Launching with Long Strides

Originally published in Hang Gliding and Paragliding Magazine

HG401: Advanced Techniques and Concepts
Making Strides

 

As babies we learn to crawl, then walk, then run.  It’s fair to say that by whatever age we begin learning to hang glide, we pretty well have it down.  And that, in a nutshell, is a problem.  Running with a hang glider isn’t quite the same as just plain running.

Let’s take a look at how it’s different, the reasons why, and what to do about it.  Continue Reading

TRIM: What is it, and what effect does wingloading or VG have?

Q: Recently, I bought a high performance glider from an experienced pilot. The previous owner of the glider weighs quite a bit less than I. I took the glider for a maiden flight a few days a go and one instructor told me that I am flying too slow. He added that the previous pilot may be a lighter pilot than I am and so, I should move my hang point forward. Continue Reading

Isn’t It Dangerous?

We’ve all been asked this at some time or another… and there’s a lot to learn- retrospectively- in how we answer that question.  Most will say it’s “safe”, or make a comparison- safer than driving in a car seems to be a common one.

Perhaps we’re lying?  And not just lying to the person asking innocently, “isn’t it dangerous?”… but lying to ourselves, too.

Jo Bostik, being Jo Bostik...

Jo Bostik, being Jo Bostik…

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Hang Gliding Instructors: PLEASE READ

I think most instructors know already- attention to detail is everything.  There is a delicate are of conveying something as complicated as human flight in such simplistic terms that someone with absolutely no experience can easily understand and execute.

Regarding “how to teach”, a while back I put together a simple 5-minute video for instructors.  It runs through a basic first-day lesson, with an emphasis on what the instructor might focus on and be looking for.  While different instructors, teaching at different training sites, in possibly very different conditions, might follow different stepping stones of progress- the key idea I tried to portray is that instruction needs to be a PROGRESSION.  This is why I called the video Simple Progression.  Please take 5 to watch it (even if you’ve already seen it!)…

In addition to teaching following a progression, I wanted to highlight the specific SKILLS we instructors should be looking for.  It’s a bit too easy to fall into a checklist mentality, and we’ve all done it at some point.  Ya know… run with the glider, check.  Run with it with the harness, check.  Ok, over to the hill now!  Continue Reading

Wingloading and “Ground Effect”

Q: Does weight affect how long you stay in ground effect?

My buddy and I fly the same model and size glider, however, he is about 30lbs less than me and it appears he stays in GE longer than I do and needs a less aggressive flair. It appears my flair window is shorter and I need to flair harder if I want a no-stepper.

Please note: He is a little on the light side of his glider and I’m more in the middle to upper end of the weight range.

A: This question follows nicely with the last question we got, which also had to do with wingloading… but this one involves a very specific phase of every flight- ground skim or “ground effect”.

Before getting into the effects of wingloading, I should really talk briefly about “ground effect”.  Let’s start with what it is in very general terms: An increase in aerodynamic efficiency (improved glide) that occurs when an aircraft flies near the ground.  Understanding where it comes from will also be important in a minute, so let’s delve into that for a second…

There are two models as to how a wing makes lift; one says it creates a difference in pressure between the top and bottom of the wing, and this difference in pressure naturally wants to equalize, and so a lifting force is applied to the wing.  The other model is that the wing works to deflect air downward, and because every action has an equal and opposite reaction, in pushing the air down the wing is also pushed upward some (lift).  It doesn’t really matter which model you like, they’re both kind of the same here (in truth, they are probably two perspectives on the same thing, and therefore both accurate).  Anyways- a wing makes lift, right?  But where the wing ends, out at the tips, some of that lift “spills” around the tip, and  swirling tip vortices occur as a result.  A flying wing is pulling the air in these vortices, and that’s called DRAG.  Glide performance is lift divided by drag… so even minor reductions in drag can noticeably improve glide.  The idea of “ground effect” is that, when the wing is close to the ground, those swirling vortices hit the ground and get broken up, and therefore the mass of air the wing is pulling is less… in other words, less drag.  Less drag = more glide.

Airplane flying through clouds shows the swirling vortices

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Wing Loading and Ballast

Q: Recently I was trying to figure out if it would be useful to put a few extra kilos in my harness to get a better glide and to become faster overall. Is it still common practice for top comp pilots to use it, now that gliders get better and better, also the smaller ones? I’m on the low side of the ideal pilot weight for my WW T2C 154, so maybe you can write a blog on this matter and give me a word of advice on this.

A: This is an excellent topic and question- because there’s a simple answer, which is mostly correct, and then there’s the “it depends” answer when you really get into understanding wing loading.

The short answer, if you’re in a hurry and want simple yes/no, is that NO, adding some ballast in your harness will NOT improve your glide.  Glide- as in Lift/Drag- remains pretty much constant regardless of wing loading.  But YES, increasing your wing loading would make you faster.  Where you go faster is unknown; do you cover more ground in a day, ending up with a longer distance flight… or do you just end up in the same place sooner… or do you end up landing sooner, and going less far?!

Let’s get into understanding the variables in this, and then hopefully you can make an educated choice for what suits your needs.  As with anything, it’s a series of trade-offs and compromises… Continue Reading

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…

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Pitch Stability

Normally this site runs on a Question and Answer format… but there’s topic that comes up time and again and I’d like to talk a bit about it for those interested in understanding it better (there’s a lot of myth and mis-information out there).

This topic has come up twice for me just recently- first in a discussion on our local pilot chat list about the inefficiencies in flying wings, and now during the FAI Hang Gliding World Championships, where a pilot experienced a tumble and had to deploy his reserve.

So let’s talk about pitch stability, and I’ll try to keep it light and simple.  In aerodynamics, stability is as a wing’s resistance to changes in attitude, or how strongly it tries to return to steady state.  Hang gliders are generally very pitch stable- they want to find ‘trim’ and stay there.  Pulling in or pushing out to change the angle of attack we experience bar pressure, which is a force created by the aerodynamics of the wing trying to return to center.

Where this force comes from is one big question we should explore.  In airplanes, it comes from the tail.  But hang gliders have no tail.  Weelllllll….. visually, that is true- hang gliders have no tail.  But aerodynamically, we have the same needs as airplanes and just meet them in a different way.  In hang gliders, the outboard part of our wings, and especially the trailing edge of the wing out near the tips, is our “tail”.  By giving a hang glider swept wings, the tips are moved aft of the center of the wing.  And by twisting the tips to a lower angle of attack, this portion of the wing is essentially our tail.  It’s a little abstract to think about the “tail” on a tail-less aircraft, but hopefully the simplicity of it makes it understandable.

In terms of efficiency, this is where we run into issues.  First, swept wings aren’t terribly efficient.  Some of the air we want flowing OVER the wings becomes span-wise flow, along the angled leading edges… resulting in a loss of potential lift, as well as increased drag.  Another efficiency issue is that a hang glider’s “tail” isn’t very far aft of the rest of the wing, so in order to create a nose-up pitching force we need a decent amount of twist in the wing- which means less of the wing is creating lift, and again more drag.  If you think about a simple lever and how mechanical advantage works… and you compare how far aft a hang glider’s “tail” is with an airplane’s… you might realize that an airplane’s tail can create the same pitch forces as our tips, but without being angled as far off the direction of airflow (IE making way less drag).

These inefficiencies are what they are… they are the price we pay for portability.  If you look at all the hot sailplanes, they have straight wings and tails… and their performance blows ours away.  But they only pack into a trailer, and you certainly can’t foot launch or land them like hang gliders.  Our glider’s need to stay tail-less to keep them what they are, and there’s nothing wrong with that…

Regarding the recent tumble at the worlds, an interesting comment was made:

“What’s really strange is that he’s flying with a tail, so it’s hard to imagine how that could have happened…”  

Let’s think for a moment about what we just talked about above- where the pitch stability of a hang glider comes from.  And then let’s think about how long the keel on a hang glider is, and how effective mounting a horizontal tail on it might be.  Hopefully what you might be realizing is that the keel doesn’t really stick out any farther than the tips- in fact, most manufacturers determine the length of a keel as just long enough to keep the tips off the ground during setup.  Unless the keel is extended dramatically, mounting a horizontal tail there in hopes of creating pitch stability will not be any more useful than twisting the tips.  It WILL allow less twist in the tips, and therefore a greater area of wing lifting… which would detrimentally impact the handling of the glider, because the effective wingspan would now be much wider, and we’re still trying to steer it by mere weight shift.  The twist in the tips also creates some nice effects, like gentile and progressive stall characteristics… so reducing that twist to make use of a tail would make the wing much less forgiving on launch and landing.

So maybe the horizontal tail is creating a pitch-up force IN ADDITION to the tips… increasing stability?  Not likely, because remember that creating pitching force means creating drag… and we’re seeing these horizontal tails on high performance ships only, where every bit of drag matters.

But there is ONE real advantage of these tails- and that is in creating a damping force during a pitch rotation.  That’s really a fancy way of saying it makes it harder to rotate along the pitch axis.  This benefit is experienced even if the tail is at a neutral angle of attack and not creating any pitch forces to speak of.  Pitch damping is an important factor in hang gliders, because we don’t have a conventional tail, and because our bodies move the CG of the wing below the wing itself (we hook in heavier than the weight of our glider).  If you experience turbulence and say the nose pitches over 20 degrees very quickly… your body, which is below the CG of the wing, will have more momentum than the wing after that 20 degrees of rotation… which can actually “push” the wing into pitching over farther!  Many tuck/tumbles appear to have some element of this, where the glider was pitched down dramatically, and it was actually the “rotational inertia” that completed the tumble.  Pitch damping, in simple terms, is designed to resist this pitching rotation- NOT TO PREVENT IT- but to slow it (hence “damping”) so that when the pitch over stops there’s less rotational momentum built up.  Make sense?

So, getting back to the comment made about the pilot with the tail that tumbled at the worlds… why shouldn’t we be surprised?!  Tumbles don’t happen very often these days, and even in this very article I’ve said that hang gliders are generally very pitch stable, and that even horizontal tails that create no pitch force are still helpful in deterring a tumble?  The answer lies in the last, but most important, factor in hang glider pitch stability.  The relationship between CG and pitch stability.

It’s a simple relationship- the farther forward the CG is (the more we pull in), the more pitch-stable our glider becomes.  Pushing out, on the other hand, moves our CG aft, decreasing the pitch stability.  Because hang gliders have a pretty short distance between the lifting part of our wings and the part acting as a tail… and because our aircraft is lighter than our bodies… we have a pretty massive amount of variance in fore/aft CG.  Translation- we have a whole lot of pitch control!  And with great power, comes great responsibility…

I’m not at the Worlds.  I didn’t see the tumble.  But knowing it’s a worlds and everyone’s likely to be flying certified gliders with pitch stability systems (sprogs) that are within the designer’s certified specs… and this pilot was even flying with a horizontal tail… I think it’s a safe bet to say he probably pushed out at exactly the wrong time.  Maybe he was climbing in a gnarly thermal, and got a little too greedy in trying to fly slower and climb faster- pushing out- and he destabilized his wing enough that turbulence was able to overcome all the pitch-safety systems.  Or maybe he was flying normally and got pitched down, and responded by pushing out to “push the nose back up”… a common instinct people have when they don’t fully understand how wrong that is.  But the point is, should we be surprised that a “safe” hang glider can tumble?  NO.  Being surprised shows a lack of understanding, and respect, for how it all works.  And if we can understand how it works, and respect what the wing needs to keep from tumbling, we can feel “safe” and confident while flying.

For more reading about pilot position and pitch stability, check out this great article with graphs and test-vehicle data published by Wills Wing.

And to see EXACTLY how to tumble a hang glider, even flying a certified and pitch-stable wing in perfectly smooth air, watch this dude who uses a stall to initiate a pitch-rotation, and then pushes out to destabilize the glider in pitch.  He did it “just right”… and in doing so, shows us exactly what NOT to do (or if we think about doing the opposite, we can see what TO do in the event of a pitch over).

Looping!

Q: I have been hang gliding for 3 year, and i would like start learning how to make a loop… But in my country there is no one who knows how to do it…

I am have a lot of doubts… what speed must i have…? what should be the amount of VG…? What do i need to practice first…?  So my email to you has two questions… 🙂
First if you can descrive in details all the process for a perfect loop…? 
And the second is if you can give me one or two exercises to practice… and i will film them and send them to you…. and you could give correction and instruct me so that when i go for it i know exactly what i am doing…
Looping Arrábida

This is my dream… possible know only on Photoshop… 🙂

Thank for your attention and let me know your thoughts and if you can help me…

A: This is a fun question and I’m surprised it’s taken someone so long to ask it!  I have to predictably preface my response by saying aerobatics are dangerous, and hang gliders are not practical aircraft for such activities.  There is also a big difference between doing “wingovers” (which are really just high-banked turns) and doing what I like to call “BIG aero” which is the large climbing maneuvers like loops.  If you can live without looping your glider, I suggest you do that.  But if you MUST… read onward…
You might want to start with our previously published article about how to get into aerobatics by building a solid foundation first, and progressively working up to the bigger/riskier maneuvers: http://freeflightadvice.com/aerobatics/
Since that article already exists, this one will be entirely dedicated specifically to LOOPING.
At first glance loops are beautifully simple.  In physics terms it’s the transfer of energy from potential to kinetic, and back again.  In layman’s terms, we take altitude turn it into airspeed by diving… then we cash in that airspeed for altitude as we climb up and over the top of the loop.  In this simplistic view, we can identify some key things to focus on.
GoPro_framegrab_RV_Loop

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RLF (Restricted Landing Field) Techniques

Q: Got any tips for RLF and/or landing downhill?  Any info you have and/or video would be great.

A: I’ll start with the easy answer, which is that landing downhill sucks.  If it’s a really gentle slope, then it can be done… but plan for a really long ground skim, especially on high performance equipment.  When it comes time to flare, a climbing flare is not advisable.  Because the ground is dropping away as you progress forward, your height above the ground is increased through the climbing flare, and the strain on your back, hips, knees, and ankles is increased.  A full-on moonwalk landing is not advised either, because with the slight slope you’ll be moonwalking forever and it won’t really stop you very well.  Instead a smooth flare, like you would for a 2-3 step landing on flat ground, works well.  Because of the slope, be mentally prepared to take more than the usual 2-3 steps that flare might yield.

Anything more than a gentle downhill slope, and it’s probably better to land across the slope, which is presumably cross-wind.  If the slope is steep enough that flying wings-level across it endangers you in catching your uphill wingtip on the slope, then it’s probably better to land uphill… even if it’s downwind.  For more depth on uphill/downwind landings, see our previous article about Fly on the Wall Landings.

The reason landing downhill is such a struggle, is one of simple mathematics.  The glide slope of our gliders has gotten better and better of the years… and today even a mellow slope is a challenge, because we glide so well.  Anything that can be done to degrade the glide slope of the glider, enables landing on that much more slope.

And- on the topic of degrading glide- we can talk about RLF, or Restricted Landing Field, techniques!  The USHPA’s RLF sign-off requires demonstrating a landing using a downwind leg, base leg and a final leg approach where the entire base leg, final and landing occur within a 300′ square.  The important thing to notice is that it isn’t just a definition of landing zone size, but also available approach area. Continue Reading