1). If a large plane dives from any height straight down into relatively flat seas, could it enter the water whole, like a bird diving for a fish, slowing from the friction, or will it always crumple on entry, or at least lose the wings?
2). If whole, would it float back to the surface?
3). If no, would it be possible for the plane to “fly” underwater for hundreds of miles before hitting a deep ocean floor?
4). Would it implode from the pressure or possibly “land” on the bottom whole?
Thanks!
In real life, planes that hit the water in a nose down attitude are usually torn to bits by the impact. The only planes that survive intact are those that glide gently and “land” on the water surface. Even that requires fairly calm seas, as many of these planes attempting to ditch in the water have had their engines hit a wave which causes the plane to cartwheel (and occasionally rips the engine and/or the wing off).
If you could somehow get the plane under water without damaging it, then yes, it would float back up to the surface. Planes aren’t water tight and it will eventually sink again. Might take a while, though.
Hundreds of miles? No. But a sinking plane could go a fair distance if the wings were still attached and it somehow maintained a relatively upright and only slightly nose down attitude.
At some point the hull will rupture from the pressure. At that point the water will rush in and equalize the pressure and the rest of the hull will remain intact. It will still look like a plane when it hits the bottom. It won’t be crushed like a tin can.
There’s no way a plane would survive impact. No plane engine, jet or propeller, would work underwater either.
birds fold their wings in before they impact.
I should have said glide instead of fly, I guess.
Would it still crash if the nose was a point instead of round? I’m assuming it’s the friction of the water that causes the impact damage.
The closest you’ll get to that scenario is a flying boat, maybe it would be possible technically to do something that would then operate underwater - but its not been done, because there is no need for it - I would be surprised if feasibility studies have not beeb done.
But a plane going into the water nosedown is no longer gliding, but is instead in freefall and thus going even faster.
This video of shows a plane that is at gliding speed (the plane ran out of fuel after it was highjacked) breaking apart as it enters the water at a shallow angle. The forces would be much greater if the jet were in a nose-down dive, and the destruction would be even greater.
Aircraft are mostly empty space. No way would a plane survive a dive into water.
The engineering requirements for an airplane are radically different than those for a submarine. With existing technology, any re-enforcement sufficient to make a hull air-tight and able to withstand the pressure of being even a few feet underwater would render it too heavy for use as an aircraft.
Would this * be really what is being asked?
Add a pilot with super duper SCUBA gear and off you go.
Will the normal controls, magical powered work well enough to guide the air/water craft around on a sightseeing tour until it is ‘landed’ on the bottom.
Pilot then uses the ‘may west.’
IMO, this would work & it would be INTERESTING to be the pilot.
Right. We’ve established that diving nose first into a body of water at flying speed will cause any large airplane to completely disintegrate, and any small airplane to break into many pieces. However, as mentioned upthread, it is possible to land on the water, as evidenced by hundreds of amphibious airplanes and also, famously, by USAir 1549.
I’d bet that an intact airplane that has sunk would glide underwater just fine. There are plenty of examples of autonomous underwater gliders that look remarkably similar to subsonic cruise missiles, which in turn look a lot like airplanes. These gliders use compressed air, a pump and a bladder to change their buoyancy. As they begin to move vertically in the water column, the wings generate lift (up or down) propelling the craft forward. They cruise around the oceans at 1-2 mph, slowly ascending and descending for weeks on end, all the time in an underwater glide. With that said, an airliner would most certainly be on a one-way trip to the bottom.
The principles are the same, so long as the airplane has survived the landing. If the engines stayed on during the ditching, the center of gravity will maintain its position relative to the center of pressure and the airplane should work its way into a stable glide. While I don’t remember enough of my aerodynamics/fluid dynamics to do the math, the forces involved should remain relatively balanced, even if the Reynolds number is extremely low.
Weight will be reduced by the amount of water displaced by the aircraft structure (negligible in the case of an airliner). Buoyancy doesn’t come into play because airplane fuselages are not airtight. Even if they were, they are built to contain tension, not resist compression. An air-filled fuselage would quickly collapse as it sank. My guess is that 5-10 psi (10-20 ft underwater) would be plenty to cause catastrophic failure. If that happened, you’d have a hulk of metal plummeting to the sea floor.
Drag will obviously be very high, but so will lift. As with any glider, thrust is provided by the forward pointing component of gravity.
My WAG is that an intact airliner would glide to the bottom relatively slowly (maybe 50 mph?) and steeply (45°?), and probably break in half upon impact with the seabed. The Boeing 787 might be an exception, as the composite fuselage structure just might be strong enough to resist crumpling under the force of impact. A small airplane would probably stay in one piece.
Upon review, ninja’d by GusNSpot.
Torpedoes (aside from supercavitating torpedoes like the Russian Skval) under power typically have a maximum speed of around 40-50 knots (46-58 mph); the British Spearfish, designed to intercept the Soviet-era Alfa high speed boomer interceptor submarine, has a max dash speed of 70 its (~80 mph). There is no way an airplane with the extremely low sectional density and massive amount of forward aspect (compared to a torpedo or submarine) will retain sufficient momentum to ‘glide’ any distance under water. When aircraft do land intact, there is generally sufficient buoyancy in the fuselage and ullage in tankage to allow it to float for some time until enough of the unpressurized areas of the fuselage (e.g. the cargo hold and inspection crawlspaces) fill up with water.
The composite fuselage of the 787 is not “stronger” than a comparable aluminum fuselage; it is lighter for the strength required to withstand the same ostensible loading conditions, but those loading conditions do not include negative internal pressure, and the fuselage is neither watertight nor reinforced to withstand more than a fraction of a negative pressure differential of one atmosphere (~10 m under water). I’m not intimately familiar with the design or layup of the 787 but composites are often optimized to resist only certain load cases to which they will be subjected and can be quite delicate in cases that are not considered in the design. For instance, composite solid rocket motor cases and pressure vessels are designed to withstand hundreds or even thousands of pounds per square inch of internal pressure in ambient conditions ranging from atmospheric (14.7 psi) to vacuum (~0.0 psi), but when unloaded (i.e. no propellant grain to reinforce the case) can often only withstand a few psi of external pressure above ambient before failing from buckling or interlaminar shear and tension, and hence have to be handled as delicately as eggshells.
It is demonstrably possible, with great skill, to land an aircraft on the water, provided it comes in flat and level with just a slight nose up attitude such that essentially bellyflops as soon as the aft fuselage contacts the water, distributing the impact across the entire fuselage and wing area. Should it come in nose first or with one wing plowing the water before the rest of the aircraft it will enter into an unrecoverable cartwheel and break up due to rotational loads and impact. It is not possible, except in Bond movies or shitty 'Eighties television shows, to land an aircraft and have it drift controllably to the seabed while maintaining fuselage integrity. (To be fair, Thunderball did have the pilot plugging a air cartridge into his onboard GOX system, but I find it unlikely to an extreme that a regulator system designed for use on high altitude aircraft would have been able to deliver sufficient pressure to overcome the 2-3 atm of ambient pressure at 60-90 feet down.
So the answers to the o.p. are maybe, no, no, and yes (implode or rupture) in that order.
Stranger
Wrong. Either US Airways 1549 did in fact glide to a landing on the surface of the Hudson River adjacent to midtown Manhattan on January 15, 2009 or it did not.
Unless you are a conspiracy theorist of the most disturbed measure, you must agree that this aircraft did in fact land on the water. It did not rip itself apart. It did not shear off the wings. In fact, there are hundreds of clear photographs and video recordings showing survivors of this landing standing on both wings.
-shrug- Those of you who say an aircraft will rip itself apart on impact are wrong.
Stranger,
The 50 knot estimate came from the assumption that the entire airplane would be filled with water. In this case, the sectional density would be only slightly less than a torpedo, would it not? I’m picturing what amounts to a slug of water encased in an aluminum tube sinking and gliding forward at something like a 1:1 ratio.
I agree that a composite fuselage such as the B787 would not be able to withstand any sort of compressive forces. I am curious, however, if it would resist crumpling or breaking in half upon impact with the seafloor any better than a typical aluminum semi-monocoque fuselage.
I mentioned AWE1549 in my first post. Also, you may have missed the discussion distinguishing a successful ditching from a plunge into the ocean.
Her initially stated question was if a plane could go in nose first which is not the same as the Hudson landing.
Bolding mine.
Doesn’t read as diving nose first. Not all birds do that. Many - as the language in #1 seems to indicate- slow from friction.
Birds do it; dive from a height and make the air-water transition by folding their wings. Gulls can stay underwater for a few seconds to catch fish. I have seen cormorants do it up close, and once underwater, they can maneuver quite well; dive further, glide and navigate for quite a distance and time (seconds, maybe minutes). That’s probably what the OP is thinking of.
But big, honkin’ planes share very few similarities with birds. Need we list the differences?
I remember reading an article once in Popular Science that said engineers were working on an idea like this. Normal submersibles work by making themselves more dense than the water which causes them to sink - they’re the equivalent of balloons. The idea was that you could in theory make the underwater equivalent of an airplane. Have a craft that was lighter than the water but with “wings” that would give it the equivalent of lift. The curve on the wings would be the reverse from the curve on a plane’s wings and rather than giving the plane lift against gravity, these wings would cause the submersible to be pulled down against its bouyancy.
Like a plane, this reverse bouyancy would be caused by the movement of the ship through the water so you couldn’t land such a submersible underwater anymore than you could stop a plane in mid-air.
If the plane were filled with water after landing, the water would not be moving 50 kts. It would be moving at whatever speed the surrounding water were moving. And regardless, the viscous friction on the skin of the fuselage would rapidly bring the vessel to a halt. Even submarines which are optimized to minimize drag slow quickly without power; an aircraft with giant wing surfaces could not “glide” at any appreciable differential to the surrounding water.
Glass or graphite fiber reinforced composites in a polymer matrix are notoriously poor at withstanding impact, hence the concerns about resistance from being struck by a bird in low altitude flight. The way they fail is completely different from metallic structures such as those made of aluminum; whereas aluminum will generally flex (elastically deform) and stretch (plastically deform) before fracturing, composite structures will often craze (fracture within the polymer matrix) long before reaching the rupture strength of the reinforcing fiber. This, in turn will reduce the strength in interlaminar shear or tension (i.e. the strength of the matrix to keep the plies or windings together) which reduces the overall capability to resist failure modes in bending, buckling, or torsion. Without a direct comparison between structures it isn’t possible to evaluate in anything but qualitative terms which would be more likely to fail under an impact-type load, but for the same ostensible capability the composite structure would likely suffer greater damage and loss of integrity.
You can verify this for yourself by going to a junkyard and taking a sledgehammer to a metallic structure and a fiberglass structure and compare the relative damage and affect upon integrity under various loading conditions. (To be fair, “fiberglass” is colloquially used to refer to short fiber reinforcement and therefore isn’t the same as a woven prepreg or long fiber wound composite, but the fact that the matrix material is the limiting case under any kind of loading that isn’t directly opposed by the tensile capability of the fiber will be demonstrated.)
Why not, since the question has been asked? First of all, birds don’t move at speeds comparable to the slowest stall speed of an aircraft, and can fly at extremely low speeds, some as little as 5 kts. Second, birds have extreme capabilities for dynamic stability in flight which exceeds the best artificial control systems. They can also reconfigure their aerodynamically shape and mass properties during landing in ways that no aircraft can do. They’re also very strong and flexible and can respond to high loading by essentially going limp and allowing the impulse to be distributed rather than just breaking. The power to weight ratio of birds at low speeds is also phenomenally higher than aircraft; although a jet-powered aircraft certainly can fly faster, farther, and higher than a bird, it cannot literally take off from a sit using wing power alone, and the amount of power required to enable a VTOL aircraft to fly with no forward speed is incredible (thousands of horsepower compared to the small fraction of h.p. which can be developed by the typical bird). There simply is no comparison to how a bird lands on water compared to a rigid-body winged aircraft being ditched by an experienced pilot, much less an uncontrolled aircraft coming in nose or wingtip down.
Stranger
US Airways Flight 1549 didn’t dive in nose-first, which is what the OP was asking. It’s also not obvious from the video, but US Airways Flight 1549 also had one of its engines ripped off during the landing. It was recovered from the bottom of the Hudson a few days after the incident.
I don’t think anyone is seriously disputing that it is possible for a plane to ditch in water. Some of them even do survive the ditching intact, though it’s rare.
The OP said “dives from any height straight down” (bolding mine). I’d like you to find a single plane that wasn’t ripped apart doing that.