Your Launching Angle of Attack

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Col.r
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Location: Australia

Your Launching Angle of Attack

Post by Col.r »

Your Launching Angle of Attack
13 hours ago
Get that right first of all

(Chelan Butte, Chelan, WA, USA)

Aaron Swepston writes:

"A few years ago a local senior pilot was giving a launch clinic at Chelan, and fortunately someone was taking video of all the launches. There were a number of poor launches. The senior pilot was trying to define and then explain why those launches were poor. The resulting round robin discussion had everyone deciding that the poor launches were due to those pilots launching with their hang straps loose.

The next day they all made a big effort to lift their gliders so that they’d begin their runs with the hang straps tight? A whole ‘nother set of poor launches were caught on video. And a whole ‘nother round robin discussion about why those launches were poor.

We got to Chelan on the second evening of this charade of a clinic, and were able to sit in on the evening’s discussion. After watching their videos, one thing was very clear; the poor launches all were the result of the angle of attacks being way too high during the launch runs.

They didn’t all start too high, some started reasonably low, but all of the poor launches achieved an angle of attack that was too high at some point during their launch process, and because of the high angle the gliders were going off the ground in a semi mush situation. Some were mildly sketchy and some were scary bad. But all were with too high of an angle of attack. What did not seem to matter at all, as I’m not having any consistency at all, was whether the hang strap was tight or loose.

They asked me what I thought was the problem. I said, angle of attack. It’s simple. The poor launches were launching with the angle of attack too high.

They asked how to control the angle of attack, tight strap or loose strap? I said either way, the first thing is to set the PROPER angle of attack and maintain it all the way through the launch. So, whether you use a proper grapevine grip or the goofy bottle grip, and whether you use the more controllable loose strap with the down tubes locked firmly in your arms or with a tight strap with the glider elevated with less leverage, the most critical part was setting and being able to maintain the proper angle of attack. They all seemed to sort of accept that, but that begged another question.

I asked them, and mostly the pilot leading this clinic, what the best angle of attack would be. Silence. The senior pilot decided that the best angle would be different for every person, every glider, even every glider of the same model line! Ah, and also that there was no way to determine what that angle of attack would be outside of trial and error for each pilot.

This was where it got fun. As an engineer in the aerospace industry and a long time pilot, I was shocked. So I asked him what the stall angle was for a hang glider. He had no idea, and estimated something like 17 degrees. 17 degrees. Check out those videos, they were launching with the keel angle as positive above the horizon as the slope was below the horizon! But then I told him no, it’s not 17 degrees, it’s more like 30 degrees. He scoffed. I asked him if he’d ever seen a certification test. Duh…, yeah but he never paid close attention.

Okay, so, on the test vehicle they do a test at stall angle of attack, best lift is just prior to stall typically. That angle shakes out to be roughly 28-30 degrees angle of attack for flex wing hang gliders, regardless of model. With the keel at 28-30 degrees to the apparent wind, whether it is a runway on a test vehicle, the runway while the glider is on a tow cart, or whether it is to the slope of the launch on a hillside, 30 degrees angle of the keel is just too high for a good, solid, safe launch. And that’s a “formula” you can take and use anywhere. At any launch.

A better angle of attack to set before starting the launch run is between 20-25 degrees angle of attack, setting the keel at 20-25 degrees to the launch surface or slope. I prefer the low end of that range for better control, less buffeting of the glider, a better acceleration, and so on.

So before you get down in the weeds about the proper technique for lifting, holding, and launching a glider, you need to know that the reason behind all of that technique is to be able to launch with the proper angle of attack, and regardless of your chosen technique, if you can’t get and maintain the proper angle of attack, you’re going to have a shitty launch.

SECONDARILY, the better technique for setting and holding the proper angle of attack is the grapevine grip, with the glider resting lower for better leverage. The tight hang strap is a non issue for launching in anything short of kiting winds, where the wind is strong enough to make the wing not only lift and fly, but actually be able to accept weight shift control. Just because the wing goes up and the strap gets tight does not mean you can weight shift it. You’ll see plenty of examples proving that one doesn’t work until you have significant weight on the strap, and response is slow at low speeds and low strap loading. So don’t rely on that as a “thing” to focus on.

Learn to set an angle of attack around 20-25 degrees to your launch surface, learn how to maintain that angle throughout the FULL run, and you’ll find your technique will improve and so will your launches. If you can’t set and maintain the proper angle of attack, you’ll have problems forever.

The angle of attack information and stalls, min sink, best glide “angles”, are things that can be known. Tested, proven, repeated, defined, and shared. Launches do NOT have to be trial and error processes. It’s 2021, and there is so much that can be known as “facts”. If you find yourself talking with someone posturing as someone with knowledge and experience, and they don’t understand the basics, help them out if you can. We need more people in the sport, but we need them to be in the sport successfully, and crashing due to a lack of understanding the basics is no way for our sport to survive."


Yes, all very true and smart advice. If I may add,I have seen quite a few instances of pilots also launching with too LOW an angle of attack.
Often with pilots stepping up to higher aspect ratio gliders-think more pitch responsive wings.

We have a ramp launch on a coastal site that is in the lift band below the top. Above 18mph,we now launch on the basebar and the side-wire man behind, this has proven to work great.
A lesson I learnt, I tried a few launches in light/no wind by holding some of the gliders weight with my grip ( getting the harness ropes to tighten sooner )- quickly went back to letting the full gliders weight on my shoulders after loosing my grip on one side while running!

After landing we would always ask the other pilots- how did my launch look? What about the landing?
Because once you got your adaptive techniques for those two areas- you could now really relax and that means enjoy your airtime..
We are all in the gutter,but some of us are looking at the stars. MT.

Youtube videos- Col Rushton
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David Glover
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Re: Your Launching Angle of Attack

Post by David Glover »

Well said Aaron. I think the best way to maintain proper angle is literally the first step in your run - which should start by NOT STEPPING - I believe the best initial movement is to lean like you are going to fall forward - which maintains the angle and only taking the step when you actually need to - this sets everything correctly for the rest of the launch. The first step in the launch starts with a lean.
David H Glover
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