Berkeley CSUA MOTD:Entry 54614
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2017/11/22 [General] UID:1000 Activity:popular
11/22   

2013/2/26-3/26 [Transportation/Airplane, Consumer, Consumer/Audio] UID:54614 Activity:nil
2/26    How does a hot air balloon pilot control the flight path?  I'd think
        one can only control the vertical movement using the flame.  Thanks.
        \_ You move vertically trying to catch wind currents blowing in the
           direction you want.  http://en.wikipedia.org/wiki/Hot_air_ballooning
2017/11/22 [General] UID:1000 Activity:popular
11/22   

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en.wikipedia.org/wiki/Hot_air_ballooning
ballooning include the exceptional quiet (except when the propane burners are firing), the lack of a feeling of movement, and the bird's-eye view. Since the balloon moves with the direction of the winds, the passengers feel absolutely no wind, except for brief periods during the flight when the balloon climbs or descends into air currents of different direction or speed. Initially equipped with a plastic envelope and kerosene fuel, Yost's designs rapidly moved onto using a modified propane powered "weed burner" to heat the air and lightweight nylon fabric for the envelope material. Today, hot air balloons are used primarily for recreation. There are some 7,500 hot air balloons operating in the United States. Since piloting a balloon requires some effort (licensing and purchase of equipment), many people opt to purchase a balloon flight from a company offering balloon rides. Hot air balloons in flight Hot air balloons are able to fly to extremely high altitudes. On November 26, 2005, Vijaypat Singhania set the world altitude record for highest hot air balloon flight, reaching 21,290 meters (69,852 feet). Breitling Orbiter 3 touched down in Egypt, having circumnavigated the globe and set records for duration (19 days, 21 hours and 55 minutes) and distance (46,759 km). With a volume of 74,000 m (2,600,000 ft), the balloon envelope was the largest ever built for a hot air craft. edit Flight techniques Early morning departures Most hot air balloon launches are made during the cooler hours of the day, at dawn or two to three hours before sunset. At these times of day, the winds are typically light making for easier launch and landing of the balloon. thermals, which are vertical air currents caused by ground heating that make it more difficult to control the balloon. In the extreme, the downdrafts associated with strong thermals can exceed the ability of a balloon to climb and can thus force a balloon into the ground. edit Preflight preparation Before a safe hot air balloon flight can begin, the pilot must check the weather and select a suitable take-off point. The current and forecast weather must have sufficient visibility for the pilot to see and avoid obstructions (little or no fog or low clouds) and sufficiently slow winds to allow take off and landing (less than 5 or 10 mph depending on skill and experience of pilot, passengers, and ground crew). power lines and poles, trees, and buildings to allow lift-off under the predicted wind conditions. Finally, the take-off point must be situated such that the predicted winds will move the balloon in the direction of suitable landing sites. Taking off from a location that is directly up wind of a hazard, such as a large body of water, a large metropolitan area, or a large uninterrupted forest, without sufficient fuel to pass over the hazard is not safe. edit Set up Hot air balloon being inflated by its propane burners prior to a dawn launch. The next step in a hot air balloon flight is unpacking the balloon from its carrying bag, laying it out on the ground, and connecting it to the basket and burner. A fan, often gasoline-powered, is used to blow cold (outside) air into the envelope. The cold air partially inflates the balloon to establish its basic shape before the burner flame is aimed into the mouth heating the air inside. A crew member stationed opposite the mouth, holds a rope (crown line) tied to the apex (crown) of the envelope. The "crown-man" role is twofold: one is to prevent the envelope from excessive sway, and two is to prevent the envelope from rising before it is sufficiently buoyant. Once the balloon is upright, pilot and passengers climb into the basket. When the pilot is ready for launch, more heat is directed into the envelope and the balloon lifts off. edit Flight During the flight, the pilot's only ability to steer the balloon is the ability to climb or descend into wind currents going different directions. Thus, it is important for the pilot to determine what direction the wind is blowing at altitudes other than the balloon's altitude. For example, to determine wind directions beneath the balloon a pilot might simply spit or release a squirt of shaving cream and watch this indicator as it falls to determine where possible turns are (and their speed). Pilots are also looking for other visual clues such as flags on flagpoles, smoke coming from chimneys, etc. To determine wind directions above the balloon, the pilot will obtain a weather forecast prior to the flight which includes upper level wind forecasts. The pilot will also send up a helium pilot balloon, known as a met-balloon in the UK and pibal in the USA, prior to launch to get information about what the wind is actually doing. Another way to determine actual wind directions is to watch other hot air balloons, which are the equivalent of a large met-balloon. edit Control The inside of a hot air balloon's envelope, seen from the gondola. The direction of flight depends on the wind, but the altitude of the balloon can be controlled by changing the temperature of the air inside the envelope. The pilot may open one or more burner blast valves to increase the temperature inside the envelope, thereby increasing lift, and thus ascend or slow or stop a descent. The pilot may also open a vent, if the envelope is so equipped, to let hot air escape, decreasing the temperature inside the envelope, thereby decreasing lift, and thus descend or slow or stop an ascent. Unless the pilot intervenes, the air inside the envelope will slowly cool, by seepage or by contact with cooler outside air, and slowly provide less lift. edit Delayed response One of the tricks involved in flying a balloon is learning to deal with the delayed response. To slow or stop a descent requires the pilot to open a burner blast valve. This sends hot combustion exhaust through the mouth into the envelope where it expands and forces some cooler air out of the mouth. This lightens the total weight of the system and increases its buoyancy, but not immediately. From the time that the burner is lit until the balloon slows or stops its descent can take 30 seconds or more, depending on its rate of descent, how cold it has become, and how powerful the burner. This delay requires a great deal of anticipation on the part of the pilot. edit Steerage The ability to change direction with altitude is called steerage. In the ideal case, in the northern hemisphere, wind direction turns to the right with an increase in altitude. Winds spiral clockwise, when seen from above, out of a high pressure system and counter clockwise into a low pressure system. However, air traveling close to the ground will tend to move in more of a straight line from high to low pressure due to drag with the ground. Thus, a pilot may hope to find a turn to the left during the descent to landing. In the southern hemisphere, the direction of the spirals are reversed. In reality, interaction with an uneven terrain may lessen or completely eliminate this phenomenon. edit Level Flight A Balloon Works Firefly 7 balloon in level flight. The burner is designed to create enough heat to warm up the balloon quickly. There is no good way to maintain the exact temperature required to maintain equilibrium. Add to that the fact that when a hot air balloon is not actively being heated, it is cooling off. This means that it is in perfect equilibrium only momentarily. The rest of the time it is either too warm or too cool and so either climbing or descending. These two facts together mean that under most conditions level flight is anything but. The goal of the pilot is to light the burner at the right interval and for the right duration (a few seconds) to keep the balloon slowly drifting up and down about the desired altitude. An exception is made when flying close to the ground, as in an approach to a landing. Then the burner may be lit for very short bursts at a much higher frequency, thus sacrificing efficiency for accuracy. edit Chase A typical chase vehicle with room for the equipment, chase crew, pilot, and all passengers. While it is certainly possible to enjoy the sport of hot air ballooning without a chase v...