Why does a helicopter float motionless but still consume gas?

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Discussion Overview

The discussion centers around the mechanics of a helicopter hovering motionlessly and the energy consumption associated with this state. Participants explore concepts related to work, energy, and aerodynamics, questioning why energy is consumed even when the helicopter appears to be stationary.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that when a helicopter hovers, the work done on it is zero, yet it still consumes energy, paralleling this with the fatigue felt when holding a weight still.
  • Others argue that the rotor blades perform significant work by pushing air down, which allows the helicopter to maintain its position against gravity, suggesting that from the air's frame of reference, the helicopter is indeed moving.
  • One participant mentions that the aerodynamics involved are more complex than initially presented and references external sources for further reading.
  • Another viewpoint suggests that both hovering and holding a weight are inefficient methods of generating static force, with energy dissipated as heat and in moving air.
  • Some participants note that helicopters do not always consume energy while hovering, indicating variability in energy consumption.
  • There is a discussion about the importance of reference frames and the definition of work, with one participant emphasizing that a helicopter operates differently than a static object like a book.
  • A participant poses a question regarding the helicopter's ability to continue hovering if the engine were turned off, prompting further inquiry into the mechanics involved.
  • Another participant clarifies that helicopters hover rather than float, challenging the terminology used in the original question.

Areas of Agreement / Disagreement

Participants express differing views on the nature of work done by a hovering helicopter, with some asserting no work is done while others contend that significant work occurs through air movement. The discussion remains unresolved with multiple competing perspectives on the mechanics of hovering and energy consumption.

Contextual Notes

Participants highlight the complexity of aerodynamics and the definitions of work and energy, indicating that assumptions about these concepts may vary among contributors. The discussion also touches on the implications of reference frames in analyzing the system.

fxdung
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When a helicopter float motionless the work done on it is zero.But why does it still consume energy?A similar question is why when we hold still a weight, we must consume energy(we feel fatigue)?
 
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It is not true that no work is being done. The rotor blades do a LOT of work pushing air down and thus causing the helicopter to accelerate upwards at 9.80665 m/sec/sec in a gravitational field that is causing it to accelerate downwards at the same rate. So ... helicopter stays motionless, air moves. From the frame of reference of the air, the helicopter is moving quite a bit and is doing a lot of work.

I think the aerodynamics of it all may be a bit more complicated than that simple explanation, but you get the idea ...

The exact same question was asked recently in the form of "if I push a box across the floor against friction, I am doing work, but in MY frame of reference the box isn't moving so I'm actually NOT doing any work. What gives?" In his frame of reference he is doing work moving the floor under him. In both his question and yours, you can't get rid of the work being done just by changing frames of reference.
 
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fxdung said:
When a helicopter float motionless the work done on it is zero.But why does it still consume energy?A similar question is why when we hold still a weight, we must consume energy(we feel fatigue)?
Both are inefficient ways to generate a static force. The energy goes into moving air and heat.
 
fxdung said:
When a helicopter float motionless the work done on it is zero.But why does it still consume energy?
They don't always consume energy when floating motionless... 😉

http://avia-proekt.ru/img/ch7_9.jpg
1564755804228.png
 
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phinds said:
I think the aerodynamics of it all may be a bit more complicated than that simple explanation, but you get the idea ...
Due to the nature of the question, the aerodynamics are unimportant and the Newton's 3rd law + definition of work (power) explanation is all that is needed.

If I had a quibble it would be on the need to discuss reference frames here. To me it's about the proper definition of the system being analyzed. A helicopter is not a book sitting on a table, it's a fan sitting on a table. The fan does work because it's a fan!
 
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Why does a helicopter float motionless but still consume gas?

If you turned the engine off, would it continue to float?
If not, why not? (Please write a sentence for that and not a one-word answer)
 
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fxdung said:
When a helicopter float motionless the work done on it is zero.
Helicopters dont float, They hover

Answer @Vanadium 50 's Q's above
 
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A.T. said:
The energy goes into moving air and heat.
Yup, that description couldn't be much closer. . . as to how the real deal works .

.
 

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