will it take off?

[txdon]

"you will move forward no matter how fast the treadmill goes" MossRoad

So, the answer is YES, IF the treadmill is long enough?

 

[LeadPoison]

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

Thanks chief. I thought that example would clarify things.

 

[Tom_Veatch]

This is a very simple dynamics problem. Draw a free-body or force diagram of the airplane and you will see that the only horizontal force applied to the airplane by the conveyor is through the almost freely spinning wheels. That force resolves itself into a force applied to the a/c via the rolling resistance of the wheels. The only other horizontal force (neglecting aerodynamic drag) felt by the airplane is thrust from the engine.

Now, the engine thrust must greatly exceed the rolling resistance of the wheels or the airplane couldn't move even if the conveyor were dead still. Since the engine thrust pulling the airplane is much greater than the force of the wheels retarding the airplane, the airplane must accelerate in response to those unbalanced forces. Sir Isaac Newton taught us that back in the 1600's. F=MA where F is the unbalanced forces acting on the object, M is the Mass (or in very loose terms, the weight) of the object, and A is the acceleration of the object.

Don't confuse displacement with force. The conveyor can be "displacing" at a phenomenal rate, but the only force it can exert on the airplane is through those freely spinning wheels. It is FORCE which accelerates and moves unrestrained objects.

Said it before, and I'll say it again. The airplane doesn't care one iota what that conveyor is doing, anymore than if the airplane were flying with the wheels .001 inch above the conveyor.

If the engine is producing, say, 1000 lb of thrust, the airplane would act just like a stationary winch was attached to the airplane and pulling with a constant 1000 lb force. That 1000 lb force, reduced by the drag of the wheels, will accelerate the airplane forward regardless of what the conveyor is doing. Neither the a/c engine nor that imaginary winch cares about, or is even aware, of the existence of the conveyor, they just continue to apply that 1000 lbs of motivating force - and that a/c motivates!

But, since the wheels spin as if the a/c is moving at twice its actual speed (relative to a stationary observer) and a/c tires are rated for a specific maximum speed (RPM) you may ruin your tires or wear out the wheel bearings, but you will fly the a/c- if the tires/wheels last long enough.

I was an aeronautical engineer in the aviation industry for going on 40 years (MSAE), and a rated a/c pilot (Private, ASEL, Instrument) longer than that. I can categorically state that this is one of those logic problems in which your intuition leads you to a dead wrong conclusion. The key is to identify the forces acting on the a/c. Everything else is totally irrelevant.

 

[Tom_Veatch]

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

Congratulations, MossRoad, you nailed it!

 

[MossRoad]

Congratulations, MossRoad, you nailed it!

Now what about that bear in the woods question?

 

[Tom_Veatch]

Now what about that bear in the woods question?

I'm gonna have to pass on that one. We didn't study no bears in airplane school.

 

[HTWT]

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.

If a car is on the track will it move???

Yes it will. The track only moves when the car moves. The tires turnng doesnot constitute moving. The speedometer only tells how fast the tires are turning. If the speedometer says 50mph then the car is going 25mph and the convayer is going 25mph in the opposite direction. The convayer only moves if the car moves. If you spin the tires the convayer doesnot move. The car will move 1/2 the speed that the speedometer indicates. The tires will turn at twice the speed as the actual movement of the car. This also applies to a plane except a plane's speed is wind speed not ground speed.

 

[RobS]

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

Same reason we make shipments by truck and transport cargo on a boat

 

[BTDT]

The question is, can a plane take off from a stand still. It's possible but highly improbable. At some point the prop has to create a lift under the wings and it ain't gonna happen on a prop driven plane. Harrier jet, yeah.

I thought all planes took off from a standstill!! Kind of like all cars, tractors, etc, take off from standstills.

 

[rback33]

Same reason we make shipments by truck and transport cargo on a boat

About time.. I was wondering if ANYONE was gonna answer MY question...lol

TV>> I was guessing you you were in Aerospace, with your answers and being in Wichita.... I am just over an hour from you.... Your not a Friends supporter are you? Big game this weekend....

 

[SeymourBota]

2 pages to this thread yesterday and 7 (or more) today!!! This could set a record.

So, I need expert commentary on this:

Normally, the engine(s) move the entire plane (and consequently the entire wingspan) through the air- even while still on the ground and not generating enough lift to fly.

In this scenario, the entire wingspan does not get to move, but rather air is drawn over it in 1,2 or 4 (or however many) points an engine exists.
Would the question not be whether the engine(s) can generate enough airflow over their localized portions of the wing to generate lift- sufficient to support the whole plane?

I have no idea how much a jet engine, for example, can generate in localized air flow, but a heck of alot is necessary over a long wing to lift a heavy jet.

A smaller, lighter prop driven plane with a large engine(s) and aggressive-pitch prop(s) seems like it would stand a better chance of creating enough airflow over enough wing area to generate the lift necessary to counter the weight of the plane, allowing it to take off.

 

[MrJimi]

There should be nothing to this.
Because a Plane WILL NOT fly without airspeed and on a treadmill? Ya wont have that.
FAA licensed Pilot and Instrument rated!!
Ask any pilot, bring on the pilot replies
Jim

 

[755inNY]

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

You missed another very important consideration. Is the transmission manual or hydrostatic?

Jeff

 

[jwnge]

All I know is I ain't standin in front of that plane when the pilot revs up the engine....

 

[DieselPower]

I have been thinking about this for a few day's now. My answer is no, the plane would not take off. There would not be sufficient lift on the wings to raise the plane. If the plane is not moving there is no lift.

 

[jwstewar]

Why does everyone keep missing the point the plane will be moving? It isn't driven by the wheels. The prop/jet engine propels it. Again the wheels will just spin faster. If the plane lifts at 300 MPH then the wheels will be doing 600 MPH but the wings and the rest of the plane will be doing 300 MPH.

 

[DieselPower]

That's just the point, the plane is not "moving". It does not matter how fast the wheels are turning, how fast the prop/jet is spinning, it is on a convyer belt that is moving backwards. The plane is stationary in one point in 3D space with no forward movement. So I say again, no forward movement, no lift, no it would not lift off.

edited to add the origina question:

"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?"

 

[shaley]

Well how do planes fly in a wind tunnel. That plane is sure sitting still just like the palne on the conveyor and they fly.
Did you look at Uler's equation. Rhymes with boiler not ruler.

 

[Tom_Veatch]

All I know is I ain't standin in front of that plane when the pilot revs up the engine....

You are a wise man! Otherwise you would surely be run over when the a/c moves forward in response to the thrust of the engine(s) as the tires freewheel against the conveyor belt. (also an FAA Instrument Rated pilot)

BTW, usually the transmissions are manually controlled but hydraulicaly actuated - hydrostatic(?). However, I once owned a 1954 V-35E Bonanza which had a geared transmission. (To you pilots who think I've flipped out, I'm talking about the propeller pitch control, which serves somewhat the same function as the transmission in a ground vehicle. Uhhh..Make that "tractor". Now we're back on topic. )

 

[RayH]

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)

Yes, the plane will take off. The conveyor (runway) is matching the planes speed but it doesnt matter what the runway is doing, what matters is what the plane is doing in relation to the air.