Aerospace/Aviation/Airships

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Question
I understand how airships rise by dumping ballast but how do they descend. I assume they release or compress helium . Is this correct or is there another mechanism ?

Answer
Hello Russell,
I had to look this one up myself and learned something new!
There are bags called "ballonets" These are bags containing air, which are inflated or deflated to maintain a constant pressure inside the envelope. This allows the helium to expand and contract. The ballonets can be pumped up with air from the outside or allowed to deflate as the helium expands and contracts. Since air is heavier than helium, inflating or deflating the ballonets will add or subtract weight from the nose or tail, thus trimming the ship. I took some of this content directly from the following sites:
http://www.goodyearblimp.com/cfmx/web/blimp/history/faq.cfm
http://www.americanblimp.com/fly.htm
Also interesting is the following site: http://www.airships.net/helium-hydrogen-airships which states that hydrogen airships (like the Hindenburg and Graf Zeppelin) would just release hydrogen to descend and compensate for fuel used while they flew.
Hopefully that helps!
Sincerely,
Laura

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Laura Laster

Expertise

I can help with questions about aviation disasters, aircraft operations especially general aviation and King Air information, aviation safety, and education questions on how to get into an aviation career. I can also answer general aviation questions as I am a commercial multi-engine pilot. I cannot answer questions about flight training or MBA schools in countries other than the USA or provide advice for non-US citizens interested in flight training. I cannot answer questions advising you what school to choose. I have no experience with aeronautical engineering so I cannot answer questions relating to engineering or schooling for aeronautical engineers. PLEASE don't ask me questions about any kind of engineering because it is outside my area of expertise, and I will NOT answer your question. I also cannot help you to choose a master's program for study as I do not have a master's degree in aviation. I cannot help with MBA advice.

Experience

I have been studying aviation disasters through doing my own research and a lot of reading since I was 13 or 14 years old. I am very interested in aviation safety and also am a commercial, multi-engine pilot. I am Director of Flight Operations at a private university working in the flight training department. I also have worked as an operations manager at a small charter airline and was involved in getting the airline certificated under Part 121 rules. I was formerly a flight operations division manager for a company operating a large fleet of King Air aircraft (60) and so I have some business aviation experience as well as having flight instructed for one year after college. My operations manager job frequently involved coordinating international projects for aerial survey clients and hiring qualified pilots to fly aerial survey missions.

Education/Credentials
Bachelor of Science, Aeronautical Science with Flight Management Concentration: LeTourneau University (2004) :: Dispatch Certificate: Sheffield School of Aeronautics (2010) :: Commercial Pilot: Single and Multi Engine Land, Instrument Rating :: Flight Instructor: Single, Multi and Instrument :: Ground Instructor: Basic and Advanced

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