
Why haven't quadcopters been scaled up yet? - vitoc
http://aviation.stackexchange.com/questions/3300/why-havent-quadcopters-been-scaled-up-yet
======
Htsthbjig
Because quadcopters are naturally unstable, so you need complex
electronics(and sensors and electric motors) to control it.

You can make helicopters very stable just with weights in the rotor, like any
RC fan knows.

Until very recently the inertial motion control complex elements were very
expensive.

Accelerometers in cars and gyros in smartphones later had made those sensors
inexpensive. The iPhone was released in 2007, that was 7 years ago.

Every air device carries gyros inside, but for controlling the plane they had
to give you a digital signal, it is not enough with the artificial horizon
sphere.

The simple helicopter design has been mass produced for decades(and wars like
Vietnam subsidized them more), and it is well tested and reliable. Any new
design has to compete in price and will have to iron lots of bugs at first.

The second most important reason is that you need to use electric motors as
normal heat engines could not respond as fast as needed.

So in order to make a quadcopter you need to generate electricity onboard,
which means a big hybrid engine.

I see quadcopters as the future, but in order to compete in price, they will
have to evolve from small UAVs.

~~~
headShrinker
You touch on a number of good points here. It's true you need accelorometers
measuring and giving feedback a few hundred times a second. Electric motors
are the only motors that can respond to feedback that fast. So the batteries
will be a big deal on a scaled up quad.

The most important aspect you didn't mention is that they are inherently
inefficient. The more blades you have, the more inefficiency is introduced.
that's why scaling them up doesn't make much sense.

~~~
mrestko
Why couldn't you use a turbine to generate electricity that is then fed to
electric motors controlling the blades? Is there actually a requirement for
large, efficient batteries?

~~~
YZF
You've just added a bunch of weight and lost a whole bunch of energy in the
process. (EDIT: vs. just not using electrical motors. vs. batteries it really
depends on the specifics but if you could get what you get out of a battery
with a turbine of lesser weight then presumably we'd all have little turbines
in our iPhones and electric cars)

------
WalterBright
An airplane is a vehicle that wants to fly, a helicopter wants to crash. A
helicopter is inherently unstable and requires constant adjustment. It has
multiple single points of failure, any one of which will result inevitably in
a crash. This is dealt with by insanely expensive quality control, constant
inspections, and constant maintenance.

The quadcopter doesn't improve on this, it makes it worse. It has 4 engines -
if one engine fails, it crashes. It has inherently 1/4 of the reliability of a
single engine helicopter. Losing one rotor blade will also cause a crash, so
its 1/4 of the reliability there as well. QA, maintenance, and overhauls will
cost 4x as much.

~~~
serf
[http://spectrum.ieee.org/automaton/robotics/aerial-
robots/ev...](http://spectrum.ieee.org/automaton/robotics/aerial-robots/every-
quadrotor-needs-this-amazing-failsafe-software)

stable flight is not impossible with the loss of a motor on a quadrotor
platform. it's currently stuck in labs, but the dynamics are doable.

~~~
miahi
That kind of stable flight is ok for an unmanned vehicle, but I don't think a
passenger/pilot would be delighted abut that kind of accelerations and spin.

~~~
louthy
I guess if it's a choice between smashing into the ground and short period of
spinning whilst an automated system landed the vehicle, I think I know what
I'd go for.

~~~
ljf
Depending on how fast you are spinning, I imagine the deceleration on landing,
for a human passenger would be lethal or life threatening.

------
milankragujevic
A quadcopter changes direction by spinning up or down the appropriate set of
propellers. The smaller the propellers, the less energy (time) it takes to
slow them down. Meaning a huge quadcopter is increadibly unstable and can't
change direction fast enough for anything. They're uselessly inefficient other
than the smallest ones (flying circuit board, ~4cm long) and the bigger ones
just use bigger batteries and have the same flight time (mainly for lifting
cameras, but they too are slower or use much more energy to go the same speed
as the small ones).

~~~
exDM69
> A quadcopter changes direction by spinning up or down the appropriate set of
> propellers.

To extend on this further... a quadcopter uses the motors to quickly change
the speed of the blades rotating. This requires a lot of power, depending on
the inertia of the rotor. The inertia of the rotor is roughly proportional to
the fifth power of the blade length. Double the blade length, 32x the inertia.
The power requirements of this forbids scaling up.

Contrast this with a traditional helicopter, where the rotor is spinning at
stable speed (low engine torque requirement) and the helicopter is controlled
by changing the pitch of the blades. The pitch of the blades changes during
every rotation and is controlled with a mechanism called a "swashplate".

There have been "hybrid" helicopter designs involving a variable pitch
propeller in a quadcopter as well as supplementing a quad with a large
propeller for lift.

But the most promising research on quadcopters is focusing on using several
independent quadcopters co-operatively.

~~~
Gravityloss
You can have collective pitch setting in a quadcopter, with which you can
scale up quite a lot without having to go to full cyclic pitch control
(helicopters).

So basically it's a spectrum of scale:

    
    
      1) fixed pitch (small quads)
      2) collective pitch (large quads, autogyros)
      3) cyclic and collective pitch (real helicopters)

------
jamesaguilar
Distilled:

\- Large rotors are more efficient than small rotors.

\- Because of the square-cube law, bigger, heavier aircraft require higher
fuel energy densities than can be delivered by batteries. Therefore you need a
relatively complex engine rather than simple motors, and you can't afford to
replicate it four times.

\- A variety of handling and safety benefits of helicopters compared to quad
rotors.

~~~
ObviousScience
Trains require a HUGE engine, yet they relay their power via electrical
linkage. This is actually more efficient than other systems, because it allows
the engine to run at its optimum power generation cycle, without worrying
about converting RPM down to the appropriate amount via mechanical linkage.

An electrical linkage would be relatively straightforward to split in to 4
components.

~~~
bdonlan
It's still a lot of weight to carry around a high-power generator, large-gauge
power cables (or heavy transformers and smaller-gauge cables), and four
electric motors. This is less of a problem on a train, because the train only
has to deal with the additional friction, and doesn't have to worry about
generating more lift to make up for the increased weight.

------
Crito
> _" The only effect that can make quadcopter stable is having centre of
> gravity below centre of lift just like normal helicopter."_

This strikes me as incorrect
([http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy](http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy)),
though I am not totally confident of that.

~~~
baddox
It sounds wrong to me as well. I would think you would want the center of lift
as close as possible to the center of gravity, and that you would also want
the flight controllers accelerometers and gyroscopes in the same spot.

------
moepstar
While it is a multi-copter instead of a quad, this thing looks promising:

[http://www.e-volo.com/](http://www.e-volo.com/)

Video of first flight is on this page: [http://www.e-volo.com/ongoing-
developement/vc-200](http://www.e-volo.com/ongoing-developement/vc-200)

------
Sami_Lehtinen
Here's one quadcopter design which is more efficient that most of older
designs: [http://www.geek.com/science/weve-been-designing-
quadcopters-...](http://www.geek.com/science/weve-been-designing-quadcopters-
incorrectly-since-day-one-1577256/)

------
utopkara
It must be the costs... Multirotors have enjoyed open source development by
enthusiasts so far, and they built heavily on the experience of the RC
enthusiasts, and they repurposed tons of hardware that is suitable for small
applications. A few thousand dollars is within the budget of many developers,
so the small UAV improvements could proceed very much like software-based
innovation curve does. But, any size/budget/project bigger than that is bound
by a different progress curve. I bet it can be done, and if it is practical,
it will be done too. Aerospace engineers were always a very innovative bunch;
check out autogyro
([https://en.wikipedia.org/wiki/Autogyro](https://en.wikipedia.org/wiki/Autogyro)).

~~~
waps
It's not the cost. The problem is electrical planes. Helicopters are known for
their agility, coming at the cost of extreme energy use (and, imho, extreme
danger. Any mechanical failure in any part of the helicopter WILL result in
contact with the ground in 2 minutes or less. Redundancy (in your standard
helicopter craft) is effectively zero). Getting a normal plane to fly
electrical is a huge challenge. Getting a helicopter to fly electrical is a
bigger challenge.

In 2011, for the first time in history, a manned helicopter took flight. More
than 1/4th of the flight mass was batteries and that afforded the craft ~2
minutes of powered flight (hover, not maneuvering). [1]

We just don't have the electrical storage solution to pull it off easily. It's
not impossible at these efficiencies either, but it's bloody hard.

It's not just electrical power that falls short. For the longest time, planes
were quite picky fuel wise and gasoline also fell short. Even today, it's not
gasoline that's used, even though most planes will fly fine on your car's
gasoline (not diesel though), even corn ethanol, but less efficient (range
reduction of ~20-30%).

The answer to most of the "can we do X with electricity" is simply : find a
way to store 4 times (or more) the electrical power in something the size and
weight of our best batteries (take lithium-polymer), and it'll work. Without
that, it's barely possible.

We do have things that store electrical power more effectively than a battery,
but you won't like them. Plutonium batteries would easily allow for an
electrical helicopter and would allow it to remain flying constantly for 40
years straight (or more if you like, thousands of years wouldn't be out of the
question, really). There are a few other nuclear options that would provide
similar performance. But I don't think I need to explain why this isn't done.
Plutonium batteries have the advantage that they do direct electricity
generation, making them very, very small and efficient. Also, in space,
temperature is supposedly -271 degrees celcius, but because there's no gas
colliding with the craft, heat will take weeks to leak away from the
spacecraft. So anything with a heat based generator (which is nearly
everything) is out. Which is why plutonium batteries are pretty much the only
answer.

[1] [http://www.industrytap.com/worlds-first-electric-powered-
hel...](http://www.industrytap.com/worlds-first-electric-powered-
helicopter/3693)

~~~
jacquesm
A couple of factual issues: most planes fly on Jet-A aka Kerosine which is
actually closer to diesel than to gasoline.

You're talking about 'avgas' which is used for piston engined planes, the
turbines typically run on cheaper fuel (they _can_ be run on just about
anything but typically you'd run them on Jet-A rather than on single malt
scotch).

Second, plutonium 'batteries' (you mean a thermoelectric generator powered by
nuclear decay) aka an RTG is not feasible for aircraft due to the weight of
the shielding that such a solution would require as well as the risks
associated with flying such a device (it can crash!), not to mention the
proliferation headaches and waste disposal issues.

So even though they are used in space they have little or no chance to ever
see deployment in commercial aviation or to power drones.

------
Arcanum-XIII
There's alternative to the common arrangement of a motor per blade, like the
[http://curtisyoungblood.com/V2/products/quadcopters/stingray...](http://curtisyoungblood.com/V2/products/quadcopters/stingray-500)
\- one motor, variable pitch. It's clearly more complex, but you gain agility,
motor efficiency and it seem to give a better running time.

------
lotsofcows
One major reason for multi rotor machines is to avoid the classic helicopter
problem of the rotor blade's leading edge approaching the speed of sound while
the trailing blade is simultaneously stalling.

Unfortunately, this would require such a scaling up of existing quadcopter
designs that it's unlikely to ever happen for all the reasons already listed.

------
tim333
The Lady Gaga copter is quite funky [http://www.10news.com/news/lady-gaga-
takes-flight-in-hoverin...](http://www.10news.com/news/lady-gaga-takes-flight-
in-hovering-dress-designed-in-part-by-carlsbad-pilot-11242013)

------
jonah
What I'd like to see are more small "drones" with alternate arrangements.
Counterrotating Coaxial for example.[1]

[http://www.youtube.com/watch?v=DUGEjQdoylY](http://www.youtube.com/watch?v=DUGEjQdoylY)

~~~
miahi
As many of the other answers say, the current multicopters are very simple,
mechanically: an electric motor directly coupled to a fixed-pitch propeller.
Everything is controlled by the amount of current the motors receive.

Any other alternate arrangement means a more complex mechanical control:
servos, gears, larger propellers, variable-pitch propellers... This makes them
less reliable, harder to mend and more dangerous (that's one of the reason
model helicopters never really caught on, even with modern electronic
stabilizers - even a smaller 450-class blade can break bones if you hit it).

------
SoftwareMaven
This is the interesting answer there, IMO. An interesting take on a real
multi-prop vehicle:
[https://www.advancedtacticsinc.com](https://www.advancedtacticsinc.com)

The video linked at the bottom is worth a watch.

------
kashkhan
They are coming...

[http://zee.aero/](http://zee.aero/)

[http://www.jobyaviation.com/S2/](http://www.jobyaviation.com/S2/)

For practical reasons and redundancy more than four rotors is better.

~~~
spacefight
Zee: Zero learned. A better insight can be gained here:

[http://www.gizmag.com/flying-car-zee-
aero/29890/](http://www.gizmag.com/flying-car-zee-aero/29890/)

S2: Interesting concept - the battery density will still be an issue.

~~~
kashkhan
yep. there are pictures floating of the zee aero plane.

[http://cdn.slashgear.com/wp-
content/uploads/2013/11/6r363-on...](http://cdn.slashgear.com/wp-
content/uploads/2013/11/6r363-on-Instagram-611x420.png)

If your mission is 100miles radius electric is doable.

200kg payload, 200kg airframe and 200kg batteries (100kWh)

6minute hover at 200kW => 20kWh

30minute flight at 200mph (60kW) => 30kWh

1/2 hour margin for legal reasons.

low hover tip speed (200m/s) for low noise.

------
ghostdiver
Does it necessarily has to be a *copter?

[http://en.wikipedia.org/wiki/Hawker_Siddeley_Harrier](http://en.wikipedia.org/wiki/Hawker_Siddeley_Harrier)

~~~
Sami_Lehtinen
There's a long list of VTOL aircrafts, but all of those are more or less
horrible compromises.
[https://en.wikipedia.org/wiki/List_of_VTOL_aircraft](https://en.wikipedia.org/wiki/List_of_VTOL_aircraft)

------
ck2
Can quadcopters safely land on three motors? How about less?

~~~
Istof
[http://diydrones.com/profiles/blogs/new-algorithm-can-
save-a...](http://diydrones.com/profiles/blogs/new-algorithm-can-save-a-
quadcopter-after-one-motor-prop-failure)

------
Terr_
The same reason the birds and the bees have radically different wings.

Scaling up insect flight to bird size does not go well, because physical
properties do not scale evenly.

~~~
keenerd
Scaled up insects work just fine when the atmosphere has 50% extra oxygen.
Birds figuratively ate them for lunch, but for several million years 70cm
wingspans were not uncommon for dragonflies.

------
dharma1
Also wondering if VTOL multi rotor/fixed wing hybrids could be scaled up

~~~
dharma1
Appears they can

[http://www.janes.com/article/42425/darpa-awards-boeing-
contr...](http://www.janes.com/article/42425/darpa-awards-boeing-contract-for-
phantom-swift-as-new-vtol-x-plane)

------
jokoon
Also electrical rotors have much finer control than a piston engine.

~~~
jacquesm
Electrical _fixed_ rotors. Once you have a swashplate to give you variable
pitch that can be used to give you the same kind of control that you get by
changing the RPM and the electrical advantage disappears.

