Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What two types of forces contribute to the lift on a wing?

  1. Jul 1, 2003 #1
    What two types of forces contribute to the lift on a wing?
     
  2. jcsd
  3. Jul 1, 2003 #2
    For the scholar solution:

    1: Air Pressure differential due to Bernouilli's law
    2: forces due to the Newtons laws. accelleration of air and reaction force, The downwash of air creates a reaction uplift in the wing.

    A good link: http://www.theken.org/forum/html/article.php?sid=5
     
    Last edited: Jul 1, 2003
  4. Jul 1, 2003 #3
    If you are using the word "lift" as the actual action of flight (lift and flight have been used interchangedly on the sites I have researched)...

    The four main forces of flight are:
    1)Lift (opposes gravtiy)
    2)Drag
    3)Thrust (opposes drag)
    4)Weight (aka Gravity)

    http://sln.fi.edu/flights/own2/forces.html

    Within the category of lift, the following exist:

    -Another name for lift, besides flight, is airfoil lift or Bernoulli's lift: (http://www.allstar.fiu.edu/aero/flight41.htm)

    Main Forces acting on Lift:

    1) Newton's Third Law of Gravity (for dynamic lift)
    2) "Angles of Attack" = these are the angles at which air pressure is exerted against the airfoil (it can be positive, neutral, or negative pressure)

    Source: http://www.allstar.fiu.edu/aero/flight41.htm
     
  5. Jul 1, 2003 #4
    1) Bouyancy
    2) Thrust

    Thats the best I can think of, without repeating other solutions. I'll be interested to see how the ans is worded.
     
  6. Jul 1, 2003 #5
    Air Pressure Is the Backbone of Lift

    "According to Bernoulli's Principle, slower air has higher pressure than faster air. That means that the air pressure pushing up on the bottom of the wing is greater than the pressure pushing down, so the wing goes up."

    This statement encompasses the forces of air pressure and the idea of Newton's 3rd Law (the second force)- Every action has an opposite and equal reaction:

    "...the air pressure pushing up on the bottom of the wing is greater than the pressure pushing down, so the wing goes up"


    Moreover, just the fact that wind is hitting the bottom of the tilted wing (airfoil) gives it lift - think of a kite. The upwardly tilted piece of fabric on a kite catches the wind to direct it upward.

    To create lift to begin with, however, one major component is neeed: thrust. The thrust, aka forward motion, is created by the plane's engine. Without forward motion wind and pressure would not pass over the plane's wings.
     
  7. Jul 1, 2003 #6
    In a bird's wing vacuum also plays a part. The bird slaps its wings together pulls them apart leaving a vacuum to begin its flight.

    Vacuum and pressure.
     
  8. Jul 1, 2003 #7
    In this question lift does not equal flight. Most of you have one answer correct, figure out the other :smile:
     
  9. Jul 1, 2003 #8
    Arrrgg mateys, back to the drawing board....
     
  10. Jul 1, 2003 #9
    Ok, let's look at this question in a different light...

    Air pressure is obviously one of the correct answers. Air pressure corresponds to Newton's Laws of motion (esp. the 3rd Law - Every action has an opposite and equal reaction) The force exerted on the lower part of the wing produces lift.

    But what about perhaps that second critical force...momentum:

    "The lift of a wing is equal to the change in momentum of the air it is diverting down. Momentum is the product of mass and velocity (mv)."

    The idea of momentum being the 2nd force is interesting because it also coincides with Newton's Seond Law.

    "The lift of a wing is proportional to the amount of air diverted down times the vertical velocity of that air (Newton's second law normally states force equals mass times acceleration)." The diversion of the mass and velocity is also linked to the Coanda Effect.

    http://137.229.52.100/~physics/p113/nowakowski/Physics_Webpage.html

    Therefore, my revised answer is Air Pressure (the diff between the upper and lower half of wing) and Momentum
     
  11. Jul 1, 2003 #10
    Fluid motion and pressure.
     
  12. Jul 1, 2003 #11
    Maybe all you guys are not thinking enough of balloons and Zeppelins. Archimedes said that any body (even a wing) in a medium feels not such a strong downward force, as it would in vacuum. The reason is gravity (of the medium, compared to the body). So my first guess is:
    1) Gravity
    Next comes all the stuff about Bernoulli, downwash, and so on (i.o.w., dynamical stuff), which is only there because air molecules are inert. So my second guess is:
    2) Inertia.
     
  13. Jul 1, 2003 #12

    enigma

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Hi all!

    This is my question, so I'm going to give a few hints to point you all in the right direction. It comes straight from one of my textbooks. Not many people (or websites I've seen) outside of aerospace specific fields think about the second answer.

    1) Newtons 2nd, d/dt(mv) = F is not a force in itself. It is a way to calculate the change in momentum, but not a force.

    2) Air pressure is one of the types of forces, so Andre gets at least 1/2 a point for the first mention of it.

    3) Gravity probably should have been one of them, since it does act in the lift direction, but since it doesn't ever contribute to positive lift, I didn't include it.

    4) I have seen something close to the second answer given. It is a very small contributor to lift compared to air pressure under normal flight situations, but in certain situations, it can get very large.
     
    Last edited: Jul 1, 2003
  14. Jul 1, 2003 #13

    drag

    User Avatar
    Science Advisor

    I hope the answer is indeed connected to forces directly.
    Well, my stupid guess (as it seems everything else was tried)
    is pressure and density differences.

    (BTW, if I win the whole contest and you still decide to
    award me the 15$, despite my objection that I wrote in
    the feedback thread, I wan'na donate it to the WWF and help
    save endangered animal species. Of course, I won't win, so -
    there go the animals I guess... )
     
  15. Jul 1, 2003 #14
    Thanks for the hint enigma, but besides the pressure mentioned (a form of dynamic lift), the only other contributing factor I can come up with is...

    Turbulence - I got this from "Physics" - 5th Ed by Giancoli (the only reason I think this one would work is because you said sometimes it has more of an effect than othertimes)
     
  16. Jul 1, 2003 #15

    enigma

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Nope

    Turbulence characteristics are affected by it as well, though.
     
  17. Jul 1, 2003 #16
    Alright, now I'm just getting downright desperate : )

    Ok, so the equation for lift is this:

    L = C(subscript L) * S x .5pv^2

    Therefore, 5 MAJOR Factors:

    1)The Cross-section Shape of the airfoil (not a force)
    2)The angle of attack (not a force)
    3)The plan form size of the wing (not a force)
    4)The Density of the air (mentioned earlier)
    5)The Velocity of flight through the liquid air (briefly commented on)

    Final Answer? (Oh God, lets hope so)

    "Lift is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid: no motion, no lift."
     
  18. Jul 1, 2003 #17

    drag

    User Avatar
    Science Advisor

    Oops... I wrote my answer and then deleted it after seeing
    Matt's answer was first but then I saw he's talking about velocity
    between the wing and the environment while my answer is the
    velocity difference below and above the wing (Bernoulli's stuff...).
    Anyway, isn't it accounted for as pressure too eventually in
    this case ?
     
  19. Jul 1, 2003 #18

    enigma

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You're going to kick yourself when you find out what it is!

    I can guarantee you know it. I can even guarantee you've done problems dealing with it (although probably not in airplane type problems... first cut through aerodynamics and it is typically discounted).

    The formula for lift you gave has the unitless coefficient CL. The actual forces are all tied up within that coefficient (using the Buckingham Pi Theorem).

    EDIT: Yes drag, Bernoulli does deal with pressures only.

    I'll give a last hint when I get home tonight, if noone has gotten it yet.
     
    Last edited: Jul 1, 2003
  20. Jul 1, 2003 #19

    drag

    User Avatar
    Science Advisor

    making a fool out of myself yet again :
    hmm... shock waves ?
     
  21. Jul 1, 2003 #20
    Well Enigma I have never taken physics before (I have only done the summer work leading up to my AP class next year), so unless it was one of the times you helped me, then I prob. haven't seen it.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: What two types of forces contribute to the lift on a wing?
Loading...