Project Hybrid airship

[markp]

Thanks for the link and spotting my silly mistake in the code.

Lockheed Martin seem quite serious about hybrid airships. Looks like it could become a real thing in the future. I'll have to mention them in the documentation.

 

[markp]

Added some dust

 

[boogabooga]

I've been thinking about this. Is there a way to reverse hover thrust? If so, you would only need to traverse the engine pods through 180 degrees. You would also have reverse thrust ready immediately, rather than waiting for the pods to swivel.

Being able to use forward/reverse thrust was the best part of the early revisions as far as piloting, I think.

Also, would you be interested in discussing some airship physics?
(In particular, I don't think that venting the lifting gas would be a thing. This would:
https://en.wikipedia.org/wiki/Ballonet)

Also, I'll leave this here:
https://www.nasa.gov/directorates/s..._Phase_II/Evacuated_Airship_for_Mars_Missions

 

[markp]

Being able to use forward/reverse thrust was the best part of the early revisions as far as piloting, I think.

That can easily be reactivated.

I have overhauled the code for animating the fan to prevent it wobbling when the whole engine is rotated quickly. It may not have been that noticeable because I had previously limited the rate of the rotation of the thrust vector. I had thought the wobbly animation was an insolvable problem (Orbiter bug?) but happily, after some experimentation, I found a solution.

The whole engine can now be turned at a rate set by the pilot. I have it currently limited to between 9 and 90 degrees per second.

Also, would you be interested in discussing some airship physics?

Yes that would be good.

I think I'll change the venting message to reflect the use of a ballonet device. Or maybe some helium compression device like used in the Aeroscraft?

Also, I'll leave this here:

Yes that's kind of surprising at first but makes sense after considering everything.

 

[boogabooga]

1) Are you imagining this as a rigid airship or a non-rigid airship?

2) How are you imagining the propulsion system? It would work very differently on say, Mars than Earth. It seems to me that the endurance is very limited right now.

 

[Urwumpe]

Now what if we also add a "ZR-3 Los Angeles" as rigid historic artifact to the park...

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930086540.pdf

(Scroll to the end of the report for many drawings)

 

[markp]

1) Are you imagining this as a rigid airship or a non-rigid airship?

I am thinking of it as a non-rigid airship.

2) How are you imagining the propulsion system? It would work very differently on say, Mars than Earth. It seems to me that the endurance is very limited right now.

Well for Mars I am assuming the engines are ducted fans like on Earth but spinning at ten times the speed like for the NASA Mars helicopter. I haven't looked into it in any depth though.

https://mars.nasa.gov/news/8335/mars-helicopter-to-fly-on-nasas-next-red-planet-rover-mission/

With regards to endurance I'm not sure if I have calculated the fuel rate to the engines properly yet. Also the fuel tanks might also have a bit of a low capacity which will be easy to modify.

Now what if we also add a "ZR-3 Los Angeles" as rigid historic artifact to the park...

They were magnificent ... must have been so great to fly one.

 

[Urwumpe]

They were magnificent ... must have been so great to fly one.

At least considering the technology back then. Some solutions had been really smart, still impressive that it was possible to cross the Atlantic with this one or fly 12500 km with minimum payload and all fuel tanks.

 

[boogabooga]

They were magnificent ... must have been so great to fly one.

When they weren't crashing and killing most of the crew, which the non-German ones did with alarming regularity (see my first post). Then a German one did crash in view of a movie camera and it was all over.

 

[Urwumpe]

When they weren't crashing and killing most of the crew, which the non-German ones did with alarming regularity (see my first post). Then a German one did crash in view of a movie camera and it was all over.

On the other hand, a crash of a German one in 1908 did actually start the Zeppelin company, by making people create the Zeppelin fund.



Also, using the Zeppelins in WW1 also did a lot there to advance technology on the German side. Quite many later improvements came from that short military career. But the citizens of London felt less impressed by seeing Zeppelins in WW1.

(But the German safety record depended largely on Hugo Eckener, who was often captain of the Zeppelins of his own company. When the Nazis came into power, they replaced him by loyal officers, who lacked the experience AND the focus on crew safety - the result was the Hindenburg accident, which was caused by a pilot error)

 

[boogabooga]

Actually, I don't understand fully what is meant by "venting" the lifting gas, even in the old days of constant volume rigid airships. A pure venting would decrease the internal density and increase the buoyant lift, right?

So it must mean replacing some of the lifting gas with air, but I'm not sure of the details.

Edit:

On further reflection I see that the old airships had separate internal gas bags that were not constant volume at all. So I assume that air would take up the space between the external and internal skin as the gas bag deflated?

I am thinking of it as a non-rigid airship.

This means that the internal gauge pressure must be kept slightly positive and probably about constant to maintain the airship's structure. Venting the lifting gas (intentionally) is probably out of the question.

Well for Mars I am assuming the engines are ducted fans like on Earth but spinning at ten times the speed like for the NASA Mars helicopter. I haven't looked into it in any depth though.

I get the ducted fans.

I mean, on Earth it would have some kind of air-breathing combustion engines. On Mars...nuclear? Solar? Fuel Cells? You might need to have a configuration option to switch propulsion systems.

 

[Urwumpe]

Actually, I don't understand fully what is meant by "venting" the lifting gas, even in the old days of constant volume rigid airships. A pure venting would decrease the internal density and increase the buoyant lift, right?

Yes. Remember: The gas cells inside the rigid hull can grow and shrink. The smaller the gas cells become, the more air is of course inside the hull. And we are talking about really small changes in volume there to have big effects.

When the pressure difference between inside the cell and outside the cell becomes too large by heating the gas or climbing, it has to be vented.

Also, if you want to land, its is one bad choice to vent gas - more skilled captains preferred to land during the evenings preserving the gas by letting it cool at altitude and the drop into a layer of warm air close to the surface, making the Zeppelin "heavy" relative to the air.

Generally, you often needed to vent during long distance trips because the fuel consumption made the Zeppelin lighter, which increased the tendency to climb. One solution to reduce this tendency was for example heating the gas before take-off. Or using large radiators to cool the engine exhaust and produce ballast water that way.

 

[boogabooga]

How much overpressure could the gas bags support?

Or using large radiators to cool the engine exhaust and produce ballast water that way.

That was used in the Akron class. Helium was very expensive in the 1930s and venting was out of the question.

 

[Urwumpe]

How much overpressure could the gas bags support?

I still try to find it out, did not find it yet. The USS Macon for example had a maximum pressure altitude of 900 meters. But I know that the German Zeppelins reached higher without problems. One military Zeppelin had a "static altitude" of 2000 meters, but had to vent 1% of its hydrogen for every 80 meters climbed.

Looks like German Zeppelins had rather been using a maximum volume of the gas cells as reference, rather than the pressure inside the gas cell. Especially the pre-129 gas cells had been really fragile, they had been made from one special skin of a cows stomach, because it is very gas tight and light, and multiple pieces can easily be glued together to one large bag by using salt water.

That was used in the Akron class. Helium was very expensive in the 1930s and venting was out of the question.

The Los Angeles also used it, since she was also filled with Helium after arriving in the USA.

---------- Post added at 19:32 ---------- Previous post was at 18:50 ----------

:facepalm:

Of course, they did not mix hydrogen and air inside the gas cells. 95% hydrogen meant that the gas cell was inflated with just 95% of its maximum capacity with pure hydrogen.

Thus, not accounting for tension by gravity on the gas cells, the pressure inside the gas cell is equal to the outside pressure until reaching maximum volume. Once the pressure starts to increase significant, the gas cell is getting overinflated. So, practically, it might be as little as just a few Pa over outside pressure to start venting.

 

[boogabooga]

Especially the pre-129 gas cells had been really fragile, they had been made from one special skin of a cows stomach, because it is very gas tight and light, and multiple pieces can easily be glued together to one large bag by using salt water.

Goldbeater's skin. Because it was a polymer before the plastic industry was a thing. The number of bovines that must have had to be slaughtered to make one of those things is incredible, though I suppose that was going to happen anyway.

Airships. They are like giant air sausages. In more ways than one.

 

[Urwumpe]

Goldbeater's skin. Because it was a polymer before the plastic industry was a thing. The number of bovines that must have had to be slaughtered to make one of those things is incredible, though I suppose that was going to happen anyway.

700000 for one WW1 military zeppelin.

Seven Hundred Thousand.

---------- Post added at 20:43 ---------- Previous post was at 20:28 ----------

Found the usual overpressure of a typical gas cell made of goldbeaters skin in a NACA report (NACA-TM-172) about the usage of this skin: 30 mm of water (294 Pa)

 

[boogabooga]

Airship Engineering (101)

 

[markp]

Uploaded version 5 to post #1

In the next version I hope to add a simple representation of the ballonets. For trimming the pitch this is already implemented via the ability to move the centre of mass in the model. I just need to revise the messages and perhaps limit the range of pitching. I also plan to add some fine control over the buoyancy within some realistic limits. I have kept the venting capability for the moment as I find it useful for testing.

This version has improved fan animations, a dust effect (not quite fully working yet), reverse thrust, larger propellant tanks and a revised manual.

 

[boogabooga]

Big improvement.

I miss the ability to vary the neutral buoyancy altitude directly in the simulation.

Perhaps the pilot could increase or decrease the payload and/or starting ballast mass when landed and get a prediction of the buoyancy altitude?

Edit:
It could be that the ceiling is being changed, but not making it to the HUD.

---------- Post added Jun 11th, 2018 at 05:04 AM ---------- Previous post was Jun 10th, 2018 at 05:25 PM ----------

Version 5 bug reports:

Some HUD messages don't disappear, such as those relating to to changing the swivel speed

Some important parameters are not saved to the scn file. Especially GAS. Speaking of which, why is the default GAS 90 now?

 

[markp]

It could be that the ceiling is being changed, but not making it to the HUD.

The current ceiling value can be viewed by pressing c after pressing 1.

Some HUD messages don't disappear, such as those relating to to changing the swivel speed

Thanks I'll look into it

Some important parameters are not saved to the scn file. Especially GAS. Speaking of which, why is the default GAS 90 now?

GAS 90 is to make the airship is heavier than air so it can fly as a hybrid airship. The other 10 percent is taken up by some imaginary air filled ballonets.

This then makes the use of a neutral buoyancy CEILING somewhat useless. Not sure what course of action to take at the moment.

One possibility would be to add a physical model of the airship which can be used to predict the airship's performance, e.g. maximum altitude, given a set of parameters, e.g. ballonet pressure? Then the predicted results could be presented to the pilot who can then adjust parameters, such as the amount of air in the ballonets, until the predicted performance matches the desired performance. Not entirely sure how it's done in real life so will have to check that a bit.