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Aircraft and gliders usually have instruments to measure air speed and angle of attack, which should be monitored to prevent stalling the aircraft.

However, it seems that most paragliders and hang-gliders lack such kind of tools.

How do the pilots avoid stalling without these kinds of instruments?

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    $\begingroup$ FWIW, in a light plane you don't usually detect stall or near stall conditions with instruments, you feel it. Though there is a stall warning in some (if not all) planes, the only times I've ever heard it go off was when practicing stalls in training. $\endgroup$
    – jamesqf
    Commented Feb 28, 2017 at 23:46

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Paraglider pilots learn "active flying", whereby you use feedback from the wing to determine what's going on. You monitor the tension in both controls (the "brakes"), and the wing's attitude (if the wing pitches forwards then you feel like you are swinging backwards).

In bumpy air (such as on the edges of thermals, or in wave) active flying is used to keep the wing more or less above your head. If the wing surges forwards then you risk a collapse; if the wing falls back then you risk a stall.

In smooth air a stall is only likely if you are pulling the brakes down too far. This can happen accidentally, especially in nil-wind landings if you mistake your ground speed for airspeed.

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  • $\begingroup$ Nice answer, and welcome to aviation.se! $\endgroup$
    – Ralph J ♦
    Commented Mar 1, 2017 at 17:16
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    $\begingroup$ +1 for mentioning the collapse. Paraglider wings are unlike fixed-wing aircraft because they need air inflating them to maintain the aerofoil shape, mess up the airflow and you can lose the shape. Personally, I know that if the wind on my face is too fast or too slow I know I'm in trouble $\endgroup$
    – Dave Gremlin
    Commented Mar 3, 2017 at 13:43
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Paraglider Pilots can induce a stall by holding the brakes at seat or waist height until the wing retards. The wing does not want to do this and will resist but a full stall will eventually be induced this way. Pilots will feel and hear the reduction in forward airspeed. To come out of a stall, the pilot may smoothly move the position of the brakes upwards anticipating a surge where the wing recovers and may dive or surge in front of the pilot. Performing a 360 in light wind conditions, the side of the wing on the inside of the turn may stall. Typically, smoothly and promptly coming out of the turn using the brakes, will cause the wing to recover, failure to recover may result in a flat spin. Flying near full speed with minimum brake also risks a deflation of the wing on the left centre or right sides. This might be exacerbated if the pilots all-up weight is at the upper or lower weight limit of the glider; typically gliders come in xs s m l xl sizes. Prompt appropriate use of the brakes is pretty much all a paraglider pilot has to recover normal flight in all the scenarios above. If in doubt pilots should follow the instructions in the gliders manual and ensure they have enough recent flying hours in the conditions they wish to fly that they can do so safely, ie not freeze, recognise the symptoms of a stall for their glider, and react appropriately. Like all aircraft it won't be possible to recover from a stall below a certain height, so a pilot should have enough skill not put themselves at risk whilst still having fun!

I imagine hang glider pilots will feel and hear the wind, and be aware of the pressure on the control bar. I'm guessing their priority will also be to get air flowing over the wing by pulling in on the control bar - but I'm only guessing as I was a PG pilot not an HG pilot.

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    $\begingroup$ So the answer to the main question is "experience"? $\endgroup$
    – Notts90
    Commented Feb 28, 2017 at 13:41
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    $\begingroup$ Your answer is very informative. However it focus on how to create a stall instead of how to predict it. Do you mean that it cannot stall without pilot action ? To predict it a pilot must then "feel" the air to anticipate a stall ? $\endgroup$
    – Antzi
    Commented Feb 28, 2017 at 16:05
  • $\begingroup$ Yes it's done by feel. If you were in a regular aircraft with no ASI and no AoA indicator how would you do it? You'd know you were about to stall because you'd hear less wind noise as air speed bleeds away and maybe a pitch up attitude. If a PG pilot applies brake they're going to increase the AoA which will reduce speed and increase lift. It takes physical effort to keep the brakes held down, just before stall the brakes will feel soft moments before the wing stops flying. The pilot must slowly let up on the brakes to get out of the stall. Again, all this is done by feel. $\endgroup$
    – IanT8
    Commented Feb 28, 2017 at 22:08
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    $\begingroup$ @Notts90 yes I guess so. I was taught to "feel for the stall" when learning. Pilots can attend Special courses, usually over water, where they are taught to put the glider into stalled position and then follow procedure to get back to normal flight - or crash land into water if they don't recover quickly enough! $\endgroup$
    – IanT8
    Commented Feb 28, 2017 at 22:13
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Well in case of hang gliders there is notable amount of force on speedbar (control handle) which always tries (in case of properly designed glider) to move speedbar back to trim speed position which is near stall + 10kph. Also, due to combination of swept wing and washout (root has higher AoA than wing tips) stall starts from the root of the wing and causes slight nose drop. If pilot won't resist to it wing will restore its speed and full stall will be prevented. Full stall usually requires pilots intended actions and is performed only during landing flare. In rare cases full stall may happen in-flight as well, but it is result of poor decisions or aerobatics which is prohibited on HG. In most cases full stall is ended up with tumble and throwing of reserve chute -

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Hang gliders are trimmed (hang point is such) that if you touch nothing you are above the stall speed. During normal flight you never push out the control bar, you pull to speed up, and you release to trim to use that speed. you only push past trim on the landing.

Also, they are built in such a way that the center of the wing stalls first (before the sides) and since that is the forward most point of the wing, a stall there will drop your nose. (while the rest of the wing is not stalled.)

if you get close to stall speed, the glider is less responsive "mushy".

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  • $\begingroup$ Not a bad answer but you might consider addressing the case of a steep thermalling turn. We do often push out (forward) quite a bit in such a case, to counteract the nose-down pitching effect created by the curvature in the airflow/ relative wind due to the circular flight path. In other words the angle-of-attack associated with no push or pull gets shifted to a much lower aoa in a steep turn. But that just makes it harder to stall; the bar would have to be ridiculously far forward to stall in a really steep turn, maybe longer than our arms can reach. $\endgroup$
    – quiet flyer
    Commented Nov 3, 2020 at 18:30
  • $\begingroup$ So first sentence of answer is still true even in very steep turn, second sentence arguably not. Change to "During normal wings-level flight" and then it's true. $\endgroup$
    – quiet flyer
    Commented Nov 3, 2020 at 18:35
  • $\begingroup$ This doesn't add anything to PM.'s answer from 3 years ago. Care to add some details that were left out of that one to add value? $\endgroup$
    – FreeMan
    Commented Nov 3, 2020 at 19:23
  • $\begingroup$ @FreeMan You are absolutely right . I had skimmed the first answers but missed that. (though I would say it is typically less than 10+stall) :-) $\endgroup$
    – vish
    Commented Nov 25, 2020 at 13:16

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