Paragliding in the rain?!
Results of testing carried out by SWING
We were not able to establish that any of the current models in SWING's product range have a tendency to deep stall under normal flying conditions within the parameters of the certification.
An accident has prompted SWING to carry out extensive test runs and simulations (with the support of the DHV and Dr. Stefan Müller) to identify the cause of deep stall in rain.
In general, there are two reasons why a paraglider may go into deep stall in rain:
1. The first risk lies in the fact that the canopy weight increases if a glider is flown in rain for a lengthy period. The centre of gravity and angle of attack then shift, which is why it can result in airflow separation/stall. It is relevant here that if a glider absorbs more water (as older gliders do because they lose their water-repellent coating over time) and is closer to the deep stall limit because of its design and aging, less water absorption and thus weight increase will put the glider into deep stall.
2. When there is rain on the top surface of a glider, it can happen that so many water drops stick that almost the entire upper surface of the glider is affected but, even so, they “bead” so the surface is not wet through. This makes the top surface so “rough” in texture from the drop formation, that the airflow over the top of the wing separates from the surface. This phenomenon has been known for some time from hang-gliding and gliding. With new gliders, the droplets are absorbed less quickly by the fabric. Thus, the newer a glider is, the greater the number of droplets caught on the top surface and the bigger those droplets are, the greater the risk that there could be airflow separation. We were also able to recreate these conditions by practical tests and computer simulations. This type of deep stall has been repeatedly observed in the past irrespective of the type of glider, material and manufacturer. Since the phenomenon is indeed very rare, but cannot be completely excluded, we are now attempting to establish the exact cause of the formation of droplets on the top surface by carrying out extensive fundamental research . At the same time, we are looking for technical solutions, e.g. a treatment for the upper surface of the fabric to minimise the risk of deep stall in rain.
It is the case in both of the above situations that the control travel and braking distance first reduce and then the deep stall is caused, mostly by alteration of the brake travel or angle of attack, e.g. by a gust or thermal.
Anyway stay away from rain with every paraglider…
We will contact you immediately if we have any new findings
SWING Flugsportgeräte GmbH