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Not an expert or anything. Never studied aerodynamic or flight in depth. As far as I understand, for helicopter to fly, it definitely has to have thrust to weig

Not an expert or anything. Never studied aerodynamic or flight in depth. As far as I understand, for helicopter to fly, it definitely has to have thrust to weight ratio greater than one. Flying things that have thrust to weight ratio > 0 are intuitive to me. They generate force and stay in the air indefinitely. Planes obviously don't require that to fly. So, they're different type of beast. They somehow squeeze more from less, exploiting some nonlinearity in forces that air exhibit on wings. I can understand that too, but the nature of that phenomenon is not explained anywhere (other than in words: this is the formula. It is correct, trust us)

Cogito 5y ago
It's the exact same principle for planes and helicopters. If a plane isn't producing more lift than weight it will fall, just like a helicopter. Planes work by pushing a wing through the air, helicopters by spinning it. In both cases the wing has to push down enough air to keep the aircraft in flight.
- hamilyon2 5y ago
  So, people answering on quora for example, are wrong? https://www.quora.com/Can-a-helicopter-having-a-power-to-weight-ratio-of-less-than-1-fly https://www.quora.com/Can-a-helicopter-having-a-power-to-wei... I am even more confused now.
  - DangitBobby 5y ago
    No, I have to conclude that the previous commenter didn't understand your point, which was the observation that heavy aircraft with very low sustained forward thrust (thrust that would not be sufficient for a helicopter to hover) results in sufficient upward lift to suspend the aircraft indefinitely, which is very surprising.
    - afterburner 5y ago
      A helicopter doesn't rely on the forward thrust of the chassis, it relies on the forward thrust of the helicopter blades in rotation. Those blades are wings.
      - DangitBobby 5y ago
        The way the thrust is generated is mostly irrelevant to this observation. The observation is about the mechanics of lift, which is some function of thrust combined with the wings, rotors, balloons, etc. You'd observe the same bizarre mechanics if the thrust were generated by releasing highly compressed air from a tank.
  - Cogito 5y ago
    I'm not sure how you're connecting that quora discussion to what we were saying above, but I think the confusion comes from what 'thrust to weight ratio' means. Helicopters and planes are both pushing down on air to generate lift. The lift generated has to be equal or greater to the weight for the aircraft to fly. Thrust can mean many things (at least colloquially). As discussed in the quora you linked, a helicopter will have a defined power to weight ratio that allows it to fly (maintain level flight) in its 'normal' flight envelope. There are a number of things the pilot can do that causes the aircraft to 'push down harder' on the air. One of these is flying close to the ground (the ground effect) which is sort of like pushing against the ground as well as the air, and another is by moving horizontally (usually forwards, like a plane, causing transational lift). Both of these allow the aircraft to maintain height while using less power than if it was hovering, but to do so it is still generating enough lift to counteract gravity.
  - marvin 5y ago
    I didn't read your link, but the "thrust" in thrust to weight ratio generally refers to the force that the engine produces. Therefore, it isn't a brilliant analogy to compare the thrust of a helicopter rotor (which does get all its power from the engine) to the thrust of an airplane propeller. The propeller doesn't contribute materially to the lifting force on an aircraft, while the rotor of the helicopter provides practically all the lifting force on the helicopter. Both machines need to (somehow) generate lift equal to their weight to stay airborne. The airplane just does this by moving a static wing through the air, which is a much more efficient way of doing it. Its engine/propeller isn't even immediately required to move the wing through the air; once airborne, the aircraft can fly downwards at an angle without engine power to maintain its speed. You'd say that a helicopter uses "powered lift" while an aircraft does not.
blueblisters 5y ago
I am not an expert either but comparing "thrust" from helicopters and airplanes is not meaningful if you are only talking about engine thrust. Thrust is a vector, although in aerodynamics it seems to refer to forward force by convention. For helicopters in a static hover, the downward "thrust" is actually the lift produced by the spinning blades. The engines produce almost no forward thrust. Whereas, for an aircraft in flight, the engine thrust pushes the plane forward and the wings generate the lift that keeps it in the air.

Cogito 5y ago

It's the exact same principle for planes and helicopters. If a plane isn't producing more lift than weight it will fall, just like a helicopter. Planes work by pushing a wing through the air, helicopters by spinning it. In both cases the wing has to push down enough air to keep the aircraft in flight.

hamilyon2 5y ago
So, people answering on quora for example, are wrong? https://www.quora.com/Can-a-helicopter-having-a-power-to-weight-ratio-of-less-than-1-fly https://www.quora.com/Can-a-helicopter-having-a-power-to-wei... I am even more confused now.
- DangitBobby 5y ago
  No, I have to conclude that the previous commenter didn't understand your point, which was the observation that heavy aircraft with very low sustained forward thrust (thrust that would not be sufficient for a helicopter to hover) results in sufficient upward lift to suspend the aircraft indefinitely, which is very surprising.
  - afterburner 5y ago
    A helicopter doesn't rely on the forward thrust of the chassis, it relies on the forward thrust of the helicopter blades in rotation. Those blades are wings.
    - DangitBobby 5y ago
      The way the thrust is generated is mostly irrelevant to this observation. The observation is about the mechanics of lift, which is some function of thrust combined with the wings, rotors, balloons, etc. You'd observe the same bizarre mechanics if the thrust were generated by releasing highly compressed air from a tank.
- Cogito 5y ago
  I'm not sure how you're connecting that quora discussion to what we were saying above, but I think the confusion comes from what 'thrust to weight ratio' means. Helicopters and planes are both pushing down on air to generate lift. The lift generated has to be equal or greater to the weight for the aircraft to fly. Thrust can mean many things (at least colloquially). As discussed in the quora you linked, a helicopter will have a defined power to weight ratio that allows it to fly (maintain level flight) in its 'normal' flight envelope. There are a number of things the pilot can do that causes the aircraft to 'push down harder' on the air. One of these is flying close to the ground (the ground effect) which is sort of like pushing against the ground as well as the air, and another is by moving horizontally (usually forwards, like a plane, causing transational lift). Both of these allow the aircraft to maintain height while using less power than if it was hovering, but to do so it is still generating enough lift to counteract gravity.
- marvin 5y ago
  I didn't read your link, but the "thrust" in thrust to weight ratio generally refers to the force that the engine produces. Therefore, it isn't a brilliant analogy to compare the thrust of a helicopter rotor (which does get all its power from the engine) to the thrust of an airplane propeller. The propeller doesn't contribute materially to the lifting force on an aircraft, while the rotor of the helicopter provides practically all the lifting force on the helicopter. Both machines need to (somehow) generate lift equal to their weight to stay airborne. The airplane just does this by moving a static wing through the air, which is a much more efficient way of doing it. Its engine/propeller isn't even immediately required to move the wing through the air; once airborne, the aircraft can fly downwards at an angle without engine power to maintain its speed. You'd say that a helicopter uses "powered lift" while an aircraft does not.

blueblisters 5y ago

I am not an expert either but comparing "thrust" from helicopters and airplanes is not meaningful if you are only talking about engine thrust. Thrust is a vector, although in aerodynamics it seems to refer to forward force by convention. For helicopters in a static hover, the downward "thrust" is actually the lift produced by the spinning blades. The engines produce almost no forward thrust. Whereas, for an aircraft in flight, the engine thrust pushes the plane forward and the wings generate the lift that keeps it in the air.