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Old 07-19-2018, 02:11 PM   #76
boogabooga
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Quote:
Originally Posted by markp View Post
 I think I understand the equations and worksheets now, thanks.

I am now thinking how best to operate the airship.

So I understand that if for some reason ballast is dropped, e.g. cargo is released, from the airship then it would rise, obviously. What I'm not clear on is would the airship have to vent (or maybe compress) gas so it doesn't rise up beyond its pressure altitude or could it adjust its ballonet volume?
Or it could use it's propulsor, COM shift, and elevator to control altitude. That's why I had you make the propulsor swivel 180 degrees .

The primary job of the ballonet (as I understand it) is to maintain a constant gauge pressure in the envelope. I guess that you have the option of inflating the ballonet more, if the envelope can handle a higher pressure. That would depend on the airship design, I guess. Probably there would be a safety margin to work with between optimal pressure and bursting.

I would say that venting should be considered a last resort to keep from damaging the envelope in cases where you have already exceeded the pressure ceiling. At least modern helium designs seem to be that way. In the old days of cheap hydrogen, they may not have minded venting so much. I'm not sure, because venting can give you problems when you try to come back down.
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Old 07-19-2018, 02:14 PM   #77
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Well, the Germans vented a lot of hydrogen for keeping the airship level, they only reduced this near thunderstorms. On the other hand, this improved safety also a lot, since it reduced the contamination of the hydrogen with air.

Of course, Helium is too expensive for this kind of procedures.
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Old 07-20-2018, 07:23 AM   #78
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Originally Posted by boogabooga View Post
 Or it could use it's propulsor, COM shift, and elevator to control altitude. That's why I had you make the propulsor swivel 180 degrees .

ok good to know there's a method in the madness!
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Old 08-10-2018, 09:07 PM   #79
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Update:

I have been working on some operational aspects for the airship. These have been 1) Landing gear and 2) Collecting and delivering cargo.

1. Landing gear

For this I experimented with adding wheels to the gondola. I also came up with a few ideas such as deploying some kind of rigid structure from the nose. In the end I simply added an animation to rotate the wings so the tips ended up a bit forward of the centre and level with the lower back fins. Not sure the wings and fins would be strong enough to support the airship in reality but it looks good ...

Image of wings rotated for landing
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Another perspective of the rotated wings
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2. Collecting and delivering cargo

An autopilot has been added so the airship positions itself over the cargo. The pilot can then decrease the altitude until the airship docks with the cargo. A marker can be used by the airship's autopilot to deliver cargo to a precise location where it can then be deposited on the surface by the pilot. The building used in the addon and featured in the images below now automatically fixes itself to the surface so it doesn't slide about as it previously did.

In the image below the cargo, a building, has been collected from a landing pad and is now being delivered to a location occupied by a marker called "foundation1"
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The cargo is positioned over the marker.
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Last edited by markp; 08-10-2018 at 09:21 PM.
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Old 09-24-2018, 04:44 AM   #80
markp
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Update:

Making some progress.

At the moment the ballonet is automatically adjusted to keep the pressure difference inside the envelope at 500 Pa above the outside pressure. A warning is displayed at 600 Pa and the airship starts venting gas at 750 Pa. These 600 and 750 Pa values are guesses so I'll have to dig out some references and maybe adjust these.

I was rather surprised when warnings were given when the airship climbs faster than a few metres per second. This is because the simple algorithm I have used doesn't change the ballonet size quickly enough to maintain the correct pressure. I am wondering if real airships climb or descent rates are have to be limited in a similar way due to a limit on the rate of air pumped into or out of the ballonet. Something to look into.

First picture below shows when the airship reaches its ceiling and a warning message is displayed. This is from a high altitude test in the alps. All my tests have recently been at Canaveral so I needed to check everything works from some higher ground.

Second picture shows the base from where I took off. It's the antarctic base copied to the alps ...

Third picture shows an example of the airship data that I display to help me figure out what is going on in the code.

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Old 09-24-2018, 05:38 AM   #81
boogabooga
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Quote:
Originally Posted by markp View Post
 Update:

Making some progress.

At the moment the ballonet is automatically adjusted to keep the pressure difference inside the envelope at 500 Pa above the outside pressure. A warning is displayed at 600 Pa and the airship starts venting gas at 750 Pa. These 600 and 750 Pa values are guesses so I'll have to dig out some references and maybe adjust these.
The 500 Pa in my spreadsheet comes from Zepplin-NT (5 millibar overpressure). Airlander uses about twice as much overpressure. This is just from Wikipedia

Quote:
Originally Posted by markp View Post
 I was rather surprised when warnings were given when the airship climbs faster than a few metres per second. This is because the simple algorithm I have used doesn't change the ballonet size quickly enough to maintain the correct pressure. I am wondering if real airships climb or descent rates are have to be limited in a similar way due to a limit on the rate of air pumped into or out of the ballonet. Something to look into.
I'm sure "pumping out" is fast and easy because you are just releasing pressure through a valve. The old Goodyear blimp used its propwash to inflate its ballonets. I'm not sure what is done these days.
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Old 09-24-2018, 07:24 AM   #82
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And yes, ascent and descent rates are limited for various factors that could harm structural integrity.

Especially the high altitude Zeppelins used in WW1 required very careful handling there and only launched in good weather. Actually that is one of the apocryphical etymologies for the German term "Bombenwetter", which describes a warm, sunny, almost windstill day with little clouds.
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Old 09-26-2018, 08:44 PM   #84
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That was great video, thanks! Now I know how to pronounce ballonet. It was good to see the inlet scoops for the ballonets.

I'm starting to getting an idea of the general properties of the valves, i.e. ballpark size and quantity, for releasing air and fan systems for pumping air into the ballonet after reading a few things. It seems quite simple stuff but not really that obvious.
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