Physics question.. can you figure it out?

[TylerDurden]

yes the wording in the original question is somewhat flawed with the use of the phrase "planes speed".....but even so, when thinking about what would happen in the sequence of events, one should conclude that the runway movement has no effect on the planes movement. Out of all the speeds I can read in the cockpit of most if not all planes, WHEEL speed is not one of them. Ground speed is measured by GPS, and TAS/IAS are measured by air movement and computers.

TAS is the movement of an object thru the air but has to be corrected for altitude and temperature. The higher you go the less molecules flow into the pitot tube and thus my IAS is lower than the actual speed of the plane thru an air mass. In a no wind situation TAS and GS would be equal. headwind=slower over ground, tailwind=faster

As mentioned before wheel speed is NOT the groundspeed of the plane (it is to the runway, but not the Earth) so the use of GS is wrong as well.

 

[Turbo Ryan]

This is a joke right

Somebody please tell me this is a big joke. I can't believe that there are still some doubters even after the skateboard video. Think about it like this. You are sitting next to a treadmill with a skateboard. Turn the treadmill on and place the skateboard on the treadmill while still holding onto the skateboard. In this scenario the skateboard is the plane and you are the thrust created by the engines planes. Now, will you be able to move the skateboard forward regardless of how fast the treadmill goes? Of course you will. The treadmill has no bearing on your ability to push the skateboard forward. The only measurable affect would be the extra drag created by excess wheel spin.

Sooo, with all of that said, the plane will be thrust forward creating enough airspeed for flight.

Ryan

P.S. I love the testimony from all of these so called experts who are pilots. Now, if any of you could let me know if any of these guys fly commercially and which airline they fly for, I would greatly appreciate it.

 

[1ARUNM]

This is typical of this kind of question. The original problem is vague and diverts you from the basic problem. Of course in the real world about any aircraft would overcome the conveyor and move forward, but when it exceeds the opposing speed of the conveyor it is not within the limits set in the original question. This is all hypothetical, not real world.

 

[jpratt]

If the plane is NOT stationary, then I take back everything I said. I thought that the plane and conveyor belt was traveling in opposite directions and the exact same speed. Meaning the the plane was stationary.

That is what this a good question. It gives you just enough info to sc*** yourself. The second to the last line says it all.

 

[1ARUNM]

From original post:

"This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

Unless the conveyor is being pull down a runway by a jet car or there is a 120 mph head wind it won't fly....because in relation to the air and ground it's sitting still.

How fast can you walk up the down escallator at Sears? Not too fast if you're going the same speed.

 

[TurboJunky]

From original post:

How fast can you walk up the down escallator at Sears? Not too fast if you're going the same speed.

Humans propel themselves forward by pushing off the ground. Aircraft propel themselves forward by pushing off AIR. Because of this difference an aircraft will not be affected by a moving conveyor runway. Make sense yet?

 

[1ARUNM]

Then it's going faster than the conveyor and violating the conditions of the original statement

 

[TurboJunky]

Then it's going faster than the conveyor and violating the conditions of the original statement

Nope. The conveyor could be spinning at 1000 mph...it really doesn't matter. It would simply spin the airplane's wheels, nothing more than that. The aircraft would still accelerate since it's using AIR (atmosphere) for propulsion and not the moving belt under it.

 

[GNandGS]

snip You are sitting next to a treadmill with a skateboard. Turn the treadmill on and place the skateboard on the treadmill while still holding onto the skateboard. In this scenario the skateboard is the plane and you are the thrust created by the engines planes. Now, will you be able to move the skateboard forward regardless of how fast the treadmill goes? Of course you will. snip

I did almost exactly that with my RC truck. VERY easy to propel the truck forward.

 

[BLACK6PACK]

Then it's going faster than the conveyor and violating the conditions of the original statement

No, say its a small plane with 70mph take off. The plane accelerates to 70mph using the air for propulsion, the conveyer is going 70 mph in the opposite direction, the wheels/tires are doing 140mph, but the plane is still only doing 70 mph forward.

By the logic you are using if the plane is stationary, then the conveyer would not be moving either since the conveyer matches the speed of the plane.

 

[GNandGS]

www.gwtra.org/temp/treadmill1.avi
www.gwtra.org/temp/treadmill2.avi

I *tried* to use the same pressure when pushing the Maxx. Fly maxx fly!

 

[denn454]

i didn't read all 4 pages of this but i can tell you its an incredible simple question with one possible and unrealistic exception.

go run on a treadmill. feel the wind in your hair? i didn't think so. now run the same speed over the ground. now you can feel the air right. ok so its established that realative to the air surounding the plane, it is stationary. without airflow to create life its unable to fly.

the same principal applies to taking off with a tail wind. say you have a 5 knot tail wind and a normal rotate speed is 60kts. there are 2 distinct differences here, airspeed vs. ground speed. your ground speed at which you rotate would now be 65 however the airspeed (the speed relitave to the airplane) would still be 60. but it would take longer to get to that airspeed.

This is assuming the thrust is equal to the speed of the convayer. if the plane can go faster, and go significantly faster flight would be possible. this is going to be a trick question because in this case the groud roll would be huge, because its working aginst its self.

heres the exception. if the airplanes wingspan is as wide as the propeller is long then the air moved by the prop is going to be suffecient to cause flight. uncontrolled but flight nonetheless.

the key here is relative wind. whats moving relative to what.

EDIT: This is really a trick question. whats the speed of the convayer? whats the rotate speed of the plane? thats whats important and thats whats missing. with that info its actually possible to calculate both ground roll over the belt and also ground roll over the solid ground(which would be very close to normal, only slightly <negligable> longer due to the added friction of the wheels spinning faster) however if the plane is using whatever power is necessary to stay stationary (0 airspeed) it will never fly.

i don't think anyone was wrong, so much as people precived the question differently.

 

[TurboJunky]

i didn't read all 4 pages of this but i can tell you its an incredible simple question with one possible and unrealistic exception.

go run on a treadmill. feel the wind in your hair? i didn't think so. now run the same speed over the ground. now you can feel the air right. ok so its established that realative to the air surounding the plane, it is stationary. without airflow to create life its unable to fly.

the same principal applies to taking off with a tail wind. say you have a 5 knot tail wind and a normal rotate speed is 60kts. there are 2 distinct differences here, airspeed vs. ground speed. your ground speed at which you rotate would now be 65 however the airspeed (the speed relitave to the airplane) would still be 60. but it would take longer to get to that airspeed.

This is assuming the thrust is equal to the speed of the convayer. if the plane can go faster, and go significantly faster flight would be possible. this is going to be a trick question because in this case the groud roll would be huge, because its working aginst its self.

heres the exception. if the airplanes wingspan is as wide as the propeller is long then the air moved by the prop is going to be suffecient to cause flight. uncontrolled but flight nonetheless.

the key here is relative wind. whats moving relative to what.

You're right, it's an incredibly simple answer. However I suggest you go back and read the 4 pages you skipped over.

 

[GNandGS]

I agree. There isnt ANY noticeable change in the force required to move my RC vehicle "up" the treadmill. If my hands were a jet engine the truck would fly off the treadmill and smack the wall.

No need for complicated formulas or lengthy explanations for ME, I tried it myself.

I CAN understand the confusion and for any that are confused all I can ask is to try it.

 

[turbobuickman]

It would definitely take off. The wheels spin independantly of the engines. The only affect the conveyor belt would have is to spin the wheels TWICE as fast as the plane is moving until it gets airborn. This will create a slight bit more drag on the wheels but given the power of the plane its negligible. Think about it...the planes engines generate thrust via moving the air through the turbines (or propellors) and act in no way on the ground (conveyor belt). If the AIR was moving at the same speed as the plane in the SAME direction, it could not take off, that is why planes usually take off/land INTO the wind.

 

[Pablo]

I know the trick to this question


It's not a PHYSICS question,

it's a READING COMPREHENSION question.



Some of you fail.

 

[1ARUNM]

I think your right

Ok, so if i get on the treadmill and run as fast as i can with a kite on a string it will fly, right???

 

[GNandGS]

A better example would be to run as fast as you can on a treadmill then throw a paper airplane.

 

[83hurstguy]

A better example would be to run as fast as you can on a treadmill then throw a paper airplane.

Yup. Bet it will fly the exact same as it would if thrown when you were standing on the ground too.

 

[Rodney87GN]

A better example would be to run as fast as you can on a treadmill then throw a paper airplane.

After 4 pages that has got to be the easiest and best example to explain it all, LOL!