Introduction to Thermalling
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- Опубліковано 22 тра 2024
- - An introduction to flying thermals for glider pilots.
This video covers:
00:00 Introduction
0:13 Why good thermalling is important
01:03 Models of typical thermals
03:12 1-26 Thermalling Superstar
3:38 Thermalling speed matters & figuring out min sink while turning
7:02 Entering thermals
8:21 Centering in thermals
12:34 Leaving thermals
13:25 closing recommendations
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Recommended Reading for further study:
From bobwander.com:
• A Gliding Mentor series book "Thermals" by Rolf Hertenstein, Ph.D.
• The Art Of Thermaling...Made Easy! by Bob Wander
The Soaring Engine V1: Ridge, Thermal & Mountain Soaring by G Dale
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Bill - Спорт
Extremely helpful and well crafted Bill, Thank You!
I´ve always wondered what the theory behind thermalling, especially centering, is, so thank you very much :))
great video!
Excellent video Bill!!
This is great!
wow, such a detailed analysis
Thanks for this video
Excellent video! Thank you very much for posting this.
super useful content. thanks =)
Excellent 2ZC
this was great, love the laid back presentation
Really superb graphics and animation!
Thank you.
Great video. Thanks for putting all those techniques together in one place. I’ve always been confused about whether to step in my bank or shallow out when encountering lift.
Great video! After hundreds of hours trying to advance my thermaling skills, the Huth method worked the best. I will skid the glider a little in small strong cores also. It’s better to be inefficient in the strong lift than efficient in the weak lift. If you can’t stay in the lift, you might fall out of the bottom of the thermal.
While some prefer to slip the glider in thermals (e.g., “The Halighaus way”. thesoaringpage.com/docs/Holighaus%202004.pdf), I don’t know of anyone who advocates any degree of SKID! (That risks spin entry) Huth says to increase from 25 to 50º of bank when the surge is detected.
thesoaringpage.com/docs/Flying%20Further%20and%20Faster%20Pt%201.pdf#page=45
A slip is a way to go straight. You want to turn. Practice skidding your glider when you have room for error. Have a little extra airspeed before anticipating the core and as soon as you hit the core pull up and bank 30° and generous rudder. Immediately push the nose down so you’re just above stall and try to hang there for a second or 2. Then opposite rudder and gently go back into the lighter lift. You’re trying to stay in the small core as long as possible. Try to get a little over a 90° turn with the skid. Takes a lot of practice. I won’t do it close to other gliders.
Sounds sketchy. The idea of thermalling with a slight slip (not skid) is to reduce the aileron deflection in the steep turn and thereby reduce drag. Recall that in a steep coordinated (yaw string centered) turn the inside aileron will need to be down slightly to compensate for its slower airspeed (approx 20% slower at the tip in a 45° bank)
@@BillPalmer That’s interesting Bill. Good technique for scratching in light lift. Some of the advanced pilots have said to try thermaling with rudder only. The only time I use the skid method is in strong small cores. I have never entered a spin skidding a glider in a core. That’s including rigid wing hang gliders. On the “ big air” days it’s better to stay in the tight cores as long as possible than to worry about centering the yaw string.
The best centering method I think is to use the vario. As the lift increases, flatten the bank angle and as it decreases steepen the bank angle. The greater the change in lift, the greater the change in bank angle. This method gets me into the best lift in usually 3 turns or less.
Anyone else want to share their favorite methods?
Do you account for any vario lag in this method?
Thanks Bill for the video, very useful to look at the various methods of thermalling. In practice, I still rely mostly on feeling, sensing the thermal. The vario indicator may go up, but I only turn towards the lift when I feel that the updraft "carries" the airplane and provides enough lift. Greetings from the Netherlands, Marc
Bob Wander's Mentor series book "Breaking the Apron Strings" by Phil Petmecky describes another interesting method: "Shallow the bank, slightly, if the vario is rising. Steepen the bank, slightly, if the vario is falling. ... Steepen the bank, quickly and much steeper, if the vario is near the top of the best lift you think is possible."
Yes!
There are many methods of thinking about correcting your position in the thermal ,but that all come down to figuring out where you are in relation to the thermal core and providing adjustments to center on the thermal, be it by constant bank angles and short periods of straight flight (a simple method often taught as the first centering method) or varying the bank angle as you gain experience. You’ve probably heard me say that in the good part of the thermal to bank steeply because you want to stay there. .
Pilots are often misguided by the display of a thermal: The seat pressure or the variometer give the impression that a thermal is present. However, it is often just a horizontal or vertical gust.
With the HAWK software in conjunction with an LX9000 vario, it is possible to almost completely eliminate these false indications.My accuracy when flying into real thermals has increased significantly over the last 2 years thanks to HAWK.
How long will it be until there’s an AI thermalling autopilot. Will we look back and say “what’s really the point here?”
A thermal will be surrounded by sinking air only in the absence of wind. In wind, the sink will be on the downwind side of the core.
Thanks for a great video. One detail is more complex than it appears though, which is 'sink around the thermal'. It's hard to know what a lay person (say the person currently programming thermals in Microsoft Flight Simulator) would make of those sink arrows on the diagram, although they do commonly appear. The most common misconception is air that goes up has to come back down, otherwise the people on the ground would suffocate and we know that doesn't happen. Not often enough to make the papers, anyway. We need to keep in mind the air that rises is expanding and cooling until its temperature matches the air around it. At that point, to a first approximation, there is no need for that air to go anywhere. The volume (~diameter) of the thermal is extremely small compared to the area of nominally non-rising air between the thermals so the air simply moving sideways (aka wind) is easily sufficient to 'backfill' the thermal. There are secondary effects such as the rising air condensing when it reaches cloudbase and that adding energy, and air descending from above to below cloudbase gets a similar boost on the way down (i.e. the moisture evaporates and takes energy out of the airmass so it speeds its descent). Those secondary effects are normally relatively small (as a UK soaring pilot I've done a lot of cloud climbs) and also any descending air has a much greater area to do that with than the relatively narrow column of rising air, so IMHO we have to be careful not to give the impression that the sink around the thermal is some kind of inevitable inverse thermal to balance the books. It might be that the sink we do experience is more to do with any rotating turbulent air around the thermal than a river flowing downwards. I do think your video is great, and I don't mean to crap on it with this apparent minor correction, but thermals are being programmed right now in MSFS and I'm fearful Microsoft will think every 6 knot thermal should be surrounded by 6 knots sink.
Thanks for your insight. This is, after all just an INTRO to thermalling, certainly not the basis for programming weather mimicking software. The point was that the sink around a thermal should not be feared, but instead a sign that a thermal may be very close and to "get ready." The exact reason for it is somewhat irrelevant, though in my (non-meteorologist) opinion when the rising thermal displaces the static air, the most likely air to fill in the gap would be that immediately surrounding it. The aspects of the thermal air rising to the temperature equilibrium is covered in my Intro to Skew-T video - and another that I'm considering on atmospheric stability (oh, there I've gone and committed my self to that now..)
Great stuff.
Curious if any sailplane pilots have that experience of 'going over the falls'. It's something I've encountered a few times while hang gliding on days with strong thermals, there's a sharp contrast of lift (or lift/sink) at the boundary inside and outside the thermal; if you exit the thermal nose first it can feel like the glider is about to tumble (not a pleasant feeling).
This must be so scary! I have not tried thermaling yet but I will this spring. I hope it will be OK. I am still a beginner (20 flights).
Not really. We are certainly aware of the sink that surrounds many thermals but the “going over the falls“ is not one I’ve heard in relation to sailplanes.
@@BillPalmer my suspicion is that the planform of a hang glider plus its slower flying speed are contributing factors.
Been there, done that… it’s an eye opening experience
👍
I'm curious, whats the highest altitude you've seen birds at? Are they only helpful indicators down low (under 300')?
Oh at least 10,000
Would you comment on how to determine the ideal bank angle? I've found myself at lower angles (30ish) "looking for surge" for a long time, when maybe I should have been steeper and closer in.
Turning performance and optimum bank angle for thermalling has some variables: the glider's performance and the size of the thermal. I wish I could say "thermal at X°", but it's not that simple as our turning performance penalty increases more quickly after 30°, and really goes up above 45°. That said, sometimes it's not only worth it, but necessary to stay within the confines of the thermal.
A good study of this is found in several "Glider Aerodynamics Puzzler" articles from Soaring Magazine. This particular subject is addressed well in the April 2020 article "Turning Flight Performance."
A collection of the Aerodynamics Puzzler articles are republished (with permission) at TheSoaringPage.com in the Learning/Ground Study section under Aerodynamics & Turning Performance.
As far as evaluating your own performance WeGlide.org offers a "Coach" function that can evaluate your performance on thermalling flights. Remember SSA members get a free subscription to WeGlide by entering your SSA account number on your WeGlide profile page.
Thanks@@BillPalmer! The "Turning Flight Performance" article is helpful, as well as your "What's so special about a 45° bank turn?" video and your "Bank angle & performance sheet". It's definitely not as simple as "thermal at X°" or the "gliders want to thermal at 45°" advice I've heard, though 30-50 does seem like a good range to start with and experiment.
@@erikburrows exactly. Now equipped with that knowledge you can practice applying it in the glider.
I fly model rc. Gliders and I have learned the best skills from watching the true masters of flight, the birds...lol..
So true!
“Intro to thermalling” von Bill Palmer … wäre hierzu mein Videotipp als Segelflieger 😊 ua-cam.com/video/z4xKYfT6aJA/v-deo.html
Vielleicht kommen ja paar motorisierte Kollegen auf den Geschmack…ok bin auch gerne mit Motor unterwegs, ist manchmal entspannender … nicht immer möchte ich mir die Höhenmeter erarbeiten müssen…
Why add 3 for 30 degree bank? Not 4?
When we do the math. 42 mph x 1.072 (the square root of the 1.15 g load at 30°) = 45.02 which is a 3 mph addition.