submersible aircraft

[rasorinc]

Would it be of interest to anyone to start a new thread on this subject?
After kind of laughing at the idea I set down some parameters and worked through a few quick problems and I believe it is possible using a maximum
depth of 80 meters or 9 bars of pressure. Stan

[Gilbert]

I hear the aliens already have this technology.

[kach22i]

USO's, they have been on the history channel.

I'm no engineer, but admire the efforts of others even if it's just a mental exercise.

The efforts of this guy (Doug) and the process (shows his math) is impressive and might be a good reference point for this thread.

SEEKER - by Doug
http://www.submarineboat.com/submarine.htm
SEEKER is a hybrid diesel powered jet boat and ambient submarine.


These projects are cool too:
http://www.navytimes.com/news/2007/02/apsubmarinedesigner070211/

http://www.hyper-sub.com/product.hs600m.php

Also, almost anything can be made to fly, or at least hover.
http://www.minimarcos.org.uk/altpics/hovermini/index.html

[Petros]

They already have one, it was used on the "Seaview" TV show of the 1960s where they used the flying sub to patrol the area around the sub's location.

When in engineering school 25 years ago I did some calculation to see if this was possible. It might be if you had an efficient engine that did not need air to breath, and you had a "wet" sub. No way to make a dry sub work, way too heavy.

But even as a wet sub, it likely would not fly well, or make a very good sub. And it would have very limited range. It would be more piratical to have a fold-up ultra-lite aircraft on a minim sub.

[rasorinc]

Well It will work. It looks like a round bodied PBY though. Stan

[big-boss]

I have thought about this as well, Civil Engineeer not a Naval like you guys. But give this some thought:
Start with a flying boat then make it submersible. Should be easy enough to make a boat fly then fill it with water, right?

[FranklinRatliff]

DARPA is serious about researching this concept as a means for delivering and recovering special ops personnel (seals).

[tspeer]

It's been don (http://www.youtube.com/watch?v=Ew1EVsEKKRA)e.

Here are some design factors to think about.

The issue of wet vs dry is of fundamental importance. Any buoyant volume is a hinderance when submerged, so dry space (if any) has to be kept to the bare minimum.

Fuel is less dense than water, so fuel volume contributes to buoyancy. And it contributes to weight when flying, so fuel quantity hurts you coming and going.

The implication of the two factors above mean it's the structural weight that has to be capable of overcoming the buoyancy of the fuel & payload. Then you have to carry that structural weight when you fly.

The alternative to negative buoyancy is to fly underwater with positive buoyancy. There's a drag associated with that, of course. But at least they already have a flying configuration. Underwater gliders (http://www-pord.ucsd.edu/~rdavis/publications/MTS_Glider.pdf) have been used for exploration and unmanned oceanographic vehicles. A good example is the UW Seaglider (http://www.apl.washington.edu/projects/seaglider/summary.html).
http://www.apl.washington.edu/projects/seaglider/images/components.jpg

[kach22i]

Now we are getting somewhere.

Good post.

[FranklinRatliff]

It's been don (http://www.youtube.com/watch?v=Ew1EVsEKKRA)e.

Here are some design factors to think about.

The issue of wet vs dry is of fundamental importance. Any buoyant volume is a hinderance when submerged, so dry space (if any) has to be kept to the bare minimum.

Fuel is less dense than water, so fuel volume contributes to buoyancy. And it contributes to weight when flying, so fuel quantity hurts you coming and going.

The implication of the two factors above mean it's the structural weight that has to be capable of overcoming the buoyancy of the fuel & payload. Then you have to carry that structural weight when you fly.

The alternative to negative buoyancy is to fly underwater with positive buoyancy. There's a drag associated with that, of course. But at least they already have a flying configuration. Underwater gliders (http://www-pord.ucsd.edu/~rdavis/publications/MTS_Glider.pdf) have been used for exploration and unmanned oceanographic vehicles. A good example is the UW Seaglider (http://www.apl.washington.edu/projects/seaglider/summary.html).
http://www.apl.washington.edu/projects/seaglider/images/components.jpg

I first saw that shape (minus the wings) back in the late sixties. There was an article in Science News about research being done by the navy on low drag shapes using both small buoyant bodies released from the bottom and streamlined projectiles dropped from the surface.

[kach22i]

http://blog.wired.com/defense/planes_copters_blimps/index.html
http://blog.wired.com/defense/images/2008/11/11/f816bb7efee24666a674e9b0308f7ba8lar.jpg

[markdrela]

Underwater gliders have been used for exploration and unmanned oceanographic vehicles. I've never figured out what advantage is obtained by "gliding" underwater. In the absence of vertical currents, the minimum energy needed to travel is Drag*Distance, and it doesn't matter whether the energy is used to run a small prop, or to pump out water at the sea bottom to regain positive bouyancy for the return glide back to the surface. But when gliding, you're dragging the wing through the water in addition to the body/payload. It seems that removing the wings/pump, setting up for near-neutral buoyancy at all times, and installing an optimized propeller will give better mileage.

[Retired Geek]

this was posted on their website today (flightglobal.com)

[rickthorn]

Within the past 2 weeks, I have heard the U.S. Navy is looking for a "flying submarine" of sorts for clandestine missions. Also, just thought the following is extremely cool...just needs a bit longer wings, more sleek design and more horsepower.

http://www.hovercraft.com/content/media/video/19xrw_04_256k_lo.wmv

[Gannet]

Would it be of interest to anyone to start a new thread on this subject?

I thought you would to see DARPA's BAA09-06 SUBMERSIBLE AIRCRAFT Proposers_Day_Presentation

http://www.darpa.mil/sto/solicitations/BAA09-06/files/Proposers_Day_Presentation.pdf

[Stumble]

Just some hairbrained scheming from a non-technical person...

It seems to me that the biggest problem in converting from an aircraft to a sub is doing something with the wings. Since they will represent a huge amount of drag when submerged. The trick then would be to in some way have the wings collapse or disappear when in boat/sub mode. To achieve this I am wondering if it wouldn't be possible to use a fabric wing instead of a hard one. Think back to the old bi-plane era but use modern materials for the construction.

Maybe two or more carbon fiber guide polls running out from the body with carbon ribbing running on the polls. When the vehicle transitions to plane mode the poles are moved into position perpendicular to the body then the ribs are pulled into position through the use of lines to lock them into place out on the wing. The fabric stretches over the framework and off you go...

An easier idea would be to use a completely soft wing, with air pressure providing the rigidity to the entire structure. Though I have no idea the amount of pressure it would take to keep a wing stiff enough to carry these loads, though I suspect quite a lot. However this would solve any component storage problems.

[wardd]

registration, where, which?

[tspeer]

this was posted on their website today (flightglobal.com)

It only takes one look at the illustration to see how far off the mark it is. A submarine with flooded ballast tanks is heavier than water. The volume of the ballast tanks in the picture is not a large percentage of the total volume of the craft. That means that when the tanks are empty, the density of the craft will be not all that much less than the density of water. That's a very heavy weight to lift when trying to fly. But as it's pictured, the plane is much lighter and floats high in the water - when the tanks are flooded, it will submerge by a little more than the height of the tanks and no more. The picture is a total contradiction with respect to the most important design requirements.

It is possible to make a airplane that can submerge and travel under water - it's been done before. However, I don't believe it is likely to have substantial volumes of dry living space. That is buoyancy one just can't afford in such a craft.

I think a flying sub will be a heavy aircraft by its nature, but will also be very light for a sub - it will need to use dynamic lift to stay submerged just like it uses dynamic lift to support itself in the air. And I think it's likely that the living areas will have to be flooded for it to make its underwater dash into the hot zone and back out, then pumped out to allow it to loiter on the surface in more comfort.