Airship Altitude

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FrozenVomit
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Airship Altitude

Post by FrozenVomit » Wed Aug 21, 2019 1:50 pm

At what altitude airship are floating. Is it written somewhere? It must be cold up there!

Just a question for better roleplay...

Bonhumm
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Re: Airship Altitude

Post by Bonhumm » Wed Aug 21, 2019 2:35 pm

Good question.

I don't remember anything in the lore about the maximum height of an airship but I think I remember reading something where a Sky Raider was boasting that they could overfly any and all mountains in Barsaive.

Based on that, we could say that a drakkar can fly at least up to 5600m/18500ft which is the height of Mont Elbrus, the highest mountain in Russia that is located in the Caucassus/Dragon Mountains.

But I doubt they would navigate at such height for long; even for fully clothed trolls, the temperature would be very low and the amount of oxygen would be intolerable for people doing such exhausting work as Air Sailing.

Supplemental oxygen is required over 14 000ft.

ChrisDDickey
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Re: Airship Altitude

Post by ChrisDDickey » Wed Aug 21, 2019 5:36 pm

True Air harvesting is also done at very high altitude, in extreme cold.

Looking at the question from a modern general aviation standpoint, airplanes get better gas mileage the higher they fly, moderated by the fuel they spend getting that high. Thus, the farther you want to fly, the more worthwhile it is climbing to a higher altitude. That is why long distance commercial jets fly between 30K or 40K feet. The FAA requires you to stay above 800 feet (height above ground, not height above sea level) except when taking off or landing. If you are in a Cessna or similar small craft, if you are only going 45 minutes or so you would probably do it at about 2000 feet. If you are planning on using most of fuel, it is usually worth climbing up to 10,000 feet or higher.

As for Oxygen, the FAA is extremely conservative. It is not that a healthy person will pass out at 14,000 feet, it is that they start to become mentally impaired. Under 14K feet a healthy pilot will suffer only inconsequential effects. Most people can still perform moderately complex tasks up to 20,000 feet but decision making start to suffer, and there is increasing risk of complete incapacitation (unconsciousness) above 18,000 feet. Mountain climbers, having given themselves several days to Acclimate themselves (a luxury most aviators don't have) have found that above 26,000 feet is the death zone, where every hour that you spend above that level is an hour that your body is slowly dying. But like I said, you need to stay up high to keep your altitude acclimation. I would imagine that True Air harvesters have a base camp that is very high up so that they keep acclimated, and function as well as possible when harvesting.

Temperature decreases an average of 5.4 degrees F for every 1000 feet. So 2000 feet of cruising altitude will turn a hot day pleasantly cool, and 10,000 feet will turn a warm day cold, but possibly not below freezing.

The weather also makes a huge difference in your choice of flight level, When operating under Visual Flight Rules (or in an area where you are not 100% certain you know where all the mountains are) you want to stay out of clouds. Also, it is safer and makes manual navigation easier if you stay under an overcast. Also, the wind blows different directions at different altitudes, and you certainly want to pick an altitude where you have a tailwind instead of a headwind.

So the short answer is that it depends!
On a short flight, you tend to stay low. On a long flight, you tend to fly high and have warm coats for all the crew. When harvesting True Air, you tend to spend all your time very high, including having a base camp where you get acclimated to high altitude so that you and your crew can actually do you job when in the harvesting area. And you try to look for a wind that is at your back.
Last edited by ChrisDDickey on Thu Aug 22, 2019 2:33 pm, edited 2 times in total.

Bonhumm
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Re: Airship Altitude

Post by Bonhumm » Wed Aug 21, 2019 11:34 pm

The FAA assume you are in a closed (or even better; pressurized) hull with at least basic heating and sitting on your butt while holding a stick, which is quite different than rowing with the wind in your face so their numbers might not completely 'fit' with Air Sailing but its a good basis.

But beside taking into account the concept of minimum temperature and air pressure/oxygen % required to survive there is also the question of 'why' would they want to fly that high? Beside flying over an obstacle (i.e. mountains) the only reason an airship would want to fly high would be to reduce the likelihood of being noticed from someone on the ground and I think something as 'tiny' as a drakkar would required a VERY good Awareness test to be noticed above, say, 8000 feet; its not like it would make contrails.

The only other advantage of altitude (speed) is due to reduced drag from lack of air... which is by itself a problem that would completely outweigh the speed advantage.

So, unless the airship is trying to be inconspicuous or flying over a mountain range, I don't see why they'd go over a 1000 feet... or even 500.

Although, one way or another, the maximum 'survivable' height an airship could go would be FAR below the 100 km mark; lets not forget that at some point the airship would completely fail anyway; Shadowrun as established that Magic cannot exist in space (i.e. outside Gaiaspace) and probably gets less and less powerful as we go up (I would assume the 'intensity' of magic would be inversely proportional to the square of the distance from the ground).

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Mataxes
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Re: Airship Altitude

Post by Mataxes » Thu Aug 22, 2019 12:23 am

Fair warning: I have not really thought about this issue except in the most vague sense. I've certainly not sat down and tried to figure out appropriate altitudes based on air density/temperature/etc. So take this as a, "here's my initial gut feeling" without any kind of research to back it up.

(Though now that I have one, I can direct some research that way and see how it plays out.)

I would be likely to put the typical operating altitude of airships in Earthdawn somewhere in the range of World War I planes (traditionally open-cockpit biplanes -- Sopwith Camel, Fokker Dr1, that kind of thing) and early WWII planes (maybe not quite that advanced).

Indeed, the WW1 angle strikes me as a really good starting point. As pointed out, there's not much real need to be too high -- as long as you're clearing the bulk of any terrain obstacles (barring mountains), and out of the range of ground-based attacks (catapults, etc)... why would you need to climb to 10k feet unless you had to? Plus, the considerations of temperature and oxygen are kind of similar to those old biplanes... *shrug*

The other factor: Wind Catcher is (at least in part) intended to allow safe landing if crew fall overboard... it would make sense that standard "cruising altitude" would be at a place where that would be expected for most Air Sailors/Sky Raiders. Max height is Rank x 100 yards -- Rank 10 would be 1,000 yards or 3,000 feet above ground level.

Some interesting things to consider.
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FrozenVomit
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Re: Airship Altitude

Post by FrozenVomit » Thu Aug 22, 2019 1:34 am

I don't really need an answer... It's just to add some more realistic role-play.

Thanks for all the good answers; well explained. But when it change nothing to the game and it get to technical, around our table we just say..."it's magic, go on!" :D

Thanks!

ChrisDDickey
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Re: Airship Altitude

Post by ChrisDDickey » Thu Aug 22, 2019 4:16 pm

Some good stuff for a roleplay? Finding the right wind!
Bonhumm wrote:
Wed Aug 21, 2019 11:34 pm
So, unless the airship is trying to be inconspicuous or flying over a mountain range, I don't see why they'd go over a 1000 feet... or even 500.
I really would not discount the importance of finding a tailwind. It is absolutely vital.

Today's racing sail boats with fancy hulls and computer designed sails, etc. are amazingly fast. I read that the max speed achieved in the America's Cup is 47 knots. But lets forget these modern racers. A "typical" sailing schooner today might average 5 knots in most conditions, and top out at 10 knots at perfect conditions. The Cutty Sark was famous for being a fast sailing ship and topped out at 17.5 knots average for one 24 hour period. I see references to Viking ships averaging 4 knots over long distances, and galleys averaging 3 knots, with short sprints to 5 knots.

Looking at the 3rd edition gamemasters companion, most water vessels have speed ratings of close to 5 (Their water sailing speeds table is ridiculous and I am ignoring it). Most Air vessels have speed ratings of 10 to 12. So they tend to go at least twice as fast as sailing vessels. According to that book a speed rating of 10 is 16 mph (14 knots) and a speed rating of 12 is 20.9 mph (18 knots).

This is all MUCH slower than gasoline powered aircraft, Even the biplanes of WWI had max speeds of 100 knots or more. If you are zooming around at 100 knots, you can mostly ignore a 10 knot headwind or tailwind if you want. In the worst case scenario you are going to take an extra 10% more time getting to your destination. But if your max speed is 14 knots, then just a 10 knot wind is going to make a HUGE difference in how fast you are traveling.

OK, here is the thing. Once you get up above the trees and the buildings. There is usually a wind, even if it is not felt on the ground. These winds are at different strengths and at different directions at different altitudes. But it is not at all uncommon for the winds (just 100 feet off the ground) to be at least 5 or 10 knots. I mean sometimes there is no wind, but more than likely there will be.

but if you are in an airship going 14 knots. it is difficult to ignore a 10 knot wind. If it is a headwind, you are only making 4 knots over the ground! If it is a tailwind, you are making 24 knots over the ground. If it is to the side, you are actually traveling downwind of your target and you need to adjust course so that your true direction of actual travel over the ground is towards where you want to go.

And if your airship is going 14 knots through the air, and you are facing a 15 knot headwind, you are actually going backwards over the ground.

So I submit that the most important skill in piloting an airship, whether sail powered, oar powered, or powered by Blood Magic, if finding a good wind. Hopefully, somewhere up there is a wind that is going more or less in your direction. Or at least it is not going against you, and you need to find it.

It is probably usual for a captain and the ships elementalist to be up at dawn, the captain looking at clouds, the elementalist talking to air spirits. The ship might launch into a headwind that is pushing them backwards, but the crew works hard at gaining altitude until at 11,000 feet, they find the 40 knot wind that is going just 30 degrees off of their preferred course. Now that 40 knots is three times faster than they could go by themselves, so the crew need not work hard, just hard enough to offset that 30 degree difference between where the wind is blowing and the course they want. Then, after a lazy day of letting the wind take them in the direction they want to go, they use the last light of the sun to land the ship again. Perhaps the next day the captain and elementalist decide that today there is no tailwind to be had an any height/route they want, and they don't launch the ship because the wind would push them farther from their destination.

Winds aloft can be quite strong, and way up where the jets are, the jet stream's are often 170 knots or more. The typical wind aloft, even at treetop level will frequently be much faster than any airship can fly. So if the wind at your flight level is not going the desired direction, you are sailing backwards as measured over the ground. But often at a different altitude there is a different wind, that might be more to your liking.

Captains need to know the typical winds to expect along their route. There might be routes that can only be traveled certain times of the year, as during some months there may not typically be winds going in certain directions. Before the technology advanced to where ships could sail against the wind, there were some trade routes where everybody sailed in one direction for 5 months out of the year, then when the winds shifted, they turned around and sailed back in the other direction. A square rigged sailing ship can sail against the wind, but it is faster for a square rigged ship in the Caribbean to sail to Europe via Boston than to sail directly. It is twice the distance, but both legs are with the wind behind it, so it is faster and easier to sail trice as far than to try to beat against the prevailing winds. Airships add an exciting and challenging third dimension. A captain need not only concern himself with surface winds, but can make use of winds aloft as well.

There are good role-playing opportunities here, and the jargon when the captain explains why he has decided to remain at anchor today need not be complex. And hey, while we are waiting, you guys could explore! Honestly, it is not a complex topic at all, but it does complicate travel times. That 3rd edition book has a nice table that tells you how many miles an airship of a certain speed can travel in 8 hours. The fact that this table should probably be talking about airspeed, not speed over the ground, and that speed over the ground depends more on what the wind is doing than how fast a ship you has is a complication that many gm's might choose to ignore.

Or of course you can ignore the whole "headwind / tailwind" thing. A GM might want to simplify the topic out of existence and rule that the magic of airships is such that the wind does not push them around (except insofar as they have sails that are designed to use the wind), and their speed is always ground-speed, not airspeed. IE: a ship that travels 14 knots into a 20 knot wind will be traveling 14 knots over the ground, and the crew will feel a 34 knot wind, but the wind will not be pushing the ship backwards. A sailing ship makes use of the interaction between the movements of air and the water it sails in to move. It could be that an airship is somehow interacting with the ground or ocean that is far below it, and it's movement is thus always in relation to the ground, not the air it is in. This keeps things extra-simple, but in my opinion the whole headwind/tailwind thing adds an exciting dimension to traveling the skies. It allows the GM to add an easily understood aspect of skill and danger to air-sailing.
Last edited by ChrisDDickey on Sat Aug 24, 2019 5:23 pm, edited 1 time in total.

Slimcreeper
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Re: Airship Altitude

Post by Slimcreeper » Fri Aug 23, 2019 6:37 pm

That’s good food for thought. Fantasy travel seems weirdly modern in a lot of games.

Altanius
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Re: Airship Altitude

Post by Altanius » Fri Aug 23, 2019 6:57 pm

"Any sufficiently advanced magic is indistinguishable from technology."
—attributed to Larry Niven
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Michael
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Re: Airship Altitude

Post by Michael » Fri Aug 23, 2019 9:31 pm

I thought I read somewhere that the airships act like real ships and are easily turned over/sunk by bad weather and strong winds. That being said, the airships stay lower to the ground then up in the air, like 1k feet or so and never try to go over mountains, go around since it's safer.

So many versions and so many books, note even sure where I read it.

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