A study regarding the feasibility of airships using real-world physics within the scope of KSP.

[Fengist]

On 11/2/2018 at 8:10 AM, farmerben said:

Steam is an excellent lifting gas.  Steam has an advantage over helium in that a steam balloon can be operated at ambient pressure and small leaks will not ruin the lifting performance.  The difficult thing with steam is to keep the temperature high enough to prevent condensation.  I propose to do this using the greenhouse effect.  The surfaces of the balloons are variously transparent, reflective, or highly absorbant to focus solar energy on the inner balloonet.  The inner steam balloonet is insulated by surrounding hot air.  

Steam has been used for a long time to attempt to make lighter than air ships.  And while it's density is 0.6 which means it can produce lift, it's a far cry from hydrogen at 0.08.  The difficulty with steam isn't just the condensation (and the resulting weight and corrosion), in order to generate steam you not only need to lift water but you need to lift the fuel to boil it as well.  And neither of those are light.  You could probably rig up a recapture system similar to what I described was designed to capture water from engine exhaust but the problem still remains that you have about 1/8 the lift of hydrogen with the same weight.  I'm sure it could be done but you'd need some serious... serious volume and then, you'd be dealing with Newton's law of cooling which would be a nightmare to figure out.  As aviators have discovered, hot air works well but even it needs massive volume to lift even small mass.  Case in point is the Skyacht which has 205,000 cu/ft of envelope just to lift a small payload.  Most hot air ballons (from what I understand) keep the air at a temperature of around 200 C.  At 204 degrees, air's density is 0.7, which is close to that of steam at the same temperature without having to lift all that water.  Now, if you could superheat that steam and keep it that way, you may be onto something but that's gonna take a lot of energy from something.

GL with it.

 

 

[farmerben]

14 hours ago, Fengist said:

Steam has been used for a long time to attempt to make lighter than air ships.  And while it's density is 0.6 which means it can produce lift, it's a far cry from hydrogen at 0.08.  The difficulty with steam isn't just the condensation (and the resulting weight and corrosion), in order to generate steam you not only need to lift water but you need to lift the fuel to boil it as well.  And neither of those are light.  You could probably rig up a recapture system similar to what I described was designed to capture water from engine exhaust but the problem still remains that you have about 1/8 the lift of hydrogen with the same weight.  I'm sure it could be done but you'd need some serious... serious volume and then, you'd be dealing with Newton's law of cooling which would be a nightmare to figure out.  As aviators have discovered, hot air works well but even it needs massive volume to lift even small mass.  Case in point is the Skyacht which has 205,000 cu/ft of envelope just to lift a small payload.  Most hot air ballons (from what I understand) keep the air at a temperature of around 200 C.  At 204 degrees, air's density is 0.7, which is close to that of steam at the same temperature without having to lift all that water.  Now, if you could superheat that steam and keep it that way, you may be onto something but that's gonna take a lot of energy from something.

GL with it.

 

 

I think those numbers are incorrect.  Bouyancy is the mass of air displaced minus mass of balloon.  

So if outside air is 1.225 kg/m3

Steam at 100C is about 0.587 kg/m3, then it lifts 0.638 kg/m3

Steam at 200C is about 0.462 kg/m3, then it lifts 0.762 kg/m3

Hydrogen being about 0.08 kg/m3, lifts 1.145 kg/m3

Air at 100C is about 0.921 kg/m3, at 200C about 0.726 kg/m3, with lift of 0.3 kg/m3 and 0.5 kg/m3 respectively 

Roughly steam has 2x more lift than hot air (at 100C).  Hydrogen has 2x more lift than steam.  Hydrogen has 4x more lift than hot air. 

 

Hot air gets relatively better the more its super heated, so the solar greenhouse balloon is potentially a big improvement for the hot air.  Steam has really great performance as long as we prevent condensation on the inner surfaces of the balloon.  Catching condensation and reboiling it works to some degree, but it's better to prevent condensation altogether as far as possible.  I propose to do this by not letting steam contact the outer surface of the outer balloon, instead keeping it in a balloonet.  If I had a 3 layer balloon, I would vent exhaust gasses into the middle layer.

Hydrogen and Helium lift twice as much as steam.  Hydrogen is dangerous, helium is expensive, and they both escape through surface.  

 

Edited November 7, 2018 by farmerben

[Higgs Bonbon]

What a fantastic post. Personally my main interest is in creating permanent dirigible bases in atmospheres, like Jool and such, maneuverability isn't quite as much of an issue. Uhh, obviously that's a bit hard when the combination of mods I need isn't currently available, here's hoping we see some updates soon, especially for ProceduralAirships!

[AloE]

On 8/27/2018 at 6:16 PM, Fengist said:

If these experiments go well, KerBalloons may be using real-world physics in the future. You can find it here.

Indeed that would be so much better than balloons just going up then 'popping'...launching them via rover then drifting them via KerbalWind is quite fun.  Thank you for this very interesting discussion!

[panarchist]

@Fengist - are you continuing to work on this? I'm definitely very interested in seeing what you come up with if/when you choose to release it to the public. I mean, I love HL, but it'd be awesome to see a more realistic treatment of buoyancy and lift for LTA vehicles in KSP.