Crash90

My Feedback: (17)

LOL. Hmmmm. The question didnn't say anything about tires.

rmh

I saw it as a logic question - not one of mechanical interplay etc. involving a belt and friction and traction
The bottom line - aircraft act independently from the earth surface .
the propulsive system simply ignores movement of the plate(earth/belt) it may be resting on.
That satisfies the original "trick" question.

Crash90

My Feedback: (17)

If it's an OS engine then it would probably take off. If it is a MDS then it probably wouldn't.

Sorry. I just had to.

Semi Retired Aviator

Lift is generated by forward movement of the wing. If the conveyor belt speed matches the potential speed of the aircraft, thereby keeping it stationary on the belt, then there is no lift generated, regardless of how much power you use, therefore no flight. This is with a jet engine.

Now for a propeller driven aircraft. If the power is increased to a ridiculous level, and the prop diameter enlarged to a point where it can generate enough airflow over the wings, then it MAY fly, but in that case it would also fly from a stationary position with no conveyor belt.

The difference is why a propeller driven aircraft is easier to pull out of a stall than a jet engine; the airflow with propellers is a large diameter, relatively low velocity airflow, allowing it to generate lift over the wing, as well as making the control surfaces more efficient with low forward speed, whereas the airflow from a jet engine is relatively small diameter, not allowing it to generate airflow over the wings. There is another reason, of course, that jet efflux doesn't flow over control surfaces; it would melt them, a typical exhaust gas temperature being close to 900 degrees C on take off.

CHassan

My Feedback: (13)

If the belt is moving 5mph backwards how fast is the plane moving? .....5mph forward. Inrelation to what?

If the plane is moving 5mph forward in relation to the conveyor surface they are both moving at 2.5 mph in oposite directions. Therfore you have 2.5 mph of airspeed. Speeds must match!!!

If the plane is moving 5mph in relation to the ground next to the conveyor surface (the stationary ground) you have 5mph airspeed.

Can you stop the plane with the conveyor, yes but not if both are moving at the same speed.

rmh

The belt could have a surface speed of 100,000,000 MPH-either direction-and it means NOTHING to the plane
wheels are just little anti friction rollers not driven by the plane -they just reduce friction- replace them in your minds eye with zero friction skids

3dbob37n

Well, I kept putting bigger and bigger props on there and nothing happened. I even souped the engine up to 25,000 RPM and still nothing.
On my last try, the prop was so large that it cut the conveyor belt and the entire machine just exploded in millions of pieces. Sorry, fellas, I screwed up the conveyor.


3dbob

rmh

These logic questions will do that to you

air mail rcu

These little anti-friction devices let the plane move forward. If the little anti-friction devices don't move forward with the plane the plane will not move forward. The treadmill will not let the anti-friction devices move forward.

Liberator

Umm err, of course it will move forward. Here we go again.

gtmattz

Think about this for a bit.............


If the conveyor is set to match the 'rotational speed' of the wheels.. as the airplane moves forward.. the belt will in turn mov forward to keep the wheels rotational speed at 0rpm, as that is the 'current speed of the wheel'.........

The plane will take off as normal, but the wheels will be moving at 0rpm and the conveyor will be moving at the speed of the aircraft.


Solution?

I think so.

britbrat

If you go back to the original question -- it said that the belt moved in the opposite direction to the AC --- it would be additive to the normal wheel rotation

gtmattz

I'm afraid it is YOU who need to re-read the original post....

this is a direct copy-paste (emphasis added by me)

<clip>
Imagine an airplane is on the beginning of a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.
<clip>


Go back to page 1 if you don't belive me. I see nowhere that mentions the belt moves in relation to the aircraft. only the WHEELS.

britbrat

Ooops -- you're quite right.[&:] Doesn't change a thing though -- the plane will fly

air mail rcu

In order for the wheels to move forward THEY must rotate FASTER then the TREADMILL. Is this not true?

boss2nine

Look lets pretend that the earth is the conveyor belt and the air surrounding it is stationary if you rotate the earth 20 mph in the opposite direction of the aircraft you have the airflow over the aircraft from back to front nothing more than a 20 mph tailwind. Can you take off in a 20 mph tail wind? Well of course you can the speed that the aircraft is moving across the ground is not a simply not a factor. Aircraft propell themselves through air via the screw effect of the prop or the pushing effect of thrust from a turbine. The reason pilots do not take off in a tail wind is because at the airspeed required to lift the aircraft off the ground the ground speed is increased by the speed of the tailwind and runways are only so long. Besides it wouldn't matter wich way the conveyor belt moved the aircraft would still take off. they can take off in a headwind, tailwind or a crosswind. So the awnser to the question is yes, absolutely, without a doubt, willing to bet vital parts of my anatomy, the aircraft will take off.

just my two cents, well mabye three.

air mail rcu

In order for the plane to move forward the wheels would have to go faster then the treadmill. How can this happen if the treadmill is matching the speed of the wheels. Now the only wind generated is from the prop. The wheels are locked because of the movement of the treadmill. How do you get enough wind over the wing to fly?

Now where can we collect those body parts? My 85 year old Grandmother needs a kidney.

Simple question: I order for the plane to fly do the wheels need to go faster then the treadmill?

rmh

no - forget them- the question was a logic exercize - the wheels have nothing to do with the plane taking off as long as they offer no restriction -which ever way they turn means nothing.
Libby pointed that out to me .

air mail rcu

Forget the wheels? Then forget the treadmill. Forget the plane. Forget the question. Where is the logic in that?

The wheels are the only thing touching the treadmill. How can you forget the wheels?

I didn't know that logic was ignoring the perameters of a question. The only way you can ignore the wheels is if there was no friction in the wheel bearings. I would like to see a set of those bearings.

So are you saying you can spin a wheel on a plane one time and that wheel will spin forever?

boss2nine

Good point air mail I never thought about it like that. I suppose it would take a quantam Physicist to determan wether the tire would have to turn faster no matter how small the amount in order to initiate the movement of the conveyor. Or even if it would be physically possible for them to move at exactly the same speed with out one initiating the movement. Interesting question non the less. But in reality all it would take to get the airplane to fly if what you say as being the reason the airplane will not pick up any speed is either a light plane or a big engine. For example I have a Tensor 4d it weighs in at 10 oz it has more than enough power to drag the wheels (if they where locked) to a speed at which it will take off. For one the the take off speed is not very high two it don't take much to drag 10 oz across the ground. The bigger the plane the bigger the engine you could use and the plane would fly. The only obstical you would have to overcome is the drag of the tires on the conveyor. So Realistically the airplane would fly.
How ever I have come to the conclusion that the question is Unanswerable, due to the fact that the question is not specific enough to a certain situation with certain variables. But entertaining non the less.

air mail rcu

There is no mention of any 3D or 4D planes. I also have this type of plane. And we all know you don't need any kind of runway. I think the question was for a standard type of plane with standard horse power that requires a runway to take off.

If like you say a plane with enough power to drag locked wheels down the runway would take off what would happen after the tires blow out the wheels come off and the axles dig into the runway .

Better have a lot of horse power for that one.

boss2nine

Yea, no kidding, it would probably have to be along the lines of "Some is good. More is better. And to much is just right."

air mail rcu

That is one of my favorite sayings: To much power is just about right.

Hatty

If you neglect the maximum wheel speed and all of that crap and just think about whether or not the plan will lift off, you will see that is will lift off. Just like what was mentioned many times, the plane is battleing the surrounding air for thrust, not the runway. The wheels will be spinning very fast, but the plane will still move forward. Very tricky question. Kind of like the bug in the jar question. PM me if you don't know what that is.

air mail rcu

For the plane to take off the wheels will need to move forward. To do that they would have to go faster then the threadmill. The question states this can not happen.