Leaving thermals

Ok theory vs practice time folks.

Some pilots say when leaving a thermal you should tighten up, roll level and exit straight across the core. Most of us, I suspect simply roll out on heading and tootle off.

Is the former practical? Is it used? In a busy thermal leaving across the middle could put you in a sticky position.

Any thoughts?

According to George Moffatt in his 'Winning on the Wind' book this technique is mentioned and he illustrates the advantage you can gain from it. I personally have many other points in my flying to try to improve before I get to things like this!

Nick.

Seems simple to me. If you have the thermal for yourself, you can focus on leaving it in the optimal way. If others are around, safety has the first priority.

Depends. If the core of the thermal is on the upwind side of the cloud frequently enough, one can climb higher than cloudbase (relative to the center of the cloud cloudbase). Sometimes there is weaker but nonetheless thermal upwind feeding the system and at times there may be wave. So, when leaving in an upwind direction, keep your mind wide open. November Bravo

That's the way I like to do it. Also, I prefer to accelerate across the core, where the rising air makes the acceleration less expensive in terms of altitude. But, it's like crossing a busy street - you have to look both ways (and also up and down) and then proceed with caution. If there's anyone in the thermal remotely near my altitude, I'll substantially moderate the maneuver (or more likely not do it at all) so that nobody else is effected.

When I'm not absolutely certain that I'm alone (and that's much of the time), I'll make a short radio call to announce my departure. Something pithy like [click]'One-eight-kilo to exit.'[/click] I figure that a two-second heads-up call like that is worth the bandwidth that it consumes.

It could just be wishful thinking, but I believe that I can feel the difference. Accelerating across the core of the thermal, the glider seems to pick up speed faster. When I just roll out of a busy thermal, it feels like I have to race the sinking air downwards substantially more to accelerate to inter-thermal cruise speed.

Bob K.

All of this assumes that you are able to stay in the core of the thermal. Most of the time I'm working hard just to stay in the lift)

Greig Glover

Here's another strategy.

Turn some of your attention to the side of the cloud faicing the course line during your climb. Notice how the cloud is forming on that side. Most Cus do not have sharp edges, but have little jetties and fisures. Look for wisps beyond the edge of the cloud. If the lift starts to die before you reach cloudbase or falls below your minimum acceptable value, exit naturally by rolling level as you come on course line. Accelerate to cruising speed and follow the jetties and wisps. These can extend for quite a distance beyond the edges of the cloud. Use them.

If the cloud has a sharp edge with no wisps, accelerate to cruisng speed and go. If you can position yourself to traverse the core, all the better, but don't waste time taking an extra turn in weaker lift setting yourself up for this. The only time it really makes sense to do a Moffat slingshot is when it's strong all the way up to cloudbase, and you're just taking the energy as speed rather than altitude.

Point is, there are almost always ways to exit a cloud that avoid the stronger sink, and may even provide additional lift for quite a distance beyond the edge of the cloud. It is seldom strong, so don't wast time flying at minimum sink. Think of it instead as a way to avoid losing several hundred feet while maintaining an efficient cruising speed.

FYI Reichmann (Cross-country Soaring 7th Ed P12) credits the technique (recommended by Moffat) to a Polish competition pilot - Adam Witek. He doesn't explicitly say what he (Reichmann) recommends!

Keith (wishing it made a difference to me!) Turner

I always like to half roll inverted and pull through onto course line. Gives great exit speed.

Al

you assume we have clouds to mark our thermals...

LOL... TIZ

Al, the half loop and rollout onto heading works better. Precede of course by accelerating up to 110 kts whilst circling the core at a radius of around 70m ,grunting loudly to fight off the G loads.

Ian