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2

If bumblebees were propelled the way fixed-wing aircraft are propelled, their wings would not be aerodynamic. An airplane needs two devices to become and remain airborne. Its engines generate thrust, and its wings provide lift. A bumblebee, however combines both thrust and lift into one integrated device. The bumblebee's wings, unlike a fixed wing ...


4

This is not true. The rumor comes from a paper written in the 30s. The scientist, Antoine Magnan, who made the paper did his calculations wrong and retracted the paper, but, of course, the media wouldn't listen.


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If the balloon was completely isolated from the outside atmosphere and contained a certain gas (in this case helium), then the helium will exert a pressure outwards, attempting to expand the balloon. The atmosphere outside will also exert a pressure inwards, attempting to keep the balloon in a small shape. These two forces compete, and the balloon will ...


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The answer to this question is very much analogous to the answer to how aeroplanes fly. See Physics SE Question "What Really Allows Airplanes to Fly?" and the best (IMO) answer is this one here. But basically the airfoils, sails or vanes - whatever they may be called - deflect the flow of air. They do this by pushing on the air and changing the latter's ...


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There is an omission in input data: glider's "fuel" is a sum of its potential and kinetic energies. So heavier glider (towed to same height and velocity) requires more work from the towing plane and starts with more energy than lighter glider.


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Every fixed-wing aircraft has a (fairly slow, just above stall) speed at which it minimizes its descent rate while gliding, so that speed is good for loitering. If it can also find an updraft, it can stay up indefinitely without any power. But if the aircraft needs high speed, that also means high drag, so it needs to expend power. In an aircraft, that ...


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How does they move slowly in air, without falling down? One possibility is soaring using a ridge lift - typically a situation when the wind is approx. perpendicular to a mountain ridge. The air is lifted at the front side of the ridge and an eagle can soar in the lifting air stream. This can also work without the wind, Which is a situation of thermal ...


9

Eagles (and most large birds) fly by soaring; it's much more energy efficient than flapping their wings. We do use the technique for our own flights. The reason eagles and other soaring birds do this rather than flap is that they generally hunt from the air and so spend a lot of time waiting for prey. They don't need to go anywhere specific and don't need ...


1

the video show that the principle of helicopter works in a zero-g (no gravity) environnement, not that the principle works in space. The helicopter is able to lift on earth (and int the space shuttle) because of the viscosity of the air. Whitout any friction, there is no move. In space, there is really few particles. So the friction would be very low and ...


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Draw a diagram. If your control surface increases lift at a point, add a force pointing up. That force, if it does not go through the center of gravity, will add a torque to the system. The direction of that torque can be seen directly from the diagram.


2

I'm still seeing explanations being pulled out of the air, so to speak. I'm a 100-hour student pilot, and let me tell you what every pilot must absolutely learn about stability in the pitch axis, because if you get it wrong just once, you void the warranty on the plane and on yourself. You don't need a PhD in physics to get the point. Let's start with a ...


1

When a plane banks the wing up-and-back (lift) force becomes partly sideways. When level average force of the 2 wings goes through the centre of gravity. When it banks the force is in front of the centre of gravity and induces a moment of force which turns the aircraft. The more the bank the more the force moves forward and more the torque. It's a 3D problem ...


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This isn't an exact description but it should give some insight. I think it's better to tackle this problem in stages. First what happens if we drop a horizontal paper? Well, it's edges curve up like this: Now what happens with 45° paper? Its edges curve up again. Pressure drag is a very sensitive function of angle of attack. It's maximum for a plate ...


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The first factor in stability is pitch inertia. Even though it is just a sheet of paper, its moment of inertia around the pitch axis is quite high, so any pitch motion is slow. Next is aerodynamic pitch damping: As the paper starts to pitch, local forces at the edges will produce a stabilizing moment. That the paper will slowly pitch up is due to the ...


2

Cool! I just had to try it. A penny may / may not have been just the right mass, and I used a slightly heavier than average grade of paper. But it was sort of stable. When I drop it, the front corners bend upward. This increases the drag at the front end. This seems to be the source of the bend you show. The nose comes up and the plane slows. Sometimes ...


3

I can't speak to what sources you were reading, but the air under a hovercraft is higher than ambient air pressure, not lower. Wikipedia: Hovercraft use blowers to produce a large volume of air below the hull that is slightly above atmospheric pressure. The pressure difference between the higher pressure air below the hull and lower pressure ...


3

The idea (theory) behind the selfsimilarity Parameters like Reynolds- or Machnumber is: that fundamental flow features of a specific flow have a dimensionless number connected to it (Dimensional homogeneity). This means: not the dimensional units (like inch, meters, tons, horsepower) should be used to describe (in this case) flow but dimensionless numbers. ...



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