Can It Take Off??

Can It Take Off??
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Can It Take Off?? - 12/2/2005 4:26:05 AM

bentwings

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From: St.Paul, MN, USA
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Here is one to use up band width. The diesel truck guys made 302 posts in 5 days. only 2 personal flames recorded

can the experts beat this???

Let's have at it. Can the "wing guys" beat the "wheel guys"

*** Brain Teaser ***

Imagine an airplane is on the beginning of a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Can the plane take off?

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bentwings

Post #: 1

RE: Can It Take Off?? - 12/2/2005 5:40:23 AM

BMatthews

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Yes, The props cut away at the air or the jets still throw out thrust to the rear and the airplane goes foward just like normal. All that will happen is that the wheels will turn twice as fast as they would on a stationary runway thanks to the belt.

The logic is that the airplane, unlike a car or truck, does not rely on the wheels for propulsion so it'll still take off just fine.... as long as the wheel bearings don't overheat and seize from the extra RPM's....

Do you have a link to the other thread?

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Proudly wasting balsa since 1965.

Free Flighters go that extra mile........

(in reply to bentwings)

Post #: 2

RE: Can It Take Off?? - 12/2/2005 5:45:25 AM

3dbob37n

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From: Franklin,, NC, USA
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Boy, Bent Wings, you are trying to keep me up all night thinking this over.

If the model cannot accelerate because the wheels are basically just spinning in one place, because the conveyor matches the wheel rotation, the aircraft will not begin its takeoff roll and will simply be batting the air.
Let's see, where can I get a big conveyor belt?
Yeeeegads, where did you get that one?

3dbob

(in reply to bentwings)

Post #: 3

RE: Can It Take Off?? - 12/2/2005 11:56:10 AM

da Rock

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From: western, NC, USA
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3dbob,
BMatthews solution isn't really hard to see if you think about a couple of things. Our models fly straight up right. That'd be on thrust alone right. After all, the wing would be lifting horizontally and nothing in the a/c is designed to lift "forward" (which would be "up" in this orientation). And our models fly downwind with no problem. And they do it with the wheels up when they have retracts. And models accelerate in dead air, wheels up or down.

quote:

If the model cannot accelerate because the wheels are basically just spinning in one place,

Hey, the model doesn't accelerate because of the wheels. And no matter what the problem states about the conveyor belt's speed matching the wheels' rotation, that won't matter to the a/c or it's prop one bit. That a/c will move forward on it's thrust and bring the wheels along for the ride.

< Message edited by darock -- 12/2/2005 12:00:51 PM >

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Post #: 4

RE: Can It Take Off?? - 12/2/2005 12:00:25 PM

da Rock

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From: western, NC, USA
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And BTW, the conveyor belt actually won't get up to very much speed. Think about this little hidden deal. If the conveyor belt is going to match the FORWARD speed of the wheels, then the wheels actually can't be turning at all right?

quote:

The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

So the a/c is taking off toward the "right". The wheels will rotate which way? Clockwise right. That means the belt has to go to the "right" since the wheels, where they contact the belt, are going "left". So the belt goes right the same speed the wheels are moving to the right. right? right!

(in reply to da Rock)

Post #: 5

RE: Can It Take Off?? - 12/2/2005 12:43:36 PM

starwoes

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From: Maple Heights, OH, USA
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hmmmm interesting. what if the aircraft in question has pontoons and is on a fast flowing river that is flowing opposite the heading of the aircraft. speed of the river matches and balances the forward motion of the craft.

BTW, in your question, i think the aircraft will fly....because they don't need wheels to fly...right?....just less friction with the surface.

< Message edited by starwoes -- 12/2/2005 12:48:01 PM >

(in reply to bentwings)

Post #: 6

RE: Can It Take Off?? - 12/2/2005 1:27:07 PM

MajorTomski

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From: Oklahoma City, OK, USA
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Good grief! this thing hit on ezone last week and went over 300 posts in two days.

See here

http://www.rcgroups.com/forums/showthread.php?t=446465

First there is a phrasing problem in the question:

quote:

The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Can the plane take off?

Go down to post #8 of the above thread and you can read the original statement.

To some people the term moving in the opposite direction of rotation means the belt will move forward in the same direction as the airplane, because the wheels rotation is opposite to this direction. The problem is the question was poorly quoted from the original site, the intent of the question is to simply have the airplane remain stationary to the rest of the world while the belt moves under it. under that condition, the airplane cannot fly because it cannot accelerat the wings to generate lift. It will sit there rolling up to full throttle.

Now then there are the arguments of bearings holding up, limited thrust, limited belt speed, lots of folks read too much into the mind game. It won't fly.

< Message edited by MajorTomski -- 12/2/2005 1:28:54 PM >

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Post #: 7

RE: Can It Take Off?? - 12/2/2005 1:37:24 PM

juanes1969

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Ýou are right Major!! If the plane is kept stationary because of the movement of the belt, it would be just the same as if we kept the plane on brakes in the runway with the engine running at full throttle. No speed on the wing equals no lift. The engine alone cannot take the plane of the runway. Right?

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RE: Can It Take Off?? - 12/2/2005 1:41:24 PM

dick Hanson

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Maybe your plane won't take off - all of mine will- easily

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RE: Can It Take Off?? - 12/2/2005 1:44:31 PM

HighPlains

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Second cut:

It would take off slower, as some energy is being stored in the wheels as rotational energy. But the airplane still has to accelerate down the conveyor or else the speed of the tires will not increase. If it doesn't get off soon enough, the tire/wheels will explode.

< Message edited by HighPlains -- 12/2/2005 3:17:55 PM >

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RE: Can It Take Off?? - 12/2/2005 2:11:50 PM

britbrat

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Airborn with no sweat (except cooked tires).

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RE: Can It Take Off?? - 12/2/2005 2:27:02 PM

DLSmith2

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I think you might be able to visualize the problem better if you think of a full scale plane like a Cessna 152. If the 152 begins flight at about 60kts airspeed it doesn't matter what rate the tires are turning, other than like BMatthews said, the overheated bearing problem, or surface friction. You can lock the wheels of the Cessna, point the nose into a 60 kt wind, pull back on the yoke and the plane will lift off, because the airspeed over the wings will provide the lift, and the wheels aren't turning at all.

The question is misleading, because it implies that the speed of the wheels, or ground speed, determines an aircraft's ability to take off, instead of the airspeed.

If you take off from a grass runway that hasn't been mowed in a while, the friction of the long grass can increase the take off distance by 10%. This is because the grass prevents the plane from reaching the airspeed it needs to lift off, until the plane has gone a little farther. Wheel friction on the conveyor belt may increase the length of ground roll necessary to get 60kts of wind going over the wing, but that doesn't matter because it's a conveyor belt, right?

Interesting question, huh?

Blue skies,

DL

This is a job for the MYTHBUSTERS!!!

(in reply to juanes1969)

Post #: 12

RE: Can It Take Off?? - 12/2/2005 2:44:56 PM

danny03

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The aircraft will fly since its forward motion is produced by a prop, Fan, or turbine and not it's wheels. If we were talking about a car or truck then the vehicle will remain in the same spot.

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RE: Can It Take Off?? - 12/2/2005 4:34:05 PM

Liberator

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Yes its all about air moving over the flight surfaces, not relational ground speed.

How about this.

Does a fly in a flying airplane add weight if the fly is flying inside the plane?

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RE: Can It Take Off?? - 12/2/2005 4:56:38 PM

3dbob37n

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I think the comparison about a seaplane trying to take off in a river going in the opposite direction is a good one. It can't take off because the current is going the opposite way to the airplane. With no forward motion, no lift is generated.
Dick, you might have a problem too. I don't think my Yak 54 would take off because the tailwheel would keep it from obtaining enough angle of attack. I can hand launch, but not from a standstill on the ground. It has to bounce at least a little during the roll in order to get off.
Don't forget the question is described as "just as fast as the wheels turn, the conveyor always matches the wheel speed in the opposite direction." So the conveyor speeds up or slowd down.
Now I realize in reality, with enough power, the model would simply yank itself into the air but that is not what the question tries to acknowledge. The question assumes the model is just an ordinary every day type model and not super powered.

3dbob

(in reply to Liberator)

Post #: 15

RE: Can It Take Off?? - 12/2/2005 5:02:37 PM

iron eagel