plane question

[Dkerwood]

Well, like Bob said, there's no engines for the wheels on an airplane.

Accelerations are due to forces. The force supplied by the conveyor comes through the friction in the wheels. If you look above there's a calculation pertaining to this.

...There's no way that it can do this through friction (and hence there's no way it can do it).

... There is no way for the conveyor to impart a sufficient amount of force through the wheels. The friction is too small.

...We don't have to consider this because the conveyor is unable to hold the plane at rest in the first place.

...The plane doesn't require a vertical force to take off. The thrust from the engines is more than sufficient.


I doubt that. Have you ever seen a plane land? 747 wheels go from 0 to more than a hundred miles perhour at the instant of landing and it doesn't crash. They leave nice rubber marks and make some smoke, but unless they are in very bad shape and explode, there's no danger to the aircraft.

Geez, Geoff. Calm down. I was just operating under the assumption that planes had some sort of engines powering the wheels, and thus would have significantly more friction than free spinning wheels (as gears, etc, began to catch). Thanks for repeating yourself, though.

 

[Bob Lee (QSC)]

Hi Bob...I remembered you were another airplane junkie.

Hi! Yup, in fact one of my non-music hobbies at home is to get on MS Flight Simulator, choose an interesting pair of airports, some interesting equipment, set up some interesting weather (or go with real-life weather downloaded from Jeppesen), file an IFR plan, and fly it. There are some pretty good Web sites for downloading additional scenery, planes, etc.

 

[bmc]

Hi! Yup, in fact one of my non-music hobbies at home is to get on MS Flight Simulator, choose an interesting pair of airports, some interesting equipment, set up some interesting weather (or go with real-life weather downloaded from Jeppesen), file an IFR plan, and fly it. There are some pretty good Web sites for downloading additional scenery, planes, etc.

Do a search for aircraft desiger Bill Black over at fltsim.com. He diesiged a Grumman Goose for me and painted it in the colors of a Goose my dad flew during WW2. We've become great internet friends over the past 10 years but have never met. Very very good aircraft designer.

...we now resume our normal TV programming.

 

[Bob Lee (QSC)]

Do a search for aircraft desiger Bill Black over at fltsim.com. He diesiged a Grumman Goose for me and painted it in the colors of a Goose my dad flew during WW2. We've become great internet friends over the past 10 years but have never met. Very very good aircraft designer.

...we now resume our normal TV programming.

Cool! I sent that info to my home e-mail so I can search for him.

My wife has gotten used to hearing ATC sounds coming from our computer.

 

[CBRStingray]

I withdraw my original post. I just realised I was wrong

The plane would take off. Engine produce thrust. Engine thrust is a force that essentially pushes against the air, not the ground. The plane would still take off unless you removed the air.

 

[Bob Lee (QSC)]

I withdraw my original post. I just realised I was wrong

The plane would take off. Engine produce thrust. Engine thrust is a force that essentially pushes against the air, not the ground. The plane would still take off unless you removed the air.

The engines require oxygen in the air to combust the fuel, and the wing requires air flow to create lift, but engine thrust does not work by pushing against air. A jet engine produces thrust because the heat released by combustion drastically expands the gases in the engine, which have nowhere to escape but out the exhaust in the back. So hurtling the mass of hot gases backwards causes an equal and opposite reaction (one of Newton's laws of thermodynamics, but I don't remember which one): the engine pushes forward, exerting a force on the mass of the plane.

When Robert Goddard spoke of one day using rocket propulsion for travel outside of the Earth's atmosphere, he was pooh-poohed by many who thought, wrongly, that even a rocket could not function in a vacuum like outer space because it had no air to "push" against.

 

[Geoff St. Germaine]

Geez, Geoff. Calm down. I was just operating under the assumption that planes had some sort of engines powering the wheels, and thus would have significantly more friction than free spinning wheels (as gears, etc, began to catch). Thanks for repeating yourself, though.

No problem. If the same argument wasn't repeatedly brought up I guess I wouldn't have to. And don't worry, I'm plenty calm.

 

[Geoff St. Germaine]

The engines require oxygen in the air to combust the fuel, and the wing requires air flow to create lift, but engine thrust does not work by pushing against air. A jet engine produces thrust because the heat released by combustion drastically expands the gases in the engine, which have nowhere to escape but out the exhaust in the back. So hurtling the mass of hot gases backwards causes an equal and opposite reaction (one of Newton's laws of thermodynamics, but I don't remember which one)...

Newton's third law of motion. Newton doesn't have any laws on thermodynamics. Newton wasn't down with entropy.

 

[AxtoOx]

Someone needs to go to google and cut and paste the answer before this gets to 11 pages. People are still making the same mistake I did they think the plane is stationary. That's why the question is decieving, yeah it says the conveyor spins at the same rate as the plane leaving you to assume the plane is stationary, it never says the plane is.
Like Geoff says, this is not a new question, and it got me.
I don't know how to word it or I'd do it.

 

[Bob Lee (QSC)]

Newton's third law of motion. Newton doesn't have any laws on thermodynamics. Newton wasn't down with entropy.

Ah, that's it. Thanks.

I get the laws mixed up because I'm not a lawyer.

 

[CBRStingray]

The engines require oxygen in the air to combust the fuel, and the wing requires air flow to create lift, but engine thrust does not work by pushing against air. A jet engine produces thrust because the heat released by combustion drastically expands the gases in the engine, which have nowhere to escape but out the exhaust in the back. So hurtling the mass of hot gases backwards causes an equal and opposite reaction (one of Newton's laws of thermodynamics, but I don't remember which one): the engine pushes forward, exerting a force on the mass of the plane.

When Robert Goddard spoke of one day using rocket propulsion for travel outside of the Earth's atmosphere, he was pooh-poohed by many who thought, wrongly, that even a rocket could not function in a vacuum like outer space because it had no air to "push" against.

I didn't know how to explain thrust, so I didn't bother trying. Instead I said something stupid like 'thrust pushes against air' When I said 'remove the air and the plane won't fly', I meant because it wouldn't produce lift, not because the engine requires air to push against.

 

[AxtoOx]

Here you go,[Invalid or Expired Link Removed]

 

[Davidoc]

Here you go,[Invalid or Expired Link Removed]

Good explanation.

 

[Geoff St. Germaine]

Here you go,[Invalid or Expired Link Removed]

Notice how people still try to disagree. One guy explains it with physics and others disagree based on some sort of intuition.

Here's another one:
http://www.physicsforums.com/showthread.php?t=101259&highlight=plane+conveyor
Another:
[Invalid or Expired Link Removed]
And another:
[Invalid or Expired Link Removed]

 

[AxtoOx]

Notice how people still try to disagree. One guy explains it with physics and others disagree based on some sort of intuition.

Here's another one:
http://www.physicsforums.com/showthread.php?t=101259&highlight=plane+conveyor
Another:
[Invalid or Expired Link Removed]
And another:
[Invalid or Expired Link Removed]

Hey, I argued the heck out of it myself. So I can't talk. It does make me feel better that a lot of pilots got it wrong too.

 

[theshadow2001]

Ok I didn't read the last 40 odd posts I appologise.

Ok to the people that say it will take of do they agree the plane won't move until it reaches its take off speed?

Will a plane take of with its breaks on i.e going nowhere and the engines shoving enough air to get it to take off speed?
Say the plane will take off with an air speed of 40 mph going straight at the wings and there's no wind.When I say the plane speed I'm saying that this would be the speed of the plane were it not on a conveyor. When I say the plane is moving I mean relative to the ground


The plane starts at 0 mph. It then changes speed to ten miles an hour the belt is moving it back at ten miles an hour the plane is stationary. 10 mph isn't moving fast enough to get it off the ground conveyor or no conveyor. There is no air flowing under the wings.

The plane moves to 20 miles an hour the conveyor moves to 20 mph.The plane can't take off conveyor or no conveyor. The plane remains stationary. There is absolutley no lift generated so far.

If there were no conveyor some lift would be generated at this point

The plane moves to 40 mph its take off speed. However its still stationary. There has been no lift generated up to this point. So there has been no upwards force on the plane to fight or push up on its weight against gravity.
So the plane is still exerting the same force on the ground as when it was at zero mph.

In fact in order for the plane to take off its engines are going to have move 40 mph faster than the conveyor belt is traveling. This can never happen because the conveyor matches the speed of the plane constantly.

Now if you don't believe me just go back to my example start at ten where the plane isn't moving forward and there's no lift and increase the speed of the plane by an amount then ask yourself does the plane move forward? If the answer is no then there will be no upwards force exerted on the plane.

Keep moving up in small increments, as small as you like until you get to 40 mph, the take off speed, each time ask is the plane moving? If it's not there's no upwards force.

This is a very nice brain excercise(the question that is) and I bet some 5 year old kid fist asked it to someone.

 

[Tired_Thumb]

I'm an active private pilot and advanced ground instructor. To the best of my knowledge, if the plane is staying in one spot and there is no induced airflow the plane will not lift off. The coveyer / tire rotation speed has absolutely no direct bearing on whether the aircraft will take off or not, it's all in the true airspeed.


Reminds me of Piper Cubs in a 40 kt headwind. It's not uncommon to see a Piper driver commence takeoff roll, lift off, travel backwards, and land in the same spot of which takeoff roll was commenced. Easy way to complete the three takeoffs/landings in ninety days requirement for carrying passengers if you can't make it up to O'Hare field in the middle of the night and do three stop-and-go's in a row on 32L.

 

[AxtoOx]

Ok I didn't read the last 40 odd posts I appologise.

Ok to the people that say it will take of do they agree the plane won't move until it reaches its take off speed?

Will a plane take of with its breaks on i.e going nowhere and the engines shoving enough air to get it to take off speed?
Say the plane will take off with an air speed of 40 mph going straight at the wings and there's no wind.When I say the plane speed I'm saying that this would be the speed of the plane were it not on a conveyor. When I say the plane is moving I mean relative to the ground


The plane starts at 0 mph. It then changes speed to ten miles an hour the belt is moving it back at ten miles an hour the plane is stationary. 10 mph isn't moving fast enough to get it off the ground conveyor or no conveyor. There is no air flowing under the wings.

The plane moves to 20 miles an hour the conveyor moves to 20 mph.The plane can't take off conveyor or no conveyor. The plane remains stationary. There is absolutley no lift generated so far.

If there were no conveyor some lift would be generated at this point

The plane moves to 40 mph its take off speed. However its still stationary. There has been no lift generated up to this point. So there has been no upwards force on the plane to fight or push up on its weight against gravity.
So the plane is still exerting the same force on the ground as when it was at zero mph.

In fact in order for the plane to take off its engines are going to have move 40 mph faster than the conveyor belt is traveling. This can never happen because the conveyor matches the speed of the plane constantly.

Now if you don't believe me just go back to my example start at ten where the plane isn't moving forward and there's no lift and increase the speed of the plane by an amount then ask yourself does the plane move forward? If the answer is no then there will be no upwards force exerted on the plane.

Keep moving up in small increments, as small as you like until you get to 40 mph, the take off speed, each time ask is the plane moving? If it's not there's no upwards force.

This is a very nice brain excercise(the question that is) and I bet some 5 year old kid fist asked it to someone.

Not trying to be rude, but did you read the links? The conveyor is irrelevent. It's a trick question. The plane still moves and gains lift and air speed.

 

[Tired_Thumb]

Ad to my last post, even this pithy advanced ground instructor got stumped (great question for CFI exams though ). Yes, the engines produce thrust against the ambient air, not the ground. Thus, the conveyer can move at ten million miles an hour, and provided there's little to no friction in the tirewells themselves, the plane can still lift off.

 

[theshadow2001]

I'm sorry I don't have time right now to read through the ohter forums right now. If you would be so kind to tell me which one of the posts does the explaining I would be happy to read it though. I have no problems with being prooved wrong and I would think it's great to see what the answer really is

Just one more thing. The jet engine is only ever doing enough to keep the plane stationary realtive to the ground. If the plane is stationary it can not take off. If the engines were blowing air on to the wing then it could take off however the engine blows air behind the plane and it's the reaction force of that air that moves the plane forward. That reaction force is only enough to keep the plane at the same speed as the conveyor and thus keeping it stationary

Why does an aircraft carrier need a runway. Why not keep the plane stationary until it's engine is doing enough for it to take off? Because if its not moving it wont take off.

Again apologies for not reading but will come back later and have some humble pie if need be.