Cruising Speed
Typically when we start with our cross-country flying, we feel like we need to take every thermal, this habit is often a hard one to break. Even pilots who are quite experienced still want to stop and climb in thermals that are less than optimum. We have to be selective when it comes to increasing our overall achieved cross-country speeds. Take the below graph, it’s for a typical 15m ballasted racing glider. If you increase your average thermal strength for the day from 3 knots to 4 knots, it will improve your speed from 100 kph to 110 kph. What do you have to remember though? These are achieved rates of climb from bottom to top, so as we’ve discussed in the past, we need to decide upon and then centre thermals quickly, which of course takes practice.
You can immediately see that it is obvious that flying through a few of those weaker climbs and pushing on to the stronger ones will make a big difference in your overall speed. Work hard at raising your confidence in being able to find that next climb, then secondly, really try to decide quickly before you commit to a turn.
Optimize Cruising Speed
From here we need to consider how fast to fly when cruising between thermals. We want to be able to arrive at a useful height to climb in the next strong thermal, but not so low that we are searching for a paddock – that is the worst! From the graph, 10 knots too fast or too slow will only mean a reduction in cross-country speed of 2 or 3 kph, no worries. Notice here that the loss is greater for flying way too slowly – flying significantly too fast does however increase your workload in finding better thermals more often. Now that we are armed with the knowledge that our chosen cruising speed is not so critical, we can look carefully at the terrain or sky ahead and decide where the next good climb may be. If it is far away, right at the limit of our range, we will need to travel more slowly, so that we don’t have to stop short and use a weak thermal, which will drag our overall speed down quite a lot. If it is close, we can push along fast and still be at a comfortable height to use it when we arrive.
I’m guessing that most of the USA is similar to Australia, we are generally blessed with consistent, predictable weather. If the last few climbs have been 5 or 6 knots, then it’s likely that the next one will be as strong too. So it’s reasonably easy to pass up a 3-4 knotter on the way, and still, be confident of staying within the chosen ideal height band as we discussed in previous articles. Given this, we can use the following graph to decide on our cruising speed for the day. Remember, this is for a typical ballasted 15 metre glider. You can re-create this graph by taking the published polar of your glider & plotting it yourself. To get the speeds to stick, you may want to draw up a table of cruising speeds for given climb rates, and stick it on your panel. They aren’t that important, but they will help with a ‘block speed’ to work with initially. What is more important is to be looking out the front and deciding whether you can push up the cruise speed, or extend the glide.
‘Block speeds’
Effectively this is where the aim is to cruise at a more or less steady speed between climbs, with only small variations when in lift or sink. If you fly block speeds then the wing doesn’t have to work as hard, because pulling up and pushing over, is wasteful energy by the classic McCready theory. It is almost impossible, even for the very best pilots, to anticipate the edge of good and bad air and to react accordingly. So smooth, steady cruising is what we are looking for – keeping up the momentum and establishing a comfortable rhythm throughout the flight is the most important.
If you work hard at this, be disciplined about your thermal selection, then this is an area that you will make your biggest gains. Happy cruising!
Adam Woolley was born into the gliding world, being the 3rd generation in his family. Going solo at 15, his thirst for efficiency in soaring flight & quest for a world championship title to his name has never wavered. One big passion is sharing his experiences & joy with other glider pilots all around the world. Adam is an airline pilot in Japan on the B767 & spends his off time chasing summer around the globe. He has now won 7 national Championships & represented Australia at 5 WGC's & 1 EGC.
