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Thread: Okay Krupski or other knowing people answer this please

  1. #81
    Team GunsNet Silver 12/2011 N/A's Avatar

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    So, if the wheels and treadmill are irrelevant, why did you say it takes so much more energy and distance to get up to speed?¿?
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

  2. #82
    Senior Member Viking350's Avatar

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    Quote Originally Posted by JTHunter View Post
    It takes almost no effort to hold the wheels of a toy against the moving treadmill, just slightly more than the treadmill is exerting because you are holding the plan against the belt as well as against the motion of the belt.
    If you want to move the model in the opposite direction of the belt, it takes more energy as long as you hold it on the belt. If you hold the model ABOVE the belt, the energy needed to hold it up is equal to gravity's force pulling it down.
    Planes fly based on the speed of the air flowing both OVER and UNDER their wings. No air motion, NO FLYING. What the planes tires and the treadmill are doing are irrelevant. It is all about the air and the wings. That's why planes have to have a certain speed of forward motion to get off the ground. Each plane is different, from single engine Cessnas to multi-engine jets.
    When a fighter jet goes straight up ballistic after lift off, what causes it to gain altitude? The wings are parallel to the force of gravity and therefore can’t be generating altitude gaining lift.
    Last edited by Viking350; 09-28-2019 at 11:01 AM.

  3. #83
    Team Guns Network Silver 04/2013 alismith's Avatar

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    Quote Originally Posted by Viking350 View Post
    When a fighter jet goes straight up ballistic after lift off, what causes it to gain altitude? The wings are parallel to the force of gravity and therefore can’t be generating altitude gaining lift.
    Thrust from the engines. It's doing the same thing a rocket ship does after liftoff. If the upward thrust is greater than the downward pull of gravity, it will rise.
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  4. #84
    Team GunsNet Silver 12/2011 N/A's Avatar

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    Quote Originally Posted by Viking350 View Post
    When a fighter jet goes straight up ballistic after lift off, what causes it to gain altitude? The wings are parallel to the force of gravity and therefore can’t be generating altitude gaining lift.
    Force lines of gravity travel straight away from a mass, thus for the wings to be parallel *|| to those force lines, ot would need to be going straight up.
    It would be just as alismith stated.

    Now, of you are thinking of the wings being parallel *= to the Earth's surface, then you can either go with the angle of attack of the wings to the air.....or the curvature of the Earth.



    Just thinking what you asked, and the way you asked it.
    Air flow over wings causing "lift" is not what causes a plane to gain altitude.

    Saying a plane goes "straight up
    ballistic" doesn't mean you are saying the plane is going straight up, nor does it denote what "ballistic" is.
    You may be saying the plane is going really fast in level flight, or that you actually mean it is going straight up.

    I have a suspicion you are playing with words.
    Last edited by N/A; 09-28-2019 at 10:01 PM.
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  5. #85
    Senior Member Viking350's Avatar

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    Quote Originally Posted by alismith View Post
    Thrust from the engines. It's doing the same thing a rocket ship does after liftoff. If the upward thrust is greater than the downward pull of gravity, it will rise.
    Exactly, that thrust is against the air. Now back to our initial question, if the jet engines are exerting thrust pushing the airplane forward, why would the type of surface the wheels were on make a differences? The thrust pushing the plane forward is relative to the air, not the ground. Another way to think of it is what would happen if you put a jet powered drag racing car on a dynamometer? Since the tires don’t drive the car, it would sit there motionless and the dyno would register zero horsepower (assuming the straps were strong enough to hold it).

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    Team GunsNet Silver 12/2011 N/A's Avatar

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    Quote Originally Posted by Viking350 View Post
    Exactly, that thrust is against the air.
    That thrust is against the pull of gravity, not against air.

    ETA: If the thrust had to be against air, then no rocket engine would work in airless outerspace.
    Last edited by N/A; 09-29-2019 at 09:37 AM.
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  7. #87
    Team Guns Network Silver 04/2013 alismith's Avatar

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    Quote Originally Posted by Viking350 View Post
    Exactly, that thrust is against the air. Now back to our initial question, if the jet engines are exerting thrust pushing the airplane forward, why would the type of surface the wheels were on make a differences? The thrust pushing the plane forward is relative to the air, not the ground. Another way to think of it is what would happen if you put a jet powered drag racing car on a dynamometer? Since the tires don’t drive the car, it would sit there motionless and the dyno would register zero horsepower (assuming the straps were strong enough to hold it).
    Not quite. The thrust is pushing against gravity. As long as the thrust is 180 degrees to that of gravity, the wings do nothing except stabilize the craft as it rises in a direction away from the full of gravity. Only when the plane turns away from that 180 degrees do the wings start providing lift (as long as it's in the atmosphere) and keeps the craft flying.

    On a rocket, or missile, the fins (not quite wings as they don't provide an airfoil) do nothing more than stabilize the rocket while the thrust pushes it in whatever direction it's headed. When a rocket's, or missile's, thrust stops, it begins to fall. If a missile is aimed at a far distant target, it has to be launched to a high enough altitude so it can coast to its target when it runs out of thrust.

    All thrust does is push the plane. The wings, with their airfoil design, allow it to fly.

    Think of a glider. No engine. The thrust of the other aircraft pulls it to an altitude where the glider can catch enough thermals to allow it to fly. As long as it has thermals, it can maintain enough altitude stay aloft. The thermals act as upward thrust for the glider and the wings allow it to fly...
    "Valar morghulis; valar dohaeris."

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    Making good people helpless won't make bad people harmless.

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  8. #88
    Administrator Krupski's Avatar

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    Quote Originally Posted by Viking350 View Post
    Exactly, that thrust is against the air.

    Thrust generated by a reaction motor (jet, rocket, balloon, etc...) does not thrust against the air.

    Thrust is generated by throwing mass in one direction (the mass being jet or rocket exhaust, or plain air in the case of the balloon).

    Throwing mass in one direction generates an equal and opposite reaction - the thing throwing the mass moves in the opposite direction. This is thrust.

    If air is in the way, part of the energy goes into pushing the air out of the way and the thrust is actually reduced.

    Don't believe me... look it up. Or look up "is a rocket more efficient on the ground or in space".
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    Administrator Krupski's Avatar

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    Quote Originally Posted by alismith View Post
    On a rocket, or missile, the fins (not quite wings as they don't provide an airfoil) do nothing more than stabilize the rocket while the thrust pushes it in whatever direction it's headed.

    Some rockets may have small fins to provide some stability as the vehicle moves through certain flight regimes (transsonic speed, for example) but the balance and stability of the rocket is accomplished by gyros, sensing vehicle attitudes, and moving the rocket engines in a direction to compensate. The engines are mounted on gimbals which allow electric or hydraulic actuators to point the thrust vector in whatever direction is necessary to keep the rocket balanced.
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    Senior Member JTHunter's Avatar

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    Quote Originally Posted by N/A View Post
    So, if the wheels and treadmill are irrelevant, why did you say it takes so much more energy and distance to get up to speed?¿?
    Because it is all about the speed of the AIR above and below the wing. The motion of the wheels and treadmill are irrelevant to whether or not a plane will fly. It is ALL about "air speed" and the wing. That's why the cockpit crew read the "air speed" rather than "MPH".
    Have you ever heard the phrase "angle of attack"? That is the angle of "climb" (as opposed to level flight) of a plane and the lower speed of the air over the wings. Too steep an angle and all lift disappears and the plane stalls. This was of greater concern when planes were propeller driven and, while fighter jets don't have to worry about this as much because of their greater "thrust to weight" ratio, a jet airliner has a much lower ratio and can stall much more easily.
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    Administrator Krupski's Avatar

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    Quote Originally Posted by JTHunter View Post

    Have you ever heard the phrase "angle of attack"? That is the angle of "climb" (as opposed to level flight) of a plane and the lower speed of the air over the wings. Too steep an angle and all lift disappears and the plane stalls. This was of greater concern when planes were propeller driven and, while fighter jets don't have to worry about this as much because of their greater "thrust to weight" ratio, a jet airliner has a much lower ratio and can stall much more easily.
    Actually, any wing can stall. Lift requires smooth laminar flow over both of it's surfaces. At too high of an angle of attack, the flow over the top of the wing breaks free of the surface and begins to swirl (i.e. the flow becomes turbulent). Lift ceases and the airplane drops. Even a military jet with a high power to weight ratio will still stall above a certain angle of attack. The jet may be able to "brute force" itself from falling, but that's not flying.... it's falling - with style!
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    Administrator Krupski's Avatar

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    Quote Originally Posted by N/A View Post
    That thrust is against the pull of gravity, not against air.

    ETA: If the thrust had to be against air, then no rocket engine would work in airless outerspace.

    Correct. In fact, at sea level the air is "in the way" of the exhaust flow and it DECREASES the thrust.
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    Senior Member JTHunter's Avatar

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    "Falling with style". I like that !
    The whole point is that, if air isn't flowing around the wing, no airplane can fly. It doesn't matter what the wheels or a giant treadmill are doing. One caveat to that - if the treadmill is being used to move the plane forward at the same time as the engines are revved up, the take-off will happen AND in a much shorter distance as the forward momentum of the plane will reach that critical threshold faster than normal. That is why carrier planes use catapults to get planes off their short decks faster.
    “I have little patience with people who take the Bill of Rights for granted. The Bill of Rights, contained in the first ten amendments to the Constitution, is every American’s guarantee of freedom.” - - President Harry S. Truman, “Years of Trial and Hope”

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    Administrator Krupski's Avatar

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    Quote Originally Posted by JTHunter View Post
    "Falling with style". I like that !
    The whole point is that, if air isn't flowing around the wing, no airplane can fly. It doesn't matter what the wheels or a giant treadmill are doing. One caveat to that - if the treadmill is being used to move the plane forward at the same time as the engines are revved up, the take-off will happen AND in a much shorter distance as the forward momentum of the plane will reach that critical threshold faster than normal. That is why carrier planes use catapults to get planes off their short decks faster.
    Well..... a catapult does not pull the airplane by the wheels (the way a "treadmill" would.) A treadmill on an aircraft carrier would just spin the landing gear wheels. The catapult is attached to the front of the airplane's structure and it pulls the airplane down the "runway", assisting the plane's engines in getting up to flying speed quickly. A "treadmill" would not help at all.
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    Team GunsNet Silver 12/2011 N/A's Avatar

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    Here is an interesting thought for you to explain to them, Krupski, and I'm not trying for a "gotcha" moment.

    The plane is sitting on the treadmill, and the treadmill is already running in the direction the plane is going to take off. Explain to them what the wheels are doing from the time it is stationary, begins it's take off run gains speed and takes off.

    Lets us put the conveyor belt moving at 150 mph and the plane's lift off speed as 250 mph.
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  16. #96
    Senior Member JTHunter's Avatar

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    N/A - again, it is about airspeed, not what the tires are doing. In the scenario you have, the tires would actually be rotating in reverse, IF the plane was being held in position while the treadmill was running. Upon release, the plane would start moving forward until it was moving at 150. But, as I stated earlier, the planes "critical speed" that you have set at 250 mph would be largely accomplished as the plane is moving forward at 150. The engines would only have to add 100 mph to reach that speed. The PROBLEM is that, when the plane reaches 250 and starts to lift off, if the engines are revved up much higher at that point, the planes airspeed will drop within a few seconds and the plane will come down again, possibly uncomfortably hard.
    That is why carrier jets rev their engines to full right before the catapult slings them off the deck. Without the power of the jet keeping their forward momentum going and increasing, they would nose-dive into the water.
    Last edited by JTHunter; 10-05-2019 at 09:03 PM.
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    Team GunsNet Silver 12/2011 N/A's Avatar

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    In this case, I am talking specfically about the wheels and what they alone are doing. I'm not asking if they help the plane achieve lift off, or prevent it from having lift off.
    I'm saying to focus solely on the wheels and what they do.

    Try and keep up.
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

  18. #98
    Senior Member JTHunter's Avatar

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    If the plane is held immobile, the tires are rolling in reverse. There will not be any air flowing around the wing so no flying.
    “I have little patience with people who take the Bill of Rights for granted. The Bill of Rights, contained in the first ten amendments to the Constitution, is every American’s guarantee of freedom.” - - President Harry S. Truman, “Years of Trial and Hope”

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    Team GunsNet Silver 12/2011 N/A's Avatar

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    Right, the wheels are turning in reverse, as if the plane is going backward. As the treadmill is moving at 150mph, what do the wheels do as the plane makes it's run down the treadmill to lift off speed?
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

  20. #100
    Administrator Krupski's Avatar

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    Quote Originally Posted by N/A View Post
    Here is an interesting thought for you to explain to them, Krupski, and I'm not trying for a "gotcha" moment.

    The plane is sitting on the treadmill, and the treadmill is already running in the direction the plane is going to take off. Explain to them what the wheels are doing from the time it is stationary, begins it's take off run gains speed and takes off.

    Lets us put the conveyor belt moving at 150 mph and the plane's lift off speed as 250 mph.
    The wheels will initially spin backwards. When the airplane reaches a "ground speed" of 150 mph, the wheel rotation will be zero. As the airplane lifts off at 250 mph, the wheels will be rotating forward at the rate they would be if the plane were on solid ground and moving forward at 100 mph.

    Right?
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