Alright then...where in the riddle does it say the plane is moving forward. It just says the plane is moving at the same speed as the treadmill...therefore creating ZERO movement other than the free spinning wheels!!!
Alright then...where in the riddle does it say the plane is moving forward. It just says the plane is moving at the same speed as the treadmill...therefore creating ZERO movement other than the free spinning wheels!!!
The riddle:
An airplane is sitting on an enormous treadmill. As the plane starts its engines, the treadmill runs in the opposite direction at the same speed the plane is moving. Can the plane take off?
If you really want to parse the riddle, cannot make assumptions. Stick with the facts!
It doesn't say that the treadmill matches speed as the plane increases speed. It says "As the plane starts its engines, the treadmill runs in the opposite direction at the same speed the plane is moving."
When the plane starts it's engines, it is not moving; therefore the treadmill is not moving. The riddle does not say that the treadmill speeds up in relation to the plane. The treadmill is not moving, so the plane takes off normally on the stationary treadmill.
yeah... wrote:
Alright then...where in the riddle does it say the plane is moving forward. It just says the plane is moving at the same speed as the treadmill...therefore creating ZERO movement other than the free spinning wheels!!!
That is not what it says. It say that the TREADMILL is moving at the same speed as the plane WHEN THE PLANE STARTS ITS ENGINES. That speed is 0.
You are correct that the plane will take-off, but your reasoning as to why it will take of is inncorrect.
The riddle:
"An airplane is sitting on an enormous treadmill. As the plane starts its engines, the treadmill runs in the opposite direction at the same speed the plane is moving. Can the plane take off?"
The riddle does not state, implicitly or explicitly that the plane is moving. It says that the treadmill runs in the opposite direction at THE SAME SPEED the plane is moving. Both the plane and the treadmill could be motionless and the conditions of the riddle would still be satisfied.
The riddle essentually boils down to a question of whether or not the treadmill acts as an opposing force to the thrust of the engines (a restorative force). If it did, the plane would not move relative to the air and would not take-off. But, since the treadmill does not act as an opposing force (due to the free spinning wheels) the plane does move relative to the air and it does infact take off.
The plane will take-off, but for the reasons stated by IT WILL FLY, Easy 10, and myself (plus some others), not because of the semantics of the riddle.
huge gigantic big guy tall wrote:
Once the engines are started they generate thrust. How can they not? Even a feathered prop will generate a small bit of thrust.
I guess I meant enough thrust to move the airplane...and thanks for the Vr V1 correction...my bad.
cgaites wrote:
This problem has nothing at all to do with the relative motion of the plane to the ground or air.
no airspeed, no lift, no fly.
PDX Track wrote:
no airspeed, no lift, no fly.
no woman, no cry
Please let this thread die. The answer has been described countless times, but no one is even going back to read those responses any more, just posting the same questions and arguments.
Yes, it flies.
I think I've figured it out wrote:
Please let this thread die. The answer has been described countless times, but no one is even going back to read those responses any more, just posting the same questions and arguments.
Yes, it flies.
I agree.
The level of stupidity shown by some in this thread is highly disturbing. I don't think the thread will ever die- unless Wejo locks it. Which isn't going to happen.
it can fly
it can't fly
it can fly
it can't fly
it can fly
it can't fly
it can fly
it can't fly
it can fly
it can't fly
it can fly
it can't fly
it can fly
it can't fly
it can fly
it can't fly
it can fly
it can't fly
it can fly
it can't fly
PDX Track wrote:
cgaites wrote:This problem has nothing at all to do with the relative motion of the plane to the ground or air.
no airspeed, no lift, no fly.
The riddle has nothing to do with the relative motion of the plane to the air (airspeed) in that the relative motion of the plane to the air (airspeed) is not effected by the treadmill. What you said is true, but despite the treadmill, yes airspeed, yes lift, yes fly. See my previous answers, and the answers of several others for an explanation as to why.
A quick google search turned up the following link (from an aviation website) with the answer explained:
http://www.avweb.com/news/columns/191034-1.html
In summary:
The plane does fly.
The explanation in its entirety:
What I learned from Old Hack was that an updated version of a question aimed at confusing folks over relative measurements of airplane motion and the medium in which it operates had shown up on the Internet, and it was causing the fracas in the Lounge.
The question that has been going around is not particularly artfully worded, and I think that has caused some of the disagreements, but I'll repeat it as it is shown: "On a day with absolutely calm wind, a plane is standing on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. The conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the airplane ever take off?"
My comment: Notice that the question does not state that the conveyor's movement keeps the airplane over the starting position relative to the ground, just that it moves in the direction opposite to any movement of the airplane.
Initially, about a third of the folks here said that the airplane could not ever takeoff, because the conveyor would overcome the speed of the airplane and it could never get any airspeed. The rest said the airplane would fly.
The "It won't fly, Rocky" group said that the conveyor would hold back the airplane. They asked us to imagine a person running on a treadmill. As he or she sped up, the treadmill would be programmed to speed up, just as the conveyor in the problem, and the person would remain over the same locus on the earth, while running as fast as possible.
The argument was that if the airplane started to move forward, the conveyor program was set up to move the conveyor at exactly that speed, in the opposite direction, thus, the airplane would never move relative to the ground, and, because the air was calm, it could never get any wind over its wings. One of the analogies presented was the person rowing at three mph upstream in a river on a calm day. However, the current was flowing downstream at three mph, so the resultant speed with reference to the stream bank and air was zero, and thus there was no wind on the rowboat.
I watched and listened to the disagreement for a while and was fascinated to see that the argument seemed to split between those who had some engineering or math background, all of whom said the airplane would takeoff and fly without any problem; and those with some other background, who visualized the airplane as having to push against the conveyor in order to gain speed. Because the conveyor equaled the airplane's push against the conveyor, the airplane stayed in one place over the ground and in the calm air could not get any airspeed and fly.
It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards.
I have posted this harmless little riddle on a UK forum.
Lets see if Great Britain is better at solving this riddle than America.
"Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards."
The last part of the above is the key. The treadmill DOES NOT MOVE THE AIRPLANE AT ALL, IT ONLY SPINS THE WHEELS.
What if it's a Harrier Jump jet with vertical take off and landing capabilities?
guesser wrote:
Easy 10 wrote:All of you are wrong. The plane does not move forward by powering its wheels. It moves forward by using its ingines to pull it through the air (which is basically stationary). The wheels are free spinning and exert a negligible amount of friction on the plane itself.
So, although the wheels will be turning twice as fast, the plane will still move normally. Which of course means it will be able to take off.
Wrong. It must move relative to the air. It is not doing this in the scenario you presented.
WRONG! If the air is stationary and the plane is moving through the air, it is moving relative to the air.
"An airplane is sitting on an enormous treadmill. As the plane starts its engines, the treadmill runs in the opposite direction at the same speed the plane is moving. Can the plane take off?"
Yes it can - if there is a 400mph hurricane blowing front-on to the plane. The treadmill will probably take off also.
cgaites wrote:
A quick google search turned up the following link (from an aviation website) with the answer explained:
http://www.avweb.com/news/columns/191034-1.htmlIn summary:
The plane does fly.
I read the article at avweb.... It ruined the riddle for me... As it proved that the treadmill does not stop the plane's movement forward... The wheels do not transfer any force from the treadmill to the plane and vice versa... The wheels just reduce the friction between the plane and the ground (treadmill). They just rotate in the reverse direction of the plane movement... Therefore the treadmill has almost no effect on the taking off of the plane.
From another board:
"Does everyone get the feeling that the person that created this riddle knew that the ambiguity of the speed part and the inability to duplicate a perfect control system would create endless discussions like this?
Evil, evil, evil bastard!"
Good synopsis!
Yes, the speed is left ambiguous. The plane only takes off because it is NOT standing in one spot, it is moving along the belt at TWICE the speed of the belt and therefore through the air at the SAME speed as the belt.
If it was moving along the belt and at the same speed as the belt and therefore not moving through the air, it would not be moving horzontally through an air mass and therefore would generate no lift.
It's obvious that most of the highly educate young men who are so sure of their simple version of the 'it will fly' answer never got a pilots license.
"No airspeed, no fly" was dead right. Groundspeed means nothing, when you're talking about lift. And it makes no difference whatsoever if the plane generates its on-ground airspeed by putting drive onto the wheels, or via the prop. All that matters is whether it is moving ALONG the belt and therefore THROUGH the air. If its sitting in one spot, it's got no lift, even if the wheels are spinning a gazillion miles an hour.
Having both flown and crashed planes, I say this with some experience. Our educational system is on the *&^%% ropes.