Other Jimness > Cinder Spires Books
Sails?
wrangler:
--- Quote from: knnn on October 23, 2015, 07:36:17 PM ---Edit: To explain, it's the constant slight downward movement of the glider that allows the airflow to create some of the lift, allowing you to manouver. A ship like the Predator could fluctuate between slight negative boyancy and slight positive boyancy (using the crystals) and use things like airfoils to change direction.
--- End quote ---
The flight of a glider is more than "slight downward movement". It's sufficient to generate enough airflow over the wing to cause enough lift for flight.
Using the crystals for vertical movement would move the airship up or down through the air mass. Sticking things out the side to create drag would certainly then be able to maneuver the airship using the airflow created during that vertical movement. It would also slow the airship somewhat with that drag. But if you've got working crystals, you can use them to maneuver without adding drag. But the sails are not adding propulsion.
Shecky:
Coupling vs. aerodynamics. Think of the main body of the ship: wood and such. Dense things that don't tend to be moved easily by wind and whose main contribution to the body's physics is largely in their inertia; i.e., the coupling coefficient is very low. Even with a lot of sails deployed and flying with the wind, the airship will never be able to move at the precise speed of the surrounding air mass. Ergo, there will be a significantly perceptible "wind." More so when balancing crystal-fed etheric force against the sails to be able to tack; there *will* be a crosswind in that case.
And don't forget that airflow is almost never a perfectly smooth laminar force; there will always be turbulence, interacting air currents and the like.
You did very well to point out that on-water sailing relies largely on the difference between the media, but it doesn't depend entirely on that particular difference. Greatly, yes (see the multiple mentions in the text about how most airship captains deplore using the wind and instead prefer to use etheric propulsion exclusively; if you stop to wonder why, you see why "greatly" ≠ "only"), but never entirely. And it's that gap that allows these airships to sail...and produces wind that the crew can feel.
TL;DR version: Throw a grocery bag in the air when there's significant wind. It moves with the air mass. Ergo, propulsion, and not quite at the speed of that air mass.
wrangler:
--- Quote from: Shecky on October 23, 2015, 10:17:39 PM ---Coupling vs. aerodynamics. Think of the main body of the ship: wood and such. Dense things that don't tend to be moved easily by wind and whose main contribution to the body's physics is largely in their inertia; i.e., the coupling coefficient is very low. Even with a lot of sails deployed and flying with the wind, the airship will never be able to move at the precise speed of the surrounding air mass. Ergo, there will be a significantly perceptible "wind." More so when balancing crystal-fed etheric force against the sails to be able to tack; there *will* be a crosswind in that case.
And don't forget that airflow is almost never a perfectly smooth laminar force; there will always be turbulence, interacting air currents and the like.
You did very well to point out that on-water sailing relies largely on the difference between the media, but it doesn't depend entirely on that particular difference. Greatly, yes (see the multiple mentions in the text about how most airship captains deplore using the wind and instead prefer to use etheric propulsion exclusively; if you stop to wonder why, you see why "greatly" ≠ "only"), but never entirely. And it's that gap that allows these airships to sail...and produces wind that the crew can feel.
TL;DR version: Throw a grocery bag in the air when there's significant wind. It moves with the air mass. Ergo, propulsion, and not quite at the speed of that air mass.
--- End quote ---
I can see density and inertia coming into play when we talk about the time it may take to accelerate to the speed of the air mass upon departure from the surface, but eventually an aircraft will reach that speed. Every airplane that flies utilizes that speed in calculating its flight path.
If you wish to postulate a mass so large that the airship will not reach the speed of the air mass during the time of its flight, then I'd expect that any sails would have negligible effect in imparting additional speed to that airship.
Mith:
Are the sails explicitly described as being deployed like traditional sails on a naval vessel? I know my mental image is of such (I am not a good study at aerodynamics, and Treasure Planet is one of my favourite movies, so I am not going to be so heavy a critique on functionality), but if they are not specifically described like that, then they could be basically canvas airfoils that work more in style of a hang glider.
wrangler:
--- Quote from: Mith on October 24, 2015, 04:45:57 AM ---Are the sails explicitly described as being deployed like traditional sails on a naval vessel? I know my mental image is of such (I am not a good study at aerodynamics, and Treasure Planet is one of my favourite movies, so I am not going to be so heavy a critique on functionality), but if they are not specifically described like that, then they could be basically canvas airfoils that work more in style of a hang glider.
--- End quote ---
They're described as canvas sails, to catch the "wind" and move the airship when other methods are not used.
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