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I recently came across this information which seems quite relevant here: When you are comparing equal disk area, then yes staggering them is better than coaxial (in the same column) by roughly 20-30%. But consider the configuration shown below. For a given fram size, when you stagger them you have less room around the circumference of the vehicle's frame ...


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A blimp or zeppelin can fly without using energy. If it's engines are turned off, it can travel with the wind. I think you're asking - can it be done while having control over where you go, or how fast, while using arbitrarily little fuel? This is an old idea, and it has been tried. It is possible, but so far not practical. To find out more, just Google ...


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Wings provide lift because they direct air downwards. They direct air downwards in two ways. In part, the bottom of the wing slopes downward a bit and just pushes the air down as it moves forward through the air. But this is a small effect. The top of the wing is more important. The top of the wing pulls the air down partially by providing a ramp. The rear ...


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The Solar Impulse flies without fuel, so the answer to the question in your title is yes. In theory you could design an airship that used very little energy. It would have to become lighter than air to take off, say by shedding some ballast, fly to where it is going, and become heavier or catch a landing rope to land. If that sounds like a helium balloon, ...


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It's a hoax. Think of a submarine—it can go towards and away from the center of the Earth due to gravity and buoyancy respectively, but it cannot do this without changing its density. And it cannot change its density without fuel. From the U.S. Office of Naval Research: To descend, water is allowed to flow in through the bottom of the submarine: To ...


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Essentially a fixed-wing aircraft flies because it moves through the air and has a fixed wing which is angled to the direction of airflow. A component of the drag force acting on the wing acts in the direction (up) opposite to the direction (down) of the aircraft's weight force. An aeroplane wing acts like a weather vane responding to the relative flow of ...


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Follow two stream lines, one above the wing and one below. You can ignore the height difference and assume that under the wing you have atmospheric pressure and normal stream speed. The two stream lines follow the Bernoulli principle and thus $$ \frac{1}{2} \rho v_{under}^2 + P_{under} = \frac{1}{2} \rho v_{top}^2 + P_{top} $$ Since you know the weight ...


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If the plane is just flying at constant altitude then a vertical force balance requires that lift from the wings be equal to the plane's weight. The lift force, $L$ comes from a pressure difference above and below the wing so that $$ L = (p_1-p_2)A = mg $$ You can use the Bernoulli equation assuming a negligible difference in height to express the pressure ...


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This is a most excellent and astute question. Ultimately it comes down to experiment: the model below works pretty well for many fluids. What this must mean therefore is that the loss is small enough that each particle of fluid, in flowing past the region of disturbance, loses a fraction of its energy that is small enough that it doesn't upset the energy ...


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1) The $sin$ term appears to be resolving the velocity of the water relative to the face of the disk. $U$ is the just the speed, it's necessary to determine what part of that velocity will produce force on the object. It might help to visualize extreme cases, setting $\alpha$ and $\beta$ to 0, $\pi /2$ etc. For $\alpha = \beta =0$ you have a perfectly level ...


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The force that lifts the skier isn't buoyancy, it's the reaction force from the angled skis pushing water down. Water skiers start with their tips out of the water so that when the boat starts pulling, they can push against the water to lift themselves up. Once on top of the water, they still hold their skis at a slight angle, meaning the water they hit is ...



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