4 ms·
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.you
by 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 agoFWIW 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 agoProp 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 agoI 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 agoThe 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 agoCompare 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 agoThe 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.