Jürgen Greil comments on the May 2023 edition of the Royal Aeronautical Society’s Aerospace magazine, Part 2

Since peo­ple are usu­al­ly com­mut­ing by them­selves and most inner urban and last mile deliv­er­ies are small­er than one cubic metre, lighter than 200 kg and below 50 km per leg, Fly­Now is focus­ing on a mod­u­lar fam­i­ly of air­craft con­sist­ing of a car­go, and a sin­gle and twin seater ver­sion.

All the derivates share the same dri­ve­train with a bat­tery at the bot­tom of the cab­in and coax­i­al rotor pro­pellers, each dri­ven by one of the two four times redun­dant elec­tric motors posi­tioned in one hous­ing, mount­ed on top of the cab­in form­ing a tilt­ing head mech­a­nism via a gim­bal joint.

This leads to the sim­plest form of con­trol­ling the six degrees of free­dom nec­es­sary for safe con­trol of an air­craft, in a three-dimen­sion­al space. Due to the posi­tion­ing of the passenger(s) or car­go and the pack­ag­ing of all the com­po­nents and mod­ules, in such a way that the cen­tre of grav­i­ty is below the dri­ve­train axis, this allows very sim­ple cab­in topol­o­gy which avoids almost all bend­ing moments.

This in return reduces the required pow­er and reduces the size of the dri­ve­train. Besides low weight, accel­er­at­ing a large amount of air at mod­er­ate speeds is always more effi­cient than accel­er­at­ing a small mass of air at high speeds to achieve the same lev­el of thrust. This can be observed in engine appli­ca­tions, which usu­al­ly have engines with very large fan diam­e­ters to move large vol­umes of air at mod­er­ate cruis­ing speed.

The same applies to pro­pellers and heli­copter rotors: the larg­er the diam­e­ter and the low­er the speed and disc load­ing, the high­er the effi­cien­cy and the low­er the noise emis­sions.

FlyNow’s mod­u­lar fam­i­ly of car­go and pas­sen­ger VTOLs, which con­sists of a large low-fre­quen­cy rotor assem­bly, is the most effi­cient, qui­etest and, due to its safe­ty-rel­e­vant topol­o­gy, the most reli­able in this field.

In 2019, Bugat­ti, Lam­borgh­i­ni, Fer­rari, and Bent­ley had a sales vol­ume of around 26,000 units, while Mer­cedes, BMW and Audi togeth­er had more than 6.2 mil­lion units, which cor­re­sponds to a 1: 238 ratio.

To realise a mean­ing­ful air traf­fic over cities, take-off and land­ing hubs are required near or on the most fre­quent­ed places or build­ings, the size of which results on the one hand from the size of the eVTOLs and their ‘stack­a­bil­i­ty’ on the ground as well as their noise emis­sions.

Noise can­not be high­er than the back­ground noise com­mon in cities today. If a pilot is need­ed to fly an eVTOL then there is obvi­ous­ly no busi­ness case since the labour cost plays an impor­tant role, because if 3D mobil­i­ty is to sig­nif­i­cant­ly replace ground-based traf­fic, the num­ber of pilots will not be avail­able.

This does not mean that it is nec­es­sary to fly autonomous­ly, since the effort in terms of sen­sors and soft­ware is much too expen­sive and time-con­sum­ing and makes the cer­ti­fi­ca­tion process at least delayed, if not impos­si­ble.

The sig­nif­i­cant­ly low­er ener­gy den­si­ty of bat­ter­ies can not be com­pen­sat­ed by high effi­cien­cy elec­tric motors, so there is no way around a dras­tic reduc­tion in weight.

Trans­port­ing urgent goods, med­ical and life sav­ing equip­ment and oth­er impor­tant things help to imple­ment new means of trans­port, mit­i­gates tech­ni­cal and finan­cial risks, and proves the ben­e­fits to the com­mon pub­lic.