And one of these multicopter things needs more energy still compared to a helicopter, they literally brute force themselves into the air.
There will never be large numbers of these things flying around the city (or anywhere else) due to noise. Just look at how offended people get by the noise of an occasional helicopter or light aircraft (see the tortuous noise abatement procedures at some small airfields that only have half a dozen movements a day). Each of these things will have 8 tiny propellers, running at high RPM, all slightly out of sync because they are fixed pitch and changing RPM is used to balance the machine – so all sorts of weird beat frequencies on machine that sounds like a loud, angry bee. You’re never even going to have tens of them over a city, let alone thousands due to the ungodly racket they will make from which there will be absolutely no refuge.
That’s before we get to the inability to autorotate (a BRS helps but there will be a gap the BRS won’t cover, and since the aircraft is uncontrollable once under the chute, it’s quite likely to land on something/someone doing damage).
I’m pretty unconvinced by all these various people proferring quad and hex copters as somehow the way we’ll all have flying cars.
alioth wrote:
I’m pretty unconvinced by all these various people proferring quad and hex copters
Just look how ridiculously simple drones such as DJI are to control, and how stable they are.
alioth wrote:
… they brute force themselves into the air … machine that sounds like a loud, angry bee.
“Helicopters don’t fly. They beat the air into submission.”
If only CGI could fly…
This CGI had it’s first flight 2 days ago:
Archie wrote:
Why would you want a single rotor system? A multi-rotor system would solve a lot of the current issues with helicopters, such as vibration, rotor/engine failure, tail rotor failure, mast bumping, control difficulty, etc.
Undoubtedly, but these companies that are trying to hawk these machines (and this has been going on since the days of Moller) are all trying to paint a future where traffic jams are a past thing as we all float by in our inexpensive flying quad/hexcopters.
The reality is that it won’t fly (pardon the pun) and you’ll never have thousands of these things flying over a city due to the sheer racket from which there will be no escape. A multi-rotor system would still have all the issues of a helicopter, but add to them. It won’t do away with vibration issues, and the multicopter idea won’t scale because you can’t make the propellers very big and still have them fixed pitch with lift control by variable RPM. You now have 4 or more motors that can fail instead of 1 or 2 and 4 rotors that can fail – a rotor on a multicopter can fail just like a tail rotor on a helicopter. You now have vibration issues caused by the multiple motors all running at slightly different speeds to control the machine causing beat frequencies, and if you avoid this by interlinking all the rotors and using variable pitch for thrust control, you’ve now got something more complex than a single rotor helicopter so you’ve not solved anything. Also many engines and small propellers is less efficient (and likely much noisier) than few engines and large rotors. In forward flight, you’re probably not going to get so much benefit from translational lift with lots of tiny rotors instead of few large rotors. They also cannot autorotate.
I just don’t see the touted “everyone will be beating traffic congestion” hype that the makers of these things seem to be pushing ever coming true. The noise problem will kill it dead before even we get onto technical issues. As I said, just look at any small airfield – a list of noise abatement procedures as long as your arm at airfields with maybe a dozen movements a day. No one will accept thousands of machines that sound like angry bees buzzing over their city.
Archie wrote:
This CGI had it’s first flight 2 days
I am sure when it was CGI it looked like an aircraft engineer did it, not some graphic artist.
That particular example
allegedly flies at 240kt for 690 NM with IFR reserves, so 3.5-4 hours. They claim it will have a 900kWh Li-ion battery (which would weigh something around 6 metric tonnes, which might cause some payload issues within the 6,350 kg MTOW).
The numbers also imply at most around 250 kW continuous power in cruise. I doubt one can haul a six-tonne aircraft through the air at that speed with that power. That is the power a DA 62 delivers at full power, and I guess it will struggle to go past 200kt.
So probably 45 minutes at 240kt, or go the distance veeeeery slowly. And it will be unmanned because all the mass is battery.
I haven’t read every post on this subject, so forgive me if I repeat something that has already been written.
My view on the acceptability of electric or hybrid aircraft is severely tainted by my experience with the new Mercedes 350e petrol hybrid I bought 6 months ago. I was fooled by the brochure claiming a fuel consumption of 100+ miles per gallon and an electric only range of 23 miles. Yes it does do 100mpg for the first 12 miles, thereafter 30mpg; and the electric only range has never reached 15, yet alone the claimed figure. So, why would I ever trust an aircraft without Avgas or Jet A1 in the tanks? Even if the type has been through the most rigorous FAA/EASA testing not being able to visually check how much gas is in the tank(s) is way beyond any flight safety parameters I could ever accept. I am of a generation that likes to physically check I have both wings still attached, oil in the engine and fuel in the tanks.
I also wonder what the continuing airworthiness regime for an electric aircraft will be. I know that the fuel tanks in my Avgas powered aircraft will always contain 243l of fuel when they are visibly full, so do my maintenance company. As a result I will always know my max range and endurance. How do you check the capacity of a battery pack, even if there are sophisticated ways of doing so will it have to be done every year, month, day or on each pre-flight? If the aircraft has a built in capacity check, will it be reliable or will it be mandatory to have duplicate or triplicate systems? And then there is the question of where will there be charging points, what incentive will there be for airfields to provide them; will they also charge us extra parking fees for the time it takes to charge the battery pack?
I have friends who come and stay at my home in their Tesla cars, the first thing they want to do is plug them into my domestic electric supply….they always seem to be suffering from range anxiety…and it probably costs me a fortune; I can’t imagine what the bill would be if they turned up in an electric Robinson R22/44.
alioth wrote:
The reality is that it won’t fly (pardon the pun) and you’ll never have thousands of these things flying over a city due to the sheer racket from which there will be no escape. A multi-rotor system would still have all the issues of a helicopter, but add to them. It won’t do away with vibration issues, and the multicopter idea won’t scale because you can’t make the propellers very big and still have them fixed pitch with lift control by variable RPM. You now have 4 or more motors that can fail instead of 1 or 2 and 4 rotors that can fail – a rotor on a multicopter can fail just like a tail rotor on a helicopter. You now have vibration issues caused by the multiple motors all running at slightly different speeds to control the machine causing beat frequencies, and if you avoid this by interlinking all the rotors and using variable pitch for thrust control, you’ve now got something more complex than a single rotor helicopter so you’ve not solved anything. Also many engines and small propellers is less efficient (and likely much noisier) than few engines and large rotors. In forward flight, you’re probably not going to get so much benefit from translational lift with lots of tiny rotors instead of few large rotors. They also cannot autorotate.
A multicopter can scale because you’re not limited to 4 motors. Also, the larger the aircraft the slower the control response needs to be. Of the two that seem closest to practicality the e-hang has 8 props and the Volocopter 2x has 18. You can tolerate multiple rotor failures and still land safely (on the E-Hang, you can even cope with multiple failures on the same corner). In contrast, a failure of either the main rotor or the tail rotor on a helicopter will spoil your day. The Volocopter blurb states it has 9 batteries so one imagines that you can cope with a battery failure or two and still land safely. One hopes they’re physically isolated so that if one ‘flameballs’ then others aren’t affected. If not, they could be. Also, if you’ve got lots of batteries they shouldn’t all fail simultaneously and provided you’re not over water this should provide some warning that it’s time to land and you should have time to put the aircraft down.
I personally wouldn’t worry about the lack of ability to autorotate and all in all I see them as potentially being much safer than conventional helicopters. Certainly my experience of radio control helicopters is that they’re finickity beasts that are always needing something to be balanced or tweaked, and I would expect a mechanically simpler multicopter to be much less burdensome to maintain than any equivalently sized helicopter.
They claim the Volocopter feels vibrationless. Intuitively, all 18 rotors will be continuously varying their speeds so you’re not going to get sustained beat frequencies the way you would in a twin prop aircraft. Nor should you get the low-frequency vibration or noise that you would with a larger helicopter with a slower rotor speed – whump, whump, whump… I would anticipate that the noise shouldn’t carry so far, being higher frequency. Given that I don’t see the other issues as being insoluble, to me noise seems the major concern. Has anybody here heard a full-size multicopter in action?
