daily pic

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Montana objects may be closer than they appear....so pointy.
 
BobDDuck said:
I almost got a picture of you. We were driving over to my wife's grandparents house for lunch and followed you north a bit but never got close enough to get a shot. She was asking all about how airships fly.
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Welp, send me some of her questions sometime, I'd be happy to answer them for you. And we're actually moored at Dupont-Lapeer airport in Lapeer, MI until Monday. We're covering the senior US Open at Indianwood Golf Course/Country club.
 
Apophis said:
Some photos from flying today
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When you have to increase/decrease your buoyancy do you just vent helium off into the atmosphere to decrease buoyancy and fill the envelope from pressure tanks as needed, or is there a compressor on board that lets you take the expanded helium in the envelope and move it back into the pressure tank?
 
Murdoughnut said:
What happens if the helium pressure gets too high? Do you just pop?
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Nope. There is an inflatable/deflatable air cell inside the envelope called the ballonet. It can be inflated or deflated as required in flight to maintain pressure within limits. We have two air ducts at the rear of the gondola, one behind each engine, that capture slipstream air from the propellers, and divert them through check valves into a plenum chamber, and from there into the ballonet. Thus the ballonet compensates for changes in helium volume to maintain a given pressure range.

There is a condition called "pressure height" which occurrs when the ballonet reaches zero volume. In fact, pressure height is what limits how high we can climb on a given day. When the ballonet reaches zero volume, any further decrease in atmospheric pressure (altitude), increase in atmospheric temperature, or any combination thereof, will cause the pressure to continue to increase (because we can't force any more air out of the ballonet, there's nothing left inside it). If you want to climb above pressure height, the only way to do so is to get rid of helium. We generally try to avoid valving helium unless absolutely necessary, becuase doing so causes us to lose static lift, and helium is expensive to replace.

Realisically, there aren't very many situations that would cause envelope failure. Getting caught in the updrafts associated with convective activity is one situation that could do it, however.

Oh, and sorry for the verbose explanation. There isn't really a simple way of describing how we operate though to those unfamiliar.
 
rframe said:
When you have to increase/decrease your buoyancy do you just vent helium off into the atmosphere to decrease buoyancy and fill the envelope from pressure tanks as needed, or is there a compressor on board that lets you take the expanded helium in the envelope and move it back into the pressure tank?
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No, we don't have compressors or helium tanks on board. We can't add helium in-flight, it can only be done on the ground while the airship is locked on its mooring mast. We can vent helium in flight, however we try to avoid that if it's possible (see my previous reply for explanation).
 
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