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Thread: Aircraft Physics - Droop Tips

  1. #1

    Aircraft Physics - Droop Tips

    Dan,
    Let me see if I can shed some light on your understanding of the
    decreased load. First, the droop tips create greater lift than the standard tips
    otherwise you would not have the slower operating speeds. Now look at the
    point where the added lift, and added drag, are applied - on the tip. Example -
    take two popsicle sticks and place one in a vice with the jaws about the
    center. Get a fish scale and attach it to the end and pull until the stick
    breaks. Note the pressure required and location of the break. Now, place the
    other stick in the vice just as before. Place the fish scale in the center
    between the end and the vice and repeat the process. Note it takes more force to
    break the stick and both sticks break near the attachment point (the vice).
    Both sticks have comparable resistance to stress and breaking. Your wing
    operates along the same principle. The fulcrum (vice) is attached at the same
    location in both cases (the wing root). The droop tips are that force
    applied to the end of the stick, your wing tip. It is a greater force than the
    standard tips just like the force applied to the fish scale. If you were able
    to apply the same amount of force to the end as you did the center of the
    stick, the stick would be deformed or already broken. So to keep the force
    within limits, the gross weight must be reduced (the force applied to the wing
    tip). True, the entire wing is producing lift but by applying the additional
    lift at a greater distance from the fulcrum point, the force is multiplied,
    not added to the stress factor on the spar and attachment points. To
    compensate for this mechanical advantage over the distance of the wing, the engineers
    formulated the new reduced weight to keep the sheer stress level within the
    manufacturers design limits.
    This additional lift is generated throughout the flight, not just in
    the T/O & landing configurations. Remember in your early flight training what
    60 degree coordinated turns produce? They produce a 2-G load. That force is
    spread over the entire wing but now a greater percentage is being developed
    at a distance farther from the attachment points and is some factor greater
    than what the standard tip develops.
    I hope this helps your understanding of the flight characteristics of
    our or any aircraft. The engineers calculate, not SWAG, at the particular
    weights, air speeds, and load factors based on the laws of physics, not laws of
    man. These laws when broken have repercussions far beyond a slap on the
    wrist or a monetary fine. And like man's laws, you may break them once or twice
    without incident but Mother Nature is not going to let you continue to break
    them. Her pay back is a matter of fact.
    Blue Skies,
    Chuz
    BAC SE Director


    [Non-text portions of this message have been removed]



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  2. #2

    Aircraft Physics - Droop Tips

    Chuz,

    Makes all the sense in the world. If I would have put
    some serious thought to it, even I might have figured
    it out. Thanks for your reply, you made it easy. Good
    to hear from you.

    Dan Kirby

    --- ChuzBear@aol.com wrote:

    > Dan,
    > Let me see if I can shed some light on your
    > understanding of the
    > decreased load. First, the droop tips create
    > greater lift than the standard tips
    > otherwise you would not have the slower operating
    > speeds. Now look at the
    > point where the added lift, and added drag, are
    > applied - on the tip. Example -
    > take two popsicle sticks and place one in a vice
    > with the jaws about the
    > center. Get a fish scale and attach it to the end
    > and pull until the stick
    > breaks. Note the pressure required and location of
    > the break. Now, place the
    > other stick in the vice just as before. Place the
    > fish scale in the center
    > between the end and the vice and repeat the
    > process. Note it takes more force to
    > break the stick and both sticks break near the
    > attachment point (the vice).
    > Both sticks have comparable resistance to stress
    > and breaking. Your wing
    > operates along the same principle. The fulcrum
    > (vice) is attached at the same
    > location in both cases (the wing root). The droop
    > tips are that force
    > applied to the end of the stick, your wing tip. It
    > is a greater force than the
    > standard tips just like the force applied to the
    > fish scale. If you were able
    > to apply the same amount of force to the end as you
    > did the center of the
    > stick, the stick would be deformed or already
    > broken. So to keep the force
    > within limits, the gross weight must be reduced
    > (the force applied to the wing
    > tip). True, the entire wing is producing lift but
    > by applying the additional
    > lift at a greater distance from the fulcrum point,
    > the force is multiplied,
    > not added to the stress factor on the spar and
    > attachment points. To
    > compensate for this mechanical advantage over the
    > distance of the wing, the engineers
    > formulated the new reduced weight to keep the sheer
    > stress level within the
    > manufacturers design limits.
    > This additional lift is generated throughout
    > the flight, not just in
    > the T/O & landing configurations. Remember in your
    > early flight training what
    > 60 degree coordinated turns produce? They produce
    > a 2-G load. That force is
    > spread over the entire wing but now a greater
    > percentage is being developed
    > at a distance farther from the attachment points
    > and is some factor greater
    > than what the standard tip develops.
    > I hope this helps your understanding of the
    > flight characteristics of
    > our or any aircraft. The engineers calculate, not
    > SWAG, at the particular
    > weights, air speeds, and load factors based on the
    > laws of physics, not laws of
    > man. These laws when broken have repercussions far
    > beyond a slap on the
    > wrist or a monetary fine. And like man's laws, you
    > may break them once or twice
    > without incident but Mother Nature is not going to
    > let you continue to break
    > them. Her pay back is a matter of fact.
    > Blue Skies,
    > Chuz
    > BAC SE Director
    >


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