This page addresses the techniques used for searching for, entering, and working mountain wave lift. Discussion of variometer use assumes a netto variometer is **not** used. ## Searching In addition to the requirements of 14 CFR §91.103, preflight preparation for a wave flight must include a through familiarization with [[Wave Soaring Weather Information]], topography of the intended soaring area, and aircraft performance and capabilities associated with the proposed flight. ### Location Knowledge of the local terrain and current weather information will largely determine where a pilot should search for wave. The pilot must also have a plan to return to the airport if unable to connect with wave lift; this plan should allow for significant performance degradations, as flight through extreme sink and rotor is still very likely. Once airborne, visually identifying the [[Anatomy of a Mountain Wave System]] can make contacting wave lift significantly easier. Searching upwind of lenticular clouds in the foehn gaps is typically the best place to start. In dry conditions, pilot reports or the presence of other gliders can eliminate much of the guesswork. Additionally, taking the time to talk to experienced local pilots is usually worth the investment. ## Towing into Wave Towing into the wave is often the easiest and most convenient way to conduct a wave soaring flight. Ideally, the tow can be planned to circumnavigate the rotor, however, this is not always possible. ![[GFH tow around rotor.png]] If it is necessary to tow through the rotor, the tow route should be briefed with the tow pilot to minimize exposure to rotor, and place the glider at the expected location and altitude of the wave lift. Moderate to extreme turbulence is present within the rotor; accepting this risk is not a decision either pilot should take lightly. Extra care must be taken to avoid an unusual attitude, abnormal tow position, or [[Slack Line]] developing; be prepared to release if any unsafe condition develops. As the tow progresses upwind, the pilots will first encounter the down-side of the rotor, marked by general down-swings of the variometer; in strong conditions, the aircraft may momentarily be **descending** on tow. As the flight continues into the up-side of the rotor, the variometer will show general up-swings. Upon contacting the smooth laminar flow of the wave, the turbulence and erratic jumps in the variometer subside. Lift will steadily increase as the tow progresses upwind, eventually peaking, then trending down as the aircraft fly into the sink immediately downwind of the wave-generating terrain. The glider should release once the pilot is certain that they have contacted a workable area of lift. ![[GFH rotor tow.png]] To ensure that the glider releases into wave lift, the pilot should be familiar with the glider and towplane's performance in neutral air (no lift or sink): - Rate of climb (variometer indication) on tow in neutral air - Rate of descent (variometer indication) off tow in neutral air, at minimum sink speed Upon releasing from tow, the glider pilot can anticipate the drop in variometer reading to be approximately the difference between these two values. With this in mind, the glider pilot can cross-check the variometer in areas of suspected lift to ensure that strong enough lift is encountered to make releasing worthwhile. As an example, let's say a particular glider and towplane average +5kts climb on tow, and the glider sinks at -2kts in neutral air on a given day. The glider pilot would expect the variometer to drop by 7kts upon releasing from tow. If the glider releases in an air mass with the variometer reading +7kts on tow, the glider would be in an area of "zero-sink", where the air mass lift equals the glider's sink rate. Releasing in anything above +7kts, the glider pilot should expect to be able to gain altitude. In practice, this means that the variometer should be cross-checked throughout the tow, especially when transitioning from the rotor to the wave. As wave lift is encountered, the air flow becomes smooth and laminar, with a steadily increasing variometer indication. If weak or marginal lift is encountered at first, the glider may simply be too low; towing further upwind and making a circuit to gain additional altitude before release can mitigate the risk of falling out of the wave prematurely. It is important to note that the rate of climb on tow is *highly* variable, based on a number of factors related to [[Performance During Takeoff and Tow]]. ## Soaring into Wave Less commonly, a glider pilot may attempt to soar into wave lift. This often occurs on days with relatively weak wave and other forms of lift present, or if the pilot has prematurely fallen out of the wave and is attempting to re-contact it. ### Thermalling Into Wave If the air below the wave flow is unstable and conducive to [[Thermal Formation]], it may be possible to thermal into the wave. As the top of the thermal becomes turbulent, the pilot should fly upwind and attempt to contact the wave lift. ![[GFH thermal into wave.png]] ### Ridge Soaring Into Wave If lee waves are in phase with the terrain downwind, it may be possible to transition from ridge soaring into the wave. Climb as high as possible in the ridge lift, then fly upwind and attempt to contact the wave lift. Do **NOT** attempt to fly downwind over rising terrain, as **substantial** sink will be encountered before the wave. ![[GFH ridge into wave.png]] ### Climbing the Rotor The most challenging and hazardous method of soaring into the wave involves climbing the rotor. This is method is usually reserved for less severe rotor conditions, if the pilot prematurely falls out of the wave, but is still in a safe position and altitude to attempt to re-contact the wave, rather than return to the airport immediately. The erratic and unpredictable nature of rotor makes maneuvering the glider to remain in lift challenging, but the up-side of the rotor typically remains stationary with respect to the ground, and can be identified with the help of mountain wave associated clouds. ## Soaring Techniques Once reliable contact with wave lift is established, the pilot must maneuver the glider to remain within, and locate the area with the strongest lift. If the wind speed is less than the glider's minimum sink speed, the minimum sink speed should be flown. If the wind speed is greater than the glider's minimum sink speed, the glider must fly fast enough to penetrate upwind until finding the area with the strongest lift, then slow to match the wind speed. The glider should not fly at less than the wind speed, as this will result in downwind drift into strong sink. ![[GFH maintaining wave.png]] Finding the area with the strongest lift is usually accomplished by first flying directly upwind, towards the wave generating terrain. The pilot should note where the lift increases, peaks, and decreases, maintaining orientation with the clouds (if present) and ground references below. The glider pilot is essentially **bracketing** the horizontal distance to the wave generating terrain (and wave associated clouds, if present). Once the area with the strongest lift is identified, the glider can be maneuvered to remain in this area. In the case of wind speed greater than or equal to the glider's minimum sink speed, the glider can remain stationary in this area by matching the wind speed exactly. If the wind speed is less than the glider's minimum sink speed, the glider must maneuver to remain in the strongest lift. In the case of a long, relatively continuous mountain ridge generating the wave, the pilot may be able to perform a series of long, straight-line tracks parallel to the ridgeline, while crabbing to maintain the correct horizontal spacing from the terrain. In the case of ridgeline discontinuities or isolated peaks generating the wave, performing S-turns into the wind can keep the glider in a relatively small area. In either case, **turns should always be made into the wind**; unlike thermal lift, a mountain wave system remains stationary with respect to the ground - turning downwind can quickly result in contact with strong sink! Depending on the goals of the flight, exploring the lateral areas of lift parallel to the ridgeline may be worthwhile. The **down** slope of the terrain is what generates wave, and any discontinuities to the ridgeline may enhance or suppress wave strength. Bowls and spurs can significantly alter the localized effects of wave, especially when winds are not exactly perpendicular to the ridgeline. As the wind speed, direction, and atmospheric stability change with altitude, so will the strength and location of the lift. ### Secondary, Tertiary, Etc In most cases, the primary wave is the strongest and most organized, but secondary, tertiary, etc waves often exist within a [[Trapped Lee Waves]] system. The same soaring techniques apply to all waves. The pilot may elect to remain within the secondary or tertiary wave for any number of reasons: closer proximity to the airport, to limit altitude gain if not properly equipped for high-altitude flight, or to avoid strong rotor conditions, to name a few. In addition, it is possible to transition between waves; a mountain wave system remains stationary with respect to the ground, so transitioning downwind is considerably easier than transitioning upwind. A pilot should anticipate **significant** sink on the downwind side of each wave, and choose a sink penetration speed accordingly. Contacting rotor is a possibility, so a pilot must also be ready to reduce speed promptly if turbulence is encountered. ![[GFH transitioning waves.png]] ## Descent When the time comes to end the flight, the pilot may have several options for how to conduct the descent. If the airport is located clear of the mountain wave system, descending may be as simple as leaving the wave, and descending normally to the airport. If the airport is located below the mountain wave system, things can become more challenging. If possible, it is often advantageous to allow the glider to drift downwind into the sink of the primary, or secondary, etc wave, while remaining upwind of the airport - this way, the glider flies *over*, rather than through the rotor on the way back to the airport. If clouds make this strategy impractical, sometimes the spoilers must be used at altitude until appropriate cloud clearances can be maintained. The pilot should also keep in mind that excessively rapid descents are not good for the pilot or the aircraft! Rapid temperature changes are not good for metal or composite aircraft, and the pilot's risk of ear or sinus block increases substantially. Plan ahead, and descend with intent.