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  #21  
Old March 14th, 2014, 02:40 AM
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Quote:
Originally Posted by aramis View Post
Ok, decision time... is the ether prop in the tail of the envelope, or in the aft of the gondola?

Airscrew propellers - off the sides of the gondola? off the sides of the gassbag? Large single one behind the tail? On the horizontal stabilizers of the tail?

Guns - sides of gondola or gasbag?
As the ether propeller is only used in abscence of the oxygen that would make fires a danger, it's the only elemente in the envelope, so it's at its aft, while the atmospheric propellers (and boiler) are at the aft of the gondola.

By the same reason, the guns are at the sides of the gondola too, as their firing sparks would be dangerous too close of the envelope or over it (as they will if at the top deck, over the envelops, as any hydrogen leack will go up to it, not doen to the gondola).
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  #22  
Old March 14th, 2014, 06:27 PM
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I don't have an opinion on location of ether prop, but am happy that you brought it up before I got started drawing it somewhere else.

I think the gun turrets at the sides of the airship structure (not the gondola) would make more sense, as it would give a little better upward traverse without accidentally shooting into the airship. The way the turrets are isolated with hatches, there should not be any issue of sparks getting into contact w free hydrogen.

Also, all of the rigid airship designs that I have been looking at for inspiration do not have free hydrogen loose in the whole structure (which is why I am referring to that structure as the airship rather than the gasbag). There are multiple individual gasbags inside the rigid airship structure, and there are also tanks and ballonets and pumps and other apparatus to maintain trim and allow adjustment of both attitude (nose up, down, or level) and altitude by controlled movement of hydrogen and regular atmosphere into or out of the gasbags and ballonets.
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  #23  
Old March 14th, 2014, 06:55 PM
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Originally Posted by SpaceBadger View Post
I don't have an opinion on location of ether prop, but am happy that you brought it up before I got started drawing it somewhere else.

I think the gun turrets at the sides of the airship structure (not the gondola) would make more sense, as it would give a little better upward traverse without accidentally shooting into the airship. The way the turrets are isolated with hatches, there should not be any issue of sparks getting into contact w free hydrogen.

Also, all of the rigid airship designs that I have been looking at for inspiration do not have free hydrogen loose in the whole structure (which is why I am referring to that structure as the airship rather than the gasbag). There are multiple individual gasbags inside the rigid airship structure, and there are also tanks and ballonets and pumps and other apparatus to maintain trim and allow adjustment of both attitude (nose up, down, or level) and altitude by controlled movement of hydrogen and regular atmosphere into or out of the gasbags and ballonets.
Yeah, all gasbags should be inside the outer skin. For the drawings, there should be a central platform fore-aft inside the envelope - partly for inspection, partly for access to the controls in the tail, and a central ladderway alongside the steam pipes for the boiler.

Really, I don't see retracting the masts as terribly practical, but folding them, sure. This has a LOT to do with the practicalities of vacuum - retractable adds multiple points where it can fail horribly. Also note: Several of the Martian Kites have hanging sails - the sails come off the sides, and hang below, removing the requirement for a vertical mast. put those on pivots off the cabin or the lower third of the envelope...
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  #24  
Old March 14th, 2014, 07:24 PM
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Quote:
Originally Posted by aramis View Post
a central ladderway alongside the steam pipes for the boiler.
McPerth/McBean specified a spiral staircase, so I am going to try to do it that way, unless we have a GM ruling to the contrary.

EDIT: Although I think a few ladders in addition would be a good idea, so as to not only have one path for moving between decks.

Quote:
Originally Posted by aramis View Post
Really, I don't see retracting the masts as terribly practical, but folding them, sure. This has a LOT to do with the practicalities of vacuum - retractable adds multiple points where it can fail horribly. Also note: Several of the Martian Kits have hanging sails - the sails come off the sides, and hang below, removing the requirement for a vertical mast. put those on pivots off the cabin or the lower third of the envelope...
Y'know, that would work really well! I have been trying to figure out how to place the sails in accord with prior discussion between you and McPerth, and having some trouble with it. But if you read the solar-boiler description in detail, it is required to be on a long boom with free-swinging access to let it align properly with the sun for maximum efficiency. So now I am envisioning on the upper deck (on top of the airship structure) a sturdy post (maybe it goes all the way down through the airship to the gondola, for maximum bracing by cross-pieces inside the rigid structure). Just above head-height, there is a collar on the post with the masts - they can be rotated out to the sides to drop the sails into position on each side, or when the sails are furled can be rotated in-line with the axis of the airship for minimum profile. Then, above the masts and capping the top of the sturdy post, there is the pivot for the solar-boiler boom, allowing it to rotate as needed for solar efficiency in space, or be aligned with the ship axis for minimum profile (and minimum wind resistance) in atmosphere.

If that is unclear, I will try to sketch it out, but it all looks workable in my head and I have a much clearer idea of how to put the airship together now.

Thanks!

PS to McPerth: In the book the conservatory is described as having a musical instrument of inventor's choice - pipe organ is suggested, although to me that seems more in line with a mad inventor like Captain Nemo. What would McBean choose for musical instrument? Or would he prefer more bookshelves, or something like a nice big fishtank for peaceful contemplation (that could double as storage for aquatic specimens! )?
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  #25  
Old March 14th, 2014, 07:44 PM
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I see you added a thumbnail view with the masts out the sides. I'm not sure how we would pivot those; what do you think about my idea of putting the masts and solar-boiler boom both on a pivot on the top deck? It works beautifully in my head; will try a sketch to upload.

Re shape of rigid airship body: I know we decided that an aerodynamic lifting shape would be too advanced - what about a slightly flattened tube? Oval-ish cross section, with flattened top and bottom for the decks. I am not sure about this - I think a circular cross section might be easier to make with a strong framework of cross-beams - but if the flat decks are considered part of the framework, then again it looks pretty strong. Again, I will try a sketch to show what I mean.

EDIT: Striking out above paragraph, as I figured out how it would work and still look good with circular cross section, except at top where flattened by top deck. It'll look cool and also workable, I promise!

EDIT 2: Oops, apparently using wrong code for strike-through, but don't want to look it up right now. Just ignore the paragraph with the [st] codes, OK?


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  #26  
Old March 14th, 2014, 09:02 PM
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Quote:
Originally Posted by SpaceBadger View Post
I see you added a thumbnail view with the masts out the sides. I'm not sure how we would pivot those; what do you think about my idea of putting the masts and solar-boiler boom both on a pivot on the top deck? It works beautifully in my head; will try a sketch to upload.

Re shape of rigid airship body: I know we decided that an aerodynamic lifting shape would be too advanced - what about a slightly flattened tube? Oval-ish cross section, with flattened top and bottom for the decks. I am not sure about this - I think a circular cross section might be easier to make with a strong framework of cross-beams - but if the flat decks are considered part of the framework, then again it looks pretty strong. Again, I will try a sketch to show what I mean.
The boiler already goes on that pivot.

Having them out to the sides, if you'll look closely, I included a darker blue hinge point. The control of the boom angle can be handled by lines to the nose and tail, and the dropped sailbooms would of course need lines rigged as well - both to the mainspars and to the body to control angle and prevent excessive flapping.

when furled and stowed, the sails would be flat along the sides of the envelope.Further, on a top down view, the turrets would be amidships (1/2 length) -while the sails would likely attach about 1/3 of the length, and fold to the 2/3 length point.

Or the sails could be attached to the gondola.

As for sails on the top - impractical. The sail mass is considerable - fully 10%, and the boiler another 6%




[tr]


Above Center of liftUniform or on centerBelow Center of lift
already placed10 Solar Boiler15 Armor
04 Ether Prop
33 Guns
01 Control Room
03 Lab
02 Conservatory
10 Passenger Quarters
01 Camera system
02 photo lab
10 Forced Draft Boiler
10 Coal Bunker
Without Sail/cargo104239 true
34 moment if coal bunker above gondola
With top sail20 true
30 due to moment
4239 true
34 Moment if coal bunker above gondola
with sail where I drew it
no cargo
10 4255 true
41 moment furled with gondola bunker
36 moement furled with envelope bunker


Please note, I'm simplifying moment. Empty cargo has no mass, and it's been operating with empty cargo.

And in general, any case where the center of moment is near or above the center of lift is unstable. And the sails would need to be rather large, so I've added 10 to the effective mass for balance purposes - but that's probably a bit low.. With a top sail, she'd only be stable with due aft winds or a full hold.
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  #27  
Old March 14th, 2014, 10:40 PM
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Default Preliminary Airship Sketches

Preliminary Airship Sketches

(Proportions probably way off, as I haven't yet calculated actual length and circumference of main airship body necessary to hold gasbags for the 150 tons of hydrogen that McPerth calculated for necessary lift.)

Here is the first sketch, a head-on view showing decks, bracing, and outer skin, along with the central post on which the masts and solar boiler mirrors will pivot. Note: as far as I can tell from the drawings in the book, only the mirrors/lenses pivot, not the whole boiler itself, so there would be no problem having this pivot on the same post as the masts, only slightly above.


Note: I expect there would be more bracing between the hexagonal main structure and the outer arcs that hold the outer skin for a circular cross-section, but these would be too small to show on this scale.

EDIT: I think also additional main braces to make each hexagon into a set of six triangles for added strength.
Next is a sideways view. This shows both the masts and the solar mirror boom in-line with the axis of the ship. In atmospheric usage, the masts would be pivoted to hang out over the sides and allow the sails to hang down. In space, the sails would be furled and the mast moved back into the position shown below, while the solar mirror booms would be pivoted as necessary to maintain the most efficient focus on the boiler.

At each end of the upper deck are posts with capstans that, by setting or removing blocks, can be used to reposition either the masts or the mirror boom.

The middle deck is divided into a main portion and a rear portion; the rear is where the ether propeller engine room is located. I haven't shown them in the drawing, but I expect catwalks and ladders located as necessary to access and maintain equipment. Certainly there is a full-length catwalk along the main beam of the ship, at the same level as the middle deck. The rear-middle deck can be reached by this catwalk, or by stairs/ramp from the lower deck, or by ladder down from the upper deck.



And finally, here is a sketch of head-on view of the ship in atmosphere, with sails furled and unfurled.




OK, you can start throwing rocks now!


EDIT: Oh, I forgot to mention the gasbags and compression tanks. Those go in the empty spaces fore and aft of the main deck, and smaller ones to either side of the main deck (fitted around the passageways to the turrets (which are seated on one of the main cross-pieces to provide a strong setting for the turrets)). Ballonets are inside the gasbags.



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  #28  
Old March 14th, 2014, 10:45 PM
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Oh, I forgot to mention the gasbags and compression tanks. Those go in the empty spaces fore and aft of the main deck, and smaller ones to either side of the main deck (fitted around the passageways to the turrets (which are seated on one of the main cross-pieces to provide a strong setting for the turrets)). Ballonets are inside the gasbags.
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  #29  
Old March 14th, 2014, 11:00 PM
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Oops, I was looking at McPerth's details of the ship and posted the sketches in that thread: McBean's Research.
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  #30  
Old March 14th, 2014, 11:10 PM
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Ummm... looking again in the book, it does appear that they intend the solar-boiler boom to have a lens/mirror at one end, and the actual boiler tank at the other.

Does that strike anybody else as extremely impractical/stupid?
1) You've got a comparatively lightweight mirror/lens assembly at one end of the boom, and a big old heavy tank full of water at the other end?

2) Exactly how is the steam from the boiler supposed to get down into the ship to perform useful work? Piping would be extremely complicated to get it through that pivot point.
Wouldn't it make a lot more sense the way I thought it was supposed to work (the way I drew it) with maneuverable mirror/lenses at both ends of the boom, both directing their concentrated sunlight at a fixed boiler that sits nice and sturdy and well-framed at the rear of the main deck, with piping going down to the ether propeller directly below, and elsewhere as needed for ship's systems?

EDIT: Either way, I see no physical obstacle to putting the boiler boom above the masts on the same pivot post. However, I admit that I do not completely understand Aramis's calculations regarding center of mass, etc, so perhaps the masts should be located at the opposite end of the central pivot post, below the gondola? I really don't see how they can pivot if located midway on the sides of the ship - giant hinges on each side???

EDIT 2: Or, if located midway up side of ship, do masts just permanently stick out to the sides, and Topmen just go out on them to raise or lower sails?



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