I think it’s vital that whoever reads this and hasn’t got butterfly landing right yet, should NOT go out there and try them without the appropriate guidance/supervision of an instructor (who can do these) and ALTITUDE for
the first time.
Ostensibly butterfly landing is a consistent and repetitive approaches to the point of stall. On NEARING the stall point the glider is allowed to regain normal flight by releasing the brakes. As it pitches forwards and begins
regaining airspeed, the uniform application of brakes again retards it. At all times the pilot needs to be really in tune with what the wing is doing and should particularly look out for either wing stalling (or the whole thing obviously) and this may require slight occasional asymmetric input (particularly on higher aspect wings).
If this sequence of events were to be viewed from the side as the glider flew by it would look something like someone doing controlled pendulums, except the frequency would be greater and the pendulums shorter because the glider is not being permitted to regain full airspeed before being retarded again.
I wouldn’t really go as far to say that the technique is an emergency one, but it is also not a standard means of executing a landing. I believe it is important for every pilot to have a thorough understanding of what butterfly landing is and when and where to use it, especially with the progress of paraglider design and performance in recent years (haven’t you noticed how people are starting to use lonnngggggg final glides at speed to land?). In
getting proficient at this sort of landing it’s also not unreasonable to misjudge a glide and land up needing a way to stop quickly (fence or power line ahead). Alternatively, you may just have a confined landing area that
requires some fancy footwork to get into.
Since butterfly landing promotes breaking and re-instating the airflow over your wing in it’s controllable form (inflated) it’s best you keep it that way. Ideally one should never feel the wing “mushing”. If you’re getting to
that point you’re being to aggressive with your brake input or you’re holding then in too long. Butterflying will take you closer to the edges of the normal envelope of your wing and therefore should only be attempted by
“switched on” higher airtime pilots who have a feeling for what they are doing. I would suggest it imperative to have had some form of formal “advanced” manoeuvres training before trying this out.
There’s no hard and fast rule about how long you should hold on, back off etc, because we all have different wings and wing loadings, but you should also not come in thinking you’re doing a butterfly landing with your hands flapping about the same frequency as a humming bird. That does nothing to the wing and looks pretty daft too. On the other hand flying along, pulling and holding brakes for 5 seconds is
the other extreme.
The dynamics of executing a decent butterfly landing are also greatly influenced by where you intend doing one (top landing at a thermic site, at a coastal ridge lift site, on flat ground, behind an obstacle, etc).
Butterflying in a top-landing situation is trickier for the simple reason that your relative airflow is not laminar and therefore the velocity at which you THINK it’s passing is higher than it actually is and you get closer to stall than you anticipate.
Butterfly landings in laminar airflow are therefore a little easier and perhaps a little safer.
The other trick is if you have to use one to get into your desired landing area and you can see you are too high on final glide, but don’t have enough height to go around again, it’s not a bad idea to use it as part of your
approach while still quite high and then exit onto a faster approach and flair to spot land. Sounds simple, but keep practising – it’s better to have the experience than to try one when you find yourself needing one and then
By the way, the typical sink rate one can achieve in a well executed and controlled butterfly landing in stable, laminar airflow is about 1.5 to 2 m/s, again a good reason to learn to land your glider correctly first.
Butterflying in a top-landing situation is trickier for the simple reason that your relative airflow is not laminar and therefore the velocity at which you THINK the air is passing over your wing is lower than it actually is and you get closer to stall than you anticipate