will it take off?

hosejockey2002 · Nov 9, 2006

Iowachild said:
If this conveyor belt is moving backwards at 60 mph, friction between the belt and the tires of the plane will move the plane backwards at 60 mph. It will take the same thrust to keep the plane from moving backwards as it would take to move the air plane forward at 60 mph on a non-moving runway.

That's only if the wheels were locked. Since they will spin freely, there will be much less friction. The plane will move backwards, but not at anywhere near 60 mph, because an object at rest tends to stay at rest. The thrust from the planes engines would overcome that inertia and the plane would accelerate. The key here is that that thrust from the engines propel the plane, not torque from the wheels.

Iowachild said:
To move forward the thrust would have to increase beyond that point. What's your ground speed when your indicated airspeed is 120 mph and you are into a 60 mph headwind. How about your ground speed with the same ISA of 120 mph and a tailwind of 60 mph?
If you find that moving runway, I'm taking all bets and then getting myself that new tactor!

The plane doesn't care at all what the ground speed is. It's airspeed that makes it fly. Now, if you could throw in a tailwind that increased at the same rate as the conveyor belt, then you would have a really tough time getting that plane off the ground.

ovrszd · Nov 9, 2006

schmism said:
Sense we were having so much fun debating the finner points of tire pressure in the other thread....

i thought this would be kinda fun...

a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.

the question is

will the plane take off or not?

(ps its been debated to death on other forums, its always fun to see how people present the theory behind there answer)

Now this is funny!!!! And I'm amazed by some people's answers!!!

There is no answer because you did not state how the plane is moved?? If you start the engines and move the plane with it's own propulsion system it will definitely acquire the necessary forward speed and take off normally. If you move the plane with a ground driven force such as my B2910 or a ground driven vehicle capable of reaching the appropriate ground speed necessary for this particular plane to normally lift off, it will never take off or move forward.

This is funny though and truly amazing at the depth of "logical" discussion to try to prove points. The best one is that the moving runway will create airspeed and lift!!! Thanks Schism!!!

schmism · Nov 9, 2006

ovrszd said:
Now this is funny!!!! And I'm amazed by some people's answers!!!

heheheh

i know i get a kick out of the answers 2. well not so much the answers as yes/no isnt that intresting... its some of the explinations that crack me up.

rback33 · Nov 9, 2006

LMAO I knew this would take off overnight. Pun intended

Now, I still think the plane will take off at some point. The treadmill example must be valid like Iowa said. The engine and props cause forward thrust to propel the plane forward through the air mass, just like the car engine and tranny propel the car forward. They both move through the mass not the mass coming to them. (unless there is headwind, which I think for arguments sake here does not exist when everything is stationary at the beginning) They just do it in very different ways. Now I am no pilot, but I did sit next to one two weeks ago on my Continental flight into Kansas City. Does this qualify me for anything?

And while we are at it.. why do we park on a driveway and drive on a parkway?

LeadPoison · Nov 9, 2006

Anyone ever see a float plane take off going up river?

So the answer is yes the plane will take off.

WVBill · Nov 9, 2006

Bingo!

I've been racking my brain trying to think of a real-life corrolary to the treadmill and you've nailed it!
You will take off when the airflow over the wings creates enough lift. regardless of how fast the river flows.

WVBill

TheKid · Nov 9, 2006

Yep, it's going to fly. It's the engines that move the plane not the wheels. With no head or tail wind the wheels will be moving twice as fast as the plane when it takes off.

For those of you who say the plane won't take off because there is no forward motion and thus no lift, think about this.

The conveyor belt only moves if the plane does. Since you're saying the plane is not moving, then neither is the conveyor belt.

MossRoad · Nov 9, 2006

If a bear poops in the woods and no one is around to hear it does it still smell?

AlanB · Nov 9, 2006

The corrollary for me with the treadmill was a mixture of that and earlier posts.

Picture the treadmill, now start riding an Impossible wheel (this is an impossible wheel by the way Unicycle.com :: Products :: Impossible Wheel )

Now for forward thrust, grab from someone else's post that we are not pulling ourselves forward by the wheel, we are pulling forward by our prop biting the air. Lets make the jump again and consider this the winch hooked to the wall on one side, your beltloop on the other.

Now, no matter how fast that treadmill turns (up to that point where bearing's fail etc.) That winch will still drag you forward, (at which point if you were an airplane you would fly)

Great post by the way, makes me really think.

I just keep wanting to say that we just need to lean to the right during this so gyroscopic precession can occur and we can fly forward....

That, and I figure everything else had been covered so had to get a Uni in there somewhere.

rback33 · Nov 9, 2006

OK so the consensus is flight will occur. Now was someone right?

And I know it wasn't me... at least not for the right reason....

turnkey4099 · Nov 9, 2006

rback33 said:
OK so the consensus is flight will occur. Now was someone right? And I know it wasn't me... at least not for the right reason....

But will it take off forward or backward if you are in Oz?

Harry K

Tim_in_IA · Nov 9, 2006

The plane wont take off. The first post says that the conveyor matches the speed of the plane. If that is true, then there is no lift since the plane is standing still in the wind....

If the plane could go faster than the conveyor then it would take off, but since it can't it doesn't. That is interesting to think about though.....

weesa20 · Nov 9, 2006

Plane does not fly...no forward motion, no lift. Running on a treatmill or a bicycle trainer is a good example, no wind in my face but my speedo on the bike says 20 MPH with the tire turning against the trainer wheel. Similiar to a dyno-drum for autos- car doesn't move but tires turn.

The float plane on the river example is incorect because the forward speed of the plane is greater than the current of the river in the opposite direction, not the same as in this example. If it were the same speed, no forward motion and no lift.

W

MrJimi · Nov 9, 2006

schmism said:
Sense we were having so much fun debating the finner points of tire pressure in the other thread....

i thought this would be kinda fun...

a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.

the question is

will the plane take off or not?

(ps its been debated to death on other forums, its always fun to see how people present the theory behind there answer)

I read this first posting and !!
He never said the plane was running. He said the wheels were turning.
Think about it.
Jim

Iowachild · Nov 9, 2006

MrJimi said:
I read this first posting and !!
He never said the plane was running. He said the wheels were turning.
Think about it.
Jim

Jim, I have thought so much about it my head hurts!

Let's discuss something easy like: "If you exceed the speed of light, will you travel backwards in time?"

HTWT · Nov 9, 2006

a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.

Everything is relative. If the plane is moving at 100fps relative to some position, then the track is moving at 100fps in the opposite direction relative to the same position.
1. If the position is a spot on earth then the plane is going 100fps relative to earth and in all reality will take off.
2. If the track is the reference position the plane will be going 200fps.
3. If the reference position is the plane the track will be going 200fps and the plane will not take off.
If we are observing and are taking the speed measurements and we are on earth and stationary?? then the plane is going 100fps and can take off. This is assuming that the plane is not laying on the track but is supported by wheels or some other support that doesn't add undue friction between the plane and track. The plane must have enough thrust to overcome a slight increase in friction in the rotation of the wheels.

sandman2234 · Nov 9, 2006

What gear is the plane in? Is it gas or diesel? What rpm is it tacking? Does it have R-1 or R-3's? Is it 4x4 or just 2wd? These answers might give us something serious to think about...
David from jax

Richard · Nov 9, 2006

Tim_in_IA said:
The plane wont take off. The first post says that the conveyor matches the speed of the plane. If that is true, then there is no lift since the plane is standing still in the wind....

If the plane could go faster than the conveyor then it would take off, but since it can't it doesn't. That is interesting to think about though.....

I would agree with that logic. I would add this twist (I've not seen it mentioned yet)

First, I must qualify that I interpret the question to mean the plan is stationary to a point in space, as such, no airflow.

For those of you who say the plane WOULD take off, I'd wonder this about LANDING said plane...

If the plane could be on a treadmill in my bedroom and take off, wouldn't it then follow that the plane could be airborn, coming in for a LANDING and land on the SAME tredmill without overshooting it?

My brain says NO way can it land like that because it's going to have forward AIRspeed, relative to the tredmills zero airspeed. As such, to land on the tredmill, it would have to stop in midair and plop straight down which isn't gonna happen.

My vote goes to it will NOT land like that, therefore, it can not take off like that!

My prize please...

Richard · Nov 9, 2006

sandman2234 said:
What gear is the plane in? Is it gas or diesel? What rpm is it tacking? Does it have R-1 or R-3's? Is it 4x4 or just 2wd? These answers might give us something serious to think about...
David from jax

those questions only apply to a hydrostatic plane... well, except for which gear is it in!

MossRoad · Nov 9, 2006

O.K. I've changed my mind. It will fly... here's an example...

Put on some roller skates and stand on a treadmill.

Don't move your feet, just keep them together.

Have someone stand in front of the treadmill and throw you a rope. Hold the rope in your hands. Think of the rope as the air and your hands as the airplane propeller. The propeller pulls against the air just as your hands pull against the rope.

Start pulling yourself towards the person holding the rope.

Have a third person turn the treadmill on. Your wheels will spin at the same speed of the treadmill no matter what speed the treadmill is going.

Keep pulling the rope hand over hand, you will move forward no matter how fast the treadmill goes or until you lose your balance and fall.