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FreeFlight Advice: High Siding (Thermal Technique)

Q: I was wondering if you can give us some more insight in “High-siding” in thermals. Why? When? When not? and How exactly

A: Great question!  “High siding” is a term that comes up pretty often when talking about climbing in hang gliding… AND it’s a often misunderstood!  Let’s explore…

 

The practice of high siding is simply when we have to hold a weight shift input toward the outside of our turn in order to maintain constant bank.  There’s not really much secret in how it’s done, actually… and often people do it without even realizing it.  The less roll-stable a hang glider is, the more high siding will be required in a 360.  So single surface gliders usually don’t require much at all… and topless wings require quite a bit, especially at steep bank angles.  If your glider has VG, the more VG you have on the more high siding you will be required to do in your 360.  For more on why this is check out our other post about strategic VG use.

So you might be thinking- if high siding is required to maintain a constant bank, how would we have a choice in doing it or not doing it?  Why would people talk about how we need to do it to climb efficiently?!  And that would be an excellent question to be asking- because YES, any particular glider will only require some specific amount of high siding to maintain constant bank… and no, we don’t get to choose to high side more (you’ll just roll out of your turn if your try!).

BUT- we can TUNE a glider to need more or less high siding, since it is a factor of roll stability.  Generally, making things tighter means requiring more high siding.  Pulling VG also increases anhedral, which decreases roll stability, which means more high siding will be needed.  Tightening the sail also means handling decreases, which means we HAVE TO shift our weight farther to the outside to maintain that same roll input to counter the glider’s tendency to roll in.

So hopefully that explains what high siding is, how it’s done, and why- from an aerodynamic standpoint.  Why high siding is generally regarded as EFFICIENT is a slightly different topic altogether… and best explained by physics.  When we weight shift in our hang glider (or paraglider), we are moving the “center of gravity” (CG) of the aircraft as a whole.  CG is the point in which gravity acts, and the rest of the object moves about this point.  Imagine for a second, a hammer.  The head is very heavy, and the handle very light.  If we were to find the balance point between the head and the handle, this would be the CG.  If we painted a dot on that point, and threw the hammer in the air… we could watch that dot follow as smooth arc while the head and the handle spun around and around.  The CG is the center of rotation in this example.  Relevance to hang gliding?  If we fly in a 500-ft circle… it is our CG that was centered on that circular path.  If we were able to shift our CG toward the outside wing… that would mean more of the glider was inside that arc than was outside, while our CG followed the same path as before.  This diagram explains it better than I ever could:

high siding by Dennis PagenThis diagram is reproduced with permission from Dennis Pagen, and is from his excellent book, “Secrets of Champions”- which is available for $29.95 in the USHPA online store.  I’ll share a few excepts from the book regarding high siding… but I strongly urge every pilot interested in improving and flying more efficiently to read this book in it’s entirety!

Secrets of Champions interview with Mike Barber:

I like to talk to students about bank angle. Most students turn too flat, especially down low when things are smaller. Sure, a steeper bank increases your sink rate, but if you are turning outside the core you’re going to sink even more. Larry Tudor pointed out long ago that every glider has a bank angle “sweet spot” that it likes and provides the best climb. It’s up to each pilot to find that bank on his or her glider.

Glider setup is important as well. Unless you’re high-siding you’re not flying efficiently. [Editor’s Note: High-siding is the term used for the technique of being on the upper side of center when in a steady-state turn. Some gliders are set up to require this more than others by virtue of anhedral adjustment]. Manfred Ruhmer says, “If you’re not high-siding, you’re not climbing.” Most people are slipping a bit in their turns, which kills their sink rate. They are pushing out but not high-siding so they are in a slight uncoordinated turn. To thermal efficiently you have to get your hips out. This technique takes effort, but there’s an added trick that helps.

Most expert pilots carry a little extra speed through the patches of poorer lift and turbulence as they circle. Then when they hit better climb they push out and high-side to adjust the bank angle. Pushing out slows the glider to take advantage of the better lift and pays off speed for extra altitude. At the same time it turns the glider so that you tighten up in the lift. Then you high-side to adjust the bank and balance. High-sid- ing is a yaw input, and this pitch and yaw control method is actually less fatiguing than trying to roll the glider in an elusive or broken core. The whole process is a form of dynamic soar- ing with finesse.

I’m not describing a process of pushing out and boating around. That’s a good way to tumble. I’m talking about dynamic pitch movements and bank control. Once you have exploited a stronger patch the bar should come back in as you con- tinue your circle.

Secrets of Champions interview with Paris Williams:

Every pilot has to tune his or her glider to suit their skills. High-siding is very important for a good climb. I set my glider up so it’s perfectly neutral in a turn with the VG off. That way I can dial in the amount of high-siding I want with the VG, since adding VG pull increases the overall anhedral in the wing. This is one reason why some glider manufacturers don’t use the new cam VG system*. The simpler, non-cam VG system changes the anhedral much more, and this is some- thing that can be used to your advantage.

High-siding is so important because it allows a tighter circle for a given bank angle. But you don’t want to be high-siding so much that you wear yourself out. In this sense it comes down to conditioning. The guys who are flying a lot of comps can high-side more.

* Note that all production gliders today use the simple pulley “non-cam” VG style mentioned

Secrets of Champions interview with Manfred Ruhmer:

Another point to make about control in thermals is I believe you should be on the high side of your glider if you are going to be maxing out the climb. Sometimes I will add some VG to help me do this. By staying on the high side, my bank will be less for a given circle radius which is more efficient. [Editor’s Note: In order for a glider to be thermaled with the pilot’s body displaced to the outside of the control bar’s centerline or high- sided as illustrated in figure 1, the glider must have a tendency to roll into the turn. This tendency increases with more anhedral— downward angling of the wing— among other factors.]

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So, I think that about covers it!  HUGE thanks to Dennis Pagen and Sport Aviation Publications for permission to reproduce his work here, as well as to all the sky-god pilots who took the time to interview and share their insights with Dennis.  There is a LOT more really, really good content in Secrets of Champions, I can’t recommend it highly enough!

And- high siding- I’d like to close with this thought: Everything is best done in balance.  While high siding can improve aerodynamic efficiency when climbing, it requires constant physical effort.  If your interest is cross-country or competition flying, something we need to keep in mind is PHYSICAL efficiency as well.  If a flight will be 4, 5, 6+ hours, we need our arm stamina to last that long… and we need to still be sharp to ensure a safe landing at the end of the flight… so some high siding is good, but be wary of too much of a good thing… Personally, I most often thermal with very low VG settings so I don’t have to work so hard… hang gliding is supposed to be FUN after all :-)

Thanks for the excellent question, and I hope everyone was able to learn a little more about this wonderful thing we all love to do!

 

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