This article first appeared in the May 2018 edition of our free newsletter, to subscribe click here

As part of the white paper I wrote on the aerial urban mobility market I had the chance to review over 60 concepts. Most of which rely on lift rotors, or vectored thrust, for some of their flight envelope. In the white paper I touch on some of the problems with this approach but there are specifics that are useful to examine.

I am not a flight dynamics expert (as the following may confirm) but a few things do appear to be readily apparent.

This is one train of thought:

  1. there is a reliance on multiple lift rotors or vectored thrust for take off and landing
  2. The highest number of lift rotors on any aircraft previously certified for civil use is two
  3. My assessment is more than two lift rotors require some form of software control or stability augmentation
  4. Software in critical aircraft systems is very, very expensive to certify

This is another:

  1. helicopters mitigate an engine failure through auto rotation
  2. If you do not have large rotors that allow this you need an alternative mitigation
  3. The most likely mitigation is a BRS system (ballistic parachute system)
  4. For a BRS system to work you need speed and time
  5. In a hover close to the ground this will not work
  6. A BRS system is heavy anyway, with projected battery capacity this must be a severe detriment to aircraft performance

For electric multi rotor systems the following train of thought then occurs:

  1. what if each rotor is fed by a totally independent shielded bank of batteries, can you argue that total power loss is practically impossible?
  2. Does that mean if you have 8 rotors you need 8 independent charging points?
  3. Does each power system has to be isolated inside an independant faraday cage type protection to mitigate lightning strike?
  4. This is giving me a headache, why don’t I just go buy a Robinson R44 helicopter?
  5. For the amount of money I would have to invest in developing a new vehicle of this type I could buy the Robinson helicopter company…….

So, do I have this all wrong? Will multirotor vehicle concepts prove to be simple to certify and will they dominate the market? As I briefly touch on in the white paper, any aerial urban mobility vehicle that makes it to market has to compete with the only existing aerial urban mobility vehicle – the helicopter. Any successful concept would have to be safer/quieter/cheaper/faster/longer range than a helicopter. How many are?