conveyor belt and plane answered at last ??

[rjm2k]

And the question is not about jets but prop engines, that need an air flow to get off the ground.

All forms of plane need airflow to get off the ground.

 

[joe-90]

It's all a red herring. The engine is creates thrust amd powers the engine forward. The wheels can do what they like - they don't come into the equation.

 

[AronSearle]

Take a treadmill running at 5mph, if you stand on it you'll go flying of the end at 5mph, now for the clever bit.

Now stand on that same treadmill with roller skates, and hold onto the bars.

Not going anywhere are you?

Now pull yourself forward with your arms, moving forward aren't you.

Your arms are a separate force from the wheels, just as the engines on a plane are. the wheels can do what they want.

And the question is not about jets but prop engines, that need an air flow to get off the ground. icon_rolleyes.gif

You have been outsmarted by joe-90, your argument is invalid.

Jet, prop engines, rocket engines, same thing, they pull the plane forward, not the wheels.

Next you will be telling me air doesn't go through propellers if the wheels are spinning backwards.

 

[doitall]

Take a treadmill running at 5mph, if you stand on it you'll go flying of the end at 5mph, now for the clever bit.

Now stand on that same treadmill with roller skates, and hold onto the bars.

Not going anywhere are you?

Now pull yourself forward with your arms, moving forward aren't you.

Your arms are a separate force from the wheels, just as the engines on a plane are. the wheels can do what they want.

Of course you're not going anywhere because you are exerting a opposite force to keep in the same position, exactly the same as an engine.

If you gradually increase the speed of the tread mill, eventually it would pull your arms off or your feet would leave the ground, eventually you'd go backwards.

 

[AronSearle]

Of course you're not going anywhere because you are exerting a opposite force to keep in the same position, exactly the same as an engine.

So you are saying that a treadmill can, by spinning free-wheels backward, apply a proportional opposite force as an air plane engine.

Cool story bro~

If you gradually increase the speed of the tread mill, eventually it would pull your arms off or your feet would leave the ground

You could crank that treadmill up to 11, and with your little finger, you could still pull yourself forward on skates.

But sure, propeller engines that provide hundreds or thousands of pounds of thrust, couldn't compete with the friction of a ball bearing free-wheel.

Man it's fun watching you be silly.

 

[Nige F]

Like I said in the last , umpteen pages long thread Let`s get a seaplane on an endless pool

 

[doitall]

I don't need to be silly.

If you stand a plane on the tread mill it we go backwards the speed of the belt, to get it stationary you would need to exert and equal force in the opposite direction to the planes travel.

Note all the time the plane is stationary on the belt the wheels are not turning, yet it's going backwards at 100mph.

To stop the travel you need to apply 100mph force in the opposite direction.

Now look at the question and read it, the belt and the wheels must be the same speed

 

[AronSearle]

replace the runway with free-spinning wheels

replace the wheels on the plane for a conveyor belt.

Turn on the engines.

Does the conveyor belt on the plane gain enough traction on the free-spinning wheels to stop the engines pulling the plane foward.

to get it stationary you would need to exert and equal force in the
opposite direction to the planes travel.

So how fast does the conveyor belt have to spin, for the friction on the ball bearings in the free-spinning wheels to be an equal force to the thousands of pounds of thrust on the engines?




Do you think when planes land that they don't need brakes, that the friction on the free spinning wheels is enough to stop them?

You are a silly sausage.

 

[doitall]

As a pilot I know exactly how to fly and land an aircraft thank you

All irrelevant if you read the original question properly.

For the plane to take off the wheels have to go faster than the conveyor.

Not allowed.

 

[Norcon]

The original question as everyone knows was flawed. Pointed out upteen
times by posters on here including physicists and highly academic professors.
So until some professor rewrites the original question then this argument will continue going down separate paths.

 

[doitall]

The original question as everyone knows was flawed. Pointed out upteen
times by posters on here including physicists and highly academic professors.
So until some professor rewrites the original question then this argument will continue going down separate paths.

Or a trick question.

The fact remains the plane cannot take off, without re-wording the question.

 

[Deleted member 63160]

Hands up, all those that think free wheeling wheels can brake 120,000lb of thrust.

Hard to believe but some do.

 

[crank39]

My take on it is this....

First, do a test run to find the speed required for lift off and also the engine rpm for that given speed, for the purposes of this explanation we'll just say it's 100mph and 5,000rpm

Now, put plane on conveyor belt, gradually build up conveyor belt speed to 100mph along with plane engine rpm to 5,000rpm.

This is the point the plane would want to take off (if it were going forward) but it can't because there is obviously
NO airflow over the wings.

Now this is where the confusion i believe sets in, IF you go beyond the 5,000rpm engine speed then you will of course start to overcome the force of the conveyor and the plane WILL start to move or creep forward, but it still won't or can't take off as it needs more airflow, technically you would need to trottle up to 10,000rpm just to achieve the 100mph target to get lift.

The wheels would of course be traveling at 200mph, 100mph because of the conveyor and a further 100mph forward motion in order for the plane to take off.

Of course though the original myth was that the conveyoe speed was matched with the take off speed/engine rpm......in which case the plane would not and could not take off, if you look closely at the mythbusters clip of the full scale experiment you will see the plane throttle up beyond the point and start to gain forward momentum thus gain lift, this was specifically not what the myth was all about, we all know it would take off if it could overcome the conveyor but the rules stated if the speeds were 'matched', that is clearly NOT what mythbusters did

 

[doitall]

The wheels were also on solid ground with a sheet of something under the wheels, therefore the weight of the plane was on the ground and not the conveyor.

Take off for a light aircraft is 2400rpm and a ground speed of 85knots.

 

[joe-90]

Why are you lot so dumb? The plane is propelled forward because Newton's Law of Motion says it must be. The only difference between taking off on a runway and a conveyor is that on the conveyor the wheels would turn at twice the speed. But so bloody what?