AMC1 31TGB.49
Limiting of operating pressure
ED Decision 2013/011/R
The envelope pressure is limited to prevent the envelope from bursting. However, the definition of the envelope's maximum operating pressure depends on the design of the tethered gas balloon system. For inflated balloon systems the operating conditions are not limited to flight but also include the parking conditions if the balloon system stays inflated for a prolonged period between the flight operations. Thus, different cases need to be considered:
(a) Balloon systems staying inflated above maximum wind speed for flight operation
These balloon systems ensure envelope tautness by a ballonet or other means of feeding/discharging gas into the envelope when moored on the ground in parking position to withstand the dynamic pressure of considerably high wind speeds. Here the maximum operating pressure is the maximum pressure established by the designer for high wind speeds whilst moored in parking condition to the ground. Under this condition the safety factors in CS 31TGB.25 are applicable. The ascent factor in CS 31TGB.23(b) is however not applicable in the parking position. The response pressure of the automatic lifting gas release valve usually is higher than the maximum operating pressure to prevent the envelope from getting pumped out below dynamic pressure of the wind by unexpected gusts. A factor of not less than 1·4 times the maximum operating pressure during mooring has been shown by practical experience to be applicable.
(b) Balloon systems other than described in (a)
These balloon systems are usually smaller and ensure envelope tautness by means other than described under (a), i.e. by flexible parts in the envelope. They are designed for maximum wind speed during flight operation and will normally be deflated during high wind speed weather conditions. Here the maximum operating pressure is the pressure for flight operation established by the designer. The response pressure of the automatic lifting gas release device is not less than 1·15 times the maximum operating pressure.
For clarification, it should be noted that in a strict sense the automatic pressure release device can only prevent the further rise of pressure for the very moment. After release the device should close again in order to minimise the loss of lifting gas. If after a while the pressure increases again for any reason, the device will also open again. This behaviour is intended and does not impair safety.
Tethered gas balloon envelope pressure must be limited to prevent bursting. Maximum operating pressure depends on the balloon's design. For balloons staying inflated in high winds, it's the pressure during mooring. For others, it's the pressure during flight. Automatic pressure release valves prevent overpressure, minimizing gas loss.
* Summary by Aviation.Bot - Always consult the original document for the most accurate information.
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