Timeline for Are wings any more efficient at creating lift, versus orienting the engine's thrust downwards?
Current License: CC BY-SA 3.0
10 events
| when toggle format | what | by | license | comment | |
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| Apr 19, 2017 at 21:47 | comment | added | reirab | @supercat Yeah, that part is definitely correct. | |
| Apr 19, 2017 at 21:42 | comment | added | supercat | @reirab: I guess I drifted a bit from my main point into issues related to hovering which aren't necessarily applicable when climbing straight vertically fast enough to keep drawing "fresh" air. The aircraft does effectively gain "momentum" from air it causes to be moves through the engine, but it takes more kinetic energy to transfer a certain mass of air through the engine at a high speed than to achieve the same transfer of momentum by accelerating a larger quantity of air to a slower speed. | |
| Apr 19, 2017 at 21:11 | comment | added | reirab | Unless, of course, you're referring to an airplane flying straight up, in which case the air would already be moving downward relative to the engine without any acceleration required and I misunderstood your meaning. And, of course, that's exactly what happens in the case of a horizontally-oriented engine flying forward through the air. | |
| Apr 19, 2017 at 21:09 | comment | added | reirab | @supercat Yes, I'm not disputing those things. I was referring to your statement about the engine creating an area of low pressure above it, but seeming to suggest the downward acceleration of that air before entering the intake does not cause an upward force to be imparted on the engine/aircraft. If work is being done on the air, surely an opposite force is being imparted on the aircraft, no? | |
| Apr 19, 2017 at 21:03 | comment | added | supercat | @reirab: The total amount of force conveyed to the planet through the air is going to have to equal the weight of the plane no matter how it is conveyed, but the amount of work required to impart acceleration to the air will vary depending upon how that air is already moving. | |
| Apr 19, 2017 at 21:01 | comment | added | supercat | @reirab: Everything is subject to Newton's third law, but the plane isn't the only thing acting upon the air. Air is supported by the planet, and if a plane were flying in large circles around a planet, most of the air it disturbs would have a chance to convey the force of the airplane to the planet before the next time the plane encounters it. | |
| Apr 19, 2017 at 20:17 | comment | added | reirab | Wouldn't the suction which creates said low pressure above the engine also be subject to Newton's Third Law, though? If the engine is causing a given parcel of air to get accelerated downward - whether before or after it enters the fan - is not an equal, but opposite force applied to the engine? | |
| Apr 19, 2017 at 14:22 | comment | added | supercat | @user9037: I judged that Martin's was a high-quality answer, but also thought it would be helpful to have a simple intuitively-clear answer as to why flying is more efficient than hovering. It would seem conceptually that a hovering vehicle should be simpler than a flying one (and indeed the whirlygig toys that predated the airplane operate by simply directing thrust downward) but I think the need for still air is something that may not be obvious until one considers it, but once considered will immediately make many things obvious. | |
| Apr 19, 2017 at 5:37 | comment | added | user9037 | Thanks to your explanation. It's more condensed than Martin's answer, but I marked his answer as valid because it has the relevant formulas. | |
| Apr 18, 2017 at 19:37 | history | answered | supercat | CC BY-SA 3.0 |