Airship as a Stirling Engine

The concept is to use the entire airship as one big solar stirling engine. The design is based on a beta sterling engine that can be seen here. The entire envelope will act as the hot cylinder and will absorb heat from the sun. A smaller internal balloon will act as a displacement piston and will be forced up and down by rods through out the cycle. A smaller cylinder will rest at bottom of the envelope to take the power stroke of a traditional piston and will be the cold cylinder. Below the cold cylinder will be a compressed air tank that takes in air from the action of the power piston (I don't yet know the specifics of how this part will work). The air tank will power the prop and any auxiliary items. 

The reason I want to use the whole ship is simple. Stirling engines are not very powerful at low temperature differentials, so I want to drastically increase the displacement to get a reasonable amount of power.

Certainly an interesting concept, Dude. A model would really be cool to have, and watch work in the sunshine. I found a good Sterling Engine site, will try to list it here.

Maybe this?

Attachment: Airship_Stirling.flv (638.0KB)

Thats a tough file to play. I had to install a codec pack to play it.

Yah that is pretty much it. Not sure about the timing though. I think the displacer and the power piston are separated by 90 degrees. 

One of the benefits of such a system would be that excess heat would be converted into power. The envelope would maintain a fairly constant temperature without any active control. When the gas gets hotter, the Stirling engine runs faster and takes more heat out of the system. As long as you have adequate sunlight, the system would be fairly self-regulating.

You could also use the concept in a less ambitious embodiment. You could put a small sterling compressor in the envelope rather than making the envelope into a Stirling engine. The operation would be pretty much the same. 

You'll need cooling fins on the bottom to dump the excess heat.

Control surfaces as radiators?

Yah, that is a good idea. Multitasking...

The only problem I see is that the action of the diaphragm etc. could induce a vibration or even oscillation (it would bob up and down) that might be annoying or even damaging.

It depends on the period of the oscillation. I Think it would be such a high frequency that it would not be that noticeable. 

If you are using the entire envelope as a cylinder and light weight materials for the piston then your not going to be able to have a very high frequency.  I am picturing nothing more than a membrane dividing the upper and lower haves and forming the "piston" with flap valves and a "connecting rod" to a crank that turns at a leisurely few 10s of RPM that is geared up to some useful speed. 

I think about as energetic as a jellyfish which is all you can reasonably expect unless you try to do some fancy thermal transfer engineering to move around and concentrate heat better. That will add weight, complexity, and cost.

Wish I'd been able to make the conference call tonight. As you can tell I've been full of IT lately. lol.

Maybe the frequency will be low. Even if the displacement is huge, the power will be relatively weak, right? Power is all about rpm's, correct? This concept would have to turn out decent RPM to make a useful amount of power. 

Power is  torque. You can convert torque to rpms (angular velocity) and back again.  So if you have thousands of cubic ft. of gas pressure pushing a piston slowly, you  have a lot of force being applied to it which you can convert to useful work by gearing. So you have... lets say 2000 ft-lbs. at 100 rpm. That might be great for a boat propeller but not for an airship. You want to goto a more useful 1000 rpm  which still leaves you with 200 fl-lbs of torque to push air around with. 
The math is, (gear reduction ratio)/input torque = output torque, or (100/1000)/2000= 200

But isn't power torque X RPM? It is force times distance. I guess I need to talk to someone who knows about stirling engines. I have an email from a guy who put out some stirling engine software. I will see if I can find it. 

i found an interesting site, read it and see they have the same idea, but stationary.

http://www.stirlingengines.org.uk/sun/sola5.html

im thinking of trying this out, on a small scale. then seeing how it can be transfered into a blimpy thing

You won't be able to to have that elaborate a system within an airship envelope.   Probably just a high absorbent (black) surface and a direct embodiment of a Stirling motor.  Though I suppose you could have a variation of that spherical envelope with a rotating solar reflector in it, maybe with freznel lens that can focus sunlight on a "hotplate" for the hot side of the stirling... Would suck to have a misalignment and burn a hole in your ship though. lol!

@Dude:
"Horsepower" is T * RPM. But HP isn't really descriptive of the characteristics of that power.  The turbine engine in an M1 tank makes over 1300 HP at 5K RPM but its torque sucks (which is what a big heavy tank needs to move its bulk) until its reduced by the transmission down to a lot of low RPM torque to turn the tracks. 

Horsepower to torque and RPM is like Watts to Amps times voltage, knowing the amps by it self does not tell you how much power you have nor if you can use it, and the same for voltage without the knowledge of amps.   So it would be best to know all three terms for a given application to avoid needing gear reduction or  (what's the opposite of reduction?....induction? subduction abduction....)  Any time you have to use a transmission you are losing power to run that, like ten percent depending on the arrangement.  If your sterling engine spins at just a few RPM you may need gears and may I suggest sprockets and bicycle chains as I have heard that they are the most efficient, though a pulley and belts would be much quieter.   The operation of this engine off warm air energy implies that it will act as a means of cooling the internal air temp by association and conduction.   Since you are not going for speed, larger props at slower rpm will give you better thrust per hp ratios I believe.