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  #51  
Old March 15th, 2014, 02:12 AM
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Originally Posted by atpollard View Post
Because I live to think outside of the box:

Rotate the internal bracing frame to form a Star of David inside the envelope.
Brace the boiler/mirror stuff off the top of the point heading straight up.

Extend each of the diagonal braces beyond the envelope to form four fixed angled masts that are long enough to be even with the bottom of the gondola (and the same length heading up diagonally).
Mount yardarms and five square-rigged sails on each mast ... just like a Clipper Ship.
Place masts at two locations along the length of the airship ... probably where it transitions from a cylinder to the rounded ends.
Now you have lots of fixed masts that do not interfere with landing, and lots of yardarms and sails that can be adjusted to balance winds from an angle or be furled and retracted up/down the mast and stored safe against the hull.
The boiler/mirror have lots of room along the top of the ship for whatever you need them to do.

Obviously, this is not my ship, so do whatever makes y'all happy.
I just enjoyed trying to come up with another solution.
I would quibble only that additional bracing would be needed for the top deck - not very sturdy balanced on one beam down the middle - although with masts out the side-angles as described there is less need of a top deck, perhaps only a small area for standing to make observations.

Also - totally minor quibble - the airship is only rounded at the front, not the back.

Otherwise, I am interested in hearing what Aramis and/or McPerth have to say about this arrangement of sails, as it sounds quite feasible to me, enough that I want to hold off on deck arrangements until it is decided.


EDIT: Also, it seems to me that this arrangement might interfere less with field-of-fire of the guns (although it still might be a good idea to take down the sails and just use props in a battle).

EDIT 2: Reconsidered based on following post.



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Last edited by SpaceBadger; March 15th, 2014 at 02:40 AM..
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  #52  
Old March 15th, 2014, 02:20 AM
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... except that now I compare it back to my original sketch with the hexagon framework, I see that the Star of David (if used in same circumference) gives much less in the way of horizontal bracing useful for decks and turrets, with only two horizontal braces and the necessity of extra bracing to attach top deck and gondola to the pointy bits at top and bottom.
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  #53  
Old March 15th, 2014, 02:33 AM
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If I were the Pilot, I would also prefer two control rooms - one right in the nose of the airship on the middle deck level for space and most atmospheric flying (best all round forward point of view) and one down in the gondola strictly for landing. Unfortunately, the rules only seem to allow for one, and even if Aramis allowed two, that would cut further into our cargo space.

I've compensated for this by providing a periscope with a fisheye lens on the outer end, extending from the gondola control room up to the midpoint of the frontal hemisphere.


EDIT: Also, just noticed that McPerth suggested conservatory in the nose; add a simple speaking tube down to the control room, and a lookout in the conservatory can also advise the pilot of things that might be hidden from the gondola control room.


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  #54  
Old March 15th, 2014, 03:46 AM
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Quote:
Originally Posted by SpaceBadger View Post
I guess I need to know two things before I go further on deckplans:

1) where do the masts/sails go? (see above #45)

2) What's the configuration of the solar boiler mirrors/lenses? (see above #42)


EDIT: If you are leaving it to me to decide the above when drawing the plans, I'm going with original configuration in sketches. I understand that might not be best configuration for sails according to balance of mass and best catch of the wind, but it looks coolest to my eye, and I don't see anything in the rules about placement of sails affecting balance or speed. (Second choice would be to put it down below the gondola, and raise the gondola up on longer (but still pretty short) legs for landing; but that would look kinda weird.) Plus I would go with having the two mirror/lenses out on the moveable boom, with the fixed boiler as drawn, for reasons stated above.



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Top mounted sails would have foundered the vessel in wind already. They're impractical to the point of taking them off with an axe rather than suffer their ill effects. (Their center of mass is the problem.) They'd make using them in anything other than downwind travel extremely hard, because the force would be multiplied.

Simply put, the math rules them out. Longwinded explanation inside the spoiler.
Spoiler:

The way you've drawn them, she'd roll over the first time she caught a sideways gust while furled, and would have the sails blocked 90% by the body when unfurled (and still centered above center of lift, but not sufficiently so as to trigger tipover). Keeping in mind - moment is force times distance from center of mass or center of lift. Center of lift in a stable air vehicle MUST be above center of mass. When it isn't, additional forces must be used to keep the center of mass directly above the center of lift. (I hated doing W&B problems in flight training.) The center of mass ALWAYS tries to remain under the center of lift.


The solar boiler has similar W&B issues. You get maximum focus by concentration on a uniform convex mirror - there was an article on why the eyepiece mirror is best centered in an old issue of Odyssey Magazine (circa 1980). So that means a central boiler heat point is on a single direction arm. Since you're still under lift when you first power the solar, you throw mass off to the side, and you tilt, and lose light. So... you have to have a counterweight - and that can't be another mirror, because it would result in offset focusing. So, may as well run the tubes a little further (convective losses are not that much an issue in the near vacuum), and use them as a counterweight to the mirror.

Midline or gondola are both viable options, with different issues.

Gondola has the issue of not being able to rig for a minimum opening.
Midline, you can rig so that the absolute minimum opening is the height of mounting to bottom of gondola. (Additional rotating spars as masts could allow for that, at additional complexity.)

Midline has the issue of half the sails being out of direct use when not flying downwind.... but those could be handled by dropping them lower still if sufficient rope is available.

Oh, and note that more than one Tall Ship has foundered from surprisingly low winds when a gust caught the side just wrong... the force moment on an empty ship can make tacking turns truly dangerous. Gunny used to love to tell us of the horrors of sailing ships. (But he never served on one. He was in VMF 214 as a mechanic... Introduced me to LtCol Greg "Pappy" Boyington.) A buddy who just came off a tall ship as crew noted how tacking could tilt the deck badly, too.)


So GM Ruling:
  • The sails can't be top mounted, because the current story so far rules it out.
  • The Boiler should be similar to the ones in the book for practical reasons.
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  #55  
Old March 15th, 2014, 04:47 AM
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Quote:
Originally Posted by aramis View Post
So GM Ruling:
  • The sails can't be top mounted, because the current story so far rules it out.
  • The Boiler should be similar to the ones in the book for practical reasons.
So where do the sails go?

I'm already swallowing my disbelief that waving the boiler tank around on the end of a boom is more stable than keeping the tank in one place and moving mirrors to focus on it (which would also gather twice as much sunshine, improving efficiency). So just tell me where the sails go, and that is where I will put them.
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  #56  
Old March 15th, 2014, 06:09 AM
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This post was made before reading what you posted tonight in this thread:

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Originally Posted by McPerth View Post
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 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...
Either retractable or foldable, what is important is that the masts don't interfere in the solar boiler, and so they need to be folded/retracted when in space.

My idea was to make the atmospheric reentry under steam power (see Canal Priests of Mars, page 32 for details), only deploying the masts when already stabilized in atmosphere.

After thinking about it, I guess two masts would be the better, anchored all across the ship (vertically) down to the gondola, having the spiral stairs rounding them through the structure.

I don't like the sails hanging on the sides, as they would interfere quite a lot with the firing arks of the guns. My guess is that having two masts instead of one, the sails on each of them could be smaller. In any case, if having them hung at the sides is the best solution, they should not be lower tan the structure, leaving the sides of the gondola free.

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Originally Posted by SpaceBadger View Post
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.
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As for sails on the top - impractical. The sail mass is considerable - fully 10%, and the boiler another 6%

(...)

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.
See that in this sense, its equilibrium would be higher tan the Skylord kite as depicted in Cloudships & Gunboats page 19, just to give you an example...

Having the guns on the gondola's sides (instead of the structure) would lower their 33 tons, lowering the centre of gravity (and so making the whole ship more stable), while giving them clearer arks of fire regardless the sails.

I'm not too concerned about having the high fire angle somewhat restricted, as:
  1. Having a very high ceiling (being even capable to leave atmosphere), few ships can fly higher than it
  2. As the guns are not high angle firing, they are already more restricted that what the structure may (IIRC a gun cannot fire at more elevation changes than hexes away is the target, but I don't remember where I did read that)
So:

Quote:
Originally Posted by SpaceBadger View Post
Quote:
Originally Posted by aramis View Post
So GM Ruling:
  • The sails can't be top mounted, because the current story so far rules it out.
  • The Boiler should be similar to the ones in the book for practical reasons.
So where do the sails go?

I'm already swallowing my disbelief that waving the boiler tank around on the end of a boom is more stable than keeping the tank in one place and moving mirrors to focus on it (which would also gather twice as much sunshine, improving efficiency). So just tell me where the sails go, and that is where I will put them.
Having them hanging at the ship's sides would have half of them (one side) not useful with lateral wind, and they would be protected from the wind by the gas structure...

So, I'd suggest the two masts I talk above on the top (if aceptable by Aramis rules) and a smaller mast (also foldabel, to allow landings) under the ship, both to enlarge sailing surface and for equilibrium pourposes (yes, I know this is against what I've been saying to now).
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  #57  
Old March 15th, 2014, 06:32 AM
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Quote:
Originally Posted by SpaceBadger View Post
So where do the sails go?

I'm already swallowing my disbelief that waving the boiler tank around on the end of a boom is more stable than keeping the tank in one place and moving mirrors to focus on it (which would also gather twice as much sunshine, improving efficiency). So just tell me where the sails go, and that is where I will put them.
No, they wouldn't gather "twice as much" - unless the beam isn't straight, at which point, it's again throwing mass around asymmetrically above the center of lift, and then taking the aim off. Assymetric offset mirrors are possible, but they're hard to design and grind, and would still need a v-shaped boom.

Further, it's not a "Tank" on the end - it's a chamber, hose-pipe fed. Don't think of it like your household boiler - think of it instead as an instant hot water tap. The focused light heats a heat sink that, when a jet of water hits it, flashes that water to steam. The expanding steam goes through a first stage turbine that pressurizes the outbound water. The actual motive power then is derived elsewhere (probably just below the strongback). I expect the "cooling system" to be run along the envelope. Once started, that boiler's going to stay at maximum operating pressure for the current light by self regulation... the steam it's generating is driving how much water it's forcing through the nozzle into the steam chamber - the efficiency score is how much energy is lost to pumping the water, not how much light is getting there.
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Duke of the Third Imperium (SPIN 0534)
Count Terra (SOLO 1827)
Count Gorod (REFT 1302)
Count of the Third Imperium (SPIN 2232)
Viscount of Adabicci (SPIN 1824)
Marquis of the Solomani Rim (SOLO 0606)
Marquis of the Third Imperium (SPIN 2410)
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