Will a plane on a conveyor belt take off? - Page 2

gtfpv · 24-10-2007, 01:58 PM

of course it will. wheel speed has nothing to do with this unless it was relying on driven wheels rasther than thrust to accelerate it forward . in which case thedriven wheels would have to be able to propel the plane forward fast enough to take off . once it left the groung it would have nothing driving it forward then it would land again .
so as long as there is thrust propelling the plane forward . it is irrelavent at what speed the conveyer belt is going . becuase forward thrust would over come the neutral wheels .

aye you · 24-10-2007, 02:07 PM

i'm gonna pull out my physics books, and my commercial theory books, mainly aerodynamics and crunch the formulas to come up with an answer.

mowog · 24-10-2007, 02:07 PM

The moving belt will produce airflow it cant help but so. The wheels on the belt have no connection with lift at all other than the fact that they will produce drag that will reduce the effect of the limited airflow produced by the belt.

The real question is does the movement of the belt produce enough airflow to generate lift? The short answer it depends on how fast the belt is going and how heavy the aircraft is.

||| · 24-10-2007, 02:07 PM

i just watched this video but it didnt have an answer

the_scotsman · 24-10-2007, 02:11 PM

Quote:

Originally Posted by mowog

The moving belt will produce airflow it cant help but so. The wheels on the belt have no connection with lift at all other than the fact that they will produce drag that will reduce the effect of the limited airflow produced by the belt.

The real question is does the movement of the belt produce enough airflow to generate lift? The short answer it depends on how fast the belt is going and how heavy the aircraft is.

Airflow produced by the belt? WTF? You must be watching a different channel...airflow is produced as the aircraft moves along the conveyor, as it does normally moving along a runway...

Please watch this video..a little crude but it demonstrates the principal exactly...

http://www.youtube.com/watch?v=-EopVDgSPAk

3vXT · 24-10-2007, 02:25 PM

In theory, it doesn't matter how fast the belt is going. It could be going a million KPH all that would change on the plane is the wheel speed which is irrelevant.

NA XR6 · 24-10-2007, 02:32 PM

No it wont take offfffffffffffffffffffffffffffffffffffffffffffffff

Windza · 24-10-2007, 02:45 PM

I really can't believe such a ridiculously simple question can generate a thread this long - the biggest issue people are having is in the wording ! It says simply - "if the plane is travelling at take-off speed"... well speed is relative, so if you're talking take-off speed relative to the conveyor belt than NO - the plane cannot lift off as the air speed will be too low... BUT if the speed is relative to the air than YES it can and will take-off. All said and done - no more arguing, no more debate - that's it !!!! And forget the rot about how it's propelled - doesn't come into it - we know its at take-off speed, we just have to assume what that speed is relative to !

aye you · 24-10-2007, 02:59 PM

lol, this has 2 answers, yes and no, but under different condititions.

1) If the converyor belt is matching the theoritical forward mometum of the aircraft, thus leaving the aircraft stationary (eg, place a barrier in front and behind the aircraft and it does not move into either) their is no possibility to generate lift. remember the only pure frictionless surface is Ice so the aircraft will excert a force to maintain its position, i'm interpreting people as saying that the aircraft could be placed onto the belt and maintain position with out exerting a force. In this situation, no forward motion will not provide airflow to the wings. As someone said in the other thread, if you run on a treadmill but maintain position, do you feel wind in your face (no, fans and open windows with a breeze do not count)?

BUT

2) If the velocity of the converyor belt is constant, due to minimal effect of friction in the wheels and providing the aircraft has enough thrust (which i'm pretty sure it would lol) then the aircraft will have to exert some effort to remain in position, but eventually will begin to travel forward, as the thrust moving rearward will exceed the velocity of the belt, it will eventually reach takeoff speeds, in basically the same distance as a conventional take off. The aircraft moves forwards relative to the earth, gains momentum thus velocity (as P(momentum) = M(mass) X V(Velocity), P & V are directily related) this will inturn allow take off because the aircraft is moving forwards along the belt, thus negating the effect of the belts velocity

Windza · 24-10-2007, 03:11 PM

Quote:

Originally Posted by aye you

lol, this has 2 answers, yes and no, but under different condititions.

1) If the converyor belt is matching the theoritical forward mometum of the aircraft, thus leaving the aircraft stationary (eg, place a barrier in front and behind the aircraft and it does not move into either) their is no possibility to generate lift. remember the only pure frictionless surface is Ice so the aircraft will excert a force to maintain its position, i'm interpreting people as saying that the aircraft could be placed onto the belt and maintain position with out exerting a force. In this situation, no forward motion will not provide airflow to the wings. As someone said in the other thread, if you run on a treadmill but maintain position, do you feel wind in your face (no, fans and open windows with a breeze do not count)?

BUT

2) If the velocity of the converyor belt is constant, due to minimal effect of friction in the wheels and providing the aircraft has enough thrust (which i'm pretty sure it would lol) then the aircraft will have to exert some effort to remain in position, but eventually will begin to travel forward, as the thrust moving rearward will exceed the velocity of the belt, it will eventually reach takeoff speeds, in basically the same distance as a conventional take off. The aircraft moves forwards relative to the earth, gains momentum thus velocity (as P(momentum) = M(mass) X V(Velocity), P & V are directily related) this will inturn allow take off because the aircraft is moving forwards along the belt, thus negating the effect of the belts velocity

What the ? Dude - all this is pointless - we already know the aircraft is travelling at "take-off speed"... forget momentum and all the other blather... read my earlier post - all we need to know is what the "take-off speed" is relative to, then its a simply Yes or No!

flappist · 24-10-2007, 03:13 PM

FFS All the theory experts......

If the aircraft is at rotational velecity then that is a speed relative to AIR, not ground, not conveyers and not even stupid school kids who saw this question on other fora.

The ground speed is irrellevent.

In the theoretical example posed and axiom must be applied to allow this to work. This axiom is "No Friction". If there is friction then it will be a race between the belt overheating and melting or the wheels overheating and melting.

The example is further flawed in that the speed on the belt must be infinite. The aircraft has no relavence to the belt other than by fricton from the wheels which in then selves have no power applied. As the aircraft is moving at "takeoff speed" the belt is trying to compensate for this by moving backwards. This will only make the wheels spin faster and as there in not friction in the bearings it will not affect the aircraft's velocity.
The belt will increase to infinity and the wheels will spin at infinite RPM and the plane will just do the same as it would on a fixed surface i.e. TAKE OFF.

N.B. I do fly AND have studied physics and engineering at Uni.........

PS. Aye you, I see from your profile you are doing CPL training. From your replies I would recommend you only apply for jobs in asian or african airlines.

sfr rob · 24-10-2007, 03:15 PM

Quote:

Originally Posted by LTDHO

This was posted last year or something.

As the wheels do not move the plane but the thrust does.
So the plane will fly with the wheels spinning at twice plane speed.

close thread

yeah more like 2 years ago hey!?

Oh, and no.... it wont "take off" .

:

ardei · 24-10-2007, 03:18 PM

aye you makes a really good point!

The question is very vague in saying the "conveyor belt matches the speed of the plane". If you take this literally, this means that initially, the plane and conveyor belt are stationary. As the plane starts to move, the conveyor belt does and so the plane remains stationary. So TECHNICALLY, the conveyor belt must stop as the plane has zero velocity. This process will repeat as if bunny-hopping a car.

That's just an example of the different situations you can interpret it as! So since the question is so vague, there is no real answer.

sfr rob · 24-10-2007, 03:19 PM

Quote:

Originally Posted by ardei

aye you makes a really good point!

The question is very vague in saying the "conveyor belt matches the speed of the plane". If you take this literally, this means that initially, the plane and conveyor belt are stationary. As the plane starts to move, the conveyor belt does and so the plane remains stationary. So TECHNICALLY, the conveyor belt must stop as the plane has zero velocity. This process will repeat as if bunny-hopping a car.

That's just an example of the different situations you can interpret it as! So since the question is so vague, there is no real answer.

Yeah, might as well have asked, how long is a piece of string!

falzoony · 24-10-2007, 03:20 PM

Quote:

Originally Posted by Windza

I really can't believe such a ridiculously simple question can generate a thread this long - the biggest issue people are having is in the wording ! It says simply - "if the plane is travelling at take-off speed"... well speed is relative, so if you're talking take-off speed relative to the conveyor belt than NO - the plane cannot lift off as the air speed will be too low... BUT if the speed is relative to the air than YES it can and will take-off. All said and done - no more arguing, no more debate - that's it !!!! And forget the rot about how it's propelled - doesn't come into it - we know its at take-off speed, we just have to assume what that speed is relative to !

Thats what I was thinking.
The question say that if the treadmill was going the same speed but reverse to the plane, that would mean the plane isn't movining anywhere. It's the same as when you run on a treadmill, you don't actually go anywhere.
As for actually getting airbourne, I have got no idea as I know nothing about physics.

aye you · 24-10-2007, 03:20 PM

Quote:

Originally Posted by Windza

...we already know the aircraft is travelling at "take-off speed"... forget momentum...

ah, this would be what i miss the whole time, thanks mate, i was assuming the aircraft was starting from a stationary position. but its makes sence now, the whole aircraft is at takeoff speeds, so your saying the wings have the required airflow over them, correct? i guess this is why you should never assume, cause it makes an *** out of U and ME lol.

Flappist, im a pilot too, but didn't read the question properly, Windza and Flappist, cheers guys, makes more sence

Perana · 24-10-2007, 03:22 PM

It will fly.. now close the thread.

BTW they are apparently going to prove this on Mythbusters soon...

Walkinshaw · 24-10-2007, 03:30 PM

The question can not be answered unless the following is made clear.

Reletave to what is the aircraft's velocity measured against?

(aircraft speed is traditionaly calculated against the air, hence if the aircraft is traveling at "take off speed" the speed of air moving across the wings is sufficent to provide enough lift for take off, hence it will fly. The wheels/road speed of the aircraft matters naught)

PS: People are dumb

flappist · 24-10-2007, 03:37 PM

Quote:

Originally Posted by ken2903

I got this from another forum and am curious about what people on here think.

If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?

The key to this is the concept that those who do not fly are missing.

Take off speed and for that matter any speeds concerned with the operation of an aircraft are relative to air nothing else. It is not a constant
It is called indicated air speed as it is affected by temperature and pressure. e.g. On a nil wind day temp or 45deg and QNH of 950 you will need to be going a lot faster relative to the ground than at 5 deg and a QNH of 1020 to maintain the SAME indicated airspeed (the reading shown on the ASI from which you determine when to rotate).

So basicly if you are at "take off speed" then that is what you will do (or wheelbarrow).

Poorboy_racer · 24-10-2007, 03:46 PM

Ok. not getting into the plane debate.
How dose a handbrake turn work? Lock up the rear wheels (front wheel drive car) and they come round faster. Where dose that extra power come from? Why when a bike seizes dose the back wheel try and catch the front, how come the wheel moves faster in relation to the ground locked up than when it was turning. My head hurts!! :(

farmernz · 24-10-2007, 03:59 PM

if it wre true why dont aircraft carriers just have a conveyer to launch from?

flappist · 24-10-2007, 04:05 PM

Quote:

Originally Posted by farmernz

if it wre true why dont aircraft carriers just have a conveyer to launch from?

They do....

They accellerate the ship up to 200kts and the F14s just float upwards........

BlackLS · 24-10-2007, 04:09 PM

Quote:

Originally Posted by Poorboy_racer

Ok. not getting into the plane debate.
How dose a handbrake turn work? Lock up the rear wheels (front wheel drive car) and they come round faster. Where dose that extra power come from? Why when a bike seizes dose the back wheel try and catch the front, how come the wheel moves faster in relation to the ground locked up than when it was turning. My head hurts!! :(

Dude all these doses are making my head hurt. Does!

Its because your front tyres are offering grip, and the rears aren't. Thats why a car skidding does not offer better braking compared to a car with ABS. Its not extra power, its a transfer of weight.

Plane: It will take off. All the aircraft has to do is overcome the reletivly minute friction of its wheel bearings freewheeling via thrust from jet/propeller and its just like a regular take off.

Poorboy_racer · 24-10-2007, 04:45 PM

Sorry about my poor spelling...lost without spell check :( (result of modern times)

Ok I understand if you throw a car into a corner the rear wheels are trying to stop the car from going sideways and if they break traction by pulling on the handbrake the rear will swing out. But thought there was something in physics (not my best subject) that stated all energy was constant or something like that. Where dose the extra energy allowing the rear to swing faster when traction is broken come from? Something to do with Potential energy ? such as the energy stored on a car on top of a cliff. Not moving or exerting any energy until the moment its pushed over then a lot of moving or Canettic (spelling) energy is present until it hits the ground. Maybe Im just thinking about it too much or just plane thick!!

Windza · 24-10-2007, 04:46 PM

I really can't get over this thread - it actually astounds me that soooo many ppl could argue/debate over what is a very simple concept (albeit poorly worded)... and PLEASE don't stoop to giving qualifications and nonsense like "I'm a pilot with a PhD in ..." to support your answer - just makes you seem very "unprofessional". Having said my piece - I'm out... enjoy, get frustrated with it but remember - never underestimate the power of stupidity in numbers !!!

flappist · 24-10-2007, 04:52 PM

Quote:

Originally Posted by Windza

I really can't get over this thread - it actually astounds me that soooo many ppl could argue/debate over what is a very simple concept (albeit poorly worded)... and PLEASE don't stoop to giving qualifications and nonsense like "I'm a pilot with a PhD in ..." to support your answer - just makes you seem very "unprofessional". Having said my piece - I'm out... enjoy, get frustrated with it but remember - never underestimate the power of stupidity in numbers !!!

But if you don't say your qualifications how do they know your not just an e-mutant keyboard warrior from outback queensland?

Windza · 24-10-2007, 04:54 PM

In reply to the swinging/braking car thing - there's no "extra" energy... the only energy the car possessed was due to momentum which is primarily dissipated through friction/heat (tyre smoke, hot brake pads) and sound (squealing tyres). The "swinging" effect is also balanced/conserved (for want of a better word) in that the "overall" or "average" speed of the vehicle is always decreasing (even if the back end does swing fast, the front is slowing rapidly)... hard to follow in text but hopefully you can get the gist of it...

Windza · 24-10-2007, 04:56 PM

Quote:

Originally Posted by flappist

But if you don't say your qualifications how do they know your not just an e-mutant keyboard warrior from outback queensland?

Believe me - the answer will speak for itself - and some already have... I laugh rather hard at some of the attempts to mimic technical explanations... it falls flat

plext · 24-10-2007, 04:57 PM

It should be patently obvious to anyone with any sort of physics understanding that this thread is worthless and was never going to fly.

View Poll Results: If the conveyor belt is matching the planes 'take off' speed but in reverse?
Yes it will get airborne.	20	58.82%
No it wont get airborne.	14	41.18%
Voters: 34. You may not vote on this poll