Principles of flight?

[vvega]

probaly the most fundimental thing you have missed as well is the fact there is air movement over the wings

what you think because youve stuck it on your converyer your engine do not now magically blow air over the wings ??

i see lots of magical things and idea's here but nothing that is suported by facts

[BZG Wagon]

I think this question could go either way.

1) Yes, it could take off as the wheels do not give the plane acceleration, the prop does, so that would give the plane momentum when it eventually overcomes the opposing force in the wheels from the travelator.

2) No, it couldnt take off, as the travelator would always match the speed off the wheels. If this is true, then for the plane to move forward it would defy the laws of physics and move faster than a travelator which would continue accelerating to an infinate speed. Alternatively, the resistance in the wheels would always keep the momentum of the plane a 0kph.

There is no answer to this question, to get this right in a physics exam, it should be based on your reasoning and assuptions and not a yes/no answer.

Its the same type of question as: Can God make an object so big that even he couldnt move it? (Assuming God can create anything and move anything).

We had this question in a physics exam and the whole class apart from me and another guy got it wrong, the people who got it wrong still didn't grasp the concept after over an hour of explaining.

Ill say it again, NCEA is stupifying our country.

[pidge]

The aeroplane will take off.

In an aircraft, the motive force is not linked to the ground using the wheels, as in a car. In fact, the motive force is not linked to the ground at all. An aeroplane is either being pulled along by propellors (where the motive force is linked to the air) or pushed along by a jet engine (where the motive force is nominally independant of the air).

Landing gear wheels (like un-driven wheels in a car) may cause some drag, but generally speaking, the engine(s) will easily overcome that drag and accelerate the aeroplane up to a speed so that the wings will provide sufficient lift to be able to lift the aeroplane off the ground.

[snwtoy]

i ask you this
if the planes wheels are so important to taking off
how dose a harrier do it

how do other VTAL aircraft do it

v

Nice

[method]

Well on a plane the wheels are not its driving force, the plane will move fowards no matter what the wheels are doing vvega and RomanV are both right.

The properler, jet or what ever the planes motive wont be what causes the air to go over the wing either, that will be the relative air speed.

No matter how fast the ground is moving under it the fact a plane will take off is dependant on the air speed. The plane could be reversing at light speed for all it cares but if the foward airspeed is great enough it will take off.

You are all assuming airspeed and ground speed have to be related, they are not.
Ive seen planes do funny things, even land moving backwards relative to the ground.

The plane will take off, no matter what the conveyor belt does it can't stop the plane from moving. If it were in a wind tunnel that would be a different story. You could get it to fly with 0 ground speed, but the air speed will still need to be XXknots for it to take off.

And oliboy you seem to think you know a lot of people in high places, or try to use credible sources in a lot of your arguments. Funny thing is you always bum up what your saying and end up being wrong. Physics is a funny thing, you cant trust your intuition on a lot of the more advanced topics even you think you understand it.

[ollieboy]

According to the New Zealand institute of Physics Test Paper. The Plane would not take off because of the fact there is no air movement over the wings.

It is true that planes take off on skis etc but they are still moving when they take off, they are being thrust by props or jets which push the plane along and cause air movement under the wings which creates lift.

If the plane on the conveyor belt was moving at huge speeds it still remains in the same position in terms of displacement relative to the earth beneath the conveyor belt. This means there is no air movement across the wings to create lift.

I want a link to this test you harp on about.
The plane engines create thrust agains the surrounding air, generating air speed and thus lift as the pressure difference above and below the wing increases.
To say that the plane never takes off is just wrong. It doesn't matter if the ground is a conveyor belt, an oil slick or a runway - so long as there is a friction reducer involved the plane will take off.

The test was an in class assesment we did in physics this year.

[vvega]

interesting
i guess they $&#$% that one up aye

you didnt go to cambrige high school did you ??

v

[ollieboy]

interesting
i guess they $&#$% that one up aye

you didnt go to cambrige high school did you ??

v

No I didnt go to cambridge high.

To those who say NCEA is screwed everyone up you are correct but the exam we did was an NZ institute of physics paper which is completely unrelated to NCEA.

VVEGA: I understand the concept involved in VTOL but that is different to the problem here. I understand that the wheels are not the driving force of an aeroplane but look at the orginal problem, the travelator is designed to match the exact speed of the wheels moving in the opposite direction. This means that as the thrust is increased from a stationary position the wheels will start to move and so will the travelator, as the speed increases of the wheels so will the speed of the travelator. This means that in relation to the earth below it, the plane is not undertaking displacement. It remains in a fixed position. Even if the thrusters are going at full throttle and they move the plane the travelator will compensate for this. This means that the plane still remains in a fixed position in terms of displacement. Because no displacement occurs, no wind is created, therefore nothing to cause lift on the wings to make the aeroplane fly.

This is why on Battleships they use a tow method to launch aircraft otherwise it would be a lot simpler to use a travelator design if it were physically possible.

To you method, you say I dont use credible sources, try this then.

Newtons 3rd law:All forces in the universe occur in equal but oppositely directed pairs.

In the case of the aeroplane problem. Because the aeroplane is not moving in relation to the earth beneath it, no thrust force is being created, therfore no opposite drag force. The only forces acting on the aeroplane are gravity force and reaction force but these are irrelevant in this problem. If the aeroplane attempted to take off nothing would happen because there is no thrust force to cause lift.

[RomanV]

Why do I keep coming back to this thread? *bangs head on wall*

Okay. REREAD the initial question. slowly.

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, 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?

Explain why it can, or cannot, take off?

This says nothing about countering every force that the plane creates, all it is doing is spinning the wheels of the plane.

If the planes speed, relative to the ground was zero, (regardless of how much thrust is applied, etc.) then the travelator would be stationary.

It is only when the plane STARTS MOVING, that the travelator moves in the opposite direction.

eg. if the plane is MOVING FOWARDS relative to the ground at 5kph, then the travelator is going to be moving backwards at 5kph.... meaning that the speed of the wheels spinning is 10kph. The plane is still moving fowards (relative to the ground, and the surrounding air) at 5kph though.....

What ever speed the plane is travelling, the plane speed relative to the travelator will be twice the plane speed relative to the ground. THAT IS ALL. It doesnt mean that the plane sits stationary, in fact if the plane isnt moving, then the travelator doesnt move either.

[ollieboy]

Well my answers are from an institute of physics paper so if you think its wrong dont take it up with me, take it up with them. Okay

Theres no point in us arguing this any furthur, we both believe strongly in our own ideas so let it rest now.

[vvega]

think of it this way
you say there is no thrust
please explane what is happening to the 30,000 off ft punds of thrust been expelled out the back of the plane

please explain why its not pushing on the air molecules


ok so in your eyes
if you put your feet on the solid ground behind the aircraft
and pushed it
the plane would not move ??

another analagy
if you put your car on a dyno
spin the dyno and the wheels up to 1.5 km's a hour (the dyno's rollers will match the car tyres perfectly


thats basically eaxtly what you have there in the exaple just useing a different situation

now stand behind the car wth a pile of ya mates and push the car off

what happens ????

the car moves off

why
because the dyno and wheels cancel the force that they apply to each other

then you push
now that force is not cancelled buy anything and to obay the 3rd law of physics it has to then move

as soon and you pitch the blades to produse thrust they will exert a forward motion when the force overcomes the frictions involed in moving the plane

as the plane moves forward(becase in order for the wheels to move it would have to move forward)
the travelater will match the speed of the wheels
unfortunatly for the wheels to contunie to move the plane again has to move forward
there would be no other way for the wheels to move(remeber there not powered)


please retort anyone but when you do quote what your retorting to and explain why its not true
or why its dosenot obay the basical laws of physics

then please quote how yours dose as well

v

[method]

This is why on Battleships they use a tow method to launch aircraft otherwise it would be a lot simpler to use a travelator design if it were physically possible.

What the heck? You have to be kidding?

A steam powered catapault is probably the easiest thing you could make.

And the travelator wouldnt hold a aircraft stationary so it wouldnt work. The travelator changes the GROUND SPEED not the AIR SPEED.

The travelator wouldnt stop the plane from moving fowards at all, the plane pushes air to move so it will go forards regardless of what the ground underneeth it does.

Why do you think a plane has wheels? The idea of the wheels are to provide as little friction between the plane and the ground.

So if the plane accelarated fowards at 10kph, the conveyor backwards at 10kph the planes ground speed would be 0kph relative to the conveyor but 10kph relative to the air. It would also be 10kph relative to the true ground speed hence moving fowards.

Ollieboy you obviosuly have no knowlage in this field, all you are doing is using your intuition. Trust me once you start studying dynamics you will quickly realise how wrong your intuition can be. Go study dynamics at university and you may have a better idea of it all, level 3 phsycis is arse, all you learn is the basics of statics (equilibrium and the likes) and a very tiny bit of dynamics, hardly anything at all.

[ollieboy]

I was thinking about this further and now I just dont know. I think of the answer given by the physics institute and because they are a reputable organisation i believe them but then I look at others answers and they make me think. I am just contemplating whether or not to ask the physics professor who lectures at University who lives just over the road but I dont know him so it might be a bit random going over there and asking.

[method]

Id say talk to him, so long as he knows his dynamics. Its good to open your mind to new things.

Its quite amazing how tricky it is to get your head around such a seemingly simple problem. When i started studying dynamics i was surprised in the ammount of things i thought i knew and understood but really didnt know SFA.

[ollieboy]

This is why on Battleships they use a tow method to launch aircraft otherwise it would be a lot simpler to use a travelator design if it were physically possible.

What the heck? You have to be kidding?

A steam powered catapault is probably the easiest thing you could make.

And the travelator wouldnt hold a aircraft stationary so it wouldnt work. The travelator changes the GROUND SPEED not the AIR SPEED.

The travelator wouldnt stop the plane from moving fowards at all, the plane pushes air to move so it will go forards regardless of what the ground underneeth it does.

Why do you think a plane has wheels? The idea of the wheels are to provide as little friction between the plane and the ground.

So if the plane accelarated fowards at 10kph, the conveyor backwards at 10kph the planes ground speed would be 0kph relative to the conveyor but 10kph relative to the air. It would also be 10kph relative to the true ground speed hence moving fowards.

Ollieboy you obviosuly have no knowlage in this field, all you are doing is using your intuition. Trust me once you start studying dynamics you will quickly realise how wrong your intuition can be. Go study dynamics at university and you may have a better idea of it all, level 3 phsycis is arse, all you learn is the basics of statics (equilibrium and the likes) and a very tiny bit of dynamics, hardly anything at all.

I will say again, I am using the NZ physics paper ok, have you understood that now? I am not using my intuition, I am using a physics paper. I'm not doing nor have I ever done or ever will do Level 3 physics so I wouldn't know what you are saying about dynamics.

[V8MOFO]

So for the people who voted yes. Is there a wind speed in your conclusion?
Is the plane moving relative to the earth? ie if the plane is on the travelator and you attach a peice of string to the front of the plane to a pole on the ground, would the string break?

eg. if the plane is MOVING FOWARDS relative to the ground at 5kph, then the travelator is going to be moving backwards at 5kph.... meaning that the speed of the wheels spinning is 10kph. The plane is still moving fowards (relative to the ground, and the surrounding air) at 5kph though.....

It sounds like you're saying here that there is no way of countering the speed of an object with a travelator. ( to make the object's speed relative to the ground 0kmph ), you have your hand placed on the wall next to you which is not moving. What happens when you walk down an esalator at 5kmph that is moving at 5kmph up? Then the speed of the escalator and the speed of you increase by 2kmph with the same acceleration at the same time? If all matters being even, your hand shouldn't be moved from that wall.

[ollieboy]

Well I went over to the professors house and had a good yarn. He said that really the question is pointless, he said he has heard the same one many times and it always leads to an argument.

His answer to the question was, it may take off and it may not.

This is impossible to work out unless the exact situation is set out. (anyone keen?) In physics there is evidence to support it taking off and against it taking off. His advice to me was this: go and choose the answer that will get you verbally abused the least, choose it even if you don't believe it.

So here I am swallowing my pride. I am sorry for what I said earlier but I believe the plane will take off.

[V8MOFO]

So here I am swallowing my pride. I am sorry for what I said earlier but I believe the plane will take off.

NO! stick with me on this one buddy. Stand up for what you believe in I'm not stopping until I'm dead.

[Bridget]

ok... the plane uses the air from the Jet Engines to propell the plane, so irrelavant of what the wheels r doing.......the air from the jet motors will move the plane relavant to the air speed

[no_8wire]

from what I understood the question to be was that for any speed the wheels were doing eg 5km/hr the belt was going -5km/hr( same speed but opposite magnitude)
Therefore with reference to a point on the ground the effective speed of the plane is zero. as 5km/hr+ -5km/hr = 0
However when you think that however fast the plane might be "moving" its not actually moving from its orginal place on the belt. However when its speed is fast enough it will be able to lift as when it reaches its lift speed ( say 150km/hr?) it will be able to lift as...actually could it reach an real lift off speed?


actually I have just confused myself...as its effective speed/movement is zero how can air be creating lift..
so I still say no...

I think anyway...