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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 engin

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.
      - Robotbeat 7y ago
        The opposite is true. The accelerated airflow over the body of the aircraft actually increases the drag whereas a pusher ingests the boundary layer from the fuselage and the suction also helps keep flow attached. The problem, however, is that turbine engines need a smooth airflow in order to operate efficiently, therefore they aren't suited for pushers as the wings (etc) produce an uneven airflow into the turbine core.
- Retric 7y ago
  Compare the number of propellers on NASA’s version. They have serious backup in the event any single engine fails. Being able to take off with one engine that’s rapidly overheating, does not mean is safe to continue a flight with a single engine. Electric aircraft don’t get lighter in flight because they don’t burn fuel.
  - naikrovek 7y ago
    The power delivered to the rear MOTOR (not engine) is not the same for take-off and cruising. A motor that would overheat at takeoff power won't necessarily overheat at cruise and would be designed not to overheat in an aircraft application. Motor control is not just on or off.
    - Retric 7y ago
      It’s possible that that could be the case, but it’s a poor assumption that it will be the case. Especially as it’s such a useful feature they likely would have mentioned it.
      - naikrovek 7y ago
        It's a very valid assumption. Cruise and takeoff throttle positions are usually quite different.

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.
    - Robotbeat 7y ago
      The opposite is true. The accelerated airflow over the body of the aircraft actually increases the drag whereas a pusher ingests the boundary layer from the fuselage and the suction also helps keep flow attached. The problem, however, is that turbine engines need a smooth airflow in order to operate efficiently, therefore they aren't suited for pushers as the wings (etc) produce an uneven airflow into the turbine core.
Retric 7y ago
Compare the number of propellers on NASA’s version. They have serious backup in the event any single engine fails. Being able to take off with one engine that’s rapidly overheating, does not mean is safe to continue a flight with a single engine. Electric aircraft don’t get lighter in flight because they don’t burn fuel.
- naikrovek 7y ago
  The power delivered to the rear MOTOR (not engine) is not the same for take-off and cruising. A motor that would overheat at takeoff power won't necessarily overheat at cruise and would be designed not to overheat in an aircraft application. Motor control is not just on or off.
  - Retric 7y ago
    It’s possible that that could be the case, but it’s a poor assumption that it will be the case. Especially as it’s such a useful feature they likely would have mentioned it.
    - naikrovek 7y ago
      It's a very valid assumption. Cruise and takeoff throttle positions are usually quite different.