Results 101 to 110 of 154
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November 10th, 2006 12:44 PM #101
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November 10th, 2006 12:49 PM #102
Contrary to what you assume, if the wheel moves, the plane DOES NOT HAVE TO MOVE! You can try that with your car, jack up a non-driven wheel, let go of the brakes and spin it with your hands. Does the car move?
What frictionless property?! You can go do the matchbox-on-paper experiment to demonstrate that your assumption is completely wrong.
The wheels are attached to the plane. Yes. If the wheelbearings got stuck, all force exerted by the runway on the tires would be transferred to the plane, keeping it from moving - IF AND ONLY IF!. However, the wheelbearings serve to minimize friction EFFECTIVELY ISOLATING ANY FORCE EXERTED BY THE RUNWAY ON THE PLANE (and vice versa). VIRTUALLY NONE OF THE ENERGY exerted by the runway goes to the plane. Almost all of the energy exerted BOTH BY THE RUNWAY ON THE TIRES and THE PLANE ON THE WHEELBEARINGS go to MAKING THE WHEEL SPIN. Thus, the wheels spin faster, but the rest of the plane gets to do whatever it wants.
I'm not saying that your FBD is wrong. It's a perfectly fine representation on what's going on with the wheel. I'm saying that your ANALYSIS of the FBD is wrong. You have not demostrated any relationship between the forces acting on the wheel and any force acting on the plane, you just concluded that since the runway exerts force on the wheel it MUST exert the same force on the plane, which is completely wrong - virtually nothing happens to the plane, except the wheels spin really fast. Two linear forces act on the wheel, the engine thrust and the runway's friction on it. However, whatever torque they create causes angular velocity in the SAME DIRECTION! Meaning all the runway is doing is spin the wheel faster!
In fact, I believe your FBD is a representation of the WHEEL and the forces acting on it, which makes it irrelevant to the question.
I can't create an FBD that models runway speed = plane speed, kasi hindi naman force ang pinag-uusapan eh!!! Mahirap ba intindihin yun (apparently oo)? SPEED IS NOT FORCE, FOR THE NTH BLOODY TIME! The runway and the plane speed are NOT a function of the forces the two bodies are acting on each other! Your FBD is a red herring. So is the runway and the wheels, all of these serve as the trick to the question. The wheelbearings make whatever force the runway exerts on the plane negligible. Almost all of the energy exerted by the friction between the runway and the tires go to spinning the tires, almost NONE go to push the plane backwards.
Last edited by Alpha_One; November 10th, 2006 at 01:13 PM.
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November 10th, 2006 01:17 PM #103
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November 10th, 2006 01:26 PM #105
IMO, (di naman ako pilot at zero bokya ako sa physics) the airplane will fly kahit na moving in opposite direction yung runway. by the sheer power of the airplane's engines, the engines will cut/bite into the air and the plane will fly.
yung mga VTOL (vertical take-off and landing) airplanes...di nila kailangan ang runway. pwede silang mag hover a few feet above the ground and then take-off. so immaterial kung me ground contact yung wheels nila o wala, dahil so powerful yung engines nila, magkakaroon ng lift yung wings nila kaya lilipad din sila.
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November 10th, 2006 01:45 PM #106then again sir, i think you missed the point that much of the thrust generated by the jet engine is directed against the wind (medium) to propel it forward and not so much on the tarmac.
would you agree that a hydroplane resting on water..water being so slippery offering not much resistance and acting much like a "conveyor belt" will be able to take off? if your answer is yes, then i guess the confusion is pretty much resolved.
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November 10th, 2006 01:47 PM #107
Pare, that was the premise. If the original premise was wrong to start with, then my answer is right. Why? Because I am basing it on the premise, while yours is wrong, because you said imposible yon. While it may be true na imposible yon, that was the original premise, and that's what we should follow in order to answer the question properly.
Like I replied on one of the pages, "read the original question" and let's get back on topic. The premise is that the plane should lift off the ground to be considered flying, correct?
From there I will leave it up to you guys who have more patience than me, because frankly, I think that this question is like the chicken and egg thing. Either way has a good point but both have an error.
1. The error in my arguement is that it does not take into account that the plane's engine pushes against the air. There is another idea beside this, that the air that goes across the wings should not come from the engine, but rather from the environment. The reason I did not include this is because there was no mention of it. I am focusing on the lift, not on the forward movement, because the question is if the plane will fly or not, and the key point for the plane to fly is the Bernoulli principle, which should generate lift when the plane moves forward. But it remains stationary.
2. On the other hand, the error in your arguement is you are negating flight. You are focusing on the forward movement, not on the lift. You cannot just forget that the plane has to fly, because that is the question. If you are basing it on forward movement, then you are not answering the question.
However, the original premise still remains, that whatever speed the plane acquires forward, the conveyor belt matches it so that it runs at an equal but opposite direction.
*Lolo pepe, the VTOL is different. The wings are now located at the large rotors, which move because they have axial rotation. The plane, on the other hand, has to move forward, which is the basic arguement of this thread. Because once it moves forward, it will generate lift if the speed is sufficient.
*Niky regarding table cloth pulling: did you mean that the plate will not move, and hence, since the plane rests on the plate, therefore the plane will NOT move?
The reason we're all having this arguement is because we're talking of two different points of views! One point of view is focused on the lift, while the other is whether or not the plane will move forward.
1. If I focus on the lift, I will not consider the engine thrust because the premise of the original question is that the conveyor belt will match the speed in the opposite direction. This means, whatever speed the plane acquires, the conveyor belt matches it, be it impossible or not. Therefore this keep the plane STATIONARY.
2. If I focus on the forward movement of the plane, the engine thrust has to be taken into account and this will provide the external force for the plane to move forward, and therefore, FLY.
End of discussion!Last edited by mbeige; November 10th, 2006 at 01:57 PM.
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November 10th, 2006 01:47 PM #108hehehe! pasakitan ng ulo dito ah! buti yun saranggola lumilipad kahit di ka tumakbo ng mabilis basta may hangin lang which i think can be dealth with propeller or jet engines... support lang talaga ang purpose ng gulong....
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November 10th, 2006 02:10 PM #110mbeige, you made some good arguments i must agree...hey no problem sir..this is just an exchange of opinions among guys i must pressume not involved in the aeronautics industry...its all good.
i think i already expressed enough of my opnions regarding this topic..sige kayo naman..i rest my case...cool lang kayo peeps.
planning to keep it for 15yrs just done 10,000 km already replaced the transfer case fluid w/...
Suzuki JIMNY [merged threads]