will it take off?
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MikeBurr
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Well, lets see.
A plane is flying just above a truck going down a highway at the same speed as the plane - will the plane fall from the sky? - relative to each other, there is no motion. Other than wind, you would be able to walk across the top of the truck and enter the plane in the same way you could if it was sitting still at an airport.
But if you were to stand at the back of the truck and jump up, you would have a brief moment to find out that both were moving away from you at a very great speed.
We must always be sure not to confuse our point of view with the real world...
A plane is flying just above a truck going down a highway at the same speed as the plane - will the plane fall from the sky? - relative to each other, there is no motion. Other than wind, you would be able to walk across the top of the truck and enter the plane in the same way you could if it was sitting still at an airport.
But if you were to stand at the back of the truck and jump up, you would have a brief moment to find out that both were moving away from you at a very great speed.
We must always be sure not to confuse our point of view with the real world...
If I understand what is being said, it's like a person running on a treadmill. Can you win the Boston Marathon running on a treadmill. You never leave the room the treadmill is in. The plane will not take off. There will be no air flow over the wings. That's what makes airplanes fly. Bernoulli's Therorem. The air must travel farther over the top of the wing causing it to speed up and the pressure drop. The wing is sucked up. (Take a 8.5" X 11" sheet of paper, hold it right under your mouth and blow across the top to see this in action.) If you really are interested in learning more about flight, read the book "Stick and Rudder"An Explanation of the Art of Flying by Wolfgang Langewiesche. Of course if you don't enjoy physics, you won't enjoy the book.
755inNY
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Iowachild said:
It is not like a person running on a treadmill because the plane's forward motion is not accomplished by a rotational force of the wheels against the surface of the movable runway. If it were a car on a movable road then it would be like a person running on a treadmill. But then it would not be the movable road matching the speed of the car but rather the rotational speed of the wheels. The only time the movable road and car would be at the same speed would be when the speed was zero.
Jeff
BillyP
Veteran Member
rback33 said:OK, now what is your explanation for this? I mean, we are defying SOOOO many physical possibilities already, what makes it IMPOSSIBLE for a prop plane of any imaginary composition to do this? Now, don't get me wrong, I don't know if there is or isn't. My degree is in biology. I just love science a whole so this discussion is fascinating to me.
rback33, I don't have a degree in anything. All I can do is close my eyes an imagine and it just don't happen
hutch4472
Silver Member
I dont know why but it's baffleing to me that people think the plane would fly. The plane isnt moving. It is using all of its applied power, to overcome the conveyour's movement, to stay in one place. It NEEDS air flow over the wings in an amount that no prop nor jet can provide alone. The engines just provide forward movement to move air over the wings and control surfaces via airspeed.
MossRoad
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When I worked at the airport in Niles, MI, there was an old dude there that had a Cub with a STOL kit. He came out on a very windy day and said, "Watch this!". He taxied out to the start of the runway, ran up his engine, rolled about 50 feet forward and it popped up into the air. He went up about a hundred feet, drifted backwards about a hundred feet and slowly brought it forward and down exactly at the start of the runway. He flew backwards. In relation to the ground, he went forward 50 feet, backwards about a hundred feet, and then forward about 50 feet again. His airspeed said he was going 40 miles an hour, but he went nowhere.
Now, had this been a calm day, he would have had to move forward up to 40 MPH in relation to the ground, before he would have been moving through the air at 40MPH, the magic number he needed for lift. He has to overcome the rolling friction with the ground first, then gain the airspeed. If he isn't going anywhere in relation to the ground first, he can't go anywhere in relation to a point in the calm air, either.
Here's another example from that same airport...
A guy came out with his weiner dog. The weiner dog was named Snoopy and was wearing a leather pilots helmet like a WWI ace. They hopped into his airplane and tried to taxi out of the flight line. He had forgotten to untie his tail from the steel cable in the grass. He gave it lots of power. He pulled about a hundred feet of cable behind him, ripping out anchor after anchor. You would think that with a cable anchored to the ground a hundred feet behind him and his engine generating max thrust that he could just pull back on the stick and pop into the air. Well, he couldn't because he had zero airspeed. The same thing would happen with an airplane on a treadmill. He has to get up some ground speed in relation to a fixed point before he can get up some airspeed. I threw in the weiner dog part because he was cute. He was disappointed that they couldn't go for a ride that day.
Now, had this been a calm day, he would have had to move forward up to 40 MPH in relation to the ground, before he would have been moving through the air at 40MPH, the magic number he needed for lift. He has to overcome the rolling friction with the ground first, then gain the airspeed. If he isn't going anywhere in relation to the ground first, he can't go anywhere in relation to a point in the calm air, either.
Here's another example from that same airport...
A guy came out with his weiner dog. The weiner dog was named Snoopy and was wearing a leather pilots helmet like a WWI ace. They hopped into his airplane and tried to taxi out of the flight line. He had forgotten to untie his tail from the steel cable in the grass. He gave it lots of power. He pulled about a hundred feet of cable behind him, ripping out anchor after anchor. You would think that with a cable anchored to the ground a hundred feet behind him and his engine generating max thrust that he could just pull back on the stick and pop into the air. Well, he couldn't because he had zero airspeed. The same thing would happen with an airplane on a treadmill. He has to get up some ground speed in relation to a fixed point before he can get up some airspeed. I threw in the weiner dog part because he was cute. He was disappointed that they couldn't go for a ride that day.
755inNY
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hutch4472 said:
Boy, I'm getting deeper into this than I thought I would. Those who feel the plane would not be moving are still thinking in terms of the wheels driving the plane forward. This is not what happens.
Let's use the example of the treadmill from Iowachild.
You are standing on one end of a long treadmill. You are holding on a cable coming from a winch at the far end of the treadmill (let's assume the cable has no weight so we don't have to worry about sag and stuff). For now, the treadmill is stationary but the cable is pulling at 3 mph. If you don't want friction burns from being dragged on the stationary belt, you will be walking at 3 mph. The cable keeps pulling you until you get to the other end of the treadmill.
OK, reset back to the other end of the treadmill. I flip the lever coupling the motor that drives the winch to also drive the treadmill. Gearing is such that the treadmill runs at exactly the same linear speed as the winch but in the opposite direction. Again, your goal is to not be dragged so you must start walking but this time to keep up with the 3 mph pull of the cable your legs must run at a 6 mph pace to keep perfect balance. You will get to the end of the treadmill in the same time as the previous run but a little more winded.
Now substitute the movable runway for the treadmill, the plane for your body, the propeller for the cable and the wheels for your legs. Why won't the plane move?
The propeller does not care what is happening between the wheels and the runway. It is pulling against the air (assuming a tractor configuration). Finally, I got tractor into the discussion!!!!
Jeff
MossRoad
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One other story....
You try to stand behind an airplane with it's brakes locked directly behind the propeller or jet exhaust at full throttle and see if you can stand up... Nope, you get knocked on your keester.
How come you can stand by the length of the entire wing and not feel any breeze on that very same plane?
The plane can't go anywhere because the brakes on the wheels are locked. If the pilot releases the brakes, the plane starts moving forward. However, if the ground started moving backwards at the exact same time(like the treadmill scenario) the plane could not move forward in relation to the ground or the air. It would not fly.
You try to stand behind an airplane with it's brakes locked directly behind the propeller or jet exhaust at full throttle and see if you can stand up... Nope, you get knocked on your keester.
How come you can stand by the length of the entire wing and not feel any breeze on that very same plane?
The plane can't go anywhere because the brakes on the wheels are locked. If the pilot releases the brakes, the plane starts moving forward. However, if the ground started moving backwards at the exact same time(like the treadmill scenario) the plane could not move forward in relation to the ground or the air. It would not fly.