Dragon Blimp

Derrick_rp · 11-10-2018, 08:18 PM

This is gonna be a weird question, but I figure that’s what these forums are for. Does anyone have any suggestions for how I would stat up a hot air balloon towed by a trained dragon as a vehicle? It’s about to come up in a game, and I’m at a loss.

johndallman · 11-10-2018, 08:31 PM

Let's try to clarify the concept a bit first.

Presumably the point of this contraption is to transport more stuff than could fit on the dragon's back? How much stuff? How many people, how much luggage or cargo?

What's going to be used to heat the air in the balloon? Is that the same for initial heating before take-off and for keeping it hot in flight?

Is the balloon purpose-made for this job, or has the setup been improvised?

Does the balloon have a skeleton or framework, allowing it to move faster through the air without pressure on the front caving it in? A normal hot-air balloon moves with the wind, and doesn't have significant pressure against the front.

How co-operative is the dragon?

Derrick_rp · 11-10-2018, 08:42 PM

The purpose of the contraption is to transport human beings, as well as a small amount of cargo, in relative comfort. I’m imagining it as something similar to “Le Geant” from the Steampunk vehicles book.

Natural gas will be used to heat the balloon.

The balloon was built for this purpose.

I hadn’t considered a skeletal framework, but that’s totally within the player’s means, so let’s say yes.

The dragon is willing and completely cooperative.

Varyon · 11-11-2018, 06:47 AM

Natural Gas (methane) is a poor choice for a portable heat source, as it's far harder to compress and liquefy than propane. This means your fuel reservoirs would have to take up a huge volume, increasing drag.

I suspect you'd be better off using coke (coal charred to remove impurities; it is to coal roughly what charcoal is to wood) as your heat source, if magic heating isn't an option. Rather than the weight of the balloon (negated thanks to the heating), what the dragon will be fighting against is the drag it produces, meaning the faster the dragon goes, the harder it will be to keep going. I previously worked out effective weight for towing things in water, but things are a bit different for a balloon, as we don't get things canceling out as nicely. I don't really have the time or inclination to work out the physics of it at the moment, however, but that thread may be a jumping-off point for you if you want to get into that.

johndallman · 11-11-2018, 06:50 AM

OK, those answers make it seem feasible so far. The next question is the flight capability of the dragon. A hot-air balloon big enough to lift several people is going to have a lot of drag when it is towed, so the dragon needs to be able to stay in the air when flying slowly.

I'm working off Dungeon Fantasy Monsters 4: Dragons, where most dragons have Flight (Winged), described on p. B56, but some get rid of the Winged limitation. Winged doesn't have penalties for flying slowly in Basic, but Powers p. 50 notes that larger creatures tend to have Cannot Hover, which requires a minimum of one-quarter speed. As GM, you need to decide on that.

A hot-air balloon is big: it needs 60 cubic feet of hot air per pound of lift. If your balloon is going to lift 1000lb, which seems plausible for several people plus a bit of cargo, it needs a volume of 60,000 cubic feet. That's a spherical balloon about 50 feet in diameter. But we also need to allow for the weight of the balloon itself, and the fuel and its burner, plus some kind of gondola, so the balloon is going to get bigger.

If this still makes sense to you, I'll try to figure out the next few steps.

The Colonel · 11-11-2018, 07:04 AM

Can the dragon maintain sufficient airspeed whilst towing a balloon?

Daigoro · 11-11-2018, 08:03 AM

A tow glider, if buildable, would be better, even if it's just a big kite.

Culture20 · 11-11-2018, 08:37 AM

Why not use baby dragons as the hot air balloon heat source? Or a second younger dragon that flies nearby and serves both as heat source and protection?

Refplace · 11-11-2018, 08:38 AM

Quote:

Originally Posted by Daigoro

A tow glider, if buildable, would be better, even if it's just a big kite.

Its a bit higher tech than a balloon I think but a glider with a top mounted tow bar or a strong rope could allow a dragon to get it up to speed and height. Then the dragon lets go and comes back as needed. Much less inconvenient for the dragon.

Phil Masters · 11-11-2018, 09:34 AM

A hot air balloon with the lifting capacity of Le Geant is going to be monstrously large, and then you need the burner... If the culture can refine natural gas, why the heck isn’t it using hydrogen, or at least coal gas, for lift?

(People today seem to have got the idea that hot air is the standard for manned balloons. Historically, that’s just nonsense. Modern recreational hot air balloons use TL7 technology, carry just a few people, and have limited endurance.)

11-10-2018, 08:18 PM	#1
Derrick_rp Join Date: Dec 2017	Dragon Blimp This is gonna be a weird question, but I figure that’s what these forums are for. Does anyone have any suggestions for how I would stat up a hot air balloon towed by a trained dragon as a vehicle? It’s about to come up in a game, and I’m at a loss.

11-10-2018, 08:31 PM	#2
johndallman Night Watchman Join Date: Oct 2010 Location: Cambridge, UK	Re: Dragon Blimp Let's try to clarify the concept a bit first. Presumably the point of this contraption is to transport more stuff than could fit on the dragon's back? How much stuff? How many people, how much luggage or cargo? What's going to be used to heat the air in the balloon? Is that the same for initial heating before take-off and for keeping it hot in flight? Is the balloon purpose-made for this job, or has the setup been improvised? Does the balloon have a skeleton or framework, allowing it to move faster through the air without pressure on the front caving it in? A normal hot-air balloon moves with the wind, and doesn't have significant pressure against the front. How co-operative is the dragon? __________________ The Path of Cunning. Indexes: DFRPG Characters, Advantage of the Week, Disadvantage of the Week, Skill of the Week, Techniques.

11-10-2018, 08:42 PM	#3
Derrick_rp Join Date: Dec 2017	Re: Dragon Blimp The purpose of the contraption is to transport human beings, as well as a small amount of cargo, in relative comfort. I’m imagining it as something similar to “Le Geant” from the Steampunk vehicles book. Natural gas will be used to heat the balloon. The balloon was built for this purpose. I hadn’t considered a skeletal framework, but that’s totally within the player’s means, so let’s say yes. The dragon is willing and completely cooperative.

11-11-2018, 06:47 AM	#4
Varyon Join Date: Jun 2013	Re: Dragon Blimp Natural Gas (methane) is a poor choice for a portable heat source, as it's far harder to compress and liquefy than propane. This means your fuel reservoirs would have to take up a huge volume, increasing drag. I suspect you'd be better off using coke (coal charred to remove impurities; it is to coal roughly what charcoal is to wood) as your heat source, if magic heating isn't an option. Rather than the weight of the balloon (negated thanks to the heating), what the dragon will be fighting against is the drag it produces, meaning the faster the dragon goes, the harder it will be to keep going. I previously worked out effective weight for towing things in water, but things are a bit different for a balloon, as we don't get things canceling out as nicely. I don't really have the time or inclination to work out the physics of it at the moment, however, but that thread may be a jumping-off point for you if you want to get into that. __________________ GURPS Overhaul

11-11-2018, 06:50 AM	#5
johndallman Night Watchman Join Date: Oct 2010 Location: Cambridge, UK	Re: Dragon Blimp OK, those answers make it seem feasible so far. The next question is the flight capability of the dragon. A hot-air balloon big enough to lift several people is going to have a lot of drag when it is towed, so the dragon needs to be able to stay in the air when flying slowly. I'm working off *Dungeon Fantasy Monsters 4: Dragons, where most dragons have Flight (Winged), described on p. B56, but some get rid of the Winged limitation. Winged doesn't have penalties for flying slowly in Basic, but Powers* p. 50 notes that larger creatures tend to have Cannot Hover, which requires a minimum of one-quarter speed. As GM, you need to decide on that. A hot-air balloon is big: it needs 60 cubic feet of hot air per pound of lift. If your balloon is going to lift 1000lb, which seems plausible for several people plus a bit of cargo, it needs a volume of 60,000 cubic feet. That's a spherical balloon about 50 feet in diameter. But we also need to allow for the weight of the balloon itself, and the fuel and its burner, plus some kind of gondola, so the balloon is going to get bigger. If this still makes sense to you, I'll try to figure out the next few steps. __________________ The Path of Cunning. Indexes: DFRPG Characters, Advantage of the Week, Disadvantage of the Week, Skill of the Week, Techniques.

11-11-2018, 07:04 AM	#6
The Colonel Join Date: Jul 2006	Re: Dragon Blimp Can the dragon maintain sufficient airspeed whilst towing a balloon?

11-11-2018, 08:03 AM	#7
Daigoro Join Date: Dec 2006 Location: Meifumado	Re: Dragon Blimp A tow glider, if buildable, would be better, even if it's just a big kite. __________________ Collaborative Settings: Cyberpunk: Duopoly Nation Space Opera: Behind the King's Eclipse And heaps of forum collabs, 30+ and counting!

11-11-2018, 08:37 AM	#8
Culture20 Join Date: Feb 2014	Re: Dragon Blimp Why not use baby dragons as the hot air balloon heat source? Or a second younger dragon that flies nearby and serves both as heat source and protection?

11-11-2018, 09:34 AM	#10
Phil Masters Join Date: Aug 2004 Location: U.K.	Re: Dragon Blimp A hot air balloon with the lifting capacity of Le Geant is going to be monstrously large, and then you need the burner... If the culture can refine natural gas, why the heck isn’t it using hydrogen, or at least coal gas, for lift? (People today seem to have got the idea that hot air is the standard for manned balloons. Historically, that’s just nonsense. Modern recreational hot air balloons use TL7 technology, carry just a few people, and have limited endurance.) __________________ -- Phil Masters My Home Page. My Self-Publications: On Warehouse 23 and On DriveThruRPG.