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Given the limited amount of energy (battery or fuel) let's reach the maximum possible altitude!

Rotary wing aircraft pushes the air directly downwards and propels itself straight up.

Fixed wing, however, must gain forward speed to produce lift, so it wastes some energy for unnecessary circling and associated drag. Anyway, eventually, its wings must somehow push the air downwards to gain altitude (that's what Newton says), energy-wise is it really different from rotary wing? (especially when circling really tightly?)

Moreover, imagine our fixed might wants to pitch up really hard and has powerful engine - at some point this makes it similar to rotary wing, in that the thrust direction becomes more and more vertical. Oh, so the distinction might be not that obvious!

Anyway, the question is, for this specific requirement of going just up, is the fixed wing still more energy efficient to reach a certain altitude than a rotary wing and why?

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    $\begingroup$ I'm not sure this is even a question, when is the last time you heard of a helicopter flying at 50,000 ft? World record is 42,500... $\endgroup$ – Ron Beyer Jun 13 '16 at 13:20
  • $\begingroup$ @RonBeyer I think that "Max Altitude" was just thrown in there because the question at the end asks more of "Is a fixed wing more efficient in getting to a given altitude than a rotary wing?". $\endgroup$ – SMS von der Tann Jun 13 '16 at 13:31
  • $\begingroup$ @SMSvonderTann Yes, exactly, I meant the cases where the limiting factor is energy, and not the unfavorable physical conditions at high altitudes. Of course this is still connected somehow... $\endgroup$ – szulat Jun 13 '16 at 13:34
  • $\begingroup$ @SMSvonderTann I rolled back your edit because it significantly changes the question, fuel efficiency can't be used to compare rotary/fixed wing in this context. $\endgroup$ – Ron Beyer Jun 13 '16 at 13:41
  • $\begingroup$ Please note that helicopters will climb faster while moving forward. To gain altitude pilots will sometimes fly a climbing spiral $\endgroup$ – TomMcW Jun 13 '16 at 18:02
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A helicopter in forward flight is more efficient than a helicopter in vertical hover, due to less induced drag (and more form drag which becomes a problem at high fwd speed).

Fixed wing aircraft are more efficient than forward flying helicopters because:

  • The rotor flow in forward flight causes fearsomely complex aerodynamic interactions in flow with the fuselage and other components, which causes a particular type of drag that a fixed wing simply does not have.

  • When the helicopter is in forward flight, the rotor disk has the same characteristics as a fixed wing: less induced drag, higher form drag. But it will be a circular wing, which is always less efficient than a beautiful slender fixed wing. The slenderer (is that a word?) the better.

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The first human powered airplane flew in 1977, and a later version https://en.wikipedia.org/wiki/MacCready_Gossamer_Albatross in 1979.

The first human powered helicopter flew in 1989. The Wikipedia article mentions several endurance records (measured in minutes), but no distance records.

It stands to reason that if a rotary wing were more efficient, human powered helicopters would have been built prior to human powered fixed wing aircraft and would have accomplished more.

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  • $\begingroup$ The first human powered helicopter flew in 1989. $\endgroup$ – Ron Beyer Jun 13 '16 at 18:59
  • $\begingroup$ @RonBeyer - thanks, I've updated the answer. $\endgroup$ – Dan Pichelman Jun 13 '16 at 21:14
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It is worth noting that on a fixed wing aircraft the aerofoil shape of the wing creates low and high pressure rather than, as you said "its wings must somehow push the air downwards to gain altitude"

Technically speaking the Rotors on Helicopters are much the same (aerofoil) shape as wings on a fixed wing aircraft. The difference is they're forced to move through the air at speed by the engines thereby creating low and high pressure in much the same way.

Fixed wing aircraft can and do fly higher. I'm not sure if helicopters can safely reach the top of Mount Everest, whereas fixed wing aircraft fly over the top of it daily. I believe (and could be wrong) air density at higher altitudes will not support the weight of a helicopter without the rotors rotating faster (there is a limit to how fast they can go) to produce more lift.

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  • $\begingroup$ Actually, a wing does end up pushing air downwards... See aviation.stackexchange.com/a/21685/69 $\endgroup$ – Lnafziger Jun 1 '17 at 21:09
  • $\begingroup$ Admiral, insofar as Mount Everest, A Squirrel did just that. On May 14th, 2005 at 7h08 (local time), a serial Ecureuil/AStar AS350 B3 piloted by the Airbus Helicopters X-test pilot Didier Delsalle, landed at 8,850 meters (29,035ft) on the top of the Mount Everest (Kingdom of Nepal). It is also a world altitude takeoff record ... but I'll offer that it's not an every day thing. $\endgroup$ – KorvinStarmast Jun 3 '17 at 17:55
  • $\begingroup$ @KorvinStarmast Well, this answer makes it sound like air is not pushed down by a wing, so a slight clarification would make this read better. Just a simple suggestion. $\endgroup$ – Lnafziger Jun 3 '17 at 19:44
  • $\begingroup$ @Lnafziger yeah, the answer could use a bit of revision. I have never preferred to use "the wing pushes air down" phrasing to explain lift. But that's a matter of style, since the more neutral view I tend to take is "where is delta P taking you, up or down?" but that's getting off topic. $\endgroup$ – KorvinStarmast Jun 3 '17 at 20:44
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Most "conventional" helicopters (those with a tail rotor or fan) cannot be as efficient as a fixed wing in any flight regime.

This is because the tail rotor or fan uses a considerable amount of the power available to counter torque and to control the helicopter in yaw. This power contributes nothing towards climbing or forward speed.

For all helicopters, the lift drag ratio is less than for fixed wing. In order to climb to high altitudes, more lift must be generated which can only be done by increasing the pitch of the blades. The rotor RPM is limited by two effects; a, dissymmetry of lift and b, a large increase of drag as the tips approach supersonic. These limits means that increasing pitch is the only way to continue to climb and eventually, you will simply run out of angle of attack as drag overcomes the ability of the engine to deliver power.

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