Figure This Out

[nb88]

The rocket-on-car thing made it easier to explain to myself anyway.

About the speedo - they cant work on the wheels surely? Otherwise they wouldnt work in the air? Or do they have seperate speedometers for taxi-ing, taking off?

[oakley]

i am on about in a car now mate, not in a plane, sorry bout that!

Edited February 22, 2006 by oakley

[nb88]

Ahh ok yeah, but that was just an example i made up myself

[Tomm]

It's a trick question, it's a Harrier jump jet so it doens't have to move

In the original problem that Tipsy Jock posted, the conveyor belt is going at the same speed as the plane. Ie plane is moving forward at 10mph, and the conveyor belt rolling backwards at 10 is of little consequence.

However, a better conundrum is if you match the speed of the conveyor belt to the speed of the wheels of the plane. Which is basically what so of you are arguing. And in that situation, it would stay still. And wouldn't take off.

(Unless you believe what Leedstrials said in the first page. If the plane's engines kept roaring and it didn't take off, I guess the thrust would get bigger and bigger and tend to infinity. And then I guess that could distort some wind over the wings and it would take off. Once in the air it'd be fine.

[Punkrider]

Internet says:

The plane is driven by the thrust of the engines acting on the air not

the ground. It *will* accelerate forward as a result, and acquire

speed relative to the air and therefore take off.

This comment is wrong. It completely ignores the friction of the

wheels on the ground.

There are two kinds of friction that are generated by wheels. The

first is the friction from the ball bearings. This type of friction

is small and irrelevant to the question. The second is the friction

of the wheels on the ground, or in this case, the conveyor belt. This

friction needs to be great enough to make the wheels grip the road

under a variety of conditions. This friction is not so great (nor

insignificant) when the wheels roll, but it is dramatically greater

when the wheels skid.

Once the airplane’s wheels start to roll, the conveyor belt will match

their speed, effectively keeping the plane in place. The rotational

speed of the wheels and the speed of the conveyor belt will both

increase together until the maximum rotational speed of the wheels is

reached. As long as the wheels roll without skidding, the plane will

go exactly nowhere. For clarity, let’s assume the maximum rotational

speed of the wheels is 300mph. Once that speed is reached, if the

airplane’s engine still has additional power, the wheels will start to

slip. The wheel’s rotational speed, and therefore the conveyor belt’s

speed, will both max out at 300mph. Let’s assume the plane needs to

achieve airspeed of 100mph to take off. The engine, then, would have

to have enough power to make the plane skid on its wheels down the

runway at 100mph. How much power is that? If the plane were not on a

treadmill, it is equivalent to locking the wheels so they cannot

rotate, and accelerating the plane on skidding wheels to 100mph. That

would take a LOT of power. And also quickly shred the tires.

Internet is always right

Adam

[JT!]

An aircraft is standing on a runway that can move (a conveyor belt). The aircraft moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the aircraft's speed and tunes the speed of the conveyor to be exactly the same, but in the opposite direction. There is no wind. The pilot begins to add thrust to the engines...

The question is:

Will the plane take off or not?

There's too many posts to read, so i may be reapeating other points etc but what they hey. It won't take off. A plane needs air speed running over it's wings to lift. If it's stationary, which it will be due to the fact that the moving runway is moving backwards the same speed, it cannot take off.

The engines on a plane only create a horizontal forse, the wings make up move vertically.

So it wont take off.

[andyroo]

Yeah that makes sense.... a preflight check is to stick the brakes on and push the engines to full power and back again, and the plane does not move - so it wont in this case either...

Good stuff Adam

[nb88]

Internet says:

blah

Internet is always right

Adam

Yeah that works if the conveyer belt moves at the speed of the wheels, it doesnt. As tomm said, if it moved at the speed of the wheels it would stay still or whatever.

It's moving at the speed of the PLANE. NOT THE WHEELS.

[andyroo]

Also I dont think the plane will be able to achieve enough thrust to counteract the conveyor belt

[PaRtZ]

this thread is like a snowball. The more people who reply to it, make it longer and longer and longer

Now if this thread WAS a snowball, what colour would it be?

[tipsy Jock]

this thread is like a snowball. The more people who reply to it, make it longer and longer and longer

Now if this thread WAS a snowball, what colour would it be?

Definately blue

[Shez.sheridan]

I'm sure a million people have said the same...but no, it will not take off. Aeroplanes fly due to the aerodynamic properites of the wing, i.e. air flowing over it. If the main body of the aeroplane is stationary, then it will not lift atall.

During take off/flight, air increasingly flows faster over the top of the wing than the bottom as the plane speeds up, creating an area of low pressure above the wing, and high pressure under..thus producing lift. This lift (speed) needs to be maintained to continue flight - if I remember my aerodynamics lessons from uni correctly.

I've always found the notion that if you walk to the back of a plane whilst in flight, it will actually speed the plane up (marginally), walking to the front slows it down; more interesting.

To propell yourself forwards whilst walking, you exhert an equal force (acting in the opposite direction to you walking) on the ground (aeroplane in this case). This means that if you walk to the back of the plane, your feet have to exhert a force (small in relation) on the aeroplane...your feet effectively push it in the opposite direction, which adds (by a miniscule amount) to the speed/thrust of the plane going forwards. We calculated it once in physics at sixth-form.

[tipsy Jock]

I'm sure a million people have said the same...but no, it will not take off. Aeroplanes fly due to the aerodynamic properites of the wing, i.e. air flowing over it. If the main body of the aeroplane is stationary, then it will not lift atall.

During take off/flight, air increasingly flows faster over the top of the wing than the bottom as the plane speeds up, creating an area of low pressure above the wing, and high pressure under..thus producing lift. This lift (speed) needs to be maintained to continue flight - if I remember my aerodynamics lessons from uni correctly.

I've always found the notion that if you walk to the back of a plane whilst in flight, it will actually speed the plane up (marginally), walking to the front slows it down; more interesting.

To propell yourself forwards whilst walking, you exhert an equal force (acting in the opposite direction to you walking) on the ground (aeroplane in this case). This means that if you walk to the back of the plane, your feet have to exhert a force (small in relation) on the aeroplane...your feet effectively push it in the opposite direction, which adds (by a miniscule amount) to the speed/thrust of the plane going forwards. We calculated it once in physics at sixth-form.

But the plane will move This thread has got seriously confusing now

[Shez.sheridan]

But the plane will move This thread has got seriously confusing now

I didn't bother reading all of it....as most other people I expect..

[SQuiT-man]

An aircraft is standing on a runway that can move (a conveyor belt). The aircraft moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the aircraft's speed and tunes the speed of the conveyor to be exactly the same, but in the opposite direction. There is no wind. The pilot begins to add thrust to the engines...

The question is:

Will the plane take off or not?

Half of the people here are misinterpreting the wording- the plane is MOVING, and therefore will have it's lift from the wings, the only difference is that it will be travelling past conveyor belt at twice the rate that it is moving RELATIVE TO THE GROUND

There's no need to even acknowledge friction or anything for the purpose of the question, as we are not making this situation for real or anything (you could include loads of other factors in that case, such as increased air restance on the plane, because of the friction between the conveyor belt and air causing air to travel backwards relative to the ground, and causing its own virtual wind)- it WILL take off.

[fruitbat]

I havnt read all the posts as its quite mad some of the things people are saying

The plane will not take off

It cant

The wheels can be moving at X mph and the converyor belt is moving also at X mph in the opposite direction, meaning that this cancels the wheels movements, therefore not allowing the plane to move from its spot

Yes the wheels will be spinning ten to the dozen but the plane will not move an inch

With the factor of thrust being brought into the equation this will simply increase the speed of the plane......ie the wheels will get faster. as you know when the wheels increase speed so does the conveyor belt to the same speed in the oppsite direction, stil as mentioned earlier this will mean no movement from the plane

All that will happen is the wheels will get faster and faster and so will the conveyor belt. Nothing at all will happen with the plane

You may as well take the plane out of the equation and just put wheels on a conveyor belt

simple really

Frooty

Edited February 22, 2006 by fruitbat

[nb88]

The plane does take off, and it doesnt need any extra thrust to take off, it just does it as normal. All this stuff about air and lift doesnt matter, all that matters is whether the plane travels forward or not, and it DOES, so it DOES take off. The wheels are totally irrelevent (assuming the hubs are friction-less), the engines are what matters, and the conveyor runway doesnt effect the engines. Plane speed isnt controlled by the wheels, they are totally free-spinning.

So, the conveyor belt is going backwards at the same speed as the PLANE, NOT THE PLANES WHEELS, this means the wheels are being pushed backwards and so are spinning because of the friction on the conveyor belt and wheel surface. The engines still provide the thrust, and so the plane speeds up, and so does the conveyor belt. As it speeds up, the conveyor belt continues to speed up, so the wheels must move twice as fast in order to counteract the conveyor belt.

To propell yourself forwards whilst walking, you exhert an equal force (acting in the opposite direction to you walking) on the ground (aeroplane in this case).

Thats because the friction on your feet are controlling your speed. Thats why a car wouldnt go forward on this conveyor belt.

The wheels can be moving at X mph and the converyor belt is moving also at X mph in the opposite direction,

No, the conveyor belt doesnt move at the same speed as the wheels.

[fruitbat]

No, the conveyor belt doesnt move at the same speed as the wheels.

Bah its all bloody confusing

that little quote of yours there has just ballsed up my way of thinking on the whole thing, im off for a cuppa to take my mind off planes on a treadmill! S:

Frooty

Edited February 22, 2006 by fruitbat

[Dan6061]

No it wouldn't.

Becuase don't planes usually take off from all the air blasting past it? (sorta)

There'll be no air if it's on a belt thingy.

[poopipe]

this thread is like a snowball. The more people who reply to it, make it longer and longer and longer

there's logic ^^

anyway - can't be arsed to read it all now. anyone who agrees with the following is right. everyone else is a dong.

if plane moves in relation to the air, plane takes off

if plane doesn't move in relation to the air, plane wont take off

the plane has to move through the air or the magic wing shape won't make it fly (i have a simplistic view of aeroynamics)

if its a magic conveyor belt that causes the plane to remain stationary (in relation to the air) the plane wont take off.

if its a normal conveyor belt then the plane can move (in relation to the air) under thrust from the engines and thus take off.

what kind of conveyor belt is it?

[JT!]

But the plane will move

This isn't an argument weather the plan will take off, but an argument into weather the plane will move forward or not.

If the moving surafce moves the same speed as the plane, the plan will not move.

[fruitbat]

An aircraft is standing on a runway that can move (a conveyor belt). The aircraft moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the aircraft's speed and tunes the speed of the conveyor to be exactly the same, but in the opposite direction. There is no wind. The pilot begins to add thrust to the engines...

The question is:

Will the plane take off or not?

It is an argument if the plane will take off or not as the question states

Now that i think about it the plane will take off, just moves forward at twice the speed due to the conveyor belt moving in the opposite direction. It is like the ground moving from underneath the object at twice the speed. At normal speed the ground will move in the opposite direction from the plane.....backwards....if the conveyor is moving at the same speed as the plane it is moving further back from the plane at twice the normal speed

Well i see i have completly changed my opinion on the matter

EDIT Ignore everything i have ever said about the matter, i am still doubting myself and i am leaving this topic well alone,,,,,until next time

Edited February 22, 2006 by fruitbat

[tom tom]

i think it will move as it is thrust and not drivin by wheels!, but if there is no air resistance anywheer then there can be any air to move out the back either so it cant move as it cant put air into the jets.

tom tom

oh my god this is so confusing

[Tony Harrison]

It's so simple! Despite the answer being explained countless times, and despite two (aptly named) idiots guides, some of you still don't get it!

The conveyor belt does NOT cancel out the speed of the plane, because the plane is not using it's wheels to propell itself.

If a car was on the conveyor belt, with it's speed matched by the conveyor belt, it would not move because they would cancel out. The plane, however, pushes against the surrounding air, which is not connected to the conveyor belt. The wheels roll along the conveyor belt just like they roll along a runway.

SIMPLE. THINK ABOUT IT.

So, the plane can take off, because it IS moving. It makes me wonder, it really does, that it's taken 7 pages of replies and some of you still don't understand. It's really seriously worrying.

[fruitbat]

It's so simple! Despite the answer being explained countless times, and despite two (aptly named) idiots guides, some of you still don't get it!

The conveyor belt does NOT cancel out the speed of the plane, because the plane is not using it's wheels to propell itself.

If a car was on the conveyor belt, with it's speed matched by the conveyor belt, it would not move because they would cancel out. The plane, however, pushes against the surrounding air, which is not connected to the conveyor belt. The wheels roll along the conveyor belt just like they roll along a runway.

SIMPLE. THINK ABOUT IT.

So, the plane can take off, because it IS moving. It makes me wonder, it really does, that it's taken 7 pages of replies and some of you still don't understand. It's really seriously worrying.

HAHA thats got to be the post that has made the most sense to me(Y)

I think this question is definatly designed to make you argue about logic and doubt yourself, cos if thats the case it has worked with me