Will the Plane Take-Off - Merged with MythBusters Show Thread
 

A plane is standing on a runway that can move (some sort of band conveyer).
The plane moves in one direction, while the conveyer moves in the opposite
direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite
direction).The question is:Will the plane take off or not?

I know the answer, it's simple physics, but thought it'd be interesting.

im gonna say no, cause there is no lift...

:yes:

this is a total repost, sorry.

so yes or no?

The wheels on a plane are free spinning, they don't generate the thrust like in a car.

The plane would liftoff just fine.

Im gonna say no, since the plane is standing still, there is no air going over the wings, which does not equal lift, essentially I just repeated stangg172004's answer :biggrin:


EDIT: I mean, it totally takes off...

it was a terrible discussion the last few times and it's been closed a couple of times already.

Get one of the pilots in here.

But, if there is insufficient air flowing over the wings, than the plane is not going to lift off.

Oh, and :repost: X 235348568294386952304

Mike

Pilot here .....

The propeller will pull the plane forward through the air by generating thrust. What it is sitting on is irrelevant as those wheels will simply spin.

Oh no...:run: not this again

:repost: and this one had the longest discussion @ 5 pages...


https://acurazine.com/forums/ramblings-12/physics-question-airplane-related-326248/









Do the lock dance? :lock:

As has been said, there's no lift. So we're not going anywhere. Only if it was a windy day and there happened to be a tornado or an amount of lift equaling the amount needed to take off would it go otherwise it'll be stationary - for the most part.

Thrust from the engines propel the plane forward, which's equally matched by the conveyor belt.

Bottom line, you'd better not be in the plane waiting to take off or you'll be there pretty damn long.

Interesting answers ...

NEgative. To fly, you need lift, for lift, you need air flowing over the wings.

the will not be any way to create more pressure under the wings w/o moving forward, so there fore no movement or lift

Yes, it will fly. Thrust pushes air and moves forward. Take a car and plane and place them on ice... floor the car and throttle up the plane... which will go forward? Take a jet engine and place wings on it... treadmill or not at full throttle it going to take off like a missle. A plane can take off in water, how... thrust! You don't need wheels to make a plane take off, so the treadmill is irrelevant!

That is a poor analogy. The plane will not take off. THe reason the car wouldnt move and the plane would is because the car relies on its wheels for traction. THe plane must be moving in order to take off. The reason the treadmill keeps the plane from moving is it is acting like a brake. The wheels would be spinning to the point where the resistance, even with bearings, etc, was equal to the force of the prop. Think of it like this, if you turned of the prop, the resistance would pull the plane back. Having the prop on is just like a giant hand keeping the plane from moving backwards on the

Bottom line: If the plane is on the treadmill, the engines are at full blast, all they are doing is countering the resistance of the wheel bearings. No air is flowing over the airfoils hence the plane will not take flight.

If the concept as some of you re-enfoce was true, any plane could be VTOL by simple turning the engines up when the brakes are applied.

Mike

:no: unless it's a Harrier or the JSF...

The wheels have nothing to do with the propulsion of the plane. The forward thrust of the engine acts against the air, not the ground. Makes no difference how the wheels are spinning. It takes off just fine.

^ er, rather, I guess thats reverse thrust for a jet engine. Same idea.

You obviously know nothing about aerodynamics. Airflight has little to do with propulsion. If airflight was strictly based on propulsion, what are the wings for? If the plane is stationary, how does air flow over and under the wings? Airflight is about creating pressure under the wings. Air pressure is built up under the wing by air flow. If the plane is stationary, how is that accomplished?

BTW, there's a reason airplanes need runways. It does NOT matter that the thrust generated by the engine acts on the air. The plane needs contact with the ground in order to reach takeoff speed. And a plane needs to reach takeoff speed in order to create air flow over the wings. If the wheels are spinning, but the plane isn't moving relative to the air, the plane isn't taking off.

I think the real question should be:

the conveyor belt tracks the plane's speed relative to what? Technically the conveyor belt would never completely stop the plane from moving forward, because if it did, then the plane's speed would be 0, and thus the conveyer would not be moving at all, but by not moving at all that allows the plane to start movement.

So I guess there would be some speed that botht hte conveyor and plane woudl be moving at the same time where the friction in the wheel bearings, and the thrust off the plane woudl be canceled out somehow.

the only way to really know whether the plane takes off or not is to know exactly how much force is exerted by the wheel bearings.

:what:

The plane wouldn't be stationary.

Think of the propulsion of the engines as a rope pulling the plane forward. It makes no difference how the wheels are spinning underneath. The plane wouldn't sit there still and then all of a sudden take off. It would move forward in pretty much the same way it would on a solid runway, just the tires would be spinning faster.


btw you can google to find the answer...

:jesuslol:

The general purpose of wheel bearings is to have friction as nearly zero as possible. The thrust of jet engines is enormously greater than the friction of the wheel bearings.

The plane takes off, and most certainly not vertically.

no lift = no fly!

The plane will not take off. It will just sit on the conveyor belt, spinning it faster and faster, until it runs out of fuel. The engines provide the forward motivation the plane needs in order to have air flow past the wings in order to create lift. Without lift, the plane will not take off. Without forward motivation, there exists no lift on the plane's wings; the conveyor belt negates the forward motivation that the engines are attempting to create.

After the plane runs out of fuel, all the passengers on the plane will get pissed and kick the poo out of the pilot for agreeing to try to take off on a conveyor belt.

My logic is undeniable.

Here's a good quote from the other thread about this.

It doesn't matter the speed of the treadmill, place an airplane on a moving treadmill going in reverse at 10,000 rpms, the wheels of the plane start moving at the same speed... correct! What's the plane now doing... sitting there while the wheels are spinning in the opposite direction. The plane will start moving because of wheel bearing friction, but when you add thrust from the air, the plane moves forward. So everyone who says you need lift for flight... you are correct. But it doesn't matter at what speed the treadmill is going, you achieve lift because the plane will go in a forward motion. If the wheels provided the forward motion (as a car) instead of thrust from the air, then it would be acting against the treadmill and it would just sit there and both wheels and treadmill would be spinning at whatever speed!

Some people seem to be missing the fact that the conveyor belt is preventing ANY forward motion, regardless of wheel bearing friction, etc.

Picture this: I tell you to stretch out to get nice and limber, then stand at the very beginning of a 50-foot long conveyor belt. Sitting on a table just past the opposite end of the conveyor belt is stack of $100 bills totalling $100,000,000. This conveyor will move in the opposite direction and match whatever speed you are running, and it will do so instantaneously. Now, begin running on the conveyor belt, and try to reach the stack of money. Can you do it?

:no:

Regardless of how fast you run, how blue in the face you get, how close you get to passing out from exhaustion, you will not move from your current position relative to the stack of money. You will not get any closer to it, and you will not get any further away from it. As long as you are on the conveyor belt, this will not change. Keep in the mind the conveyor matches your speed instantaneously.

The conveyor belt under the plane prevents it from moving forward, which is required in order to create lift on the wings. The only way the plane can take off is if the engines can provide enough thrust to overcome the gross weight of the plane, which is how the space shuttle takes off. But that's not what we're talking about here.

If we are talking about your standard 747 or the like that are built common commercial use, the plane's engines cannot produce enough thrust to overcome its own weight, and it will not take off.

How many terrorist are on the plane? :shrug:

Fixed

Hahah. I looked at this thread and before I read the "repost" smileys, I wondered who resurrected this thread.

I cant get over how many folks in the thread think that wheels provide thrust for a plane...

Here is an analogy... Stand beside a moving treadmill, place a bike on the treadmill. You might feel some minor pulling on the bike due to resistance - easily overcome. The wheels will be spinning now. Now start walking , pulling your bike beside you. Does the treadmill stop your forward motion? No.

The treadmill can have no effect on the thrust provided by the engines since the thrust is relative to the air around the engines, not the surface on which the plane sits....

:no: it's not going to fly.

Two words: Bernoulli Effect

Wheels do not provide the movement of a plane, but legs provide movement to a person. So, to use your analogy correctly, have yourself standing on the conveyor belt with roller skates on. Place a fan pack on your back or have someone not standing on the belt to pull along (acting like thrust) you will go down the conveyor just fine, but your skate wheels with go fast the faster as you move down the belt.

Everyone who uses an example with a human involved, use it with skates on their feet... plane= wheels- person= skates/wheels.

Sned this thread to Mythbusters so they can test it.

The shape of an airplane wing is such that air flowing over the top of the wing must travel faster than the air flowing under the wing, and so there is less pressure on the top than on the bottom, resulting in lift.

Remember, the plane is not moving, the wheels are so there is no air flowing over or under the wings.

Hmm... :ponder:

The bolded text seems to make some sense. Well, I know what experiment I'm trying this weekend! And yes, and I'm somewhat of a nerd, so :finger: :biggrin:

However, I guess now the question may be this: if the plane's engine(s) have enough power to overcome the friction of the wheels on the treadmill, allowing the plane to move forward, can it overcome the friction to the point where it can pick up enough forward movement to create lift on the plane's wings? For "regular 'ol planes" we cannot deny that lift is still necessary for takeoff, and a certain airspeed is necessary to create enough lift for takeoff.

If the plane's engines cannot overcome the conveyor to the point where that airspeed can be achieved, then the answer is still no, the plane will not take off. However, I will admit that I may have been wrong about part of my previous argument...