guillemot and gannets do it . Phalacrocorax carbo and kingfishers do it . Even the diminutive insect - eating dipper does it . And if a plan by the Pentagon’sDefense Advanced Research Projects Agency(DARPA ) win , a remarkable airplane may one solar day do it too .
Plunge beneath the wave to haunt its prey , before re - egress to fly home .
TheDARPA architectural plan , announced in October 2008 , calls for a surreptitious aircraft that can fell low over the sea until it nears its target , which could be an opposition ship , or a coastal land site such as a port . It will then climb down on the water and transform itself into a submarine that will cruise under water to within striking distance , all without alerting defences .
That , at least , is the plan . The government agency is known for taking on head - twistingly unmanageable challenge . So what about DARPA ’s dipper ? Is it a preposterous dream ? “ A few years ago I would have said that this is a silly idea , ” says Graham Hawkes , an locomotive engineer and submarine room decorator based in San Francisco . “ But I do n’t remember so any more . ”
DARPA , which has a $ 3 billion annual budget , has begun to study proposed designs . In the next year or so it could start allocating funding to developers . Though the agency itself is unwilling to comment , Hawkes and others working on rival designs have unveil to New Scientist how they would solve the key problems involved in construct a plane that can jaunt under piddle – or , to put it another way , a fly submarine .
The challenges are vast , not least because airplane and submarines are normally pole apart . Aircraft must be as low-cal as potential to minimize the locomotive power they need to get airborne . Submarines are heavyweight withmassive hulls strong enough to resist crushing forcesfrom the surrounding water . Aircraft apply face lifting from their annexe to last out aloft , while Italian sandwich operate like underwater balloons , adjusting their buoyancy to sink or rise . So how can engineers balance the conflicting demand ? Could a slyness be designed to plunge into the sea like a gannet ? And how will it be propelled – is a jet engine the good solution , both above and below the waves ?
According to Norman Polmar , former advisor on naval strategy and engineering science to the US government , the start point must be to find a way to make an aircraft that can sink in water . “ Submarines can not fly , ” he says , “ but seaplanes can overwhelm . ” This was the thinking behind what was probably the first pang at a flying sub . In 1934 Boris Petrovich Ushakov , a bookman engineer at a Soviet military honorary society , formulate a fly subaqueous sauceboat – athree - engined floatplanedesigned to reconnoitre out opposition ship and then ambush them . Ushakov envisaged his craft fly ahead of the aim , landing on the sea and then flooding its fuselage so that it could lie in in wait beneath the aerofoil and torpedo the ship as they sail by . Ushakov submitted his radical excogitation , which included a conning tower and periscope , to senior police officer in 1936 . But the concept was never put into practice , being deemed too heavy to be effective .
It pick out another three X before a flying hero sandwich appeared for real . This was a craftsmanship built in 1962 by Donald Reid , an railroad engineer at aircraft manufacturing business North American Aviation . TheReid Flying Submarine(RFS-1 ) was a true mongrel , constructed by Reid in his spare time using remnant parts from other aircraft and , like Ushakov ’s pattern , it was a pontoon plane . The trade proved able-bodied to plunk to a depth of a few meter in tests , but was so cloggy it could only make short hops into the air . Though this was at the height of the cold war , the US naval forces showed little sake in Reid ’s machine .
That may have been because the navy had already commissioned another aircraft manufacturer , Convair , to progress what became known as the “ subplane “ . It parcel out with great floats , swear or else on its aerodynamic fuselage , like the Kingston-upon Hull of a flying boat , to land on the body of water . In a paper in the September 1964 upshot of Naval Institute Proceedings ( p 144 ) , hydrodynamics applied scientist Eugene Handler at the US Bureau of Naval Weapons claim this flying sub would be ideal for attacking Soviet shipping in the Baltic , Black and Caspian seas . Convair drew up detailed pattern and even built scale models which were tested in water tanks . Though the result looked promising , the project never made it any further ; it was cancelled by Congress in 1966 .
So is DARPA ’s new projection destined for a similar luck ? “ What the Americans desire sounds incredibly challenging , ” says UK Royal Navy commander Jonty Powis , head of NATO ’s submarine rescue service . “ If they accomplish half of what they want from this machine they will be doing well . ” Others are more affirmative , particularly in the luminousness of advances in technology and materials science since the last attempt – notably in lightweight carbon paper fiber complex and energy - dim batteries . “ There ’s believably no reasonableness why it ca n’t be done , ” says Hawkes .
There is general arrangement that Convair ’s hull figure was sound . Landing on a flying - gravy boat - style fuselage and doing away with clumsy air bladder should make the foxiness lighter and faster both in the line and under weewee . But once the trade is on the pee , how good to get it to dive ?
Simply deluge the fuselage with body of water is one solution , but this means the crew would have to be kitted out with Aqua-Lung equipment . trapping the work party in a watertight cabin is apparently preferable , and to counter its perkiness Polmar suggests borrowing another idea from Convair ’s purpose – floodable fuel tanks . If the fuel in the tanks is held in a gum elastic bladder , the craft can be submerged by let water into the vacancy revoke by fuel used on the outward trip . When it ’s time to come up , the water can but be pump out .
For propulsion under body of water , galvanising top executive is the preferable choice , according to Ian Poll , an aerospace engineer at Cranfield University in the UK . “ Using batteries to drive electric motors when submerged could have another welfare , ” he says : their weight would assist counter the foxiness ’s airiness .
Unfortunately batteries could severely undermine the sub ’s airworthiness . In a report titled “ Conceptual Design of a Submersible Tactical Insertion Aircraft ” , published last year by the American Institute of Aeronautics and Astronautics , a team of applied science students at Auburn University in Alabama calculated that the batteries ask for a U-boat capable of travelling 44 km under H2O – a aloofness specified by DARPA – will press as much as all the other component of the watercraft combined , making it too heavy to pilot .
So rather than using electric big businessman , the Auburn team favours actuate the watercraft with a gas turbine fed by breeze draw off in through a 10 - metre schnorkel . That intend the torpedo will have to outride close to the surface . While DARPA has yet to specify at what profoundness the flying sub should operate , being restricted to a special depth might not matter . “ As long as it is not visible , there ’s not much reason to dive far below the Earth’s surface , ” says Bob Allwood , locomotive engineer and main executive director of the Society for Underwater Technology in London . “ The problem is that the craft has still got to be slimly denser than water supply to submerge . ”
Hawkes , however , does not see this as a problem . In fact he does n’t go for that the craft has to be made heavier to sink beneath the waves , any more than a normal aircraft has to become more buoyant to take off . “ You ca n’t build an plane that is also a balloon , and an aeroplane ca n’t go under water in the same way a pigboat does . You ’re mixing two basically different modality of operation . ”
Hawkes already builds zep that are lighter than water ( New Scientist , 28 March 2025 , p 36 ) . To whelm their natural buoyancy and keep them below the surface , they are equip with wings that generate downward “ lift ” . “ Think about it as fly under urine , ” he say . “ It can be done . It just need a mass of oeuvre . ”
To operate below the waves as well as above them , these wings will have to be a turn out of the average . “ One important thing is that the craftiness ’s wings will necessitate a symmetrical control surface , unlike the unsymmetrically curved wing that gives aircraft face lifting , ” he says . So when the craft is airborne , the annexe will call for a electropositive “ angle of attack ” : in other word , it will necessitate to be angled upwardly relative to the airflow . To achieve this , the trade will have to vanish in a nose - up mental attitude . Conversely , when under water it will postulate a negative slant of attack , so the craft will jaunt nose - down ( see diagram ) .
Hawkes has already built a stubby - winged submersible called the Super Falcon that can “ flee ” down to 300 metres , about 10 meter deeper than a scuba diver . Redesigned with aero engines and large wings , it could be made to vanish at about 900 kilometres per 60 minutes with its nozzle angled up by about 5 degrees , Hawkes says . Under water it should superintend around 10 knot ( 18 kilometre per 60 minutes ) . At these speed , the characteristics of the air and water flowing – delineate by a parameter known as the Reynolds telephone number – are roughly the same , so the craft ’s ascendance surface should exploit in both environments .
Hawkes admits that an direful pot of force will be needed to get the Super Falcon airborne , and only jet engines have enough oomph to do the job . Polmar agree , and points out that the plunger locomotive used in conventional light planes are ruled out for other reasons : they would fail if any water leaked into the cylinder . “ you’re able to not immerse a reciprocate locomotive engine and expect it to work , ” he suppose . But protect a special K engine against saltwater corrosion and position it high on the wiliness so the spray does n’t enter the inspiration during take - off and landing , and it will shape o.k. . Russian aircraft God Almighty Beriev has proved this with its Be-200 amphibious plane .
In fact , Hawkes foresees jet engines playing a dual use , propel the plane through the water as well as through the tune . There ’s no intellect why the compressor and turbine blades in a jet plane railway locomotive ca n’t be driven by an electric motor to generate thrust under water , he says . It should be possible to build an railway locomotive that runs on kerosene in tune and switches to electricity when submerged .
Others are already thinking along these lines . Last class , aircraft manufacturer Airbus patented a hybrid galvanic jet engine for airliner which can be powered by both conventional kerosene and electricity . Most jet engines have an electric starter motor , and this motor could spin around the turbine ’s shaft under water , Hawkes suggest . The blades would rotate more easy than normal , he says , and the railway locomotive wo n’t be particularly effective . “ But I think this could work perfectly well . ”
The Auburn scholarly person come up with much the same strategy in their figure , opt for a type of gas turbine holler a turboshaft to get the best carrying out . Equipped with big rotor coil leaf blade and gears to correct its speed , a turboshaft unit offer “ satisfactory efficiency ” in both air and water , they say . Alternatively the air could be fed to a fuel jail cell to generate electrical energy to spin the blades .
Should Hawkes ’s buoyant design winnings out , beat it to sink low enough in the water for its annex to start make down forces could also be a problem . Hawkes has a striking solution : re-create what diving birds do . “ You might have to put the nose down and literally dive , smack , into the water , ” he says . deal inspiration from birds would put submersible - aircraft technologist in famous company : nineteenth - century glider pioneer Otto Lilienthal and the early 20th - C inventors of powered flight , the Wright pal , are among those who did so – though it ’s no guarantee of achiever in this slip . Whatever happens , order Hawkes , “ it would certainly be spectacular ” .
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