The Steampunk Forum at Brass Goggles
October 24, 2017, 01:33:07 am *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with username, password and session length
News: Support BrassGoggles! Donate once or $3/mo.
 See details here.
 
   Home   Blog Help Rules Login Register  
Pages: 1 [2] 3   Go Down
  Print  
Author Topic: Airship specifics  (Read 2357 times)
RodDuncan
Gunner
**
United Kingdom United Kingdom



« Reply #25 on: January 22, 2014, 09:33:00 am »

Reading all this brings back the memory of my father telling me about seeing the R101 flying when he was a child. It was a test flight of some sort and went over their house. Everyone went out to see it flying overhead. It was rather big!

Logged
Angus A Fitziron
Zeppelin Overlord
*******
United Kingdom United Kingdom

Research Air Ship R.A.S. 'Saorsa'


« Reply #26 on: January 22, 2014, 12:48:16 pm »

Yes Rod, I too remember tales from my Grandmother who told about airships (they were always 'Zeppelins' no matter what they really were) flying over the East coast in the Great War. It was a memory clearly printed on the mind - it must have been awesome and terrifying in equal doses. A fearsome enemy bringing the war with its death and destruction to your back door and seeing that enemy in the biggest, scariest man made thing you have ever seen probably, let alone one that flew. Just imagine looking at a vessel flying overhead, manned by the enemy, safely out of reach, dropping bombs on you before returning safe to base in just a few hours! Fortunately they became much more vulnerable during the war, but what an imprint that must have left on a young girl's mind?

My dad never would have seen those airships as he grew up in Thurso and not even the UK airships from RAF Fortune went that far! It must have been tremendous to see those leviathans - the Zeppelin NTs were impressive but nothing to that scale and in any case we are used to seeing massive aeroplanes flying about all the time, so the awesomeness has rather disappeared unless you study the subject, in which case it is still pretty amazing.
Logged

Airship Artificer, part-time romantik and amateur Natural Philosopher

"wee all here are much troubled with the loss of poor Thompson & Sutton"
Steampunk Away
Zeppelin Captain
*****
United States United States


Long Live The Icarus!

https://twitter.com/Steam
WWW
« Reply #27 on: January 22, 2014, 06:18:23 pm »

It is not just with dirigibles that the awe has disappeared. So many things are commonplace now that we are no longer horrified or struck in marvel by the things that should have such an affect on us.
Logged

Welcome aboard Steampunk Away! We are a small custom order shop, creating jewelry, props, costumes, drawings, and models. Email us at steampunkaway@gmail.com to have us create your special order on commission! Have a mechanical day!
George Salt
Zeppelin Captain
*****
United Kingdom United Kingdom



« Reply #28 on: January 22, 2014, 08:42:50 pm »

Tom Swift's airship, the Red Cloud, was an anomaly. It was described as half dirigible, half airplane.

The Red Cloud had float tanks that could be filled with buoyant gas that was stored compressed in a storage tank. When this gas was released from the float tanks, the ship descended. I don't think that the writer (Howard Garris writing as Victor Appleton) had a full grasp of how buoyancy actually works. If I had to build a model, I would give it air tanks that telescoped, but nothing of that sort was described in the text of the novel.

The Red Cloud could take of from a runway with it's floats empty, or fill the floats and rise like a balloon.

The Red Cloud had a deck and a cabin, float tanks, front and rear propellers, and a 20 cylinder internal combustion engine. But the overall appearance of the ship was not fully described.

Not an anomaly anymore. Scientist are creating a half-Dirigible, half-airplane to be used commercially, that will dominate the old flying times of airplanes. PopSci even did an article on it a few years ago I believe.

I take it you are talking about the lifting body airships like Skycat? These use conventional lift from air displacement but also forward thrust pushes the shape into the air which if tilted to the airflow, causes added lift due to the thrust of the propulsers. Another form of hybrid lift is with Zeppelin NT which uses vectoring thrust fans. These are used to force the ship down to land and to hold it there whilst mooring. They are then vectored on take off to aid climbing performance. Altitude stability in an airship is about balancing the internal volume of gas with mass of the airship against the density (pressure) of the air at the selected altitude. Vectoring thrusters and dynamic lifting bodies are all about transition flight rather than steady cruising flight. I think most recent airships (1920's to date) use some form of air displacement ~ for example air ballonets ~ which squeeze the lift bags thus reducing their volume (and increasing internal pressure) and so reducing lift. This does introduce physical strength problems and I think the early Zeppelins could compress hydrogen from the gas bags into cylinders - but it may be that they vented excess hydrogen from the gas bags, replacing it with hydrogen from compressed aluminium tanks. I think with Helium lift gas they need to be more environmentally aware as it is not a good gas to release into the atmosphere and so vectoring control of altitude and balancing air ballonets is probably how they do it. It would be interesting to read up how Zeppelin NT do it but I have not found any English language articles about altitude control (or anything else for that matter!) I visited the Zeppelin Museum a couple of years ago and they had a few items about NT construction and that was it...

At least one of the zeppelins started out with one or two hydrogen burning engines for consuming excess lift gas.  Long distance airships gradually lost weight over the course of a voyage, as fuel and supplies were consumed.  One alternative to releasing lift gas is to retain water condensing on the envelope.
Logged
Steampunk Away
Zeppelin Captain
*****
United States United States


Long Live The Icarus!

https://twitter.com/Steam
WWW
« Reply #29 on: January 22, 2014, 08:50:41 pm »

Tom Swift's airship, the Red Cloud, was an anomaly. It was described as half dirigible, half airplane.

The Red Cloud had float tanks that could be filled with buoyant gas that was stored compressed in a storage tank. When this gas was released from the float tanks, the ship descended. I don't think that the writer (Howard Garris writing as Victor Appleton) had a full grasp of how buoyancy actually works. If I had to build a model, I would give it air tanks that telescoped, but nothing of that sort was described in the text of the novel.

The Red Cloud could take of from a runway with it's floats empty, or fill the floats and rise like a balloon.

The Red Cloud had a deck and a cabin, float tanks, front and rear propellers, and a 20 cylinder internal combustion engine. But the overall appearance of the ship was not fully described.

Not an anomaly anymore. Scientist are creating a half-Dirigible, half-airplane to be used commercially, that will dominate the old flying times of airplanes. PopSci even did an article on it a few years ago I believe.

I take it you are talking about the lifting body airships like Skycat? These use conventional lift from air displacement but also forward thrust pushes the shape into the air which if tilted to the airflow, causes added lift due to the thrust of the propulsers. Another form of hybrid lift is with Zeppelin NT which uses vectoring thrust fans. These are used to force the ship down to land and to hold it there whilst mooring. They are then vectored on take off to aid climbing performance. Altitude stability in an airship is about balancing the internal volume of gas with mass of the airship against the density (pressure) of the air at the selected altitude. Vectoring thrusters and dynamic lifting bodies are all about transition flight rather than steady cruising flight. I think most recent airships (1920's to date) use some form of air displacement ~ for example air ballonets ~ which squeeze the lift bags thus reducing their volume (and increasing internal pressure) and so reducing lift. This does introduce physical strength problems and I think the early Zeppelins could compress hydrogen from the gas bags into cylinders - but it may be that they vented excess hydrogen from the gas bags, replacing it with hydrogen from compressed aluminium tanks. I think with Helium lift gas they need to be more environmentally aware as it is not a good gas to release into the atmosphere and so vectoring control of altitude and balancing air ballonets is probably how they do it. It would be interesting to read up how Zeppelin NT do it but I have not found any English language articles about altitude control (or anything else for that matter!) I visited the Zeppelin Museum a couple of years ago and they had a few items about NT construction and that was it...

At least one of the zeppelins started out with one or two hydrogen burning engines for consuming excess lift gas.  Long distance airships gradually lost weight over the course of a voyage, as fuel and supplies were consumed.  One alternative to releasing lift gas is to retain water condensing on the envelope.

Sorry for the long quote, but wouldn't the water condensation possibly weaken structural integrity?
Logged
George Salt
Zeppelin Captain
*****
United Kingdom United Kingdom



« Reply #30 on: January 22, 2014, 10:32:12 pm »

Sorry for the long quote, but wouldn't the water condensation possibly weaken structural integrity?

If it does (why would it?), you're going to be in trouble with all those boilers you specified for your airship!
Logged
Steampunk Away
Zeppelin Captain
*****
United States United States


Long Live The Icarus!

https://twitter.com/Steam
WWW
« Reply #31 on: January 22, 2014, 10:50:06 pm »

True, true...
Logged
Keith_Beef
Snr. Officer
****
France France


« Reply #32 on: January 22, 2014, 11:13:06 pm »

At least one of the zeppelins started out with one or two hydrogen burning engines for consuming excess lift gas.  Long distance airships gradually lost weight over the course of a voyage, as fuel and supplies were consumed.  One alternative to releasing lift gas is to retain water condensing on the envelope.

Now there are a few things to consider, here.

The first being, how long is an airship voyage, and how many passengers and crew need to be fed and watered during the voyage?

This dictates the supplies that need to be taken aboard, and the amount by which the total airship weight can be reduced in transit. This weight reduction is the sum of consumed fuel for propulsion and supplies consumed (presumably, no waste being retained aboard).

This would seem to indicate that an airship could begin a voyage with a certain volume of gas in its envelope in order to lift a certain load, and not require that amount of lift throughout the voyage ; were the buoyant gas to be usable as fuel, the excess lift gas could be consumed as fuel.

All this tallies with your post, but I fail to see how this relates to "retain[ing] water condensing on the envelope". The envelope being filled with a dry gas, the water could only condense on the outside of the envelope. This would only happen if the envelope has an outside surface temperature that is colder than the dew point of the ambient air.

To reduce the envelope's skin temperature below the dew point would require usually either climbing very quickly, or cooling the temperature of the buoyant gas, very quickly. I do not foresee either of those two cases coming about.
Logged

--
Keith
George Salt
Zeppelin Captain
*****
United Kingdom United Kingdom



« Reply #33 on: January 23, 2014, 12:36:53 am »

My car doesn't move overnight, it neither rapidly ascends nor does it rapidly change temperature.  But dew condenses upon it.  The dew condenses because it doesn't change temperature fast enough.

All that's required is for the structure of the airship to change temperature at a rate different from that at which the air temperature changes.  If the air cools at night and warms in the morning, or a cold moist pocket of air is encountered there is the potential for condensation if the structure cannot change temperature as quickly as the surrounding air.  There is also the likelihood of the structure providing nucleation sites for precipitation of water vapour directly onto the surface.

Doing some searching on this side-tracked me into technologies to condense water vapour from engine exhaust and retain this as ballast to offset the mass of fuel concerned.  An interesting concept, because most of the mass of this water will be from atmospheric oxygen rather than the fuel.  Anyone care to work out the mass balance?


(nb.  I am specifically considering rigid airships rather than blimps, as rigid designs appear better suited to long-distance travel)
Logged
Kevin1632
Snr. Officer
****
United States United States

Steam breakfast of Champions


« Reply #34 on: January 23, 2014, 12:55:18 am »

Actually the USS Macon and the USS Akron had condensers on the exhausts of the engines. When you burn hydrocarbons you dump the exhaust overboard, in an airship, you compensate for the weight loss by bleeding off gas, (H is cheap) if you are using He, it costs a lot so the Navy had a system where the recovered the water in the exhaust and stored it until landing and servicing.

As for condensate from the atmosphere, the sun and good ventilation are sufficient to mitigate the problem.

Regards,
Kevin
Logged

Fairley B. Strange
Zeppelin Overlord
*******
Australia Australia


Relax, I've done much dumber things and survived..


WWW
« Reply #35 on: January 23, 2014, 07:51:50 am »

Another method of checking the feasibility of your planned airships is to compare them against the various technical specs given for the RL ships.

A quick rummage in Wikipedia will show the differing sizes and abilities between a new pre- or early-ww2 zeppelin to a larger and more developed later example like the Hindenburg. Yes, for a SP ship you can add in a few years of additional R&D plus a bit of Handwavium, but it's a base to start from.
e.g. If you've got 30 pirates in your crew, plus guns and loot, you won't get much liftoff from a 20foot long envelope and 1 dinky motor.
Logged

Choose a code to live by, die by it if you have to.
Angus A Fitziron
Zeppelin Overlord
*******
United Kingdom United Kingdom

Research Air Ship R.A.S. 'Saorsa'


« Reply #36 on: January 23, 2014, 04:17:47 pm »


At least one of the zeppelins started out with one or two hydrogen burning engines for consuming excess lift gas.  Long distance airships gradually lost weight over the course of a voyage, as fuel and supplies were consumed.  One alternative to releasing lift gas is to retain water condensing on the envelope.


Interesting idea - hadn't heard that one before - so, they had cracked the problems of burning hydrogen in I/C engines that long ago! The early Zeppelin passenger 'ships used Blugas because it had roughly the same density as air -

Quote
The Graf Zeppelin burned blau gas, similar to propane, stored in large gas bags below the hydrogen cells, as fuel. Since its density was similar to that of air, it avoided the weight change when fuel was used, and thus the need to valve hydrogen. The Graf was a great success and compiled an impressive safety record, flying over 1,600,000 km (990,000 mi) (including the first circumnavigation of the globe by air) without a single passenger injury.[48]
Wikipedia

Also, they did not dispose of waste - human or otherwise - on a journey but retained it for the reasons stated, it maintained the mass of the airship. I guess in an emergency it could be dumped  Wink
reference Dr.Eckener's Dream Machine http://www.amazon.co.uk/Dr-Eckeners-Dream-Machine-Zeppelin/dp/0805064583

Logged
Steampunk Away
Zeppelin Captain
*****
United States United States


Long Live The Icarus!

https://twitter.com/Steam
WWW
« Reply #37 on: January 23, 2014, 04:21:59 pm »

I'm thinking that it is a long voyage ship, possibly transatlantic (which was achieved). I am going to have steam vents for excess steam to be released after it is used to power the fans and heating of the ship.
Logged
Angus A Fitziron
Zeppelin Overlord
*******
United Kingdom United Kingdom

Research Air Ship R.A.S. 'Saorsa'


« Reply #38 on: January 23, 2014, 04:34:50 pm »

Steam is gaseous water - when you are using steam to drive the fans and heating, it will lose energy, hence temperature, whilst doing work. So, finish condensing the water and send it back to the boilers. That way you lose no weight requiring venting lift gas nor do not have to expend additional energy bringing fresh cold water up to the temperature of the expended water you are releasing. Water is a major problem for all steam powered vehicles and it is usually more of a problem carrying enough water than carrying enough fuel! It is very precious and being able to harvest it from condensation on the airship skin is a very realistic ambition. If you want to know about the problems and perils of long distance airship flight then you should really read the book I mentioned above http://www.amazon.co.uk/Dr-Eckeners-Dream-Machine-Zeppelin/dp/0805064583 It is one of the best books I have read on the subject and a great read to boot.
Logged
Narsil
Immortal
**
United Kingdom United Kingdom



WWW
« Reply #39 on: January 23, 2014, 10:08:49 pm »

Steam is gaseous water - when you are using steam to drive the fans and heating, it will lose energy, hence temperature, whilst doing work. So, finish condensing the water and send it back to the boilers. That way you lose no weight requiring venting lift gas nor do not have to expend additional energy bringing fresh cold water up to the temperature of the expended water you are releasing. Water is a major problem for all steam powered vehicles and it is usually more of a problem carrying enough water than carrying enough fuel! It is very precious and being able to harvest it from condensation on the airship skin is a very realistic ambition. If you want to know about the problems and perils of long distance airship flight then you should really read the book I mentioned above http://www.amazon.co.uk/Dr-Eckeners-Dream-Machine-Zeppelin/dp/0805064583 It is one of the best books I have read on the subject and a great read to boot.


Also most modern steam plant will deionised and use quite a few additives in the water to control corrosion and scaling so the water used as the working fluid is generally kept in a completely closed circuit, although in static power generation plants different water will often be used for cooling the condensers, usually from a convenient lake or river. 

For something like an airship where weight is at a premium there is a trade-off between conserving water and the additional weight of condensation and recirculation equipment needed for a completely closed system. So for short hops between airfields it may not be worth conserving every drop of water as it can just be topped up when you drop off the cargo but for longer flights it becomes much more of an issue.

The other problem is cooling, all heat engines need to be able to dump waste heat. IC engines have the advantage that they can easily dump the working fluid (air) with each cycle as exhaust and even reclaim a certain amount using a turbocharger. For closed cycle steam engines this tends to be a bit more of a problem.
Logged







A man of eighty has outlived probably three new schools of painting, two of architecture and poetry and a hundred in dress.
Lord Byron
Steampunk Away
Zeppelin Captain
*****
United States United States


Long Live The Icarus!

https://twitter.com/Steam
WWW
« Reply #40 on: January 23, 2014, 10:31:10 pm »

For heat, wouldn't the high altitude help cool off the engines? And I am trying to see if I could put a closed circuit in after several suggestions.
Logged
Angus A Fitziron
Zeppelin Overlord
*******
United Kingdom United Kingdom

Research Air Ship R.A.S. 'Saorsa'


« Reply #41 on: January 24, 2014, 12:22:11 am »

For heat, wouldn't the high altitude help cool off the engines? And I am trying to see if I could put a closed circuit in after several suggestions.


I think as a general principle the energy generated in a heat engine is proportional to the change in temperature across the heat cycle. So, if the lower temperature reached is lower due to high altitude then the efficiency is higher. However at high altitude (low pressure) the boiling point of water is lower so efficiency is reduced. This suggests that a sealed, pressurised system would be advantageous. Note the complete absence of numbers here. I am guessing steam power on this kind of scale is unlikely so it needs to sound plausible even if the actual numbers disprove it! And yes, I know that one of the first successful dirigibles was powered by a steam engine...

Jules Henri Giffard
Logged
Lt.Mycroft
Snr. Officer
****
United States United States



« Reply #42 on: February 10, 2014, 02:17:59 am »

Here is a link to a show on zeppelins used during ww1
http://www.pbs.org/wgbh/nova/military/zeppelin-terror-attack.html
 
Logged
Narsil
Immortal
**
United Kingdom United Kingdom



WWW
« Reply #43 on: February 10, 2014, 03:09:53 pm »


The effect of high altitude on engine performance can be difficult to predict without looking at specific numbers and specifications.

For example, although the air may be colder it is also less dense, which will tend to make radiators (actually the term 'radiators' is unhelpful here as they work by convection not radiation) less effective for a given surface area. The lower density of air will also mean a greater volume is required through the furnace for combustion although this is not nearly as big an issues as it is with internal combustion engines.

There is also the possible complication that is it's very cold icing may become an issue, not so much in the main water system, which will obviously be at the least permanently warm but it's something which would need to be considered for things like reserve tanks and redundant or intermittently used pipes and steam lines.

On the plus side lower air density means less drag so less engine thrust is required to maintain speed, although propellers will be less efficient for the same reason.

The lower atmospheric pressure won't really effect the generation of steam as a pressure-generating boiler is by definition, a closed system so the boiling point of water is unaffected by the ambient pressure.

So overall the specific effects of high altitude are something which would need to be calculated on a case by case basis in reference to a particular design.
Logged
Keith_Beef
Snr. Officer
****
France France


« Reply #44 on: February 10, 2014, 04:18:07 pm »


The effect of high altitude on engine performance can be difficult to predict without looking at specific numbers and specifications.

For example, although the air may be colder it is also less dense, which will tend to make radiators (actually the term 'radiators' is unhelpful here as they work by convection not radiation) less effective for a given surface area. The lower density of air will also mean a greater volume is required through the furnace for combustion although this is not nearly as big an issues as it is with internal combustion engines.

There is also the possible complication that is it's very cold icing may become an issue, not so much in the main water system, which will obviously be at the least permanently warm but it's something which would need to be considered for things like reserve tanks and redundant or intermittently used pipes and steam lines.

On the plus side lower air density means less drag so less engine thrust is required to maintain speed, although propellers will be less efficient for the same reason.

The lower atmospheric pressure won't really effect the generation of steam as a pressure-generating boiler is by definition, a closed system so the boiling point of water is unaffected by the ambient pressure.

So overall the specific effects of high altitude are something which would need to be calculated on a case by case basis in reference to a particular design.


The Wikipedia article states that the newer model Zeppelins used in 1917 were capable of climbing to 5000m. I've jogged at 4320m with no ill effects, and according to this page air pressure at 5000m is around 58% of what is is at sea level.

I think that if the airships that are written into stories are flying at lower than 1917 limits (say 2500m to 3000m), that reduces the design constraints considerably and make it easier to write with convincing truthiness. 
Logged
CPT_J_Percell
Board Moderator
Zeppelin Captain
**
England England


The werewolf Airship Captain.


WWW
« Reply #45 on: February 12, 2014, 06:25:28 pm »

Just a thought, I should have followed this earlier.

My airship is a converted wooden hulled sailing ship, the power is generated via a train style boiler and furnace via a rotary steam generator. Would the heat generated help keep the engine deck warm enough to prevent the icing effect in cold weather and warm the ship or would I need heat exchangers on the outside to "Dump" the heat. As a safety feature the ship is modified with a lower hatch that can be opened so that the ship can drop into a river to drown the deck in a fire.

The ship generally flies at only a few hundred feet above buildings but all this discussion about thermal dynamics and altitude has me thinking about the realistic ability's of the engine combo.
Logged

I suffer from a random misfiring synapse and a bad case of wolfen the turns me into a seven-foot-tall werewolf or a seven-foot great wolf!
https://dragon-rehoming-centre.myshopify.com/
http://purbry.wordpress.com
Steampunk Away
Zeppelin Captain
*****
United States United States


Long Live The Icarus!

https://twitter.com/Steam
WWW
« Reply #46 on: February 12, 2014, 06:32:44 pm »

If you could theoretically make no dew or condensation appear on the deck then yes it could possibly work.
Logged
CPT_J_Percell
Board Moderator
Zeppelin Captain
**
England England


The werewolf Airship Captain.


WWW
« Reply #47 on: February 12, 2014, 09:00:50 pm »

If you could theoretically make no dew or condensation appear on the deck then yes it could possibly work.
I'm just theorising as I like to make my story as realistic as possible.
I should have mentioned it earlier but, the coal I used to get for our open fire was always damp. When a ship is full of several dozen tons of wet coal, would the damp not cause problems?
Logged
RJBowman
Zeppelin Captain
*****


« Reply #48 on: February 12, 2014, 09:41:28 pm »

Reading all this brings back the memory of my father telling me about seeing the R101 flying when he was a child. It was a test flight of some sort and went over their house. Everyone went out to see it flying overhead. It was rather big!


Now you can see it too:
final flight, R101 AIRSHIP, CARDINGTON. cardington.weebly.com


Do you think that it would it be possible to process an old film like this into 3-D IMAX format? The film as it is can't possibly reproduce the feeling of being next to these behemoth ships.
Logged
Steampunk Away
Zeppelin Captain
*****
United States United States


Long Live The Icarus!

https://twitter.com/Steam
WWW
« Reply #49 on: February 12, 2014, 10:05:12 pm »

If you could theoretically make no dew or condensation appear on the deck then yes it could possibly work.
I'm just theorising as I like to make my story as realistic as possible.
I should have mentioned it earlier but, the coal I used to get for our open fire was always damp. When a ship is full of several dozen tons of wet coal, would the damp not cause problems?

You could instead cryo-chamber the coal instead of making it damp, you would just have to mitigate the affect of the cold on the wood.
Logged
Pages: 1 [2] 3   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines Valid XHTML 1.0! Valid CSS!
Page created in 0.732 seconds with 16 queries.