Modular aircraft: Flexibility to save costs

Modular aircraft and cabins allow air­lines to respond more quickly to dif­fer­ent pas­sen­ger needs and market situations, making air transport more efficient.

02.2019 | Text: Denis Dilba

Denis Dilba holds a degree in mechatronics, is a graduate of the German School of Journalism, and founded the “Substanz” digital science magazine. He writes articles about a wide variety of technical and business themes.


The trans­porta­tion of goods in stan­dard­ized con­tain­ers, which were in­vent­ed in 1956 by U.S. trans­port en­tre­pre­neur Mal­com McLean, is con­sid­ered one of the most im­por­tant de­vel­op­ments in lo­gis­tics. Once loaded in­to the met­al box­es, car­go can be car­ried over large dis­tances on var­i­ous modes of trans­port, in­clud­ing trucks, trains and ships. Group­ing car­go in this way does away with time-con­sum­ing un­load­ing and re­load­ing and re­duces ware­hous­ing and lay­time costs in ports. This rev­o­lu­tion­ized goods trans­porta­tion on land and at sea. Now, Clau­dio Leonar­di from the Swiss Fed­er­al In­sti­tute of Tech­nol­o­gy Lau­sanne (EPFL) hopes to achieve a sim­i­lar rev­o­lu­tion in air car­go with his Clip-Air con­cept. The re­searcher has been work­ing on this fu­tur­is­tic air­craft study since 2009.

Video: Combined transportation: Train and plane Article with video

Combined transportation: Train and plane

The Clip-Air concept could bring air travel directly to city centers and industrial locations—with far-reaching consequences for our mobility concepts. To the video

Flying-wing aircraft with flexible-use container capsules

Clip-Air con­sists of two el­e­ments: First, there is the fly­ing part: a fly­ing-wing air­craft. And then there are cap­sules that stack in a sim­i­lar way to con­tain­ers on a ship and sim­ply dock to the fly­ing mod­ule. De­pend­ing on the con­fig­u­ra­tion se­lect­ed, they can then serve as a cab­in or a car­go hold. What makes Clip-Air in­ge­nious is that the cap­sules can al­so be used as rail­cars. “This would ef­fec­tive­ly let us bring air­craft right in­to the cen­ters of cities,” says EPFL re­searcher Leonar­di. Pas­sen­gers would board their “flight” at the train sta­tion. The train would then bring the cab­in mod­ules to the air­port, where they would be cou­pled to the fly­ing-wing unit. There would be no need for pas­sen­gers to trans­fer to the flight or board it sep­a­rate­ly; they could sim­ply sit back and re­lax. This would make stress as peo­ple rush to their gate a thing of the past, and air­ports and air­lines would al­so ben­e­fit from the time saved. An­oth­er ad­van­tage of the mod­u­lar air­craft con­cept is that op­er­a­tors could re­spond flex­i­bly to de­mand, adds Leonar­di. “For ex­am­ple, you could at­tach on­ly sec­ond-class or on­ly first-class mod­ules.” De­pend­ing on the book­ings for a giv­en flight con­nec­tion, this would avoid fly­ing with an emp­ty first-class cab­in, which is a waste of space and of fu­el. It would al­so rep­re­sent an in­no­va­tion in rail trans­port, en­abling freight and pas­sen­ger mod­ules to be trans­port­ed at the same time.

The EPFL sci­en­tists have cal­cu­lat­ed that with a wingspan of 60 me­ters, the air­craft would have a range of up to 4,000 kilo­me­ters. Un­der the main wing struc­ture, it could car­ry three mod­ules mea­sur­ing about 30 me­ters in length and four me­ters in di­am­e­ter—each of which cor­re­sponds rough­ly to an Air­bus A320 in size. This of­fers space to car­ry ei­ther three sets of 150 pas­sen­gers or a large vol­ume of car­go. Re­plac­ing one of the three car­go mod­ules with an ad­di­tion­al, mo­bile fu­el tank would al­so in­crease the range of Clip-Air, says Leonar­di, which is an added bonus. If and when the con­cept will be­come re­al­i­ty, how­ev­er, is still very much an open ques­tion. Leonar­di hopes, of course, that Clip-Air will take off one day, but he un­der­stands that the pro­ject is a long-term en­deav­or.

Coupling poses a technical challenge

Kay Plöt­ner, Head of Eco­nom­ics and Trans­porta­tion at the Bauhaus Luft­fahrt re­search in­sti­tute, doubts whether such a mod­u­lar air­craft con­cept will ever get off the ground. And the sci­en­tist knows the sub­ject mat­ter well: In 2013, col­lab­o­rat­ing with de­sign stu­dents from the Uni­ver­si­ty of Glas­gow, he and his Bauhaus Luft­fahrt col­leagues al­so de­vel­oped a mod­u­lar air­craft study that com­bined rail and air trans­port.

“Where such sys­tems of­ten fall down is that the air­craft them­selves be­come too heavy and in­ef­fi­cient,” says Plöt­ner. The cou­pling mech­a­nism for the mod­ules has to be de­signed in such a way as to be se­cure. As the forces are con­cen­trat­ed on a few points, a more sol­id de­sign is re­quired, which ul­ti­mate­ly adds more weight. An­oth­er com­pli­ca­tion is that the com­plex­i­ty at air­ports would in­crease un­less the in­fra­struc­ture un­der­goes sig­nif­i­cant over­haul. “This means you’d have to make very cost­ly al­ter­ations to air­ports and in some cas­es to train sta­tions as well.” These prob­lems al­so ap­ply to the cur­rent Link & Fly con­cept from the French tech­nol­o­gy con­sult­ing com­pa­ny Ak­ka Tech­nolo­gies, which in­volves cou­pling just one train mod­ule with a fly­ing mod­ule.

The Bauhaus Luft­fahrt ex­pert reck­ons that the mod­u­lar Trans­pose con­cept from the Air­bus re­search unit A3 based in Sil­i­con Val­ley has a some­what greater chance of suc­cess. At the start of 2017, the team led by pro­ject di­rec­tor Ja­son Chua pre­sent­ed a con­cept for mod­u­lar air­craft cab­ins.

Clip-Air aircraft compared to conventional commercial aircraft

Clip-Air aircraft compared to conventional commercial aircraft

Flexible aircraft The individual modules are docked under the main wing structure of a flying-wing aircraft. It can fit up to three modules—each of which corresponds roughly to the size of an Airbus A320.

Adaptable cells

These mo­bile mod­ules are de­signed to be switched in and out at air­ports with­in a mat­ter of min­utes, which would al­low air­lines to adapt their air­craft to the in­di­vid­ual needs of pas­sen­gers on cer­tain routes in the fu­ture. Ac­cord­ing to A3, be­tween ten and 14 of these cab­in com­part­ments would fit in­side an A330. Chua’s idea is to have mod­ules con­tain­ing fa­cil­i­ties like kids’ play ar­eas and child­care for fam­i­lies, fly­ing con­fer­ence rooms, gyms and cafés. “This added val­ue for cus­tomers should, of course, be an in­cen­tive for them to pay a lit­tle ex­tra,” says Plöt­ner. Some­thing sim­i­lar ex­ist­ed once in the past: spe­cial mod­ules were de­signed for the low­er deck of the Air­bus A340-600. These mod­ules housed the re­strooms for econ­o­my class, the main kitchen and a re­lax­ation room for flight at­ten­dants—al­beit at the ex­pense of the us­able car­go space. More­over, they were per­ma­nent­ly in­stalled and not ex­change­able, as they are in the A3 con­cept. “The­o­ret­i­cal­ly, the Air­bus idea would be fea­si­ble,” says Plöt­ner.

(strich:Versatile) The Clip-Air concept is based on interchangeable modules of different sizes for carrying freight, passengers or fuel, depending on demand. Hover over the image for a bigger view

Versatile The Clip-Air concept is based on interchangeable modules of different sizes for carrying freight, passengers or fuel, depending on demand.


Versatile The Clip-Air concept is based on interchangeable modules of different sizes for carrying freight, passengers or fuel, depending on demand.

(strich:Travel in comfort) Clip-Air’s passenger modules can be transferred straight from the airfield to the train station while passengers sit back and relax. Hover over the image for a bigger view

Travel in comfort Clip-Air’s passenger modules can be transferred straight from the airfield to the train station while passengers sit back and relax.


Travel in comfort Clip-Air’s passenger modules can be transferred straight from the airfield to the train station while passengers sit back and relax.

Aircraft from a pool

Whether the de­mand is there and the mod­u­lar cab­ins guar­an­tee high­er or at least the same rev­enue, how­ev­er, is some­thing that Plöt­ner and oth­er ex­perts are doubt­ful about. In ad­di­tion, the air­lines would have to car­ry out new weight cal­cu­la­tions for each new con­fig­u­ra­tion of the cab­in. Chua is con­fi­dent nonethe­less that a Trans­pose pro­to­type will take off in just a few years’ time. A3 is al­ready in con­tact with the Fed­er­al Avi­a­tion Ad­min­is­tra­tion re­gard­ing ap­proval, he adds. Plöt­ner and his col­leagues are more op­ti­mistic about an idea that al­so takes in­to ac­count the up­com­ing in­di­vid­u­al­iza­tion trend in air trans­port, but does not re­ly on mod­u­lar con­cepts: “My re­sponse to the de­mand for flex­i­bil­i­ty in the fu­ture is to have a large pool of air­craft with dif­fer­ent con­fig­u­ra­tions avail­able at an air­port, so the air­line can sim­ply de­cide based on their book­ing sit­u­a­tion which one they want to use,” says the ex­pert. “We call this an air­craft shar­ing mod­el.” In this sce­nario, the air­craft would no longer be­long to the air­lines, but to a large leas­ing com­pa­ny, for ex­am­ple.

“We be­lieve this mod­el would in­volve rel­a­tive­ly lit­tle al­ter­ation to the trans­port sys­tem—you wouldn’t have to make any ma­jor changes to the jets or the air­ports,” says Plöt­ner. The on­ly rad­i­cal thing about this is the way it changes plan­ning, op­er­a­tions and crew sched­ul­ing for the air­craft serv­ing in the net­work. If all air­lines world­wide agreed to take part and, for ex­am­ple, all Boe­ing 737 air­craft and Air­bus A320 jets were com­bined in one shar­ing pool, the Bauhaus Luft­fahrt re­searchers cal­cu­late that be­tween 20 and 25 per­cent few­er air­craft would be re­quired. “This would leave trans­port ca­pac­i­ty un­changed but open the door to low­er op­er­at­ing costs,” says Plöt­ner. In ad­di­tion, the glob­al air­craft shar­ing mod­el large­ly avoids the cost­ly tran­si­tion to mod­u­lar hard­ware. “Wher­ev­er pos­si­ble, we use things that can be changed via soft­ware: light, dig­i­tal la­bels and dis­plays.” So, in the same way you in­stall an app on a smart­phone, in the fu­ture you might be able to switch a leased air­craft from Lufthansa to easy­Jet with the sim­ple tap of a but­ton.

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