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So Lilium states that its jet is a tailless design. Now, you can see that it has engines on both sides of the centerline.

Lets imagine that all of the engines on one side fail, how does it counter that asymmetric thrust?

We could speculate that their jet actually has a tail, if you look at the landing gear (It is kinda shaped like a vertical stabilizer - ignoring the fact that I cannot see a rudder there), but even then, it does not seem big enough to counter that thrust.

The winglets could be used as one, but again, I do not see any rudders there.

So how does it counter asymmetric thrust?

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    $\begingroup$ Has this aircraft actually flown? If not arn't we asking for a theoretical answer to a theoretical question? $\endgroup$
    – Jamiec
    Oct 5, 2022 at 8:08
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    $\begingroup$ @Jamiec: It has, actually. It is currently in prototype flight trials. $\endgroup$ Oct 5, 2022 at 9:17
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    $\begingroup$ My assumption is: it doesn't. Most multi-engine airplanes are designed to survive the failure of one engine, maybe two. The situation you refer to requires 18 engine failures. $\endgroup$ Oct 5, 2022 at 9:19
  • $\begingroup$ It did test-fly indeed. According to lilium's web page the systems are built redundant so a case like that should never happen - obviously unless something definitely worse has happened but then there would be another issue to be managed. Anyway in that case the full aircraft parachute should allow a safe landing. $\endgroup$
    – sophit
    Oct 5, 2022 at 10:18
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    $\begingroup$ @sophit it sounds like you can actually write a referenced answer then. (referring to "According to their web page") $\endgroup$
    – Jamiec
    Oct 5, 2022 at 10:25

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Since Lillium's "engines" are electric ducted fans under computer control (for thrust control and balancing for yaw, and pitch when in hover) anyway, it would be trivial for the computer to match thrust reduction on the opposite wing to any reasonable level of failures.

Say two fans on the left wing ingest parts of a bird big enough to destroy the fan disk itself -- the computer can detect the loss of load on those two motors, shut them down, and either shut down corresponding motors on the right wing, or reduce thrust on all the right wing fans to compensate. As noted in comments on the question, the two fan arrays on the canard can also be used in compensating yaw, with less authority but also with less effect on overall thrust.

Good design would suggest the aircraft be designed to hover with at least two (or more) fans out on each wing or canard, as well, just because one of the most likely failures (FOD/bird strike) has a high chance of destroying more than one fan simultaneously due to their close-packed installation.

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  • $\begingroup$ so they are basically betting that a situation of one side failing completely never occurs $\endgroup$ Oct 5, 2022 at 15:20
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    $\begingroup$ @VincentCerowski Just as all those piloted quadcopters and even the V-22 Osprey do (yes, it's got crossover shafts and gearing, but if the gearbox in one engine fails in hover, they're done). $\endgroup$
    – Zeiss Ikon
    Oct 5, 2022 at 15:38
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    $\begingroup$ @VincentCerowski: Just like conventional aircraft are betting that all 4 engines, all 3 hydraulic systems, all 3 electrical systems, and all 5 flight computers failing while all three pilots simultaneously die of a heart attack never occurs. $\endgroup$ Oct 5, 2022 at 21:17

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