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I don't understand anything in aerodynamics, so pardon my stupid question: planes are the most wide-spread flying machines because they are vastly more efficien

I don't understand anything in aerodynamics, so pardon my stupid question: planes are the most wide-spread flying machines because they are vastly more efficient than a rotary-wing aircraft due to the lift generated by wings. Why then a quadcopter is the default shape for smaller drones? Is it because small wings don't generate enough lift for the drone to make a difference? But they surely provide additional stability and won't hurt at a glance.

blacksmith_tb 6y ago
Not an aeronautic engineer, but to compare to a similar mass like a bird, having wings would make the hobby-sized drones quite a bit bigger. I assume there's also the ease of changing direction / altitude that comes from having the paired motors, controlling tiny planes would take tiny ailerons and flaps (which, like you say, may not scale down effectively).
giomasce 6y ago
Not an expert, but I'd guess quadcopters are much easier to pilot. You press a button and they go that way. Taking off and landing on wings is very difficult in comparison, requires more space, more facilities, more organization.
- alkonaut 6y ago
  But they have tiny wings (arms) and if they were airfoil shaped then it would give some lift in straight and level flight. Then at start/landing/low speed, they would just do nothing. Perhaps the air is so turbulent around the wings due to the propellers that wings just don't get any airflow to create lift, or would need to be much longer to be out of the way of the propellers, that it's not worth it?
  - mikepurvis 6y ago
    Adding foldable wings would be a massive complexity and weight increase relative to the standard scheme which pretty much boils down to 4 motors + an IMU, with the rotors being the only moving parts. The closest thing in the real world to the hybrid that you describe would probably be the tiltrotor, where the same engines which supply lift can turn 90 degrees to become forward thrusters on wings: https://en.wikipedia.org/wiki/Tiltrotor https://en.wikipedia.org/wiki/Tiltrotor
    - alkonaut 6y ago
      I don’t mean foldable I just mean airfoil shaped cross sections that still fit within the normal “wingspan” of the multirotor. Amazon have made at least two designs, one that flies “tilted” and uses the boundary ring as wings, another with more separate wings and forward propulsion Version 1: https://techcrunch.com/2020/08/31/amazons-prime-air-drone-delivery-fleet-gains-faa-approval-for-trial-commercial-flights/ https://techcrunch.com/2020/08/31/amazons-prime-air-drone-de... Version 2: https://www.amazon.jobs/en/teams/prime-air https://www.amazon.jobs/en/teams/prime-air
- nuccy 6y ago
  Actually it is not easier at all, the complexity is obscured by an onboard computer, which constantly helps to keep position, not to flip upside down and lose control completely. By applying differential thrust on different propellers it executes commands from operator to tilt and rotate. If the computer fails, operator, even with a direct control of the propellers, will not be able to maintain a stable flight. From aerodynamic standpoint planes are much easier to pilot (all but military, same story with computers for better maneuverability) since they are designed to be inherently stable. So if all power is lost and you still have control of aerodynamic surfaces, there is not problem to land a plane after planning for some tens or even hundreds of kilometers (depends on initial altitude). This is obviously not the case with quadropters, loss of a single propeller leads to complete loss of control.
  - mikepurvis 6y ago
    It leads to loss of six-dimensional control, though interestingly you can still maintain five-dimensional control (losing yaw) with only three or even just two props, see demonstration from ETH Zurich: https://www.youtube.com/watch?v=t369aSInq-E https://www.youtube.com/watch?v=t369aSInq-E
    - nuccy 6y ago
      Yes, indeed, though this seems to be an experimental drone. Most common commercially available DJI drones fall if single motor or propeller fails, though in future they may gain such functionality, which would be great for safety. A nice example of a different approach is a variable angle of attack propellers which are driven by a single motor [1]. See after 0:52 and 7:13. In case battery is dead since all the propellers are synchronized they auto-rotate and stabilize the drone (near the earth the pilot activates the motor just to land softly, but likely similar effect can be reached by properly adjusting the angle of propellers in proper time, like in case of auto-rotation landing for helicopters). [1] https://youtu.be/TnGhEInTXYc?t=52 https://youtu.be/TnGhEInTXYc?t=52 (this video was posted below by @jcims)
      - mikepurvis 6y ago
djrogers 6y ago
Planes with wings, by and large, do none of the following: hover, fly sideways, fly backward, fly straight upon or down, land or take off vertically. I say by and large because there are exceptions, but they are complex, expensive, and compromised.
- demosito666 6y ago
  Well, yes, this is true I guess. However, this drone is advertised not for those things, but for long range predominantly. This is what I find a bit strange. As for complex and expensive the first google result for "rc plane vtol" for me is this one [1] and it costs around $50. And then there are things like [2]... [1] https://www.youtube.com/watch?v=xFISwEQbaz0 https://www.youtube.com/watch?v=xFISwEQbaz0 [2] https://www.youtube.com/watch?v=MDxHamYEQNU https://www.youtube.com/watch?v=MDxHamYEQNU
  - imtringued 6y ago
    I'm surprised. The first vtol plane you linked works so well I don't even understand why quadrocopters even exist at this point. So quadrocopters are just a modern fad and will disappear eventually.
    - asutekku 6y ago
      It looked really unstable and the shape meant that even a smallest wind will screw it up.
    - s1artibartfast 6y ago
      It really depends on the application. For most industrial applications, they are really apples and oranges, with planes being unsuitable for many missions. There is no shortage of fixed wing drones and commercial operators are not idiots. They buy what they need for their application.
    - jlcortex 6y ago
      Quadcopters are equivalent to helicopters in terms of performance. VTOL-planes fly as a plane, they do not have hovering endurance, barely a few minutes at the most, just for take off and landing. So they cannot perform missions that require hovering capabilities. A hybrid multicopter has the advantage of longer-endurance, traditionally exclusive of planes, while still keeping all the advantages in simplicity, ease of use and versatility of multicopters.
Tossrock 6y ago
Quantum Systems makes drones that do this, and they get massively longer flight times than standard quadcopters. Their Vector drone can fly for 120 minutes, comparable to this fossil fuel powered quadcopter, on batteries alone: https://www.quantum-systems.com/project/vector/ https://www.quantum-systems.com/project/vector/
zepearl 6y ago
Just guessing (in addition to what others already mentioned - btw. I was wondering the same thing hehe): maybe one big part involves the landing & takeoff: for plane-like drones both are a lot more dangerous (therefore more difficult to be automated) and need a lot more space than quadcopters (and the likes). Saying this because I remember that, when I was a kid, my RC-plane (which took weeks and $$ to build) crashed 1.8 seconds after the first take-off attempt (damn, I got so angry & depressed...). I guess that soon or later we'll see mixed designs that can take off & land like a quadcopter but which can increase their range/efficiency by "transforming" in mid-air into an airplane-like form? (something similar to https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey or maybe just a passive design that works by changing the fixed orientation of the whole drone from horizontal to almost vertical, or the opposite depending on the form of the drone?) In any case complexity would increase, therefore more specific demand for long-range capability is probably needed to go towards developing something in this area?
- primitivesuave 6y ago
  I remember how depressed I was when I crashed my RC plane on its maiden flight. Took a turn that was too sharp and didn't have the piloting skills to avert the subsequent nosedive. I crashed my first Phantom drone as well since I didn't know you have to warm up the batteries in cold weather. Live and learn I guess :)
- meheleventyone 6y ago
  Hybrids already exist in a variety of forms and it’s not beyond hobbiests to crank them out: https://www.youtube.com/playlist?list=PLj3Bh6Krv9CXC8L8c3bPgonU7mtuRoIIa https://www.youtube.com/playlist?list=PLj3Bh6Krv9CXC8L8c3bPg... Most commercial versions opt for simplicity and use a separate set of propellers for quad and forward flight configurations.
  - zepearl 6y ago
    Thx - maybe there are some additional complexities related to the payload/cargo (center of gravity, can the payload be rotated yes/no and if not then how to keep it level without increasing too much the weight, etc...)?
TylerE 6y ago
Drones are usually copters so they can do vertical takeoffs and hover. They're quadcopters rather than single mainrotor + tailrotor because it greatly simplifies the mechanics. Single rotors need a cyclic mechanism to vary the blade pitch depending on where the blade is in the rotation and the control inputs. This is VERY complicated with a lot of moving parts that have to maintained and adjusted. (See https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Sikorsky_S-92_rotor_P1230176.jpg/1024px-Sikorsky_S-92_rotor_P1230176.jpg https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Si... for one example) Quads (and hexes, etc) can have full control authority via RPM only, using a simple injection molded constant pitch prop.
- imdsm 6y ago
  You have to admire the balancing effect of the torque on quad-rotors. Two CW and CCW rotors cancelling out the yaw (or introducing it, when required).
- cjsawyer 6y ago
  Quadcopters take simple hardware and control it elegantly with complex software. The beauty is that you only need to write the software once. All other tech requires more complicated hardware.
- modeless 6y ago
  To underscore the relative simplicity, you can make a quadrotor with just 4 moving parts. Each electric motor has only one moving part, the rotor, and the prop is attached directly to it without even any gears.
  - pfundstein 6y ago
    Just noting cheaper quads often use geared props to compensate for their under-powered motors.
- subculture 6y ago
  I used to fly gas RC helicopters and the joke was that RC helis are collections of small expensive parts desperately trying to get away from each other.
myself248 6y ago
Controls got easy, batteries got good. Computer-controlling a fixed-wing plane requires a lot of sensors, and a lot of math, and a lot of space, and forward airspeed. Computer-controlling a quadcopter requires a lot of sensors, and a lot of math, and a lot of power. Arduplane exists alongside arducopter, and it's easy enough to build both, but I can't fly a fixed-wing model in my backyard. I can fly a quadcopter just fine.
voldacar 6y ago
With wings, you have to be moving forward to stay in the air. With rotors, you can hover if the control circuitry is up to the task
Const-me 6y ago
> I don't understand anything in aerodynamics Same here. > Why then a quadcopter is the default shape for smaller drones? Large fixed-wing planes are expensive. Piloting them requires jumping through many high-hanging and heavily regulated hoops. The most dangerous parts of the flight near the airports happen in well-known space, according to pre-defined paths known to all parties. In many places of the airspace, pilots are guided by data from the ground. Optical from visual approach slope indicator (these weird light arrays around airports which are visible as 0-4 red circles depending on whether you’re too high or too low). Radio from beacons. Most importantly humans, the job title is “air traffic controller”. For the scale of a conventional airplanes, accurate map data is available. GPS data+SRTM height map is accurate enough for most cases. Also, real-time weather data is pretty accurate at that scale. None of the above applies to small drones. They’re cheap, most are piloted by amateurs and no licensing is required. They can take off and land whenever. No ground control is available. At their scale, no offline map data is available, and ground-induced wind turbulence is borderline unpredictable. This might change in a few years. We might get chips smart enough to reliably do right things based on the limited input data despite the unpredictable factors. We might get sensors sensitive enough to generate much better data for these chips. E.g. if you have spatial data for 1x1x1km space around the drone, with 1mm spatial precision, and 20ms refresh rate consistent over the whole volume, today’s mobile chips will do mostly OK in good weather. We might get good enough sensors to cover all airspace with them, and make robotic equivalent of air traffic controllers, a software that detects future collisions and tells the drones to do something about it. Or broadcast current wind conditions at 1m^3 resolution. Least likely but still, we might get good enough actuators & power sources to combine these two. Birds do OK, many of them can hover, glide, and arbitrarily combine hovering with gliding. When you can stop flying and hover, or land almost everywhere, collision avoidance becomes way simpler. That’s one reason how birds and modern-day small drones are functional.
NegativeLatency 6y ago
The wings help for covering longer distances efficiently but make hovering and vertical takeoff tricky, tail-sitters combine positive features from both types of aircraft https://en.wikipedia.org/wiki/Tail-sitter https://en.wikipedia.org/wiki/Tail-sitter
Tomminn 6y ago
I think there will be a large market for plane-like drones with very malleable wings for exactly the reason you state. The cost (in terms of both price and structural integrity) of gratuitously dynamic wings (think turning the whole wing 45 degrees to horizontal, bending the wing to 90 degrees at it's half way point) are much smaller for small aircraft. Such gratuitously dynamic wings give more degrees of freedom for automated piloting software to work with when it comes to optimizing near vertical take-off and landing when compared to a fixed wing aircraft, while retaining fixed wing efficiency advantages during elevated flight.
seasonalallergy 6y ago
Why the quad set up over the classic single rotor seen in helicopters?
- jlcortex 6y ago
  A hybrid drone like HYBRiX has power redundancy. If the engine stops for some reason, it still has some minutes of endurance in electric-only mode, for an emergency landing. With an unmanned helicopter, if the engine fails, the crash is mostly warranted, even with the autorotation function. Besides, the mechanics are simpler and therefore more reliable. And the propellers are smaller than a helicopter rotor, which is safer. Multirotors are also much simpler to operate than a helicopter. Most industrial customers do not want to operate unmanned helicopters because of their complexity.
- bri3d 6y ago
  Mechanical complexity. A collective pitch helicopter requires a bunch of expensive moving parts and linkages to run the swash plate. The most traditional design requires 3 relatively powerful linear actuators of some sort as well as a spherical bearing at the swash plate, then 2 linkages to the rotor head and 2 more bearings on the rotor head itself. A quadcopter requires brushless motors (usually with 2-3 typical sealed ball bearings each) and props. Less moving parts, broadly generalizing, means fewer ways to fail.
pengaru 6y ago
TL;DR: It's because they can hover. They have a stable and basically stationary anywhere in 3-space mode (until the juice runs out). Human and automated control is much simpler as a result.
meheleventyone 6y ago
Small wings are less efficient particularly when things get really small but at this weight there are a lot of fixed wing UAVs. This is also not terribly small at 1.6m long.
- jlcortex 6y ago
  Fix wings are amazing for some applications. The problem with them starts when you want to carry heavier payloads. Taking-off and landing gets more and more complicated as they scale-up, while you only need 10 sq. meters to take-off HYBRiX drone. In the end, the different drone types are suitable for different purposes.
  - meheleventyone 6y ago
    Yeah most obviously this is useful if you need to land and then take off again somewhere where you don't have infrastructure to relaunch a fixed wing UAV. For example collecting something. Although that presents its own challenges in terms of how non-experts safely handle attaching the payload to the UAV. I think its a super interesting piece of kit so I hope you find success with it!
extropy 6y ago
To add to all the other responses, multirotors are the least power efficient setup by far. And fixed wing the most, and regular helicopter somewhere in the middle. Several hours of flight time is trivial with a battery powered fixed wing model airplane.
baybal2 6y ago
> Why then a quadcopter is the default shape for smaller drones? Because somebody, somewhere published the first opensource autopilot code, and that first code was for the quadcopter.
- serf 6y ago
  a stupid nit to pick about an obvious off-the-cuff statement, but the whole drone hobby is older than quadcopters, as are open-source 'drone' solutions with route planning/loitering/all the stuff you'd expect a drone to do. But before quadcopters we used large-wingspan EPO foam / balsa / plastic planes. It's still common place.
  - baybal2 6y ago
    Yes, but I say that the quadcopter boom was almost singlehandedly due to appearance of the single firmware which was "copypasteable," and suitable for garage factories.
matheusmoreira 6y ago
Fixed wing aircraft must have air moving along the wings in order for them to generate lift. In other words, the aircraft must always be moving through the air. If its speed drops below some minimum value, it will stall and drop out of the sky like a rock. This is also why they need runways in order to take off. They need to accelerate to a minimum speed in order to even get airborne. https://en.wikipedia.org/wiki/V_speeds https://en.wikipedia.org/wiki/V_speeds Rotary wing aircraft use their engines to constantly move the wings through the air instead of moving the aircraft itself. So the wings are always generating lift and the aircraft is free to move in much more flexible patterns. A very useful maneuver is hovering in place: the aircraft is able to simply hold its position in the air. Since only the wings need to move to generate lift, the aircraft itself does not need to accelerate in order to take off and therefore a long runway is not necessary. Civilian drones usually have rotary wings because this allows people to do useful things like having the drone stay in one place in order to film or photograph something. A fixed wing aircraft would have to establish a loitering pattern around an area in order to do the same thing. In other words, rotary wings can just hover in place while a fixed wing would have to fly around in circles. Fixed wing aircraft are more fuel efficient. Rotary wing aircraft must constantly spend fuel in order to keep their wings spinning. They lose lift otherwise. A fixed wing aircraft would probably be able to glide great distances and even land safely even if it lost all engines in the middle of its flight.
- jaclaz 6y ago
  There are also unpowered rotating wings. Maybe it is possible to combine a "normal" quadrirotor (for vertical takeoff and hovering) with a rotating wing aircraft, the autogyro: https://en.wikipedia.org/wiki/Autogyro https://en.wikipedia.org/wiki/Autogyro to save a lot of energy when traveling horizontally. There is actually this thing here that is already a sort of cross-breed between a helicopter and an autogyro: https://airialrobotics.com/ https://airialrobotics.com/ https://airialrobotics.com/gt20-gyrotrak/ https://airialrobotics.com/gt20-gyrotrak/
  - matheusmoreira 6y ago
    That's really cool! I've read about the use of autorotation but only in the case of emergencies. I had no idea there were entire aircraft based around the concept. Since the rotary wings are unpowered, the autogyro loses many of the properties that make the helicopter so valuable. It requires forward motion in order to move air through the unpowered rotary wings and maintain lift. Looks like they have propellers providing forward thrust just like fixed wing aircraft. The article also states that they're not capable of vertical take off and landing. They need a runway to accelerate just like fixed wing aircraft.
teleforce 6y ago
Having involved in UAV development projects for agriculture monitoring and have used both rotary-wing and fixed-wing UAVs, I'm now firmly believe that neither of them is fit for purpose in aerial monitoring. The rotary-wing UAV is a power hungry gussler while fixed-wing UAV is not that versatile (e.g. for hovering, etc). The best compromise will be Gyrocopter or Autogyro since it is both energy efficient and flexible. It can also easily fly at sustain high speed wind of more than 50 knots. [1]https://en.m.wikipedia.org/wiki/Autogyro https://en.m.wikipedia.org/wiki/Autogyro
- wnkrshm 6y ago
  Yeah I've wondered for quite a while why autogyro drones aren't popular. They should be efficient and safe - since one problem with autogyros was the noise they made due to large rotor size, drone sized ones shouldn't have that problem.
ajuc 6y ago
Planes work similarly well at small and big scales. They are more efficient than quadcopters even at small scale. Quadcopters are just much safer and easier to control. Compare "fall down at random without input" vs "stop without input". As for why quadcopters aren't used at big scale - moment of inertia scales with cube of the propeller radius. And to control a quadcopter you're constantly speeding up and down each propeller. That's a huge loss of energy when your propellers are big enough. So instead at big scales we use very complicated mechanically designs like helicopter. It uses a propeller that rotates at constant speed (so moment of inertia doesn't matter), and instead changes the angle of attack to control the aircraft. BTW moment of inertia is also why nobody in their right mind would build huge mech robots like in sci-fi. Wheeled vehicles move forward without fighting inertia - wheels spin at constant speed and you just add the energy lost to friction. Mechs constantly swing their huge legs back and forth fighting the whole inertia twice with each step. Fine for toys, not fine for big vehicles.

blacksmith_tb 6y ago

Not an aeronautic engineer, but to compare to a similar mass like a bird, having wings would make the hobby-sized drones quite a bit bigger. I assume there's also the ease of changing direction / altitude that comes from having the paired motors, controlling tiny planes would take tiny ailerons and flaps (which, like you say, may not scale down effectively).

giomasce 6y ago

Not an expert, but I'd guess quadcopters are much easier to pilot. You press a button and they go that way. Taking off and landing on wings is very difficult in comparison, requires more space, more facilities, more organization.

alkonaut 6y ago
But they have tiny wings (arms) and if they were airfoil shaped then it would give some lift in straight and level flight. Then at start/landing/low speed, they would just do nothing. Perhaps the air is so turbulent around the wings due to the propellers that wings just don't get any airflow to create lift, or would need to be much longer to be out of the way of the propellers, that it's not worth it?
- mikepurvis 6y ago
  Adding foldable wings would be a massive complexity and weight increase relative to the standard scheme which pretty much boils down to 4 motors + an IMU, with the rotors being the only moving parts. The closest thing in the real world to the hybrid that you describe would probably be the tiltrotor, where the same engines which supply lift can turn 90 degrees to become forward thrusters on wings: https://en.wikipedia.org/wiki/Tiltrotor https://en.wikipedia.org/wiki/Tiltrotor
  - alkonaut 6y ago
    I don’t mean foldable I just mean airfoil shaped cross sections that still fit within the normal “wingspan” of the multirotor. Amazon have made at least two designs, one that flies “tilted” and uses the boundary ring as wings, another with more separate wings and forward propulsion Version 1: https://techcrunch.com/2020/08/31/amazons-prime-air-drone-delivery-fleet-gains-faa-approval-for-trial-commercial-flights/ https://techcrunch.com/2020/08/31/amazons-prime-air-drone-de... Version 2: https://www.amazon.jobs/en/teams/prime-air https://www.amazon.jobs/en/teams/prime-air
nuccy 6y ago
Actually it is not easier at all, the complexity is obscured by an onboard computer, which constantly helps to keep position, not to flip upside down and lose control completely. By applying differential thrust on different propellers it executes commands from operator to tilt and rotate. If the computer fails, operator, even with a direct control of the propellers, will not be able to maintain a stable flight. From aerodynamic standpoint planes are much easier to pilot (all but military, same story with computers for better maneuverability) since they are designed to be inherently stable. So if all power is lost and you still have control of aerodynamic surfaces, there is not problem to land a plane after planning for some tens or even hundreds of kilometers (depends on initial altitude). This is obviously not the case with quadropters, loss of a single propeller leads to complete loss of control.
- mikepurvis 6y ago
  It leads to loss of six-dimensional control, though interestingly you can still maintain five-dimensional control (losing yaw) with only three or even just two props, see demonstration from ETH Zurich: https://www.youtube.com/watch?v=t369aSInq-E https://www.youtube.com/watch?v=t369aSInq-E
  - nuccy 6y ago
    Yes, indeed, though this seems to be an experimental drone. Most common commercially available DJI drones fall if single motor or propeller fails, though in future they may gain such functionality, which would be great for safety. A nice example of a different approach is a variable angle of attack propellers which are driven by a single motor [1]. See after 0:52 and 7:13. In case battery is dead since all the propellers are synchronized they auto-rotate and stabilize the drone (near the earth the pilot activates the motor just to land softly, but likely similar effect can be reached by properly adjusting the angle of propellers in proper time, like in case of auto-rotation landing for helicopters). [1] https://youtu.be/TnGhEInTXYc?t=52 https://youtu.be/TnGhEInTXYc?t=52 (this video was posted below by @jcims)
    - mikepurvis 6y ago

djrogers 6y ago

Planes with wings, by and large, do none of the following: hover, fly sideways, fly backward, fly straight upon or down, land or take off vertically. I say by and large because there are exceptions, but they are complex, expensive, and compromised.

demosito666 6y ago
Well, yes, this is true I guess. However, this drone is advertised not for those things, but for long range predominantly. This is what I find a bit strange. As for complex and expensive the first google result for "rc plane vtol" for me is this one [1] and it costs around $50. And then there are things like [2]... [1] https://www.youtube.com/watch?v=xFISwEQbaz0 https://www.youtube.com/watch?v=xFISwEQbaz0 [2] https://www.youtube.com/watch?v=MDxHamYEQNU https://www.youtube.com/watch?v=MDxHamYEQNU
- imtringued 6y ago
  I'm surprised. The first vtol plane you linked works so well I don't even understand why quadrocopters even exist at this point. So quadrocopters are just a modern fad and will disappear eventually.
  - asutekku 6y ago
    It looked really unstable and the shape meant that even a smallest wind will screw it up.
  - s1artibartfast 6y ago
    It really depends on the application. For most industrial applications, they are really apples and oranges, with planes being unsuitable for many missions. There is no shortage of fixed wing drones and commercial operators are not idiots. They buy what they need for their application.
  - jlcortex 6y ago
    Quadcopters are equivalent to helicopters in terms of performance. VTOL-planes fly as a plane, they do not have hovering endurance, barely a few minutes at the most, just for take off and landing. So they cannot perform missions that require hovering capabilities. A hybrid multicopter has the advantage of longer-endurance, traditionally exclusive of planes, while still keeping all the advantages in simplicity, ease of use and versatility of multicopters.

Tossrock 6y ago

Quantum Systems makes drones that do this, and they get massively longer flight times than standard quadcopters. Their Vector drone can fly for 120 minutes, comparable to this fossil fuel powered quadcopter, on batteries alone: https://www.quantum-systems.com/project/vector/ https://www.quantum-systems.com/project/vector/

zepearl 6y ago

Just guessing (in addition to what others already mentioned - btw. I was wondering the same thing hehe): maybe one big part involves the landing & takeoff: for plane-like drones both are a lot more dangerous (therefore more difficult to be automated) and need a lot more space than quadcopters (and the likes). Saying this because I remember that, when I was a kid, my RC-plane (which took weeks and $$ to build) crashed 1.8 seconds after the first take-off attempt (damn, I got so angry & depressed...). I guess that soon or later we'll see mixed designs that can take off & land like a quadcopter but which can increase their range/efficiency by "transforming" in mid-air into an airplane-like form? (something similar to https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey or maybe just a passive design that works by changing the fixed orientation of the whole drone from horizontal to almost vertical, or the opposite depending on the form of the drone?) In any case complexity would increase, therefore more specific demand for long-range capability is probably needed to go towards developing something in this area?

primitivesuave 6y ago
I remember how depressed I was when I crashed my RC plane on its maiden flight. Took a turn that was too sharp and didn't have the piloting skills to avert the subsequent nosedive. I crashed my first Phantom drone as well since I didn't know you have to warm up the batteries in cold weather. Live and learn I guess :)
meheleventyone 6y ago
Hybrids already exist in a variety of forms and it’s not beyond hobbiests to crank them out: https://www.youtube.com/playlist?list=PLj3Bh6Krv9CXC8L8c3bPgonU7mtuRoIIa https://www.youtube.com/playlist?list=PLj3Bh6Krv9CXC8L8c3bPg... Most commercial versions opt for simplicity and use a separate set of propellers for quad and forward flight configurations.
- zepearl 6y ago
  Thx - maybe there are some additional complexities related to the payload/cargo (center of gravity, can the payload be rotated yes/no and if not then how to keep it level without increasing too much the weight, etc...)?

TylerE 6y ago

Drones are usually copters so they can do vertical takeoffs and hover. They're quadcopters rather than single mainrotor + tailrotor because it greatly simplifies the mechanics. Single rotors need a cyclic mechanism to vary the blade pitch depending on where the blade is in the rotation and the control inputs. This is VERY complicated with a lot of moving parts that have to maintained and adjusted. (See https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Sikorsky_S-92_rotor_P1230176.jpg/1024px-Sikorsky_S-92_rotor_P1230176.jpg https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Si... for one example) Quads (and hexes, etc) can have full control authority via RPM only, using a simple injection molded constant pitch prop.

imdsm 6y ago
You have to admire the balancing effect of the torque on quad-rotors. Two CW and CCW rotors cancelling out the yaw (or introducing it, when required).
cjsawyer 6y ago
Quadcopters take simple hardware and control it elegantly with complex software. The beauty is that you only need to write the software once. All other tech requires more complicated hardware.
modeless 6y ago
To underscore the relative simplicity, you can make a quadrotor with just 4 moving parts. Each electric motor has only one moving part, the rotor, and the prop is attached directly to it without even any gears.
- pfundstein 6y ago
  Just noting cheaper quads often use geared props to compensate for their under-powered motors.
subculture 6y ago
I used to fly gas RC helicopters and the joke was that RC helis are collections of small expensive parts desperately trying to get away from each other.

myself248 6y ago

Controls got easy, batteries got good. Computer-controlling a fixed-wing plane requires a lot of sensors, and a lot of math, and a lot of space, and forward airspeed. Computer-controlling a quadcopter requires a lot of sensors, and a lot of math, and a lot of power. Arduplane exists alongside arducopter, and it's easy enough to build both, but I can't fly a fixed-wing model in my backyard. I can fly a quadcopter just fine.

voldacar 6y ago

With wings, you have to be moving forward to stay in the air. With rotors, you can hover if the control circuitry is up to the task

Const-me 6y ago

> I don't understand anything in aerodynamics Same here. > Why then a quadcopter is the default shape for smaller drones? Large fixed-wing planes are expensive. Piloting them requires jumping through many high-hanging and heavily regulated hoops. The most dangerous parts of the flight near the airports happen in well-known space, according to pre-defined paths known to all parties. In many places of the airspace, pilots are guided by data from the ground. Optical from visual approach slope indicator (these weird light arrays around airports which are visible as 0-4 red circles depending on whether you’re too high or too low). Radio from beacons. Most importantly humans, the job title is “air traffic controller”. For the scale of a conventional airplanes, accurate map data is available. GPS data+SRTM height map is accurate enough for most cases. Also, real-time weather data is pretty accurate at that scale. None of the above applies to small drones. They’re cheap, most are piloted by amateurs and no licensing is required. They can take off and land whenever. No ground control is available. At their scale, no offline map data is available, and ground-induced wind turbulence is borderline unpredictable. This might change in a few years. We might get chips smart enough to reliably do right things based on the limited input data despite the unpredictable factors. We might get sensors sensitive enough to generate much better data for these chips. E.g. if you have spatial data for 1x1x1km space around the drone, with 1mm spatial precision, and 20ms refresh rate consistent over the whole volume, today’s mobile chips will do mostly OK in good weather. We might get good enough sensors to cover all airspace with them, and make robotic equivalent of air traffic controllers, a software that detects future collisions and tells the drones to do something about it. Or broadcast current wind conditions at 1m^3 resolution. Least likely but still, we might get good enough actuators & power sources to combine these two. Birds do OK, many of them can hover, glide, and arbitrarily combine hovering with gliding. When you can stop flying and hover, or land almost everywhere, collision avoidance becomes way simpler. That’s one reason how birds and modern-day small drones are functional.

NegativeLatency 6y ago

The wings help for covering longer distances efficiently but make hovering and vertical takeoff tricky, tail-sitters combine positive features from both types of aircraft https://en.wikipedia.org/wiki/Tail-sitter https://en.wikipedia.org/wiki/Tail-sitter

Tomminn 6y ago

I think there will be a large market for plane-like drones with very malleable wings for exactly the reason you state. The cost (in terms of both price and structural integrity) of gratuitously dynamic wings (think turning the whole wing 45 degrees to horizontal, bending the wing to 90 degrees at it's half way point) are much smaller for small aircraft. Such gratuitously dynamic wings give more degrees of freedom for automated piloting software to work with when it comes to optimizing near vertical take-off and landing when compared to a fixed wing aircraft, while retaining fixed wing efficiency advantages during elevated flight.

seasonalallergy 6y ago

Why the quad set up over the classic single rotor seen in helicopters?

jlcortex 6y ago
A hybrid drone like HYBRiX has power redundancy. If the engine stops for some reason, it still has some minutes of endurance in electric-only mode, for an emergency landing. With an unmanned helicopter, if the engine fails, the crash is mostly warranted, even with the autorotation function. Besides, the mechanics are simpler and therefore more reliable. And the propellers are smaller than a helicopter rotor, which is safer. Multirotors are also much simpler to operate than a helicopter. Most industrial customers do not want to operate unmanned helicopters because of their complexity.
bri3d 6y ago
Mechanical complexity. A collective pitch helicopter requires a bunch of expensive moving parts and linkages to run the swash plate. The most traditional design requires 3 relatively powerful linear actuators of some sort as well as a spherical bearing at the swash plate, then 2 linkages to the rotor head and 2 more bearings on the rotor head itself. A quadcopter requires brushless motors (usually with 2-3 typical sealed ball bearings each) and props. Less moving parts, broadly generalizing, means fewer ways to fail.

pengaru 6y ago

TL;DR: It's because they can hover. They have a stable and basically stationary anywhere in 3-space mode (until the juice runs out). Human and automated control is much simpler as a result.

meheleventyone 6y ago

Small wings are less efficient particularly when things get really small but at this weight there are a lot of fixed wing UAVs. This is also not terribly small at 1.6m long.

jlcortex 6y ago
Fix wings are amazing for some applications. The problem with them starts when you want to carry heavier payloads. Taking-off and landing gets more and more complicated as they scale-up, while you only need 10 sq. meters to take-off HYBRiX drone. In the end, the different drone types are suitable for different purposes.
- meheleventyone 6y ago
  Yeah most obviously this is useful if you need to land and then take off again somewhere where you don't have infrastructure to relaunch a fixed wing UAV. For example collecting something. Although that presents its own challenges in terms of how non-experts safely handle attaching the payload to the UAV. I think its a super interesting piece of kit so I hope you find success with it!

extropy 6y ago

To add to all the other responses, multirotors are the least power efficient setup by far. And fixed wing the most, and regular helicopter somewhere in the middle. Several hours of flight time is trivial with a battery powered fixed wing model airplane.

baybal2 6y ago

> Why then a quadcopter is the default shape for smaller drones? Because somebody, somewhere published the first opensource autopilot code, and that first code was for the quadcopter.

serf 6y ago
a stupid nit to pick about an obvious off-the-cuff statement, but the whole drone hobby is older than quadcopters, as are open-source 'drone' solutions with route planning/loitering/all the stuff you'd expect a drone to do. But before quadcopters we used large-wingspan EPO foam / balsa / plastic planes. It's still common place.
- baybal2 6y ago
  Yes, but I say that the quadcopter boom was almost singlehandedly due to appearance of the single firmware which was "copypasteable," and suitable for garage factories.

matheusmoreira 6y ago

Fixed wing aircraft must have air moving along the wings in order for them to generate lift. In other words, the aircraft must always be moving through the air. If its speed drops below some minimum value, it will stall and drop out of the sky like a rock. This is also why they need runways in order to take off. They need to accelerate to a minimum speed in order to even get airborne. https://en.wikipedia.org/wiki/V_speeds https://en.wikipedia.org/wiki/V_speeds Rotary wing aircraft use their engines to constantly move the wings through the air instead of moving the aircraft itself. So the wings are always generating lift and the aircraft is free to move in much more flexible patterns. A very useful maneuver is hovering in place: the aircraft is able to simply hold its position in the air. Since only the wings need to move to generate lift, the aircraft itself does not need to accelerate in order to take off and therefore a long runway is not necessary. Civilian drones usually have rotary wings because this allows people to do useful things like having the drone stay in one place in order to film or photograph something. A fixed wing aircraft would have to establish a loitering pattern around an area in order to do the same thing. In other words, rotary wings can just hover in place while a fixed wing would have to fly around in circles. Fixed wing aircraft are more fuel efficient. Rotary wing aircraft must constantly spend fuel in order to keep their wings spinning. They lose lift otherwise. A fixed wing aircraft would probably be able to glide great distances and even land safely even if it lost all engines in the middle of its flight.

jaclaz 6y ago
There are also unpowered rotating wings. Maybe it is possible to combine a "normal" quadrirotor (for vertical takeoff and hovering) with a rotating wing aircraft, the autogyro: https://en.wikipedia.org/wiki/Autogyro https://en.wikipedia.org/wiki/Autogyro to save a lot of energy when traveling horizontally. There is actually this thing here that is already a sort of cross-breed between a helicopter and an autogyro: https://airialrobotics.com/ https://airialrobotics.com/ https://airialrobotics.com/gt20-gyrotrak/ https://airialrobotics.com/gt20-gyrotrak/
- matheusmoreira 6y ago
  That's really cool! I've read about the use of autorotation but only in the case of emergencies. I had no idea there were entire aircraft based around the concept. Since the rotary wings are unpowered, the autogyro loses many of the properties that make the helicopter so valuable. It requires forward motion in order to move air through the unpowered rotary wings and maintain lift. Looks like they have propellers providing forward thrust just like fixed wing aircraft. The article also states that they're not capable of vertical take off and landing. They need a runway to accelerate just like fixed wing aircraft.

teleforce 6y ago

Having involved in UAV development projects for agriculture monitoring and have used both rotary-wing and fixed-wing UAVs, I'm now firmly believe that neither of them is fit for purpose in aerial monitoring. The rotary-wing UAV is a power hungry gussler while fixed-wing UAV is not that versatile (e.g. for hovering, etc). The best compromise will be Gyrocopter or Autogyro since it is both energy efficient and flexible. It can also easily fly at sustain high speed wind of more than 50 knots. [1]https://en.m.wikipedia.org/wiki/Autogyro https://en.m.wikipedia.org/wiki/Autogyro

wnkrshm 6y ago
Yeah I've wondered for quite a while why autogyro drones aren't popular. They should be efficient and safe - since one problem with autogyros was the noise they made due to large rotor size, drone sized ones shouldn't have that problem.

ajuc 6y ago

Planes work similarly well at small and big scales. They are more efficient than quadcopters even at small scale. Quadcopters are just much safer and easier to control. Compare "fall down at random without input" vs "stop without input". As for why quadcopters aren't used at big scale - moment of inertia scales with cube of the propeller radius. And to control a quadcopter you're constantly speeding up and down each propeller. That's a huge loss of energy when your propellers are big enough. So instead at big scales we use very complicated mechanically designs like helicopter. It uses a propeller that rotates at constant speed (so moment of inertia doesn't matter), and instead changes the angle of attack to control the aircraft. BTW moment of inertia is also why nobody in their right mind would build huge mech robots like in sci-fi. Wheeled vehicles move forward without fighting inertia - wheels spin at constant speed and you just add the energy lost to friction. Mechs constantly swing their huge legs back and forth fighting the whole inertia twice with each step. Fine for toys, not fine for big vehicles.