Porosity test
Wing porosity is understood as air permeability of the cloth, measured in l/m2/min (litre per square metre per minute) under standard pressure of 200 mm water column, that is 20 mb.
The measurement is taken with a POROSIMETER JDC MK-1 (rev.A), produced by Swiss JDC Electronic S.A. company (www.jdc.ch). It works with a 100 mm water column pressure (10 mb) and is an improved version of this device, characterised by a stronger magnet and better fitting, eliminating undesired air flow between cloth and device corpus.
The result is given in seconds needed for 0.25 litre of air to permeate through cloth of 38.5 cm2 area under 10 mb pressure. It is then recalculated into standard units and 20 mb pressure with the formula: permeability [l/m2/min] = 5400 / time of measurement [s]
The device is mounted at midpoint on the wing chord. Before commencing measurement this place must be checked, as even the smallest tears can drastically alter the results. It is advised to look at the cloth against the light.The results are then recalculated to obtain an arithmetical average, that will describe the wing porosity. If any of the results radically differ from the average, the site of measurement on the wing surface must be carefully checked again and possibly changed.
Following table is used in interpreting the results:
0 - 20 - "as new" cloth condition
20 - 50 - excellent cloth condition
50 - 100 - good cloth condition
100 - 150 - satisfactory cloth condition
150 - 300 - well-used cloth, paraglider airworthy
300 and above - worn-out cloth, safety cannot be guaranteed
Dudek Paragliding considers airworthy only paragliders with porosity of less than 300 [l/m2/min].
All the information is included in a porosity report.
