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Started By
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re: Myth Busters/Can a plane take off on a conveyor belt
Posted on 12/6/07 at 7:13 am to LSUBoo
Posted on 12/6/07 at 7:13 am to LSUBoo
quote:
Okay, so... what propels the jet forward during takeoff, the wheels, or the jet engines?
It's always the engines that propel an aircraft forward. But it's the wings that get the lift from the wind.
This post was edited on 12/6/07 at 7:14 am
Posted on 12/6/07 at 7:31 am to LSUBoo
what you are failing to understand is that the backwards movement of the tread mill is going to impose a tailwind which will counteract the lift. I think if you had a infinite runway that the plane would take off, but not on a normal sized runway.
a jet may be able to, only because there is no way a treadmill could move fast enough to counteract the thrust of the engine. I dont believe that will be the case with a cesna or ultralight.
a jet may be able to, only because there is no way a treadmill could move fast enough to counteract the thrust of the engine. I dont believe that will be the case with a cesna or ultralight.
This post was edited on 12/6/07 at 7:34 am
Posted on 12/6/07 at 7:44 am to just me
I dont see where the problem says the plane is moving forward RELATIVE TO THE GROUND. I assumed, yes I know that is a bad word, that the plane is moving forward relative to the conveyor. Therefore the plane would not fly unless there is a helluva head wind. This answer to this question hinges on to what reference point are you measuring the SPEED of the airplane. NOTE: I said speed not velocity.
I cant believe this thread has 12 pages!
I cant believe this thread has 12 pages!
Posted on 12/6/07 at 8:41 am to MulesAFpilot
quote:Why? How does that work?
It's always the engines that propel an aircraft forward.
Where does the engine's thrust go? What does it push against?
Where does the engine's thrust go when the aircraft is on a treadmill. (The aircraft is not in a vacuum. It's just on a treadmill.)
So unless the air behind the engines disappears when it is on a treadmill, the aircraft will move forward. The wheels will just turn faster.
Posted on 12/6/07 at 8:59 am to just me
what do you think the tailwind will do to the thrust of the engines?
Posted on 12/6/07 at 9:00 am to diat150
quote:
tailwind
can a plane take of on an escalator ... that is the real question
This post was edited on 12/6/07 at 9:05 am
Posted on 12/6/07 at 9:04 am to diat150
quote:First off, what tailwind?
what do you think the tailwind will do to the thrust of the engines?
But assuming for the sake of argument that there is a tailwind, the tailwind will make the thrust even more powerful. Not only is the thrust pushing against something (air), that something is also pushing against the thrust.
Posted on 12/6/07 at 9:04 am to diat150
quote:
what you are failing to understand is that the backwards movement of the tread mill is going to impose a tailwind which will counteract the lift
I've always had a problem with the wording of the situation. Because if the treadmill always moves the EXACT opposite of however fast the wheels are spinning (yes, I understand the wheels aren't motorized), then the plane will never move.
Posted on 12/6/07 at 9:09 am to just me
quote:
First off, what tailwind?
But assuming for the sake of argument that there is a tailwind, the tailwind will make the thrust even more powerful. Not only is the thrust pushing against something (air), that something is also pushing against the thrust.
this shows you dont know what you are talking about. the tailwind moving the plane backwards will create a tailwind. as the plane attempts to gain speed so will the speed of the escalator which will add even more tailwind. even a small tailwing causes a significant increase in runway length needed to takeoff. If you had a infinite amount of runway space I think it may eventually take off, but IRL, the plane will run out of runway space behind it because it wont be able to counteract the tailwind fast enough.
Posted on 12/6/07 at 9:11 am to diat150
quote:
the tailwind moving the plane backwards will create a tailwind
this is dumb on so many levels
in fact ...
this posts dumbness creates its dumbness
This post was edited on 12/6/07 at 9:12 am
Posted on 12/6/07 at 9:12 am to CocomoLSU
quote:You are absolutely correct. Excellent point. But that is just a phraseology mistake; sometimes the question is misworded. And it doesn't really work in the real world if the aircraft's engines are providing the thrust.
I've always had a problem with the wording of the situation. Because if the treadmill always moves the EXACT opposite of however fast the wheels are spinning (yes, I understand the wheels aren't motorized), then the plane will never move.
Posted on 12/6/07 at 9:18 am to CocomoLSU
quote:
I've always had a problem with the wording of the situation. Because if the treadmill always moves the EXACT opposite of however fast the wheels are spinning (yes, I understand the wheels aren't motorized), then the plane will never move.
You're essentially correct, but the problem is that you've described a physically impossible situation. The thrust of the jets will move the plane regardless of whether the plane is resting on wheels on a conveyor belt, skids on an ice pond, pontoons on a lake, or whatever. As soon as that happens, the rotational velocity of the wheels and the rotational velocity of the conveyor are different. End of story. The conveyor can't cancel the wheels.
Posted on 12/6/07 at 9:19 am to diat150
quote:I can't argue with that. God can't argue with that. But I have a feeling He would be as confused as me.
the tailwind moving the plane backwards will create a tailwind
quote:Where did the escalator come from? Is it causing that damn tailwind . . . or is the tailwind causing the tailwind?
as the plane attempts to gain speed so will the speed of the escalator which will add even more tailwind.
quote:What would a small Darkwing do?
even a small tailwing causes a significant increase in runway length needed to takeoff.
Posted on 12/6/07 at 9:25 am to diat150
Conveyor belts =/= fans.
Conveyor belts don't make any wind any higher than an inch or so off the surface.
Conveyor belts don't make any wind any higher than an inch or so off the surface.
Posted on 12/6/07 at 9:26 am to just me
Seriously, anyone who thinks the plane will take off is a complete idiot. The engines provide thrust to push the airplane on a horizontal plane, they don't pull air over the wings, if this were true, then the wing span would just end at the engine and not extend far beyond them. When the airplane is pushed through the air, this air provides the lift for the plane. I can promise you it will not fly. Planes do not use the engine to push it up, they use them to pull through the air to create the lift and to pull the plane forward.
Posted on 12/6/07 at 9:31 am to VanRIch
As of page 14:
Colonel Hapablap
just me
Powerman
LSUBoo
aggie dude who started the thread
Putty
---karma line---
VanRich
Coco
diat150
MulesAFPilot (he gets extra points since he's a pilot)
SCTiger
SG_Geaux
Dale Murphy
faxis
Who else? We intend to make fun of you when the plane takes off...
Colonel Hapablap
just me
Powerman
LSUBoo
aggie dude who started the thread
Putty
---karma line---
VanRich
Coco
diat150
MulesAFPilot (he gets extra points since he's a pilot)
SCTiger
SG_Geaux
Dale Murphy
faxis
Who else? We intend to make fun of you when the plane takes off...
This post was edited on 12/6/07 at 10:51 am
Posted on 12/6/07 at 9:35 am to CocomoLSU
quote:
Because if the treadmill always moves the EXACT opposite of however fast the wheels are spinning (yes, I understand the wheels aren't motorized), then the plane will never move.
Very true... but the problem states that the treadmill is moving in the opposite direction matching the takeoff speed of the plane... making the speed the wheels are turning irrelevant.
If the wheels bearings were a frictionless system (impossible, I know) then the takeoff distance wouldn't even change from it being a concrete runway. As it is, the frictional forces are mostly negligible anyway when compared to the forces of the jet engines, so the takeoff distance would barely be changed at all with the plane being on a treadmill.
Posted on 12/6/07 at 9:43 am to Colonel Hapablap
quote:Cocomo has a definitional excuse. He's exempt.
Can we get a tally of all the people who don't think it'll fly? On page 12:
VanRich
Coco
diat150
MulesAFPilot (he gets extra points since he's a pilot)
SCTiger
Who else? We intend to make fun of you when the plane takes off...
Make fun of MulesAFPilot at your own risk, and don't even think about questioning his statements.
You should just thank him for providing you the blanket of freedom that allows you to be an arse on this website and assume that an aviator knows more about flying a plane than you.
Posted on 12/6/07 at 9:47 am to Colonel Hapablap
quote:
Who else? We intend to make fun of you when the plane takes off...
ETA: was boxcarbarney ever convinced? He seemed pretty adamant at one point.
SG_Geaux
Dale Murphy
FlyinTiger (more bonus points maybe?)
I think we convinved boxcarbarney that it would take off.
This post was edited on 12/6/07 at 9:49 am
Posted on 12/6/07 at 9:48 am to CocomoLSU
quote:
I've always had a problem with the wording of the situation. Because if the treadmill always moves the EXACT opposite of however fast the wheels are spinning (yes, I understand the wheels aren't motorized), then the plane will never move.
agreed. that's always the point of contention. Supposedly in the way i've seen this hypothetical, the treadmill matches the speed of the plane, no matter how great.
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