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The information on basic surface winds and winds aloft readings gathered by this method can be used by a pilot to project a flight path and anticipated landing sites with a sectional or topographic map. This plot will form a “V,” with the cone beginning at the launch site. The two legs will represent the extremes of the plotted measurements. The difference between these two extremes is called steerage. Flying higher will track the flight path closer to the winds aloft reading, while contour flying will put the balloon closer to the ground track leg. Varying altitude will allow the pilot to fly down the middle of the “v.” Accuracy will depend on the consistency of the conditions, but flight paths and landing sites may be predicted, after practice, with a high degree of reliability.
The balloon pilot, more than pilots who fly other types of aircraft, must have the capability of visualizing the winds aloft in three dimensions. Continued spatial awareness (how the balloon is moving through the air), is important for maintaining control of the balloon and navigating to the desired point on the ground. Every other safety measure taken is compromised by inflating a balloon and taking off without proper planning and an understanding of the winds and terrain to be navigated. [Figure 3-12]
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Figure 3-12. As the balloon ascends, the flightpath inclines to the right. Correlate this visualization to a map to determine the ground track of the balloon during flight.
Figure 3-11. Additional practice pibal plots. Performance Planning
Prior to a discussion of performance planning, a number of terms must be defined.Maximum Allowable Gross Weight is that maximum amount of weight that the balloon may lift, under standard conditions. This figure is usually stipulated in design criteria, and addressed in the Type Certificate Data Sheet pertaining to that balloon. It can also be found on the weight and balance page of the flight manual for that particular balloon. An average of 1,000 cubic feet of air, when heated, will lift 20 pounds.Useful lift (load) in aviation is the potential weight of the pilot, passengers, equipment, and fuel. It is the basic empty weight of the aircraft (found in the flight manual for each balloon) subtracted from the maximum allowable gross weight. This term is frequently confused with payload, which in aviation is defined as the weight of occupants, cargo, and baggage.
Density altitude is defined in the Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25) as “pressure altitude corrected for nonstandard temperature.” Density altitude is determined by first finding pressure altitude, and then correcting this altitude for nonstandard temperature variations. For example, when set at 29.92, the altimeter may indicate a pressure altitude of 5,000 feet. Under standard temperature conditions (59 °F), this may allow for a useful load of 1,050 pounds. However, if the temperature is 20° above standard, the expansion of the air raises the density altitude level (the air is less dense, thereby mimicking the density of the air at a higher altitude). Using temperature correction data from tables or graphs, it may be found that the density level is above 8,000 feet, and the useful load is then reduced to 755 pounds. This definition, however, has a tendency to confuse many new (and some not-so-new) pilots, so a more thorough explanation is justified.
The AIM explains density altitude as being nothing more than a way to comparatively measure aircraft performance. Paragraph 7-5-6 states, in part, “Density altitude is a measure of air density. It is not to be confused with pressure altitude, true altitude or absolute altitude. It is not to be used as a height reference, but as a determining criteria [sic] in the performance capability of an aircraft.” With respect to ballooning, this is a more useful definition of the term.
How does density altitude affect balloon performance? Density altitude affects balloon performance in two ways. First and more important, as a balloon gains altitude, it loses capacity, insofar as its lifting capability is concerned. This means a balloon capable of lifting 1,400 pounds at sea level may only be able to lift 1,150 pounds or less at 4,000 feet. For a pilot who seldom leaves the local area, this rarely causes a problem. For the pilot who travels from the low area of the Southeast to fly in the mile-high altitudes of Albuquerque,
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12345101570°90°110°130°150°170°190°210°230°250°275°-1010305070901101,4351,4001,3001,2001,1001,000900800700600500400Envelope TemperaturePressure AltitudePressure Altitude (x1,000 ft)Ambient Temperature (°F)Gross Lift (lb)Data Base: CalculatedSample Calculation: Ambient Temperature 60 °F Envelope Temperature 190 °F Pressure Altitude 1,500 ft 1. Enter the chart with ambient temperature (Point ).2. Trace right to the desired envelope temperature (Point ).3. Trace down to the pressure altitude (Point ).4. Trace left to read GROSS LIFT (Point = 1,120 lb)ABCDABCDEXPECTED GROSS LIFT
　
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