are either more or less than the median speed of 5 knots, increase or decrease the distance between plot points on the graph
paper as appropriate. (eg: 2 squares = 5 kts / 3 squares = 7.5 knots) [Figure 3-6]
1st pibal reading 150 feet
Figure 3-6. First pibal plot showing 300° at 30 seconds.
At 1 minute, take a second reading. The pibal will be at approximately 300 feet AGL. In this example, the reading taken
is 310°. Using the plotter, draw a line 10° off the original azimuth (the A-B line), and make another mark approximately
two squares away from the mark labeled “B.” For clarity, this is be labeled “C”. See the example in Figure 3-7. (Note: The
angles in the successive graphics are exaggerated for clarity.)
2nd pibal reading 300 feet
Figure 3-7. Second pibal plot showing 310° at 1 minute.
At 1:30 minutes, take another reading. The pibal will be at approximately 450 feet. Using the plotter, draw a line 30° off
the original azimuth (the A-B line), and make another mark approximately two squares away from the mark labeled “C.”
This mark may be labeled “D” for clarity. [Figure 3-8]
3rd pibal reading 450 feet
C D
Figure 3-8. Third pibal plot showing 330° at 1:30 minutes
Although plotting can be continued as long as the pibal remains in sight, only the three points marked will be used for this
exercise. Figure 3-9 illustrates the results of the above sequence.
300°
310°
330°True track at 450 feet
your locationA
Figure 3-9. A line drawn through the last two plots provides a basis to measure the angle and determine the wind at that altitude. In
this case, it is 450 feet.
To determine the wind directions at different altitudes, extend lines between the plotted points as shown in Figure 3-9 back
through the initial azimuth. Using the plotter, measure the angle between the lines (the angle between the A-B line and
the C-D line). That angle, added to the original azimuth heading, gives a good approximation of the winds at that altitude.
For the example shown in this sequence, the true track at 450 feet AGL is 005°. A grid appropriate for this computation is
located in Appendix B.
This exercise demonstrates a practical method for determining approximate wind directions using items readily available
to most pilots. It does not require expensive handheld calculators, laptop computers, or a theolodite that costs thousands
of dollars. There is some error inherent in this process that can be lessened with experience and practice, but the readings
obtained by this method can offer real time, on site weather data no forecast or briefer can provide. [ Figure 3-10 and
Figure 3-11]
Figure 3-10. Practice pibal plots. These exercises are designed to assist the student pilot in devleoping proficiency in using the pibal
plotting method. (answers on next page)
Figure 3-11. Additional practice pibal plots.
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]
Figure 3-12. As the balloon ascends, the flight path inclines to the right. Correlate this visualization to a map to determine the ground
track of the balloon during flight.
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 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]
3 4 5 10 15
70° 90° 110° 130° 150° 170° 190° 210° 230°
250°
275°
-10
1,435
1,400
1,300
1,200
1,100
1,000
Envelope Temperature
Pressure Altitude
Pressure Altitude (x1,000 ft)
Ambient Temperature (°F)Gross Lift (lb)
Data Base: Calculated
Sample 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)
EXPECTED GROSS LIFT
Figure 3-13. Typical performance chart for a 77,000 cubic foot balloon.
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 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,