Plane on a conveyor belt
-
Dammit, this thread was put to bed... who woke it up?
Bassplayer, you are making the mistake that a plane and a car are propelled the same way. You are correct that a car will be stationary on a treadmill, because it is driven by it's wheels (which are tied to the treadmill). A airplane will not be stationary, because it's driven forward by a propellor or jet. It doesn't matter how fast you have the treadmill spinning under the airplane because the wheels on an airplane just free-wheel. The plane will start moving forward just like always (except the wheels will be turning like a mofo on the treadmill), gain airspeed, and take off.
Bassplayer;203005 wrote:
Wtf i never said anything about the wheels. Bernoulli's principle defines lift, and if there isn't low velocity below the wing creating high pressure than the plane won't rise.Ex if you're running on a tread mill is there wind going by you? NO there isn't.
Ex2 If you drive a car on a tread mill at 100mph and stick you're head out the window will you feel any thing? NO
Its not going to fly.
DaveH
'94 Supra- 7.77 @ 176mph -
Bassplayer;203005 wrote:
Wtf i never said anything about the wheels. Bernoulli's principle defines lift, and if there isn't low velocity below the wing creating high pressure than the plane won't rise.Ex if you're running on a tread mill is there wind going by you? NO there isn't.
Ex2 If you drive a car on a tread mill at 100mph and stick you're head out the window will you feel any thing? NO
Its not going to fly.
Now, what is going to make the car go 100mph?
Put it in neutral and the wheels spin at 100mph cause thats how fast the treadmill is going?If you set a hotwheels on a treadmill and turn it off, what happens? It will just fly of the end. If you would strap it down, it would stay still and not move.
This is talking about having the treadmill speed match the speed that the aircraft is moving(doesn't matter what kind). If the aircraft is going 1mph forwad the treadmill would be going 1mph in the oposite direction........... same thing goes for 100mph, and even 1000mph.
-
-
Bassplayer;203005 wrote:
Wtf i never said anything about the wheels. Bernoulli's principle defines lift, and if there isn't low velocity below the wing creating high pressure than the plane won't rise.Ex if you're running on a tread mill is there wind going by you? NO there isn't.
Ex2 If you drive a car on a tread mill at 100mph and stick you're head out the window will you feel any thing? NO
Its not going to fly.
That was exactly my thinking when this thread first started. Unfortunately, you're forgetting that the wheels don't make the plane go forward, the jets or propellers do, and they're not connected to the wheels in any way.
-
Bassplayer;203005 wrote:
Wtf i never said anything about the wheels. Bernoulli's principle defines lift, and if there isn't low velocity below the wing creating high pressure than the plane won't rise.Ex if you're running on a tread mill is there wind going by you? NO there isn't.
Ex2 If you drive a car on a tread mill at 100mph and stick you're head out the window will you feel any thing? NO
Its not going to fly.
Read my responses. The plane moves forward relative to the ground and there isn't a darn thing the conveyor belt can do to stop it. So long as the conveyor belt is long enough for the plane to accelerate to take off speeds, the plane takes off. Basically, the plane is as likely to be stopped by the wheels rolling along the conveyor belt as it is to fall out of the sky every time it flies over a conveyor belt.
-
just skimmed through 7 pages of this thread to take the intellectual pulse, so to speak. I've seen a lot of arguments with a lot of concepts and rationalization used in an attempt to support them. I've seen a lot of stupidity, too. But what I haven't see is any real analysis of the problem.
What would a physicist do?
The first thing he'd do is draw a free body diagram and label the forces acting on the plane.
I'm not going to draw a free-body diagram, but I will use the picture below as a substitution:
The forces acting on the plane, in the horizontal (or x) direction are:
T (thrust - positive x direction)
R (rolling friction - negative x direction)
D (drag - negative x direction)The TOTAL force is given by summing these up:
F=T-R-D
Everybody knows that F=ma, so we can calculate the acceleration of the plane:
F=ma=T-R-D
a=(T-R-D)/m
The acceleration of a plane is pretty high, therefore we can conclude that T is much much greater than R and D.
Now a quick word about rolling friction:
A spinning tire has rolling friction, due to the bearings, air, etc... This friction is constant. So a tire spinning at 10 rpm has the same amount of friction as a tire spinning at 100 rpm, or 1000 rpm. But the diagram shows that rolling friction decreases as the plane's velocity increases. How can this be? This is because friction is a function of force, or weight. As the plane picks up speed, lift is generated due to the wings, the force due to weight reduces, and so does the friction.
Now if you consider a plane sitting on a treadmill. The brakes are off and the engines are off. The plane is free to roll in the +/- x direction.
If you turn the treadmill on such that it's surface is moving in the -x direction and speed it to 100 mph, what happens to the plane? What forces are acting on it?
The only force acting on it is rolling friction. The plane will begin to accelerate in the -x direction at a rate given by the amount of friction. And we know that the rolling friction is pretty small. So the plane will not instantly move at 100 mph in the -x direction. It will slowly accelerate to 100 mph in the -x direction. And when I say "slowly", I mean slowly. Rolling friction is approximately equivalent to a coefficient of 0.003. At that rate of acceleration, it would take approximately 25 minutes to "catch up" to the speed of the treadmill of 100 mph.
However, since rolling friction is constant, this is the same acceleration working against the plane during a normal runway takeoff.
So let's now look at the forces acting on a plane under the treadmill scenario, where the treadmill matches the speed of the plane.
The forces are:
T (thrust - positive x direction)
R (rolling friction - negative x direction)
D (drag - negative x direction)The TOTAL force is given by summing these up:
F=T-R-D
the acceleration of the plane on the treadmill is found by:
F=ma=T-R-D
a=(T-R-D)/m
Are any of these forces different from the runway condition?
Thrust from the engines T is the same, regardless of runway or treadmill.
Rolling friction R is the same, regardless of runway of treadmill.
Drag D is the same, regardless of runway or treadmill.So a plane will take off from a treadmill just the same as it would take off on a runway. Therefore,
The treadmill is irrelevant
So if you said it wont take off, your a dumbass, end of story
Gary -
^^^^^ The reason I wouldn't do such an analysis, is cuz i can think about it in my head and understand that the wheels and whatever they are on have nothing to do with the plane taking off. So why do all of that??
-
JN210;203041 wrote:
lol, you actually counted?......Its like this,If a plane lands on a train going in the opposite direction at the same speed does that mean it stops flying?
All you have to do is view poll results and 14 ppl said it wouldn't fly, im guessing even more idiots thought it.
And yes, if it LANDS on the train, it will stop flying you idiot.
-
gary, I'm stealing your response and posting it elsewhere.
-
inspector01;203044 wrote:
All you have to do is view poll results and 14 ppl said it wouldn't fly, im guessing even more idiots thought it.And yes, if it LANDS on the train, it will stop flying you idiot.
perhaps I should have rephrased that a little better......If a plane landed (without the brakes or any type/way of slowing down) on a train could it just take off again?
sorry....
*1989 Nissan 300ZX Z31 *
> DelSlow;262050 wrote:
> I like the new JN210 -
BassPlayer, I made the same mistake as you did when first thinking about this theory. Think of hotwheels on a treadmill with a bottle rocket attached to it... If the bottle rocket has enough force to overcome the friction created by the rotating wheels, it will launch the car off the front of the treadmill right? now imagine the treadmill being way longer and the hotwheels having wings, eventually it will create enough speed to make enough lift to take off.
Hello! It looks like you're interested in this conversation, but you don't have an account yet.
Getting fed up of having to scroll through the same posts each visit? When you register for an account, you'll always come back to exactly where you were before, and choose to be notified of new replies (either via email, or push notification). You'll also be able to save bookmarks and upvote posts to show your appreciation to other community members.
With your input, this post could be even better 💗
Register Login