Will the plane take off?
 

This is a big topic on Honda-tech, just wondering what you guys think about it.

yes, the plane is powered by jet engines pushing on the plane body, not spinning the wheels. The wheels would just be spinning double the rate of normal.

Blah, i voted no.

I'm wrong.

I have a plane, but never tried flyin it off a conveyor belt.

Quick thinking owns me.

This is already a thread like 2 years ago

omg omg omg omg omg.

http://www.macguff.fr/goomi/unspeaka...003-repost.jpg

but since it is SOOO old, and some members probably weren't around for its torture...ENJOY!

^agreed.

This goddamn "riddle" doesn't go away does it? If someone doesn't get the right answer to this they are pretty dumb.

http://www.tristatetuners.com/forum/...ad.php?t=7435&
Found it.

Theoretically, yes, it could take off. It depends on the exact controlled variables.

When someone talks about speed it is always relative to the ground (earth), not the conveyor belt. There's a hint. High school physics teaches you this. The speed you might see on a hypothetical "speedometer" inside the airplane measures the speed of the wheels, not the plane itself.

No, with the conveyor keeping it in spot the plane will not recieve the amount of lift it would need at the speed in which it is capable of taking off at normally, if that makes sense.

Harrier Jet FTW.

holy super old topic

Thrust isn't the same as a car being propelled by traction. A car on a dyno stays still but a jet on a dyno wouldn't matter how fast the rollers move because the jet doesn't rely on the wheels to move it. The thrust would just move it forward. (I'm putting it in car terms :roll: )

The friction of the bearings in the wheels won't be enough to hold a jet back with the thousands of pounds of thrust it puts out. Then again if the jet were to reach takeoff speed the bearings in the wheels would just explode because of all the thousands of watts of energy it needs to displace.

So basically it won't take off because the wheels would just explode before any other variable could happen if the conveyor belt was keeping it still, but if it could move across the conveyor belt (like it should) then it "could" take off.

fair enough, lock it, its a repost. it is a great off topic discussion though.

No.

Just cause.

Yes it will take off as long as the wheels can spin as fast as they need to. Let's assume the jet powers up and starts moving forward at 1mph. The belt will then start moving 1mph in the opposite direction. Since the engines are pushing on the body of the plane and the wheels are simply there to hold up the plane and rotate freely, the wheels would be spinning forward at 2mph.

The problem with the whole riddle is that it isn't specific enough. If the conveyor matches the speed of the plane, then yes it will take off. However, if it is matching the speed of the wheels then the plane would never move and the wheels and conveyor would spin to infinite.

Yes.

The wheels are only a way to decrease friction with the ground, not a means of producing propulsion. The wheels of the jet would simply be spinning at twice the air speed of the jet at take off. Think of it in reverse. If an F-18 was coming into land on an aircraft carrier and there was a conveyor belt spinning at the exact speed, but opposite direction of travel, to the jet would it stop dead if hitting a brick wall? NO, it would simply continue forward at a slightly slower speed, due to some resistance in a bearings, and if not caught by the cable it would go into the ocean.

^ thanks to the lift generated by its wings during its slow descent, of course......

Yes it needs air flow across and under the wings to create low pressure and lift to fly, so NO the plane would not take off!

looks like this may be a good thread after all :)

I don't see how this relates to my post at all. Not once did I mention thrust, nowhere does the riddle say that it's a jet plane.:confused:

It will take off.

Speed is distance/time.

With a jet, the propulsion would push to body forward regardless of how fast the wheels are spinning.

The wheels are just bearings, there is no power too them, its the speed of the body of the plane that matters.

So if the plane is going at liftoff speed, it is, by definition, moving forward fast enough to create the necessary lift to take off.

The trick is to not think of it like a car. With a car the wheels are what drives the body, so a conveyor effect would reverse that energy.

A plane uses propulsion applied to the body, not the wheels. All it means is the wheels are gonna spin faster b/c of the conveyor, but the propulsion will still push the body forward at the speed needed to take off.

Have you ever seen a plane powered by wheels? B/c it would have to be in order for the conveyor to counter the forward motion of the plane.

the plane will fly!

So you meen to tell me the plane will be moving forward with its wheels spinning backwards at the same speed

Ughhh....

If a plane is using propulsion to attain any kind of speed, it will be moving forward.

If that speed is the equivalent of takeoff speed, it will fly.

The wheels will have to spin twice as fast as the speed of the plane b/c it is going against the conveyor belt as well, but that wont stop the plane from moving forward.

The speed of the wheels is INDEPENDENT of the speed of the plane.

I'm taking physics right now in high school, so let's see how well my teacher is doing his job...

If the plane is moving at takeoff speed relative to the conveyor belt, but the conveyor belt is moving in the opposite direction at the same speed, then the net velocity of the plane relative to the air should be zero. And since velocity relative to the air is what matters when it comes to lift, it won't take off.

I guess we're assuming the thrust is only directed straight back and isn't pointed down or anything because this problem isn't fun with thrust vectoring.

Airplane wheels have no drive line, they are simply a means of reducing friction for an easier take off. They spin freely and are not meant to inhibit forward motion of the body of the aircraft. The propulsion is generated by the jet engines thrusting against the air, not the ground. So yes, the wheels will be spinning at twice the aircraft speed and the jet will take off.

Hes not doing his job. You are doing the same thing others are doing, focusing on the wheel speed and assuming that is responsible for airspeed. You could spin the conveyor belt at twice the speed of the aircraft and the only result will be wheels that are spinning three times faster than the airspeed of the aircraft, over the ground.

Yeah, exactly.

You could make the airplane still and move a conveyor belt and the wheels would turn. But it would stand still. (well, in a frictionless environment but the principle is there) Speed is relative to the earth, not wheel rotation.

Are we both looking at this the same way? The way I see it, the plane is moving forward at takeoff speed relative to the conveyor belt and the belt is moving at the same speed in the opposite direction relative to the air/ground (assuming no wind) and taking the plane with it. So someone watching wouldn't see the plane moving forward at all, right?

I interpreted the problem as trying to say that the conveyor belt is influencing the motion of the plane rather than moving freely under the wheels without moving the plane at all.

The conveyor belt doesn't have speed. The conveyor belt is standing still on the earth, it is just rotating surface for the wheels to spin on. Wheel RPM doesn't have any bearing on the speed of the airplane (speed being in relation to the earth).

As soon as the jets turn on, the thrust it makes would override any bearing friction the motion of the wheels would produce and then they would start turning in reverse while the plane moved forward.

If the plane used it wheels to propel itself along the ground in order to gain speed then your theory would be correct. However, planes are not propelled like a car so you can not think of it as one. You could seize all the bearings, turn on the jet engines and go to full power and the plane will skid down the runway and take off. All the conveyor belt is doing is doubling the wheel speed but having no effect on the relative motion, to a person standing at the side of the experiment, over the ground and more importantly through the air of the aircraft itself.

But the surface of it has to have speed - the problem says it's moving in reverse at takeoff speed. So the surface of that conveyor belt is definitely moving with some speed.

Again, I think the main thing here is whether you assume that the question says that the conveyor belt is moving the plane in reverse with it or if you're going to say that the wheels more or less spin freely and that the motion of the surface of the conveyor belt isn't moving the plane at all. I think it's up for grabs since it's not made clear.

The answer is NO.

First you need to understand the quesiton. The question is stating that the conveyor belt is moving at the planes take off speed in the opposite direction of the planes motion, therefore making the plane stationary with the wheels spinning at take off speed.


Since the jets/propellers on planes create a force called thrust to only push the plane so that ambient air in the atmosphere can rush over the wings, which in turn causes a negative pressure on the underside of the wings creating lift. BUT since the plane is on a conveyor belt the plane will be stationary; so there will be no air rushing over the wings there for no pressure difference on the wings and no lift.


and if you try to argue that if you were to use wing/nose mounted prop plane the answer will still be NO. the rushing air created by the props will provide the necessary wind speed to create lift. However the props are only creating a wind velocity great enough on a narrow portion of the wing(s); the ENTIRE surface of the wings need to be experiencing the sufficient wind velocity to create enough enough lift.

It'd be nicer if the question clarified whether the plane is traveling at takeoff speed relative to the earth or relative to the surface of the conveyor belt that's underneath it. Without that, I think snobordr could be right... or me and Turbo... depending on how you read into it.

Uh no? Where did You come up with an idea like that? Its all about air getting under the wings (lift) to get the plane off of the ground (to fly)

Except planes dont measure speed at the wheels.

Ill say it again, THE SPEED THAT THE WHEELS ARE SPINNING IS INDEPENDENT OF THE SPEED OF THE PLANE.

The airplanes thrust has absolutely no effect on what happens at the conveyor belt, it effect the air. If air is going through the jets, or being pulled by a prop, the plane will move forward. All the wheels do is reduce/eliminate friction b/n the plane and whatever surface is below it.

I have an airplane, I fly it regularly during the summer.

I understand the concepts of lift, bernoulli's law etc..

If the plane's engine is pulling air through a jet or with a prop, the plane will move forward.

The wheels are freewheels with almost no friction, the conveyor belt therefore provides minimal force on the plane as a whole.

Takeoff speed is measured in airspeed, not groundspeed.

And it does that by pushing on the air, not the ground. Since the bearings in the wheels are supposed to be as frictionless as possible, they will spin freely at 2, 4, 10 or 100 times the standard ground take off speed while the aircraft gains the all important air speed smoothly and unimpeded.

Off topic, what kind of plane do you have? I just started towards my private, I am thinking I want to fly commercially, it is amazing! I fly again Friday and Saturday, weather permitting.