AMC1 31TGB.45 Protection of envelope against tearing

• ED Decision 2013/011/R found in: CS-31TGB Initial issue - Tethered Gas Balloons (Jul 2013)

AMC1 31TGB.45 Protection of envelope against tearing ED Decision 2013/011/R Demonstration of sufficient rip-stopping capability of the envelope material. The objective of this demonstration is to show that the envelope material is sufficiently damage resistant. It therefore needs to be determined that the envelope material would not continue to tear under the maximum tension and conditions (temperature) experienced in normal operation. In order to establish that the determined damage resistance is sufficient, the critical damage should be reviewed in relation to local damage foreseeable in normal operation. The local damages to be considered are: - existing damage that may be undetected during pre-flight inspection, and - limited damage, inflicted during flight where the size of the damage in itself would not result in a catastrophic failure. The resistance of envelope fabric to damage propagation is determined by test. It is shown by test that a crosswise slit of at least 5 cm in the most unfavourable direction to the envelope fabric at the maximum tension experienced in service does not propagate. Test results from tests on similar fabric at the equal or higher tension and damage equal or larger than 5 cm are considered compliant. A typical test set-up is provided below. The tension in the test area of the specimen of the fabric should be equal to the maximum tension experienced in service and the test method should not create unacceptable tension re-distributions in the test area when the test is conducted.  If the balloon is equipped with a net to distribute and reduce the loads in the envelope, the net is regarded as a tear-prevention device.