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Thread: pretty basic aerplane question

  1. #1 pretty basic aerplane question 
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    yo yo yo people of science
    if evolution is true then how come in the old days snakes could talk but now they can't?

    Anyway,
    my understanding of bernolli's principle is that fast moving air is lighter that slower moving air, thus aerplanes fly.
    Then how come jet engines are on the underside of the wing
    would it not be more efficient to put these drivers of fast moving air on top of the wing.

    Peter


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    Quote Originally Posted by pedronaut View Post
    yo yo yo people of science
    if evolution is true then how come in the old days snakes could talk but now they can't?

    Anyway,
    my understanding of bernolli's principle is that fast moving air is lighter that slower moving air, thus aerplanes fly.
    Then how come jet engines are on the underside of the wing
    would it not be more efficient to put these drivers of fast moving air on top of the wing.

    Peter
    As air is pulled into the jets under the wing it increases the adjacent airflow rate under the wings providing more lift and therefore efficiency. Uneven airflow over the top of the wing could instead push the craft downward.

    if evolution is true then how come in the old days snakes could talk but now they can't?
    Snakes can still communicate with humans by making hissing and rattling sounds. I think the serpent was telling Eve that forbidden fruit are pretty tasty, right?


    Last edited by forrest noble; February 17th, 2013 at 01:06 AM. Reason: changed "increased" to uneven
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    Anti-Crank AlexG's Avatar
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    Quote Originally Posted by forrest noble View Post
    Quote Originally Posted by pedronaut View Post
    yo yo yo people of science
    if evolution is true then how come in the old days snakes could talk but now they can't?

    Anyway,
    my understanding of bernolli's principle is that fast moving air is lighter that slower moving air, thus aerplanes fly.
    Then how come jet engines are on the underside of the wing
    would it not be more efficient to put these drivers of fast moving air on top of the wing.

    Peter
    As air is pulled into the jets under the wing increases the adjacent airflow rate under the wings providing more lift and therefore efficiency. Increased airflow over the top of the wing would instead push the craft downward.
    Quite the opposite. Faster airflow over the top of the wing surface results in lower pressure on the top of the wing, higher pressure on the underside of the wing and so produces lift.

    There have been planes built with the engines on the top, but never large jets. The engine on the top of the wing would disrupt the smooth airflow over the airfoil.
    jocular likes this.
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  5. #4  
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    Quote Originally Posted by AlexG View Post
    Quote Originally Posted by forrest noble View Post
    Quote Originally Posted by pedronaut View Post
    yo yo yo people of science
    if evolution is true then how come in the old days snakes could talk but now they can't?

    Anyway,
    my understanding of bernolli's principle is that fast moving air is lighter that slower moving air, thus aerplanes fly.
    Then how come jet engines are on the underside of the wing
    would it not be more efficient to put these drivers of fast moving air on top of the wing.

    Peter
    As air is pulled into the jets under the wing increases the adjacent airflow rate under the wings providing more lift and therefore efficiency. Uneven airflow over the top of the wing could instead push the craft downward.
    Quite the opposite. Faster airflow over the top of the wing surface results in lower pressure on the top of the wing, higher pressure on the underside of the wing and so produces lift.

    There have been planes built with the engines on the top, but never large jets. The engine on the top of the wing would disrupt the smooth airflow over the airfoil.
    I agree. I expect jets on top of the wing would result in uneven and undesirable airflow over the top of the wing. Wing aerodynamics is the key factor.

    .
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  6. #5  
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    Quote Originally Posted by pedronaut View Post
    yo yo yo people of science
    if evolution is true then how come in the old days snakes could talk but now they can't?
    Snakes could not talk in the old days. This is a myth, propagated by a popular work of fiction.
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    Quote Originally Posted by pedronaut View Post
    if evolution is true then how come in the old days snakes could talk but now they can't?
    What makes you "think" that they could?

    Then how come jet engines are on the underside of the wing
    Apart from the above answers it's also more efficient from an access point of view (for maintenance) to have them mounted as low as possible.
    All aircraft designs are a compromise.
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    if evolution is true then how come in the old days snakes could talk but now they can't?
    They evolved into lawyers.
    Fixin' shit that ain't broke.
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  10. #9  
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    And then, too, there is the question of where under the wings, along their length, to locate the engines. Check out the Lockheed Electra, a fairly large, turbo-prop jet of years back, which experienced severe "wing flutter", due to resonance effects, because the engines happened to be mounted in the wrong place!
    Boeing Aircraft Co. became deeply involved in wing flutter studies when designing the 747, then the world's largest aircraft (kind of after the Spruce Goose). They found experimentally, in wind tunnel tests, that the "window" of engine location along the wing was only 18 inches wide, to negate possible flutter effects.

    Flutter caused the wings of Electras to fail in flight, as I recall, a goodly number of aircraft (and lives) lost. jocu;lar
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    Not quite true.
    It wasn't wing flutter but "whirl mode", and force was transmitted, from the propellers, through the engine mounts into the wing .
    In fact the Electra is, obviously, considered to be safe since it's also in service as the P-3 Orion.

    As an example the Electra had 6 fatal crashes between its introduction in 1959 and 1985.
    6 crashes in 26 years? Doesn't sound that disastrous to me...
    Last edited by Dywyddyr; February 18th, 2013 at 12:19 AM.
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    Thanks for the feedback, esp Dywyddyr for- "All aircraft designs are a compromise."
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    Brassica oleracea Strange's Avatar
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    All design is a compromise.
    pedronaut likes this.
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  14. #13  
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    Quote Originally Posted by Strange View Post
    All design is a compromise.
    Human beings, especially their minds, being undoubtedly one of the most extensive compromises ever...... jocular
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    Quote Originally Posted by Dywyddyr View Post
    Not quite true.
    It wasn't wing flutter but "whirl mode", and force was transmitted, from the propellers, through the engine mounts into the wing .
    In fact the Electra is, obviously, considered to be safe since it's also in service as the P-3 Orion....
    Apparently, then, Boeing was producing deceiving and technically incorrect information when it made public it's finfdings regarding engine location on wings, eh? Fact is, aircraft wings deflect quite a bit, producing nodes and antinodes whose locations make for good or poor engine ;location choices.

    Thank you for illuminating my error regarding wing flutter. jocular
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    Quote Originally Posted by pedronaut View Post
    yo yo yo people of science
    if evolution is true then how come in the old days snakes could talk but now they can't?

    Anyway,
    my understanding of bernolli's principle is that fast moving air is lighter that slower moving air, thus aerplanes fly.
    Then how come jet engines are on the underside of the wing
    would it not be more efficient to put these drivers of fast moving air on top of the wing.

    Peter
    First of, the same book that is alleged to contradict evolution, is also the one that puts forward talking animals. Hence your own question disproves the bible as such.

    Second. That is not how airplanes work.

    Wings fly, due to the so called 'Boundary layer' which is the one that creates a lower pressure on the wing making it go forward. It is a small region often no more then a few centimeters high, which is easily broken, where air flows in the direction of the plane. This because at the wing air mus essentially stand still with respect to the plane. (since the wings don't fly away from the plane)
    This layer is relatively thin. Jet engine's are blaced beneath, or more accurately, behing the wing, because the propel the turbulance of a wing backwards, increasing the airflow, whilst at the same time propelling. That is why there is often a small jet at the back of the plane (it is a small hole at the tail, check it out)
    In the information age ignorance is a choice.
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    Quote Originally Posted by jocular View Post
    Apparently, then, Boeing was producing deceiving and technically incorrect information when it made public it's finfdings regarding engine location on wings, eh? Fact is, aircraft wings deflect quite a bit, producing nodes and antinodes whose locations make for good or poor engine ;location choices.
    Boeing may well have been correct, with regard to their own aircraft: but Boeing didn't make (or design) the Electra.
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  18. #17  
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    Quote Originally Posted by Kerling View Post
    Wings fly, due to the so called 'Boundary layer'
    Huh?
    The boundary layer is the main cause of DRAG. And provides very little lift.

    This because at the wing air mus essentially stand still with respect to the plane. (since the wings don't fly away from the plane)
    Since the wing remains attached to the plane (in the same position regardless of speed), and air MUST flow relative to the wing, then the air must NOT "stand still" with respect to the plane.

    Jet engine's are blaced beneath, or more accurately, behing the wing
    Except that, as will be seen from a quick Google image check, jet engines can be placed in virtually ANY position with regard to the wing. The actual position depends upon numerous factors - in fact in my post #8 I gave links to at least 2 different aircraft with the jets mounted exactly as per the OP - one of those, the AN-72/ 74, has been in service for ~30 years.
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