Orbiter-Forum [Project] Hybrid airship
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 06-13-2018, 06:41 AM #46 markp Orbinaut That volume might be for a box that encompasses the mesh. I am thinking that the airship's envelope mesh volume could be scaled to the required volume calculated from information given in the scenario file. Controlling the neutral buoyancy altitude by the pilot would be made perhaps by adding or dropping the ballast. The rigid airship sounds like a good idea for now. I haven't found any good sources yet to compare performance capabilities of rigid and non rigid airships.
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 06-14-2018, 11:51 AM #48 boogabooga Bug Crusher
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 06-14-2018, 12:58 PM #49 Urwumpe Certain Super User The NACA report to the first half of this video: https://ntrs.nasa.gov/archive/nasa/c...9930091641.pdf
06-14-2018, 07:02 PM   #50
boogabooga
Bug Crusher

Hello Mark,

Are you able to use Excel?

Ignoring ballonets for now, I've worked out the math(s) for an airship. This version assumes a constant envelope volume with the lifting gas at atmospheric surface pressure and temperature regardless of the gauge pressure (think non-rigid airship-or a gas bag- made out of a super-strong material).

It demonstrates for instance how to account for the lifting gas mass. It also demonstrates how to calculate either the payload mass or the ballast mass required to achieve a desired neutral buoyant altitude. I think that this technique would make more physical sense than keeping the mass constant and varying the envelope volume. We might change our minds about the "effective" envelope volume once ballonets get implemented, but I think that in general ballonets are there to keep the pressure from rupturing the envelope.

I don't have time now to go through the equations, but I can help you later. I might be able to take over the math modeling in the code, if you wish.

I'll work on a more sophisticated version of the workbook later with ballonets, more atmospheres, etc.

*gauge pressure is the pressure difference between the inside and outside of the envelope.

P.S., if anyone could help me provide atmospheric constants for other planets, that would be great.
Attached Files
 AirshipCalcs_0_1_0.zip (14.2 KB, 6 views)

Last edited by boogabooga; 06-14-2018 at 07:41 PM.

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 06-15-2018, 08:02 AM #51 markp Orbinaut Thanks for the calculations, that's great. I had a look. That would make things more convenient. I guess the pilot could query an onboard 'flight computer', consisting of your calculations, to determine how much ballast to add or what payload weight could be carried. The calculations could also be used to automatically inform the pilot of the new neutral buoyancy altitude if ballast is dropped or when the payload is released from the airship.
 06-15-2018, 08:07 AM #52 Urwumpe Certain Super User Quote: Originally Posted by markp  Thanks for the calculations, that's great. I had a look. That would make things more convenient. I guess the pilot could query an onboard 'flight computer', consisting of your calculations, to determine how much ballast to add or what payload weight could be carried. The calculations could also be used to automatically inform the pilot of the new neutral buoyancy altitude if ballast is dropped or when the payload is released from the airship. Luckily Orbiter is not giving you many surprises there. In real airships, this is a lot tougher since the atmosphere can be very dynamic. Also, for a hybrid airship, you should usually be above neutral buoyancy altitude, since you make use of dynamic lift.
 06-15-2018, 11:34 AM #53 boogabooga Bug Crusher That's the weird thing, If you run the numbers in my workbook for Airlander 10, 38000 cubic meters of Helium at 20000 kg solid mass is not heavier than air, not even close.
 06-15-2018, 12:20 PM #54 Urwumpe Certain Super User One cubic meter of Helium results in 10.9 N lifting force at sea level. So, you should get 42222 kg maximum weight. Makes sense. In reality, the ballonets should be fully filled with air on the ground, so you have much less than 38000 m³ helium volume then. And since the ballonets are not shrinking to zero, this explains why the maximum payload of the airlander is less than the theoretical maximum.
 06-15-2018, 04:46 PM #55 markp Orbinaut boogabooga if you could add a function or routine into the code to calculate the ceiling that can be queried from the main program. That would be fairly easy to implement I think. Are you planning to factor in the engine thrust and aerodynamic lift into the calculation of a 'ceiling' as well? The code is a bit of a mess at the momemt but I can spend a small amount of effort to make it more readable, without breaking anything, then post the updated version within the next few days. I think it is ok to have a lighter-than-air hybrid airship, at least for now, although hybrid airships are supposed to be heavier-than-air. I would certainly like it to have a lighter-than-air capability to enable it to do what I'd like it to do, i.e. delivery of heavy oversized objects like buildings. It also needs the ability to take on ballast. This is to maintain its neutral buoyancy altitude after delivery of the payload.
 06-15-2018, 05:50 PM #56 Urwumpe Certain Super User What I wonder - would it be possible to produce a H2/He mixture that can't ignite? Of course, the gas in the cells would need to be circulated, because otherwise, the H2 would concentrate on the ceiling of the cell. But just being a bit crazy there: Maybe this could increase payload capacity of a Helium airship significant. If the mix would have just 2% more lift force than helium, it would already be a huge difference in payload after subtracting the deadweight.
 06-15-2018, 06:39 PM #57 kuddel Donator Someone thought of this earlier http://www.madsci.org/posts/archives...2816.Ph.r.html 8.7% (Hydrogen) is stated there as a "save" mixture
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 06-15-2018, 06:44 PM #58 Urwumpe Certain Super User Quote: Originally Posted by kuddel  Someone thought of this earlier http://www.madsci.org/posts/archives...2816.Ph.r.html 8.7% (Hydrogen) is stated there as a "save" mixture OK, even a bit less than I thought. Nevermind.
 06-19-2018, 11:08 AM #59 markp Orbinaut Been playing around with boogabooga's excellent spreadsheet that calculates the lift capability of a non-rigid airship. To fly on Mars I think the airship envelope would most likely have to be at least 3 times its current length or about 30 times the volume of Airlander 10 to fly on Mars. I can post my guesstimates and sources for the hybrid airship mass budget if anyone's interested. During the course of tidying up the code I added the ability to configure the airship envelope size plus aerodynamic surfaces in the scenario file. The gondola and engines remain the original size and are not scaled. A few more days until I'll be ready to post a new version with the tidied up and commented code.
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 06-19-2018, 01:36 PM #60 boogabooga Bug Crusher I don't have time this week to look at this but I'll try more next week.
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