A philosophical/technical question about # of rotors

Dark Skies

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So I'm sitting and musing about things last night, and I got to wondering, why are multi-rotor (usually four) configurations so ubiquitous in the consumer/recreational drone space? Is there a practical technical reason for this? Are there any single/dual rotor consumer drones? I know that r/c copters are a thing, why not make them semi-autonomous, ergo, drones? And if there is something better about quadrotor setups, why aren't there any (or more) full-sized, passenger-capable quadrotor aircraft? I'm interested to hear any thoughts/insights on this.
 
Probably not used for manned flight due to chances of one motor going out and it crashing. Would be 4 times the failure chance of a helicopter.
 
Yes, that makes sense. To my original question, why is the quad+ configuration so popular with small UAVs?
Okay, I decided to look up some tech sheets about this, which in retrospect I should've figured out - a single rotor drone would have a miniature version of the ridiculously complex drivetrain of a manned chopper, swash plates and all the other tech necessary to manipulate that one rotors blades to provide directional control. With multirotors the only thing necessary is to vary the rotational speed of each motor to getcha where you want to go, no pivoting blades or swiveling masts. Cool, got it. Now to the next question I'll come up with while drunk. 🥃🍸🍷 Cheers.
 
Probably not used for manned flight due to chances of one motor going out and it crashing. Would be 4 times the failure chance of a helicopter.
That's not entirely fair. bearing in mind that single engine failure is less serious in 4-engined aeroplanes than in 2-engined aeroplanes, and in turn single failure is less serious in 2-engined than in in single-engined. If one specifies that in a 4 motor drone two are sufficient to keep it aloft then the third can be used to control pitch/yaw/roll as appropriate
 
That's not entirely fair. bearing in mind that single engine failure is less serious in 4-engined aeroplanes than in 2-engined aeroplanes, and in turn single failure is less serious in 2-engined than in in single-engined. If one specifies that in a 4 motor drone two are sufficient to keep it aloft then the third can be used to control pitch/yaw/roll as appropriate
Respectfully, that's comparing aerodynamic apples and oranges. Rotor aircraft get ALL their lift from the engines turning the rotors, airPLANES get their lift from their wings thanks to our friend Mr. Bernoulli. Their engines are only responsible for propelling the plane fast enough for the wings to generate lift. Yes, multiengine airplanes can absolutely survive partial engine failures as long as the remaining engine(s) can keep them above stall speed. Hell, some airplanes can lose all their engines or engine and can still be glided in for a landing. But, in, say, a quadrotor manned aircraft, if you lose one engine 25% of your lift is gone, not only that, but your remaining lift vectors are severely unbalanced at that point which would be asking a lot of the remaining rotors. You might be able to feather it down for a hard landing, just as chopper pilots can sometimes do in the event of engine failure, but it's definitely a worse scenario than losing an engine on a multiengine airplane.
Thanks to all who've participated in this thread started by my random inebriated question. Have a good one. Also, we're getting some serious snow here in NC this evening, I was wondering if anyone has flown a drone in a snowstorm? Assuming, of course, that it's not windy. I know rain would be a problem, but would a steady but gentle snow cause issues? Just curious (again!).
 
Respectfully, that's comparing aerodynamic apples and oranges. Rotor aircraft get ALL their lift from the engines turning the rotors, airPLANES get their lift from their wings thanks to our friend Mr. Bernoulli. Their engines are only responsible for propelling the plane fast enough for the wings to generate lift. Yes, multiengine airplanes can absolutely survive partial engine failures as long as the remaining engine(s) can keep them above stall speed. Hell, some airplanes can lose all their engines or engine and can still be glided in for a landing. But, in, say, a quadrotor manned aircraft, if you lose one engine 25% of your lift is gone, not only that, but your remaining lift vectors are severely unbalanced at that point which would be asking a lot of the remaining rotors. You might be able to feather it down for a hard landing, just as chopper pilots can sometimes do in the event of engine failure, but it's definitely a worse scenario than losing an engine on a multiengine airplane.
Thanks to all who've participated in this thread started by my random inebriated question. Have a good one. Also, we're getting some serious snow here in NC this evening, I was wondering if anyone has flown a drone in a snowstorm? Assuming, of course, that it's not windy. I know rain would be a problem, but would a steady but gentle snow cause issues? Just curious (again!).
I repeat: "if one specifies that in a 4 motor drone two are sufficient to keep it aloft". Yes, this is more power than most drones have, but it is an engineering possibility. If one motor fails two can continue to keep it aloft while the 3rd motor can then function as an attitude controller. It is probably easiest to envisage this with two diagonal motors providing the lift with the third alongside for attitude, but if the computer is adjusted appropriately then any pair will do
 

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