User talk:Michael Belisle

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[edit] Hello

Wow, you must be a good editor, to have been participating for so many months and not had anyone complain on your talk page yet! ;-) Have a good time! --tiny plastic Grey Knight ⊖ 13:43, 13 July 2007 (UTC)

[edit] Welcome

Hello, Michael Belisle, and welcome to Wikipedia. Thank you for your contributions. I hope you like the place and decide to stay. If you are stuck, and looking for help, please come to the New contributors' help page, where experienced Wikipedians can answer any queries you have! Or, you can just type {{helpme}} and your question on this page, and someone will show up shortly to answer. Here are a few good links for newcomers:

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[edit] Lift

Hi Michael, I’m responding to you edit of Lift. I agree with much of what you say and I like the way your words flow. However I do have some comments that I hope you will find as constructive.

The Article (before your contribution) was a complete mess. However this is inevitable as the debate over the years has not really been about the truth of the mechanism of lift (even though it may often appear to be), rather it is a debate about the best way to describe it. As there are so many ways, so many editors and edits can be continuously made what we have is a dynamic system that occasionally reaches an unstable equilibrium (I’m referring to the drafting of the article here not the mechanism of lift!)

In a way different approaches to describing lift are Original Research. There are arguments to suggest that your piece of work should be better published elsewhere and the Article entirely re-written outlining the various was of describing lift with links to them.

If you look back over the long history (not something I particularly recommend as an enjoyable pastime) you will see that just about everything that can be said has already been said several times (as well as a lot of things that should not be said).

The primary challenge is to explain to the layman how a wing works. Unfortunately we always immediately vanish down rabbit holes about how to mathematically model lift. Most things in this world are a challenge to mathematically model but many are easy to understand and indeed were well understood a long time before they were accurately modelled.

Turning to your edits of “basic explanation”. You are adopting the famous “show higher speed = lower pressure then explain why the speed is higher” approach. It is part of the well-worn cycle of the Article’s continuous evolution, although your approach is more eloquent than most.

While it is not wrong, I suggest there are both what could be called high level and low level challenges. At the high level any explanation that does not placate both the pressure lobby and the vertical momentum lobby will always be subject to substantial modification by those feeling excluded.

At a low level I offer the following observations (I hope I am not being argumentative but just looking for ways to help us improve).

Bernoulli’s principle does not dictate that increasing the speed of a fluid inevitably results in decreasing its pressure – some energy change must also take place but it does not define what that may be. We pragmatically use a simplified version of Bernoulli’s equation in some areas of modelling the flow over a wing. This simplified version is full of inaccuracies but they can be acceptable in controlled application. However, this simplified version is derived empirically and not from principles. Reliance on merely stating the word “Bernoulli” to prove an absolute link between speed and pressure is fundamentally flawed.

While I tend to warm to the streamtube conceptual model it does have a limitation as it implies finite boundaries to the air that is part of the mechanism.

There is a big conceptual leap where you assert that the streamtube is squashed. While I am sure it is true you provide no evidence or explanation of how.

Unfortunately between the "squashed streamtube" and the "speed means low pressure" logical steps there lies another – mass per unit time can be constant in a squashed tube by ways other than changing speed, density can also change. Rolo Tamasi (talk) 13:39, 20 April 2008 (UTC)

I'm not sure what your background is, so I apologize if my responses here are too basic or too technical. I responded to some other stuff on the talk page for Lift.
  • At the high level any explanation that does not placate both the pressure lobby and the vertical momentum lobby will always be subject to substantial modification by those feeling excluded.
This is a difficulty in communicating complex but intriguing topics to a general audience. (If an electrician doesn't understand general relativity, then surely Einstein was wrong, right?) I don't think this means we should give up and devote equal time to both camps. In this specific case, viscosity (through complex mechanisms) creates pressure differences that cause lift, but that's hard to explain. So, according to JD Anderson, a reasonable explanation is to say that pressure pushes on the airfoil and creates lift. In steady state, this is correct; viscosity is negligible at that point (but it was responsible for the shape of the flow field). Downwash by Newton's third law is an effect of lift, not the cause. And circulation is a mathematical model.
A good high-level explanation here will explain the most correct answer and explain how everything works together.
  • Bernoulli’s principle does not dictate that increasing the speed of a fluid inevitably results in decreasing its pressure....
In inviscid, incompressible, steady flow it does along a streamline and by extension, inside a streamtube formed by the flow between two streamlines. In this sense, the principle as employed here can be derived by integrating the Euler equations along a streamline in incompressible, steady flow. In an discussion of an established flow around a airfoil outside of the boundary layer, it's appropriate.
  • While I tend to warm to the streamtube conceptual model it does have a limitation as it implies finite boundaries to the air that is part of the mechanism. There is a big conceptual leap where you assert that the streamtube is squashed. While I am sure it is true you provide no evidence or explanation of how.
There are discernible boundaries in the sense that you can identify streamlines where the local velocity is everywhere tangent to the streamline. By definition, fluid will never cross a streamline. It would be helpful to insert a picture, which I'll construct in a few days. The streamtube and “squashing” comes from JD Anderson, where I omitted too many details because I threw it in there when he derailed my train of thought (now in “Stages of Lift Production“).
  • Unfortunately between the "squashed streamtube" and the "speed means low pressure" logical steps there lies another – mass per unit time can be constant in a squashed tube by ways other than changing speed, density can also change.
In low-speed flight, it is safe to assume that the flow is incompressible, that if ρVA = constant, then a decrease in area will result in an increase in speed. Assuming otherwise is rightly outside the scope of a basic article on lift. True, there may be problems with this explanation for flow around a 777 at in cruise at M = 0.9, but a physical description of transonic flow is not in any way accessible to the layman. (Interestingly, the simplest explanation is in hypersonic flow where Newton's third law reasoning provides a reasonable approximation.) Michael Belisle (talk) 22:26, 20 April 2008 (UTC)