4 ms·

Those tweets have been deleted, and where’s the evidence of these claims?

Robotbeat 7y ago
Yeah, I see this kind of thing repeated any time Eviation comes up. I don't believe them. The design is sound, if radical in the decision to be mostly-battery. And I think that's partly why people are so skeptical: it definitely goes counter to the industry grain. But it IS the right way to build a serious electric aircraft for regional/commuter passenger travel. Pressurized, extremely high lift-to-drag ratio, very high battery mass fraction, focus on high propulsive efficiency by ingesting boundary layer with the pusher propeller and countering wing-tip vortices with wing-tip propeller. The passenger count is also right, at the limit of FAR-23, allowing you to use a single pilot. The only thing I would do differently is probably have a higher cruise altitude and higher aspect ratio wings (and probably counter-rotating dual-motor pusher propellers) instead of using wing-tip propellers and gettin, but theirs is a valid design choice as well. So much group-think especially with the larger aerospace companies. They insist on hybrids for flight (notice how whenever Airbus or Boeing buy one of these exciting electric flight startups, they all of a sudden switch to hybrid?), which ends up compromising the design and adding a whole new propulsion system to validate and certify. Others have a valid approach of retrofitting electric onto older airframes, but that is not going to get anywhere near the operational efficiencies of a clean-sheet design. And still others insist on VTOL, but I have my doubts as to whether the focus on VTOL by so many of these electric flight startups is going to really be worth it in the end except for niche cases.
- tristanb 7y ago
  The design is "sound" ? It is ridiculous! Those engines are at each end of a wing. That is a 100% no no. They are feet from the ground, and would make one engine out operation impossible. Even someone with a cursory understanding of aerodynamic could see this is a ridiculous design.
  - inflatableDodo 7y ago
    >Those engines are at each end of a wing. That is a 100% no no. I assume they are at the end of the wings on purpose to deliberately interact with the wingtip vortices. The back prop is power, those wingtips are for drag reduction.
  - Robotbeat 7y ago
    Better tell NASA, then, which is building a design (X-57) with the same kind of wing-tip propellers: https://www.youtube.com/watch?v=No9Rq3VE0FI https://www.youtube.com/watch?v=No9Rq3VE0FI The key is that the Alice aircraft is capable of take-off with just the rear propeller. That's possible because electric motors (unlike jet engines) can operate at much higher power for short periods of time. It was addressed recently at the Paris airshow Q&A for Eviation. If a wingtip motor (not engine) fails, the other side is designed to immediately stop (electric motors such as these respond immediately to input) and flight continues with the remaining tail motor. Additionally, electric motors are fundamentally more reliable than jet engines.
    - tristanb 7y ago
      FWIW my thoughts: 1. Rear prop strikes. 2. Wing tip prop strikes. 3. Wing tip inertia 4. Prop wash over a wing is a good thing If (big if) this thing ever flies, it won't be in this form
      - Robotbeat 7y ago
        Prop wash over a wing is good if you're lift-starved at take-off (which you aren't with this design). But otherwise it actually increases drag. Pusher configuration is superior in that you can ingest boundary layer air which has been slowed down by the fuselage and get an increase in efficiency. That efficiency gain is partially why pushers are often used in long-duration drones.
        NickNameNick 7y ago
        I had the impression that pushers were typically less efficient than pullers. A puller takes advantage of the volume behind the prop taken up by the body of the aircraft to offset the loss of air volume caused by accelerating the air (Bernoulli's theorem). A pusher can't do that.
- marvin 7y ago
  Just wanted to say thanks for the insightful comments you have in this thread. Lots of interesting musings on the state of the art.
rootusrootus 7y ago
Try this link: https://twitter.com/BenBrelje_says/status/1064842200910041089 https://twitter.com/BenBrelje_says/status/106484220091004108... I believe tristanb cut & paste his own post from six months ago on this same topic, and it broke the links.
- deleted 7y ago
  [deleted]
tristanb 7y ago
My links were bad - fixed.

Yeah, I see this kind of thing repeated any time Eviation comes up. I don't believe them. The design is sound, if radical in the decision to be mostly-battery. And I think that's partly why people are so skeptical: it definitely goes counter to the industry grain. But it IS the right way to build a serious electric aircraft for regional/commuter passenger travel. Pressurized, extremely high lift-to-drag ratio, very high battery mass fraction, focus on high propulsive efficiency by ingesting boundary layer with the pusher propeller and countering wing-tip vortices with wing-tip propeller. The passenger count is also right, at the limit of FAR-23, allowing you to use a single pilot. The only thing I would do differently is probably have a higher cruise altitude and higher aspect ratio wings (and probably counter-rotating dual-motor pusher propellers) instead of using wing-tip propellers and gettin, but theirs is a valid design choice as well. So much group-think especially with the larger aerospace companies. They insist on hybrids for flight (notice how whenever Airbus or Boeing buy one of these exciting electric flight startups, they all of a sudden switch to hybrid?), which ends up compromising the design and adding a whole new propulsion system to validate and certify. Others have a valid approach of retrofitting electric onto older airframes, but that is not going to get anywhere near the operational efficiencies of a clean-sheet design. And still others insist on VTOL, but I have my doubts as to whether the focus on VTOL by so many of these electric flight startups is going to really be worth it in the end except for niche cases.

tristanb 7y ago
The design is "sound" ? It is ridiculous! Those engines are at each end of a wing. That is a 100% no no. They are feet from the ground, and would make one engine out operation impossible. Even someone with a cursory understanding of aerodynamic could see this is a ridiculous design.
- inflatableDodo 7y ago
  >Those engines are at each end of a wing. That is a 100% no no. I assume they are at the end of the wings on purpose to deliberately interact with the wingtip vortices. The back prop is power, those wingtips are for drag reduction.
- Robotbeat 7y ago
  Better tell NASA, then, which is building a design (X-57) with the same kind of wing-tip propellers: https://www.youtube.com/watch?v=No9Rq3VE0FI https://www.youtube.com/watch?v=No9Rq3VE0FI The key is that the Alice aircraft is capable of take-off with just the rear propeller. That's possible because electric motors (unlike jet engines) can operate at much higher power for short periods of time. It was addressed recently at the Paris airshow Q&A for Eviation. If a wingtip motor (not engine) fails, the other side is designed to immediately stop (electric motors such as these respond immediately to input) and flight continues with the remaining tail motor. Additionally, electric motors are fundamentally more reliable than jet engines.
  - tristanb 7y ago
    FWIW my thoughts: 1. Rear prop strikes. 2. Wing tip prop strikes. 3. Wing tip inertia 4. Prop wash over a wing is a good thing If (big if) this thing ever flies, it won't be in this form
    - Robotbeat 7y ago
      Prop wash over a wing is good if you're lift-starved at take-off (which you aren't with this design). But otherwise it actually increases drag. Pusher configuration is superior in that you can ingest boundary layer air which has been slowed down by the fuselage and get an increase in efficiency. That efficiency gain is partially why pushers are often used in long-duration drones.
      - NickNameNick 7y ago
        I had the impression that pushers were typically less efficient than pullers. A puller takes advantage of the volume behind the prop taken up by the body of the aircraft to offset the loss of air volume caused by accelerating the air (Bernoulli's theorem). A pusher can't do that.
marvin 7y ago
Just wanted to say thanks for the insightful comments you have in this thread. Lots of interesting musings on the state of the art.

rootusrootus 7y ago

Try this link: https://twitter.com/BenBrelje_says/status/1064842200910041089 https://twitter.com/BenBrelje_says/status/106484220091004108... I believe tristanb cut & paste his own post from six months ago on this same topic, and it broke the links.

deleted 7y ago
[deleted]

tristanb 7y ago

My links were bad - fixed.