A plane on a runway, how smart is r3vlimited?

[george graves]

Wow - have you guys beat this to death...

[Justin B]

Ritalinkid -

Your diagrams show the conveyor belt cancelling out all of the thrust of the airplane by matching the resistance of the wheels at a certain speed. Do yourself a favor and I mean no offense by it, but go read the question again if you're going to go as far as draw diagrams about what you're thinking.

The question clearly states that the conveyor belt is matching the speed of the plane. If the plane is stopped relative to the surrounding ground, the conveyor belt should not be moving either. I see where you're coming from but its wrong. The conveyor belt in your diagram should be moving at half its speed so that the forward motion and the belt are both moving at the same rate, and the same rate of acceleration etc. The point is that on a normal runway, lets say for the plane to fly it needs to get up to a certian speed we'll call S, and to do that, it will need the thrust T to over come not only the rolling resistance of the wheels, but the airflow and drag over the whole plane. Now, move it onto our special runway with a moving track, all it needs is a radar gun on one side attatched to a speed control for the track to roll only at the speed the plane is actually moving forward. That is the question. Will it fly? Yes, of course, to get up to S, it will need a little more than T, but less than 2T as it wont be pushing twice the air, just overcoming the slight bit of more rolling resistance from the runway at twice the speed the plane is actually traveling through the air/ surrounding ground.

The plane will take flight, but using your model of the rolling resistance, which really isnt included in the question, all it needs is a little more thrust to overcome the wheels spinning underneath, which should be entirely doable. The worst that could happen would be that the runway would have to be a little bit longer for the plane to get up to speed.

[trent]

Wow - have you guys beat this to death...

Uh, r3v didnt even hit the surface.

Go here, its a phyiscs forum.

http://forum.physorg.com/index.php?showtopic=2417

Try 6695 (NOT A TYPO) replies, over 447 PAGES.

That beats our measly 100+ posts.

[AdironRider]

Seriously boys, the plane will take off. I cant believe some of you continue to argue this point.

The wheels do nothing but spin. Sure they create some drag from the bearings, but its practically nil compared to the immense thrust of the engines. The engines offset the air resistance, so while it will take a little more thrust than normal to take off, it still will.

[Justin B]

The wheels are a considerable amount of drag at rest, and still are at take off speed, but nothing compared to the wind drag over the rest of the plane, and should be easily doable to over come the extra resistance. Heck, even if at full throttle and speed the plane doesnt take off just because the wheels are spinning too fast and creating a lot of drag, if its never going ot take off on an infinately long runway, then the pilot could increase the flap angle, which will create a significant amount of more lift for the time being over what the take-off flap angle typically should be, have the flaps up and go as fast as possible then lower them and the plane will hop up.



Now regarding the ice comment I made back a few pages. Whatever about the air/whatever its called that actually expands in the ice. Great, that's fine, whatever it is though expands thats already in the water (yeah, true, how is extra air going to get in there...) and that lets it float, now when it all the ice melts, whatever was expanded either goes away or blends back in at its normal volume. Regardless, the ice is less dense and thats why it floats, if you ever find ice that is PURE water, just the same as normal liquid water if it were flash frozen and nothing expanded in it, it will not float at the top with anything sticking out since it will have the same exact density. Infact, it should be able to be suspended within the water, whether its a glass, jug, swimming pool, ocean, whatever, and remain there and flow with the water since it would be the same exact density. Back on subject though, the ice is less dense than the water surrounding it, and when it melts, it becomes more dense and the ice that is poking out of the top, just by it floating, will make up for it. It only works if the boyouncy (sp) of any amount of ice in whatever body of water it is in, is acting on pushing upwards on either the same piece of ice and out of the water, or transmitting its entire upward intention to float at the top into another piece that is at the top or doing the same thing, otherwise the water line will fall. The best way to test that one would be in like a small glass with one large ice cube in it to eliminate anything that could mess it up.

[Mike325]

Seriously boys, the plane will take off. I cant believe some of you continue to argue this point.

The wheels do nothing but spin. Sure they create some drag from the bearings, but its practically nil compared to the immense thrust of the engines. The engines offset the air resistance, so while it will take a little more thrust than normal to take off, it still will.

I am seeing this now too. This plane will fly.

Who has the number for the mythbusters? This needs to be addressed. I will try to email them now about it.

[Mike325]

I just posted on the mythbusters forum. Lets see them bust this myth. That would be sweet if they did.

[Justin B]

Busted, as in that it wont fly? The only way they'll bust the myth is to lock the wheels of a model airplane that they'd probably be using and keeping the rolling drag higher than the propeller can drag it, or something. As long as its got enough thrust, it will fly.

[benDASHDASH]

jets propel the aircraft, but to get it off the ground in the first place it would need lift - airflow beneath the wings - which the jets do not apply. it would not fly unless you had jets pumping air INTO the wings. simple as that.

[E30 Wagen]

This is fun to think about. Why don't we remove the plane from the scenario?

Picture Jordan's e30 with a jet engine duct taped on the roof and reluctantly sitting on the conveyor belt. With yourself behind the wheel, and the transmission in neutral, you fire up the jet engine and the e30 lurches forward. At the exact same time, the conveyor belt recognizes the movement and matches the velocity of the e30, not the rotation speed of the wheels (or whatever terminology that would be).

The way I interpreted the scenario, the conveyor belt is intended to cancel out all efforts of the jet engine, not the rotation speed of the wheels, and you will NOT move as the conveyor belt works to match the velocity of Jordan's jet powered e30. Let's hope the duct tape holds up.

You throttle the jet engine up some more and your lurch forward again. But, the conveyor belt says "Nice try" and speeds up some more to again match your velocity. You are yet NOT moving. Again, the speed of the conveyor belt cancels out all efforts of the jet engine. Finally, you put the jet engine on full throttle but yet again the conveyor belt catches up to you and you are yet standing still, although the conveyor belt is working rediculously fast to keep up and Jordan's tires are about to explode and his wheel bearings fry -- too late, they do, and his car is flung off the conveyor belt, but luckily you dove out the door just in time to watch the most tastefully modded e30 explode in a giant fireball.

Now, to potentially kill that explanation:

Let's say that you started Jordan's car off on stationary ground and got up to speed via jet engine, and headed it straight at a conveyor belt which has matched your velocity (let's assume no tires will explode). I'm not sure what would happen. I guess this is where elements of friction come in.

[Jand3rson]

I think that this is the single most relevant and important follow up question posted yet in this thread.

That is the funniest fucking thing I have heard all day. I'm still laughing.

[bwanac]

jets propel the aircraft, but to get it off the ground in the first place it would need lift - airflow beneath the wings - which the jets do not apply. it would not fly unless you had jets pumping air INTO the wings. simple as that.

Yes... that is how a plane flies.

But what many are saying is that jet engines DO make the plane move forward as normal, thus creating the lift the wings need.

[Justin B]

jets propel the aircraft, but to get it off the ground in the first place it would need lift - airflow beneath the wings - which the jets do not apply. it would not fly unless you had jets pumping air INTO the wings. simple as that.

Ben, did you read anything? I think you're smarter than that :) lol. The plane IS moving. Ive explained it, along with several others to a point where a 5 year old would understand. Unless of course you were replying to me, but I know it will fly.

This is fun to think about. Why don't we remove the plane from the scenario?

Picture Jordan's e30 with a jet engine duct taped on the roof and reluctantly sitting on the conveyor belt. With yourself behind the wheel, and the transmission in neutral, you fire up the jet engine and the e30 lurches forward. At the exact same time, the conveyor belt recognizes the movement and matches the velocity of the e30, not the rotation speed of the wheels (or whatever terminology that would be).

The way I interpreted the scenario, the conveyor belt is intended to cancel out all efforts of the jet engine, not the rotation speed of the wheels, and you will NOT move as the conveyor belt works to match the velocity of Jordan's jet powered e30. Let's hope the duct tape holds up.

You throttle the jet engine up some more and your lurch forward again. But, the conveyor belt says "Nice try" and speeds up some more to again match your velocity. You are yet NOT moving. Again, the speed of the conveyor belt cancels out all efforts of the jet engine. Finally, you put the jet engine on full throttle but yet again the conveyor belt catches up to you and you are yet standing still, although the conveyor belt is working rediculously fast to keep up and Jordan's tires are about to explode and his wheel bearings fry -- too late, they do, and his car is flung off the conveyor belt, but luckily you dove out the door just in time to watch the most tastefully modded e30 explode in a giant fireball.

Now, to potentially kill that explanation:

Let's say that you started Jordan's car off on stationary ground and got up to speed via jet engine, and headed it straight at a conveyor belt which has matched your velocity (let's assume no tires will explode). I'm not sure what would happen. I guess this is where elements of friction come in.

LOL at the whole scenario, but.... Are you serous? lol :tsk: The riddle specifies that the belt matches the speed of the plane, thats the whole point. THAT is what is supposed to confuse you! It did to me too, but look at it and read it LITERALLY. It does NOT match the effort of the jet (it does not specify that, so it doesn't) by spinning so fast that the wheels create enough drag (a gadzillion RPM) to cancel out a jet.
You're still thinking it acts like a car. If it is in neutral, the jet will push the car forward. Even if it was slowly, the conveyor would have to be moving at ridiculous speeds to cancel out the propulsion of the jet itself through the drag of the drivetrain in neutral. Unless thats what you mean, which would have to be the case to keep the car still. Of course back to the
whole original question, the plane is moving, its not motionless on top of a spinning conveyor. BOTH are moving, just opposite of each other but the conveyor belt allows the plane/car to move forward.

Yes... that is how a plane flies.

But what many are saying is that jet engines DO make the plane move forward as normal, thus creating the lift the wings need.

Just folllwing the question, yes, the plane moves. Read it closely. Its just physics, if something is not included in the question or problem, then assume everything else is a perfect world. As far as the question is concerned, this is a hoverboard. Reason I say that, is because it specifies nothing about drag on the wheels, wind drag, weight, thrust available, lift, etc....just whether or not the plane can theoretically get up to speed and fly if it had infinate high or low values of everything I listed.

[adept]

What the hell do the wheels matter to the plane taking off? Of course it will take off.

[Brew]

I can't believe people are still arguing this.

Forget the plane, picture a missile sitting on the same runway with a few casters on it. Someone try and tell me that it wont accelerate, I dare you.