Erich
2015-03-19 16:31:18 UTC
Una delle macchine volanti di Leonardo da Vinci sembra essere una gigantesca trivella. Questo progetto non avrebbe sfruttato il principio di Bernoulli, ma piuttosto utilizzato la rotazione della lama per spingere l'aria sotto di essa verso il basso per mantenere il velivolo in volo.
Immagine : Wikimedia
Ci sono state macchine volanti costruite in questo modo che sono effettivamente decollate?
EDIT: Quindi forse io hanno frainteso Bernoulli, a giudicare dalla discussione.
paper airplanes
AilipdsoirCMT - Paper airplanes are still technically Bernoulli. Just at a very small scale.
AilimpmamtCMT No, there is no pressure differential on a flat wing. Of course, a paper airplane has no lift, but I would still classify it as a flying machine of a type. Another answer would be a kite.
But a paper airplane's wings aren't completely flat. It's just very minuscule. Or it's curved, which still exhibits Bernoulli's. So does a kite. Or a boat sail. The first two have an excess of "thrust", but they'll still glide. And the first 2 can demonstrate lift and stalls if thrown lightly or gliding. No different than a curved wing. There's still a pressure differential. I think a sail can demonstrate those too, but I'm not a sailor, so not as familiar.
@Shawn Non penso che questo abbia nulla a che fare con la curvatura. Ci sono aerei con ali completamente piatte (modellini di aeroplani) che possono volare. Se questo conta come Principio di Bernoulli è apparentemente [una questione di definizione] (http://amasci.com/wing/airfoil.html). Nel mio libro, le ali piatte funzionano deviando l'aria verso il basso, ma questo collegamento suggerisce che è equivalente alla spiegazione di Bernoulli.
[Here is a question](http://aviation.stackexchange.com/questions/1157/why-is-the-wrong-explanation-of-air-travels-a-longer-distance-and-creates-a-lif) that clarifies why asking about Bernoulli's principle to the exclusion of other fluid-based lift generation makes no sense.
AilipeisjnCMT - I would agree with that. And that would probably mean that the OPs question would pretty much be answered that _EVERY_ flying machine operates on various aerodynamic properties, not just Bernoulli.
It would be good to define the term *flying machines*. For example, a regular bullet is not flying from the gun to the target, or is it?
@mins "macchina" probabilmente era un termine troppo generico. "Superficie volante" sarebbe stato meglio. Anche se la domanda originale riguardava le "macchine". Direi che un proiettile mostra ancora le caratteristiche di "volo", anche se come un pallone da calcio o da baseball, "vola" più a causa di un eccesso di "spinta". Anche la forma del proiettile può determinarne la portata, anche se questo comincia a entrare nella definizione di "volo". :-)
AilijokpxyCMT Except rockets in general; they deal with atmosphere, but in general they rely solely on the rocket for lift. In particular, the Apollo LEM didn't rely on any atmospheric effects for anything :)
AilifylgucCMT Good! I was thinking of excluding stuff which have a trajectory mainly because of their initial velocity (otherwise everything can be thrown and be claimed to fly). That would exclude spacecraft in orbit, but not rocket before engine cut-off.
AililiqiegCMT - It would depend on where the rocket is. A rocket is an object with a way excess of thrust to its weight. If it's in a fluid (even air) then it would still exhibit characteristics of "flight" and be affected by Bernoulli. But that's getting way into the depths of the physics of "flight". Essentially, anything that moves fast enough will "fly" because of pretty much the same physics that allow an airplane wing to do it slower. And I would argue that anything operating in space is missing the critical ingredient for Bernoulli - fluid.
Credo che il principio di Bernoulli si applichi anche nel caso di un'ala di aeroplano di carta perfettamente piatta, proprio come si applica a un'ala simmetrica o anche a un'ala rovesciata. Fondamentalmente, l'angolo di attacco fa comunque sì che l'aria prenda un percorso più lungo sulla superficie superiore dell'ala. Vedi http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html
Space Shuttle on re-entry - flies like a brick :-)
AilirjnzwzCMT McMahon - Good example of what I said. Space Shuttles were excellent gliders provided they were moving fast enough. --- Nice. Mach 3 on re-entry and above Mach 1 until about 25 miles out from touchdown. It comes in on a 19 degree glide slope and touches down at 220 MPH. That's moving pretty quickly. Considering there's no go-around option, that's _VERY_ impressive piloting. http://spaceflight.nasa.gov/shuttle/reference/basics/landing.html Up until the "flare" that seems more Newton than Bernoulli. :-)
Vedo il "volo" degli aeroplani di carta avere più a che fare con l'attrito e il taglio nell'aria che con l'attribuzione di bernoulli. o fa parte del principio? perché le piume "galleggiano" a terra quando cadono?
AilijwlcueCMT In fact, one NASA site talking about incorrect-but-popular lift explanations says that the Shuttle on re-entry is just about the one time the popular "action-reaction" theory of lift (in which lift is the physical deflection of air downwards when it hits the wing) gives accurate numbers (as density is very low and speed very high).
AilihfaawxCMT A paper airplane _when flying_ generates lift in much the same way as any airfoil, including the role of Bernoulli's principle. If you simply _drop_ the paper airplane so that it falls perpendicularly to its wing surface, then only drag is holding it up. My recollection of what is written about this is it falls faster that way. Some dust particles hardly fall at all. A feather's fall is somewhere between these two phenomena.
AilioimnurCMT Three words "Angle of Attack".