4. LESSON 27 - RIDGE LIFT AND MOUNTAIN WAVE
- Keep a good lookout for other gliders, paragliders, cables, zip lines, et cetera.
- Always have an escape route ready
- Maintain a safe airspeed at all times
- Remember that the glider with the ridge on the right has priority
- Overtake with caution, bearing in mind the other glider can suddenly change
- Approach the ridge at a shallow angle
- Make all turns away from the ridge
- All turns need to be perfectly coordinated
It’s great to fly in the mountains and the view is often breath-taking! Flying in the mountains and along ridges is mostly considered suitable for advanced glider pilots only, because you are often very close to the ground, which requires perfect control of the glider. If your airfield lies close to – or in between – mountains or hills, this lesson will be useful for you, but please bear in mind that we will cover the absolute basics only. For example, it’s much harder to judge where your horizon is when you are flying along a ridge. Because of the upsloping terrain it may look as if the horizon is moving up in the canopy, while your pitch attitude remains the same. Avoid pulling back on the stick when this happens, because this reduces the airspeed when you need it most. Traffic wise, it can be very busy along a ridge. So look outside as much as possible and pay close attention to other gliders, aircraft, paragliders, electricity cables, zip lines and so forth. Finally, remember that other traffic may be very hard to see when the sun is low. Weather conditions can change rapidly in mountainous terrain. Be aware of poor visibility and severe turbulence.
You will not be ready to fly along ridges safely after one short briefing. Keep a lot of distance from others when you familiarize yourself with flying in the mountains. Do not push your limits without the guidance of an experienced instructor.
A ridge lift starts with wind that is being deflected by a ridge. As you know, glider pilots can use upward moving air to climb or to gain extra energy and increase airspeed, so they can fly long distances along the ridge. The air on the lee side of the ridge sinks. If the wind direction changes, the airflow around the ridge changes. Valleys can act like channels between higher mountain ranges and very often the wind direction in a valley will change during the day. Also, the wind direction at a low height can be completely different from the wind direction higher up. So a mountain ridge that was perfect for flying in the morning can be challenging in the afternoon.
Wave lift (also called mountain wave or lee wave) is very different from ridge lift. It occurs on the downwind or lee side of a ridge and we can use this kind of lift to reach incredible altitudes. The formation of mountain wave has to do with gravity and the elasticity of the air, but also with a suitable ridge shape, the right wind strength and temperature. Two ridges parallel to each other with a suitable shape, under the right conditions, can start resonating and cause the air between the ridges to follow a wavy pattern. Finding the mountain wave is not easy; it is considered an advanced gliding technique. If you are lucky enough to experience some mountain wave during your basic training, you will quickly notice that the big difference with wave lift and thermal lift is that wave lift feels much more smoothly.
ESCAPE ROUTE AND AIRSPEED
When flying along a ridge you always need to have an escape plan ready at the back of your mind. Never enter a narrow valley without being 100% certain that you can also get out again. Remember that you will need additional airspeed to effectively use the flight controls and to account for sudden sink, thermals or turbulence. If it has been raining, sloping terrain dries quicker and the slopes are drier earlier than the surrounding flatlands. If the sun comes out and heats these slopes at the right angle, they warm up quickly and often generate new thermals. Such thermals will cause some very strong drafts (both upwards and downwards) along the ridge.
BASIC RULES OF RIDGE FLYING
Never approach the ridge at a 90° angle. When flying in a tailwind your groundspeed is much higher and you might end up closer to the ridge than you wanted. Instead, take a shallow angle to intercept your track along the ridge and take a suitable drift correction to avoid being blown closer to the slope. All the turns you make need to be away from the ridge until you are well above the crest! If conditions force you to circle in order to climb; make “figure-8” turns. When flying into the wind, decrease your bank angle for 3 or 4 seconds before turning downwind in the direction of the slope again. It is an absolute no-go to turn in the direction of the mountain because this is extremely dangerous. Fly coordinated turns and pay special attention to your pitch attitude and your airspeed.
The illustration above shows two gliders approaching each other at the same altitude: the glider with the ridge on its righthand side has priority. For him or her it is impossible to turn right to avoid a collision. The other glider (having the ridge on its left-hand side) must veer off to the right. Overtaking another glider alongside the ridge is always done into the wind. Pay a lot of attention before, during and after overtaking, because the other glider has priority.