Timeline for Relationship between hover power and climbing power
Current License: CC BY-SA 4.0
23 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jul 19, 2021 at 18:09 | comment | added | Michael Hall | No worries, it's all just chit chat. No ruffled feathers here! Cheers. | |
| Jul 19, 2021 at 17:53 | comment | added | Preston Becker | @MichaelHall I didn't realize how much trouble I would stir up by invoking infinity. Perhaps I should have talked about the rotor blades getting arbitrarily large, or I should have talked about the asymptotic values for energy. With that said, talking about infinity was quick and dirty, and in the end led to the excellent and insightful answer by Peter below. And without already knowing about inflow angle, I'm not sure if there was a different way to ask the question to get the same answer. So, sorry to ruffle feathers, but as they say, all's well that ends well | |
| Jul 19, 2021 at 17:19 | comment | added | Michael Hall | @Koyovis, to the extent that thought experiments are bounded by reality, I agree. | |
| Jul 19, 2021 at 6:03 | vote | accept | Preston Becker | ||
| Jul 19, 2021 at 2:17 | comment | added | Koyovis | @MichaelHall Aviation is ruled by physics, and Einstein has shown us how useful thought experiments can be. | |
| Jul 18, 2021 at 21:29 | comment | added | Michael Hall | @Koyovis, Yes... really! I agree with Ralph J: Musings about the function of helicopter blades that exceed the diameter of our planetary atmosphere, no, the solar system, no, the known universe and beyond have no bearing whatsoever on "aviation" as we experience it in actual reality. (i.e. defined as the finite physical interaction of an air vehicle within the confines of earth's atmosphere and gravitation field...) I'm not voting to close because I think debunking absurd conclusions can be useful, but I agree that this is a hypothetical physics question with no practical application. | |
| Jul 18, 2021 at 16:59 | comment | added | jamesqf | "As it moves steadily upward, it will need the same force as when it was just hovering." WRONG! It will need more force -> energy input to overcome gravity. If it didn't, you could use it to create a perpetual motion machine. | |
| Jul 18, 2021 at 16:06 | comment | added | Michael Hall | Exactly what Jpe61 said - extrapolating a simple equation to infinity serves no practical purpose, and ignoring physical boundary conditions moves the discussion rapidly from a potentially educational abstraction to complete absurdity. (i.e. does "infinitely slowly" equal stopped?!) I'm DVing the question for gross violations of common sense. (i.e. "not useful"...) | |
| Jul 18, 2021 at 15:51 | comment | added | Jpe61 | You see where this is going? Nowhere. No point in playing with infinities in cases like this. | |
| Jul 18, 2021 at 15:01 | answer | added | Peter Kämpf | timeline score: 4 | |
| Jul 18, 2021 at 14:43 | comment | added | Peter Kämpf | @Jpe61 An infinite rotor creating finite lift will turn infinitely slowly. Don't look at the infinite case but several with increasingly large rotors and see where this is heading. The asymptotic case will be the solution. | |
| Jul 18, 2021 at 12:30 | answer | added | Guy Inchbald | timeline score: 0 | |
| Jul 18, 2021 at 10:51 | answer | added | Frog | timeline score: 1 | |
| Jul 18, 2021 at 10:11 | answer | added | xxavier | timeline score: 1 | |
| Jul 18, 2021 at 8:49 | comment | added | Jpe61 | Infinitely long rotor blades have one problem: they cannot be rotated, as they would instantly exceed the speed of light at their infinitely far away blade tips. One should not use infinities in calculations such as this. | |
| Jul 18, 2021 at 8:38 | comment | added | Koyovis | @RalphJ Really? Helicopters and rotors are not about aviation? Voting to Leave Open, welcoming PrestonBecker to this site. Very good question. | |
| Jul 18, 2021 at 8:35 | answer | added | Koyovis | timeline score: 1 | |
| Jul 18, 2021 at 4:32 | review | Close votes | |||
| Jul 21, 2021 at 16:35 | |||||
| Jul 18, 2021 at 4:21 | comment | added | Ralph J♦ | So we have an infinitely long rotor, hovering over an infinitely long/wide flat earth, powered by an engine that had infinite power to get those infinitely long blades moving in the first place, but perhaps no power required to keep them moving, so that all the air in the universe is being swept by these infinitely long blades, whose tip velocity would be infinite except that there ARE no rotor tips (tho much of the blade itself will be supersonic+ )... we're pretty far into the realm of theoretical / detached from reality here. VTC as not being about aviation, as defined in the Help Center. | |
| Jul 18, 2021 at 1:47 | comment | added | Preston Becker | The rotor is powered by an engine. To achieve steady thrust, the rotor needs to spin at some speed and will consume some amount of power. As the rotor increases in size, the amount of power needed to stay aloft decrease. In the limit where the rotor diameter approaches to infinity, the power requirement approaches zero. | |
| Jul 18, 2021 at 0:40 | comment | added | Michael Hall | So on your theoretical helicopter with the infinitely large rotor, is the rotor stationary? If so, how does it impart any downward thrust to allow it to hover? And if not, what causes it to rotate? | |
| Jul 18, 2021 at 0:26 | review | First posts | |||
| Jul 18, 2021 at 4:21 | |||||
| Jul 18, 2021 at 0:25 | history | asked | Preston Becker | CC BY-SA 4.0 |