If you are an aircraft designer, will you be moved when you see the two pictures of a fish eagle entering the water and a flying fish leaving the water? Do you want to design a flying machine with similar functions and able to travel freely between sea and air?

I believe you will, many designers will have such a dream. When mankind has challenged the seaplane, flying car and airplane, the sea-air trans-media aircraft has become a logical new dream for mankind to pursue.

I. What is a sea-air trans-media vehicle?

Medium, literally speaking, if a substance exists inside another substance, the latter is the medium of the former.

In the case of a flying machine, if it flies in the air, then the air is its flying medium. If a flying machine can fly in the air, but also can navigate in the sea, and can freely cross between the two, this kind of flying machine is the air-sea cross-media flying machine. By extension, if a vehicle can operate in two or more media and can traverse freely between them, this vehicle is a cross-media vehicle.

When distinguishing various vehicles, in addition to media, we will encounter concepts such as multi-perching and multi-use.

The original meaning of "perch" is to rest and stay in the sunset, when the birds return to the wood. For flying vehicles, it means where to park and take off and land from. Land-based aircraft park and take off and land on the ground, and seaplanes park and take off and land mainly on the water, but also can park and take off and land on the ground. Those with two or more parking and takeoff and landing methods are called multihomed aircraft.

Use, refers to where the aircraft is used, that is, the operating space of the aircraft. Use and habitat, are independent of each other, not necessarily related. Land-based aircraft and seaplanes have different habitats, but both operate in the air; flying cars parked and landed on the ground, can operate both on the ground and in the air; air and space aircraft parked and landed on the ground, operating in the dense atmosphere and thin atmosphere; sea and air cross-media aircraft can be parked on the surface or underwater, operating in the water, underwater and air. By extension, a multi-role vehicle is one that can operate in two or more operating spaces.

With the above concept, the characteristics and classification of existing vehicles can be better grasped. For example, conventional aircraft, land-based, air-use, single-media; seaplanes, amphibious, air-use, single-media; flying cars, land-air dual-use, single-perched, single-media; air-space aircraft, land-based, air-space dual-use, across dense atmosphere/thin atmosphere; air-sea cross-media vehicles, amphibious, water/submersible/air triple-use, cross-media. Habitat, with, medium, the three are juxtaposed, can exist at the same time, but also can be used separately.

Second, what is the use of air and sea cross-media vehicle?

Air-sea cross-media vehicle has the dual characteristics of aircraft and submarines, suitable for both military and civilian use. In the military field, it is mainly used to carry out information reconnaissance, firepower strike and force delivery tasks in maritime operations by using the broad vision, range and mobility of aircraft and the underwater concealment of submarines. The civilian sector is mainly used for sea rescue, underwater exploration, undersea tourism, etc. So far, typical projects and uses are mainly as follows

1. attack surface ships from the air. In 1934, the Soviet Union proposed the "Flying Submarine" program, which attempted to integrate the broad vision and maneuverability of aircraft with the submarine's underwater concealment capabilities, using the air to quickly approach, submerged in silence, waiting for an opportunity to break through the water and launch torpedoes from the air to attack enemy surface ships. The project was imaginatively called "flying submarine" or "diving aircraft". However, under the technical conditions at that time, the project had great technical risks, and with the imminence of World War II, more resources had to be invested in projects with less technical risks and quicker results, and the project was terminated in 1938 after the program design was completed.

In the 1970s, after the establishment of the Trinity nuclear strategy, the U.S. proposed a large submarine aircraft program in order to integrate air-based maneuverability and sea-based stealth capabilities. The aircraft was required to have a takeoff weight of 180 tons, a combat radius of more than 4,000 km, and the ability to carry two Polaris A-3 submarine-launched strategic missiles; when submerged, it could stay underwater for five days and have a certain degree of underwater maneuverability, but it did not require the ability to navigate underwater. After the U.S. nuclear strategy adjustment, all sea-based nuclear strike missions to the strategic nuclear submarines, surface ships and other nuclear strike missions no longer, the project also ended after the completion of the concept design.

In 2008, in response to the U.S. Navy's "sea-to-land" operational needs, the Defense Advance Research Projects Agency (DARPA) proposed a submarine aircraft development program for special operations, soliciting proposals from around the world, aiming to develop a submarine aircraft that can fly in the air, but also navigate on the surface and underwater. DARPA has proposed a special operations submersible aircraft that can fly in the air and navigate on the surface and underwater for use in special operations raids on enemy shores. The basic use scenario is: first carried by surface ships, in the high seas will be released; diving aircraft from the surface taxi takeoff, close to the opponent's territorial waters when landing on the surface, diving underwater, turn into underwater navigation; arrival at the destination moored underwater, special operations personnel use underwater thrusters to reach the enemy shore to carry out the task, after the completion of the mission back to the diving aircraft; after that, the diving aircraft surfaced and flew back to the high seas. The follow-up of the project has not been reported and is unknown.

In 1996, Lockheed Martin and Northrop Grumman jointly developed the "Seafinder" submarine-launched UAV, which was successfully submarine-launched. With this as a pioneer, a large number of submarine-launched UAVs have been introduced. Such as the U.S. XFC, "Cormorant", "spring knife", "Black Hawk" and so on. Submarine-launched UAVs, carried by submarines, can be launched through torpedo tubes, missile tubes or other special devices on ships, and can perform maritime intelligence surveillance and reconnaissance and inspection missions, and are currently under rapid development, with some projects already installed. Because the submarine-launched UAV can not independently complete the underwater diving, so it is not strictly speaking cross-media vehicle.

5. underwater exploration, underwater tourism, etc. In 2009, the U.S. San Francisco-based Hawks Ocean Technology developed a "deep-water flight Super Falcon" submersible for underwater exploration, underwater tourism, etc.. The submersible looks like an airplane, the shell is made of carbon fiber composite material, allegedly based on the principle of air flight design, the use of short and thick wings to generate downward "lift", the abolition of the traditional ballast tank, the submersible becomes more lightweight and flexible, "can roll freely like a whale ", the maximum dive depth of 457 meters. This submersible verifies the feasibility of the aircraft shape for deep-sea navigation, providing a new idea of cross-media vehicle design. The designers said that if a jet engine is added and a larger wing is changed, air flight can be achieved and the flight speed can reach 900 km / h. Currently, the submersible uses electric propulsion and a submerged speed of 18 km / h.