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Figure 3-13. Typical performance chart for a 77,000 cubic foot balloon.
New Mexico, the changes in balloon capability and decrease in burner performance are important considerations while planning for the flight.
Second, heater performance is degraded at a rate of 4 percent per 1,000 feet of altitude. This means on a standard reference day, a particular heater will have lost 12 percent of its efficiency at 3,000 feet, or be performing at 88 percent of its capability. This is due to the loss of the partial pressure of oxygen, a necessary component of combustion.
Preflight planning requires consideration of balloon loading and performance with respect to altitude and expected temperatures. Balloon manufacturers have provided the information necessary to determine these factors in the form of a performance chart in the flight manual. Referred to as nomographs or nomograms, performance charts are simple to use and provide excellent planning information. [Figure 3-13]
If three of the above factors are known, a fourth may be determined. The performance charts may be used in many ways to determine performance of the balloon on a given day. This process does not have to be computed at the beginning of each flight. Many pilots develop a listing of possible weights, temperatures, and altitudes, depending on the average flying conditions for their home area. This is an acceptable practice
3-10
as long as the information is available and consulted when appropriate.
Using the chart in Figure 3-13, determine the maximum gross lift that may be expected on a 60 °F day, with decisions not to exceed 190 °F envelope temperature and 1,500 feet pressure altitude. In this example, the established parameters equate what many pilots consider when doing performance planning. They decide they do not want to exceed a given altitude or envelope temperature.) To determine the maximum gross lift available, the nomograph should be entered at point A, at the ambient temperature of 60 °F. Move right, to the line indicating an envelope temperature of 190 °F (point B). Then, move down vertically to a point equidistant between the lines denoting altitude of 1,000 and 2,000 feet (point C). Then, move horizontally to the left to the gross lift axis of the chart and read the result (point D). In the illustrated example, this computation results in a maximum gross lift of 1,120 pounds.
Using the chart again in Figure 3-13, determine the maximum altitude to which the balloon may climb, given the same maximum gross lift figure of 1,150 pounds. In this example, it is simply a matter of extending the lines appropriately. The A-B line would be extended to the diagonal line indicating a maximum temperature of 250 °F (which is the maximum continuous operating temperature for most balloons). Then, a perpendicular line would be drawn from that intersection point. After that line is drawn, extend the C-D line to the right, and the intersection of those two lines will indicate the maximum altitude. In this example, this computation results in a maximum altitude of 10,000 feet. Special Conditions
Most balloon flying is done in non-hostile terrain and benign weather. There are, some instances in which the terrain may be more difficult, both for the pilot and the chase crew, and the weather may become a significant factor. With proper preflight planning, the problems inherent in mountain flying and cold weather flying can be resolved. While somewhat riskier than normal flying, this type of flying can be safely conducted.Cold Weather Flying
Some pilots prefer flying in cold weather, which offers the advantages of more stable air and less fuel consumption to maintain flight. This means long, gentle flights for the pilot. There are two main disadvantages to cold weather flying: the need to maintain adequate pressure in the balloon’s fuel system and the difficulty of keeping the pilot, crew, and passengers warm.
As propane gets colder, it has less vapor pressure. (See chart of propane and butane partial pressures, Appendix C). To ensure adequate pressure in cold weather, follow the manufacturer’s recommended method, which will be described in the flight manual. Many manufacturers recommend the use of nitrogen, an inert gas that may be added to the fuel tanks by means of a regulator. This is perhaps the easiest way to pressurize tanks, as it may be done on site, and with little or no prior planning. It does require the use of a nitrogen tank and a two-stage regulator. These items must be available to the pilot before the flight. If the flight is cancelled after pressurization, and the anticipated rise in temperature is expected to be more than 30°, the pressure will need to be bled off by using the fixed liquid level gauge.
Balloon systems using a vapor feed pilot system may not be able to use nitrogen as it can result in an unreliable pilot light. Those systems commonly use heat tapes or heated tank covers in order to warm the propane. Heat tapes, similar to those used to prevent water pipes from freezing, are reliable. They do require frequent inspection, as normal wear and tear may cause an electrical short, with potential danger of damage to the fuel tanks. Among the aftermarket types of heat tapes, the ones with an internal thermostat will cycle once a particular temperature is reached, reducing the possibility of overheating the tanks.
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Balloon Flying Handbook(35)
