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I'm thinking this question had to been asked before, but I did a search and couldn't find anything on it. It's really bugging me, because I never could find out the right answer.
Suppose you have a jet airplane sitting on a runway. But this runway acts like a treadmill. The jet starts it's thrusters and for every mile an hour the Jet's wheels move forward, the treadmill moves a mile an hour in the opposite direction.
NO BC you are wrong - because the wheels will be spinning and the engines would develope enough thrust to make the a/c to roll forward and reach its takeoff speed, the weels are not what makes a a/c to move forward, the engines are not in any way connected to the wheels as it is in a car, or truck ect. ect. the tires will start to skid over the tredmillas thrust is incresed and the faster the a/c roll forward the lighter it becomes on the treadmill which starts from the time the a/c starts moveing , andf befor it reaches the point of rotation,( LIFTOFF OR TAKE OFF ) All a/c have a point in speed for rotation , every a/c is different speeds, but there has been times that i was not at rotation point and was able to take off with the use of fllaps, ( Once lift = weight you have lift off ) HAVE A GOOD DAY & GOD BLESS:::: F.B.E.
A treadmill is not a frictionless platform! The wheels are not frictionless! The motion of the treadmill will push backwards on the wheels of the aircraft.
If there is no thrust - the aircraft would move backwards! The thrust must overcome that friction just to make the aircraft stay in one position.
A treadmill is not a frictionless platform! The wheels are not frictionless! The motion of the treadmill will push backwards on the wheels of the aircraft.
If there is no thrust - the aircraft would move backwards! The thrust must overcome that friction just to make the aircraft stay in one position.
BCDurbin - I do not believe that you know the princibles of flight< One thing there is no tread mill made that could hold back a a/c with engines at full thurst GOOD DAY & GOD BLESS :: F.B.E.
A treadmill is not a frictionless platform! The wheels are not frictionless! The motion of the treadmill will push backwards on the wheels of the aircraft.
If there is no thrust - the aircraft would move backwards! The thrust must overcome that friction just to make the aircraft stay in one position.
Put it this way...
Imagine a skateboard on a treadmill. Tie a rope to the skateboard and stand along side of the treadmill. Now turn the treadmill on. The skateboard will start moving backward, but you can easily run along side the treadmill pulling the skateboard forward. The reason you can do this is because you yourself are not on the treadmill. In other words, the forward force is completely independent of the treadmill AND the skateboard's wheels
The above example is also the principle of thrust. The thrust 'pushes' the jet forward independent of the aircraft's (wheels). If you're still having trouble, imagine another plane flying overhead with a tow rope attached to the plane on the treadmill. Regardless of how fast the treadmill is going in the reverse direction, the flying plane would not only be able to pull the plane on the treadmill forward, but would pull it forward at the speed in which it was flying. Again, thrust works the same way. Since it is independent of the aircraft's wheels it would eventually reach rotation.
Lobrobster - Boy did you say the RIGHT THINGS, I hope maybe he will understand now that the a/c will move forward as the pilot advances the throttle and increases the thrust of the engines,and will increase the speed of the a/c and reach the ROTATION POINT AND TAKE OFF> ALso as he increses the speed ,he starts to have lift and will start loosing contact with the treadmill,;: thanks Lobrobster you earned a greenie for your answer ;;; Have a good day and GOD BLESS :: F.B.E.
Imagine a skateboard on a treadmill. Tie a rope to the skateboard and stand along side of the treadmill. Now turn the treadmill on. The skateboard will start moving backward, but you can easily run along side the treadmill pulling the skateboard forward. The reason you can do this is because you yourself are not on the treadmill. In other words, the forward force is completely independent of the treadmill AND the skateboard's wheels
no - turn the treadmill on first then see how much force it takes to hold the skateboard in place - there is friction there! the original question did not say this was frictionless.
The above example is also the principle of thrust. The thrust 'pushes' the jet forward independent of the aircraft's (wheels). If you're still having trouble, imagine another plane flying overhead with a tow rope attached to the plane on the treadmill. Regardless of how fast the treadmill is going in the reverse direction, the flying plane would not only be able to pull the plane on the treadmill forward, but would pull it forward at the speed in which it was flying. Again, thrust works the same way. Since it is independent of the aircraft's wheels it would eventually reach rotation.
The rope is an outside force - very much different than thrust. Without that rope the skateboard would move backwards at exactly the same pace as the treadmill. The rope is a force that would keep it in place. Your holding the rope and walking is an ADDITIONAL force that would propel the skateboard! I agree that if you tow the aircraft off it will fly eventually but that is not the premise of the original question - it said that all forces (thrust and treadmill travel) are equal. It would take more thrust than treadmill travel for the aircraft to fly - equally, more treadmill travel than thrust - and the aircraft would move backwards!!
BCDurbin - I do not believe that you know the princibles of flight< One thing there is no tread mill made that could hold back a a/c with engines at full thurst GOOD DAY & GOD BLESS :: F.B.E.
You are talking reality - the original question was just theoretical. I have no doubt that a jet could outthrust a REAL treadmill - the question stated if the 'treadmill travel' and the aircrafts speed (thrust) were equal! And in the opposite direction! Am I right? Any additional force by the aircraft (rope or thrust!) would propel the aircraft forward - just as any additional force would move the aircraft backwards! but if all forces are equal there will be no movement.
BCDurdin - I have one question to ask you first???? DO YOU HAVE ANY EXPER> ON A?C OR AS SA PILOT< IN ANY WAY?????? F.B.E.
easy on the keyboard there buddy! but after figuring out your question - to answer it in a word yes! you wouldn't believe me if I told you, but so far it's about 25 years! Next question! - BCD
...... Tie a rope to the skateboard and stand along side of the treadmill. Now turn the treadmill on. The skateboard will start moving backward, but you can easily run along side the treadmill pulling the skateboard forward. ........
put a scale/g-force meter on the end of that rope and see how much force it takes to hold the skateboard in place. now stand on the skateboard and see if takes more force. I have no doubt you could pull it off the treadmill but it will take excess force in the forward direction to do it. especially after you stand on it. try two people - it's more fun that way when you fall down! - BCD
The jet starts it's thrusters and for every mile an hour the Jet's wheels move forward, the treadmill moves a mile an hour in the opposite direction.
The question has to do with a hypothetical situation. A body with lift that ordinarily could fly is in a situation where it cannot achieve any velocity relative to the wind. If the jet accelerates to 100 kts, the treadmill accelerates to 100 kts in the opposite direction. Relative to the surface of the earth, the jet is not moving. Relative to the wind, it is not moving. No movement through the wind...no lift.
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