5 ms·

It definitely is heavy lift as far as drones are concerned. But I am disappointed that there has been so few drones trying to go in this direction that 200kg is

It definitely is heavy lift as far as drones are concerned. But I am disappointed that there has been so few drones trying to go in this direction that 200kg is considered “heavy.” (You can make arguments that the multi rotor approach has lower maintenance needs than swashplate-based conventional helicopters, besides the use of electricity instead of hydrocarbons… these all potentially allow lower operating costs. And the higher pitch sound of multi rotors travels less far than low frequency of helicopter blades.)

idiotsecant 5y ago
It's not just maintenance issues - it's fundamental aerodynamics. Efficiency scales with the diameter of the rotor in rotary wing aircraft. Larger rotors are more efficient. In a helicopter you lose a bit of that efficiency from the tail rotor, but past a certain size helicopters are always going to be more efficient, until you get the size regime that materials drive all designs to become multi-rotor. It seems like maybe there is a niche for very large fixed-pitch propeller vehicles like quadrotors but at that scale why stick with fixed pitch at all? You could still have variable pitch rotors with variable speed drivers and get the best of both worlds, like a Kaplan turbine in hydraulics, but in reverse.
- nradov 5y ago
  Single rotor designs remain efficient to a rather large size regime. The largest helicopter in operational use today is the Mil Mi-26 which has only a single rotor. The prototype Mil V-12 was a little larger and had two rotors but was not successful.
  - idiotsecant 5y ago
    That is indeed a very big main rotor. I wonder what the material limitations are on rotor length?
    - blacksmith_tb 5y ago
      Not an aerospace engineer, but my instinct is that spinning larger and larger rotors at the speeds needed to provide lift would likely become an issue before material strength, though obviously it's a consideration also.
  - Robotbeat 5y ago
    In part that’s because combustion engines scale down extremely poorly (they lose efficiency like mad… a micro turbine gets like 5% efficiency whereas a full sized turbine gets upward of 30%) and have high complexity. They’re also difficult to throttle on command with high responsiveness (hence the swashplate). Electric motors are far better suited to distributed lift concepts. That’s a huge reason why existing vertical lift doesn’t use multiple rotors. Electric motors using high energy magnets, modern solid state power controllers, and modern batteries are only just now becoming available & only now are they starting to impact the aviation trade space.
- Robotbeat 5y ago
  That's kind of a misconception. You can use a whole bunch of smaller rotors to have nearly the same efficiency as a single rotor of the same diameter (okay fine there are also Reynolds Number effects from going smaller, but not as important in this context). The difference is roughly the packing ratio of circles, about 90%. VoloDrone takes this approach.
  - idiotsecant 5y ago
    For a real-word cargo flight there are climb conditions and cruise conditions and a fixed-pitch rotor can't possibly be efficient at both - it will be tuned for a given rotation speed and a given airspeed across the disk. At any ambient conditions outside those regions efficiency will suffer. variable-pitch rotors can adjust to high efficiency in cruise and good climbing performance, depending on requirements. Electric cargo vehicles are neat, and maybe the loss in efficiency is acceptable, but you undeniably lose efficiency with a fixed rotor design.
    - Robotbeat 5y ago
      But all of that has maintenance overhead, and whether hover or translational flight dominate the energy consumption determines which to optimize… there’s no great efficiency loss to going fixed pitch unless these two flight regimes have near equal average energy usage per flight. Additionally: Variable pitch is one thing, but swashplate flight is another. There’s no significant efficiency reason to change blade pitch multiple times per second. Much slower variable pitch propellers, aka on horizontal flight aircraft, is much lower maintenance and overall complexity than a swashplate based helicopter.

idiotsecant 5y ago

It's not just maintenance issues - it's fundamental aerodynamics. Efficiency scales with the diameter of the rotor in rotary wing aircraft. Larger rotors are more efficient. In a helicopter you lose a bit of that efficiency from the tail rotor, but past a certain size helicopters are always going to be more efficient, until you get the size regime that materials drive all designs to become multi-rotor. It seems like maybe there is a niche for very large fixed-pitch propeller vehicles like quadrotors but at that scale why stick with fixed pitch at all? You could still have variable pitch rotors with variable speed drivers and get the best of both worlds, like a Kaplan turbine in hydraulics, but in reverse.

nradov 5y ago
Single rotor designs remain efficient to a rather large size regime. The largest helicopter in operational use today is the Mil Mi-26 which has only a single rotor. The prototype Mil V-12 was a little larger and had two rotors but was not successful.
- idiotsecant 5y ago
  That is indeed a very big main rotor. I wonder what the material limitations are on rotor length?
  - blacksmith_tb 5y ago
    Not an aerospace engineer, but my instinct is that spinning larger and larger rotors at the speeds needed to provide lift would likely become an issue before material strength, though obviously it's a consideration also.
- Robotbeat 5y ago
  In part that’s because combustion engines scale down extremely poorly (they lose efficiency like mad… a micro turbine gets like 5% efficiency whereas a full sized turbine gets upward of 30%) and have high complexity. They’re also difficult to throttle on command with high responsiveness (hence the swashplate). Electric motors are far better suited to distributed lift concepts. That’s a huge reason why existing vertical lift doesn’t use multiple rotors. Electric motors using high energy magnets, modern solid state power controllers, and modern batteries are only just now becoming available & only now are they starting to impact the aviation trade space.
Robotbeat 5y ago
That's kind of a misconception. You can use a whole bunch of smaller rotors to have nearly the same efficiency as a single rotor of the same diameter (okay fine there are also Reynolds Number effects from going smaller, but not as important in this context). The difference is roughly the packing ratio of circles, about 90%. VoloDrone takes this approach.
- idiotsecant 5y ago
  For a real-word cargo flight there are climb conditions and cruise conditions and a fixed-pitch rotor can't possibly be efficient at both - it will be tuned for a given rotation speed and a given airspeed across the disk. At any ambient conditions outside those regions efficiency will suffer. variable-pitch rotors can adjust to high efficiency in cruise and good climbing performance, depending on requirements. Electric cargo vehicles are neat, and maybe the loss in efficiency is acceptable, but you undeniably lose efficiency with a fixed rotor design.
  - Robotbeat 5y ago
    But all of that has maintenance overhead, and whether hover or translational flight dominate the energy consumption determines which to optimize… there’s no great efficiency loss to going fixed pitch unless these two flight regimes have near equal average energy usage per flight. Additionally: Variable pitch is one thing, but swashplate flight is another. There’s no significant efficiency reason to change blade pitch multiple times per second. Much slower variable pitch propellers, aka on horizontal flight aircraft, is much lower maintenance and overall complexity than a swashplate based helicopter.