Sails?

[wrangler]

So how do sails propel these airships, since there's no "wind" within an air mass?

Perhaps it's revealed later?  I just started this book.

[Rygar]

There is another type of energy, etheric energy, that also flows about the world in currents.  The ship has sails, called a Web, that when powered catch this energy and propel the ship forward.  Some craft also utilize traditional wind sails as a backup propulsion method.

[wrangler]

I've now finished the book.  The canvas sails to catch "wind" don't make sense.

Apparently this is a fundamental misunderstanding of air movement on the author's part.  It's illustrated further by a character explaining that an airship felt a "crosswind" at one point.  While you would expect to feel any abrupt change in air direction or speed momentarily, you don't feel a steady "crosswind".

Once you've got something floating in the air, it moves with the air.  For example, stick your hand out of the basket under a balloon as you move across the ground, and you'll feel still air.  The concept of "wind" relates to a frame of reference anchored against the air movement, such as a ground-based observer, or a boat in the water.

[Quantus]

I've now finished the book.  The canvas sails to catch "wind" don't make sense.

Apparently this is a fundamental misunderstanding of air movement on the author's part.  It's illustrated further by a character explaining that an airship felt a "crosswind" at one point.  While you would expect to feel any abrupt change in air direction or speed momentarily, you don't feel a steady "crosswind".

Once you've got something floating in the air, it moves with the air.  For example, stick your hand out of the basket under a balloon as you move across the ground, and you'll feel still air.  The concept of "wind" relates to a frame of reference anchored against the air movement, such as a ground-based observer, or a boat in the water.

There are at least three different types of locomotion used by the airships.  Etheric Webs are the most common and are what are usually in use in the novels these are self-propelling and operate based on principle of Etheric energy which I havent completely worked out yet.  Wind sails are used as a backup system or when stealth is preferred, but have the noted difference of being less free in movement because you have to care about wind direction and speed, etc. where you do not with Etheric webs.  Steam turbines are also used as a backup to the primary etheric systems, but are big and dangerous and loud (I think they mentioned they are favored by larger ships for that reason) but can also be used for short-term boosts when used alongside the primary etheric system.

What do you mean when you say there is no wind within an airmass, in the context of the spires?

[wrangler]

For example:
When you're standing on the ground, and the air moves by at 10mph, that's a wind of 10mph.  When you launch in a balloon, that "wind" will take your balloon along at 10mph.  So the air's moving at 10mph across the ground, and so are you and your balloon.  There's no difference in the speed of your balloon and the air mass surrounding it.  You can stick out your hand and not feel a breeze.  You can hang out a sail, and it will hang limp.

[Quantus]

For example:
When you're standing on the ground, and the air moves by at 10mph, that's a wind of 10mph.  When you launch in a balloon, that "wind" will take your balloon along at 10mph.  So the air's moving at 10mph across the ground, and so are you and your balloon.  There's no difference in the speed of your balloon and the air mass surrounding it.  You can stick out your hand and not feel a breeze.  You can hang out a sail, and it will hang limp.

Ah, ok sure.  But that only applies when the air/wind is both the motive force and the supporting media, as in hot air ballon or similar, which is not the case on these types of ether-powered airships, or even traditional sailboats.

[knnn]

To expand on Quantus' response, this only happens when you are going at the exact velocity of the wind.  This is generally true of hot air balloons, because of the large surface size of the ballon compared to the basket and because the circular shape means it can only go in the direction of the wind.   

However, on a ship with multiple sails (like the Predator) this is definetly *not* going to be the case.  If the ship was only capable going in the direction of the wind, it would be impossible to manouver.  Instead, you "tack to the wind", angling the sails so you capture only the parts of the wind you want.  And any time you're not going exactly in the direction of the wind you will feel a breeze.

[wrangler]

Ah, ok sure.  But that only applies when the air/wind is both the motive force and the supporting media, as in hot air ballon or similar, which is not the case on these types of ether-powered airships, or even traditional sailboats.

The book mentions using wind instead of ether or engines.  Deploying a sail when under power would simply add drag and slow the airship; there's no "wind" to utilize for additional motive force.  The only perceptible air motion is equal and opposite to the direction of travel, and a sail would oppose that.  When you're free of the surface, you're moving along with the air.

Sailboats, as I pointed out, can use wind, since they are not free of the surface.  That doesn't apply to airships.

[Griffyn612]

The book mentions using wind instead of ether or engines.  Deploying a sail when under power would simply add drag and slow the airship; there's no "wind" to utilize for additional motive force.  The only perceptible air motion is equal and opposite to the direction of travel, and a sail would oppose that.  When you're free of the surface, you're moving along with the air.

Sailboats, as I pointed out, can use wind, since they are not free of the surface.  That doesn't apply to airships.

I think there were two types of sail.  One was the silk weaver material that caught ether wind (not air wind) and propelled it on those waves.  The other sails were wind sails, which were backup propulsion that they had no real control over.

[knnn]

The book mentions using wind instead of ether or engines.  Deploying a sail when under power would simply add drag and slow the airship;

In fact, while they get the sail ready, they only ever use the sails when not under power.

[wrangler]

To expand on Quantus' response, this only happens when you are going at the exact velocity of the wind.

As do all aircraft, unless another force is applied; surface area, etc., don't matter.  Once you leave the surface, and are in the air, you're moving with that air.  And when you add power (or force), the only air motion relative to the aircraft is due to the aircraft motion because of that power (or force).  A sail wouldn't help an airship under power any more that it would help an airplane.  You'll note that sails have never been used on dirigibles or blimps.  They won't work.

[knnn]

As do all aircraft, unless another force is applied; surface area, etc., don't matter.  Once you leave the surface, and are in the air, you're moving with that air.  And when you add power (or force), the only air motion relative to the aircraft is due to the aircraft motion because of that power (or force).  A sail wouldn't help an airship under power any more that it would help an airplane.  You'll note that sails have never been used on dirigibles or blimps.  They won't work.

And how do you explain the ability of powerless hand gliders to manouver? 

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.

[wrangler]

And how do you explain the ability of powerless hand gliders to manouver?

The force of gravity will pull a glider "downhill", resulting in airflow over the wing and tail.  Control surfaces on the wing and tail will change their airfoil shape slightly, changing lift and drag, causing changes in pitch, yaw, and roll.

I used the term "force" in my earlier post with gravity and gliders in mind.

[knnn]

The force of gravity will pull a glider "downhill", resulting in airflow over the wing and tail.  Control surfaces on the wing and tail will change their airfoil shape slightly, changing lift and drag, causing changes in pitch, yaw, and roll.

I used the term "force" in my earlier post with gravity and gliders in mind.

That's what I was suggesting above (notice my edits).  That the Predator create a slight negative/positive boyancy (with the crystals), allowing the sails to act as airfoils.

[wrangler]

That's what I was suggesting above (notice my edits).  That the Predator create a slight negative/positive boyancy (with the crystals), allowing the sails to act as airfoils.

As I pointed out, there's no "wind" for the sails.  Any research you do will usually refer to balloons as "moving with the wind", because it takes another force to move them.

Perhaps the FAA's Balloon Flying Handbook: https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/media/FAA-H-8083-11.pdf