burnt of torn.
The basket has a set of propane tanks, which are used to fuel the burners. The burners are placed on top of nylon poles so that they cannot drop down onto the occupants of the balloon on landing. The cables that attach the basket to the burner frame are then connected using carabiners.
Next, the fuel lines are connected to the propoane tanks by the pilot. Once the hoses are attached to fuel tanks, most pilots will test the burners. While the pilot is doing the burner test the rest of the ground crew will begin to take the envelope out of the bag and position it downwind of the basket.
Once the pilot has finished the burner tests the basket is tipped over in the direction of the canopy. The envelope cables are connected to the carabiners at the basket. Next the bottom set of load tapes (the tapes that create the bulges in the balloon) are pulled out so the balloon looks like a flat balloon.
Now the balloon is ready to be inflated and all that remains is to pull out the crown line, which will allow the top of the balloon to be controlled during the inflation.
Inflating The Balloon
To inflate the balloon we first need to fill the envelope with cold air that will then be heated with the burners. If we tried heating without putting air in the envelope all that we would accomplish would be a very burnt envelope. The mouth (the opening at the bottom) is held open. A large fan positioned next to the basket blows cold air into the balloon.
While the balloon inflates the pilot or an experienced member of the ground crew will go to the top of the balloon (the crown) and begin to attach the parachute top. This is what gives the pilot a ‘valve’ with which to let out hot air during flight and landing but must be sealed prior to launch.
When the pilot feels that the envelope is filled with enough cold air he/she will use the burners to slowly heat the air. The two ground crew on the mouth must take care to stay clear of the flames and be careful not to become tangled in any lines as the envelope begins to rise.
During the inflation process there will be a crewmember holding the crown line to control the envelope as it stands up. Once the balloon is upright the pilot will have passengers get into the basket while the ground crew keeps weight on the basket.
When everything is ready the crown line is brought to the pilot for securing, the ‘tie-off’ rope is released and the pilot uses the burners get sufficient lift to leave the ground. Now you’re on your way!.
Flying The Balloon
When flying the balloon the pilot will control the vertical motion by either heating the air in the envelope to achieve ‘lift’ or by allowing it to cool in order to ‘descend’. Sometimes hot air will be released by pulling out and re-sealing the parachute top but normally the natural cooling of the balloon is enough. The balloon will only go where the wind takes it.
Typically the winds are different at different altitudes. The pilot uses these different wind directions to ‘steer’ the balloon by ascending and descending into the desired altititude and direction.
When the pilot has found a desireable landing spot he/she will allow the balloon to descend at a controlled rate of speed. Once the balloon contacts the ground the pilot will release hot air by pulling on the parachute top. Depending on the wind speed at ground level, the landing will either be gentle and the balloon will remain standing or, if it is windy on the surface the balloon may lay on it’s side and drag for a short distance.
It is important to listen closely to the pilot’s instructions before landing so that you are sufficiently prepared for your landing, especially if he/she anticipates a ‘windy landing.’
Steering The Balloon
Below is an animation that shows the principles of wind direction at different altitudes and how the pilot uses them to steer the balloon.
Landing and Packing Away
Once the balloon is firmly on the ground the ground crew will be asked to pull the crown line so that when the balloon deflates it will fall away from the basket.
The crew then gathers the balloon to remove the air. While the envelope is being packed away the pilot and other experienced crew will disassemble and pack away the burners and basket.
The envelope is packed or ‘stuffed’ into its bag and loaded onto the trailer or truck with the basket, fan and any other equipment — ready for another day.