7 ms·

A way around this risk is to come up with a design for which a total power loss is extremely unlikely (i.e. it would take multiple simultaneous non-correlated f

by Centmo 5y ago

A way around this risk is to come up with a design for which a total power loss is extremely unlikely (i.e. it would take multiple simultaneous non-correlated failures in a short span of time). This could be achieved through a distributed battery system where each motor has its own battery physically and electrically separated from the others, and critical flight electronics have their own backup batteries. A ballistic parachute is always nice as a last-resort hail mary.

GravitasFailure 5y ago
Redundancy does go a long way, but that also introduces a lot of extra weight and complexity into an already heavy aircraft and can screw with your weight distribution. The parachute can work since there are ones for air dropping tanks, but at the same time I'm not sure I've seen anyone try to use a parachute as safety equipment on an aircraft this heavy.
- Centmo 5y ago
  Agreed, the distributed battery system does not seem practical for the Lilium design but you could get at least part way there by segmenting the central battery into parallel modules with separate safety disconnects. Not sure about the feasibility of the parachute system, it may be impractical due to the aircraft weight as you mention.
- faeyanpiraat 5y ago
  Would it be enough for the safety batteries at the motors to be only as big as to provide power for the aircraft for an emergency landing? Like for a 30 sec full thrust? That might not bother the weight distribution that much.
  - GravitasFailure 5y ago
    Maybe? Honestly my weight distribution comment is a tad silly since complexity and weight are far bigger concerns, and two that just don't seem to have any avenue to go away.
  - DuskStar 5y ago
    Most batteries don't have the power density to output their entire capacity in 30 (or 60, or 120) seconds though, if I'm remembering correctly.
- reasonabl_human 5y ago
  Cirrus Airframe Parachute System https://en.wikipedia.org/wiki/Cirrus_Airframe_Parachute_System?wprov=sfti1 https://en.wikipedia.org/wiki/Cirrus_Airframe_Parachute_Syst... Unless the eVTOL up for discussion is significantly heavier than the above, looks like a fair approach to last-resort failure recovery

by Centmo 5y ago

GravitasFailure 5y ago

Redundancy does go a long way, but that also introduces a lot of extra weight and complexity into an already heavy aircraft and can screw with your weight distribution. The parachute can work since there are ones for air dropping tanks, but at the same time I'm not sure I've seen anyone try to use a parachute as safety equipment on an aircraft this heavy.

Centmo 5y ago
Agreed, the distributed battery system does not seem practical for the Lilium design but you could get at least part way there by segmenting the central battery into parallel modules with separate safety disconnects. Not sure about the feasibility of the parachute system, it may be impractical due to the aircraft weight as you mention.
faeyanpiraat 5y ago
Would it be enough for the safety batteries at the motors to be only as big as to provide power for the aircraft for an emergency landing? Like for a 30 sec full thrust? That might not bother the weight distribution that much.
- GravitasFailure 5y ago
  Maybe? Honestly my weight distribution comment is a tad silly since complexity and weight are far bigger concerns, and two that just don't seem to have any avenue to go away.
- DuskStar 5y ago
  Most batteries don't have the power density to output their entire capacity in 30 (or 60, or 120) seconds though, if I'm remembering correctly.
reasonabl_human 5y ago
Cirrus Airframe Parachute System https://en.wikipedia.org/wiki/Cirrus_Airframe_Parachute_System?wprov=sfti1 https://en.wikipedia.org/wiki/Cirrus_Airframe_Parachute_Syst... Unless the eVTOL up for discussion is significantly heavier than the above, looks like a fair approach to last-resort failure recovery