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Posted on 12/6/07 at 4:53 pm to TSmith
In this conveyor belt scenario, the only thing the plane needs to overcome is the friction produced in the wheel bearings of the landing gear. An airplane should be able to do this with no problem, and take off. Thoughts?
Posted on 12/6/07 at 4:56 pm to TSmith
I don't know. Ever been skating and try to skate forward yet you move nowhere, you just sit there and run and run and run and never move?
Or is that just me.
Or is that just me.
This post was edited on 12/6/07 at 5:00 pm
Posted on 12/6/07 at 4:57 pm to TSmith
quote:
In this conveyor belt scenario, the only thing the plane needs to overcome is the friction produced in the wheel bearings of the landing gear. An airplane should be able to do this with no problem, and take off. Thoughts?
exactly.
Posted on 12/6/07 at 4:59 pm to Dale Murphy
The only danger I could see would be the tires exceeding their intended speed rating. Plane overcomes whatever wheel bearing friction that may exist from the belt (say moving 100mph), begins moving forward, achieves a takeoff speed of say 150mph... meaning that the wheels of the landing gear are spinning at what would be 250mph without the belt. Tires explode.
Posted on 12/6/07 at 5:02 pm to Dale Murphy
for one, I think that the wheels of the airplane have more friction that being given credit for, which is why I said that the way the experiment is performed is going to make a huge difference. if they plot out the speed of the plane on a normal runway on average, and then program the conveyer to counteract that I think the plane will not have enough runway to take off. if they go by what the plane is currently moving instead of plotting out a regular takeoff, the plane is going to have enough time to takeoff, albeit on a slightly longer runway.
Posted on 12/6/07 at 5:41 pm to Dale Murphy
quote:
I don't know. Ever been skating and try to skate forward yet you move nowhere, you just sit there and run and run and run and never move?
Unless you were skating with 2 or 3 jet engines attached to you, your example is irrelevant.
Posted on 12/6/07 at 5:47 pm to TSmith
quote:
The only danger I could see would be the tires exceeding their intended speed rating.
Agreed, but the tires and assemblies are over-designed for safe landing speeds, not take-off. I would imagine the stresses are a lot greater when they hit the runway coming in for a landing than when they take off? So... hopefully they would still hold up at twice their normal speed...
Posted on 12/6/07 at 5:53 pm to MikeBRLA
I think I do understand what you guys are saying. You're saying that the plane will move forward on the conveyer belt? I think my whole point, is that the test is set up for the belt to prevent the plane from moving forward relative to its surroundings? Do you guys understand my view? I know for a fact, that if this test works out like they are intending and the plane does not move in relation to the air around it, it will not take off? Will you agree, you do know that the plane moving forward is the only thing that can supply enough air moving over the wings to cause lift? I will agree how you guys think the airplane will move forward because its pushing the air, once it overtakes the friction of the belt. I think my whole issue, was it seemed like most on here assumed the engines provide the lift in some way, I've studied aerodynamics and flight most of my life, just as a hobby, and this is not how flight works. I apologize for calling anyone stupid, I still don't think it will work how they intend it to work, but if how you guys say it will work happens, the plane starts to move forward, of course it will take off. But I honestly don't see the point of that test. What are they testing for, to see if the thrust can overtake the speed of a treadmill. I don't get that angle on the issue.
Posted on 12/6/07 at 5:59 pm to VanRIch
quote:
I think I do understand what you guys are saying. You're saying that the plane will move forward on the conveyer belt? I think my whole point, is that the test is set up for the belt to prevent the plane from moving forward relative to its surroundings? Do you guys understand my view? I know for a fact, that if this test works out like they are intending and the plane does not move in relation to the air around it, it will not take off? Will you agree, you do know that the plane moving forward is the only thing that can supply enough air moving over the wings to cause lift? I will agree how you guys think the airplane will move forward because its pushing the air, once it overtakes the friction of the belt. I think my whole issue, was it seemed like most on here assumed the engines provide the lift in some way, I've studied aerodynamics and flight most of my life, just as a hobby, and this is not how flight works. I apologize for calling anyone stupid, I still don't think it will work how they intend it to work, but if how you guys say it will work happens, the plane starts to move forward, of course it will take off. But I honestly don't see the point of that test. What are they testing for, to see if the thrust can overtake the speed of a treadmill. I don't get that angle on the issue.
Ok... Van you are are making the same assumption that I made at first... that the plane is stationary on the conveyor belt. It is not. The conveyor belt is JUST A DIVERSION. Eliminate it from your mind.
The only thing the plane needs to overcome is the drag placed on the plane by the landing gear wheel bearings. That drag is not much.
So therefore, while the wheels of the landing gear will be moving at a rate faster than normal (whatever speed the conveyor belt is moving added to the required takeoff speed for the aircraft), it will still take off.
Only land vehicles REQUIRE interaction with the surface to move forward. An airplane does not. It creates thrust by sucking air into the jet engine, introducing fuel burn causing the air to expand rapidly and expell from the rear nozel of the engine at a rate much faster than the front fans on the jet engine introduce air to the burn chamber.
So, while the wheels will be spinning faster, the plane will take off. The only danger here is the tires exceeding their speed rating and possibly rupturing or exploding.
__________________
Posted on 12/6/07 at 5:59 pm to MikeBRLA
Ok...
First question: How many people are still below the "Karma Line"?
:lol:
Have been enjoying the thread from work all day
(But I can't post from work) 
So, place me high above the Karma Line, in the it will fly supporters. This is a long running debate with many a seasoned aviator on the wrong side of the issue.
Originally, the question was posed with a long runway moving in the opposite direction and the speed of the runway movement matched the airspeed of the aircraft. As time went by, the moving runway began being described as a conveyor, which brought the mental image of a shorter surface for the aircraft to move over.
Then there is also the natural tendency to think of the aircraft wheel as we think of an automobile's wheel. So, combining those two errant assumptions, many people immediately say it can't fly.
Several people have discussed the "treadmill and roller skates" example and that is the best analogy to help describe that the aircraft can move based on a source of propulsion independent of the moving conveyor.
Thanks again for all the laughs....
First question: How many people are still below the "Karma Line"?
:lol: Have been enjoying the thread from work all day
(But I can't post from work) So, place me high above the Karma Line, in the it will fly supporters. This is a long running debate with many a seasoned aviator on the wrong side of the issue.
Originally, the question was posed with a long runway moving in the opposite direction and the speed of the runway movement matched the airspeed of the aircraft. As time went by, the moving runway began being described as a conveyor, which brought the mental image of a shorter surface for the aircraft to move over.
Then there is also the natural tendency to think of the aircraft wheel as we think of an automobile's wheel. So, combining those two errant assumptions, many people immediately say it can't fly.
Several people have discussed the "treadmill and roller skates" example and that is the best analogy to help describe that the aircraft can move based on a source of propulsion independent of the moving conveyor.
Thanks again for all the laughs....
Posted on 12/6/07 at 6:04 pm to VanRIch
OK, say there is a conveyor belt from LA to NYC. The belt is moving 10 miles per hour in one direction and you are on a CAR on that belt with its WHEELS going 20 miles per hour. So your ACTUALLY speed is 10 miles per hour right? Eventually you will get from LA to NYC.
The difference is that in this example of the plane the wheel speed really is pretty much irrelevant b/c wheel speed has nothing to do with if a plane takes off and flies. Yes there will be more friction on the wheels bearings, but I don't think that little amount of friction will even be noticeable since the plane is being propelled by rather powerful engines.
Do you realize that it is an FAA REQUIREMENT that any commercial passenger plane be able to TAKE OFF (not just fly, but take off) with one of its engines turned off? That just tells you how much extra power they have.
Last time I checked, when a plane is in flight, its wheels are stopped so that right there tells you wheel speed, and thus the conveyor belt, are irrelevant.
The difference is that in this example of the plane the wheel speed really is pretty much irrelevant b/c wheel speed has nothing to do with if a plane takes off and flies. Yes there will be more friction on the wheels bearings, but I don't think that little amount of friction will even be noticeable since the plane is being propelled by rather powerful engines.
Do you realize that it is an FAA REQUIREMENT that any commercial passenger plane be able to TAKE OFF (not just fly, but take off) with one of its engines turned off? That just tells you how much extra power they have.
Last time I checked, when a plane is in flight, its wheels are stopped so that right there tells you wheel speed, and thus the conveyor belt, are irrelevant.
Posted on 12/6/07 at 6:05 pm to TSmith
I agree with you and I understand what everyone is saying. My initial point is that I think the test is designed that the plane is static. When they do the test, it's possible that the plane will move forward. And then it will create lift. Through all my arguments I've said that it has to move forward, and no one agreed with me. If the plane does not move relative to the air it won't lift, simple aerodynamics. But I do kinda understand how you guys say it will lift, but whats the point of that?
SO, does everyone at least agree, that the plane has to move forward in relation to the air around it, and achieve lift speed before it takes off? I think our conflicting theories were not really on the same page. This whole time I'm assuming the conveyer belt is meant to keep the plane stationary, which I still think is what they think will happen and what the test is designed for. Now my point becomes, if at any point the plane starts to move forward on the conveyer belt, the test is moot.
SO, does everyone at least agree, that the plane has to move forward in relation to the air around it, and achieve lift speed before it takes off? I think our conflicting theories were not really on the same page. This whole time I'm assuming the conveyer belt is meant to keep the plane stationary, which I still think is what they think will happen and what the test is designed for. Now my point becomes, if at any point the plane starts to move forward on the conveyer belt, the test is moot.
Posted on 12/6/07 at 6:06 pm to LSUBoo
quote:
I tried a few days ago... didn't have that episode listed yet... need to check again this evening
It's there now. Just checked and set my DVR...I just scrolled to Wednesday and hit record. So this is your reminder to do so.
Posted on 12/6/07 at 6:15 pm to CocomoLSU
quote:
It's there now. Just checked and set my DVR...I just scrolled to Wednesday and hit record. So this is your reminder to do so.
So it's being aired this coming Wednesday, 12/12/08?
Posted on 12/6/07 at 6:23 pm to VanRIch
quote:yes.
SO, does everyone at least agree, that the plane has to move forward in relation to the air around it, and achieve lift speed before it takes off?
quote:The test is to see IF IT WILL keep it stationary.
This whole time I'm assuming the conveyer belt is meant to keep the plane stationary, which I still think is what they think will happen and what the test is designed for.
Those of us who think the plane will fly are saying that the conveyor belt WILL NOT keep it stationary. No matter how hard they try, no matter how fast the conveyor belt moves, the wheels of the plane will match that speed AND EXCEED IT because of the stronger force being exerted by the engines on the air. The plane will move forward relative the object it is pushing against - the air. It will be slowed relatively little by the backwards movement of the conveyor belt because the wheels of the plane are intended to provide as little friction as possible. The plane will move forward until it is fast enough for the wings to achieve lift and it will fly.
I just don't think I can break it down any more than that. If you still can't get it, yOu'll have to watch the show. I'm certain it will fly.
Posted on 12/6/07 at 6:31 pm to VanRIch
quote:
This whole time I'm assuming the conveyer belt is meant to keep the plane stationary, which I still think is what they think will happen and what the test is designed for.
The conveyor is a trick to make people think the plane will remain stationary... and they're testing it because even knowing the facts some people still refuse to think the plane will take off.
Posted on 12/6/07 at 6:34 pm to LSUBoo
quote:
The conveyor is a trick to make people think the plane will remain stationary... and they're testing it because even knowing the facts some people still refuse to think the plane will take off.
Well said.
Just to add...
Yes, the plane MUST achieve takeoff speed relative to the ground. Absolutely. The conveyor belt's effect on achieving takeoff speed will be negligible. Sure the wheels will be spinning their arse off... but the plane will still take off.
A car needs torque to get moving... a force against an immovable, or nearly immovable surface. A plane needs thrust. A plane doesn't rely on interaction with land to achieve speed... it relies on the physics of air interaction and manipulation, etc... That's the difference that some people in this thread are getting confused with.
It is definitely a good mind-twister.
This post was edited on 12/6/07 at 6:35 pm
Posted on 12/6/07 at 6:43 pm to Colonel Hapablap
quote:
I'm starting to get nervous about flying. I think that the only pilot who understands this so far is Az,
Roger that!
quote:
and he's too old to drive, much less fly.
Damn Colonel, that was cold....
Posted on 12/6/07 at 6:49 pm to CocomoLSU
quote:
So this is your reminder to do so.
gracias!
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