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Recently, I have been conducting research on more efficient means for vertical lift transportation. One direction I was thrown in was the use of a quadrotor system with vector thrust and artificial stability. All of this is done using a system of ducted fans and electric motors. I would love your answer on "Does a system like this sound like a safe and quiet means to transport passengers?"

The name of the program is UV-4, and although it is being tested on flight simulation as an unmanned cargo delivery craft, I wonder if it also makes sense as a passenger aircraft.

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  1. Would this type of aircraft produce less noise than a traditional transport category helicopter of the same size? Length = 41ft (Prop blades are ducted and aircraft has two electric motors)

  2. Can a ducted fan rotorcraft create regenerative energy using magnets or other method to create square waves?

  3. This experimental is a UAV; could you picture a piloted passenger aircraft?

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Farhan
    Commented Oct 26, 2017 at 17:45

4 Answers 4

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The three most important factors in passenger air travel are safety, safety & safety. So that is where most of the questions will focus on, and where most of the engineering effort will be put into. Couple of questions:

  • Artificial stability: what happens if the stability circuit breaks down?
  • What happens if one of the motors fails, for instance one of the big aft ones? Can the craft still stay upright or does it topple over? If it stays upright, can the remaining motors still provide enough lift to keep the craft flying?
  • What happens if the battery runs down or fails during flight?

These are redundancy problems that need to be solved. Any system that causes an unsafe situation when it fails must have a redundant layout. So at least a penticopter instead of a quadcopter: upon engine failure, 4 props can safely land the craft.

The redeeming feature for quadcopter is ease of manoeuvring with variable rotational speed per propeller, instead of having to make a swash plate arrangement. But light single rotor helicopters have been around for a long time and the technology is mature - I don't see what particular problem the quadcopter can solve that for instance an R44 might have.

On your questions:

  • Q1 Noise: yes electric motors are nice and quiet, and the shrouds shield noisy tips in most directions.
  • Q2 Regenerate energy: it can only do that during authoritative descent, which would be frighteningly fast due to the relatively small total rotor disk area.
  • Q3 Not a UAV: sure, tilt rotors exist already

From the wiki

Edit: the propulsion system you draw is not so revolutionary. If you travel to Niagara Aerospace Museum, you can see the X-22, built in 1967.

http://www.diseno-art.com/encyclopedia/strange_vehicles/bell_x-22.html

From a comment:

•I have had one rotor fail (larger) and be able to land the aircraft safely, even maintain a hover but not climb. Aircraft does not topple in simulations, software used Xplane 10 and 11 ultra releastic. – Robert Gomez

That is a claim that sounds hollow. It depends on the location of the centre of gravity: if it is within the triangle formed by the remaining three rotors, it will stay upright. Picture an X cross connecting fwd left - right aft, fwd right - left aft.

  • If CoG is behind the middle point of the cross, either one of the front rotors can fail and the craft will fly stable on the remaining rotors, because CoG is within the triangle formed by the operational rotors. But not when one of the aft rotors fail.
  • If CoG is forward of cross centre, either one of the aft rotors can fail. But not a front rotor.
  • If CoG is exactly at cross centre, the rotor diagonally opposite the failed rotor cannot exert thrust otherwise the craft will roll. So one rotor fails means only two can be operational.
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  • $\begingroup$ Conventional rotors have known limitations and are known to be vibration prone. Smaller rotor reduce aircraft vibration and vector thrust gives a vertical lift vehicle the ability to join the super manuerverabily class of aircraft. $\endgroup$
    – Robert Gomez
    Commented Oct 25, 2017 at 10:09
  • $\begingroup$ •artificial stability is an added feature, the aircraft does fly without it. It is designed to assist the pilot in adverse conditions and gives the pilot a near perfect hover and stable flight condition. $\endgroup$
    – Robert Gomez
    Commented Oct 25, 2017 at 10:11
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    $\begingroup$ @RobertGomez current airworthiness standards require multi-engine aircraft to be able to climb with a failed critical engine. Furthermore auto-rotation is not a catch-all, as Koyovis pointed out, it would have to be done at significant speeds for a multi-rotor design like this one. In addition, super-maneuverability, while a fine buzzword, is not something pax tend to enjoy :) $\endgroup$
    – AEhere supports Monica
    Commented Oct 25, 2017 at 10:46
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    $\begingroup$ @RobertGomez I'd like to know what glide ratio you envision that body to have, even a rough approximation. $\endgroup$
    – AEhere supports Monica
    Commented Oct 25, 2017 at 10:48
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    $\begingroup$ The V22, a work of art that you wouldn`t like to use for your daily commute, related SE: aviation.stackexchange.com/questions/22491/… $\endgroup$
    – Caterpillaraoz
    Commented Oct 25, 2017 at 13:06
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What are the advantages that quadrocopters have over conventional helicopters?

  1. Super cheap flight control achieved via electronic control of individual electric motors. (Basically, it means avoiding the mechanically complex main rotor hub.)
  2. Self-cancelling torque thanks to counter-rotating propellers, further simplifying construction.

Now, let's look at the disadvantages:

  1. Quadrupled points of failure - any motor goes down, entire craft goes down.
  2. Abysmal power-to-weight ratio due to electric propulsion and power storage. That's why quadrocopters have flight times of around 5 minutes.
  3. Crappy efficiency due to few small rotors instead of one big.

To sum it up: quadrocopters trade safety and economy of operation for economy of manufacture.

Now, what qualities are important for commercially operated craft, especially ones that carry passengers? First is safety. Then economy of operation. Price of the craft is not very relevant - if it can be operated cheaply enough, the initial investment will pay off sooner or later.

Conclusion: quadrocopters are the worst possible solution for commercial operation, particularly ill-suited to carrying people. The only imaginable commercial scenario is when the operation involves very high risk to the craft. Real life validates this claim: so far the only successful applications of quadrocopters are high-risk drug delivery, drone racing and toys - in all those, cost of acquiring the aircraft dominates.

BTW, your project is not a pure quadrocopter in the common understanding of the term. The thrust vectoring adds complication. You have already traded some cost of manufacture to get better operating efficiency. Follow that trend, and you'll eventually reach the typical helicopter layout with a combustion engine. Or tiltwing/tiltrotor if you need very long range.

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    $\begingroup$ FTR, the bad power-to-weight ratio is not inherent to electric propulsion but to batteries. If the main source of electricity was a turbine-driven generator, this wouldn't be so much of an issue anymore. Of course the generator and motors would still be dead-weight compared to a conventional chopper. $\endgroup$
    – leftaroundabout
    Commented Oct 25, 2017 at 20:31
  • $\begingroup$ @leftaroundabout yeah, I was comparing whole package to whole package, including tanks / batteries. $\endgroup$
    – Agent_L
    Commented Oct 26, 2017 at 12:33
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An important point is that that type of aircraft can't glide in autorotation, as helicopters are able to do in case of engine trouble. It will drop like an stone...

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  • $\begingroup$ This has been one of the most interesting subjects to investigate and study with this airfoil. Turns out the aircraft can conduct a non power glide for quite a distance with its lifting properties. The idea is to let air rush the ducts and allow for ground effect at altitude, this is relying on safe deploy of landing gear. However, a system like this could also employ a brs because it has no large prop in the center... $\endgroup$
    – Robert Gomez
    Commented Oct 25, 2017 at 9:24
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    $\begingroup$ @Robert Gomez Small-diameter rotors don't give enough lift in autorotation, and the descent speed will be very high. Even the Osprey V-22, whose rotors are not particularly small, can't rely in autorotation in case of an emergency... And concerning ground effect, it doesn't exist during autorotational descent, because the wake goes upward from the disk. It's true that, in the last stage of an autorotational descent, the pilot manipulates the collective in order to cushion the landing, thus using the potential energy accumulated in the rotor, but –obviously– that can't be done 'at altitude'... $\endgroup$
    – xxavier
    Commented Oct 25, 2017 at 9:40
  • $\begingroup$ Oh course, at altitude no auto rotation occurs. Similar to the V-22 it relies on trim and glide ratio. Ground effect can be a factor at near ground level. $\endgroup$
    – Robert Gomez
    Commented Oct 25, 2017 at 10:01
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    $\begingroup$ @ Robert Gomez Autorotation can take place at any altitude. For doubters, autogyros fly always in autorotation, and have no trouble at all with altitude... $\endgroup$
    – xxavier
    Commented Oct 25, 2017 at 11:28
  • $\begingroup$ This is true xxavier, thank you for pointing this out. What I ment to say is, auto rotation can happen at any altitude, however I used the term in the statement to refer to a power off descent in a vertical lift aircraft. Helos with a large diameter propeller do this well as they produce lift simply by the spinning caused by free flowing air, this aircraft relies on a combination of free rotation of propellers, however more from its lifting surfaces like a fixed wing aircraft in a power off configuration. $\endgroup$
    – Robert Gomez
    Commented Oct 26, 2017 at 1:42
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maybe this idea is interesting for you for further resesarch. They are developed in my region: Flying taxis: http://www.businessinsider.com/r-dubai-starts-tests-in-bid-to-become-first-city-with-flying-taxis-2017-9?IR=T

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