Submersible Aircraft Design

I was thinking that it might actually make more sense for the Russians to develop something like this than for Americans to.

If someone sees some other mission for these things than the one I thought of (hide a bomber underwater so that if it is ordered to attack the enemy will not know just what direction it will come from, when it might arrive, and get little or no early warning until it is approaching national territory) please say what! I'd like to broaden my thinking about it.

The technical challenge is daunting, but exactly how daunting it is depends on how demanding the mission parameters are, and therefore on the mission.

I'd think that for the purpose I've thought of, it would not need to dive very deep--just deep enough to hide from surface detection. Wouldn't 100 meters down be more than enough? (That's still 10 atmospheres overpressure though!) And it would not be necessary (nor possible really!:p) to move very fast while submerged; just creeping along. So that would make the challenges of providing a power source and keeping the thing silent that much less difficult.

A big stumbling block I see is the basic matter of buoyancy. Generally speaking human beings tend to make vehicles that, if sealed against leaks, would float, and float high in the water too. Of course we do that deliberately for boats and ships, but just about any vehicle you care to name would float if water didn't pour into it. We need a certain amount of elbow room for one thing, for another a lot of our cargo and even equipment tends to be less dense than water itself.

So designing a submarine so it is heavy enough to be on the verge of sinking, so that a bit of flooding the ballast tanks would tip the balance and it dives, is a bit tricky, whereas airplanes are generally designed to be as light as possible. Making an airplane that will sink, even if all the void space within is flooded with water, is tricky, and you can't flood all of it to submerge--you have to leave air in the engine interiors for instance, not to mention access paths for human mechanics and so on.

The power source while submerged, even for a creeping motion (as much for stealth as for frugality) is another hurdle. It has to be air-independent, since relying on a snorkel would tend to defeat the purpose of diving in the first place.

The idea of some kind of metal such as sodium, or some other substance that reacts violently with water, as "fuel" is interesting, but I challenge anyone who seriously proposes it to show that someone has at least tried to develop it in the past; I'd think someone as fanatical and driven on the subject of air-independent submarine propulsion as Germany's Walter (he of the hydrogen-peroxide engines:eek:) would have considered it as an alternative to peroxide-hydrocarbon engines if it were at all competitive with them.

It's not enough to get heat from something reacting with water; you have to harness the power somehow. It occurs to me that any heat source can drive a steam engine or a Stirling-type (which has the advantage of being inherently quiet) so some type of external-"combustion" may work out.

But aside from nuclear power, the only air-independent systems I've ever heard of being tried out involve either peroxide (as an oxygen source) or compressed or liquid air or oxygen for that purpose, and engines--internal or external combustion. Or batteries of course, or fuel cells. Or compressed air not as an oxygen source but for power storage. Another notion tried has been to use the latent heat of steam to drive a steam engine some time after diving with residual heat left over in the boiler water and vapor.

Nowhere in this laundry list that includes some rather outre options is there a sodium-fueled engine! Not one I've heard of anyway.

As for nuclear power--well we wouldn't need a whole lot for a slow creep. But as I understand it, it's difficult to scale a proper fission reactor down below a certain size. There is the alternative of isotope decay as a heat source, which could provide a very modest but steady power flow (you can't turn it off; power you don't usefully use must simply be wasted:().

Again it depends critically on just who does this, when, and why.

I'd think that bombers submerged off an enemy's coastline for stealth would be an option the Soviets would have needed and benefited from much more than the Western Allies, due to the fact that the nations of the west have extensive warm (more or less, not icebound is the point) water shores and indeed their populations and industries are oriented largely to these littorals, whereas the USSR has extensive coastlines only on the Arctic Ocean and to a lesser geographic extent on the northwest Pacific. But although what lies within say a few degrees of the Maritime Far East coast is a better target than what lies the same distance inland from the Arctic coast, and of course much more accessible due to there being no to limited ice year-round offshore, still even places like Vladivostock or Madigan are hardly prime targets. To approach Moscow, or even Leningrad or Kiev, one has to either break through Arctic ocean ice cap or sneak up narrow passages; even with Turkey granting Americans free passage of the Straits and cover in territorial Turkish waters, presumably the Soviets had the northern part of the Black Sea well patrolled!

On the other hand, Russians could hope to station their planes anywhere along the US/Canadian Atlantic and Pacific coasts, or of course off Europe.

So, operational plane is Soviet design, I'm thinking.

Assuming that is that anyone anywhere can justify such an oddly hare-brained looking scheme in the face of the alternative of developing submarine-launched missiles--cruise missiles or ballistic--instead.
 
As for nuclear power--well we wouldn't need a whole lot for a slow creep. But as I understand it, it's difficult to scale a proper fission reactor down below a certain size.

The problem isn't the reactor, it's the shielding. The US had a huge aircraft nuclear propulsion project around this time, although they never ended up flying anything. The smallest atomic-powered manned plane that was seriously studied that I've found mention of was the X-6, which was a B-36 with atomic turbojets, and there are some serious questions as to whether it could have flown at all without chemical assistance. Most designs started at half a million pound weight and went up from there.

There is the alternative of isotope decay as a heat source, which could provide a very modest but steady power flow (you can't turn it off; power you don't usefully use must simply be wasted:().

The US aircraft nuclear propulsion program studied this too, although nowhere near as in-depth. I have a report from the Lexington Project, a study group that worked in 1948, on the use of radio-polonium as a power source. Radiopolonium emits almost solely alpha particles, which require very little shielding mass, so the plane wouldn't have the titanic shielding that doomed the atomic-powered airplane.

However, the report estimates that, for every B-29-sized airplane, you'd need a 5 GW atomic pile used as a dedicated neutron source for transmutation to keep it powered. You'd also need a chemical processing facility to separate the radioactive polonium from the untransmuted bismuth. So it would be very expensive, probably too expensive to be worth building. But if you did build it would probably work pretty well as a propulsion system.
 

Cook

Banned
I'd think that for the purpose I've thought of, it would not need to dive very deep--just deep enough to hide from surface detection. Wouldn't 100 meters down be more than enough?

100 metres is a hell of a lot of depth, most British submarines of World War Two could only just make it that deep. Imagine an aircraft frame as thick as a submarine?

As to hiding in depths that could conceivably be reached by something that could actually get airborne, I suggest you get in a light aircraft and go flying over the coast sometime, everything on the sea bottom is easily visible in good weather. I’ve seen the Catalina Flying-boats that were dumped in the ocean south of Rottnest Island at the end of the Second World War while flying and they are too deep for recreational scuba divers!
 

As to hiding in depths that could conceivably be reached by something that could actually get airborne, I suggest you get in a light aircraft and go flying over the coast sometime, everything on the sea bottom is easily visible in good weather. I’ve seen the Catalina Flying-boats that were dumped in the ocean south of Rottnest Island at the end of the Second World War while flying and they are too deep for recreational scuba divers!

That very much depends on which coast your flying over. In a lot of coastal areas you would have a job seeing something at a depth of 10 meters never mind a 100 meters. Along the coast of the North Sea for example there are a lot of silt bearing rivers flowing into the sea and the water is often like soup.
 

Cook

Banned
Along the coast of the North Sea for example there are a lot of silt bearing rivers flowing into the sea and the water is often like soup.

Great, so in addition to immersion, and salt corrosion you now have all the problems associated with silt in working parts.

Believe me there are easier ways of hiding an aircraft.
 

archaeogeek

Banned
If it's only for very short term submersion (say, launch, then land), I could see it as having potential for a Ohio-to-above sized submersible carrier (the Typhoon had a cargo version), but require ridiculously elaborate safety and use of ballasts for launch and recovery at skimming depths.

That said, none of these designs look seaworthy :p
 
The problem isn't the reactor, it's the shielding. The US had a huge aircraft nuclear propulsion project around this time, although they never ended up flying anything. ....

Understand, I'm not talking about fission or radioisotope power for flight; I'm talking about a power source for motion while submerged--and while we are at it, we need power for the "hotel" load and basic operations while below as well; compared to the power needed for a 5 knot creep this is probably the major power draw. Something like 1 percent of the sort of power output needed to propel the airplane while airborne!

If one did have a fission or radioisotope source that could keep a plane airborne, then it would probably last something like a year at full power. The thing to do then is simply keep the plane flying and rely on its mobility for defense. The whole question of submerging to loiter would not come up at all.

I've seen a RAND Corporation study of big airplanes (to nominally replace the C-5, so the target payloads were something like if a C-5 were scaled up to mass 1000 tons) that considered various possible alternative fuels--liquid hydrogen, liquid methane, even ammonia--and compared the planes needed to match a baseline plane based on conventional jet fuel (which, for purposes of economic comparison of the costs of the other fuels, was assumed to be synthetic--this study was from the late 1970s or early '80s and was considering the future in the light of exhaustion or strategic denial of petroleum). And included in the mix was a possible nuclear fission option--the power source would be a sealed liquid-metal cooled reactor unit, one that would feed a secondary loop of molten sodium-potassium mix (pumped electromagnetically) to a heat exchanger that would be basically equivalent to the combustion chamber of a conventional turbofan. (Unlike the conventional locations of the turbofans in pods below the wings on the other versions, the fission-heated jets were located in a cluster right above the power plant which was installed at the wing/fuselage junction for reasons of mass balance, thus dividing the volume of the fuselage in two, forward and aft of the nuclear installation). As a concession to safety, the plane would have to take off and land with the fission core shut down, burning conventional (synthesized) jet fuel in the engines instead to serve as conventional jet engines. Upon reaching cruise speed and altitude, at a good safe distance from the probably inhabited airport region (and avoiding other populated areas, ideally flying mainly over the ocean) the nuke plant is activated and the plane switches over to nuclear operations. Before landing, the plant is shut down and the engines are again switched over to jet fuel. Also there was a reserve in case the nuclear plant had to be shut down for some other reason while airborne.

This mode of operations did tend to rob the nuclear plane of much of its advantage as the jet fuel needed for these auxiliary but vital operations was substantial; the silver lining was that the fuel reserves could serve as shielding! The nuclear version was the heaviest alternative by far; the lightest though bulkiest was the hydrogen-fueled one.

Anyway had it been possible to actually make such a plane, the study pointed out the radical options its year-long endurance could enable, as a recon plane, command platform, or missile carrier. And while using it for the nominal design purpose as a cargo transporter would involve landing and taking off twice (thus using up the fuel reserves and requiring more--plus the study did not discuss the typical problem fission plants have that when they shut down they "poison" themselves with decay isotopes that absorb neutrons and so can't be restarted until these decay, a process that takes days--perhaps certain fission reactor core designs can avoid or minimize this, allowing the plant to be restarted mere hours after being shut down?) at least range is obviously no problem--once airborne, this thing can haul your cargo as far as you like, even if the world were a lot bigger than Earth!

I wish I could look that volume up again but it was at a university library in another state from where I live now.

I have thought up an alternative mission, analogous to attack subs versus "boomer" strategic missile subs--the plane could be meant to attack ships. In that sense it is more like conventional submarines, but with range and attack options like an attack plane so it is also an alternative to having aircraft carriers. Being submersible not only helps avoid detection until the attack is underway, it also enables the plane to stay on station despite the possibility of storms that might sink a surface-parked plane, by being submerged safely below the waves of the storm.
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To get away from the nuke tangent, I tried a couple Google searches for using sodium and water as a power source but have not yet come up with anything but fuel cell proposals. Of course a good fuel cell design that can use seawater as a reactant would be perfectly good, even better actually than using the reaction as a heat source!

A magic word seems to be "pyrophoricity." Anyway, I have yet to come with anyone proposing to fuel a submerged vessel with any kind of metal/water reaction, for heat or for direct electric current. Searches on "sodium submarine" mostly come up with either references to the USS Seawolf (the second US nuclear powered sub, that used a sodium-cooled low-pressure reactor as an alternative to Rickover's now-conventional pressurized water reactor--it was not very successful and its reactor was eventually replaced with a pressurized-water one) or to the salt content of sandwiches!

Oh, and this.

Is that helpful?:D
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Well, damn. On the second page of the search, there was this! Still, since this is for a fuel cell that again uses stuff onboard (that happens to include sodium) and does not use seawater as a reactant, it's conceptually the same as any other battery or fuel cell concept. I suppose if I keep digging I might find that someone somewhere sometime has proposed something more serious than a bathtub model submarine based on baking soda bubbling, but the more of these kinds of things I find the stronger my conviction that the notion has been considered--and rejected, in favor of alternatives we already know are limited.

I'm down to page 10 of that search--still the same mix of baking-soda bubbling toy subs (but one from the Clabber Girl site, so that's authorative!:D) articles on the Seawolf, stuff about submarine sandwiches and health, and battery/fuel cell systems, with miscellaneous stuff about the chemistry of the Dead Sea and so on.

Lotsa luck, y'all! I'm assuming any submersible plane designed in the 1950s or after is going with some kind of small nuclear plant for submerged power, or plans to surface occasionally to recharge batteries a la conventional diesel sub operations. (A bad idea for a strategic boomer but possibly OK for maintaining an attack-plane fleet in being on dispersed stations).

Just a hundred or so horsepower should be more than enough for slow submerged motion; you need more than that to keep the lights on, the air purifiers flowing, the controls operational, etc...
 

archaeogeek

Banned
For compact nuke, the only option I could see is molten salt, but it was pretty much experimental in the 50s, and didn't catch on because you can't make bombs with thorium.

Otherwise the smallest nuke sub is still France's six Rubis class SSN at 2400 tons.
 
The problem isn't the reactor, it's the shielding.
1) Be as it may, lets discard nuclear power sources from the discussion, ok? It has too many caveats.
2) As for the pressure. I think the best solution is to keep the crew within an elongated spheroid with internal controls connected to the plane's mechanism by electrical cables. A near-spherical shapes maximizes pressure resistance, and eliminating mechanical re-entrances minimizes weaknesses. It also facilitates underwater ejection, since the "egg" would be designed to break free whole from he remains of the plane/sub in case of catastrophe.
3)As for ballast, we could use disposable tanks, transparent plastic tanks to be inflated (with water) in order to sink, and to be dumped whole in order to emerge.
4)The plane wouldn't be expected to move significantly while underwater, so battery power would be enough.
 
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