Will it take off?

[mas]

I never heard of anyone measuring the speed of a plane by its wheel speed. Airspeed would be the only obvious candidate and that would be measured relative to the ground, as always.

When you are in an aircraft and the pilot comes onto the intercom with the words "we are cruising at a height of 30,000 feet and a speed of 550 knots" what do you think he means?

Farts don't come into it.

Except on this site...where they dominate.

The trick is to post pictures. They stop all thinking and impress even the staunchest of critics. Especially when a concept is misapplied.

[jacksonbart]

What movie are they showing on the flight?

[mas]

What movie are they showing on the flight?

Ah...Slapshot?...Made In Canada?...Used Cars?...Oblomov?...Head Office?...Borat?

[bodcaw boy]

should have figured that ole coyotee-o would have restarted this. and the answer is

no.

have a blessed day,

roy

[dtximages]

Im not about to read 40+pages so heres my answer. My first answer was NO. Second answer was YES because wheel speed is irrelevant as airspeed gives lift.

However, if you think about the question literally (if it could ever happen) the plane would actually never move and crash. Heres why,

Engine thrust WILL ATTEMPT to move the plane forward. If the plane moves forward the wheels spin. The However, the runway is constantly negating the wheel speed EQUALLY. IFFFF the plane ever has forward motion then that means the runway did not directly offset the wheelspeed.. Since the runway perfectly offsets wheelspeed, within a few seconds the wheel speed would increase exponentially and the wheels would dissenegrate, plane would collapse on the fuselage and crash right where it attempted to take off.

Confused? The plane WILL ALWAYS move forward, BUT to do so, would mean the runway would have to match the wheelspeed. Since the plane WILL move forward slightly, that means wheel speed has overcome the belt and the belt will increase speed until zero forward movement is possible from the plane.

So there are two absolutes working in opposite directions here. Plane/air and runwayspeed/wheelspeed. Where plane is directly proportional to wheel speed and runway speed is directly proportional to wheel speed.

SO the wheel speed would increase by xsquared each time interval until infinity.

[sputnik]

Im not about to read 40+pages so heres my answer. My first answer was NO. Second answer was YES because wheel speed is irrelevant as airspeed gives lift.

However, if you think about the question literally (if it could ever happen) the plane would actually never move and crash. Heres why,........

You were right the second time. Now, you'll have to go back and read through the entire thread as your punishment. []

[jacksonbart]

Ok I now the movie but what are they serving in terms of chow?

[dtel's wife]

And.....the answer is....????????[*-)]

The answer is Coytee-o is a TROUBLEMAKER![]

[pauln]

Those who insist that the conveyor belt runway or wheels have any real effect on the plane taking off are revealing no sense of understanding the problem at all.

First, the only thing relevant about the wheels turning is that they have mass, therefore angular momentum when they turn. Accelerating the wheels with the conveyor or the relative motion of the plane will impart a slight reverse torque to the plane in the nose down direction to the degree that the wheel bearing have friction, but for the purposes of this question that effect will be practically nothing. In a thought experiment like this, the wheel bearing friction, rolling friction, air resistance of the wheels, and other second, third, and higher orders of magnitude effects are properly given to be zero. Part of the analysis in a thought experiment includes identifying the irrelevant attributes and ommiting them from consideration. In this case, the wheels and conveyor dynamics are trivial and only serve to make the question challenging by first having one to first recognise that they serve no bearing on the solution. After realizing they are little straw men in disguise, the answer is straight forward and clear.

Let's take more extreme cases of the problem to see what happens... this will help you see that the minimal case of the question is a subset of a family of cases that all have the same solution.

1] Let's say that instead of simply matching the speed in the reverse direction the match is two or three fold... no difference, plane takes off.

2] Let's say that the matched speed reverses direction every five seconds so the rate of the conveyor is like a sine wave and the conveyor alternates going backwards and forwards... no difference, the plane takes off.

3] Let's say that the plane is angled on the conveyor so that it is not aligned to the direction of the conveyor movement. This could crash the plane if the wheels are fixed in their orientation to the plane, but if we allow the plane to use swiveling wheels like on the front of a shopping cart (this is a thought experiment, remember? Keep in mind what is important and what is not...), then the wheels will adjust to an intermediate angle and the plane will "crab", which means the plane's wheels will be slightly more angled into the alignment of the conveyor movement than the angle of the planes longitudinal axis - the effect on the plane is the same as when the plane is flying in a cross wind... "crabing"; slight difference between the direction of travel and the direction which the plane is pointing, but no real difference, the plane takes off.

4] Does it land? Imagine the reverse question... can the plane land on a moving conveyor... yes, in all cases, and even in the case of the angle of conveyor misaligned to the angle of the planes motion if the swivel wheels are stipulated as in part [3 above.

5] Imagine that instead of wheels the plane has ice skates, and the runway is an ice flow floating free in the ocean. The ice flow is accelerated by an hugh and powerful motor so that it can match the speed of the plane in the reverse direction... does that help to see how the mechanics of the wheels are irrelevant to the question?

The bottom line is that the speed of the conveyor and wheels is a red herring to the question. They have no bearing on the motion and take off (or landing) of the plane. The reason is that there is no drive being put to the wheels by the plane (the wheels are driven solely by the runway), only the prop or the jet is making the plane move, and that is independent of the wheels and runway surface.

For those to whom this is still an arguable mystery, please refrain from designing, building, or operating anything that could be dangerous if not thought through correctly! Darwin Karma will get you!

[jacksonbart]

was that a yes or no?

[DizRotus]

The following You Tube video is crude but illustrates the correct answer.

Of course, that won't stop the debate.

[oldtimer]

Amy, of all the threads you have deleted, this should be one of them.

[dtximages]

pauln: you bring up good points but i dont think anyone understands my answer.

this is a null point. its two infinities working in opposing directions. we can assume sine waves but thats not what the original problem indicated. heres the point.

the plane WILL attempt to move forward. but as soon as it does, this means the conveyor belt has NOT done its job to offset the wheel speed. therefore the plane cant move forward without the runway failing its purpose. therefore, the runway will continually increase speed.

i go back to the plane WILL move forward by nature, but as soon as it does the wheel speed would increase to infinity (destruction). now, if the runway takes time to measure, calculate and respond, then theres some time for the plane to move.. but here, we assume that the runway always negates wheel speed. in which case, the plane would fall on its fuselage right where it attempts to move.

The argument that the plane will take off regardless of wheelspeed is usually correct, but for that to happen; the runway obviously did not match wheel speed.. so this premise ruins the original concept of the runway perfectly negating wheelspeed.

if the runway were not perfectly tuned to negate wheelspeed then the plane would take off easily. but thats not what the original problem stated.

[pauln]

Amy, of all the threads you have deleted, this should be one of them.

Aren't you missing the point? This thread has less to do with airplanes and everything to do with how to approach a problem, how to analyze a physical scenario, how to order one's thoughts, and how to communicate ideas. That is part of what we do in this forum - especially the more technical aspects.

In some ways this problem is repeated in disguise many times on this forum when folks seeking help or advice ask questions about how things work, will things work, why doesn't my thing work... the forum helps provide a basis for approaching a problem, reading of experience with similar situations, and enjoying a format for reviewing others' thoughts and ideas.

And as sometimes happens in the forum with audio questions, the plane problem did not attract only one kind of answer. The beauty of the plane problem is that there is a clear and correct answer, and the division between those that understand the plane problem and those that do not (take off vs no take off) serves to enlighten us all.

[maxg]

pauln: you bring up good points but i dont think anyone understands my answer.

this is a null point. its two infinities working in opposing directions. we can assume sine waves but thats not what the original problem indicated. heres the point.

the plane WILL attempt to move forward. but as soon as it does, this means the conveyor belt has NOT done its job to offset the wheel speed. therefore the plane cant move forward without the runway failing its purpose. therefore, the runway will continually increase speed.

i go back to the plane WILL move forward by nature, but as soon as it does the wheel speed would increase to infinity (destruction). now, if the runway takes time to measure, calculate and respond, then theres some time for the plane to move.. but here, we assume that the runway always negates wheel speed. in which case, the plane would fall on its fuselage right where it attempts to move.

The argument that the plane will take off regardless of wheelspeed is usually correct, but for that to happen; the runway obviously did not match wheel speed.. so this premise ruins the original concept of the runway perfectly negating wheelspeed.

if the runway were not perfectly tuned to negate wheelspeed then the plane would take off easily. but thats not what the original problem stated.

The orginal question does not mention wheel speed at all. It talks about the conveyor matching the plane's speed. Wheel speed was introduced by Dr.Who as a possible measure of plane speed - but that ain't how it works - ever. The plane's speed and the wheel's speed are not the same thing. This is why the plane will, indeed, take off.

[Jay481985]

airplane needs air to move......

airplane has jet engine or propeller that moves air over wing

wing creates lift

wheels only hold airplane up.wheels do not aid or transfer in lift

even if wheels where replaced with say skis there might be more friction and the airplane might need more power but it still would have lift to fly.

[DizRotus]

Before anyone again attempts to explain how the plane would be prevented by the moving conveyor from taking off, please watch the video at:

Then please explain why the hpothetical jet plane would have more difficulty overcoming the opposite movement of the hypothetical conveyor belt runway than did the battery powered toy plane with the actual treadmill belt/runway actually moving rapidly in the opposite direction. As unsophisticated as it is, the video accurately demonstrates that THE PLANE WOULD TAKE OFF irrespective of the the motion of the runway/conveyor. The child correctly explains the difference between a wheel driven car and a thrust driven aircraft on the same hypothetical moving belt.

[LarryC]

the plane WILL attempt to move forward. but as soon as it does, this means the conveyor belt has NOT done its job to offset the wheel speed. No.

therefore the plane cant move forward without the runway failing its purpose. Not so.

therefore, the runway will continually increase speed. No, it will increase its speed up to the plane's takeoff speed, which could be over 150 mph (in the reverse direction) for jet transports. The wheels would spin up to over 300 mph in that case, but that's irrelevant to the plane moving up to takeoff speed -- and taking off. After it takes off, the runway can do whatever it likes, speedwise, it won't make any difference (but then it won't make any difference anyway).

i go back to the plane WILL move forward by nature, but as soon as it does the wheel speed would increase to infinity (destruction). No. But, the wheel speed will by definition be twice what it ordinarily would be at a given speed. So what? The wheels are 100% free-wheeling, exerting no force whatsoever in either direction.

now, if the runway takes time to measure, calculate and respond, then theres some time for the plane to move.. but here, we assume that the runway always negates wheel speed. No. Negates in what way? in which case, the plane would fall on its fuselage right where it attempts to move. No.

The argument that the plane will take off regardless of wheelspeed is usually correct, but for that to happen; the runway obviously did not match wheel speed.. so this premise ruins the original concept of the runway perfectly negating wheelspeed. No. Wheel speed is completely irrelevant.

if the runway were not perfectly tuned to negate wheelspeed then the plane would take off easily. but thats not what the original problem stated.

The orginal question does not mention wheel speed at all. It talks about the conveyor matching the plane's speed. Wheel speed was introduced by Dr.Who as a possible measure of plane speed - but that ain't how it works - ever. The plane's speed and the wheel's speed are not the same thing. This is why the plane will, indeed, take off.

Plane speed is measured solely by air speed. Not by wheel speed, because it's so irrelevant to operating the plane.

[dtximages]

I agree that plane speed is measured by air speed only and the wheels only hold the plane up. However, there is a direct correlation between the speed of the plane and the spinning speed of the wheels.

An experiment of a model is insufficient as the treadmill has limited top speed, the model aircraft would quickly overcome the limits of the treadmill and take off. This is not applicable to the story because the runway perfectly keeps up with the plane speed.

PLANE SPEED = WHEEL SPEED WHEEL SPEED = (RUNWAY SPEED) therefore PLANE SPEED = (RUNWAY SPEED)

1 = 1 1 = (1) 1 = (1)

For the plane to move forward, the wheel speed would have to over come the runway speed at some point.

PLANE SPEED = WHEEL SPEED WHEEL SPEED = (RUNWAY SPEED) therefore PLANE SPEED = (RUNWAY SPEED)

2 = 2 2 = (1) 2 = (1)

this would send the plane forward at a speed of 1 somethings. if the plane has positive forward motion, then something is wrong. somewhere theres a hitch.

for the plane to move forward, it had to beat the odds on the wheel speed. they are not independent as the wheels are a product of both the plane and the runway. the problem here is acceleration! the plane would never have the opportunity to accelerate. becuase once it did, our conveyor belt is no longer perfect.

think about it.. how did the plane get from point A to point B. Wheel speed relative to the runway had to be greater than the runway speed in the opposing direction to get forward movement from the plane (i.e. if runway speed was negative (100mph) then wheel speed had to have at least been 101mph). argument over right there, the runway simply cant keep up with the plane. what if it could though? the plane would never move but the wheels would spin too fast immediately and the plane is now on its belly.

someone call mythbusters! haha

[Jay481985]

the one thing that still bugs me and I have mentioned it before is thrust per pound......

Rockets and missiles develop lift without any wings or so due to having a better thrust per weight ratio..... your firecracker weighs less the the thrust of the engine creates hence it accelerates.

Airplanes mostly do not have a better thrust to weight ratio..... There are only two planes off the top of my head that actually do have more thrust then weight ratio. That is the F-15, and the Mig 29. Technically they could launch upwards but it is doubtful since their thrust to weight is not as great as needed to accelerate. Though they can climb at a true 90 degree angle (great for dog fighting) without the plane stalling..... Every play microsoft flight simulator? when you go straight up most of the time your engines will stall and you will crash.

Since most aircrafts cannot lift themselves up without the use of the wings I still wonder.