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The airship returns: what surprises are left in store?

Olivier Doaré
Professor in fluid mechanics at ENSTA (IP Paris)
Robin Le Mestre
PhD in Fluid and Solid Mechanics
Jean-Sébastien Schotté
Research fellow at ONERA
Key takeaways
  • Airships (i.e. blimps) could make a comeback, as they have undeniable advantages over other means of transport.
  • However, because of their lightness, they are subject to hazards and bad weather: more precise means of prediction and control must therefore be developed.
  • Computer simulation, the design of more resistant materials and wind prediction tools are making it possible to improve the new airships.
  • They will not replace large-scale air transport but can be useful for tourism or inter-regional travel.
  • Several companies, such as Flying Whales and Thales, are increasingly interested in the new airships.

Air­ships are often per­ceived as a tech­nol­o­gy from anoth­er era. When they came onto the mar­ket at the end of the 19th Cen­tu­ry. This new means of trans­port was a world­wide rev­o­lu­tion: in these enor­mous bal­loons, it was pos­si­ble to cross the Atlantic in less than 60 hours and to trav­el at speeds of over 130 km/h. 

How­ev­er, this tech­nol­o­gy did not come to a hap­py end. The Hin­den­burg dis­as­ter in 1937 – a colos­sus bare­ly small­er than the Eif­fel Tow­er that burst into flames in the skies over New Jer­sey – is still seen as trau­mat­ic even today. How­ev­er, air­ships have unde­ni­able advan­tages, and this acci­dent has nev­er called them into question. 

Olivi­er Doaré, a pro­fes­sor of flu­id mechan­ics, direct­ed Robin Le Mestre’s the­sis aimed at mod­el­ling the effects of exter­nal and inter­nal flu­ids on the dynam­ic behav­iour of air­ships in flight1. This research is there­fore in line with a poten­tial revival of air­ships, as Olivi­er Doaré main­tains: “Since this dis­as­ter, there has been a cen­tu­ry of tech­no­log­i­cal progress.”

Dependence on the wind

The Hin­den­burg was inflat­ed with hydro­gen, a high­ly flam­ma­ble gas. The Ger­mans did not choose to use this gas by chance: heli­um, which is much less flam­ma­ble, was already rec­om­mend­ed at the time, but was much hard­er to find. The lack of sup­ply was due to the geopo­lit­i­cal con­text of the peri­od. The Unit­ed States, which had a vir­tu­al monop­oly of the heli­um mar­ket, want­ed to keep its lead in this technology.

“Nowa­days, the vast major­i­ty of air­ship projects are inflat­ed with heli­um for safe­ty rea­sons,” explains Olivi­er Doaré, “even though, for the same lift force, this requires a greater vol­ume of gas than with hydro­gen”. How­ev­er, the idea of a hydro­gen-fuelled air­ship has not been com­plete­ly aban­doned: “In the case of elec­tric propul­sion pro­vid­ed by a fuel cell, hydro­gen could be the car­ri­er gas and the fuel at the same time,” sug­gests Robin Le Mestre. 

The Hin­den­burg dis­as­ter (CC).

These two gas­es are used because they are lighter than air. “The air­ship is self-sup­port­ing thanks to Archimedes’ thrust (in oth­er words, buoy­an­cy),” explains Robin Le Mestre, “so it requires almost no ener­gy to keep it in flight. This is a con­sid­er­able advan­tage, espe­cial­ly in the cur­rent eco­log­i­cal con­text, but it does imply con­straints that must be tak­en into account. “Because of its light­ness, the machine will be high­ly exposed to the vagaries of the weath­er,” admits Robin Le Mestre. 

To mark the return of air­ships, it will there­fore be nec­es­sary to mas­ter these already iden­ti­fied mete­o­ro­log­i­cal con­straints. “This is the whole point of my the­sis,” says the PhD. “To go against the action of the wind, we need much more pre­cise means of pre­dic­tion and control.”

The poten­tial of this the­sis has also attract­ed the atten­tion of the French aero­space research cen­tre, ONERA. Jean-Sébastien Schot­té, a research offi­cer at ONERA, helped devel­op these pre­dic­tion tools. Accord­ing to him, “bet­ter mod­el­ling of the cou­plings between the air­ship’s deformable struc­ture and the flow of the sur­round­ing gas­es will make it pos­si­ble to improve sim­u­la­tions of the air­ship’s in-flight behav­iour, for exam­ple in the face of gusts of wind, and this could help in the design and siz­ing of future air­ship projects.”

Better prediction

In addi­tion to these advances in the field of dig­i­tal sim­u­la­tion, oth­er progress has been made in the design of mate­ri­als: “The mate­ri­als used today are more resis­tant, more water­tight, while being lighter,” says Jean-Sébastien Schot­té. “More­over, wind pre­dic­tion tools exist and are very effec­tive,” says Olivi­er Doaré. LiDAR tech­nol­o­gy, for exam­ple, these wind pre­dic­tion lasers, which are cur­rent­ly use­ful for opti­mis­ing the con­trol of wind farms, could also be use­ful for air­ships. “How­ev­er, to pre­dict the actu­al tra­jec­to­ry of an air­ship, and thus ensure its safe­ty, a mul­ti­tude of envi­ron­men­tal fac­tors must be tak­en into account,” says the pro­fes­sor. “So much so that it is dif­fi­cult, with today’s resources, to per­fect­ly sim­u­late the behav­iour of the craft on a computer.”

In flu­id mechan­ics, the Navier-Stokes equa­tions are fun­da­men­tal. They allow us to rep­re­sent the most com­plex move­ments of flu­ids – and there­fore many of these envi­ron­men­tal fac­tors – but they are far too cum­ber­some to be used in com­plete sim­u­la­tions of the in-flight behav­iour of large flex­i­ble struc­tures such as air­ships. “The first step was there­fore to sim­pli­fy the Navier-Stokes equa­tions to retain only the essen­tial ele­ments,” explains Robin Le Mestre. “By pos­tu­lat­ing hypothe­ses on each inter­ac­tion to be stud­ied, we were able to for­mu­late sim­pli­fied, but nev­er­the­less real­is­tic, equa­tions in order to be able to mod­el the sys­tem and its oper­a­tion through a set of math­e­mat­i­cal oper­a­tors, which can be digitised.”

Air­ships are self-sup­port­ing thanks to their buoy­an­cy so require almost no ener­gy to stay in flight.

With this sim­pli­fi­ca­tion, the researchers were able to offer a real­is­tic sim­u­la­tion that could be accessed by rapid cal­cu­la­tions. In the long term, the engi­neers hope to be able to adapt the con­trols of the air­craft to real-life sit­u­a­tions. “A plane has so much pow­er, because of its weight and its engines, that if the pilot wants to go left, he takes the con­trols and, what­ev­er the wind and his behav­iour, he will go left,” says Olivi­er Doaré. An air­ship will be great­ly affect­ed by the wind, and its engines may not be suf­fi­cient. There is a greater inter­est in com­bin­ing our knowl­edge of the effects of the wind with that of the craft’s controls. 

The research work in progress, of which Robin Le Mestre’s the­sis is a part, there­fore aims to help man­u­fac­tur­ers opti­mise the design of air­ships, for exam­ple by enabling them to devel­op tools for pre­dict­ing con­trols in real time based on wind data.

A specific use

Size, impres­sive as it is, remains a draw­back to the poten­tial use of air­ships. Blimp mod­els are inflat­ed bal­loons with a min­i­mum of struc­ture. The advan­tage of this type of mod­el lies not in the safe­ty aspect, but in its pay­load. How­ev­er, in com­par­i­son with an aero­plane, for the same num­ber of pas­sen­gers or goods, the vol­ume required will be much greater. “From a per­son­al point of view,” admits Olivi­er Doaré, “I don’t think that the air­ship of tomor­row will replace the plane. First­ly because of the weight of the aero­nau­ti­cal indus­try, but also because of the dis­ad­van­tage of the size of the structures.”

Indeed, an air­port requires a fair­ly large space to accom­mo­date air­craft. For a fleet of air­ships, the space required would be “insane”. Pas­sen­ger trans­port will only be pos­si­ble on a small scale and could be ben­e­fi­cial in a few sit­u­a­tions: “From a touris­tic point of view, the air­ship can offer ser­vices sim­i­lar to a hot-air bal­loon ride,” says Robin Le Mestre. As far as trans­port is con­cerned, there is a grow­ing inter­est in inter-region­al trav­el, or to areas with­out air­ports, such as many islands.

Aerostats: the large fam­i­ly of airships 

Air­ships are machines that belong to the fam­i­ly of aerostats. This fam­i­ly includes hot-air bal­loons and teth­ered bal­loons. Both of these devices use tech­nol­o­gy sim­i­lar to that of air­ships, and the results of this the­sis can also be applied to them. 

Teth­ered bal­loons, for exam­ple, are used for obser­va­tion mis­sions. They allow sur­veil­lance of areas for mil­i­tary, eco­log­i­cal, topo­graph­i­cal, or sim­ply fish­eries con­trol pur­pos­es. They are also use­ful for com­mu­ni­ca­tions pur­pos­es. What is more, once deflat­ed, their light­ness allows for rapid trans­port and deploy­ment in sen­si­tive areas. 

Con­trol­ling the behav­iour of the craft in bad weath­er, while being able to pre­dict it, would give them the advan­tage of great sta­bil­i­ty in the air. This char­ac­ter­is­tic, com­bined with the low amount of ener­gy need­ed to keep them in the air, makes them very use­ful, even in the face of their com­peti­tors, the drones.

“The tech­nol­o­gy is not intend­ed to replace large-scale pas­sen­ger air trans­port, but its many advan­tages make it use­ful in many oth­er areas. Air­ships can still car­ry sev­er­al dozen tonnes,” he says. They will be use­ful for spe­cif­ic sec­tors, espe­cial­ly those where time is of lit­tle importance.

Visu­al of an air­ship from the start-up com­pa­ny Fly­ing Whales (cred­it: Fly­ing Whales).

The com­pa­ny Fly­ing Whales, for exam­ple, is inter­est­ed in this the­sis. “The com­pa­ny wants to devel­op a pro­to­type air­ship in a few years’ time, for trans­port­ing loads in inac­ces­si­ble areas, such as forests in moun­tain­ous regions,” adds Robin Le Mestre. Trans­port­ing wood to an inac­ces­si­ble for­est by truck in this type of craft will be more effi­cient than by heli­copter, for which the stor­age space is small­er and the jour­ney more expensive. 

The com­pa­ny Thales, in part­ner­ship with ONERA, has also launched the “Stra­to­bus” project2, an air­ship designed to fly in the stratos­phere. This air­ship will ful­fil mis­sions that are com­ple­men­tary to those of satel­lites, in a sur­veil­lance, com­mu­ni­ca­tion and defence func­tion. It should be not­ed that many projects are cur­rent­ly flour­ish­ing in indus­try: air­ships are there­fore not yet finished!

Pablo Andres
1Le mestre, R. Mod­éli­sa­tion des effets de flu­ides externes et internes sur le com­porte­ment dynamique des dirige­ables flex­i­bles. (Insti­tut poly­tech­nique de Paris, 2022).

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