Plane and a Treadmill - DPChallenge Forums

Canon EF 17-40mm f/4.0L USM

12/06/2006 04:30:16 PM · #126

Originally posted by jhonan:

Originally posted by Gordon:
You assume the wheel speed and plane speed are somehow connected.

That is true for a car.

Not for a plane.

But they are connected! - Okay, lets say I glued the wheels to the treadmill using an incredibly powerful glue. What then? Are they connected?

pick up a roller skate. Hold it in your hand. Spin the wheels.

How fast is the skate moving forward now ?

Double the speed of the wheels.

How fast is the skate moving now ?

Skate speed and wheel speed are independent.

Same principle. Do the same with the rear wheels of a front wheel drive car.

LoudDog

Canon EOS-350D Rebel XT

12/06/2006 04:30:19 PM · #127

Okay, with the wheels on the landing gear, there is minimal friction between the plane and the ground. To make this easier to understand, it's the same as if the treadmill was coated with ice and the plane was on skies. The treadmill moving has little to no effect on the plane moving.
This is easily demonstrated. if you are at your desk, put your stapler (upsidedown if it has a rubber bottom like mine) on a piece of paper. quickly remove the paper. The stapler hardly moves. Now imagine your stapler had a jet pack on. as you pulled that paper back do your really think you can stop your jet powered stapler from gaining enough speed to achieve lift?

Note, if you put your stapler rightside up on the rubber it would be the same as the plane having it's brakes on, or not on wheels, and if you pull fast enough it still won't move.

12/06/2006 04:30:34 PM · #128

Originally posted by Gordon:

Originally posted by sodoff:

Explain where thrust actually makes the plane go faster than the wheels can go/where the treadmill cannot keep up.

We have. Ad infinitum. Repeating it isn't apparently going to help you get it. You assume the wheel speed and plane speed are somehow connected.

That is true for a car.

Not for a plane.

No, you are assuming. I would like an explanation how you think there is no connection between plane speed and wheel speed. I may be a complete moron, but I understand that an aircraft from standstill can accelerate down a runway until it takes off. But now you are saying that the wheels don't speed up, go faster, whatever...as the plane goes faster. That they are not connected in anyway.

So, why is there a treadmill??

12/06/2006 04:31:06 PM · #129

Originally posted by BrennanOB:

The planes are different in that the could push the air past themselves while stationary relative to the ground.

Urm, that isn't how planes create lift.

Canon EF 100mm f/2.8 USM Macro

12/06/2006 04:31:39 PM · #130

Originally posted by LoudDog:

I want a jet powered stapler.

Spork99

OM System OM-1

12/06/2006 04:31:43 PM · #131

Originally posted by sodoff:

So, why is there a treadmill??

To confuse you.

Sigma 30mm f/1.4 EX DC HSM for Nikon

12/06/2006 04:32:16 PM · #132

Originally posted by Spazmo99:

Originally posted by sodoff:

So, why is there a treadmill??

To confuse you.

Okay, that works for me!!

Zal

Nikon D200

12/06/2006 04:32:20 PM · #133

Originally posted by BrennanOB:

Originally posted by Zal:
That's why they have rear spoilers--they are essentially upside down wings that provide downforce ("upside down lift") to keep the car on the pavement.

Put that F1 on our treadmill and floor the engine. How much downward thrust is being exerted? None. The spoiler works because it cuts through the air. No relative air movment, no push on the spoiler.

And that's EXACTLY how airplane wings work too. A wing has to "cut through the air" in order to generate lift.

12/06/2006 04:32:33 PM · #134

Originally posted by jhonan:

Put a car on a dynamometer (or lift the drive wheels off the ground) and the speedometer may show you going 100 MPH, but would you say the car is moving?

Same thing for a treadmill.

Note that the top of the wheel is moving at twice the speed as the center of the wheel, and the bottom of the wheel is not moving, as it should always be at rest with respect to the ground.

Message edited by author 2006-12-06 16:37:13.

12/06/2006 04:33:05 PM · #135

Originally posted by sodoff:

The aircraft accelerates down the runway. The wheels spin. But the wheels spinning does not accelerate the plane down the runway.

A car accelerates down a runway. The wheels spin. The wheels spinning does accelerate the plane down the runway.

Originally posted by sodoff:

So, why is there a treadmill??

To confuse you ?

Olympus 14-54mm f/2.8-3.5 Zuiko Digital Zoom

12/06/2006 04:33:46 PM · #136

Originally posted by hankk:

Originally posted by jhonan:

Originally posted by Gordon:
You assume the wheel speed and plane speed are somehow connected.

That is true for a car.

Not for a plane.

But they are connected! - Okay, lets say I glued the wheels to the treadmill using an incredibly powerful glue. What then? Are they connected?

Put a car on a dynamometer (or lift the drive wheels off the ground) and the speedometer may show you going 100 MPH, but would you say the car is moving?

Same thing for a treadmill.

Yes, I'd agree entirely if you were talking about a car.

We aren't.

TomH1000

Olympus E-3

12/06/2006 04:34:16 PM · #137

Originally posted by Spazmo99:

Originally posted by Zal:
The "pro-takeoff" people are assuming that the plane will out-accelerate the treadmill, eventually achiive forward motion, and hence lift and takeoff.

No, the treadmill will simply make the wheels spin faster, but it does nothing to retard the forward motion of the plane itself.

You are correct. If the wheels were the power of thrust (like a car) then no, the plane would not fly but, since thrust is achieved by the turbine pushing against the air which is not in anyway tied to the treadmill the plane will fly.

BrennanOB

Canon EOS-1D Mark II

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

12/06/2006 04:36:43 PM · #138

Originally posted by jhonan:

Lift isn't caused by 'pulling air towards' the wings. It's caused by pushing the wings through the air at a high speed

Push the plane forward, or pull the air towards the plane, the same forces will apply themselves. Only their relative speeds matter. If I stand on the wing of a moving plane, or stand in a wind tunnel, though my ground speed is different, the air speed will create the exact same effect because the relative forces don't care which direction the objects ( me and the air ) are moving in as long as the forces are the same the effect will be the same.

Sigma 30mm f/1.4 EX DC HSM for Nikon

12/06/2006 04:37:24 PM · #139

Originally posted by Gordon:

[quote=sodoff]

No, you are assuming. I would like an explanation how you think there is no connection between plane speed and wheel speed. I may be a complete moron, but I understand that an aircraft from standstill can accelerate down a runway until it takes off. But now you are saying that the wheels don't speed up, go faster, whatever...as the plane goes faster. That they are not connected in anyway.

So why is there a treadmill??

Sorry, Gordon, but that doesn't answer my question. I have stated all along that the wheels move at a set speed in relation to the acceleration of the aircraft. The treadmill matches the speed of the wheels, so where is the forward motion coming from?

Zal

Nikon D200

12/06/2006 04:38:11 PM · #140

Originally posted by TomH1000:

Originally posted by Spazmo99:

Originally posted by Zal:
The "pro-takeoff" people are assuming that the plane will out-accelerate the treadmill, eventually achiive forward motion, and hence lift and takeoff.

No, the treadmill will simply make the wheels spin faster, but it does nothing to retard the forward motion of the plane itself.

You are correct. If the wheels were the power of thrust (like a car) then no, the plane would not fly but, since thrust is achieved by the turbine pushing against the air which is not in anyway tied to the treadmill the plane will fly.

But an airplane needs LIFT to takeoff--it doesn't matter how THRUST is generated!!

The only way to generate LIFT is to have airflow over the wings, either by moving the airplane (accelerating down a runway) or by moving the air (wind tunnel where the plane is stationary).

Do we all agree that unless the airplane is physically moving, it will not take off?

Message edited by author 2006-12-06 16:39:52.

12/06/2006 04:38:13 PM · #141

Originally posted by sodoff:

Originally posted by Gordon:
[quote=sodoff]

No, you are assuming. I would like an explanation how you think there is no connection between plane speed and wheel speed. I may be a complete moron, but I understand that an aircraft from standstill can accelerate down a runway until it takes off. But now you are saying that the wheels don't speed up, go faster, whatever...as the plane goes faster. That they are not connected in anyway.

So why is there a treadmill??

Sorry, Gordon, but that doesn't answer my question. I have stated all along that the wheels move at a set speed in relation to the acceleration of the aircraft. The treadmill matches the speed of the wheels, so where is the forward motion coming from?

Yes, you've incorrectly stated that the wheels move at a set speed in relation to the acceleration of the aircraft.

I can't help that.

This is true for a car.

It is not true for a plane.

Wheel speed causes car speed.
Wheel speed does not cause plane speed.

Message edited by author 2006-12-06 16:39:32.

Nikon AF-S DX Zoom-Nikkor 18-70mm f/3.5-4.5G IF-ED

12/06/2006 04:38:36 PM · #142

What is the speed of the plane relative to? What do we consider to have a speed of 0 MPH?

eqsite

Nikon D7100

12/06/2006 04:38:53 PM · #143

Originally posted by Zal:

Do we all agree that unless the airplane is physically moving, it will not take off?

Yes, we all agree that (I hope). The argument is over whether the plane will move forward or not.

Apple iPhone 5

Nikon AF-S DX Zoom-Nikkor 18-55mm f/3.5-5.6 ED

12/06/2006 04:39:28 PM · #144

Originally posted by Gordon:

The aircraft accelerates down the runway. The wheels spin. But the wheels spinning does not accelerate the plane down the runway.

The treadmill applies a horizonal decellerating force to the wheels. I agree that the main force applied on the wheels by the tradmill is rotary, but there is also a (smaller) horizontal force happening. If the treadmill can accelerate enough then the horizontal force can counteract the forward acceleration.

In other words assuming the treadmill can keep up this ridiculously high level of acceleration, and we're talking thousands of miles per hour here, then the force would be enough to hold the plane in place no matter how much thrust you applied.

eqsite

Nikon D7100

Nikon AF-S DX Zoom-Nikkor 18-70mm f/3.5-4.5G IF-ED

12/06/2006 04:39:56 PM · #145

I'd like to turn the question around. How does the treadmill stop the plane from moving forward? How is the force from the treadmill imparted on the plane to counter the force generated by the engines?

12/06/2006 04:40:49 PM · #146

Originally posted by eqsite:

Originally posted by Zal:
Do we all agree that unless the airplane is physically moving, it will not take off?

Yes, we all agree that (I hope). The argument is over whether the plane will move forward or not.

If the airplane is not moving with respect to the air it will not take off. Airplanes have been lifted by hurricane-force winds while parked, but that's a red herring.

12/06/2006 04:40:54 PM · #147

Originally posted by Gordon:

Originally posted by sodoff:
[quote=Gordon] [quote=sodoff]

No, you are assuming. I would like an explanation how you think there is no connection between plane speed and wheel speed. I may be a complete moron, but I understand that an aircraft from standstill can accelerate down a runway until it takes off. But now you are saying that the wheels don't speed up, go faster, whatever...as the plane goes faster. That they are not connected in anyway.

So why is there a treadmill??

Sorry, Gordon, but that doesn't answer my question. I have stated all along that the wheels move at a set speed in relation to the acceleration of the aircraft. The treadmill matches the speed of the wheels, so where is the forward motion coming from? [/quote

Yes, you've incorrectly stated that the wheels move at a set speed in relation to the acceleration of the aircraft.

What do you mean, incorrectly?? Surely this is basic science a 12 year old can understand?

I can't help that.

Nikon AF-S DX Zoom-Nikkor 18-55mm f/3.5-5.6 ED

12/06/2006 04:41:13 PM · #148

Originally posted by jhonan:

In other words assuming the treadmill can keep up this ridiculously high level of acceleration, and we're talking thousands of miles per hour here, then the force would be enough to hold the plane in place no matter how much thrust you applied.

Yes, but the original question does not state that the treadmill matches the force of the plane. If you rephrase it and say force instead of speed, then you are right.

F=ma, for huge a, you can generate a counteracting force which would keep the plane still.

However, the treadmill doesn't match the acceleration force of the plane. It matches the forward speed of the plane, which provides a massively smaller acceleration, consequently a much smaller force, which is vastly overwhelmed by the plane acceleration.

Apple iPhone 5

12/06/2006 04:41:21 PM · #149

Originally posted by hankk:

What is the speed of the plane relative to? What do we consider to have a speed of 0 MPH?

An observer at the side of the runway.