At this point in the planning process, a flight instructor can begin to create a lesson plan based on the forecasted winds at their location. Using a paper map and plotter, or mapping software for an iPad such as MotionX, the instructor can plot out a take-off location which, based on the forecasted winds, would take the balloon to appropriate areas to practice maneuvers. Using the forecasted wind profiles, the instructor can plan ascents, descents, and level flight to navigate the balloon to suitable areas to practice landings before taking off again to resume the flight.
As the instructor and student approach flight time, small helium balloons called pibals can be used to measure the actual wind direction. By releasing a pibal and reading the direction on a compass, the instructor can fine-tune the planned flight plan based on the actual winds. In order to read a pibal correctly, instructors must be careful to visualize the balloon flight in three dimensions.
Some pilots release a pibal in a field and then as it ascends and turns with the direction of the wind, they sprint down the road to get an accurate pibal reading. There’s no need to work that hard! Use the following steps to accurately measure the wind direction.
As stated in the FAA’s Balloon Flying Handbook, the average pibal climbs at 300 feet per minute provided that there are no significant wind speed changes. With some quick calculations, we know that after 30 seconds, a pibal will be approximately 150 feet above ground (AGL).
To begin plotting the pibal recording information, release the pibal and track it with a compass. At 30 seconds, take a reading and make a mark on graph paper to represent the starting point. Make a second mark to represent the direction plotted. In Figure 3-6, a track of 300° at 5 mph is depicted. Label the first two points “A” and “B.”
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 your 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 will be labeled “C.” See the example in Figure 3-7. (NOTE: The angles in the successive graphics are exaggerated for clarity.)
Figure 3-7. Second pibal plot showing 310° at 1 minute.
At 1:30 minutes, take another reading. The pibal should 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 (see Figure 3-8). This plotting can be continued as long as the pibal remains in sight.
Figure 3-8. Third pibal plot showing 330° at 1:30 minutes.
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°.
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.
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, or a tablet. 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 (i.e., flying close to the surface) 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, through practice, with a high degree of reliability.
The balloon pilot, more so than pilots who fly other types of aircraft, must have the capability of visualizing the winds 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 taking off without proper planning and an understanding of the winds and terrain to be navigated.