Benelli lift theory under question

Discussion in 'All Things Boats & Boating' started by Frosty, Dec 5, 2012.

1. Number4Previous Member

A circular wing would make a venturi, a flat venturi would make a wing.
Carburettors and wings both ice up under certain conditions due to pressure and therefore temperature dropping across them.
Watch a big jet land on a very humid day. The mist above the wings is caused in the same way.
This is Mr Bernoulli's Principle clearly in action!

Place a symetrical aerofoil on a table, it will sit there with an angle of attack, and would therefore create lift. Fill in the gap between the leading edge and the table, and hey presto, we have an aerofoil that creates lift at zero degrees angle of attack.

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rwatsonSenior Member

You are the one who ascribed the study of aerofoils to Bernoulli !!!

and how John Joseph Montgomery observed birds had curved upper wing surfaces, and resulted in working gliders.

The fact that the mechanical principles worked the same as Bernoulli fluid experiments, is just the principle of parallel discovery.

Once again, both attack angle and flow BOTH contribute to flying, not one or the other. You could build a plane like a kite ( all attack angle ) and it would work, but it would take an enormous amount of fuel to get anywhere.

You cant go around saying that lift from a curved surface doesnt happen - cause it DOES!

3. watchkeeperPrevious Member

YAWN...same old same old BS

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rwatsonSenior Member

Its part of the charity work to keep old sailors happy and cantankerous as they slide into drug induced senility.

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rwatsonSenior Member

Oh, by the way Frosty, everyone knows that "The Equal Transit Time statement is complete nonsense.".

You have been quoted about 3 or 4 times how the nonsense got started in links provided

Finish the bottle, and get to bed

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daiquiriEngineering and Design

Bernoulli, Frosty...

Not Benelli,
not Benoulli,

but Bernoulli.

7. watchkeeperPrevious Member

I concur with the charity but they shoot old horses too

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upchurchmrSenior Member

Frosty plus the Wikipedia expertise - anyone who writes something is instantly an expert.
It was also "proven" that you couldn't fly.
Right up there with the Flat Earth Society.

"Experts" do make mistakes, and we move on. The point is to move on, not dwell in dead ends.

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daiquiriEngineering and Design

Wish it was the Wikipedia... Here we have proofs coming from sites like Dinosaurtheory.com .

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troy2000Senior Member

That's a seriously entertaining site, daiquiri. Thanks for posting the link.

A sample:

11. Number4Previous Member

I went to flight school in New Zealand, and studied for a commercial pilots license. I was compelled to attend class, or I would have had my student visa revoked. One of my instructors was a little boy who had been a former class mate of mine. I used to kick him to keep him awake in lectures. He milked the student loan scheme and became an instructor and lecturer of aerodynamics. Good for him.
I remember being taught the equal path theory and I thought "What a load of bollocks!"
I have taken an exam for an Airline Transport Pilots Licence in Aerodynamics, and picked many wrong multiple choice answers, simply because I knew they would be considered correct by the examiner. I scored 97%.

Since then I have learned that bumble bees should not fly, we can not build mechanical birds, and that no one really agrees on how planes fly. Yet millions more people than ever are travelling the globe.

http://www.dinosaurtheory.com/flight.html
"The correct short explanation of flight is that as the air flows over the top wing surface it follows the form of the wing. As the air travels over and past the thickest part of wing, the air is diverted downward as it sticks to the profile of the wing. In the process of the wings diverting a tremendous amount of air down, an upward reactionary force is exerted on the wings of the plane that lifts the airplane up."

Is this guy correct? Or is it as much nonsense as the equal transit theory?

We have the well established equation
Lift= Coefficient of Lift x (1/2 fluid density x fluid velocity squared) x surface area.

The coefficient covers whichever theory you believe. The only problem I see with it, is that it does not consider aspect ratio.

If anybody out there can actually tell me how a wing makes lift and a sail produces drive I will buy you a case of cold beer.

Cheers

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daiquiriEngineering and Design

The answer depends on how much math you're willing to swallow...

13. Number4Previous Member

I prefer to swallow Kronenbourg.
I can cut it 50% 50% with extra proof maths, and it still tastes ok.
Go for your life my friend!

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daiquiriEngineering and Design

Ok, I didn't get this one, but guess it doesn't really matter...

Oh no, quite the contrary - the coefficient Cl covers the aspect ratio two.
There are two coefficients of lift in use wit this equation, the "cl" and the"Cl". The one with the lower-case "c" is used for airfoils, which are 2-D wing sections. The ones with the capital "C" is used when dealing with 3-D wings.
And since the 2-D airfoils behave aerodynamically like infinite-span wings, we take just a unit-length span for 2-D analysis, which has an area of S=1*c, where "c" is the chord.
So your equation becomes, for 2-d and 3-D case respectively:
l = 0.5 rho V^2 c cl
L = 0.5 rho V^2 S Cl
The coefficient cl doesn't take into account the aspect ratio, since it is relative to an infinite-span wing (2-D case), but the coefficient Cl does contain the AR too, as well as other geometric characteristics of the wing (planform shape, twist, taper etc.).

I'd invite you to read this discussion, for a more in-depth treatment of differences between 2-D and 3-D lifting body aerodynamics: http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/lift-without-downwash-44937.html

Cheers

15. Number4Previous Member

"Go for your life my friend!" Is an expression.
It means
"Fire Away!"
" Do Not Hold Back!"
You may also say it to a sportsman, or a military person.