| That latitude is provided in the form of collapsible air bags, called ballonets, inside the helium envelope. |
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| Unless perfectly synchronized, dual ballonets tend to tip the craft toward the tail or nose. |
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| Besides, it is possible to go to the fore and aft set of the ballonets and into the gas volume. |
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| As a rigid airship, it had no need of ballonets, which are used only in pressure airships, or blimps. |
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| Prior art methods of pressurizing and filling the ballonets typically involved the use of ram air scoops. |
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| The pressure of the helium in the envelope is adjusted by changing the amount of air in the ballonets. |
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| Air is pumped in to or out of these ballonets to adjust the helium pressure. |
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| Therefore ballonets are needed for semi-rigid airships to keep the envelope pressure constant. |
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| The two air chambers inside the envelope called ballonets can be expanded and contracted to add or subtract weight from the nose or the tail, trimming the airship. |
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| Air is squeezed out of the ballonets as the gas expands with increasing altitude and forced back in again as the helium contracts when the airship descends. |
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| When the ballonets are filled with air, the dense air contained within different balloons but the same envelope as the helium has an effect on the buoyancy. |
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| The envelope also houses one or two ballonets, as can be found in normal airships. |
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| If two ballonets are used, one at the front and one at the rear, this gives an additional mechanism for adjusting pitch. |
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| Multiple ballonets located fore and aft in each of the hulls provide pressure control. |
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| Ballonets inside the envelope keep the internal pressure constant in each flight situation. |
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