Physics Question for you.....

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Physics Question for you.....

    A plane is standing on runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

    The question is:

    Will the plane take off or not? Will it be able to run up and take off?
    Mike
    Lakota's Dad

    If at first you don't succeed, deny you were trying in the first place.

  • #2
    No.
    I don't think so. The air around the plane isn't moving. Its sitting still. You will wear out the landing gear bearings and tires that way though. Don't hit the brakes either unless you can fly in reverse.
    Lee

    Comment


    • #3
      Nope

      Since the plane will be essentially standing still, there will be no "wind beneath its wings". No airflow, no lift, no fly.
      To do is to be.

      Comment


      • #4
        How big is the conveyor relative to the plane size?

        Bob

        Comment


        • #5
          Yes, the plane uses air to push, not friction with the ground. Let's say it needs a speed of 100 to take off. At the moment of takeoff it is moving 100. The converyor is moving at 100 backwards. The wheels are effectively spinning at 200. Assuming the wheels can handle double speed without blowing out, should be able to take off.
          Mark
          --------
          "There are no stupid questions - just stupid people"

          Comment


          • #6
            If the plane isn't moving, neither is the conveyor belt or since the belt takes it speedcue from the speed of the plane it will always lag a bit and eventually the plane will take off.
            Oh forget it!

            Tim
            Sometimes my mind wanders. It's always come back though......sofar!

            Comment


            • #7
              Plane wing is profiled so that when airflow is present, an elevated pressure zone is formed under the wing, and near-vacuum above it. This produces an upward thrust (antiwings on racing cars act int the opposite direction, pressing the car to ground for more traction) If plane is not moving relative to the air around it, no upward thrust is generated, and plane will not lift off.

              Comment


              • #8
                No, the plane will never take off, no matter how fast the conveyor belt is running, because the wings are not moving relative to the air.

                It's similar to a car engine hooked to a dyno. No matter how many RPM it turns, how much torque is produced, or how much horsepower is cranked out ... the engine stays right where it is until it's either shut down, runs out of fuel, or blows up.
                Larry

                Comment


                • #9
                  No it won't be able to take off. There would be no air lift to allow it to become airborne. I think it would be similar to a boat motoring at say 10 MPR with a 10 MPR current, it's not going anywhere. That's my simple thinking anyway.
                  May you die and go to heaven before the Devil knows you're dead. My Best, Mac

                  Comment


                  • #10
                    Scorppio got it exactly right.

                    Papa

                    Comment


                    • #11
                      plane on a conveyor belt

                      Originally posted by jspelbring View Post
                      Since the plane will be essentially standing still, there will be no "wind beneath its wings". No airflow, no lift, no fly.
                      Got it dead on...no airflow, no lift, no fly...and by the way, I understand lift off speed to be 188 mph for a modern passenger jet.

                      Comment


                      • #12
                        I think a Harrier might pull it off. If this were really possible, don't you think we'd have conveyor belts instead of catapults on an aircraft carrier?
                        Lee

                        Comment


                        • #13
                          But what if the conveyer is very long and the friction between the conveyer and the air around it creates a boundary layer? Thus the conveyer moves the air enough so that the air is pushed into the plane at 100MPH?????

                          OK, I know I'm reaching....

                          Comment


                          • #14
                            Originally posted by scorrpio View Post
                            Plane wing is profiled so that when airflow is present, an elevated pressure zone is formed under the wing, and near-vacuum above it. This produces an upward thrust (antiwings on racing cars act int the opposite direction, pressing the car to ground for more traction) If plane is not moving relative to the air around it, no upward thrust is generated, and plane will not lift off.

                            Real close, but not quite.

                            It's not 'thrust', but SUCTION and THRUST that lifts a plane up. As the wind travels over and under the wing, the air that has to go over has to travel farther because of the shape of the wing. This decreases the density of the air above the wing, sucking the wing up because the density of the air below the wing is higher. Suck and thrust, so to speak. Everything is relative to wind speed above and below the wing that causes the air density differential.

                            The entire plane is pushed by jets or propellors in order to move the wings through the air at a certain speed to create the 'lift' (short for thrust and suck) effect on the wings.

                            That's what a helocopter does too. The blades are realy wings that are moved through the air at speeds to cause lift on each wing/blade. The wing/blades then lift the helocopter because they're attached via the rotating shaft.

                            And my physics teacher thought I wasn't paying attention back in high school.

                            (But nobody's convinced me that the Low Oil light isn't the same as the Low Fuel light.)
                            Last edited by gjat; 12-08-2006, 08:03 PM.

                            Comment


                            • #15
                              It's going to fly.
                              The airplane propellor or turbine or jet creates thrust against the air behind it, not by rolling the wheels like a car.

                              remember that the air will be still, relative to the ground (assuming wind = 0).

                              The airplane will move forward at some velocity V (relative to the ground and hence, air). The belt will have a velocity of -V and the wheels will spin like crazy at 2 x V. The air right at at the surface of the belt will actually be moving at 2 x V (due to the boundary surface drag of the belt) relative to the airplane but the air just below the wings will be moving at just over V respective to the plane and more importantly the air over the wings will be moving at V. So when V = takeoff velocty the plane will lift, no problem.

                              There of course will be extra wear and tear on the conveyor belt and the landing gear, so you don't want to do this too often.
                              Last edited by LCHIEN; 12-08-2006, 11:04 PM.
                              Loring in Katy, TX USA
                              If your only tool is a hammer, you tend to treat all problems as if they were nails.
                              BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                              Comment

                              Working...
                              X