The "Plane on a Treadmill" Question

[xoxoxoBruce]

By the way, the question doesn't say it's a jet.
Just as it doesn't say the planes movement is relative to any thing.:p

[tw]

Originally Posted by hideouse

I believe that the navy's catapult system is an application of this logic: a very short takeoff that achieves adequate airflow over the wings so as to allow the plane to fly.

Airplane on a catapult has zero relation to his problem. F=ma . Plane must have sufficient "a" to achieve airspeed on a short runway. Planes engines do not provide enough '"F" . So catapult adds more "F" . Carrier planes are catapulted on a runway (not a treadmill) as defined by numbers in post 152 .

[tw]

Originally Posted by glatt

The question was written from the point of view of an observer, right? That observer is the one doing the measuring of the forward speed. It's forward speed relative to the observer.

That observer could be:
1. standing on the ground,
2. floating in the air,
3. standing on the treadmill, or
4. sitting in the plane

We simply do the answer as demonstrated in post 152 and then change the answer to that 'observers' reference.

We do same thing with electricity. Which is ground? Earth? Breaker box? Computer motherboard? Any one can be ground. We can define any point as the reference point. We select any reference point only to make the problem easier to solve. Same applies to this problem.

We have three possible 'grounds' - points of reference. Four if we complicate the problem by considering an observer. The observer is completely unnecessary to the question - airspeed - velocity between airplane and air.

Air is a perfect reference point because a clearly defined relationship exists between air and the plane.

When the plane's engines throttle up, ...

And we have a known relationship between air and the runway or treadmill. Break a problem into parts. We do all numbers relative to air AND therefore have a simple answer.

Obviously - and this is just too simple for all the speculation - obviously -As the engines throttle up, the plane does take off whether it is on a runway or on a treadmill. Obviously because what the treadmill does is completely irrelevant to (independent of) airplane and air. Obviously plane's airspeed only involves a relationship between air and airplane. Obviously observer’s location and what treadmill does are completely irrelevant. Obviously wheels make that treadmill movement completely separate of (independent - not connected to) airplane and air. Obviously location of observer is completely separate from (independent of) airplane and air.

It is quite scary that so many cannot grasp these obvious and simple relationships. Some of these replies are making me feel like a genius. That scares me.

[tw]

Originally Posted by Flint

The question does not define "forward speed" in a way that makes the question answerable.

J Just because they did not tell you which to use as the reference point, then you cannot arbitrarily choose one? Nonsense. See the previous post. Choose air as the reference point. As engines throttle up, velocity of air to airplane increases until takeoff speed is achieved. All this occurs regardless of runway, treadmill, or catapult.

Engine defines a relationship between airplane and air. That makes the problem simple and completely solvable (once we include numbers for engine force, plane mass, and minimum speed for takeoff). It's just not that complex. This is a trivial high school physics problem where a runway / treadmill is completely irrelevant.

So many unable to grasp this so simple problem is scary.

[tw]

Originally Posted by Flint

The question does not define "forward speed" in a way that makes the question answerable, ...

Of course it does.

When the plane's engines throttle up, it begins to move forward,

The classic F=ma relationship and the classic v=ma . Foreward speed is defined once we have numbers for these simple equations. And again, treadmill and observer will only confuse one with irrelevant parameters.

[tw]

Clearly this problem has so confused so many and yet no one has yet asked about landing. Are there terrorists among us?

Just another reference point to keep us confused.

[Torrere]

Originally Posted by tw

Of course it does. The classic F=ma relationship and the classic v=ma .

the classic v = ma? I'm not familiar with that one. Are you confusing yourself with v=at or p=mv?

Originally Posted by tw

Just because they did not tell you which to use as the reference point, then you cannot arbitrarily choose one? Nonsense. See the previous post. Choose air as the reference point.

The problem is not explicit, therefore you must do whatever tw tells you to do.

[hideouse]

Originally Posted by tw

Airplane on a catapult has zero relation to his problem. F=ma . Plane must have sufficient "a" to achieve airspeed on a short runway. Planes engines do not provide enough '"F" . So catapult adds more "F" . Carrier planes are catapulted on a runway (not a treadmill) as defined by numbers in post 152 .

But the force here is relevant only so far as it contributes to air moving over the airfoil, no? So the movement of the treadmill, not contributing any positive or negative to getting air moving about the airfoil, contributes nothing, either positive or negative to the ability of the plane to fly.
I think.

[Flint]

Originally Posted by tw

Just because they did not tell you which to use as the reference point, then you cannot arbitrarily choose one?

Depending on what you interpret the plane's forward motion as being relative to, you get a different answer.

Originally Posted by tw

Some of these replies are making me feel like a genius.

The question is designed to make you feel like a genius. But, I'm sure you're the one who finally found the "right" answer, huh?

[MaggieL]

Originally Posted by Undertoad

I used to be friends with this guy, Scott. He was always right, no matter what, and if it looked like he was wrong he'd press the issue until he was right, in some sense. Any sense.

Oh, my dear Ghod...and you know what? That person's not much different today. :-)
At least in that respect. :-)

[lookout123]

What TW Meantto say

It's George Jr's fault...mental midget....seven seconds... top management... limbaugh disciples... no WMD...

[skysidhe]

The original question says the treadmill matches the planes speed. It cancels out. The plane isn't moving forward to create airflow over and under the wings so it isn't going to fly.

[Undertoad]

That is actually good to hear. I always felt like she lost some of her personality through the transition. Like Scott would push back, but Lisa wouldn't. I liked that push back sometimes.

[MaggieL]

As long as the "it won't fly" people are continuing to be maroons, let me point out that an airplane sitting on the runway with the engine *off* (or with no engine at all) will take off all by itself if the wind speed exceeds the stall speed. This is why we tie aircraft down: wheel chocks aren't sufficient in the case of a lightly wing-loaded aircraft in the presence of a stiff breeze.

With sufficient wind speed, an airplane can take off (or be landed) with *zero* forward motion relative to the ground. There's a standard airshow demo that's done in STOL-type airplanes (Piper Cub, or maybe a Maule or Zenith CH-701) that involves hovering and even flying backwards when the wind speed is high enough.

[Flint]

Originally Posted by Flint

Any attempt to re-write the question means you are not answering the original question.