That depends on whether all four props have one power source/motor or if they are individually powered. If it's the former, it crashes because it has no auto-rotation ability. If it's the latter and one fails, it probably crashes unless it can cut power to the opposite prop and still have enough on the remaining two to make a semi-controlled descent.
The difference is plummeting like a dead duck or like a wounded one.
No, since there are four propellers which serve partially redundant functions. Lose one, and you still have three propellers serving partially redundant functions. By altering the outputs in just the right way, you could compensate for the loss of one enough for a controlled landing.
What I am meaning is that this new design can be thought of as more comparable to a helicopter than a conventional fixed wing aircraft.
Loosing a rotar on either this drone or a helo is "not good"; with a helo, you may or may not be able to have a semi controlled crash landing via the auto-gyro, while with the "drone" you may or may not have the ability to run on three engines for a period, but neither craft will glide to any degree like a plane might..
Obviously thats not going to be a show stopper for the new design, in the same way as its not a show stopper for helicopters just a "consideration" thats all...
It would be interesting to see if they could intergrate the four rotar idea into a sort of "flying wing" or saucer design although a similar saucer idea was tried by Avro Canada back in the 1950's.
![[Linked Image]](http://www.roadabletimes.com/images/avro_VZ9V-4.jpg)
More recently there was also the "sky car"
![[Linked Image]](http://www.editinternational.com/images/gallery/08-saucer_low.jpg)
(Not sure whether the above photo is genuine or a mock-up for promotional purposes]
![[Linked Image]](http://i492.photobucket.com/albums/rr288/Bwnci/welsh-flag-large-anim.gif)
