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I'm glad people take on crazy projects and push them to some level of completion. That's how we learn and progress overall. Unfortunately for the people who d

by z9znz 4y ago

I'm glad people take on crazy projects and push them to some level of completion. That's how we learn and progress overall. Unfortunately for the people who do follow through with unconventional ideas, actually getting a thing to work doesn't necessarily mean (financial) success. In this case, there's really one big benefit at the cost of a lot of negatives. It can VTOL/VSTOL. Most fixed wing airplanes cannot do that. So it can theoretically take off in a parking lot or a helipad or a small field. That's really the only plus as I can tell. The negatives are many compared to a traditional plane. In no particular order: Less efficient cruising due to much more drag from all the ducts and engines. Much less likely to fly with engine failures as they can dramatically affect control (since they are essential parts of the control system). Less control surface stability with mechanical or hydraulic failures. Those engines mounted on the surfaces hanging off a hinge are very heavy, and in some failure cases they would hang low and create immense drag. Yaw (rotational) control is highly dependent on working engines on both sides. The glide ratio of the aircraft would be very poor with all the drag, even assuming the surfaces were still controllable (not hanging). I didn't see, but I assume a parachute is part of the plan for this. I doubt it could pass certifications (at least to carry passengers) without it.

engineer_22 4y ago
You repeatedly mention engines, but I'd point out there are no engines on this craft. This craft has electric motors. I don't know if electric motors are more reliable than ICE, but I speculate that they are. ------ Edit, my opinion below: VTOL is a HUGE WIN. It's the holy grail of flight. Fixed wing aircraft are inconvenient because they need a mile of flat blacktop for takeoff and landing. Affordable eVTOL craft could change general aviation forever. The problem with helicopters is insane maintenance overhead and low fuel efficiency. The problem with fixed wing is you can't land it in your back yard. EVTOL is interesting in that it could bridge the gap between these two to provide a personal aircraft that has the best of both. Napkin math shows it's possible, and we're seeing some really cool products now.
- a_shovel 4y ago
  For most people, "motor" and "engine" are synonyms. Is there a technical difference between the two terms?
  - yodon 4y ago
    There are people who feel strongly that one is only for electric, on non-electric, or combustion, or thermodynamic, or other classes of thing, kind of like a boat-vs-ship distinction. It is certainly more common to talk about an electric motor than an electric engine, for example. That said, both terms have been used for a very long time for a very wide range of overlapping things. MIT has a nice history[0] of the words and why they are essentially synonyms in most cases (with engine being more appropriate to use in non-mechanical contexts like search engines and economic engines and motor being more appropriate to use as a gerund like motoring through something or motoring around the countryside). [0] https://engineering.mit.edu/engage/ask-an-engineer/whats-the-difference-between-a-motor-and-an-engine/ https://engineering.mit.edu/engage/ask-an-engineer/whats-the...
  - andyferris 4y ago
    I thought the term was originally "motor engine" (a piece of engineering that produces motion) in the same way we can have a "compute engine" or a "siege engine" or a similar name for any other _ingenious_ creation. From there we tend to shorten it to either motor or engine. Perhaps in current times people here the terms "combustion engine" and "electric motor" most commonly and assume there is an implied distinction.
- balderdash 4y ago
  The VTOL only matters if it’s cheap. Most of the airports in the US are lightly used because general aviation is expensive, not because people are thinking “I would buy/charter a plane, but driving 20min to the local airfield is just not convenient enough”. Typical general aviation aircraft (which this seems comparable to) need <1/4 mile runway (e.g. a Cessna 172 is less than 1000ft) which in the US means ~20k available airports. My point being, the reason those airports are lightly used is driven by cost not that they inconvenient.
crhulls 4y ago
I'm not sure if all your comments are fair. For example, fly by wire is extremely reliable, and the large number of engines provides huge redundancy and arguably much more safety in certain constrained environments. If a plane engine fails, you can glide, but you need a nearby road or field. If a helicopter engine fails, you can auto-rotate but have very little margin for error and need forward momentum. There are also more single point failure parts in both helicopters and fixed wing planes. If you get a partial failure on a Lilium you probably have much more flexibility to do an emergency landing as you have the other engines for control and redundancy. I'm sure it will take a while to work the kinks out, and sure there are tradeoffs, but I'm not sure this is a jack of all trades master of none situation. I could see the jet carving out its own niche. And yes, it could be a huge flop, just sharing a counterpoint.
- _hypx 4y ago
  All VTOL aircraft have the same issue: Insane energy consumption. There's a reason why quadcopters have flight times measured in minutes, and why helicopters never came close to displacing small aircraft. This will be no different.
  - zlsa 4y ago
    Quadcopters have short flight times because they need to use batteries. Commercial helicopters regularly have 3+ hours of flight time. (Of course, Lillium's aircraft is battery-powered. But it's not fair to say that an aircraft capable of VTOL will always have a dramatically reduced endurance compared to a non-VTOL aircraft, especially since this one can transition to fixed-wing flight.)
    - _hypx 4y ago
      That's the point. Lillium is also battery powered. It will have minutes of runtime in all likelihood.
      - ReactiveJelly 4y ago
baybal2 4y ago
jasonwatkinspdx 4y ago
I think you're mistaken about a few things. > Less efficient cruising due to much more drag from all the ducts and engines. So, I read through some of Boeings research in this area years ago. The array of fans ends up acting like an insanely high bipass ratio turbofan. In the case of hybrid aircraft the combination is more efficient when cruising. The efficiency of a fan producing a given thrust or drag goes up with disk area, as it can spin slower and the local speed mismatch to the airstream is less. The array of fans acts like a giant disaggregated disk in this regard. > Much less likely to fly with engine failures as they can dramatically affect control (since they are essential parts of the control system). These are electric motors and batteries. Electric motors are extremely reliable, and in this case we have a high degree of redundancy. This thing is almost certainly more reliable than a single engine helicopter. > Yaw (rotational) control is highly dependent on working engines on both sides. The flaps can help with that, it's not solely reliant on differential thrust. There's plenty of precedent for yaw control of flying wings. > The glide ratio of the aircraft would be very poor with all the drag, even assuming the surfaces were still controllable (not hanging). You can't evaluate aerodynamics by eyeball, and that goes doubly for active devices like these wings. It's the net circulation pattern around the wing that matters, and you have no actual information about that, just assumptions. Likewise that there's some novel fault problem with a movable flap just because it has fans on it. You realize airliners have huge flaps that deal with much more substantial forces?
- ehnto 4y ago
  On top of being reliable, an array of electric motors in a control loop will be able to compensate for a loss of one or more motors. I imagine this thing could probably fly with a number of it's motors offline.
14 4y ago
I agree with your assessment but also think with the size of this plane it is a good candidate for the parachute system some planes already have. Maybe making that a requirement is a good middle ground.
anovikov 4y ago
As for the engine failures, it's a lot safer because it has so many of them. It can fly with engine out, probably counterbalanced with another engine being switched off on the other side.

by z9znz 4y ago

engineer_22 4y ago

You repeatedly mention engines, but I'd point out there are no engines on this craft. This craft has electric motors. I don't know if electric motors are more reliable than ICE, but I speculate that they are. ------ Edit, my opinion below: VTOL is a HUGE WIN. It's the holy grail of flight. Fixed wing aircraft are inconvenient because they need a mile of flat blacktop for takeoff and landing. Affordable eVTOL craft could change general aviation forever. The problem with helicopters is insane maintenance overhead and low fuel efficiency. The problem with fixed wing is you can't land it in your back yard. EVTOL is interesting in that it could bridge the gap between these two to provide a personal aircraft that has the best of both. Napkin math shows it's possible, and we're seeing some really cool products now.

a_shovel 4y ago
For most people, "motor" and "engine" are synonyms. Is there a technical difference between the two terms?
- yodon 4y ago
  There are people who feel strongly that one is only for electric, on non-electric, or combustion, or thermodynamic, or other classes of thing, kind of like a boat-vs-ship distinction. It is certainly more common to talk about an electric motor than an electric engine, for example. That said, both terms have been used for a very long time for a very wide range of overlapping things. MIT has a nice history[0] of the words and why they are essentially synonyms in most cases (with engine being more appropriate to use in non-mechanical contexts like search engines and economic engines and motor being more appropriate to use as a gerund like motoring through something or motoring around the countryside). [0] https://engineering.mit.edu/engage/ask-an-engineer/whats-the-difference-between-a-motor-and-an-engine/ https://engineering.mit.edu/engage/ask-an-engineer/whats-the...
- andyferris 4y ago
  I thought the term was originally "motor engine" (a piece of engineering that produces motion) in the same way we can have a "compute engine" or a "siege engine" or a similar name for any other _ingenious_ creation. From there we tend to shorten it to either motor or engine. Perhaps in current times people here the terms "combustion engine" and "electric motor" most commonly and assume there is an implied distinction.
balderdash 4y ago
The VTOL only matters if it’s cheap. Most of the airports in the US are lightly used because general aviation is expensive, not because people are thinking “I would buy/charter a plane, but driving 20min to the local airfield is just not convenient enough”. Typical general aviation aircraft (which this seems comparable to) need <1/4 mile runway (e.g. a Cessna 172 is less than 1000ft) which in the US means ~20k available airports. My point being, the reason those airports are lightly used is driven by cost not that they inconvenient.

crhulls 4y ago

I'm not sure if all your comments are fair. For example, fly by wire is extremely reliable, and the large number of engines provides huge redundancy and arguably much more safety in certain constrained environments. If a plane engine fails, you can glide, but you need a nearby road or field. If a helicopter engine fails, you can auto-rotate but have very little margin for error and need forward momentum. There are also more single point failure parts in both helicopters and fixed wing planes. If you get a partial failure on a Lilium you probably have much more flexibility to do an emergency landing as you have the other engines for control and redundancy. I'm sure it will take a while to work the kinks out, and sure there are tradeoffs, but I'm not sure this is a jack of all trades master of none situation. I could see the jet carving out its own niche. And yes, it could be a huge flop, just sharing a counterpoint.

_hypx 4y ago
All VTOL aircraft have the same issue: Insane energy consumption. There's a reason why quadcopters have flight times measured in minutes, and why helicopters never came close to displacing small aircraft. This will be no different.
- zlsa 4y ago
  Quadcopters have short flight times because they need to use batteries. Commercial helicopters regularly have 3+ hours of flight time. (Of course, Lillium's aircraft is battery-powered. But it's not fair to say that an aircraft capable of VTOL will always have a dramatically reduced endurance compared to a non-VTOL aircraft, especially since this one can transition to fixed-wing flight.)
  - _hypx 4y ago
    That's the point. Lillium is also battery powered. It will have minutes of runtime in all likelihood.
    - ReactiveJelly 4y ago

baybal2 4y ago

jasonwatkinspdx 4y ago

I think you're mistaken about a few things. > Less efficient cruising due to much more drag from all the ducts and engines. So, I read through some of Boeings research in this area years ago. The array of fans ends up acting like an insanely high bipass ratio turbofan. In the case of hybrid aircraft the combination is more efficient when cruising. The efficiency of a fan producing a given thrust or drag goes up with disk area, as it can spin slower and the local speed mismatch to the airstream is less. The array of fans acts like a giant disaggregated disk in this regard. > Much less likely to fly with engine failures as they can dramatically affect control (since they are essential parts of the control system). These are electric motors and batteries. Electric motors are extremely reliable, and in this case we have a high degree of redundancy. This thing is almost certainly more reliable than a single engine helicopter. > Yaw (rotational) control is highly dependent on working engines on both sides. The flaps can help with that, it's not solely reliant on differential thrust. There's plenty of precedent for yaw control of flying wings. > The glide ratio of the aircraft would be very poor with all the drag, even assuming the surfaces were still controllable (not hanging). You can't evaluate aerodynamics by eyeball, and that goes doubly for active devices like these wings. It's the net circulation pattern around the wing that matters, and you have no actual information about that, just assumptions. Likewise that there's some novel fault problem with a movable flap just because it has fans on it. You realize airliners have huge flaps that deal with much more substantial forces?

ehnto 4y ago
On top of being reliable, an array of electric motors in a control loop will be able to compensate for a loss of one or more motors. I imagine this thing could probably fly with a number of it's motors offline.

14 4y ago

I agree with your assessment but also think with the size of this plane it is a good candidate for the parachute system some planes already have. Maybe making that a requirement is a good middle ground.

anovikov 4y ago

As for the engine failures, it's a lot safer because it has so many of them. It can fly with engine out, probably counterbalanced with another engine being switched off on the other side.