We check that the fabric of your wing will keep the internal pressure high enough to maintain normal resistance to collapse and parachutal tendencies.
This is the first test we do on a service. It’s particularly important for an older glider that may be approaching the end of its serviceable life. The porosity meter measures how long it takes to draw a given volume of air (0.25 litres) through a small (38.5 cm2) area of fabric. For a new glider, this will take over 275 seconds, but reduces with age, use and the conditions the wing is exposed to. We examine much more closely if the result is less than 20 seconds. Poor results in conjunction with weaker fabric strength revealed by a Bettsometer tester may indicate that a glider is no longer safe to fly.