Isn't water just "thick' air? (NA)

[Dart]

Winged luxury submarines 'fly' underwater


http://www.cnn.com/2009/TECH/03/06/eod.luxury.submarines/index.html


I've seen this before but it now seems to be in actual commercial production. I think having one would be cool. I think the school concept is pretty smart from a liability and delay of regulation view. How long before you need a submariner's "certificate" to fly one?

 

[tonycondon]

yea that looked pretty cool to me too. I think they said there was an open cockpit version?

and a fluid is a fluid.

 

[fgcason]

Interesting. I remember seeing early drawings for Deep Flight 1, or the equivalent, in the mid 1980's. It looks like he kept working on the concept and got it working. One of the big points that it had over typical submarines is that in the event of a propulsion system failure, instead of sinking to the bottom like a rock, it floats to the surface where survivability is a bit better.

 

[steingar]

Yeah, they've been working on these for a long time. There were a couple running around in the 80's where you had to wear scuba gear, but they worked well. I hope these guys do better than Moller.

 

[wanttaja]

yea that looked pretty cool to me too. I think they said there was an open cockpit version?

Been there, done that.

http://www.wanttaja.com/avlinks/sub.htm

and a fluid is a fluid.

Makes a bit of difference if the fluid is incompressible, and whether you're getting your "lift" from Bernoulli. Pull back on the stick of an airplane, and you just go up until you run out of speed. Pull back on the stick of your minisub, and when you go up the water pressure decreases. The air in your ballast tanks expand, forcing water out and making the sub lighter. The lighter sub thus wants to continue rising, which makes the ballast tank air expand even more, etc, etc....

Ron Wanttaja

 

[Dart]

Been there, done that.

http://www.wanttaja.com/avlinks/sub.htm


Makes a bit of difference if the fluid is incompressible, and whether you're getting your "lift" from Bernoulli. Pull back on the stick of an airplane, and you just go up until you run out of speed. Pull back on the stick of your minisub, and when you go up the water pressure decreases. The air in your ballast tanks expand, forcing water out and making the sub lighter. The lighter sub thus wants to continue rising, which makes the ballast tank air expand even more, etc, etc....

Ron Wanttaja

Cool story.

I guess "flying subs" make Newton blow the "Bernoulli vs Newton" argument outta the water.

 

[Capt. Geoffrey Thorpe]

I guess "flying subs" make Newton blow the "Bernoulli vs Newton" argument outta the water.

The laws of physics blow the idea that there is a "vs." argument out of the water.

 

[Greebo]

Are there compressible fluids? Or would that be the definition of a gas?

 

[Capt. Geoffrey Thorpe]

Are there compressible fluids? Or would that be the definition of a gas?

All real fluids (including water and air) are "compressible", but for lower speed (not approaching the speed of sound) applications air can often be considered to be "incompressible".

http://en.wikipedia.org/wiki/Compressibility

Compressibility is an important factor in aerodynamics. At low speeds, the compressibility of air is not significant in relation to aircraft design, but as the airflow nears and exceeds the speed of sound, a host of new aerodynamic effects become important in the design of aircraft.

 

[Clark1961]

Are there compressible fluids? Or would that be the definition of a gas?

Gas is a fluid, liquid is a fluid, a situation can be fluid but it is not a fluid

DakotaDriver is an engineer IRL (if'n ya hadn't guessed it already)

 

[Dart]

All real fluids (including water and air) are "compressible", but for lower speed (not approaching the speed of sound) applications air can often be considered to be "incompressible".

http://en.wikipedia.org/wiki/Compressibility

At low speeds and liquid temperatures, water is essentially incompressible. But, that does not mean pressures are not transmitted through the medium. Hence, vessel hulls and keels can be designed to take advantage of "lift" much like a wing is.

Reduce pressure enough and you'll achieve cavitation, the "boiling" of dissolved air as a result of lowered pressure, even though the expansion of the water volume itself is negligible. Cavitation is a real-life problem for screw (aka propeller) design.

 

[Clark1961]

Reduce pressure enough and you'll achieve cavitation, the "boiling" of dissolved air as a result of lowered pressure, even though the expansion of the water volume itself is negligible. Cavitation is a real-life problem for screw (aka propeller) design.

From the mostly useless trivia department: Cavitation is when the local pressure is less than the vapor pressure of the fluid. Thus the gas bubbles are just the vapor phase of the fluid. Dissolved air is not generally involved in cavitation prediction.

Of course from a functional point of view it doesn't really matter of what the bubbles are composed. From a design point of view the material does matter since one has to know the pressure ranges to avoid.

I used to have to consider this stuff when specifying pumps...great fun hunh?

 

[Dart]

From the mostly useless trivia department: Cavitation is when the local pressure is less than the vapor pressure of the fluid. Thus the gas bubbles are just the vapor phase of the fluid. Dissolved air is not generally involved in cavitation prediction.

Correct. My bad

I used to have to consider this stuff when specifying pumps...great fun hunh?

And I often work with dissolved gas measurement. Hence, my brain following a familiar (but incorrect) path. :smile: