I always wondered why there are no "real life" sized quadcopters in use for manned flight. From what I understand the design is simpler and requires less maintenance compared to "normal" helicopters.
Are there any reasons why we're not flying quadcopters around instead?
I always wondered why there are no "real life" sized quadcopters in use for manned flight.
The explanation is simple: quadrotor physics do not scale up. The rotational inertia of the rotors is proportional to the length of the rotor blade to the fifth power. Double the rotor blade length and the inertia of that rotor goes up by a factor of 32.
High inertia rotors are not suitable for quadrocopter because fast changes in the rotation of the rotors required for maneuvering them.
Having one big rotor for lift and three (or more) small ones for control is a very good idea. Another idea that is being researched is having multiple quadrotor copters flying in co-operation.
Mass is not linearly proportional to length, because a longer rotor needs to be a lot heavier to be structurally sound. A uniform rod is not a good analog for a rotor blade. It's not a far fetched idea to think that the mass is cubically or at least quadratically proportional to the length of the rotor.
Unfortunately I can't remember the source where I saw the 5th power figure.
In addition, the aerodynamics of a rotor don't scale up linearly either.
Your assumption is way too simple. Mass increases with the cube of the scale, while cross section area increases with the square of the scale. The cross section will need to increase to cope with the extra mass, and that in turn will increase the mass itself, and this mass is specifically the rotating mass.
There was some crazy man/scammer building a manned flying thing with six snowmobile engines powering six rotors. I remember this because I was working for Ray Ozzie at the time and he was telling people in the office about it because he had invested in it.
I'm by no way an expert on this topic. I just skimmed over the wikipedia article[1] where I read the following:
First, quadcopters do not require mechanical linkages to vary the rotor blade pitch angle as they spin. This simplifies the design and maintenance of the vehicle.
As already mentioned I'm blatantly ignorant about this topic so it would be nice if someone who knows this stuff could chime in :)
small quadcopters basically speed up and slow down the motor itself to control how much lift is generated. As the size and weight of the blade increase, inertia makes that impractical, so you have to go to variable pitch for control.
For the hobby sized quads, it's simple enough to swap a motor. It is definitely easier to maintain since a spare is only 20 bucks and attaches in minutes with zip ties.
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I always wondered why there are no "real life" sized quadcopters in use for manned flight. From what I understand the design is simpler and requires less maintenance compared to "normal" helicopters.
Are there any reasons why we're not flying quadcopters around instead?
The explanation is simple: quadrotor physics do not scale up. The rotational inertia of the rotors is proportional to the length of the rotor blade to the fifth power. Double the rotor blade length and the inertia of that rotor goes up by a factor of 32.
High inertia rotors are not suitable for quadrocopter because fast changes in the rotation of the rotors required for maneuvering them.
Having one big rotor for lift and three (or more) small ones for control is a very good idea. Another idea that is being researched is having multiple quadrotor copters flying in co-operation.
The moment of inertia for a uniform rod pivoting on end is (1/3)ML^2 where M is mass and L is length.
Assuming mass scales with length, inertia should be proportional to the third power. Where am I wrong?
Mass is not linearly proportional to length, because a longer rotor needs to be a lot heavier to be structurally sound. A uniform rod is not a good analog for a rotor blade. It's not a far fetched idea to think that the mass is cubically or at least quadratically proportional to the length of the rotor.
Unfortunately I can't remember the source where I saw the 5th power figure.
In addition, the aerodynamics of a rotor don't scale up linearly either.
Your assumption is way too simple. Mass increases with the cube of the scale, while cross section area increases with the square of the scale. The cross section will need to increase to cope with the extra mass, and that in turn will increase the mass itself, and this mass is specifically the rotating mass.
Lady Gaga flies with a hexacopter @ http://www.dailymail.co.uk/sciencetech/article-2499954/How-L...
... what the world is coming to?
Morning coffee, this put a big smile on my face.
She (or, probably, her team) has been hacking the entertainment scene for a while.
Dubbing "a dress" what would otherwise be considered a nerd toy is genius. What's not a dress for her?
She will also fly with Virgin Galactic: http://www.vanityfair.com/online/oscars/2013/11/lady-gaga-fi...
There was some crazy man/scammer building a manned flying thing with six snowmobile engines powering six rotors. I remember this because I was working for Ray Ozzie at the time and he was telling people in the office about it because he had invested in it.
Moller?
Yeah! That's the guy! HOly moley moller.com still exists. EDIT: Wow, this has been going on since the '70s: http://www.downside.com/scams/moller/
The name "Discojet" is way more badass name than "Skycar." Just another sign of lowered expectations.
Yeah, the Moller Skycar has been an impressively long-running scam. It felt like he got his own article in Popular Mechanics on an annual basis.
I wonder how much damage he does to the nascent industry if personal flying vehicles by sucking all the oxygen out of the room.
there are :) human powered at least:
http://www.youtube.com/watch?v=syJq10EQkog
I wouldn't say less maintenance, you've got 4 times as much motors running than a conventional helicopter.
I'm by no way an expert on this topic. I just skimmed over the wikipedia article[1] where I read the following:
As already mentioned I'm blatantly ignorant about this topic so it would be nice if someone who knows this stuff could chime in :)
[1] http://en.wikipedia.org/wiki/Quadcopter
The advantage doesn't scale up well.
small quadcopters basically speed up and slow down the motor itself to control how much lift is generated. As the size and weight of the blade increase, inertia makes that impractical, so you have to go to variable pitch for control.
For the hobby sized quads, it's simple enough to swap a motor. It is definitely easier to maintain since a spare is only 20 bucks and attaches in minutes with zip ties.