The number one rule of safe cross-country soaring is always stay within glide range of a suitable landing area. The alternate landing area may be an airport or a farmer’s field. If thermaling is required just to make it to a suitable landing area, safe cross-country procedures are not being practiced. Sailplane pilots should always plan for high sink rates between thermals as there are always areas of sink around a lifting thermal to fill in the void vacated by the lifting air.
Before venturing beyond gliding distance from the home airport, thermaling and cross-country techniques can be practiced using small triangles or other short courses. Three examples are shown in Figure 11-10. The length of each leg depends on the performance of the glider, but they are typically small, around 5 or 10 miles each. Soaring conditions do not need to be excellent for these practice tasks but should not be so weak that it is difficult just to stay aloft. On a good day, the triangle may be flown more than once. If other airports are nearby, practice finding and switching to their communication frequency and listening to traffic in the traffic pattern. As progress is made along each leg of the triangle, frequently cross check the altitude needed to return to the home airport and abandon the course if needed. Setting a minimum altitude of 1,500 feet or 2,000 feet AGL to arrive back at the home site adds a margin of safety. Every landing after a soaring flight should be an accuracy landing.
Determining winds aloft while en route can be difficult. Often an estimate is the best that can be achieved. A first estimate is obtained from winds aloft forecasts provided by the AFSS. Once aloft, estimate windspeed and direction from the track of cumulus shadows over the ground, keeping in mind that the winds at cloud level are often different than those at lower levels. On cloudless days, obtain an estimate of wind by noting drift while thermaling. If the estimate was for a headwind of 10 knots but more height is lost on glides than the glide calculator indicates, the headwind estimate may be too low and will need to be adjusted. When flying with GPS, determine windspeed from TAS by simple subtraction. Some flight computers automatically calculate the winds aloft while other GPS systems estimate winds by calculating the drift after several thermal turns.
It is important to develop skill in quickly determining altitude needed for a measured distance using one of the glide calculator tools. For instance, while on a cross-country flight and over a good landing spot with the next good landing site a distance of 12 miles into a 10-knot headwind. [Figure 11-11] The glide calculator shows that 3,200 feet is needed to accomplish the glide. Add 1,500 feet above ground to allow time to set up for an off-field landing if necessary, to make the total needed 4,700 feet. The present height is only 3,800 feet, not high enough to accomplish the 12-mile glide, but still high enough to start along course. Head out adjusting the speed based on the MacCready ring or other speed director. After two miles with no lift, altitude is almost 3,300 feet, still not high enough to glide the remaining 10 miles, but high enough to turn back to the last landing site. After almost 4 miles, a 4-knot thermal is encountered at about 2,700 feet and provides for a climb to 4,300 feet.
When using the glide calculator tool, keep in mind that these calculations account for only the glider’s calm air rate of descent. Any sink can drastically affect these calculations and make them worthless. In times of good lift, there will also be areas of strong sink. A sailplane pilot must learn to read the sky to find the lift and avoid or pass through the sink as quickly as possible. Time in lift is good and time in sink is bad. A good sailplane pilot will be thoroughly aware of that particular sailplane’s polar curves and the effects from different conditions of lift, sink, and winds.
During the climb, the downwind drift of the thermal moves the glider back on course approximately a half mile. Now, there is almost 9 miles to glide to the next landing spot, and a check of the glide calculator indicates 2,400 feet are needed for the glide into the 10-knot headwind, plus 1,500 feet at the destination, for a total of 3,900 feet. Now, there is 400 feet above the minimum glide with a margin to plan the landing. In the previous example, had the thermal topped at 3,600 feet (instead of 4,300 feet) there would not be enough altitude to glide the 9 miles into the 10-knot headwind. However, there would be enough height to continue further on course in hopes of finding more lift before needing to turn downwind back to the previous landing spot. Any cross-country soaring flight involves dozens of decisions and calculations such as this. In addition, safety margins may need to be more conservative if there is reason to believe the glide may not work as planned, for example, other pilots reporting heavy sink along the intended course.
On any soaring flight, there is an altitude when a decision must be made to cease attempts to work thermals and commit to a landing. This is especially true of cross-country flights in which landings are often in unfamiliar places and feature additional pressures like those discussed in Chapter 8, Abnormal and Emergency Procedures. It is even more difficult on cross-country flights to switch the mental process from soaring to committing to a landing. For beginners, an altitude of 1,000 feet AGL is a recommended minimum to commit to landing. A better choice is to pick a landing site by 1,500 feet AGL, which still allows time to be ready for a thermal while further inspecting the intended landing area. The exact altitude where the thought processes should shift from soaring to landing preparation depends on the terrain. In areas of the Midwest in the United States, landable fields may be present every few miles, allowing a delay in field selection to a lower altitude. In areas of the desert southwest or the Great Basin, landing sites may be 30 or more miles apart, so focusing on a landing spot must begin at much higher altitudes above the ground.
Once committed in the pattern, do not try to thermal away again. Accidents occur due to stalls or spins from thermaling attempts in the pattern. Damage to the glider’s airframe can and has occurred after a pilot drifted away from a safe landing spot while trying to thermal from low altitudes. When the thermal dissipates, the pilot is too far beyond the site to return for a safe landing and is left with a less suitable landing choice. It is easy to fall into this trap. In the excitement of preparing for an off-field landing, do not forget a prelanding checklist.
A common first cross-country flight is a 50-kilometer (32 statute miles) straight distance flight with a landing at another field. The distance is short enough that it can be flown at a leisurely pace on an average soaring day and also qualifies for part of the FAI Silver Badge. Prepare the course well and find out about all available landing areas along the way. Get to the soaring site early so there is no rush in the preflight preparations. Once airborne, take time to get a feel for the day’s thermals. If the day looks good enough and height is adequate to set off on course, commit to the task! Landing away from the home field for the first time requires skill, planning, and knowledge but is a confidence builder whether the task was accomplished or not.