FLYER Forums

http://www.bbc.co.uk/news/technology-38967235

Apols of already posted - didn't find it elsewhere..

One engine failure and you're stuffed.

PMSL 31 miles yeah good one, sign me up.

VRB_20kt wrote:One engine failure and you're stuffed.

Probably still a great deal safer than in most cars

Why do you say that, John? (@johnm )

VRB_20kt wrote:One engine failure and you're stuffed.

2 engines on each corner and 2 independent electric systems:
http://www.ehang.com/ehang184

Johnm has probably experienced the driving in Dubai.....

Dave W wrote:Why do you say that, John? (@johnm )

Because statistically the appalling standard of driving in most places is more likely to kill you than any mechanical failure.

Well, yes - but some reasons for that are the safety and regulatory systems in place to ensure that fail-safe designs are taken to market. For this type of air vehicle, those aren't too mature yet - but I bet it's coming.

It would be fascinating (but no doubt unlikely!) to get sight of the eHang safety case, and in particular how much power each motor demands in the hover (especially high DA - e.g. Dubai) and whether there is sufficient margin for control in the event of a motor failure throughout the intended flight envelope.

A fascinating job for some in the Dubai CAA, regardless.

2 engines on each corner and 2 independent electric systems:
http://www.ehang.com/ehang184

I stand corrected.

However, don't forget that having two motors a corner isn't the whole story; it's not an inherent redundancy.

The motors provide lift and control together. In the event of a motor failure, the remaining motor on that corner not only has to maintain balanced lift, but also needs sufficient thrust margin to maintain control of the aircraft.

I've no idea if the eHang design covers this - presumably it does.

Edit: Re-reading the BBC report at the OP, it seems it's not the DCAA looking at this, but rather the Dubai Roads and Transportation Agency. Hmm.

Their website says it has a 100kg, payload, 241kg net weight, so MAUW of 341kg.
Each motor is 152kW.
There is a stated 100% redundancy, so max 608 kW of power available (4 of 8 motors).
So a power to weight ratio of 1783W/kg
A Robinson R22 has a ratio of 223W/kg
So that seems (on the face of it) pretty healthy.

Of course - this is "back of a fag packet" stuff, I don't know the efficiency of any part of it and their safety case may also assume one pylon has failed (losing perhaps 50% power, as the opposite corner would presumably also have to power down to compensate).

If it did that (opposite corner powering down) there'd be no 3 axis control - so I doubt that's a mitigation.

As above, I suspect you're misinterpreting the available lift redundancy.

Dave W wrote:A fascinating job for some in the Dubai CAA, regardless.

Given the head of Emirates is the head of the GCAA is the head of the local safety board is going to have a hand in any company involved in this I'm not entirely sure it's going to get the regulatory scrutiny it deserves.

There will be those who think this is wonderful, the way of the future perhaps, but will it be 'The Jetsons' or 'Blade Runner'?
Whichever, it's not for me. I like aeroplanes, flying machines with wings. Even acknowledging that the pilot is arguably the weak link in the system I like a (capable) pilot with his life on the line up front.