Evolo VC-200 Volocopter Electric Multicopter

Posted by Flucloxacillin25pc@reddit | WeirdWings | View on Reddit | 39 comments

German company e-volo GmbH conducted the first flight of its VC-200 Volocopter on March 30, 2016. After receiving its “Permit to Fly” as an ultralight aircraft in February, e-volo described its VC-200 as “the world’s first certified Multicopter.”

The Volocopter is made of lightweight composite material and runs on 9 independent batteries, powering 18 electric motor-driven variable-speed/fixed-pitch propellers. The inherent redundancy ensures stability in the event of component failures.

Control about the roll and pitch axes results from differential variation of motor speeds across the propeller plane, while yaw control is achieved by appropriate combinations of motor torques. Collective speed/thrust is used to control altitude. In combination with tilting the aircraft thrust plane, the VC200 is able to control flight in all six rotational and translational degrees of freedom.

[-]

night_flash@reddit

All rotorcraft can use autorotation to reduce their decent rate and maintain some control during engine failure. However, the efficiency of autorotation is related to rotor RPM. Larger radius rotors that operate at slower RPMs and low disk loading are more efficient. So much so that you can have rotorcraft such as autogyros that do not power their lifting rotors in flight at all, using a propeller for forward propulsion and relying on autorotation for lift.

Lifting efficiency is a major part of autorotation efficiency. It ensures that less energy is consumed by drag. But the rotor RPM is also very important. Especially with fixed pitch rotors like this prototype has.

For these rotors to create lift, they will need to operate at fairly high RPM. When operating in autorotation, rotor RPM is proportional to the velocity of the air it is wind-milling through. The pitch of the blade can be thought of as the amount of forward distance (assuming no slip) the blade travels at its angle of attack in a single distance. The blades trace an imaginary spiral line though the air in a forward direction. This can actually be observed under specific conditions. For a given pitch, a higher RPM travels a greater distance in the same time.

Inversely, for a given pitch, when powered by the airflow, greater velocity is required to achieve the same RPM. Considering that firstly, these blades look to be fixed pitch, meaning the pilot cannot set the collective to the best pitch for autorotation, and secondly, they require a greater RPM to produce the required lift, the decent velocity required for autorotation would be very high.

Due to the also very high number of blades for a given disk area, increasing drag significantly, the amount of slip could be significant. This suggests the required decent velocity for autorotation would be even greater than the ideal formula projects.

A high decent rate during autorotation is inherently more dangerous, and without the ability to control blade pitch or lift, a flare before touchdown becomes impossible. So if all power was lost to the lifting motors, this design would be less safe than if a design with a traditional helicopter style rotor system suffered the same power failure.

[-]

Wolffe_In_The_Dark@reddit

I'm aware of autorotation, that doesn't change that it's still a falling brick if the power fails.

It's a falling brick that's still producing thrust, sure, but a falling brick nonetheless.

[-]

night_flash@reddit

Except that in the case of other possible designs for similar or the same intended mission, you can achieve a far safer failure mode than what this design presents. Failures are almost never all or nothing, and part of safe designs is considering what happens during partial failures. Especially considering partial failures are more likely.

In aviation and air sports, there's basically nothing that is a complete brick if it has a failure. The argument that failure is failure and doom is inevitable is a very pessimistic one and ignores the nuance of engineering.

I agree that this design is basically a brick if it loses power. I used a lot of words to describe why I think that's the case. However, the idea that this is common in aviation is not true. Partially because of redundant systems as well, but also because of designing aircraft in a way that can cope with failures in more ways than simply duplicating everything important.

A modern conventional helicopter could lose all engine power, and in some designs even power assists for the controls as well, and still have some capability to slow its descent. The amount of failures required to become a brick is almost impossibly unlikely, especially with due care and attention to maintenance and inspection.

[-]

Wolffe_In_The_Dark@reddit

Yeah, and the point my post was that, in the case of total power failure, nearly all modern aircraft are falling bricks. Partial failure wasn't being addressed, because if this is a certified airframe, it's reasonable to believe it has similar redundancies.

[-]

Schmittiboo@reddit

I mean, yeah, I would somebody did a FMEA during approval of this thing... right.. RIGHT?

[-]

Substantial-Quit-151@reddit

So... It's a falling brick if the power fails?

[-]

Schmittiboo@reddit

A slightly slower falling brick if power fails..

[-]

night_flash@reddit

I think that could very much be the case yes

NSYK@reddit

Looks like a falling brick if the power fails

So is pretty much every other powered-lift VTOL, electric or not, and power failure is still a death sentence for most aircraft in general nowadays (FADEC engines die, fly-by-wire dies, radio dies, instruments die, etc.)

Basically all modern aircraft are "falling bricks" if power fails. That's why it's the most redundant system on the aircraft.

This is not true at all

Source?

Because mine is the college education I'm taking for this shit.

Old-Let6252@reddit

The source is the FAA, dipshit. Every helicopter is required to be able to autorotate to a safe landing in the event of power failure.

What’s happening here is that you think “power failure” refers to electrical power, when it actually refers to engine stoppage. Electrical power failure is a completely separate thing.

Buddy, this comment chain was explicitly referring to electrical power.

Take off the Redditor Um Ackshually cap and genuinely shut the fuck up. I am literally going to college for this shit, I know that power is often used to refer to thrust, I do not care.

Coriolis.

ScrubbingTheDeck@reddit

Die by wire

zoinkability@reddit

If they want to scale it up they just need to add a third ring of 24 rotors.

Apocalypsis_velox@reddit

How many for the Chinook version?

Let's do the math! For simplicity's sake let's assume the only metric that matters is lift and not speed, range, etc, and let's ignore that this is battery powered which would likely make any Chinook-sized version far heavier.

This requires 18 rotors to lift a total gross weight of 450kg, so it can lift 25 kg per rotor.

A Chinook lifts a total gross 24,494 kg. Divide that by 25, and you find that you would require 980 VC-200 rotors to lift that same amount.

If we take my initial concept and assume that you can only add rotors in rings that double the number of rotors in the previous ring, we can't just have an arbitrary number of rotors. Instead we need to have one of the following:

6 (one ring)
18 (two rings)
42 (three rings)
90 (four rings)
186 (five rings)
378 (six rings)
762 (seven rings)
1,530 (eight rings)

So the scaled up Chinook-lift version of this would have to have 1,530 rotors, with the outermost ring having 768 rotors.

The inherent redundancy ensures stability in the event of component failures.

At what point does inherent redundancy become more to go wrong?