Airplane physics question

I read the first 3 posts only and the answer is YES the aircraft WILL take off. The aircraft IS NOT propelled by its wheels..... Think about it.

 

You read what you wanted to read. The question allows for both possibilities, depending on what conditions you focus on:
- the engines firing up (it moves forward, air flows past wings, there is lift, it takes off) or
- the wheels rotate to match the treadmill (it is not moving, no air flow, no lift, no takeoff).

The question, as stated, poses an impossible situation. Both things cannot happen at the same time: either the engines are off and the wheels can match the belt speed, or the engines are fired up and the wheel and belt speeds do not match. Yet the question says both are happening. Impossible.

In all practical applications, the moment the engines are fired up, it would move and therefore it would take off. The moment it is moving, the wheel speed is not matching the treadmill speed and therefore that condition of the question is broken. While that condition holds, the plane is not moving forward and not experiencing the lift needed to take off.

Stupid question. Someone shoot it and put it out of its misery.

 

You get past the mechanical abilities of the wheel assembly, it will tear itself apart. Friction, heat buildup, bearing seizure, whatever.

But, up to that point, at that point, and even beyond that point, if the thrust from the engines is sufficient, the plane will move forward, whether rolling on wheels, sliding on skis, or tearing itself apart as it slides on its belly. But slide it will.

As a plane and its wings move forward, air flows past them. Bernoulli effect will then create lift, and the plane will lift off. The nose does not have to be rotated. It will "rise" when there is sufficient lift, and if the wings are placed to keep it fairly balanced fore and aft.

The engines thrust the plane forward. The wheels rotate freely and the wheel assemblies simply support the plane sitting on top of them. There is nothing in the freewheeling wheels to stop the plane from moving forward.

Push a tricycle. The wheels rotate freely. Push it harder. It moves faster and the wheels rotate faster. The whole bicycle accelerates and moves faster. There is nothing to prevent the acceleration, or retard the forward motion. Sure, there is some friction where the wheel meets the road surface and within the axles. It is negligible. In a plane, with greased axle bearings, this friction is much, much less. And the thrust from the jets or propellors is much, much more. That sucker's gonna move.

 

They do not have moving treadmills for runways because the treadmills would need to be just as long as normal runways. It's not the speed of the treadmill that matters. It is the speed of air flowing past the wings. And if you put a giant fan in front of the plane, it would take off in place, but as soon as it got past the fan, it would drop down again, unless it had sufficient speed relative to the still air to stay aloft at the same altitude. It's stupid and impractical and virtually impossible, except maybe in some mountainous areas which act like natural wind tunnels.

As for landing on a treadmill, it's an even more bizarre idea. Imagine trying to land a huge jet on a small treadmill. You would have to have virtually zero margin of error and not land short or overshoot it. And as you touched down, the surface would have to match the rotational speed of the wheels for the given linear landing speed of the aircraft. And then the conveyor belt would have to slow down at exactly the rate needed to keep the aircraft from moving fore or aft on its surface as it decelerated, whether that is linear or non-linear. The calculations needed to convert that to the rotational speed of the wheels are trivial and could be computed quickly enough, but to actually get the belt surface to change its speed so quickly, while supporting the mass of the airplane...good luck with that!

Cannot happen with today's technology. And it's pointless. Think of the risk, the energy requirements, etc. Why not just have smooth ground that allows for error, and requires no energy once it has been flattened.

It happens all day long in sci-fi though. Except they don't need moving belts. The space crafts slow in the air and settle gently onto the surface which matches their speed...zero mph.

I wonder if people would take as long to get off those spaceships as they do on today's flights. I wish the whole plane would split in half and allow us to step out on to a jetway that spans the length of the aircraft. Or the chairs would get hooked up to a motorized chain and get pulled out and we could just get up and step off the moving line of chairs (and overhead lockers).

 

Oops, confused myself a bit there. An airplane cannot land on a conveyor belt unless it's as long as a runway. It doesn't matter how fast it moves, or how closely it matches the deceleration of the plane. It will need to be at least as long as the shortest distance the plane needs to come to a stop.

Completely pointless exercise to build such a conveyor--a runway is much, much cheaper and simpler.

 

How can 122 people say "Yes, it can take off?"
No air moving over the tops of the wings? It's a dirt clod then.

 

I want to thank those people for opening my eyes. I had to sweat like a pig on my turbo trainer until now, unlike them

Now going to the Patents office to patent a new type of short aircraft carrier and get ultra rich, bye losers!

 

Plane will take off. Wheels and treadmill don't matter...it's all about air speed, not ground speed.

As an example...assume you're running on a treadmill. You are holding an inflated balloon that hasn't been tied off with a knot...you let go of the balloon and it shoots forward through the air regardless of the speed of the treadmill. Now substitute a jet engine for the balloon...it will shoot forward through the air regardless of the speed of the treadmill. This creates air movement across the wing and lift results.

 

Let go.

There is a shockingly large group that doesn't live in a real World.

It's a trick question. The plane flies, every time.

 

Why the hell did this get revived?

 

with respect to position on tread mill and the surface below it there is no movement, hence no air flow for foils to do their work... no flight

question combines two mutually exclusive event, which in reality cannot occur... apples and orange

 

I can't believe this is still being argued. The plane takes off. I'm glad I live in the real world.

 

tread mill by definition implies the tread is the only thing moving NOT any object on it...

if the object ( plane on tread mill ) had a pitot, how much air flow would the pitot be measuring

flight can only be accomplished by air moving over foils capable of lift, how much still air can flow over a fixed object, if the object is NOT moving with respect to the medium it is in

no flight is possible

 

Let's modify the question a little bit and see if it changes anybody's mind on whether the plane flies or not.

Let's use a Rutan Long-EZ airplane which has the prop in the rear (see picture below).
This eliminates any prop wash flowing over the wind surfaces.

And, let's put 50-foot-long thin metal cables on each of the two tails and connect them to two 100-foot-high metal poles mounted 50 feet behind the plane.

Underneath the plane's landing gear, we'll have a conveyor belt that moves in the direction from the front of the plane to its rear.

Get the plane started and do a static run-up with the cables holding the plane in place.
Use the same RPM setting as for a take-off run, let's say hypothetically it is 2000 RPM.

Once the plane is fully revved up, start the conveyor belt and speed it up until its movement matches the thrust of the propeller. That is, right at the conveyor belt speed where the metal cables holding the plane start to slacken a bit.

Do you think the plane, in this steady state, with no relative wind going over its wings, will start to fly?
.
Image Unavailable, Please Login

 

KEY: is the conveyor able to keep the plane from moving forward?

- If it is, the plane will never take off... BUT that would take an unreal conveyor and unreal landing gear on the plane that wouldn't destroy at crazy conveyor speeds.

- If the thrust of the plane can overcome the conveyor action then it will fly, slowly gaining airspeed till take off... BUT hey, that goes against initial proposition because at some point the conveyor isn't keeping up.

This is it. You need to understand this. Unfortunately and no matter how adamant some are, this is not a YES/NO question, it needs a little thinking.

 

No modifying -

- This is the Original Post

Sent from my iPhone using Tapatalk

 

by definition of flight, rockets do not fly

they are a projectile

 

Forget physics. This thread is an entertaining study in psychology.

 

Does it depend on how fast the earth rotates?

 

I'm glad that half of you guys are dumber than me

 

My god this thread has some amusing comments. Talk about wheel bearings, length of the conveyer belt...

forget the word "wheels". Someone earlier said something about a car on a dino going 60 MPH, put your hand out and no wind. Again focusing on the "wheels".

Think about a float plane in a rapidly flowing river. The float plane need 80 knots (airspeed) to fly but the river is flowing at 80 knots the pilot points the plane up river and accelerates to 80 knots. In relation to the river he hasn't moved but he reaches the speed he needs and...FLYS!

 

Might want to recheck your next post then.