Topic: Can this airplane lift off?

[333]

(Crying) Make it stop.  Of the humanity of it all.

Hmmmm......

Upon re-reading the original wording of the question...

Wouldn't the conveyor and therefore the wheel speed accelerate to infinity.  Each time the plane moved forward relative to the ground (not the conveyor), the conveyor would sense an increase in speed and then match that speed.  The friction of the wheel bearings (no matter how small) would eventually overcome the ability of the plane to move forward relative to the atmosphere.  Granted, the bearings would burn up and be destroyed in short order.

NO.  Assuming that the conveyor only senses what is in direct contact with it will only go as fast as the plane, just in the opposite direction, thereby simulating a "difference" of speed between the plane and the belt, and that would be only twice the speed of the plane.

But, if the belt senses the speed of the plane regardless of the contact, then the belt will only go as fast as the plane flies.  AND IT DOES FLY!!!!

[bunghole]

Have you guys ever heard of the "Monty Hall Problem"?  It goes like this:

Suppose you’re on a game show, and you’re given a choice of three doors: Behind one door is a car; behind the others, goats.  You pick a door, say number 1, and the host, who knows what’s behind the doors, opens another door, say number. 3, which has a goat.  He says to you, ‘Do you want to pick door number 2?’  Is it to your advantage to switch your choice of doors?

[333]

Or maybe this;

Suppose you’re on a game show, and you’re given a choice of three doors: Behind one door is a sandcast CB750; behind the others, a swift kick in the "back up singers".  Before Monty says anything, you say that you want a lifeline.  So when Monty open one of the loser doors, your life line gets his back up singers whacked.  After that, it's a crap shoot.

[Gordon]

Have you guys ever heard of the "Monty Hall Problem"? 

Oh man, don't even go there!  Yes, I've heard it, and I know the answer, and even though the correct answer can be mathematically, and definitively proven, there are still people who refuse to accept it.  

I think you're trying to start an all-out war here!

[my78k]

Ofcourse you should change your answer...the first time there was only a 33% chance of being right. The scond time you have a 50-50 shot of being right!!

Dennis

[bunghole]

Ofcourse you should change your answer...the first time there was only a 33% chance of being right. The scond time you have a 50-50 shot of being right!!

Dennis

You actually have a 67% chance of being right by changing your answer.

[my78k]

Damn I am going to regret this....how?

Dennis

[bunghole]

You originally had a 33% chance of being right.  The fact that the host showed you a losing door doesn't change that fact, so the remaining door that you DIDN'T choose must have a 67% chance of having the good prize behind it.

[my78k]

lol...ok! But then by that logic wouldn't the door that you chose first have the same odds?

Man this reminds me of all those hockey coaches who demanded I give 110% on every shift...

Dennis

[sangyo soichiro]

Damn I am going to regret this....how?

Dennis

Scenario 1:
You picked door 1
Say prize is in door 1
Host opens either door 2 or 3
You switch
You lose.

Scenario 2:
You picked door 1
Say prize is in door 2
Host opens door 3
You switch
You win.

Scenario 3:
You picked door 1
Say prize is in door 3
Host opens door 2
You switch
You win.

You'll win 2 out of 3 times by switching.  2/3 ~ 0.67 => 67%

[Gordon]

Yep.  Mathematically, you actually double your chances of winning the car by switching doors.  It doesn't seem to make sense, but it's true.  


Or how about this:

The question doesn't give enough information, and there's too many assumptions being made!  How do we know the contestant wouldn't prefer a goat instead of the car?  Which way do the doors swing open?  What kind of oil does the car need!?  Monty Hall is a socialist and there's really no car behind any of the doors!!  It's goats for everyone!!!!!  

[bunghole]

The fact that the host will never open the door with the winning prize and ask you if you want to re-choose changes the odds.

[bunghole]

Monty Hall is an ASS!!

[Gordon]

Monty Hall is an ASS!!

He's a socialist ASS!!

[DammitDan]

After sleeping on it this is what I can agree with. Not enough information given to come up with and accurate answer, too many assumptions have to be made. Like I said in the beginning, this is a thought problem, meant to excercise the mind.

Too many assumptions about what?  I think you're just being obstinate.  

I read TT's answer as this:

If the plane is capable of flight, it can take off.  If incapable, it will not.  You can decide on either depending on which assumptions you make about A and forces placed upon it.

You have to keep in mind that logical assumptions (e.g. airplanes will logically operate within an atmosphere) are still in fact logical.  It is a simple exercise to logically assume that the airplane will take off with sufficient thrust, given the brakes are not applied and the airplane has healthy wheel bearings which have received regular maintenance and don't offer a drag force enough to counteract the thrusting force.

Aerodynamic physics, while not necessarily simple, are still based on logic and reason, not magic.  The wheels (and their rotation) are a neutral player in the process of takeoff, given that thrust is being generated by the propeller (or jet) and not by the wheels.  And besides a glider is an aircraft, not an airplane.

(from Merriam-Webster Online Search)
Airplane: a powered heavier-than-air aircraft with fixed wings from which it derives most of its lift
Glider: an aircraft similar to an airplane but without an engine

So does my allegory of a wagon on a conveyor belt being pulled with a rope attached stand?

[my78k]

Damn I had hoped that taking the bait on the whole Monty Hall thing would change the subject enough but alas...

Oh and Gordon...you never fail to make me laugh! Goats for everyone 

Dennis

[DammitDan]

Boo!  Hiss!   

[Gordon]

After sleeping on it this is what I can agree with. Not enough information given to come up with and accurate answer, too many assumptions have to be made. Like I said in the beginning, this is a thought problem, meant to excercise the mind.

Too many assumptions about what?  I think you're just being obstinate.  

Often times, when you've dug yourself so deep into a hole, it's easier to just make yourself comfortable at the bottom than it is to climb all the way back out.

[mystic_1]

A jet is unaffected as most are made to operate at elevations well over 10000 feet. I doubt you would notice much change.

I guess that is what I was trying to point out. It seems to me, the calculation of airspeed vs groundspeed is independent of the type of aircraft..no?

Only for vehicles that stay within the atmosphere.

Technically a object/space vehicle in a  "stationary" orbit is in fact doing several thousand MPH.
And if you wanna get picky, the earth and all things on it are doing what 18,000 mph around the sun?
Sorry, it traqvels at 65,000 mph (105,000 kph) along it's orbit around the sun.
If it weren't for internet searches, i'd look like the idiot I am.
With them, i just look like the arse I can be
 

The earth rotates on its axis once each day. Since the circumference of the earth at the equator is 24,901.55 miles, a spot on the equator rotates at approximately 1037.5646 miles per hour (1037.5646 times 24 equals 24,901.55) (1669.8 km/h).

At the North Pole (90 degrees north) and South Pole (90 degrees south), the speed is effectively zero since that spot rotates once in 24 hours, a very, very slow speed.

So it depends on where on the earth you are as to your actual speed as compared to a fixed point in the universe...



l8r

mystic_1

[shacolaid]

Mea culpa everyone,

I admit I am wrong and yes it took two days and 13 pages to realize it. I called a pilot friend of mine and explained the question and very quickly he said yes the plane would take off. Sorry but I trust him more than most of you. 

But as we were talking he said that if the plane landed on a conveyor belt going in the opposite direction of the wheels, the plane would stay in one place.

How's that for a new question!

[sangyo soichiro]

...I called a pilot friend of mine...

...as we were talking he said that if the plane landed on a conveyor belt going in the opposite direction of the wheels, the plane would stay in one place.

How's that for a new question!

 

[DammitDan]

Oh no... 

[sangyo soichiro]

You folks seem mechanically-minded...

There is an airplane on a runway. The runway is like a conveyor belt, and can detect the speed of the wheels of the airplane. When the runway senses the wheels moving, the runway will match the speed of the airplane's wheels, but in the opposite direction.

Can this airplane take off?

Discuss.

Sounds like an engineering question....

Here are the givens:
Airplane = A
Runway = R
Conveyor belt = C  (C=R)
Wheel speed = WS
Conveyor Speed = CS (Where CS = WS-WS)
Take off speed  = TOS
TOS is a direct function of A's design, which is an unknown variable and not given in support of the following question. (airplane could be a glider, or VTOL capable)
No external effects are are defined or placed for the A in the the equation.  There is no link between A,  and R, C, WS, or CS.  You even have to make assumptions about gravity.

The question makes the reader toil over facts given which are irrelevant to A's capability or the forces placed upon it.  In fact, the sentences before the question actually have nothing to do with the ending question.

If the plane is capable of flight, it can take off.  If incapable, it will not.  You can decide on either depending on which assumptions you make about A and forces placed upon it. 

Essential missing data:
Does it have thrust against an air medium?  (Is there an air medium?) Are the wings strong enough to support the rest of the plane?  Are the wheels even free to rotate about an axis attached to the plane.  (parking brake applied?  If so, neither the wheels or the conveyor surface moves.)

In the end, the real question becomes, do you want the plane to fly or not?  Is your glass half empty or half full?  You can manufacture either answer depending on the assumptions made, none of which are supported or presented in the original post.

In fact, the question has no relevance to being mechanically minded, either.  It is a psychology question to gauge a person' optimism or pessimism.

If you answer no, you're a pessimist.
If you answer yes, you're an optimist.

Unless you have a fear of flying...  Then a plane that can't fly is considered a good thing.  Ain't it great that it can't crash and kill the occupants.  That's optimism!

Cheers,

After sleeping on it this is what I can agree with. Not enough information given to come up with and accurate answer, too many assumptions have to be made. Like I said in the beginning, this is a thought problem, meant to excercise the mind.

click

Essential missing data:
Does it have thrust against an air medium?  (Is there an air medium?) Are the wings strong enough to support the rest of the plane?  Are the wheels even free to rotate about an axis attached to the plane.  (parking brake applied?  If so, neither the wheels or the conveyor surface moves.)

Assume that this same plane would take off if the conveyor was turned off.


Edit:  I guess I'm hinting that there are some things that were not properly addressed that could change some minds....

[TwoTired]

Assume that this same plane would take off if the conveyor was turned off.

If the airplane's wheels had any effect on the planes flight capability, they would also have a function in flight.  They are often retracted in flight to reduce drag, which gives an indication of how important spinning wheels have on flight characteristics.
  Even on planes with exposed wheels, their rotation factor in flight neither aids or detracts from the flight characteristics.

The wheels/tires don't generate thrust for flight regardless of which way they are spinning.

If the wheels don't explode spinning at twice the take off speed, and the conveyor belt movement doesn't whip up too much turbulence for the wings, it's off to the wild blue yonder.

Conveyor belt movement or a moving aircraft carrier deck are similar.  Carriers turn into the wind for flight ops.  If the plane in question can fly in 20-40 knot heads winds, it can rise off the deck in formation with the carrier vertically, with no wheel movement.  Clearly the deck is moving.

It's about airspeed not ground speed.

Another viewpoint.  The earth spins west to east at the equator at 1000 miles an hour.  If the air is still, and moving exactly with the earth's rotation, the take off distance east to west will be the same as west to east, even though the "conveyor belt" is moving 1000 miles an hour in one direction only.

Flight is about airspeed not ground speed.

Cheers,

[sangyo soichiro]

Interpretation 1:

Hmmmm......

Upon re-reading the original wording of the question...

Wouldn't the conveyor and therefore the wheel speed accelerate to infinity.  Each time the plane moved forward relative to the ground (not the conveyor), the conveyor would sense an increase in speed and then match that speed. 

Interpretation 2:

Assuming that the conveyor only senses what is in direct contact with it will only go as fast as the plane, just in the opposite direction, thereby simulating a "difference" of speed between the plane and the belt, and that would be only twice the speed of the plane.

Both of these are valid depending on how one chooses to interpret the (purposely vague) problem.  Clearly, the latter of these two will fly, and that is the case the Mythbusters most closely simulated.

The free spinning wheels....

Forget, for the moment, about bearings, grease, friction, etc.  There is an intrinsic property of all rotating bodies.  The value of this property will be non-zero if it's an extended body of non-zero mass.  This property is called the moment of inertia.



This concept, combined with that of the first interpretation, has not been properly discussed.  This is the more difficult of the two problems and is perhaps better suited as a physics Ph.D. candidacy question.