Bernoulli was a Swiss Plumber.
Bearfoil,
I have to admit I always had difficulties with the circulation model at AoA = 0 for an asymmetrical foil like e.g. NACA4312.
It's clear if we have a high AoA where the air on the lower side is decellerated. In that case we get a flow around the TE which tries to 'fill the void'.
To stay in your very nice example like in real life the molecules want to have equal space around them. I.e. they alway try to go there where the density is lower, i.e. where there seems to be a void.
That is what you see in animations of the circulation model.
If you now take a semi- symmetrical Profile at Alpha = 0, you don't have a decelleration. You only have less acceleration on the lower side than on the upper side. And that is a case where I don't really see a significant equalising flow from Upper to lower side at the TE. I see more or less just the added vertical speed component which gives the Newton Part of the Lift.
From my point of view the circulation only becomes really relevant at certain AoA. For very low AoA I tend to consider in negligeable,
Would be interesting to make such a simulation in coloured water for different AoA's to see when the effect really kicks in.
Very interesting discussion !
Thanks for the thread !
regards,
henra
I have to admit I always had difficulties with the circulation model at AoA = 0 for an asymmetrical foil like e.g. NACA4312.
It's clear if we have a high AoA where the air on the lower side is decellerated. In that case we get a flow around the TE which tries to 'fill the void'.
To stay in your very nice example like in real life the molecules want to have equal space around them. I.e. they alway try to go there where the density is lower, i.e. where there seems to be a void.
That is what you see in animations of the circulation model.
If you now take a semi- symmetrical Profile at Alpha = 0, you don't have a decelleration. You only have less acceleration on the lower side than on the upper side. And that is a case where I don't really see a significant equalising flow from Upper to lower side at the TE. I see more or less just the added vertical speed component which gives the Newton Part of the Lift.
From my point of view the circulation only becomes really relevant at certain AoA. For very low AoA I tend to consider in negligeable,
Would be interesting to make such a simulation in coloured water for different AoA's to see when the effect really kicks in.
Very interesting discussion !
Thanks for the thread !
regards,
henra
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henra
It is after all, all circulation. The descriptor (Bernoulli) at 0A is negligible. That is the problem I have with it. Volume (circulation) is only drag until the LE rises relative to flow, (for all intents and purposes).
A mental image I use is that the wing is an expensive air compressor. Blow on your hand, there is a rise in Pressure. It isn't contained, and nothing happens to imitate actual work. That is why, to me, Ground effect is a critical concept for the novice, one uses it (instinctively, one hopes), for a lifetime. The deck is a dynamic "container", and gives a freebie in "Lift".
Another is that I present the a/c at speed as a ski boat, "Planing" on the dense water, oblivious to the "top" of the "wing". I have set up a complicated model in the tunnel that is two "layers", a dense lower layer, and a very LP "Upper". If separated successfully, the "wing" needs no incidence at all, it rises magically.
Well, Newton is my preference. I've seen diagrams of Bernoulli with thousands of little arrows, but in the time it takes to get anything out of it, Goose has kicked the tires while Mav lights the fires, and they are heading downtown for a knife fight.
Newton would have loved to fly, but other pilots might have avoided him, that is another thread, (for the National Enquirer). Or The Guardian.
it has been fun, take care.
bear
It is after all, all circulation. The descriptor (Bernoulli) at 0A is negligible. That is the problem I have with it. Volume (circulation) is only drag until the LE rises relative to flow, (for all intents and purposes).
A mental image I use is that the wing is an expensive air compressor. Blow on your hand, there is a rise in Pressure. It isn't contained, and nothing happens to imitate actual work. That is why, to me, Ground effect is a critical concept for the novice, one uses it (instinctively, one hopes), for a lifetime. The deck is a dynamic "container", and gives a freebie in "Lift".
Another is that I present the a/c at speed as a ski boat, "Planing" on the dense water, oblivious to the "top" of the "wing". I have set up a complicated model in the tunnel that is two "layers", a dense lower layer, and a very LP "Upper". If separated successfully, the "wing" needs no incidence at all, it rises magically.
Well, Newton is my preference. I've seen diagrams of Bernoulli with thousands of little arrows, but in the time it takes to get anything out of it, Goose has kicked the tires while Mav lights the fires, and they are heading downtown for a knife fight.
Newton would have loved to fly, but other pilots might have avoided him, that is another thread, (for the National Enquirer). Or The Guardian.
it has been fun, take care.
bear
Originally Posted by henra
Edit:
It's a combination of Newton and Bernoulli, the proportion depending of the shape of the foil.
Thick Profile with steep TE => Lots of Newton
S-Shaped profile (flying wing) => very little Newton.
/Edit
It's a combination of Newton and Bernoulli, the proportion depending of the shape of the foil.
Thick Profile with steep TE => Lots of Newton
S-Shaped profile (flying wing) => very little Newton.
/Edit
Aerocat, (Bearfoil)
I really have to work on the way I describe things!!
I had the same misunderstandings with Bearfoil, so I derive it's got to be me who is messing the descriptions up! (obviously badly
)
Btw. I re-read my own stuff and it is indeed misleading.
Sure Newton and Bernoulli are two equally valid ways of calculating the Lift. Both will deliver Lift as a result, that is the complete Lift, not additional. Sorry for bad explanation, will have to work on that...
I really have to work on the way I describe things!!
I had the same misunderstandings with Bearfoil, so I derive it's got to be me who is messing the descriptions up! (obviously badly
)Btw. I re-read my own stuff and it is indeed misleading.
Sure Newton and Bernoulli are two equally valid ways of calculating the Lift. Both will deliver Lift as a result, that is the complete Lift, not additional. Sorry for bad explanation, will have to work on that...
