Yes there will be lift. The propellor will pull the airframe forward, the conveyor will spin the wheels in the opposite direction faster. The wheels are freewheeling on the axles of the aircrafts landing gear. Since they "free wheel" the only force the apply against the airframe is drag through the wheel bearing. Since this drag is minute (sp) the aircrafts engine can overcome the friction. and move forward. When the airframe moves forward through the air so do the wings . When the wings move through the air they create lift. When the wings create enough lift the airframe will lift into the air and the wheels will no longer be in contact with the conveyor . Since the conveyor now has no effect on the wheels the propellor will continue to move the airframe through the air and the wings will continue to generate lift. WHEEEEEW .
------------------ HARDCORE SBC CRONIE AND PROUD OF IT ! GOT TQ ?
Specifics are irrelivant. I just had a Huge debate with members of Electrocalgary over this.
Here's the basics.
But the treadmill has nothing to do with the thrust of the airplane because the wheels aren't anchored to any point. So, if the engines were providing enough thrust to push the plane forward at 100mph, and the treadmill countered by going 100mph in the opposite direction, the plane would still move forward at 100mph. The only thing the treadmill will do is cause the wheels to spin at 200mph.
If you were standing on a skateboard that was on a treadmill and the treadmill started spinning, your wheels would turn, but you would essentially stay in the same place. Now, in that position, push off a wall - even if the treadmill speeds up to compensate, it won't matter. The amount of force you put on the wall will dictate how far you move, any it will be the same whether the treadmill is there or you're on flat ground. Now, apply this to the airplane and think of the engines sucking and pushing air as the wall.
You think that maybe after 10 pages of this stuff that 99.99% of us don't already know that?
For those of you who still believe that this plane will not fly (despite all the valid info posted to the contrary), the Flat Earth Society is having their annual general meeting next month...
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04:54 PM
GoldFiero86SE Member
Posts: 224 From: Calgary,Alberta, Canada Registered: Mar 2006
Ha!! Here is the answer!! The plane will fly in theory, in this analogy!!!! Put the plane on the conveyor belt.Put a winch on the plane, and attach the winch cable to a mounting that is fixed to the ground, in front of the conveyor belt.Start the winch, which will roll in the cable.That will pull the plane forward. The conveyor will start to move backwards at the same speed as the winch pulls the plane forward.But, because the cable will not stretch, the winch will continue to pull the plane forward, in relation to the fixed ground all around. Why? Because the motive force is applied between the static mounting, and the winch mounted on the plane, not the conveyor belt.Now, transfer this analogy this way. The winch on the plane is the jet engine/ propeller, and the cable is the air.Which is static., as is the cable, as it is rolled in by the winch..the cable doesn't move. The winch rolls it onto the windlass, thereby pulling the plane forward, irrespective of the speed of the conveyor belt. Of course, in reality, the winch would eventually roll all the cable onto its windlass, and that would stop the plane moving forward. However, the static air is unlimited, so the plane would be pulled forward faster and faster, as the throttle was opened up.And it would reach takeoff speed, and fly.
In reality, the winch is the motive power that would power the plane ( jet or prop), and the cable and its mounting point is the static air all around the plane, against which the motive power (jet or prop) exerts its force. QED!!! Nick
------------------ fierofetish.PFF'S self-confessed Snowbird!! Responsibility: the solution for our World's Dilemmas.. Yahoo messenger:nickcannspain MSN Messenger-nicholascann@hotmail.com
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05:11 PM
Formula88 Member
Posts: 53788 From: Raleigh NC Registered: Jan 2001
You're assuming the plane won't move forward. That is wrong. As the plane accelerates forward, the conveyor accelerates backwards. Fine. But that won't slow the plane down. All it will do is cause the wheels to spin faster.
The only way the conveyor can have any affect on the plane's speed is if the brakes are locked.
This has been explained every which way from Sunday. This is probably one of the better explanations. Read it. Read it again, then ask a physics professor to explain it to you. http://www.straightdope.com/columns/060203.html
[This message has been edited by Formula88 (edited 04-06-2006).]
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06:18 PM
PFF
System Bot
Patrick Member
Posts: 37857 From: Vancouver, British Columbia, Canada Registered: Apr 99
Well, I had just come back from fighting in electrocalgary, being called about 330983903 different names, before proving that I was right and that the people calling me names were in fact, the ones who were wrong. :P
My bad, I also missed that other post
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06:41 PM
Firefighter Member
Posts: 1407 From: Southold, New York, USA Registered: Nov 2004
Ha!! Here is the answer!! The plane will fly in theory, in this analogy!!!! Put the plane on the conveyor belt.Put a winch on the plane, and attach the winch cable to a mounting that is fixed to the ground, in front of the conveyor belt.Start the winch, which will roll in the cable.That will pull the plane forward. The conveyor will start to move backwards at the same speed as the winch pulls the plane forward.But, because the cable will not stretch, the winch will continue to pull the plane forward, in relation to the fixed ground all around. Why? Because the motive force is applied between the static mounting, and the winch mounted on the plane, not the conveyor belt.Now, transfer this analogy this way. The winch on the plane is the jet engine/ propeller, and the cable is the air.Which is static., as is the cable, as it is rolled in by the winch..the cable doesn't move. The winch rolls it onto the windlass, thereby pulling the plane forward, irrespective of the speed of the conveyor belt. Of course, in reality, the winch would eventually roll all the cable onto its windlass, and that would stop the plane moving forward. However, the static air is unlimited, so the plane would be pulled forward faster and faster, as the throttle was opened up.And it would reach takeoff speed, and fly.
In reality, the winch is the motive power that would power the plane ( jet or prop), and the cable and its mounting point is the static air all around the plane, against which the motive power (jet or prop) exerts its force. QED!!! Nick
You have the colors reversed. The plane should be blue-------------------------------------------------------------------------------------------------and the conveyor should be "herring red".
Some people just can't get that conveyor out of their minds, and in fact it's effects, and even it's existance is all but irrelevant.
If any of the naysayers would actually go stand in front of a selfpowered treadmill and place any wheeled vehicle on it, they will instantly feel verrry foolish.
[This message has been edited by maryjane (edited 04-06-2006).]
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07:24 PM
Patrick Member
Posts: 37857 From: Vancouver, British Columbia, Canada Registered: Apr 99
If any of the naysayers would actually go stand in front of a selfpowered treadmill and place any wheeled vehicle on it, they will instantly feel verrry foolish.
Or failing that, have them just read the original scenario again without any preconceived notions...
Good gawd, how many times does it need to be explained to some people!
it will fly... the wheels have nothing to do with the thrust. you people comparing it to a car on a dyno, think about that for a bit... completely different.
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09:32 PM
blayde8 Member
Posts: 262 From: Golden Valley, MN Registered: Jun 2000
the only thing with that video is that there is air getting to the wings. So there will be lift. The only reason the planes prop goes faster so it will match the take off speed.
Doesn’t a plane need air to make lift?
If so the plane is not moving. The belt and the wheels might be going 100MPH but the plane is not moving.
Yes, if you were standing by a conveyor belt and the reason the skateboard will move back, is because of FRICTION!
If friction wasn't an issue, it would stay put.
Why don't you kneel down, and put your hand on the skateboard, would you get tossed forward?
No, the board will stay. If you were to pull the skateboard towards you, would you get it to move forward towards you? Yes it will. So what happens? The wheels are just spinning twice the speed.
So once again, threadmill in front of you, you kneeling next to it on the floor, skateboard on threadmill belt, you just hold the top of it, and start the belt. Are you going to get tossed across the room? Think before you answer. Your hand are the jet's propeller.
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01:55 AM
Patrick Member
Posts: 37857 From: Vancouver, British Columbia, Canada Registered: Apr 99
The belt and the wheels might be going 100MPH but the plane is not moving.
If "the plane is not moving", why then would the belt and wheels "be going 100MPH"?
Read the following line from the original scenario:
quote
Originally posted by naskie18:
This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction).
See that part about the "plane speed"? Note it doesn't say anything about tracking the "wheel" speed.
If “the plane is not moving”, then neither would the belt (and therefore the wheels) be moving. So how can it even be suggested that "the belt and the wheels might be going 100MPH" if "the plane is not moving". That logic does not fit the scenario.
The plane’s speed is relative to the ground (and/or to the air), NOT to the conveyor belt. For the conveyor belt to go 1 MPH backwards, the plane must be moving 1 MPH forward, relative to the ground and/or air. The wheels would then turn at a speed of 2 MPH to compensate as the plane continues to creep forward at 1 MPH.
An increase in thrust would result in an increase in the plane's forward speed, followed by an immediate increase in the speed of the conveyor belt going backwards. The wheels would continue to spin at twice the forward (or backward) speed until liftoff, at which time they'd stop spinning altogether.
"The belt and the wheels might be going 100MPH but the plane is not moving."
Yes, it is moving--relative to the air above, beside, and below the wings, and that is all that matters. The conveyor is a non-issue--thrown in to confuse people.
You even can spin the conveyor's belt many times faster than the plane's speed, and it will still move right on down the runway to take off. Think Think Think
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03:36 AM
Cheever3000 Member
Posts: 12400 From: The Man from Tallahassee Registered: Aug 2001
If so the plane is not moving. The belt and the wheels might be going 100MPH but the plane is not moving.
This is where your error is. You're assuming the plane won't move. The plane WILL move. The belt cannot slow the plane down unless you put the brakes on.
The plane moves forward. There is air flow. There is lift. The plane will fly.
You are correct that if the plane doesn't move through the air it won't take off. Now, explain why you think the plane won't move? How does the conveyor keep the plane from moving if the wheels are free to rotate?
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09:35 AM
Cheever3000 Member
Posts: 12400 From: The Man from Tallahassee Registered: Aug 2001
All wheels are for is to reduce friction on takeoff and landing, thats it.
The wheels spin free.
The people who think the plane will not fly, do not realize the WHEELS SPIN INDEPENDANT OF THE SPEED OF THE ENGINES. Think of spinners, the speed spinners on a car spin is not relative to the speed the vehicle is going. If the vehicle stops, then the spinners still spin, why? Because they spin free. Just like the wheels on the airplane.
This allows the plane to move forward at 100km/h, and the treadmill in response to move backward at 100km/h. But the wheels spin freely, and are being acted upon by TWO DIFFERENT AND INDEPENDANT FORCES. Therefor, 2x100km/h = wheels spinning at 200km/h and the plane moving ahead 100km/h. Allowing for friction, and the plane would be still moving ahead at a minimum of 90km/h. All the treadmill does is spin the wheels really fast, IT DOES NOT AFFECT THE AMOUNT OF ROOM STILL NEEDED FOR THE PLANE TO ATTAIN LIFT. It also DOES NOT PREVENT THE PLANE FROM MOVING FORWARD.
Cheever3000: The wheels on the plane are completely unpowered. They have no motor hooked up to them. Like putting a car in neutral. The wheels just spin on their bearings, the planes Engines power the plane and allow it to move.
[This message has been edited by GoldFiero86SE (edited 04-07-2006).]
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10:24 AM
AntiKev Member
Posts: 2333 From: Windsor, Ontario, Canada Registered: May 2004
Originally posted by Cheever3000: So why does a plane even NEED wheels? Just run the prop up fast enough to lift off the ground, right?
Yep...pretty much. Explain how floatplanes and skiplanes work. It's all about relative airflow. I've seen an extreme short field takeoff in a Piper Super Cub where the pilot rotated the tail off the ground before he was moving...he was off the ground in ~10 feet. Granted the wind was very strong, but the important thing is relative airflow. An airplane will lift off with the propeller stopped if the relative airflow is above the stall speed. End of story.
Glider winches use this concept. Connect a 5000 foot cable to a reel (with a big torquey engine) and a glider. Spin up the engine and pull the cable in, the glider acts like a kite and moves up in a parabolic arc, the pilot releases at the apex of the arc and is now flying.
So why does a plane even NEED wheels? Just run the prop up fast enough to lift off the ground, right?
Actually, that is sort of correct. Depends how big the prop is and where it (they) are located. During design testing, with a V-22 Osprey sitting on scale pads, like the mobile scales the troopers use to see if a 18 wheeler is overweight, it was found that the Osprey did in fact 'lighten up", when those huge props were turned up, and the brakes locked. Or wait for a bit of wind, and yep, it will begin to try to lift.
But, You're missing the point he's making Chuck. The plane is NOT sitting still in relation to the air around the wing, or in relation to anything else. There is NOTHING to prevent it from moving right on down the conveyor belt runway.
1. Go buy one of those rubber band powered toy airplanes with the wheels. 2. Find a powered treadmill. 3. Before setting the plane on the running treadmill, experiment to find out how few turns of the rubberband engine it takes to make the plane move at it's slowest speed. Just enough to make it move along the floor. 4. Now, set the treadmill on it's maximum speed. 5. Now, with the rubberband wound the minimum amt, and the treadmil just whizzing along at it's max fpm, set the toy plane on the running treadmill, (Facing opposite the treadmill's direction of travel) and you will see the plane just move on down the "runway", even tho the treadmill conveyor has not only matched the plane's speed, it has exceeded it, and it is still unable to prevent the plane from moving fwd relative to the surrounding world. The surrounding world is anything and everything outside the conveyor--including the air.
I've done this at work several times, on one of our powered conveyor systems, much to the amazement of some very intelligent people who also claimed the plane would not fly. A $4 investment and a trip to a physical fitness place or your workout room will clear all of this up, but I'm betting none of you doubters will attempt it.
[This message has been edited by maryjane (edited 04-07-2006).]
As I think I wrote somewhere earlier in this thread, it really depends how nitpicky and anal you want to get. If you want to get real anal, the wheels will always have some sort of friction, especially due to the weight of the aircraft sitting on top of them. If this conveyer can spin up to infinite, which I assume it can, then it will always be moving slightly faster than the drag of the wheels allow it to (of course the conveyer will always be accelerating). I assume it would keep accelerating rapidly 'up to infinite'.
I really don't know how to phrase that. It makes sense in my head before it was translated to words though. If someone can word that better, feel free.. Of course if it's not some magical infinite speed conveyer, than sure it'll take off. But as long as the conveyer has the ability to keep accelerating, and there is friction and weight, then it won't.. Anyone see where I'm going with this?
Yes, I see where you are going with it Johnny, but if you are going to place those magical attributes toward the conveyor, you also have to place them on the plane. The friction in the bearings of the conveyor will suffer not just equal to that of the plane's landing gear, but more so on the conveyor's rollers, because the conveyor supports not only it's own weight, but the weight of the plane as well--all of which means nothing, because the plane will be airborne within seconds-regardless of how fast the conveyor is spinning. Try my little excersize and you will see. I tell people to set the plane's power to minimum and the conveyor travel in fpm to maximum to prove no matter how fast the conveyor moves, the plane will outrun the belt. The toy and the treadmill is a pretty close scale-weight wise, but if you want, add more weight to the plane. Remember, it doesn't have to take off from the conveyor to prove it will fly--just as long as it moves in the real world--ie--air passes above/below the wing. Do some trial runs beside the running treadmill first, to satisfy yourself that the belt is in fact moving much faster than the plane.
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01:37 PM
Patrick Member
Posts: 37857 From: Vancouver, British Columbia, Canada Registered: Apr 99
If this conveyer can spin up to infinite, which I assume it can...
Johnny, one more time, read the following:
quote
Originally posted by naskie18:
This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction).
See where it states "that tracks the plane speed and tunes the speed of the conveyer to be exactly the same"? That part is SO important.
Where are you getting this idea that the conveyor belt can or would spin up to an "infinite" speed? It's been set up to match the speed of the plane (NOT THE FRIGGEN WHEELS!!!!). That's clearly what the scenario states. You are making the same FALSE assumption that I did originally (which I realized and rectified about three pages ago).
Come on Johnny, you're representing Canada here. Smarten up!
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03:22 PM
GoldFiero86SE Member
Posts: 224 From: Calgary,Alberta, Canada Registered: Mar 2006
This is where those that think it will not fly are missing the boat, based on the original question.
This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction).
It does NOT say that the conveyor is moving fast enough to stop forward motion of the aircraft. It says that the conveyer is tuned to match the speed (of the belt) to the forward speed of the aircraft.
IOW, if you're flying a Cessna 172 that will lift off at 55 knots, you advance the throttle and the aircraft starts moving on the belt at 10 knots, the belt goes the other way at 10 knots but the aircraft is still moving at 10 knots, the wheels are just spinning at 20 knots. At 30 knots the aircraft is moving forward at 30 knots, the belt is moving backwards at 30 knots, and the wheels are spinning at 60 knots. At liftoff, the plane is moving forward at 55 knots, the belt is moving backwards at 55 knots, and the wheels are spinning at 110 knots.
This is only possible because of the precise conditions set forth in the original question. "tunes the speed of the conveyer to be exactly the same(but in the wrong direction)."
Now if the question had been written such that the statement read, instead, This conveyer has a control system that racks the forward motion of the plane and tuned the speed of the conveyer to hold the aircraft motionless then the aircraft would not take off. But that is not the original question. The belt will only move at a speed that exactly matches the speed of the aircraft, 55 knots forward speed, 55 knots belt speed. Period.
In fact, the way the question is written, it's impossible to interpret it any other way. If the belt moved fast enough that the aircraft did not move, then the belt speed would have to be "0", by definition, since the controls system "tracks the plane speed".
John Stricker
quote
Originally posted by Patrick:
See where it states "that tracks the plane speed and tunes the speed of the conveyer to be exactly the same"? That part is SO important.
Where are you getting this idea that the conveyor belt can or would spin up to an "infinite" speed? It's been set up to match the speed of the plane (NOT THE FRIGGEN WHEELS!!!!). That's clearly what the scenario states. You are making the same FALSE assumption that I did originally (which I realized and rectified about three pages ago).
Come on Johnny, you're representing Canada here. Smarten up!
