Will it take off?

Originally posted by Travellar
The net speed of the aircraft in relation to stationary ground is not zero, and is in fact not even affected by the treadmill. Which means the plane is actually moving, will generate airflow over the wings, will generate lift, and will fly.
[edit on 15-2-2006 by Travellar]

How do you figure?

There is no airspeed! If you assumption is true, Why do airplanes like a 7474 need a runway?

In the above sinareo, the Wheels are moving, but the plane is not!

No offense, but you might want to take high school level Physics. Are you assuming that you have a head wind? If that were the case, you could (theoretically) take off without ever turning the engine on!

Tim

Originally posted by ghost
There is no airspeed! If you assumption is true, Why do airplanes like a 7474 need a runway?

In the above sinareo, the Wheels are moving, but the plane is not!

There is an airspeed - the conveyor belt will need to be the length of a runway.

The wheels are moving, and so is the plane.






I really cannot believe the amount of wrong answers here. Can someone who believes the aircraft doesn't take off please explain how such a thing can happen mathematically?

Are you saying the thrust from (say a 777) is balanced by the friction from the wheels at 1 kt? Or 2 kts? Or 10? or 100?

[edit on 15-2-2006 by kilcoo316]

Originally posted by kilcoo316
I really cannot believe the amount of wrong answers here. Can someone who believes the aircraft doesn't take off please explain how such a thing can happen mathematically?

Are you saying the thrust from (say a 777) is balanced by the friction from the wheels at 1 kt? Or 2 kts? Or 10? or 100?

[edit on 15-2-2006 by kilcoo316]

B.T.W.: Net Speed = F-G (F is the Forward speed of the plane, G is the speed at which the ground is moving backwards)

There the fomula!

Here's a simple test you can do on you own to see the logic I'm explaining:

We all know you need wind to fly a kite (That's a given)!

Now, go get yourself a kite and fallow these steps:

1. Find a room with a treadmill and no indoor draft (Fans, open windows, ECT.)

2. Set up the kite behind you

3. Get on the treadmill and start it.

4. Hold onto the kite.

See if you can get the kite to fly!

Tim

Originally posted by ghost
B.T.W.: Net Speed = F-G (F is the Forward speed of the plane, G is the speed at which the ground is moving backwards)

There the formula!

As far as the aerofoils are concerned, F is all that matters.

Besides, Net speed is actually F



Try to balance the forces:


Thrust from engine > friction from wheels (until something like 500 mph airspeed [1000mph tyre speed] I guess!)

- so the aircraft can accelerate up to 500 mph and take off well before this.

Originally posted by ghost


B.T.W.: Net Speed = F-G (F is the Forward speed of the plane, G is the speed at which the ground is moving backwards)

There the fomula!

Here's a simple test you can do on you own to see the logic I'm explaining:

We all know you need wind to fly a kite (That's a given)!

Now, go get yourself a kite and fallow these steps:

1. Find a room with a treadmill and no indoor draft (Fans, open windows, ECT.)

2. Set up the kite behind you

3. Get on the treadmill and start it.

4. Hold onto the kite.

See if you can get the kite to fly!

Tim

Tim

Really expect more for an experienced poster like you

In your example the forward propulsion is generated by the leg pushing against the treadmill that is moving so the forward motion is negated by the backward motion of the treadmill, thus no movement as you correctly state.

HOWEVER, in the 'trick' question the aircraft propulsion is created by the jet thrust pushing against the air NOT THE TREADMILL, as the air is not moving backward at a speed equal to the thrust (the treadmill is) and the air is NOT connected to the treadmill its forward motion is independant of any motion of the treadmill (I am of course talking a theoretical firctionless system in reality there would be greater friction operating the wheel but not enough to stop taking off unless the wheels blow out).

Remember this is a trick question there would be airflow over the wings as the equal equal and oppoisite force to the jet thrust is operating on a system separate to the treadmill ("the air" not the ground)

Thus the aircraft would travel forward a Xmph throught the air - the tread mill backwards at Xmph the relative speed between the two would be 2Xmph. The airspeed over the wings would be Xmph +/- the current head/tail wind speed.

In reality there would an impact on the take off performance as as there would be an increase in the resistive force caused by the increased friction in the wheels.



PS I was initial caught out by the question

[edit on 15-2-2006 by Popeye]

Assuming no head wind of anything of that sort, the plane will never take off, imagine a plane on a treadmill, that's basically what the question is posing.

I asked my teacher(a pilot for over 20 years) and everyone else in the class(who are training to become pilots) said that the plane will never take off, one of the students who is educated enough, said that it is really based on friction, because in the perfect world, there is no friction, no wind, no nothing, so the plane in fact, in the perfect world would take off due to no friction, but because the plane is NOT in a perfect world, friction is one of the biggest factors, and if something defies physics, but is proved by mathetmatics, I believe it doesn't count, physics overpowers math, despite the fact that physics uses math alot, I believe we are using the wrong equations.

Just be because the wheels are moving twice as fast, does not mean that the aircraft will take off faster. I think what people are arguing is that the airplane is on a converyor and the conveyor is moving in the SAME direction of the aircraft(this was posed in my class, and we had a 5 min argument of people yelling back and forth, until we all figured out that half the kids had actually thought the converyor was moving forward, allowing for the aircraft to take off faster and in a shorter distance, of course when this was corrected, everyone came to the same conclusion, the plane will not take off).

Now, like Ghost said, BASIC PHYSICS and Aerodynamics, this is what I'm basing my answer on.

Remember little kiddies, you need lift to get airborne, and you get lift through the motion of air through the air foil, low pressure on top, high pressure on the bottom of the airfoil, and thrust helps with that motion, if the wheels, which are connected to the struts which are connected to the airplane as a whole are not gaining DISTANCE but are gaining a higher VELOCITY, then it's scalar, it's velocity without a direction. So in retrospect, the plane is not gaining DISTANCE which it needs in order for the airmasse around the airfoil to start moving over it. Bernoullis principle tends to help too.

Shattered OUT...

Originally posted by HowardRoark
Let me see if I can explain it to you.

It is a trick question.

The way the question is worded, you think that the plane is motionless on the conveyor belt.

It is not. The belt speed is related to the forward speed of the craft. If the craft were motionless, the belt would be motionless also.


Think of it this way. Imagine that instead of a plane, you have a rocket on wheels on a conveyor on the moon.

No air.

Will the rocket move forward?

Answer: yes, since the motion of a rocket in space is entirely dependent of Newton's third law. The opposite reaction is the forward motion of the rocket, not the retrograde motion of the belt.

The plane will take off.

But also, can you get a plane to act in space like it would in the atmosphere?



Already countered, since Earth as an atmosphere unlike the moon, everything is different, so how can you possibly apply this?

Shattered OUT...

For all you non-believers that don't believe it will get off the ground


ooine.com...

It will not take off, simple explanation:

An example would be like sitting on those gym bikes with no wheels. You can peddle as fast as you want, but you wont feel the fresh breeze of that speed. No breeze, no wind... no lift!

Propeller pulls a plane through the air creating life, a jet engine pushes a plane through the air creating lift, and a swimmer pulls through water creating lift.

God be with you,
Mfourl


[edit on 15-2-2006 by mfourl]

I finally understand the question and think I can kinda explain it better.

No assumption was made about the length of the conveyor belt first of all.

Let's take, for example, a plane taking off on ice. There will be minimal friction from skis or whatever, but still it only takes X amount of thrust and Y amount of lift to get it off the ground. The plane will move forward.

THE WHEELS AND CONVEYOR ACT AS THE SKIS ON ICE. Think about it .... the wheels are near-frictionless ... it doesn't matter AT ALL what's moving beneath it (or how fast actually). The plane will still take X amount of thrust and Y amount of lift to get off the ground (there's actually friction, but assume its near the quantity that ice/skis encounter).

People assume that the conveyor is only long enough to hold the plane. In this case, it will not take off .... it will accelerate until it hits the end of the conveyor and then fall off or whatever. But if the conveyor is as long as a typical runway, the plane will take off with no problem. The thrust is independent of the wheels/conveyor ... they could even be air for all it matters (which is why a plane in free fall can still recover ... give it enough forward thrust to recreate lift and you are flying forward again).

Once you realize that the wheels/conveyor are the equivalent of teflon, it's easy to see that the plane will take off.

The trick is in the wording, as someone mentioned above. For the belt to me moving AT ALL the plane has to be moving ... and we've already shown that the wheels and conveyor allow the plane to move freely. So as the plane accelerates the belt does too ... but because of the near-frictionless aspect of the wheels/conveyor, the plane will move forward nearly as normal and take off when the proper lift has been achieved.

EDIT: oops, I see that kilcoo316 already put up a link that explains it the same way I did ... kudos!

[edit on 15-2-2006 by Fiverz]

Again, read the thread i posted earlier for truly scientific breakdowns on this topic from people that know what they're talking about

I dont care what you posed there Toby. The principle is the same as if a gun could fire a bullet at 200mph but if you fired it on a train that was moving at 200mph the bullet would travell at 400mph.

Lift makes a plane fly not how fast the engines turn, if that was the case don't you think we would get rid of run ways and make planes stationary until the engines reached max speed then say hey let them go.

God be with you,
Mfourl

mfourl, what is preventing the plane from moving forwards if the wheels are castoring beneath the aeroplane? The propeller is pulling it forwards but the wheels are spinning freely below unconnected. Apart from the initial effect of the conveyor cancelling out the initial slow movement forward of the plane there is no effect other than to make the plane stay on the ground slightly longer (ok, maybe twice as long) until this effect is countered by the propeller, once the engine and propeller speed are sufficiently high they will pull the plane forwards until take off speed is reached and whatever is happening under the wheels is irrelevant. Its nothing like an excercise bike, nor does it involve magical vertical take off, it is simply that the disconnected and undriven wheels slow initial progress and once this is overcome they no longer retard the aircrafts travel. Simple.

Quote
1. Find a room with a treadmill and no indoor draft (Fans, open windows, ECT.)

2. Set up the kite behind you

3. Get on the treadmill and start it.

4. Hold onto the kite.

See if you can get the kite to fly!
Unquote

It's not the same... your feet are your propulsion.
If you were on roller skates with a fan on your back with a very looong treadmill it would be like the plane, and the kite would fly!

For anyone who thinks this is simple has another thing coming, so far ALOT of people can't seem to agree on what is right, and simply saying "No, you're all wrong, and I'm right" isn't really going to do anything, it'll just make that person out to be arrogant.

I'm having a really hard time trying to understand the otherside's argument, as I believe why the plane WILL NOT take off, I am having trouble trying to understand why it will take off. It's not that I'm an imbecil(just to keep any of you wise arses to start throwing insults around) I just can't seem to understand the otherside's argument and take it as "simple".

Shattered OUT...

ShatteredSkies, it is very simple. It just has to be worded different.

The plane is sitting on a treadmill, the engines are started and it starts rolling forward, right?
The engine is pushing against the air, not the treadmill. So no matter how fast it moves forward it has literally no connection to the treadmill. The wheels aren't powered, they just roll.
So the plane, pushing against the air, starts to move forward. The pilot increases speed and it moves faster through the air creating lift on the wings.
The treadmill belt is just rushing past under the plane, increasing the speed of the plane wheels, but nothing else.
Relative to the earth, the plane is moving and creating lift. It's not powered by its wheels so it's not just sitting in one spot. It's moving through the air because its pushing against the air.

You could actually just pretend the treadmill doesn't exist, because it has no effect on the plane taking off.

Don't worry Shattered, I wrote 'simple' at the end of my post as an act of facetiousness after typing a quite convoluted explanation, British humour

I don't know if I can get my viewpoint across to you in simple terms because its not really simple, like you say, however, here goes.

Yes, I agree that the conveyor belt is moving backwards and all that but he question is 'are the wheels trying to push the plane forward?' If the answer was 'yes' then the plane would remain stationary and rooted to the ground because their motion is cancelled out.

BUT the answer to this is 'no' because the propeller is pulling it forward and the wheels are just like the castors on an office chair. Therefore because the wheels are not the driving force it matters not a jot what the belt is doing. The analogy that was posted earlier about it being like a plane on skis taking off from ice sort of works quite well because that illustrates how the prop is pulling the plane along all by itself without any influence from anywhere else, the whole bit about wheels and converyor belts is a red herring, the propeller imparts the speed that makes the plane fly, not the wheels.

Where it gets a bit more complex is that as the plane starts to move forward the reversal of the belt WILL keep it stationary until, that is, the engine could be revved up enough to overcome this, therefore at full throttle the plane will actually move physically forward at an ever increasing speed until take off speed is reached, only the wheels will accelerate twice as fast, but to no avail.

I've probably made the whole thing worse now, oh dear.

edit to remove the evidence of an inability to type and think at the same time.

[edit on 15-2-2006 by waynos]

I'll add my analogy to the plenty already listed.


You are on a bike without a gear chain in a corridor, and there are handrails on the walls of the corridor. The bike is the conveyor belt, the handrails are the air, your legs are the wheels, and your arms are the jet engines.

In a car, your wheels move you forward. So in this case, your legs would be pedalling, but not getting anywhere, due to the conveyor belt cancelling out your motion with your wheels.

In a plane, your jet engines move you forward. So in this case, your arms are pulling on the handrails, and are moving you forward. Your legs don't do anything - they just sit there and keep you stable.

The jet engine provides thrust through the air, so you move forward. Your wheels do nothing but spin like crazy lepers.


For initial start up you might roll back a bit, but that's to be expected. Your engines will move you through the air, regardless of what the wheels are doing on the ground.

I have to admit this question tricked me... But after reading the answer, it makes a lot of sense.


Edit:

To add another thing, while swimming it's like using your arms to drag you along the lane rope, where it doesn't matter if your legs provide any thrust at all.

[edit on 15/2/06 by Xar Ke Zeth]

Beer_Guy's post did it, I understand why the plane is moving forward, all of this, and all someone had to say was "The engines are pushing against the air", I was thinking too much into it, which is why I couldn't understand it, but it is in fact simple once you get it, the plane isn't being pulled by means of the wheels, but of the engines, so no matter what, the plane will move because it is pushing against the air, not the ground. And it is the basis on which thrust aids lift when taking off, the plane must be pushed forward through the air, not over the ground.

Shattered OUT...

Without looking at all the other replies, yes.. cos the plane could be like a jump jet with vertical take off...