In favorable terrain, and when the wind is blowing strong enough and from the right direction, it is possible to achieve very long flights by using nothing but ridge lift. Jean-Marie Clément recounts the history of world record flights flown in ridge lift in his book Dancing with the Wind (p 44). The Appalachian Mountains in the United States are famous for providing long and straight ridge lines where many record breaking flights were achieved. Similar feats are possible in the European Alps. E.g., In 1998, Wolfgang Janowitsch and Hermann Trimmel were the first to fly over 1,500 km out and back between Wiener Neustadt and Innsbruck, solely in ridge lift.
Before attempting any XC-flight along the ridges it’s important to practice all the techniques covered in the section of How to Fy in Ridge Lift including ridge transitions, spur crossings, pass crossings, etc. and gain some experience in all the different types of terrain that we plan to use along our route.
How do I plan my route?
Detailed route planning is critical for ridge flights, much more so than in thermal conditions. E.g., we have seen that upwind transitions between ridges can be extremely difficult and often impossible. So we would not want to plan a route that requires such transitions!
Start with the wind and if it works for the terrain
Obviously we must carefully study the wind and weather forecast for the entire task area. Wind directions can vary widely, especially in mountainous terrain. We want to have a good sense for the wind at the level of the ridges but also further down in the valleys. What’s the height band along the ridges that will likely work best, and what’s the altitude relative to the ridge tops that we have to maintain to stay in lift?
Account for any gaps in the ridge line
If the ridge is interrupted by gaps I study the length of these gaps as well as the height and bottom of the ridge line before and after the gap. Will the altitude that I am able to gain before the crossing be enough to bridge the gap and arrive at the next ridge high enough to connect with lift? And if I plan an out and back flight, will the same be true on the return leg?
The image above shows an approx. 60 km long flight path along a mountain ridge that is interrupted by good sized gaps of 10-15 km. In planning a flight along this ridge I look at the altitude MSL at the top foot of each of the mountains. I would like to arrive at the next one not lower than about 1/3 below the top of the terrain-height (the difference between the top and foot of the mountain) and, at least in this area, well above tree line. This, plus the length of the gap and the performance of my glider considering the anticipated cross-wind tells me how high I have to be when I leave a ridge to bridge the gap to the next one.
Consider the upwind terrain
If there are other ridges further upwind of the ones we plan to use, we must prepare for the possibility of wave impacting the lift along our route. We have seen before that a wave motion aloft can amplify or destroy the lift along a slope (based on whether the ridge is positioned in synch with the wave-length or not). There’s really no way to accurately predict the length of such a wave motion in advance so we have to be prepared for the possibility that a ridge may not be working. (And remember, if a ridge isn’t working, we must fly away from it! If we’re lucky we are able to climb in rotor and/or wave lift a little further upwind.)
Always have a Plan B
Finally, we must know all the potential land-out fields along our task and remember that our glide computer may be far too optimistic when it comes to the distance that we can glide before we reach them. If there is strong lift along the ridges, there is also strong sink somewhere else and the flight path to our land out field could very well lead through the strongest sink. Furthermore we may also have to deal with very difficult landing conditions: most airports and even most potential land-out fields are in the middle and along the bottom of the valleys; this is often the place where we may find strong crosswind and/or rotor turbulence. I’ve experienced what massive sink in the landing pattern can do. It pays to remain conservative!
How fast should I fly?
First of call, considering safety, near terrain one must always maintain an appropriate safety cushion. The recommended final approach speed for the glider should be the absolute minimum. If the wind is strong, turbulent, or if there is a risk of thermals breaking off below, then it’s better to add another 10-15kt.
In very strong conditions it is possible to fly quite fast without losing altitude. Those conditions are usually rough, so don’t fly faster than rough air speed!
In terms of cruising speed to cover long distances quickly I have found that there is no simple rule that works for ridge flying. McCready theory doesn’t really apply to flying along the ridges because most or the time you’re climbing as you move forward and not stopping to gain altitude. It’s more important to fly in the height band that produces the strongest lift. That means that I may need to slow down if I run the risk of dropping below the best height band, and speed up just before I’m getting so high that the lift gets weaker.
It’s also important to adjust the speed well in advance of a transition or gap crossing. In this case it’s often important to gain as much altitude as possible, ideally without having to stop and turn, so it’s best to slow down to the minimum safety speed, especially in areas where the lift is strongest (e.g. in bowls that face directly into the wind). Obviously I want to speed up during a transition or gap crossing but not so much that I arrive at the next ridge so low that I can’t connect with good lift right away. I don’t know if there’s a flight computer that can consider all these variables but I’ve found that getting this right is more art than science.