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Helicopters or dual/quadcopters stop rising after reaching some height from the ground. What causes that? And what one should do if he want to prevent this, if he want the helicopter to keep rising up?

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  • $\begingroup$ Density of air decreases as you go up, and when helicopter goes up it looses lift until it reaches point where air density is so low that helicopter's lift isn't enough to go up $\endgroup$
    – G B
    Jun 19 '14 at 15:09
  • $\begingroup$ have you Googled for helicopter maximum altitude or something similar? I just had a quick look and Google found dozens of relevant articles. $\endgroup$ Jun 19 '14 at 15:09
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    $\begingroup$ This question appears to be off-topic because it shows insufficient effort $\endgroup$ Jun 19 '14 at 15:10
  • $\begingroup$ How can I know where the helicopter stops lifting? $\endgroup$ Jun 19 '14 at 15:11
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In the most simplified view, a helicopter is basically a really powerful fan, which is something that pushes air (and therefore feels a force in the opposite direction). When you get high enough, the air starts thinnning, so there is less to push, so that force becomes too low to hold it up. Imagine the limiting case of outer space: nothing would happen.

There's nothing you can really do to combat this, except run your motors faster and faster as the air gets thinner. Eventually you have to rely on things like rockets that don't need an atmosphere to gain momentum.

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  • $\begingroup$ Thanks, How can I know where the helicopter stops lifting? $\endgroup$ Jun 19 '14 at 15:14
  • $\begingroup$ That would probably be very complicated in reality, but you could start by searching google for the thrust your motor and blades can produce at a given air density, find the density as a function of height, and see when that matches the weight of the helicopter. You might be able to come up with ballpark numbers easily. $\endgroup$ Jun 19 '14 at 15:20
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A helicopter is not fundamentally different from a fixed-wing aircraft. Fixed-wing craft also have maximum altitudes for the same basic reason - thrust (or airspeed at the wing) vs. air density.

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