Skill's weekend teaser

[MrGecko]

Mr charts, you could put a 747 in a wind tunnel and it would take off if the air was moving over the wings fast enough - all with the engines off.

 

[Mr. Charts]

Did I say the towed aircraft wouldn't take off?
Nope.
I said,
"Air speed and therefore flight would be limited without engine power......."

 

[Skill Leverage]

But they wouldn't be limited, at all. The only thing limiting them in that instance is how hard the plane is being pulled.

 

[Mr. Charts]

Indeed MrGecko, and I have seen a few wind tunnels, I merely implied by saying,
"Air speed and therefore flight would be limited without engine power......."
that it wouldn't travel far.
Richard

 

[barjon]

mmmm, ok then:

1. If this flippin' conveyor belt is frictionless then when the thrust is applied the wheels won't turn at all and the ruddy plane will just skid along the belt and take off when airspeed is reached.

2. With friction involved when the thrust is applied the plane rolls along the ground on its wheels and its forward motion is measured by the turn of those wheels. If the ground (conveyor belt) underneath the wheels moves backwards to the same degree then the damn plane remains motionless. Unless...

3....... the applied thrust is so great as to overcome friction and cause the wheels to skid as well as turn in which case the forward motion is no longer measured by the turn of those wheels and the poor old abused plane will move forward until it reaches airspeed and takes off.

 

[Mr. Charts]

"It" being the aircraft in the original question powered by jet engines, not a glider.
They behave differently once the motive force is not operating.

 

[Skill Leverage]

"It" being the aircraft in the original question powered by jet engines, not a glider.
They behave differently once the motive force is not operating.

Who ever said that the motive force wasn't in effect?

 

[Mr. Charts]

Oh barjon, stop trying to use your brain, you'll get abused

 

[Skill Leverage]

mmmm, ok then:

1. If this flippin' conveyor belt is frictionless then when the thrust is applied the wheels won't turn at all and the ruddy plane will just skid along the belt and take off when airspeed is reached. there is friction between the wheels and the belt, but not between the wheels and their axels. If you look again I said the co-efficients of the belt and the tarmac were the same. I acknowledge the OP could have been worded slightly better

2. With friction involved when the thrust is applied the plane rolls along the ground on its wheels and its forward motion is measured by the turn of those wheels. If the ground (conveyor belt) underneath the wheels moves backwards to the same degree then the damn plane remains motionless. Unless...this is the point that you, and everyone else who got it wrong can't understand - a plane's forward motion has nothing to do with how fast its wheels are spinning.

3....... the applied thrust is so great as to overcome friction and cause the wheels to skid as well as turn in which case the forward motion is no longer measured by the turn of those wheels and the poor old abused plane will move forward until it reaches airspeed and takes off. See above

.

 

[Mr. Charts]

Who ever said that the motive force wasn't in effect?

"if someone pulled on the plane hard enough they are exerting horizontal force, which is exactly the same as the thrust provided by a jet. If another plane towed this one off the runway with the same force its engines would provide, "

I take that to imply the motive force was not supplied by the jet's engines.

Got to go and trade for my living now with the US opening shortly, much fun as this thread has been

 

[Skill Leverage]

No, the motive force is now coming from the plane towing it... I mean, this is really basic stuff.

 

[Mr. Charts]

"I acknowledge the OP could have been worded slightly better"
Aha !

 

[Mr. Charts]

Perhaps then there wouldn't have been quite so much disagreement.
Basic stuff, I reckon.

 

[Skill Leverage]

Charts stop being a sarcastic twat; you do not even understand the concept, I am acknowledging that there could have been better wording but in no way would it affect an intelligent person's understanding of the question; most people do not have to have it spoonfed to them like I have had to do with you.

'The plane might have been getting towed'... Most people would assume that, unless written, the plane is, in fact, not being towed. Ever. I'd hate to have to try and mark your physics exams at school, they were doubtless just a string of irrelevant questions that only confused you more about how wrong you are.

 

[ezreddy]

Just to show that Bramble/ezreddy or whoever that may be actually does understand the problem, I would like to rephrase the initial problem. Overall, this has actually been a fun exercise for the brain and a nice respite from work. Here is the same question phrased in a different manner:

Imagine an airplane sitting on a very large conveyor belt. The belt has the same dimensions as a runway at an airport. Assume no wind and that the required ground speed for this airplane to take off is 180 km/hr. The conveyor can reach a speed of 300 km/hr from a dead standstill in 4 seconds and is set to run in the opposite direction of the aircraft takeoff. For this exercise, the friction within the wheels of the aircraft is negligible at a speed up to 700 km/hr. The coefficient of friction for the conveyor belt is the same as that of a typical runway (both starting and sliding friction). The aircraft has no maintenance issues and will typically achieve its required speed of 180 km/hr using three quarters of the runway. If the aircraft were to attempt a takeoff and the conveyor were started up one second after (edit in) the airplane began forward motion(completed edit) this attempt, what would happen?

This aircraft will take off using the normal amount of runway (unless the pilot has been drinking).

 

[barjon]

"this is the point that you, and everyone else who got it wrong can't understand - a plane's forward motion has nothing to do with how fast its wheels are spinning."

I didn't say that Skill. While the plane is on the ground its forward motion (or "distance of travel" if you like) is measured by the turn of the wheel. Say the wheel's circumference is 20 feet then the plane will have move forward by 20 feet after one revolution - if the ground underneath the wheel has moved backwards by 20 feet then the plane won't have moved will it?

jon

 

[TheBramble]

This is what you cannot understand:

it takes no more effort to move the plane when the belt is spinning at a million miles an hour than is required when the belt is stationary.

Skills, I'm going to have to leave you shortly as I believe I can see the back of my own head in my rear-view space-time curved mirror, but before I do....

You're on about effort (again). Firget effort. Forget what's possible or likely. You posed a theoretical question.

Skills, for both out sakes just answer this one, simple question. Does any movement transmitted to the wheels of the plane, regardless of HOW that force is transmiitted, cause the wheels to move relative to a fixed reference point off the moving conveyor belt?

 

[Skill Leverage]

"this is the point that you, and everyone else who got it wrong can't understand - a plane's forward motion has nothing to do with how fast its wheels are spinning."

I didn't say that Skill. While the plane is on the ground its forward motion (or "distance of travel" if you like) is measured by the turn of the wheel. Say the wheel's circumference is 20 feet then the plane will have move forward by 20 feet after one revolution - if the ground underneath the wheel has moved backwards by 20 feet then the plane won't have moved will it?

jon

I say again; the plane's forward motion has nothing to do with how many revolutions the wheels have done, are doing, or will do.

 

[Skill Leverage]

Skills, I'm going to have to leave you shortly as I believe I can see the back of my own head in my rear-view space-time curved mirror, but before I do....

You're on about effort (again). Firget effort. Forget what's possible or likely. You posed a theoretical question.

Skills, for both out sakes just answer this one, simple question. Does any movement transmitted to the wheels of the plane, regardless of HOW that force is transmiitted, cause the wheels to move relative to a fixed reference point off the moving conveyor belt?

No. the engine causes the wheels to move relative to a fixed point off the conveyor belt. The belt does nothing but spin the wheels on their axes.

 

[Mr. Charts]

"Charts stop being a sarcastic twat"
I love it. If that is so, thank you for the inspiration and example LOL