Friday, February 12, 2010

14400 lbs of cement blocks

With the annual inspection coming up, preparations are being made for one of the more exotic phases of the process -- the transfer of the helium from the ship, over to 3 helium storage bags.

To keep our helium storage bags out of the rafters we'll need 36 movable blocks of 400 pounds each -- that's 180 bags of Quikrete!

A rule of thumb is that 1 cubic meter of helium at sea level, provides 1 kilogram of lift. We'll have roughly 7000 cubic meters to store, and enough blocks to keep it all weighted down.


Dan Dawson said...

Always been curious... in party balloons, or even the Mylar variety, they only maintain enough helium to float for a week or so.

Does the membrane used on Eureka just have so much less porosity such that the helium doesn't escape as easily? Does it need to be "topped off" regularly?

Brian Hall said...

As in many things airship, there is a balance to be struck in the envelope material selected. The main trade-offs are between weight, porosity, and longevity. Eureka uses a material made by ILC Dover called Tedlar. It is about in the middle as far as porosity and weight goes, and excels in longevity (10-15 years). As replacing the envelope is a non-trivial expense (7 figures), this isn't a bad attribute to have!

Airships of the Great War era used to contain the lifting gas with "Goldbeaters Skin", made from the intestines of animals, laminated to cotton or silk fabric. This was the best material of the day, but had a shelf life of only a few years.

An advantage of rigid and semi-rigid airships, is that the lifting gas can be contained in an envelope that does not also need to bear structural loads. In a non-rigid (blimp) design, the weight of the gondola, engines, and other "payload" must be distributed/borne over the envelope. Of course by dispensing of the airframe, the blimp itself has lower weight for a given volume of lifting gas -- and thus you are back to the series of design trade-offs again!