Hang Glider Physics

So what did the Physicist learn?

Let's be frank about it. Hang gliding courses mention glider physics but they have to major on the motor skills to launch safely, fly an accurate track and do landings you walk away from. I need more than that to stay sane.
There are some little tricks the physicist learnt that didn't feature in the course.

Wings level

When you are standing at the launch point get the instructor to let go of the nose as soon as possible. They are going to be going on about 'wings level' but while they are holding the nose it isn't going happen. So what is the trick? First keep the nose down so it isn't wibbling about but then physics takes over. A glider that is pointing into the wind sits wings level. It's designed that way, it simply can't help it. If a wing drops it is just because you are not pointing it into the wind any more. Fix it. Turn away from the dipping wing. This probably only involves swinging the nose left or right six inches if you were there a moment ago and the glider flies back to wings level. This is the 'no effort' way while trying to force something to go level when the wind is saying go not level is daft. That wing can pick you off the ground so you're better off not fighting it as it will win.
Sorry? You wanted that in physics? Swept wings are normally stable in yaw. The swept planiform, when yawed out of the relative wind, creates more lift on the advancing wing and also more drag, stabilizing the wing in yaw. What you are feeling is the increased lift of the forward wing so you turn towards it, that is away from the dipping wing, and you yaw back into wind and everything is equal again.

Once you have that trick settled the crosswind launch becomes easy. Point the glider into wind. Since you have some reason not to run that way then sight up your launch run and go. Expect the the thing will dip a wing as you run faster but just keep turning the nose away from the dipping wing, which should bring it more onto the launch line as you keep coming back onto level until you feet loose the ground and you can tuck them away in the harness with a nice smug grin that comes from doing something you were told was going to be hard and was actually easy. Get this habit and a skew gust in the middle of your run doesn't phase you in the slightest.

Weight shifting

Weigh shifting is a good way to describe how we control things but I've fallen into the trap of just twisting my body and seen countless other beginners do it too. You are hanging from a big strap. Visualise it. If you want to bank left pull that strap to the left. It looks more stylish if you keep your body straight but us noobs really don't need to care about style yet. Give the strap a push left then let it come back to centre, give the glider a second or so to get its act back together and then decide if it needs another one. Only what you do to the strap counts. If your chest goes one way and your feet go the other and the strap stays vertical you have done absolutely nothing.

Look at the picture (deliberatly a long shot to protect the guilty). Glider going one way and the poor guy wants to weight shift to his left but his shoulders are going left and his legs are going right and that crucial hang strap is still dead vertical. When I went from moving my chest to moving my bottom the glider went from ignoring me to being a bit lurchy as I was now over controlling it. However that was the easiest fault to fix.

Pull the glider not push it on launch

"Run!" he shouts encouragingly "Dive through the frame!" He's telling you what he does not what you need to do. It's all down to that hang strap again. Your hands don't push the glider once it lifts off your shoulders, it's their job to fly the wing and that means a light grip and control, probably pulling the bar in a bit. Look at the picture. Here's somebody doing it so well I have to hate him on principle.

So how can I tell he's pulling the glider along? Look at the hang strap. The glider is starting to take his weight so the glider pulls up however the fact that the strap is sloping backwards proves he is pulling the wing forward. Move to the diagram. The force in a strap can only be tension. If it is the black line in my diagram then it is applying two forces at the bottom. One is a pull up and the other is a pull backwards. If it is pulling backwards, and I can assure you it isn't dragging John back up the hill, then John is pulling it along by the strap. His hands, meanwhile, are just getting on with the business of flying.

Now if you're going down hill, which I assume you are, tilt my diagram up. We don't actually care about vertical here just perpendicular to the direction of travel. You want to tow that glider so your arms come back to fly the wing and you lean forward to dig your toes in and run so you do indeed "dive through the frame." I've looked at web-forum pictures of people complaining about their launch and I draw a right-angle from the ground and compare it to the hang strap and now it all makes sense. If you are pushing on the frame you are telling the glider to nose up. That's how you land not take off.

Control inputs
A glider does not work on control forces just control positions. This sums up as don't make detail changes just do it There may be a masochistic streak in gliders but they do like nice clear orders. All those years I spent teaching racing motorcycles to go round corners just on the limits of sliding off into the gravel by being gentle with them are now wrong. If you want to go left bump it left. Bump works. You can smooth it out later once experience gives you more time to think.

This is especially true when you want to land. Go in fast. Remember a glider does not have an up/down control just a fast/slow one. Dial in fast and wings level and then, when you get low enough that the height doesn't bother you any more but the ground speed is beginning too, get your hands up to ear level, make sure you're looking at something way out in front and start to let the bar pull out. Now you're playing the 'see how far I can make it go' game. When the bar finally goes slack in your hands, that is you stop having to pull it back to get it where you want it, count one second then push it right out. Don't worry about getting your feet in a 'good' position to land on because when the wing stands up like that it will stop and you will be swung forward and dumped on your feet for a slick looking stand up landing. Lots of Cred for very little effort.

Where am I going to land?

This was a real worry to me at first. I hadn't a clue how far it would fly and just had to rely on the instructors but once I started flying more complex plans it was my job to get it right. However it's quite simple: unless we find rising or falling air we will descend at about 8 to 9 degrees. Hold your arm out and make a fist with your thumb tucked in. If top of your fist is horizontally out from your eyes in no wind you will land just under your fist. Don't actually do it, you need to keep your hands on the bar but that's the approximation, visualise it. For a ten mile per hour head wind you can roughly double that. Two fists (please don't take both hands of the bar). It's not so good as you run off from a hill as there is a lot of wind to come but it gets better and better as you close in on the landing point and it's great for decisions like 'zig-zag a bit, the canal at the far end of the field is starting to look a bit close' or 'left a bit to avoid the down slope.' If you know there isn't much wind budget for one fist, if there is a lot for more. It's only a starter guess and you soon get the feel of it but I keep using it as a check when I'm wondering where the next safe 'no lift' field is.

Oh and the picture is a cut from a video. I know exactly where he landed. Also remember that if there is a hill in front of you horizontal will not be the horizon.